@article{grozema_castellano_2024, title={<i>Chemical Physics Reviews</i> as a platform for the chemical physics community: The first four years}, volume={5}, ISSN={["2688-4070"]}, url={https://doi.org/10.1063/5.0235808}, DOI={10.1063/5.0235808}, number={4}, journal={CHEMICAL PHYSICS REVIEWS}, author={Grozema, Ferdinand C. and Castellano, Felix N.}, year={2024}, month={Dec} }
 @article{rather_vallabhuneni_pyrch_barrubeeah_pillai_taassob_castellano_kota_2024, title={Color morphing surfaces with effective chemical shielding}, volume={15}, ISSN={["2041-1723"]}, url={https://doi.org/10.1038/s41467-024-48154-y}, DOI={10.1038/s41467-024-48154-y}, abstractNote={Abstract Color morphing refers to color change in response to an environmental stimulus. Photochromic materials allow color morphing in response to light, but almost all photochromic materials suffer from degradation when exposed to moist/humid environments or harsh chemical environments. One way of overcoming this challenge is by imparting chemical shielding to the color morphing materials via superomniphobicity. However, simultaneously imparting color morphing and superomniphobicity, both surface properties, requires a rational design. In this work, we systematically design color morphing surfaces with superomniphobicity through an appropriate combination of a photochromic dye, a low surface energy material, and a polymer in a suitable solvent (for one-pot synthesis), applied through spray coating (for the desired texture). We also investigate the influence of polymer polarity and material composition on color morphing kinetics and superomniphobicity. Our color morphing surfaces with effective chemical shielding can be designed with a wide variety of photochromic and thermochromic pigments and applied on a wide variety of substrates. We envision that such surfaces will have a wide range of applications including camouflage soldier fabrics/apparel for chem-bio warfare, color morphing soft robots, rewritable color patterns, optical data storage, and ophthalmic sun screening.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Rather, Adil Majeed and Vallabhuneni, Sravanthi and Pyrch, Austin J. and Barrubeeah, Mohammed and Pillai, Sreekiran and Taassob, Arsalan and Castellano, Felix N. and Kota, Arun Kumar}, year={2024}, month={May} }
 @article{castellano_rosko_2024, title={Correction to “Steric and Electronic Influence of Excited-State Decay in Cu(I) MLCT Chromophores”}, url={https://doi.org/10.1021/acs.accounts.4c00720}, DOI={10.1021/acs.accounts.4c00720}, journal={Accounts of Chemical Research}, author={Castellano, Felix N. and Rosko, Michael C.}, year={2024}, month={Dec} }
 @article{mara_weingartz_leshchev_hsu_valentine_mills_roy_chakraborty_kim_biasin_et al._2024, title={Deciphering Charge Transfer Processes in Transition Metal Complexes from the Perspective of Ultrafast Electronic and Nuclear Motions}, volume={5}, ISSN={["1948-7185"]}, DOI={10.1021/acs.jpclett.4c00735}, abstractNote={Chemical transformations in charge transfer states result from the interplay between electronic dynamics and nuclear reorganization along excited-state trajectories. Here, we investigate the ultrafast structural dynamics following photoinduced electron transfer from the metal–metal-to-ligand charge transfer state of an electron donor, a Pt dimer complex, to a covalently linked electron acceptor group using ultrafast time-resolved wide-angle X-ray scattering and optical transient absorption spectroscopy methods to disentangle the interdependence of the excited-state electronic and nuclear dynamics. Following photoexcitation, Pt–Pt bond formation and contraction takes up to 1 ps, much slower than the corresponding process in analogous complexes without electron acceptor groups. Because the Pt–Pt distance change is slow with respect to excited-state electron transfer, it can affect the rate of electron transfer. These results have potential impacts on controlling electron transfer rates via structural alterations to the electron donor group, tuning the charge transfer driving force.}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, author={Mara, Michael W. and Weingartz, Nicholas P. and Leshchev, Denis and Hsu, Darren and Valentine, Andrew and Mills, Alexis and Roy, Subhangi and Chakraborty, Arnab and Kim, Pyosang and Biasin, Elisa and et al.}, year={2024}, month={May} }
 @article{kessinger_whittemore_grandi_danilov_caramori_castellano_meyer_2024, title={Direct Evidence for Buffer-Enhanced Proton-Coupled Electron Transfer in Metal Aquo Bond Formation}, url={https://doi.org/10.26434/chemrxiv-2024-l776x}, DOI={10.26434/chemrxiv-2024-l776x}, abstractNote={Proton-coupled electron transfer (PCET) reactions play a crucial role in the interconversion of metal-aqua and metal-hydroxo species present in transition metal complexes and oxide surfaces (M(III)-OH + e− + H+ M(II)-OH2). For ruthenium-based water oxidation catalysts, PCET reactions involved in the mechanism of oxygen evolution have demonstrated a strong dependence on the identity and concentration of the proton donor and acceptor with significant rate enhancements observed for electrocatalysis performed in acetate, phosphate, and borate buffered electrolytes. However, the systematic study of this phenomenon has been hampered by the inability to independently measure discrete rates for electron transfer (ET) and proton transfer (PT) under electrochemical applied potentials. Herein, the PCET kinetics and mechanism of metal aqua bond formation in a ruthenium water oxidation catalyst [Ru(tpy)(bpy′)H2O]2+, Ru(II)−OH2 where tpy is 2,2′:6′,2″-terpyridine and bpy′ is 4,4′-diaminopropylsilatrane-2,2′-bypyridine were investigated at a conductive metal oxide interface as a function of buffer identity and concentration. The reaction of interest was triggered by visible light excitation of the catalyst and the kinetics of the independent ET and PT steps of the PCET mechanism were determined through nanosecond transient absorption spectroscopy. Kinetic measurements performed in aqueous acetate, phosphate, or borate buffer solutions revealed two distinct regimes of PT kinetics solely dependent on the buffer concentration. At the greatest buffer concentrations investigated (2 M acetate) spectral signals corresponding to the discreet ET and PT steps were absent indicative in a change in underlying PCET mechanism. Likewise, kinetic modeling indicated that PT from protonated acetate or phosphate occurred with rate constants that were 2-4 orders of magnitude greater than those for bulk water. In all, these results suggest that the presence of buffer-bases can significantly enhance PCET rates and, in this reaction, may alter the underlying mechanism.}, author={Kessinger, Matthew and Whittemore, Thomas and Grandi, Silvia and Danilov, Evgeny and Caramori, Stefano and Castellano, Felix and Meyer, Gerald}, year={2024}, month={Sep} }
 @article{rosko_wheeler_alameh_faulkner_durand_castellano_2024, title={Enhanced Visible Light Absorption in Heteroleptic Cuprous Phenanthrolines}, volume={63}, ISSN={["1520-510X"]}, url={https://doi.org/10.1021/acs.inorgchem.3c04024}, DOI={10.1021/acs.inorgchem.3c04024}, abstractNote={This work presents a series of Cu(I) heteroleptic 1,10-phenanthroline chromophores featuring enhanced UVA and visible-light-harvesting properties manifested through vectorial control of the copper-to-phenanthroline charge-transfer transitions. The molecules were prepared using the HETPHEN strategy, wherein a sterically congested 2,9-dimesityl-1,10-phenanthrolne (mesPhen) ligand was paired with a second phenanthroline ligand incorporating extended π-systems in their 4,7-positions. The combination of electrochemistry, static and time-resolved electronic spectroscopy, 77 K photoluminescence spectra, and time-dependent density functional theory calculations corroborated all of the experimental findings. The model chromophore, [Cu(mesPhen)(phen)]+ (1), lacking 4,7-substitutions preferentially reduces the mesPhen ligand in the lowest energy metal-to-ligand charge-transfer (MLCT) excited state. The remaining cuprous phenanthrolines (2-4) preferentially reduce their π-conjugated ligands in the low-lying MLCT excited state. The absorption cross sections of 2-4 were enhanced (εMLCTmax = 7430-9980 M-1 cm-1) and significantly broadened across the UVA and visible regions of the spectrum compared to 1 (εMLCTmax = 6494 M-1 cm-1). The excited-state decay mechanism mirrored those of long-lived homoleptic Cu(I) phenanthrolines, yielding three distinguishable time constants in ultrafast transient absorption experiments. These represent pseudo-Jahn-Teller distortion (τ1), singlet-triplet intersystem crossing (τ2), and the relaxed MLCT excited-state lifetime (τ3). Effective light-harvesting from Cu(I)-based chromophores can now be rationalized within the HETPHEN strategy while achieving directionality in their respective MLCT transitions, valuable for integration into more complex donor-acceptor architectures and longer-lived photosensitizers.}, number={3}, journal={INORGANIC CHEMISTRY}, author={Rosko, Michael C. and Wheeler, Jonathan P. and Alameh, Reem and Faulkner, Adrienne P. and Durand, Nicolas and Castellano, Felix N.}, year={2024}, month={Jan}, pages={1692–1701} }
 @article{barth_pyrch_mccormick_danilov_castellano_2024, title={Excited State Bond Homolysis of Vanadium(V) Photocatalysts for Alkoxy Radical Generation}, volume={8}, ISSN={["1520-5215"]}, url={https://doi.org/10.1021/acs.jpca.4c04250}, DOI={10.1021/acs.jpca.4c04250}, abstractNote={Advancements in photocatalysis have transformed synthetic organic chemistry, using light as a powerful tool to drive selective chemical transformations. Recent approaches have focused on metal-halide ligand-to-metal charge transfer (LMCT) photoactivated bond homolysis reactions leveraged by earth-abundant elements to generate valuable synthons for radical-mediated cross-coupling reactions. Of recent utility, oxovanadium(V) LMCT photocatalysts exhibit selective alkoxy radical generation from aliphatic alcohols upon blue light (UVA) irradiation under mild conditions. The selective photochemical liberation of alkoxy radicals is valuable for applying late-stage fragmentation approaches in organic synthesis and depolymerization strategies for nonbiodegradable polymers. Steady-state and time-resolved spectroscopy were used to assign the electronic structure of three well-defined V(V) photocatalysts in their ground and excited states. We assign the excited state for this transformation at earth-abundant vanadium(V), interrogating the electronic structure using static UV–visible absorption, ultrafast transient absorption, and electron paramagnetic resonance spectroscopy coupled to computational approaches. These findings afford assignments of the short-lived excited state intermediates that dictate selective homolytic bond cleavage in metal alkoxides, illustrating the valuable insight gleaned from fundamental investigations of the molecular photochemistry responsible for light-escalated chemical transformations.}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Barth, Alexandra T. and Pyrch, Austin J. and McCormick, Conor T. and Danilov, Evgeny O. and Castellano, Felix N.}, year={2024}, month={Aug} }
 @article{arshad_castellano_2024, title={Homomolecular Triplet-Triplet Annihilation in Metalloporphyrin Photosensitizers}, volume={128}, ISSN={["1520-5215"]}, url={https://doi.org/10.1021/acs.jpca.4c05052}, DOI={10.1021/acs.jpca.4c05052}, abstractNote={Metalloporphyrins are ubiquitous in their applications as triplet photosensitizers, particularly for promoting sensitized photochemical upconversion processes. In this study, bimolecular excited state triplet-triplet quenching kinetics, termed homomolecular triplet-triplet annihilation (HTTA), exhibited by the traditional triplet photosensitizers-zinc(II) tetraphenylporphyrin (ZnTPP), palladium(II) octaethylporphyrin (PdOEP), platinum(II) octaethylporphyrin (PtOEP), and platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP)─were revealed using conventional transient absorption spectroscopy. Nickel(II) tetraphenylporphyrin was used as a control sample as it is known to be rapidly quenched intramolecularly through ligand-field state deactivation and, therefore, cannot result in triplet-triplet annihilation (TTA). The single wavelength transients associated with the metalloporphyrin triplet excited state decay─measured as a function of incident laser pulse energy in toluene─were well modeled using parallel first- and second-order kinetics, consistent with HTTA being operable. The combined transient kinetic data enabled the determination of the first-order rate constants (}, number={36}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Arshad, Azka and Castellano, Felix N.}, year={2024}, month={Sep}, pages={7648–7656} }
 @article{sridhar_khansari_o'donnell_barth_danilov_castellano_maggard_dougherty_2024, title={Ligand field exciton annihilation in bulk CrCl<sub>3</sub>}, volume={161}, ISSN={["1089-7690"]}, url={https://doi.org/10.1063/5.0223772}, DOI={10.1063/5.0223772}, abstractNote={The layered van der Waals material CrCl3 exhibits very strongly bound ligand field excitons that control optoelectronic applications and are connected with magnetic ordering by virtue of their d-orbital origin. Time-resolved photoluminescence of these exciton populations at room temperature shows that their relaxation is dominated by exciton–exciton annihilation and that the spontaneous decay lifetime is very long. These observations allow the rough quantification of the exciton annihilation rate constant and contextualization in light of a recent theory of universal scaling behavior of the annihilation process.}, number={11}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Sridhar, Samanvitha and Khansari, Ario and O'Donnell, Shaun and Barth, Alexandra T. and Danilov, Evgeny O. and Castellano, Felix N. and Maggard, Paul A. and Dougherty, Daniel B.}, year={2024}, month={Sep} }
 @article{kim_rosko_castellano_gray_teets_2024, title={Long Excited-State Lifetimes in Three-Coordinate Copper(I) Complexes via Triplet-Triplet Energy Transfer to Pyrene-Decorated Isocyanides}, volume={7}, ISSN={["1520-5126"]}, url={https://doi.org/10.1021/jacs.4c04288}, DOI={10.1021/jacs.4c04288}, abstractNote={There has been much effort to improve excited-state lifetimes in photosensitizers based on earth-abundant first-row transition metals. Copper(I) complexes have gained significant attention in this field, and in most cases, sterically driven approaches are used to optimize their lifetimes. This study presents a series of three-coordinate copper(I) complexes (Cu1–Cu3) where the excited-state lifetime is extended by triplet–triplet energy transfer. The heteroleptic compounds feature a cyclohexyl-substituted β-diketiminate (CyNacNacMe) paired with aryl isocyanide ligands, giving the general formula Cu(CyNacNacMe)(CN-Ar) (CN-dmp = 2,6-dimethylphenyl isocyanide for Cu1; CN-pyr = 1-pyrenyl isocyanide for Cu2; CN-dmp-pyr = 2,6-dimethyl-4-(1-pyrenyl)phenyl isocyanide for Cu3). The nature, energies, and dynamics of the low-energy triplet excited states are assessed with a combination of photoluminescence measurements at room temperature and 77 K, ultrafast transient absorption (UFTA) spectroscopy, and DFT calculations. The complexes with the pyrene-decorated isocyanides (Cu2 and Cu3) exhibit extended excited-state lifetimes resulting from triplet–triplet energy transfer (TTET) between the short-lived charge-transfer excited state (3CT) and the long-lived pyrene-centered triplet state (3pyr). This TTET process is irreversible in Cu3, producing exclusively the 3pyr state, and in Cu2, the 3CT and 3pyr states are nearly isoenergetic, enabling reversible TTET and long-lived 3CT luminescence. The improved photophysical properties in Cu2 and Cu3 result in improvements in activity for both photocatalytic stilbene E/Z isomerization via triplet energy transfer and photoredox transformations involving hydrodebromination and C–O bond activation. These results illustrate that the extended excited-state lifetimes achieved through TTET result in newly conceived photosynthetically relevant earth-abundant transition metal complexes.}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Kim, Dooyoung and Rosko, Michael C. and Castellano, Felix N. and Gray, Thomas G. and Teets, Thomas S.}, year={2024}, month={Jul} }
 @article{kim_roy_valentine_liu_kromer_kim_li_castellano_chen_2024, title={Real-time capture of nuclear motions influencing photoinduced electron transfer}, volume={8}, ISSN={["2041-6539"]}, url={https://doi.org/10.1039/D4SC01876A}, DOI={10.1039/D4SC01876A}, abstractNote={This study explores vibronic wavepacket dynamics in photoinduced electron transfer (PET). The dynamic interplay of PET and coherent wavepacket motions highlights the crucial role of vibrations in influencing efficient PET process.}, journal={CHEMICAL SCIENCE}, author={Kim, Pyosang and Roy, Subhangi and Valentine, Andrew J. S. and Liu, Xiaolin and Kromer, Sarah and Kim, Tae Wu and Li, Xiaosong and Castellano, Felix N. and Chen, Lin X.}, year={2024}, month={Aug} }
 @article{bateni_sadeghi_orouji_bennett_punati_stark_wang_rosko_chen_castellano_et al._2024, title={Smart Dope: A Self-Driving Fluidic Lab for Accelerated Development of Doped Perovskite Quantum Dots (Adv. Energy Mater. 1/2024)}, volume={14}, ISSN={["1614-6840"]}, DOI={10.1002/aenm.202470001}, abstractNote={Advanced Energy MaterialsVolume 14, Issue 1 2470001 Cover PictureFree Access Smart Dope: A Self-Driving Fluidic Lab for Accelerated Development of Doped Perovskite Quantum Dots (Adv. Energy Mater. 1/2024) Fazel Bateni, Fazel Bateni Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorSina Sadeghi, Sina Sadeghi Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorNegin Orouji, Negin Orouji Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorJeffrey A. Bennett, Jeffrey A. Bennett Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorVenkat S. Punati, Venkat S. Punati Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorChristine Stark, Christine Stark Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorJunyu Wang, Junyu Wang Department of Chemistry, Brown University, Providence, RI, 02912 USASearch for more papers by this authorMichael C. Rosko, Michael C. Rosko Department of Chemistry, North Carolina State University, Raleigh, NC, 27695-8204 USASearch for more papers by this authorOu Chen, Ou Chen Department of Chemistry, Brown University, Providence, RI, 02912 USASearch for more papers by this authorFelix N. Castellano, Felix N. Castellano Department of Chemistry, North Carolina State University, Raleigh, NC, 27695-8204 USASearch for more papers by this authorKristofer G. Reyes, Kristofer G. Reyes Department of Materials Design and Innovation, University at Buffalo, Buffalo, NY, 14260 USASearch for more papers by this authorMilad Abolhasani, Milad Abolhasani Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this author Fazel Bateni, Fazel Bateni Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorSina Sadeghi, Sina Sadeghi Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorNegin Orouji, Negin Orouji Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorJeffrey A. Bennett, Jeffrey A. Bennett Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorVenkat S. Punati, Venkat S. Punati Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorChristine Stark, Christine Stark Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this authorJunyu Wang, Junyu Wang Department of Chemistry, Brown University, Providence, RI, 02912 USASearch for more papers by this authorMichael C. Rosko, Michael C. Rosko Department of Chemistry, North Carolina State University, Raleigh, NC, 27695-8204 USASearch for more papers by this authorOu Chen, Ou Chen Department of Chemistry, Brown University, Providence, RI, 02912 USASearch for more papers by this authorFelix N. Castellano, Felix N. Castellano Department of Chemistry, North Carolina State University, Raleigh, NC, 27695-8204 USASearch for more papers by this authorKristofer G. Reyes, Kristofer G. Reyes Department of Materials Design and Innovation, University at Buffalo, Buffalo, NY, 14260 USASearch for more papers by this authorMilad Abolhasani, Milad Abolhasani Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695-7905 USASearch for more papers by this author First published: 05 January 2024 https://doi.org/10.1002/aenm.202470001AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Graphical Abstract Self Driving Lab In article number 2302303,Milad Abolhasani and co-workers present a self-driving lab, called Smart Dope, for the fast-tracked discovery of doped quantum dots (QDs) for applications in clean energy technologies. Smart Dope utilizes machine learning-guided operation of flow reactors integrated with an in-situ characterizationmodule in a 'closed-loop' fashion to discover the best-in-class QD within one day of autonomous experiments. Volume14, Issue1January 5, 20242470001 RelatedInformation}, number={1}, journal={ADVANCED ENERGY MATERIALS}, author={Bateni, Fazel and Sadeghi, Sina and Orouji, Negin and Bennett, Jeffrey A. and Punati, Venkat S. and Stark, Christine and Wang, Junyu and Rosko, Michael C. and Chen, Ou and Castellano, Felix N. and et al.}, year={2024}, month={Jan} }
 @misc{castellano_rosko_2024, title={Steric and Electronic Influence of Excited-State Decay in Cu(I) MLCT Chromophores}, volume={57}, ISSN={["1520-4898"]}, url={https://doi.org/10.1021/acs.accounts.4c00476}, DOI={10.1021/acs.accounts.4c00476}, abstractNote={ConspectusFor the past 11 years, a dedicated effort in our research group focused on fundamentally advancing the photophysical properties of cuprous}, number={19}, journal={ACCOUNTS OF CHEMICAL RESEARCH}, author={Castellano, Felix N. and Rosko, Michael C.}, year={2024}, month={Sep}, pages={2872–2886} }
 @article{loague_heidari_mann_danilov_castellano_galoppini_meyer_2024, title={Structural Gating Enhances Long-Distance Light-Driven Interfacial Electron Transfer}, volume={11}, ISSN={["2374-7951"]}, url={https://doi.org/10.1021/acscentsci.4c01106}, DOI={10.1021/acscentsci.4c01106}, journal={ACS CENTRAL SCIENCE}, author={Loague, Quentin R. and Heidari, Marzieh and Mann, Hayden J. and Danilov, Evgeny O. and Castellano, Felix N. and Galoppini, Elena and Meyer, Gerald J.}, year={2024}, month={Nov} }
 @article{castellano_2024, title={Upconversion Optical Materials}, url={https://doi.org/10.1021/acsaom.4c00343}, DOI={10.1021/acsaom.4c00343}, journal={ACS Applied Optical Materials}, author={Castellano, Felix N.}, year={2024}, month={Sep} }
 @article{volk_epps_yonemoto_masters_castellano_reyes_abolhasani_2023, title={AlphaFlow: autonomous discovery and optimization of multi-step chemistry using a self-driven fluidic lab guided by reinforcement learning}, volume={14}, ISSN={["2041-1723"]}, url={https://doi.org/10.1038/s41467-023-37139-y}, DOI={10.1038/s41467-023-37139-y}, abstractNote={AbstractClosed-loop, autonomous experimentation enables accelerated and material-efficient exploration of large reaction spaces without the need for user intervention. However, autonomous exploration of advanced materials with complex, multi-step processes and data sparse environments remains a challenge. In this work, we present AlphaFlow, a self-driven fluidic lab capable of autonomous discovery of complex multi-step chemistries. AlphaFlow uses reinforcement learning integrated with a modular microdroplet reactor capable of performing reaction steps with variable sequence, phase separation, washing, and continuous in-situ spectral monitoring. To demonstrate the power of reinforcement learning toward high dimensionality multi-step chemistries, we use AlphaFlow to discover and optimize synthetic routes for shell-growth of core-shell semiconductor nanoparticles, inspired by colloidal atomic layer deposition (cALD). Without prior knowledge of conventional cALD parameters, AlphaFlow successfully identified and optimized a novel multi-step reaction route, with up to 40 parameters, that outperformed conventional sequences. Through this work, we demonstrate the capabilities of closed-loop, reinforcement learning-guided systems in exploring and solving challenges in multi-step nanoparticle syntheses, while relying solely on in-house generated data from a miniaturized microfluidic platform. Further application of AlphaFlow in multi-step chemistries beyond cALD can lead to accelerated fundamental knowledge generation as well as synthetic route discoveries and optimization.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Volk, Amanda A. and Epps, Robert W. and Yonemoto, Daniel T. and Masters, Benjamin S. and Castellano, Felix N. and Reyes, Kristofer G. and Abolhasani, Milad}, year={2023}, month={Mar} }
 @article{rosko_espinoza_arteta_kromer_wheeler_castellano_2023, title={Employing Long-Range Inductive Effects to Modulate Metal-to- Ligand Charge Transfer Photoluminescence in Homoleptic Cu(I) Complexes}, volume={62}, ISSN={["1520-510X"]}, url={https://doi.org/10.1021/acs.inorgchem.2c04315}, DOI={10.1021/acs.inorgchem.2c04315}, abstractNote={Four Cu(I) bis(phenanthroline) photosensitizers formulated from a new ligand structural motif (Cu1-Cu4) coded according to their 2,9-substituents were synthesized, structurally characterized, and fully evaluated using steady-state and time-resolved absorption and photoluminescence (PL) measurements as well as electrochemistry. The 2,9-disubstituted-3,4,7,8-tetramethyl-1,10-phenanthroline ligands feature the following six-membered ring systems prepared through photochemical synthesis: 4,4-dimethylcyclohexyl (1), tetrahydro-2H-pyran-4-yl (2), tetrahydro-2H-thiopyran-4-yl (3), and 4,4-difluorocyclohexyl (4). Universally, these Cu(I) metal-to-ligand charge transfer (MLCT) chromophores display excited-state lifetimes on the microsecond time scale at room temperature, including the three longest-lived homoleptic cuprous phenanthroline excited states measured to date in de-aerated CH2Cl2, τ = 2.5-4.3 μs. This series of molecules also feature high PL quantum efficiencies (ΦPL = 5.3-12% in CH2Cl2). Temperature-dependent PL lifetime experiments confirmed that all these molecules exhibit reverse intersystem crossing and display thermally activated delayed PL from a 1MLCT excited state lying slightly above the 3MLCT state, 1050-1490 cm-1. Ultrafast and conventional transient absorption measurements confirmed that the PL originates from the MLCT excited state, which remains sterically arrested, preventing an excessive flattening distortion even when dissolved in Lewis basic CH3CN. Combined PL and electrochemical data provided evidence that Cu1-Cu4 are highly potent photoreductants (Eox* = -1.73 to -1.62 V vs Fc+/0 in CH3CN), whose potentials are altered solely based on which heteroatoms or substituents are resident on the 2,9-appended ring derivatives. It is proposed that long-range electronic inductive effects are responsible for the systematic modulation observed in the PL spectra, excited-state lifetimes, and the ground state absorption spectra and redox potentials. Cu1-Cu4 quantitatively follow the energy gap law, correlating well with structurally related cuprous phenanthrolines and are also shown to triplet photosensitize the excited states of 9,10-diphenylanthracene with bimolecular rate constants ranging from 1.61 to 2.82 × 108 M-1 s-1. The ability to tailor both photophysical and electrochemical properties using long-range inductive effects imposed by the 2,9-ring platforms advocates new directions for future MLCT chromophore discovery.}, number={7}, journal={INORGANIC CHEMISTRY}, author={Rosko, Michael C. and Espinoza, Eli M. and Arteta, Sarah and Kromer, Sarah and Wheeler, Jonathan P. and Castellano, Felix N.}, year={2023}, month={Feb}, pages={3248–3259} }
 @article{kromer_roy_yarnell_taliaferro_castellano_2023, title={Excited state processes of dinuclear Pt(II) complexes bridged by 8-hydroxyquinoline}, volume={3}, ISSN={["1477-9234"]}, url={https://doi.org/10.1039/D3DT00348E}, DOI={10.1039/D3DT00348E}, abstractNote={Two novel dinuclear Pt(ii) complexes featuring 8-hydroxyquinoline bridges were synthesized and found to have photophysical properties dominated by ligand-centered transitions mirroring that of a mononuclear model system, [Pt(8HQ)2].}, journal={DALTON TRANSACTIONS}, author={Kromer, Sarah and Roy, Subhangi and Yarnell, James E. and Taliaferro, Chelsea M. and Castellano, Felix N.}, year={2023}, month={Mar} }
 @article{leshchev_j. s. valentine_kim_mills_roy_chakraborty_biasin_haldrup_hsu_kirschner_et al._2023, title={Revealing Excited-State Trajectories on Potential Energy Surfaces with Atomic Resolution in Real Time}, volume={5}, ISSN={["1521-3773"]}, DOI={10.1002/anie.202304615}, abstractNote={AbstractPhotoexcited molecular trajectories on potential energy surfaces (PESs) prior to thermalization are intimately connected to the photochemical reaction outcome. The excited‐state trajectories of a diplatinum complex featuring photo‐activated metal–metal σ‐bond formation and associated Pt−Pt stretching motions were detected in real time using femtosecond wide‐angle X‐ray solution scattering. The observed motions correspond well with coherent vibrational wavepacket motions detected by femtosecond optical transient absorption. Two key coordinates for intersystem crossing have been identified, the Pt−Pt bond length and the orientation of the ligands coordinated with the platinum centers, along which the excited‐state trajectories can be projected onto the calculated PESs of the excited states. This investigation has gleaned novel insight into electronic transitions occurring on the time scales of vibrational motions measured in real time, revealing ultrafast nonadiabatic or non‐equilibrium processes along excited‐state trajectories involving multiple excited‐state PESs.}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Leshchev, Denis and J. S. Valentine, Andrew and Kim, Pyosang and Mills, Alexis W. and Roy, Subhangi and Chakraborty, Arnab and Biasin, Elisa and Haldrup, Kristoffer and Hsu, Darren J. J. and Kirschner, Matthew S. and et al.}, year={2023}, month={May} }
 @article{bateni_sadeghi_orouji_bennett_punati_stark_wang_rosko_chen_castellano_et al._2023, title={Smart Dope: A Self-Driving Fluidic Lab for Accelerated Development of Doped Perovskite Quantum Dots}, volume={11}, ISSN={["1614-6840"]}, DOI={10.1002/aenm.202302303}, abstractNote={AbstractMetal cation‐doped lead halide perovskite (LHP) quantum dots (QDs) with photoluminescence quantum yields (PLQYs) higher than unity, due to quantum cutting phenomena, are an important building block of the next‐generation renewable energy technologies. However, synthetic route exploration and development of the highest‐performing QDs for device applications remain challenging. In this work, Smart Dope is presented, which is a self‐driving fluidic lab (SDFL), for the accelerated synthesis space exploration and autonomous optimization of LHP QDs. Specifically, the multi‐cation doping of CsPbCl3 QDs using a one‐pot high‐temperature synthesis chemistry is reported. Smart Dope continuously synthesizes multi‐cation‐doped CsPbCl3 QDs using a high‐pressure gas‐liquid segmented flow format to enable continuous experimentation with minimal experimental noise at reaction temperatures up to 255°C. Smart Dope offers multiple functionalities, including accelerated mechanistic studies through digital twin QD synthesis modeling, closed‐loop autonomous optimization for accelerated QD synthetic route discovery, and on‐demand continuous manufacturing of high‐performing QDs. Through these developments, Smart Dope autonomously identifies the optimal synthetic route of Mn‐Yb co‐doped CsPbCl3 QDs with a PLQY of 158%, which is the highest reported value for this class of QDs to date. Smart Dope illustrates the power of SDFLs in accelerating the discovery and development of emerging advanced energy materials.}, journal={ADVANCED ENERGY MATERIALS}, author={Bateni, Fazel and Sadeghi, Sina and Orouji, Negin and Bennett, Jeffrey A. and Punati, Venkat S. and Stark, Christine and Wang, Junyu and Rosko, Michael C. and Chen, Ou and Castellano, Felix N. and et al.}, year={2023}, month={Nov} }
 @article{rafiq_weingartz_kromer_castellano_chen_2023, title={Spin-vibronic coherence drives singlet-triplet conversion}, volume={7}, ISSN={["1476-4687"]}, url={https://doi.org/10.1038/s41586-023-06233-y}, DOI={10.1038/s41586-023-06233-y}, abstractNote={Design-specific control over the transitions between excited electronic states with different spin multiplicities is of the utmost importance in molecular and materials chemistry 1-3 . Previous studies have indicated that the combination of spin-orbit and vibronic effects, collectively termed the spin-vibronic effect, can accelerate quantum-mechanically forbidden transitions at non-adiabatic crossings 4,5 . However, it has been difficult to identify precise experimental manifestations of the spin-vibronic mechanism. Here we present coherence spectroscopy experiments that reveal the interplay between the spin, electronic and vibrational degrees of freedom that drive efficient singlet-triplet conversion in four structurally related dinuclear Pt(II) metal-metal-to-ligand charge-transfer (MMLCT) complexes. Photoexcitation activates the formation of a Pt-Pt bond, launching a stretching vibrational wavepacket. The molecular-structure-dependent decoherence and recoherence dynamics of this wavepacket resolve the spin-vibronic mechanism. We find that vectorial motion along the Pt-Pt stretching coordinates tunes the singlet and intermediate-state energy gap irreversibly towards the conical intersection and subsequently drives formation of the lowest stable triplet state in a ratcheting fashion. This work demonstrates the viability of using vibronic coherences as probes 6-9  to clarify the interplay among spin, electronic and nuclear dynamics in spin-conversion processes, and this could inspire new modular designs to tailor the properties of excited states.}, journal={NATURE}, author={Rafiq, Shahnawaz and Weingartz, Nicholas P. and Kromer, Sarah and Castellano, Felix N. and Chen, Lin X.}, year={2023}, month={Jul} }
 @article{kim_rosko_dang_castellano_teets_2023, title={Sterically Encumbered Heteroleptic Copper(I) <i>β</i>-Diketiminate Complexes with Extended Excited-State Lifetimes}, volume={10}, ISSN={["1520-510X"]}, url={https://doi.org/10.1021/acs.inorgchem.3c02042}, DOI={10.1021/acs.inorgchem.3c02042}, abstractNote={One of the main challenges in developing effective copper(I) photosensitizers is their short excited-state lifetimes, usually attributed to structural distortion upon light excitation. We have previously introduced copper(I) charge-transfer chromophores of the general formula Cu(N^N)(ArNacNac), where N^N is a conjugated diimine ligand and ArNacNac is a substituted β-diketiminate ligand. These chromophores were promising regarding their tunable redox potentials and intense visible absorption but were ineffective as photosensitizers, presumably due to short excited-state lifetimes. Here, we introduce sterically crowded analogues of these heteroleptic chromophores with bulky alkyl substituents on the N^N and/or ArNacNac ligand. Structural analysis was combined with electrochemical and photophysical characterization, including ultrafast transient absorption (UFTA) spectroscopy to investigate the effects of the alkyl groups on the excited-state lifetimes of the complexes. The molecular structures determined by single-crystal X-ray diffraction display more distortion in the ground state as alkyl substituents are introduced into the phenanthroline or the NacNac ligand, showing smaller τ4 values due to the steric hindrance. UFTA measurements were carried out to determine the excited-state dynamics. Sterically encumbered Cu5 and Cu6 display excited-state lifetimes 15-20 times longer than unsubstituted complex Cu1, likely indicating that the incorporation of bulky alkyl substituents inhibits the pseudo-Jahn-Teller (PJT) flattening distortion in the excited state. This work suggests that the steric properties of these heteroleptic copper(I) charge-transfer chromophores can be readily modified and that the excited-state dynamics are strongly responsive to these modifications.}, journal={INORGANIC CHEMISTRY}, author={Kim, Dooyoung and Rosko, Michael C. and Dang, Vinh Q. and Castellano, Felix N. and Teets, Thomas S.}, year={2023}, month={Oct} }
 @article{chen_pedersen_dow_fayad_hauke_rosko_danilov_blakemore_dechert-schmitt_knauber_et al._2022, title={A Unified Approach to Decarboxylative Halogenation of (Hetero)aryl Carboxylic Acids}, volume={144}, ISSN={["1520-5126"]}, url={https://doi.org/10.1021/jacs.2c02392}, DOI={10.1021/jacs.2c02392}, abstractNote={Aryl halides are a fundamental motif in synthetic chemistry, playing a critical role in metal-mediated cross-coupling reactions and serving as important scaffolds in drug discovery. Although thermal decarboxylative functionalization of aryl carboxylic acids has been extensively explored, the scope of existing halodecarboxylation methods remains limited, and there currently exists no unified strategy that provides access to any type of aryl halide from an aryl carboxylic acid precursor. Herein, we report a general catalytic method for direct decarboxylative halogenation of (hetero)aryl carboxylic acids via ligand-to-metal charge transfer. This strategy accommodates an exceptionally broad scope of substrates. We leverage an aryl radical intermediate toward divergent functionalization pathways: (1) atom transfer to access bromo- or iodo(hetero)arenes or (2) radical capture by copper and subsequent reductive elimination to generate chloro- or fluoro(hetero)arenes. The proposed ligand-to-metal charge transfer mechanism is supported through an array of spectroscopic studies.}, number={18}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, publisher={American Chemical Society (ACS)}, author={Chen, Tiffany Q. and Pedersen, P. Scott and Dow, Nathan W. and Fayad, Remi and Hauke, Cory E. and Rosko, Michael C. and Danilov, Evgeny O. and Blakemore, David C. and Dechert-Schmitt, Anne-Marie and Knauber, Thomas and et al.}, year={2022}, month={May}, pages={8296–8305} }
 @article{reichle_sterzel_kreitmeier_fayad_castellano_rehbein_reiser_2022, title={Copper(ii)-photocatalyzed decarboxylative oxygenation of carboxylic acids}, volume={58}, ISSN={["1364-548X"]}, url={https://doi.org/10.1039/D2CC00570K}, DOI={10.1039/D2CC00570K}, abstractNote={Choosing the right coordination geometry for the light-induced Cu(ii)-catalyzed oxidative decarboxylation.}, number={28}, journal={CHEMICAL COMMUNICATIONS}, publisher={Royal Society of Chemistry (RSC)}, author={Reichle, Alexander and Sterzel, Hannes and Kreitmeier, Peter and Fayad, Remi and Castellano, Felix N. and Rehbein, Julia and Reiser, Oliver}, year={2022}, month={Feb} }
 @article{zhang_hudson_castellano_2022, title={Engineering Long-Lived Blue Photoluminescence from InP Quantum Dots Using Isomers of Naphthoic Acid}, volume={144}, ISSN={["1520-5126"]}, url={https://doi.org/10.1021/jacs.1c12207}, DOI={10.1021/jacs.1c12207}, abstractNote={Leveraging triplet excitons in semiconductor quantum dots (QDs) in concert with surface-anchored molecules to produce long-lifetime thermally activated delayed photoluminescence (TADPL) continues to emerge as a promising technology in diverse areas including photochemical catalysis and light generation. All QDs presently used to generate TADPL in QD/molecule constructs contain toxic metals including Cd(II) and Pb(II), ultimately limiting potential real-world applications. Here, we report newly conceived blue-emitting TADPL-producing nanomaterials featuring InP QDs interfaced with 1- and 2-naphthoic acid (1-NA and 2-NA) ligands. These constitutional isomers feature similar triplet energies but disparate triplet lifetimes, translating into InP-based TADPL processes displaying two distinct average lifetime ranges upon cooling from 293 to 193 K. The time constants fall between 4.4 and 59.2 μs in the 2-NA-decorated InP QDs while further expanding between 84.2 and 733.2 μs in the corresponding 1-NA-ligated InP materials, representing a 167-fold time window. The resulting long-lived excited states enabled facile bimolecular triplet sensitization of 1O2 phosphorescence in the near-IR and promoted sensitized triplet-triplet annihilation photochemistry in 2,5-diphenyloxazole. We speculate that the discovery of new nanomaterials exhibiting TADPL lies on the horizon as myriad QDs can be readily derivatized using isomers of numerous classes of surface-anchoring chromophores yielding precisely regulated photophysical properties.}, number={8}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, publisher={American Chemical Society (ACS)}, author={Zhang, Xingao and Hudson, Margaret H. and Castellano, Felix N.}, year={2022}, month={Mar}, pages={3527–3534} }
 @article{kim_kim_mills_chakraborty_kromer_valentine_castellano_li_chen_2022, title={Ligand-Structure-Dependent Coherent Vibrational Wavepacket Dynamics in Pyrazolate-Bridged Pt(II) Dimers}, volume={7}, ISSN={["1932-7455"]}, url={https://doi.org/10.1021/acs.jpcc.2c02256}, DOI={10.1021/acs.jpcc.2c02256}, abstractNote={Bimetallic transition metal complexes have gained increasing attention because of their versatile functions in solar energy conversion and photonics applications arising from intermetal electronic coupling. In bimetallic platinum (Pt) complexes, electronic communication between the Pt-centered and ligand-centered moieties has been shown to be critical for defining their excited-state dynamic trajectories undergoing either localized ligand-centered (LC)/metal-to-ligand charge-transfer (MLCT) transitions or delocalized metal–metal-to-ligand charge-transfer (MMLCT) transitions. The branching of the excited-state intersystem crossing (ISC) trajectories is modulated through structural factors that alter the relative energies of the different states. In this study, we investigated the correlation of the structural factors influencing the excited-state trajectories. With the use of femtosecond broad-band transient absorption (fs-BBTA) spectroscopy, ultrafast dynamics in the excited state of two select Pt(II) dimers have been mapped out using their coherent vibrational wavepacket signatures in the corresponding transient absorption spectra. To examine how the ligand moieties of the Pt(II) dimers influence excited-state dynamics and the coherent vibrational wavepacket behavior, we carried out comparative studies on two pyrazolate-bridged Pt(II) dimers of the general formula [Pt(tBu2Pz)(N^C)]2 [tBu2Pz is 3,5-di-tert-butylpyrazole; N^C is 7,8-benzoquinoline (bzq, 1) or 1-phenylisoquinoline (piq, 2)]. We found that photoexcitation into the low-energy absorption bands of 1 and 2, respectively, induces the formation of 1MMLCT states from which ultrafast ISC proceeds, resulting in stimulated emission quenching and decoherence of the vibrational wavepacket motions. The results obtained in this study suggest that both the energetics and the structural rigidity of the aromatic cyclometalating ligands in 1 and 2 can significantly influence the dynamics along the excited-state trajectory characterized by dephasing of the coherent oscillations. The collective results provide direct evidence of how ligand structure alters electronic dynamics along excited-state trajectories associated with ISC processes, providing insight into using ligand design to steer photochemical processes.}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Kim, Tae Wu and Kim, Pyosang and Mills, Alexis W. and Chakraborty, Arnab and Kromer, Sarah and Valentine, Andrew J. S. and Castellano, Felix N. and Li, Xiaosong and Chen, Lin X.}, year={2022}, month={Jul} }
 @article{gowda_lee_rosko_petersen_castellano_milsmann_2022, title={Long-Lived Photoluminescence of Molecular Group 14 Compounds through Thermally Activated Delayed Fluorescence}, volume={5}, url={https://doi.org/10.1021/acs.inorgchem.2c00182}, DOI={10.1021/acs.inorgchem.2c00182}, abstractNote={Photoluminescent molecules exploiting the sizable spin-orbit coupling constants of main group metals and metalloids to access long-lived triplet excited states are relatively rare compared to phosphorescent transition metal complexes. Here we report the synthesis of three air- and moisture-stable group 14 compounds E(MePDPPh)2, where E = Si, Ge, or Sn and [MePDPPh]2- is the doubly deprotonated form of 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine. In solution, all three molecules exhibit exceptionally long-lived triplet excited states with lifetimes in the millisecond range and show highly efficient photoluminescence (Φ ≤ 0.49) due to competing prompt fluorescence and thermally activated delayed fluorescence at and around room temperature. Temperature-dependent steady-state emission spectra and photoluminescent lifetime measurements provided conclusive evidence for the two distinct emission pathways. Picosecond transient absorption spectroscopy allowed further analysis of the intersystem crossing (ISC) between singlet and triplet manifolds (τISC = 0.25-3.1 ns) and confirmed the expected trend of increased ISC rates for the heavier elements in otherwise isostructural compounds.}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Gowda, Anitha S. and Lee, Tia S. and Rosko, Michael C. and Petersen, Jeffrey L. and Castellano, Felix N. and Milsmann, Carsten}, year={2022}, month={May} }
 @article{dara_mast_razgoniaev_hauke_castellano_ostrowski_2022, title={Real-Time and In Situ Viscosity Monitoring in Industrial Adhesives Using Luminescent Cu(I) Phenanthroline Molecular Sensors}, volume={7}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.2c06554}, DOI={10.1021/acsami.2c06554}, abstractNote={Monitoring the viscosity of polymers in real-time remains a challenge, especially in confined environments where traditional rheological measurements are hard to apply. In this study, we have utilized the luminescent complex [Cu(diptmp)2]+ (diptmp = 2,9-diisopropyl-3,4,7,8-tetramethyl-1,10-phenanthroline) as an optical probe for real-time sensing of viscosity in various adhesives during the curing process (viscosity increases). The emission lifetime of the triplet metal-to-ligand charge transfer (3MLCT) state of [Cu(diptmp)2]+ in epoxy adhesive increased exponentially during curing, similar to viscosity values obtained from oscillatory rheology. The longer lifetime in higher viscosity materials was attributed to changes in the excited-state deactivation processes from a known Jahn-Teller distortion in the Cu(I) geometry from tetrahedral in the ground state to square planar in the excited state. The real-time viscosity was also monitored reversibly by emission lifetime during polymer swelling (viscosity and lifetime decrease) and unswelling (viscosity and lifetime increase). Monitoring emission lifetime, unlike measuring the excited-state lifetime via transient absorption measurements in our previous study, allowed us to measure viscosity in opaque samples which scatter light. The optical probe [Cu(diptmp)2]+ in Gorilla Glue adhesive showed a clear correlation of the emission intensity or lifetime to viscosity during the curing process. We have also compared these lifetime changes using [Ru(bpy)3]2+ (bpy = bipyridine) as a control. [Cu(diptmp)2]+ showed not only a higher emission lifetime but also more ubiquity as a real-time viscosity sensor.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Dara, Ankit and Mast, Derek M. and Razgoniaev, Anton O. and Hauke, Cory E. and Castellano, Felix N. and Ostrowski, Alexis D.}, year={2022}, month={Jul} }
 @article{huffman_bein_atallah_donley_alameh_wheeler_durand_harvey_kessinger_chen_et al._2022, title={Surface Immobilization of a Re(I) Tricarbonyl Phenanthroline Complex to Si(111) through Sonochemical Hydrosilylation}, volume={12}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.2c17078}, DOI={10.1021/acsami.2c17078}, abstractNote={A sonochemical-based hydrosilylation method was employed to covalently attach a rhenium tricarbonyl phenanthroline complex to silicon(111). fac-Re(5-(p-Styrene)-phen)(CO)3Cl (5-(p-styrene)-phen = 5-(4-vinylphenyl)-1,10-phenanthroline) was reacted with hydrogen-terminated silicon(111) in an ultrasonic bath to generate a hybrid photoelectrode. Subsequent reaction with 1-hexene enabled functionalization of remaining atop Si sites. Attenuated total reflectance-Fourier transform infrared spectroscopy confirms attachment of the organometallic complex to silicon without degradation of the organometallic core, supporting hydrosilylation as a strategy for installing coordination complexes that retain their molecular integrity. Detection of Re(I) and nitrogen by X-ray photoelectron spectroscopy (XPS) further support immobilization of fac-Re(5-(p-styrene)-phen)(CO)3Cl. Cyclic voltammetry and electrochemical impedance spectroscopy under white light illumination indicate that fac-Re(5-(p-styrene)-phen)(CO)3Cl undergoes two electron reductions. Mott-Schottky analysis indicates that the flat band potential is 239 mV more positive for p-Si(111) co-functionalized with both fac-Re(5-(p-styrene)-phen)(CO)3Cl and 1-hexene than when functionalized with 1-hexene alone. XPS, ultraviolet photoelectron spectroscopy, and Mott-Schottky analysis show that functionalization with fac-Re(5-(p-styrene)-phen)(CO)3Cl and 1-hexene introduces a negative interfacial dipole, facilitating reductive photoelectrochemistry.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Huffman, Brittany L. and Bein, Gabriella P. and Atallah, Hala and Donley, Carrie L. and Alameh, Reem T. and Wheeler, Jonathan P. and Durand, Nicolas and Harvey, Alexis K. and Kessinger, Matthew C. and Chen, Cindy Y. and et al.}, year={2022}, month={Dec} }
 @article{zhang_castellano_2022, title={Thermally Activated Bright-State Delayed Blue Photoluminescencefrom InP Quantum Dots br}, volume={13}, ISSN={["1948-7185"]}, url={https://doi.org/10.1021/acs.jpclett.2c00582}, DOI={10.1021/acs.jpclett.2c00582}, abstractNote={Thermally activated delayed photoluminescence (TADPL) generated from organic chromophore-functionalized quantum dots (QDs) is potentially beneficial for persistent light generation, QD-based PL sensors, and photochemical synthesis. While previous research demonstrated that naphthoic acid-functionalized InP QDs can be employed as low-toxicity, blue-emissive TADPL materials, the electron trap states inherent in these nanocrystals inhibited the observation of TADPL emerging from the higher-lying bright states. Here, we address this challenge by employing the heterocyclic aromatic compound 8-quinolinecarboxylic acid (QCA), whose triplet energy is strategically positioned to bypass the electron trap states in InP QDs. Transient absorption and photoluminescence spectroscopies revealed the generation of bright-state TADPL from QCA-functionalized InP QDs resulting from a nearly quantitative Dexter-like triplet-triplet energy transfer (TTET) from photoexcited InP QDs to surface-anchored QCA chromophores followed by reverse TTET from these bound molecules to the InP QDs. This modification resulted in a 119-fold increase in the average PL intensity decay time with respect to the as-synthesized InP QDs.}, number={16}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, publisher={American Chemical Society (ACS)}, author={Zhang, Xingao and Castellano, Felix N.}, year={2022}, month={Apr}, pages={3706–3711} }
 @article{brown_mandzhieva_tomhon_theis_castellano_2022, title={Triplet Photosensitized para-Hydrogen Induced Polarization}, volume={11}, ISSN={["2374-7951"]}, url={https://doi.org/10.1021/acscentsci.2c01003}, DOI={10.1021/acscentsci.2c01003}, abstractNote={Despite its enormous utility in structural characterization, nuclear magnetic resonance (NMR) spectroscopy is inherently limited by low spin polarization. One method to address the low polarization is para-hydrogen (p-H2) induced polarization (PHIP) which uses the singlet spin isomer of H2 to generate disparate nuclear spin populations to amplify the associated NMR signals. PHIP often relies on thermal catalysis or, more infrequently, UV-activated catalytic hydrogenation. Light-activated hydrogenation enables direct and timed control over the hyperpolarization of target substrates, critical for identifying short-lived intermediates. Here, we use an established Ir(III) triplet photosensitizer (PS) to visible light sensitize the triplet ligand-field states in the d6-transition metal dihydride Ru(CO)(PPh3)3(H)2 (1). Excitation inside a 9.4 T NMR spectrometer with the PS and a 420 nm blue LED, under 3 atm of p-H2, successfully photosensitized hyperpolarization in 1 and in a range of unsaturated substrates at and below room temperature, up to 1630-fold. In otherwise identical experimental conditions without light activation, no polarization was realized in 1 or the substrates evaluated. We believe triplet-sensitized PHIP (Trip-PHIP) represents a facile experimental means for probing triplet sensitized light activation in transition metal catalysts possessing low-lying triplet ligand-field states, providing mechanistic insight of potentially tremendous value in chemical catalysis.}, number={11}, journal={ACS CENTRAL SCIENCE}, author={Brown, Emily E. and Mandzhieva, Iuliia and TomHon, Patrick M. and Theis, Thomas and Castellano, Felix N.}, year={2022}, month={Nov} }
 @article{kim_valentine_roy_mills_castellano_li_chen_2022, title={Ultrafast branching in intersystem crossing dynamics revealed by coherent vibrational wavepacket motions in a bimetallic Pt(ii) complex}, volume={6}, ISSN={["1364-5498"]}, url={https://doi.org/10.1039/D2FD00009A}, DOI={10.1039/D2FD00009A}, abstractNote={Herein, we investigate the coherent vibrational wavepacket dynamics during the intersystem crossing processes in a bimetallic Pt(ii) complex.}, journal={FARADAY DISCUSSIONS}, author={Kim, Pyosang and Valentine, Andrew J. S. and Roy, Subhangi and Mills, Alexis W. and Castellano, Felix N. and Li, Xiaosong and Chen, Lin X.}, year={2022}, month={Jun} }
 @article{cesana_li_shepard_ting_hart_olson_alvarado_son_steiman_castellano_et al._2022, title={A biohybrid strategy for enabling photoredox catalysis with low-energy light}, volume={8}, ISSN={["2451-9294"]}, DOI={10.1016/j.chempr.2021.10.010}, abstractNote={Natural systems drive the high-energy reactions of photosynthesis with efficient and broadband energy capture. Transition-metal photocatalysts similarly convert light into chemical reactivity, and yet suffer from light-limited operation and require blue-to-UV excitation. In photosynthesis, both light capture and reactivity have been optimized by separation into distinct sites. Inspired by this modular architecture, we synthesized a biohybrid photocatalyst by covalent attachment of the photosynthetic light-harvesting protein R-phycoerythrin (RPE) to the transition-metal photocatalyst tris(2,2′-bipyridine)ruthenium(II) ([Ru(bpy)3]2+). Spectroscopic investigation found that absorbed photoenergy was efficiently funneled from RPE to [Ru(bpy)3]2+. The utility of the biohybrid photocatalyst was demonstrated via an increase in yields for a thiol-ene coupling reaction and a cysteinyl-desulfurization reaction, including recovered reactivity at red wavelengths where [Ru(bpy)3]2+ alone does not absorb.}, number={1}, journal={CHEM}, author={Cesana, Paul T. and Li, Beryl X. and Shepard, Samuel G. and Ting, Stephen I and Hart, Stephanie M. and Olson, Courtney M. and Alvarado, Jesus I. Martinez and Son, Minjung and Steiman, Talia J. and Castellano, Felix N. and et al.}, year={2022}, month={Jan}, pages={174–185} }
 @article{wells_yarnell_sheykhi_palmer_yonemoto_joyce_garakyaraghi_castellano_2021, title={Accessing the triplet manifold of naphthalene benzimidazole-phenanthroline in rhenium(I) bichromophores}, volume={8}, ISSN={["1477-9234"]}, url={https://doi.org/10.1039/D1DT02329B}, DOI={10.1039/D1DT02329B}, abstractNote={Two new Re(i) metal–organic bichromophores containing a phenanthroline appended perinone are shown to quantitatively generate extremely long-lived triplet ligand-centered excited states.}, journal={DALTON TRANSACTIONS}, publisher={Royal Society of Chemistry (RSC)}, author={Wells, Kaylee A. and Yarnell, James E. and Sheykhi, Sara and Palmer, Jonathan R. and Yonemoto, Daniel T. and Joyce, Rosalynd and Garakyaraghi, Sofia and Castellano, Felix N.}, year={2021}, month={Aug} }
 @article{volk_epps_yonemoto_castellano_abolhasani_2021, title={Continuous biphasic chemical processes in a four-phase segmented flow reactor}, volume={6}, ISSN={["2058-9883"]}, url={https://doi.org/10.1039/D1RE00247C}, DOI={10.1039/D1RE00247C}, abstractNote={A four-phase segmented flow regime for continuous biphasic reaction processes is introduced, characterized over 1500 automatically conducted experiments, and used for biphasic ligand exchange of CdSe quantum dots.}, number={8}, journal={REACTION CHEMISTRY & ENGINEERING}, publisher={Royal Society of Chemistry (RSC)}, author={Volk, Amanda A. and Epps, Robert W. and Yonemoto, Daniel and Castellano, Felix N. and Abolhasani, Milad}, year={2021}, month={Jul} }
 @article{yonemoto_papa_sheykhi_castellano_2021, title={Controlling Thermally Activated Delayed Photoluminescence in CdSe Quantum Dots through Triplet Acceptor Surface Coverage}, volume={12}, ISSN={["1948-7185"]}, url={https://doi.org/10.1021/acs.jpclett.1c00746}, DOI={10.1021/acs.jpclett.1c00746}, abstractNote={Quantum-dot/molecule composites (QD/mol) have demonstrated useful photochemical properties for many photonic and optoelectronic applications; however, a comprehensive understanding of these materials remains elusive. This work introduces a series of cadmium(II) selenide/1-pyrenecarboxylic acid (CdSe/PCA) nanomaterials featuring bespoke PCA surface coverage on CdSe585 (coded by the peak of the first exciton absorption band) to glean insight into the QD/mol photophysical behavior. Tailoring the energy gap between the CdSe585 first exciton band (2.1 eV) and the lowest PCA triplet level (T1 = 2.0 eV) to be nearly isoenergetic, strong thermally activated delayed photoluminescence (TADPL) is observed resulting from reverse triplet-triplet energy transfer. The resultant average decay time constant (τobs) of the photoluminescence emanating from CdSe585 is deterministically controlled with surface-bound PCAn chromophores (n = average number of adsorbed PCA molecules) by shifting the triplet excited state equilibrium from the CdSe585 to the PCA molecular triplet reservoir as a function of n.}, number={15}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, publisher={American Chemical Society (ACS)}, author={Yonemoto, Daniel T. and Papa, Christopher M. and Sheykhi, Sara and Castellano, Felix N.}, year={2021}, month={Apr}, pages={3718–3723} }
 @article{antami_bateni_ramezani_hauke_castellano_abolhasani_2021, title={CsPbI3 Nanocrystals Go with the Flow: From Formation Mechanism to Continuous Nanomanufacturing}, volume={11}, ISSN={["1616-3028"]}, url={https://doi.org/10.1002/adfm.202108687}, DOI={10.1002/adfm.202108687}, abstractNote={AbstractDespite the groundbreaking advancements in the synthesis of inorganic lead halide perovskite (LHP) nanocrystals (NCs), stimulated from their intriguing size‐, composition‐, and morphology‐dependent optical and optoelectronic properties, their formation mechanism through the hot‐injection (HI) synthetic route is not well‐understood. In this work, for the first time, in‐flow HI synthesis of cesium lead iodide (CsPbI3) NCs is introduced and a comprehensive understanding of the interdependent competing reaction parameters controlling the NC morphology (nanocube vs nanoplatelet) and properties is provided. Utilizing the developed flow synthesis strategy, a change in the CsPbI3 NC formation mechanism at temperatures higher than 150 °C, resulting in different CsPbI3 morphologies is revealed. Through comparison of the flow‐ versus flask‐based synthesis, deficiencies of batch reactors in reproducible and scalable synthesis of CsPbI3 NCs with fast formation kinetics are demonstrated. The developed modular flow chemistry route provides a new frontier for high‐temperature studies of solution‐processed LHP NCs and enables their consistent and reliable continuous nanomanufacturing for next‐generation energy technologies.}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Antami, Kameel and Bateni, Fazel and Ramezani, Mahdi and Hauke, Cory E. and Castellano, Felix N. and Abolhasani, Milad}, year={2021}, month={Nov} }
 @article{weingartz_mara_roy_hong_chakraborty_brown-xu_phelan_castellano_chen_2021, title={Excited-State Bond Contraction and Charge Migration in a Platinum Dimer Complex Characterized by X-ray and Optical Transient Absorption Spectroscopy}, volume={125}, ISSN={["1520-5215"]}, url={https://doi.org/10.1021/acs.jpca.1c07201}, DOI={10.1021/acs.jpca.1c07201}, abstractNote={Interactions between metal centers in dimeric transition metal complexes (TMCs) play important roles in their excited-state energetics and pathways and, thus, affect their photophysical properties relevant to their applications, for example, photoluminescent materials and photocatalysis. Here, we report electronic and nuclear structural dynamics studies of two photoexcited pyrazolate-bridged [Pt(ppy)(μ-R2pz)]2-type Pt(II) dimers (ppy = 2-phenylpyridine, μ-R2pz = 3,5-substituted pyrazolate): [Pt(ppy)(μ-H2pz)]2 (1) and [Pt(NDI-ppy)(μ-Ph2pz)]2 (2, NDI = 1,4,5,8-naphthalenediimide), both of which have distinct ground-state Pt-Pt distances. X-ray transient absorption (XTA) spectroscopy at the Pt LIII-edge revealed a new d-orbital vacancy due to the one-electron oxidation of the Pt centers in 1 and 2. However, while a transient Pt-Pt contraction was observed in 2, such an effect was completely absent in 1, demonstrating how the excited states of these complexes are determined by the overlap of the Pt (dz2) orbitals, which is tuned by the steric bulk of the pyrazolate R-groups in the 3- and 5-positions. In tandem with analysis of the Pt-Pt distance structural parameter, we observed photoinduced electron transfer in 2 featuring a covalently linked NDI acceptor on the ppy ligand. The formation and subsequent decay of the NDI radical anion absorption signals were detected upon photoexcitation using optical transient absorption spectroscopy. The NDI radical anion decayed on the same time scale, hundreds of picoseconds, as that of the d-orbital vacancy signal of the oxidized Pt-Pt core observed in the XTA measurements. The data indicated an ultrafast formation of the charge-separated state and subsequent charge recombination to the original Pt(II-II) species.}, number={40}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, publisher={American Chemical Society (ACS)}, author={Weingartz, Nicholas P. and Mara, Michael W. and Roy, Subhangi and Hong, Jiyun and Chakraborty, Arnab and Brown-Xu, Samantha E. and Phelan, Brian T. and Castellano, Felix N. and Chen, Lin X.}, year={2021}, month={Oct}, pages={8891–8898} }
 @article{mills_valentine_hoang_roy_castellano_chen_li_2021, title={General Design Rules for Bimetallic Platinum(II) Complexes}, volume={125}, ISSN={["1520-5215"]}, url={https://doi.org/10.1021/acs.jpca.1c05044}, DOI={10.1021/acs.jpca.1c05044}, abstractNote={A series of platinum(II) bimetallic complexes were studied to investigate the effects of ligands on both the geometric and electronic structure. Modulating the Pt-Pt distance through the bridging ligand architecture was found to dictate the nature of the lowest energy electronic transitions, localized in one-half of the molecule or delocalized across the entire molecule. By reducing the separation between the platinum atoms, the lowest energy electronic transitions will be dominated by the metal-metal-to-ligand charge transfer transition. Conversely, by increasing the distance between the platinum atoms, the lowest electronic transition will be largely localized metal-to-ligand charge transfer or ligand centered in nature. Additionally, the cyclometalating ligands were observed to have a noticeable stabilizing effect on the triplet excited states as the conjugation increased, arising from geometric reorientation and increased electron delocalization of the ligands. Such stabilization of the triplet state energy has been shown to alter the excited state potential energy landscape as well as the excited state trajectory.}, number={43}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, publisher={American Chemical Society (ACS)}, author={Mills, Alexis W. and Valentine, Andrew J. S. and Hoang, Kevin and Roy, Subhangi and Castellano, Felix N. and Chen, Lin X. and Li, Xiaosong}, year={2021}, month={Nov}, pages={9438–9449} }
 @article{gallaher_wright_frazer_macqueen_crossley_castellano_schmidt_2021, title={High efficiency deep red to yellow photochemical upconversion under solar irradiance}, url={https://doi.org/10.1039/D1EE02197D}, DOI={10.1039/D1EE02197D}, abstractNote={Photochemical upconversion is performed using champion sensitizers and annihilators to achieve high efficiencies under one sun.}, journal={Energy & Environmental Science}, publisher={Royal Society of Chemistry (RSC)}, author={Gallaher, Joseph K. and Wright, Katherine M. and Frazer, Laszlo and MacQueen, Rowan W. and Crossley, Maxwell J. and Castellano, Felix N. and Schmidt, Timothy W.}, year={2021} }
 @article{yang_sheykhi_zhang_milsmann_castellano_2021, title={Low power threshold photochemical upconversion using a zirconium(iv) LMCT photosensitizer}, volume={12}, ISSN={["2041-6539"]}, url={https://doi.org/10.1039/D1SC01662H}, DOI={10.1039/D1SC01662H}, abstractNote={The LMCT photosensitizer Zr(MesPDPPh)2 paired with DPA-based acceptors enabled low power threshold photochemical upconversion with record-setting quantum efficiencies.}, number={26}, journal={CHEMICAL SCIENCE}, publisher={Royal Society of Chemistry (RSC)}, author={Yang, Mo and Sheykhi, Sara and Zhang, Yu and Milsmann, Carsten and Castellano, Felix N.}, year={2021}, month={Jun} }
 @article{roy_lopez_yarnell_castellano_2021, title={Metal-Metal-to-Ligand Charge Transfer in Pt(II) Dimers Bridged by Pyridyl and Quinoline Thiols}, volume={12}, ISSN={["1520-510X"]}, url={https://doi.org/10.1021/acs.inorgchem.1c02469}, DOI={10.1021/acs.inorgchem.1c02469}, abstractNote={The investigation of two distinct species of square planar dinuclear Pt(II) dimers based on anti-[Pt(C∧N)(μ-N∧S)]2, where C∧N is either 2-phenylpyridine (ppy) or benzo(h)quinoline (bzq) and N∧S is pyridine-2-thiol (pyt), 6-methylpyridine-2-thiol (Mpyt), or 2-quinolinethiol (2QT), is presented. Each molecule was thoroughly characterized with electronic structure calculations, static UV-vis and photoluminescence (PL) spectroscopy, and cyclic voltammetry, along with transient absorbance and time-gated PL experiments. These visible absorbing chromophores feature metal-metal-to-ligand charge-transfer (MMLCT) excited states that originate from intramolecular d8-d8 metal-metal σ-interactions and are manifested in the ground- and excited-state properties of these molecules. All five molecules reported (anti-[Pt(ppy)(μ-Mpyt)]2 could not be isolated), three of which are newly conceived here, possess electronic absorptions past 500 nm and high quantum yield PL emission with spectra extending into the far red (λem > 700 nm), originating from the charge-transfer state in each instance. Each chromophore displays excited-state decay kinetics adequately modeled by single exponentials as recorded using dynamic absorption and PL experiments; each technique yields similar decay kinetics. The combined data illustrate that pyridyl and quinoline-thiolates in conjunction with select cyclometalates represent classes of MMLCT chromophores that exhibit excited-state properties suitable for promoting light-energized chemical reactions and provide a molecular platform suitable for evaluating coherence phenomena in transient metal-metal bond-forming photochemistry.}, journal={INORGANIC CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Roy, Subhangi and Lopez, Antonio A. and Yarnell, James E. and Castellano, Felix N.}, year={2021}, month={Dec} }
 @article{rosko_wells_hauke_castellano_2021, title={Next Generation Cuprous Phenanthroline MLCT Photosensitizer Featuring Cyclohexyl Substituents}, volume={60}, ISSN={["1520-510X"]}, url={https://doi.org/10.1021/acs.inorgchem.1c01242}, DOI={10.1021/acs.inorgchem.1c01242}, abstractNote={A new long-lived, visible-light-absorbing homoleptic Cu(I) metal-to-ligand charge transfer (MLCT) photosensitizer, [Cu(dchtmp)2]PF6 (dchtmp = 2,9-dicyclohexyl-3,4,7,8-tetramethyl-1,10-phenanthroline), has been synthesized, structurally characterized, and evaluated in terms of its molecular photophysics, electrochemistry, and electronic structure. Static and time-resolved transient absorption (TA) and photoluminescence (PL) spectroscopy measured on the title compound in CH2Cl2 (τ = 2.6 μs, ΦPL = 5.5%), CH3CN (τ = 1.5 μs, ΦPL = 2.6%), and THF (τ = 2.0 μs, ΦPL = 3.7%) yielded impressive photophysical metrics even when dissolved in Lewis basic solvents. The combined static spectroscopic data along with ultrafast TA experiments revealed that the pseudo-Jahn-Teller distortion and intersystem crossing dynamics in the MLCT excited state displayed characteristics of being sterically arrested throughout its evolution. Electrochemical and static PL data illustrate that [Cu(dchtmp)2]PF6 is a potent photoreductant (-1.77 V vs Fc+/0 in CH3CN) equal to or greater than all previously investigated homoleptic Cu(I) diimine complexes. Although we successfully prepared the cyclopentyl analog dcptmp (2,9-dicyclopentyl-3,4,7,8-tetramethyl-1,10-phenanthroline) using the same C-C radical coupling photochemistry as dchtmp, the corresponding Cu(I) complex could not be isolated due to the steric hindrance presented at the metal center. Ultimately, the successful preparation of [Cu(dchtmp)2]+ represents a major step forward for the design and discovery of novel earth-abundant photosensitizers made possible through a newly conceived ligand synthetic strategy.}, number={12}, journal={INORGANIC CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Rosko, Michael C. and Wells, Kaylee A. and Hauke, Cory E. and Castellano, Felix N.}, year={2021}, month={Jun}, pages={8394–8403} }
 @article{zhang_hudson_castellano_2021, title={Passivation of Electron Trap States in InP Quantum Dots with Benzoic Acid Ligands}, volume={125}, ISSN={["1932-7455"]}, url={https://doi.org/10.1021/acs.jpcc.1c05594}, DOI={10.1021/acs.jpcc.1c05594}, abstractNote={Low toxicity indium phosphide (InP) quantum dots represent an attractive alternative to heavy-metal-based quantum dots (QDs) in numerous applications including lighting, displays, and photosensitization. However, low photoluminescence quantum yields (PLQYs) resulting from a high density of surface trap states ultimately limit the applications of as-synthesized InP QDs in commercial products. Postsynthetic treatment with Z-type ligands (two-electron acceptors) is often used to passivate the surface traps of the InP QDs, while approaches using X-type ligands (one-electron donors) are less prevalent due to the lack of understanding of how the X-type ligands function to passivate the surface traps. In this study, we report a postsynthetic surface passivation utilizing benzoic acid (BZA) as an X-type surface ligand. To understand how BZA impacts their electronic structure, we conducted spectroscopic studies on InP QDs with various surface modifications, including in situ fluorination and postsynthetic BZA treatment. A comparison of a variety of time-resolved spectroscopic techniques reveals that BZA can selectively remove electron trap states in InP QDs by passivating unsaturated indium atoms at the QD surface. When the BZA treatment is used in combination with a well-established fluoride treatment, the PLQYs of these unshelled InP QDs exceeds 20%. This research advances our understanding of the function of X-type ligands at the InP QD surface and their role in the passivation of unsaturated indium atoms to reduce electron trap states.}, number={33}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, publisher={American Chemical Society (ACS)}, author={Zhang, Xingao and Hudson, Margaret H. and Castellano, Felix N.}, year={2021}, month={Aug}, pages={18362–18371} }
 @article{stratakes_wells_kurtz_castellano_miller_2021, title={Photochemical H2 Evolution from Bis(diphosphine)nickel Hydrides Enables Low-Overpotential Electrocatalysis}, volume={12}, url={https://doi.org/10.1021/jacs.1c10628}, DOI={10.1021/jacs.1c10628}, abstractNote={Molecules capable of both harvesting light and forming new chemical bonds hold promise for applications in the generation of solar fuels, but such first-row transition metal photoelectrocatalysts are lacking. Here we report nickel photoelectrocatalysts for H2 evolution, leveraging visible-light-driven photochemical H2 evolution from bis(diphosphine)nickel hydride complexes. A suite of experimental and theoretical analyses, including time-resolved spectroscopy and continuous irradiation quantum yield measurements, led to a proposed mechanism of H2 evolution involving a short-lived singlet excited state that undergoes homolysis of the Ni-H bond. Thermodynamic analyses provide a basis for understanding and predicting the observed photoelectrocatalytic H2 evolution by a 3d transition metal based catalyst. Of particular note is the dramatic change in the electrochemical overpotential: in the dark, the nickel complexes require strong acids and therefore high overpotentials for electrocatalysis; but under illumination, the use of weaker acids at the same applied potential results in a more than 500 mV improvement in electrochemical overpotential. New insight into first-row transition metal hydride photochemistry thus enables photoelectrocatalytic H2 evolution without electrochemical overpotential (at the thermodynamic potential or 0 mV overpotential). This catalyst system does not require sacrificial chemical reductants or light-harvesting semiconductor materials and produces H2 at rates similar to molecular catalysts attached to silicon.}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Stratakes, Bethany M. and Wells, Kaylee A. and Kurtz, Daniel A. and Castellano, Felix N. and Miller, Alexander J. M.}, year={2021}, month={Dec} }
 @article{karimi_tabei_fayad_saber_danilov_jones_castellano_gabbai_2021, title={Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear Pt-II -> Ge-IV Complex}, volume={9}, ISSN={["1521-3773"]}, url={https://doi.org/10.1002/anie.202107485}, DOI={10.1002/anie.202107485}, abstractNote={AbstractSearching for a connection between the two‐electron redox behavior of Group‐14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o‐(Ph2P)C6H4)2GeIVCl2]PtIICl2 and [(o‐(Ph2P)C6H4)2ClGeIII]PtIIICl3, two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o‐(Ph2P)C6H4)2ClGeIII]PtICl with quantum yields of 1.7 % and 3.2 % for the GeIV–PtII and GeIII–PtIII isomers, respectively. Conversion of the GeIV–PtII isomer into the platinum germyl complex is a rare example of a light‐induced transition‐metal/main‐group‐element bond‐forming process. Finally, transient‐absorption‐spectroscopy studies carried out on the GeIII–PtIII isomer point to a ligand arene–Cl. charge‐transfer complex as an intermediate.}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, publisher={Wiley}, author={Karimi, Mohammadjavad and Tabei, Elham S. and Fayad, Remi and Saber, Mohamed R. and Danilov, Evgeny O. and Jones, Cameron and Castellano, Felix N. and Gabbai, Francois P.}, year={2021}, month={Sep} }
 @article{karimi_tabei_fayad_saber_danilov_jones_castellano_gabbaï_2021, title={Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear PtII→GeIV Complex}, url={https://doi.org/10.1002/ange.202107485}, DOI={10.1002/ange.202107485}, abstractNote={AbstractSearching for a connection between the two‐electron redox behavior of Group‐14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o‐(Ph2P)C6H4)2GeIVCl2]PtIICl2 and [(o‐(Ph2P)C6H4)2ClGeIII]PtIIICl3, two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o‐(Ph2P)C6H4)2ClGeIII]PtICl with quantum yields of 1.7 % and 3.2 % for the GeIV–PtII and GeIII–PtIII isomers, respectively. Conversion of the GeIV–PtII isomer into the platinum germyl complex is a rare example of a light‐induced transition‐metal/main‐group‐element bond‐forming process. Finally, transient‐absorption‐spectroscopy studies carried out on the GeIII–PtIII isomer point to a ligand arene–Cl. charge‐transfer complex as an intermediate.}, journal={Angewandte Chemie}, author={Karimi, Mohammadjavad and Tabei, Elham S. and Fayad, Remi and Saber, Mohamed R. and Danilov, Evgeny O. and Jones, Cameron and Castellano, Felix N. and Gabbaï, François P.}, year={2021}, month={Oct} }
 @article{lai_liu_luo_chen_han_lv_liang_chen_zhang_di_et al._2021, title={Shallow distance-dependent triplet energy migration mediated by endothermic charge-transfer}, volume={12}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-021-21561-1}, abstractNote={AbstractConventional wisdom posits that spin-triplet energy transfer (TET) is only operative over short distances because Dexter-type electronic coupling for TET rapidly decreases with increasing donor acceptor separation. While coherent mechanisms such as super-exchange can enhance the magnitude of electronic coupling, they are equally attenuated with distance. Here, we report endothermic charge-transfer-mediated TET as an alternative mechanism featuring shallow distance-dependence and experimentally demonstrated it using a linked nanocrystal-polyacene donor acceptor pair. Donor-acceptor electronic coupling is quantitatively controlled through wavefunction leakage out of the core/shell semiconductor nanocrystals, while the charge/energy transfer driving force is conserved. Attenuation of the TET rate as a function of shell thickness clearly follows the trend of hole probability density on nanocrystal surfaces rather than the product of electron and hole densities, consistent with endothermic hole-transfer-mediated TET. The shallow distance-dependence afforded by this mechanism enables efficient TET across distances well beyond the nominal range of Dexter or super-exchange paradigms.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Lai, Runchen and Liu, Yangyi and Luo, Xiao and Chen, Lan and Han, Yaoyao and Lv, Meng and Liang, Guijie and Chen, Jinquan and Zhang, Chunfeng and Di, Dawei and et al.}, year={2021}, month={Mar} }
 @article{castellano_2021, title={The chemical landscape of Chemical Physics Reviews}, volume={2}, url={https://doi.org/10.1063/5.0059231}, DOI={10.1063/5.0059231}, abstractNote={First Page}, number={2}, journal={Chemical Physics Reviews}, publisher={AIP Publishing}, author={Castellano, Felix N.}, year={2021}, month={Jun}, pages={020401} }
 @article{kim_valentine_roy_mills_chakraborty_castellano_li_chen_2021, title={Ultrafast Excited-State Dynamics of Photoluminescent Pt(II) Dimers Probed by a Coherent Vibrational Wavepacket}, volume={12}, ISSN={["1948-7185"]}, url={https://doi.org/10.1021/acs.jpclett.1c01289}, DOI={10.1021/acs.jpclett.1c01289}, abstractNote={Intricate potential energy surfaces (PESs) of some transition metal complexes (TMCs) pose challenges in mapping out initial excited-state pathways that could influence photochemical outcomes. Ultrafast intersystem crossing (ISC) dynamics of four structurally related platinum(II) dimer complexes were examined by detecting their coherent vibrational wavepacket (CVWP) motions of Pt-Pt stretching mode in the metal-metal-to-ligand-charge-transfer excited states. Structurally dependent CVWP behaviors (frequency, dephasing time, and oscillation amplitudes) were captured by femtosecond transient absorption spectroscopy, analyzed by short-time Fourier transformation, and rationalized by quantum mechanical calculations, revealing dual ISC pathways. The results suggest that the ligands could fine-tune the PESs to influence the proximity of the conical intersections of the excited states with the Franck-Condon state and thus to control the branching ratio of the dual ISC pathways. This comparative study presents future opportunities in control excited-state trajectories of TMCs via ligand structures.}, number={29}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, publisher={American Chemical Society (ACS)}, author={Kim, Pyosang and Valentine, Andrew J. S. and Roy, Subhangi and Mills, Alexis W. and Chakraborty, Arnab and Castellano, Felix N. and Li, Xiaosong and Chen, Lin X.}, year={2021}, month={Jul}, pages={6794–6803} }
 @article{wells_palmer_yarnell_garakyaraghi_pemberton_favale_valchar_chakraborty_castellano_2021, title={Understanding the influence of geometric and electronic structure on the excited state dynamical and photoredox properties of perinone chromophores}, volume={23}, ISSN={["1463-9084"]}, url={https://doi.org/10.1039/D1CP03870B}, DOI={10.1039/D1CP03870B}, abstractNote={Modulating electronic and geometric structure of perinone chromophores is easily achieved via systematic alteration of aromatic diamine and anhydride building blocks, eliciting deterministic photoredox and excited state dynamical properties.}, number={42}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Wells, Kaylee A. and Palmer, Jonathan R. and Yarnell, James E. and Garakyaraghi, Sofia and Pemberton, Barry C. and Favale, Joseph M. and Valchar, Mary Katharine and Chakraborty, Arnab and Castellano, Felix N.}, year={2021}, month={Nov}, pages={24200–24210} }
 @article{ting_garakyaraghi_taliaferro_shields_scholes_castellano_doyle_2020, title={3d-d Excited States of Ni(II) Complexes Relevant to Photoredox Catalysis: Spectroscopic Identification and Mechanistic Implications}, volume={142}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.0c00781}, DOI={10.1021/jacs.0c00781}, abstractNote={Synthetic organic chemistry has seen major advances due to the merger of nickel and photoredox catalysis. A growing number of Ni-photoredox reactions are proposed to involve generation of excited nickel species, sometimes even in the absence of a photoredox catalyst. To gain insights about these excited states, two of our groups previously studied the photophysics of Ni(t-Bubpy)(o-Tol)Cl, which is representative of proposed intermediates in many Ni-photoredox reactions. This complex was found to have a long-lived excited state (τ = 4 ns), which was computationally assigned as a metal-to-ligand charge transfer (MLCT) state with an energy of 1.6 eV (38 kcal/mol). This work evaluates the computational assignment experimentally using a series of related complexes. Ultrafast UV-Vis and mid-IR transient absorption data suggest that a MLCT state is generated initially upon excitation but decays to a long-lived state that is 3d-d rather than 3MLCT in character. Dynamic cis,trans-isomerization of the square planar complexes was observed in the dark using 1H NMR techniques, supporting that this 3d-d state is tetrahedral and accessible at ambient temperature. Through a combination of transient absorption and NMR studies, the 3d-d state was determined to lie ∼0.5 eV (12 kcal/mol) above the ground state. Because the 3d-d state features a weak Ni-aryl bond, the excited Ni(II) complexes can undergo Ni homolysis to generate aryl radicals and Ni(I), both of which are supported experimentally. Thus, photoinduced Ni-aryl homolysis offers a novel mechanism of initiating catalysis by Ni(I).}, number={12}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Ting, Stephen I. and Garakyaraghi, Sofia and Taliaferro, Chelsea M. and Shields, Benjamin J. and Scholes, Gregory D. and Castellano, Felix N. and Doyle, Abigail G.}, year={2020}, month={Mar}, pages={5800–5810} }
 @article{yang_yarnell_el roz_castellano_2020, title={A Robust Visible-Light-Harvesting Cyclometalated Ir(III) Diimine Sensitizer for Homogeneous Photocatalytic Hydrogen Production}, volume={3}, ISSN={2574-0962 2574-0962}, url={http://dx.doi.org/10.1021/acsaem.9b02269}, DOI={10.1021/acsaem.9b02269}, abstractNote={A cyclometalated Ir(III) diimine complex [Ir(NBI)2(phen)]PF6, NBI = 1,8-naphthalenebenzimidizole and phen = 1,10-phenanthroline, exhibits excellent photostability as a sensitizer in a three-compone...}, number={2}, journal={ACS Applied Energy Materials}, publisher={American Chemical Society (ACS)}, author={Yang, Mo and Yarnell, James E. and El Roz, Karim and Castellano, Felix N.}, year={2020}, month={Jan}, pages={1842–1853} }
 @article{fayad_engl_danilov_hauke_reiser_castellano_2020, title={Correction to “Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)”}, volume={11}, url={https://doi.org/10.1021/acs.jpclett.0c02010}, DOI={10.1021/acs.jpclett.0c02010}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to "Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)"Remi FayadRemi FayadMore by Remi Fayad, Sebastian EnglSebastian EnglMore by Sebastian Engl, Evgeny O. DanilovEvgeny O. DanilovMore by Evgeny O. Danilovhttp://orcid.org/0000-0002-5551-3749, Cory E. HaukeCory E. HaukeMore by Cory E. Haukehttp://orcid.org/0000-0001-8822-0961, Oliver Reiser*Oliver ReiserMore by Oliver Reiserhttp://orcid.org/0000-0003-1430-573X, and Felix N. Castellano*Felix N. CastellanoMore by Felix N. Castellanohttp://orcid.org/0000-0001-7546-8618Cite this: J. Phys. Chem. Lett. 2020, 11, 14, 5749Publication Date (Web):July 7, 2020Publication History Published online7 July 2020Published inissue 16 July 2020https://pubs.acs.org/doi/10.1021/acs.jpclett.0c02010https://doi.org/10.1021/acs.jpclett.0c02010correctionACS PublicationsCopyright © 2020 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views1112Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (442 KB) Get e-Alertsclose Get e-Alerts}, number={14}, journal={The Journal of Physical Chemistry Letters}, publisher={American Chemical Society (ACS)}, author={Fayad, Remi and Engl, Sebastian and Danilov, Evgeny O. and Hauke, Cory E. and Reiser, Oliver and Castellano, Felix N.}, year={2020}, month={Jul}, pages={5749–5749} }
 @article{zhang_lee_favale_leary_petersen_scholes_castellano_milsmann_2020, title={Delayed fluorescence from a zirconium(iv) photosensitizer with ligand-to-metal charge-transfer excited states}, volume={12}, ISSN={1755-4330 1755-4349}, url={http://dx.doi.org/10.1038/s41557-020-0430-7}, DOI={10.1038/s41557-020-0430-7}, abstractNote={Advances in chemical control of the photophysical properties of transition-metal complexes are revolutionizing a wide range of technologies, particularly photocatalysis and light-emitting diodes, but they rely heavily on molecules containing precious metals such as ruthenium and iridium. Although the application of earth-abundant ‘early’ transition metals in photosensitizers is clearly advantageous, a detailed understanding of excited states with ligand-to-metal charge transfer (LMCT) character is paramount to account for their distinct electron configurations. Here we report an air- and moisture-stable, visible light-absorbing Zr(iv) photosensitizer, Zr(MesPDPPh)2, where [MesPDPPh]2− is the doubly deprotonated form of [2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine]. This molecule has an exceptionally long-lived triplet LMCT excited state (τ = 350 μs), featuring highly efficient photoluminescence emission (Ф = 0.45) due to thermally activated delayed fluorescence emanating from the higher-lying singlet configuration with significant LMCT contributions. Zr(MesPDPPh)2 engages in numerous photoredox catalytic processes and triplet energy transfer. Our investigation provides a blueprint for future photosensitizer development featuring early transition metals and excited states with significant LMCT contributions. Understanding the photophysical properties of transition-metal complexes is paramount to advances in photocatalysis, solar energy conversion and light-emitting diodes. Now, long-lived emission via thermally activated delayed fluorescence has been demonstrated from an air- and water-stable zirconium complex featuring excited states with significant ligand-to-metal charge transfer character.}, number={4}, journal={Nature Chemistry}, publisher={Springer Science and Business Media LLC}, author={Zhang, Yu and Lee, Tia S. and Favale, Joseph M. and Leary, Dylan C. and Petersen, Jeffrey L. and Scholes, Gregory D. and Castellano, Felix N. and Milsmann, Carsten}, year={2020}, month={Mar}, pages={345–352} }
 @article{fayad_engl_danilov_hauke_reiser_castellano_2020, title={Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)}, volume={11}, ISSN={1948-7185 1948-7185}, url={http://dx.doi.org/10.1021/acs.jpclett.0c01601}, DOI={10.1021/acs.jpclett.0c01601}, abstractNote={Developments in the field of photoredox catalysis that leveraged the long-lived excited states of Ir(III) and Ru(II) photosensitizers to enable radical coupling processes, paved the way for explorations of synthetic transformations that would otherwise remain unrealized. While first row transition metal photocatalysts have not been as extensively investigated, valuable synthetic transformations covering broad scopes of olefin functionalization have been recently reported featuring photoactivated chlorobis(phenanthroline) Cu(II) complexes. In the current study, the photochemical processes underpinning the catalytic activity of [Cu(dmp)2Cl]Cl (dmp = 2,9-dimethyl-1,10-phenanthroline) were investigated. The combined results from static spectroscopic investigations and conventional photochemistry, ultrafast transient absorption, and electron paramagnetic resonance (EPR) spin trapping experiments, strongly support blue light (ex = 427 or 470 nm) induced Cu-Cl homolytic bond cleavage in [Cu(dmp)2Cl]+ occurring in less than 100 femtoseconds. Based on electronic structure calculations, this bond breaking photochemistry corresponds to the Cl → Cu(II) ligand-to-metal charge transfer (LMCT) transition, unmasking a Cu(I) species [Cu(dmp)2]+ and a Cl• atom, thereby serving as a departure point for both Cu(I)- or Cu(II)-based photoredox transformations. No net photochemistry was observed through direct excitation of the ligand-field transitions in the red (ex = 785 or 800 nm), and all combined experiments indicated no evidence of Cu-Cl bond cleavage under these conditions. The underlying visible light-induced homolysis (VLIH) of a metal-ligand bond yielding a one electron reduced photosensitizer and a radical species, may form the basis for novel photoredox transformations based on first row transition metal complexes.}, number={13}, journal={The Journal of Physical Chemistry Letters}, publisher={American Chemical Society (ACS)}, author={Fayad, Remi and Engl, Sebastian and Danilov, Evgeny O. and Hauke, Cory E. and Reiser, Oliver and Castellano, Felix N.}, year={2020}, month={Jun}, pages={5345–5349} }
 @article{wells_yarnell_palmer_lee_papa_castellano_2020, title={Energy Migration Processes in Re(I) MLCT Complexes Featuring a Chromophoric Ancillary Ligand}, volume={59}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.0c00644}, DOI={10.1021/acs.inorgchem.0c00644}, abstractNote={We present the synthesis, structural characterization, electronic structure calculations, and ultrafast and supra-nanosecond photophysical properties of a series of five Re(I) bichromophores exhibiting metal to ligand charge transfer (MLCT) excited states based on the general formula fac-[Re(N∧N)(CO)3(PNI-py)]PF6, where PNI-py is 4-piperidinyl-1,8-naphthalimidepyridine and N∧N is a diimine ligand (Re1–5), along with their corresponding model chromophores where 4-ethylpyridine was substituted for PNI-py (Mod1–5). The diimine ligands used include 1,10-phenanthroline (phen, 1), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bcp, 2), 4,4′-di-tert-butyl-2,2′-bipyridine (dtbb, 3), 4,4′-diethyl ester-2,2′-bipyridine (deeb, 4), and 2,2′-biquinoline (biq, 5). In these metal–organic bichromophores, structural modification of the diimine ligand resulted in substantial changes to the observed energy transfer efficiencies between the two chromophores as a result of the variation in 3MLCT excited-state energies. The photophysical properties and energetic pathways of the model chromophores were investigated in parallel to accurately track the changes that arose from introduction of the organic chromophore pendant on the ancillary ligand. All relevant photophysical and energy transfer processes were probed and characterized using time-resolved photoluminescence spectroscopy, ultrafast and nanosecond transient absorption spectroscopy, and time-dependent density functional theory calculations. Of the five bichromophores in this study, four (Re1–4) exhibited a thermal equilibrium between the 3PNI-py and the 3MLCT excited state, drastically extending the lifetimes of the parent model chromophores.}, number={12}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Wells, Kaylee A. and Yarnell, James E. and Palmer, Jonathan R. and Lee, Tia S. and Papa, Christopher M. and Castellano, Felix N.}, year={2020}, month={Jun}, pages={8259–8271} }
 @article{favale_hauke_danilov_yarnell_castellano_2020, title={Ligand-triplet migration in iridium(iii) cyclometalates featuring π-conjugated isocyanide ligands}, volume={49}, ISSN={1477-9226 1477-9234}, url={http://dx.doi.org/10.1039/D0DT02100H}, DOI={10.1039/d0dt02100h}, abstractNote={The degree of ancillary ligand conjugation determines Ir(iii) polychromophoric photophysical properties via manipulation of the triplet excited state manifolds.}, number={29}, journal={Dalton Transactions}, publisher={Royal Society of Chemistry (RSC)}, author={Favale, Joseph M. and Hauke, Cory E. and Danilov, Evgeny O. and Yarnell, James E. and Castellano, Felix N.}, year={2020}, pages={9995–10002} }
 @article{luo_han_chen_li_liang_liu_ding_nie_wang_castellano_et al._2020, title={Mechanisms of triplet energy transfer across the inorganic nanocrystal/organic molecule interface}, volume={11}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-019-13951-3}, DOI={10.1038/s41467-019-13951-3}, abstractNote={AbstractThe mechanisms of triplet energy transfer across the inorganic nanocrystal/organic molecule interface remain poorly understood. Many seemingly contradictory results have been reported, mainly because of the complicated trap states characteristic of inorganic semiconductors and the ill-defined relative energetics between semiconductors and molecules used in these studies. Here we clarify the transfer mechanisms by performing combined transient absorption and photoluminescence measurements, both with sub-picosecond time resolution, on model systems comprising lead halide perovskite nanocrystals with very low surface trap densities as the triplet donor and polyacenes which either favour or prohibit charge transfer as the triplet acceptors. Hole transfer from nanocrystals to tetracene is energetically favoured, and hence triplet transfer proceeds via a charge separated state. In contrast, charge transfer to naphthalene is energetically unfavourable and spectroscopy shows direct triplet transfer from nanocrystals to naphthalene; nonetheless, this “direct” process could also be mediated by a high-energy, virtual charge-transfer state.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Luo, Xiao and Han, Yaoyao and Chen, Zongwei and Li, Yulu and Liang, Guijie and Liu, Xue and Ding, Tao and Nie, Chengming and Wang, Mei and Castellano, Felix N. and et al.}, year={2020}, month={Jan} }
 @article{zhou_castellano_schmidt_hanson_2020, title={On the Quantum Yield of Photon Upconversion via Triplet–Triplet Annihilation}, volume={5}, ISSN={2380-8195 2380-8195}, url={http://dx.doi.org/10.1021/acsenergylett.0c01150}, DOI={10.1021/acsenergylett.0c01150}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVViewpointNEXTOn the Quantum Yield of Photon Upconversion via Triplet–Triplet AnnihilationYan ZhouYan ZhouDepartment of Chemistry & Biochemistry, Florida State University, Tallahassee, Florida 32306, United StatesMore by Yan Zhouhttp://orcid.org/0000-0002-7290-1401, Felix N. Castellano*Felix N. CastellanoDepartment of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States*Email: [email protected]More by Felix N. Castellanohttp://orcid.org/0000-0001-7546-8618, Timothy W. Schmidt*Timothy W. SchmidtARC Centre of Excellence in Exciton Science, School of Chemistry, UNSW, Sydney, NSW 2052, Australia*Email: [email protected]More by Timothy W. Schmidthttp://orcid.org/0000-0001-6691-1438, and Kenneth Hanson*Kenneth HansonDepartment of Chemistry & Biochemistry, Florida State University, Tallahassee, Florida 32306, United States*Email: [email protected]More by Kenneth Hansonhttp://orcid.org/0000-0001-7219-7808Cite this: ACS Energy Lett. 2020, 5, 7, 2322–2326Publication Date (Web):June 22, 2020Publication History Received26 May 2020Accepted4 June 2020Published online22 June 2020Published inissue 10 July 2020https://pubs.acs.org/doi/10.1021/acsenergylett.0c01150https://doi.org/10.1021/acsenergylett.0c01150article-commentaryACS PublicationsCopyright © 2020 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views9758Altmetric-Citations144LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (952 KB) Get e-AlertscloseSUBJECTS:Absorption,Excited states,Luminescence,Quantum mechanics,Quantum yield Get e-Alerts}, number={7}, journal={ACS Energy Letters}, publisher={American Chemical Society (ACS)}, author={Zhou, Yan and Castellano, Felix N. and Schmidt, Timothy W. and Hanson, Kenneth}, year={2020}, month={Jun}, pages={2322–2326} }
 @article{fayad_bui_shepard_castellano_2020, title={Photochemical Upconversion in Water Using Cu(I) MLCT Excited States: Role of Energy Shuttling at the Micellar/Water Interface}, volume={3}, ISSN={2574-0962 2574-0962}, url={http://dx.doi.org/10.1021/acsaem.0c02492}, DOI={10.1021/acsaem.0c02492}, abstractNote={Photochemical upconversion (UC) through triplet–triplet annihilation (TTA), which employs a visible absorbing triplet photosensitizer and an annihilator, is a process that generates a high energy photon from two lower energy photons. TTA-UC has been largely developed in pure organic solvents and solid-state polymeric constructs while featuring near exclusive use of rare and expensive metals within the photosensitizer. In this current investigation, we demonstrate that TTA-UC from the long lifetime earth-abundant photosensitizer [Cu(dsbtmp)2](PF)6 (dsbtmp = 2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline), abbreviated as Cu-PS, functions in water through encapsulation within a cationic-based assembly. Cetyltrimethylammonium bromide was the surfactant of choice as it electrostatically binds the negatively charged water-soluble 10-phenylanthracene-9-carboxylate (PAC) acceptor/annihilator and ultimately facilitates energy transfer across the interface. Efficient triplet–triplet energy transfer (TTET) from Cu-PS to the PAC acceptor was achieved in this aqueous assembly. Unfortunately, the hindered mobility of the PAC moieties ultimately hampered the annihilation process, and this was reflected in attenuated TTA rates and efficiencies. The combined experimental data illustrated that the water-soluble PAC acceptor was able to vectorially deliver the excited-state energy stored in Cu-PS across the interface into the bulk aqueous solution by engaging in excited-state electron transfer with methyl viologen acceptors. These results are important for remotely operating photoredox reactions in water while rendering a photosensitizer spatially isolated in the hydrophobic core of a micelle.}, number={12}, journal={ACS Applied Energy Materials}, publisher={American Chemical Society (ACS)}, author={Fayad, Remi and Bui, Anh Thy and Shepard, Samuel G. and Castellano, Felix N.}, year={2020}, month={Dec}, pages={12557–12564} }
 @article{atallah_taliaferro_wells_castellano_2020, title={Photophysics and ultrafast processes in rhenium(i) diimine dicarbonyls}, volume={49}, ISSN={1477-9226 1477-9234}, url={http://dx.doi.org/10.1039/D0DT01765E}, DOI={10.1039/d0dt01765e}, abstractNote={A series of nine Re(i) diimine dicarbonyl complexes of the general molecular formula cis-[Re(N^N)2(CO)2]+ (N^N are various 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) derivatives) were prepared and spectroscopically investigated.}, number={33}, journal={Dalton Transactions}, publisher={Royal Society of Chemistry (RSC)}, author={Atallah, Hala and Taliaferro, Chelsea M. and Wells, Kaylee A. and Castellano, Felix N.}, year={2020}, pages={11565–11576} }
 @article{valentine_radler_mills_kim_castellano_chen_xiaosong_2020, title={Resolving the ultrafast intersystem crossing in a bimetallic platinum complex (vol 151, 114303, 2019)}, volume={152}, ISSN={["1089-7690"]}, url={https://doi.org/10.1063/5.0009294}, DOI={10.1063/5.0009294}, abstractNote={First Page}, number={16}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Valentine, Andrew J. S. and Radler, Joseph J. and Mills, Alexis and Kim, Pyosang and Castellano, Felix N. and Chen, Lin X. and Xiaosong, Li}, year={2020}, month={Apr} }
 @article{papa_garakyaraghi_granger_anthony_castellano_2020, title={TIPS-pentacene triplet exciton generation on PbS quantum dots results from indirect sensitization}, volume={11}, ISSN={2041-6520 2041-6539}, url={http://dx.doi.org/10.1039/d0sc00310g}, DOI={10.1039/d0sc00310g}, abstractNote={Many fundamental questions remain in the elucidation of energy migration mechanisms across the interface between semiconductor nanomaterials and molecular chromophores.}, number={22}, journal={Chemical Science}, publisher={Royal Society of Chemistry (RSC)}, author={Papa, Christopher M. and Garakyaraghi, Sofia and Granger, Devin B. and Anthony, John E. and Castellano, Felix N.}, year={2020}, pages={5690–5696} }
 @article{yonemoto_papa_mongin_castellano_2020, title={Thermally Activated Delayed Photoluminescence: Deterministic Control of Excited-State Decay}, volume={142}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.0c03331}, DOI={10.1021/jacs.0c03331}, abstractNote={Thermally activated photophysical processes are ubiquitous in numerous organic and metal-organic molecules, leading to chromophores with excited state properties that can be considered an equilibrium mixture of the available low-lying states. Relative populations of the equilibrated states are governed by temperature. Such molecules have been devised as high quantum yield emitters in modern organic light-emitting diode technology and for deterministic excited state lifetime control to enhance chemical reactivity in solar energy conversion and photocatalytic schemes. The recent discovery of thermally activated photophysics at CdSe nanocrystal-molecule interfaces enables a new paradigm wherein molecule-quantum dot constructs are used to systematically generate material with predetermined photophysical response and excited state properties. Semiconductor nanomaterials feature size-tunable energy level engineering, which considerably expands the purview of thermally activated photophysics beyond what is possible using only molecules. This Perspective is intended to provide a non-exhaustive overview of the advances that led to the integration of semiconductor quantum dots in thermally activated delayed photoluminescence (TADPL) schemes and to identify important challenges moving into the future. The initial establishment of excited state lifetime extension utilizing triplet-triplet excited-state equilibria is detailed. Next, advances involving the rational design of molecules composed of both metal-containing and organic-based chromophores that produce the desired TADPL are described. Finally, the recent introduction of semiconductor nanomaterials into hybrid TADPL constructs is discussed, paving the way towards the realization of fine-tuned deterministic excited state lifetime control. It is envisioned that libraries of synthetically facile composites will be broadly deployed as photosensitizers and light emitters for numerous synthetic and optoelectronic applications in the near future.}, number={25}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Yonemoto, Daniel T. and Papa, Christopher M. and Mongin, Cedric and Castellano, Felix N.}, year={2020}, month={Jun}, pages={10883–10893} }
 @article{zhang_chung_huang_vetter_seyitliyev_sun_gundogdu_castellano_danilov_yang_2020, title={Towards radiation detection using Cs2AgBiBr6 double perovskite single crystals}, volume={269}, ISSN={0167-577X}, url={http://dx.doi.org/10.1016/j.matlet.2020.127667}, DOI={10.1016/j.matlet.2020.127667}, abstractNote={In this work, we studied the optical- and electrical- properties of emerging Cs2AgBiBr6 double perovskite single crystals and demonstrated their potential for detecting ionizing radiation. We prepared Cs2AgBiBr6 double perovskite single crystals from a saturated aqueous solution. Low-temperature photoluminescence (PL) was employed to determine the bandgap energies of Cs2AgBiBr6, which are 2.00 eV (indirect) and 2.26 eV (direct) respectively. Using the space charge limited current method, we estimated the density of trap states and mobility of charge carriers as 1.44 × 1010 cm−3 and 7.02 cm2/V-s respectively. A lower bound value of the mobility-lifetime (μ-τ) product of 2.48 × 10−3 cm2/V was determined using 450 nm laser excitation, which was sufficient for ensuring a long drift distance of charge carriers for several radiation detector applications. Furthermore, we tested the direct response of Cs2AgBiBr6 single crystals to X-ray radiation. Our Cs2AgBiBr6 single crystal device with gold electrodes deposited on the two parallel surfaces exhibited excellent linear response to low energy X-rays.}, journal={Materials Letters}, publisher={Elsevier BV}, author={Zhang, Zheng and Chung, Ching-Chang and Huang, Zhengjie and Vetter, Eric and Seyitliyev, Dovletgeldi and Sun, Dali and Gundogdu, Kenan and Castellano, Felix N. and Danilov, Evgeny O. and Yang, Ge}, year={2020}, month={Jun}, pages={127667} }
 @article{van stokkum_jumper_lee_myahkostupov_castellano_scholes_2020, title={Vibronic and excitonic dynamics in perylenediimide dimers and tetramer}, volume={153}, ISSN={0021-9606 1089-7690}, url={http://dx.doi.org/10.1063/5.0024530}, DOI={10.1063/5.0024530}, abstractNote={Broad-band pump–probe spectroscopy combined with global and target analysis is employed to study the vibronic and excitonic dynamics of two dimers and a tetramer of perylenediimides. A simultaneous analysis is developed for two systems that have been measured in the same conditions. This enhances the resolvability of the vibronic and excitonic dynamics of the systems, and the solvent contributions that are common in the experiments. We resolve two oscillations of 1399 cm−1 or 311 cm−1 damped with ≈30/ps involved in vibrational relaxation and two more oscillations of 537 cm−1 or 136 cm−1 damped with ≈3/ps. A relaxation process with a rate of 2.1/ps–3.2/ps that is positively correlated with the excitonic coupling was discovered in all three model systems, attributed to annihilation of the one but lowest exciton state.}, number={22}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={van Stokkum, Ivo H. M. and Jumper, Chanelle C. and Lee, Tia S. and Myahkostupov, Mykhaylo and Castellano, Felix N. and Scholes, Gregory D.}, year={2020}, month={Dec}, pages={224101} }
 @article{palmer_wells_yarnell_favale_castellano_2020, title={Visible-Light-Driven Triplet Sensitization of Polycyclic Aromatic Hydrocarbons Using Thionated Perinones}, volume={11}, ISSN={1948-7185 1948-7185}, url={http://dx.doi.org/10.1021/acs.jpclett.0c01634}, DOI={10.1021/acs.jpclett.0c01634}, abstractNote={Metal-free chromophores that efficiently generate triplet excited states represent promising alternatives with respect to transition metal containing photosensitizers, such as those featuring metal-to-ligand charge transfer (MLCT) excited states. However, such molecular constructs have remained underexplored due to the unclear relationship(s) between molecular structure and efficient/rapid intersystem crossing. In this regard, we present a series of three thionated perinone chromophores serving as a newly conceived class of heavy-metal-free triplet photosensitizers. We demonstrate that thionation of the lone C=O substituent in each highly fluorescent perinone imparts red-shifted absorbance bands that maintain intense extinction coefficients across the visible spectrum, as well as unusually efficient triplet excited state formation as inferred from the measured singlet O2 quantum yields at 1270 nm (Φ∆ = 0.78 - 1.0). Electronic structure calculations revealed the emergence of a low energy S1 (n → π*) excited state in close proximity to a slightly higher energy S2 (π → π*) excited state. The distinct character in each of the two lowest lying singlet state manifolds resulted in the energetic inversion of the corresponding triplet excited states due to differences in electron exchange interactions. Rapid S1 → T1 intersystem crossing (ISC) was thereby facilitated in this manner through spin-orbit coupling as predicted by the El Sayed rules. The lifetimes of the resultant triplet excited states persisted into the microsecond time regime, as measured by transient absorbance spectroscopy, enabling effective bimolecular triplet sensitization of some common polycyclic aromatic hydrocarbons. The synthetically facile interchange of a single O atom to an S atom in the investigated perinones resulted in marked changes to their photophysical properties, namely, conversion of dominant singlet-state fluorescence in the former to long-lived triplet excited states in the latter. The combined results suggest a general strategy for accessing long-lived triplet excited states in organic chromophores featuring a lone C=O moiety resident within its structure, valuable for the design of metal-free triplet photosensitizers.}, number={13}, journal={The Journal of Physical Chemistry Letters}, publisher={American Chemical Society (ACS)}, author={Palmer, Jonathan R. and Wells, Kaylee A. and Yarnell, James E. and Favale, Joseph M. and Castellano, Felix N.}, year={2020}, month={Jun}, pages={5092–5099} }
 @article{awwad_bui_danilov_castellano_2020, title={Visible-Light-Initiated Free-Radical Polymerization by Homomolecular Triplet-Triplet Annihilation}, volume={6}, ISSN={2451-9294}, url={http://dx.doi.org/10.1016/j.chempr.2020.08.019}, DOI={10.1016/j.chempr.2020.08.019}, abstractNote={Polymerization reactions initiated by ultraviolet light are ubiquitous in scores of industrial applications but would markedly benefit from visible-light activation to overcome stability, energy consumption, light penetration, and sample geometry limitations. The current work leverages visible-light-driven homomolecular triplet-triplet annihilation (TTA) in zinc(II) meso-tetraphenylporphyrin (ZnTPP) to initiate facile free-radical polymerization in trimethylolpropane triacrylate (TMPTA) and methyl acrylate (MA) monomers through ultrafast electron transfer quenching. Selective Q-band (S1) excitation of ZnTPP in the green or yellow sensitizes TTA occurring between two 3ZnTPP∗ energized chromophores, ultimately generating the highly reducing S2 excited state on one ZnTPP molecule (Ered = −2.13 V versus saturated calomel electrode, SCE). Subsequently, this S2 state engages in electron transfer with TMPTA or MA, thereby initiating the radical polymerization process. Bimolecular electron transfer was confirmed through optically gated fluorescence upconversion. FT-IR and EPR spin-trapping experiments verified visible-light-initiated polymerization leading to the formation of well-defined macro- and microscopic objects.}, number={11}, journal={Chem}, publisher={Elsevier BV}, author={Awwad, Nancy and Bui, Anh Thy and Danilov, Evgeny O. and Castellano, Felix N.}, year={2020}, month={Nov}, pages={3071–3085} }
 @article{castellano_longobardi_sulicz_2020, title={Welcome to the Debut of Chemical Physics Reviews}, volume={1}, url={https://doi.org/10.1063/5.0036623}, DOI={10.1063/5.0036623}, abstractNote={First Page}, number={1}, journal={Chemical Physics Reviews}, publisher={AIP Publishing}, author={Castellano, Felix N. and Longobardi, Luigi and Sulicz, Amanda N.}, year={2020}, month={Dec}, pages={010401} }
 @article{karki_paul_deitz_poudel_rajan_belfore_danilov_castellano_grassman_arehart_et al._2019, title={Degradation Mechanism in Cu(In,Ga)Se-2 Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer}, volume={9}, ISSN={["2156-3381"]}, url={https://doi.org/10.1109/JPHOTOV.2019.2912707}, DOI={10.1109/JPHOTOV.2019.2912707}, abstractNote={The impact of moisture and heat treatment on the microstructural, chemical, and electrical properties of Cu(In,Ga)Se<sub>2</sub> films and their collective effect on the solar cell device performance was studied. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements show that water exposure causes surface modification and alters the alkali metal distribution, while no composition or structural effect was observed. Deep level transient and optical spectroscopies revealed that the trap densities (<italic>N<sub>T</sub></italic>) for both the <italic>E<sub>V</sub></italic> + 0.65 eV and <italic>E<sub>V</sub></italic> + 0.98 eV traps increase after water exposure, while the majority carrier concentration (<italic>N<sub>A</sub></italic>) decreases. Time-resolved photoluminescence (PL) and steady-state PL measurements indicated the presence of static, not dynamic, quenching. Reduction of open-circuit voltage (<italic>V</italic><sub>OC</sub>) and fill factor (FF) was observed for the devices but was not associated with a change of recombination mechanism, which remains in the absorber space charge region. A small increase in series resistance and shunt conductance accounts for most of the FF change, while the modification in both <italic>N<sub>A</sub></italic> and <italic>N<sub>T</sub></italic> yield most of the change in <italic>V</italic><sub>OC</sub>. A gradient of majority carrier concentration, related to the alkali profile, also yields a small voltage-dependent current collection after moisture and heat treatment.}, number={4}, journal={IEEE JOURNAL OF PHOTOVOLTAICS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Karki, Shankar and Paul, Pran and Deitz, Julia I. and Poudel, Deewakar and Rajan, Grace and Belfore, Benjamin and Danilov, Evgeny O. and Castellano, Felix N. and Grassman, Tyler J. and Arehart, Aaron and et al.}, year={2019}, month={Jul}, pages={1138–1143} }
 @article{yarnell_wells_palmer_breaux_castellano_2019, title={Excited-State Triplet Equilibria in a Series of Re(I)-Naphthalimide Bichromophores}, volume={123}, ISSN={1520-6106 1520-5207}, url={http://dx.doi.org/10.1021/acs.jpcb.9b05688}, DOI={10.1021/acs.jpcb.9b05688}, abstractNote={We present the synthesis, structural characterization, electronic structure calculations, and the ultrafast and supra-nanosecond photophysical properties of a series of five bichromophores of the general structural formula [Re(5-R-phen)(CO)3(dmap)](PF6), where R is a naphthalimide (NI), phen = 1,10-phenanthroline, and dmap is 4-dimethylaminopyridine. The NI chromophore was systematically modified at their 4-positions with -H (NI), -Br (BrNI), phenoxy (PONI), thiobenzene (PSNI), and piperidine (PNI), rendering a series of metal-organic bichromophores (Re1-Re5, respectively) featuring variability in the singlet and triplet energies in the pendant NI subunit. Five closely related organic chromophores as well as [Re(phen)(CO)3(dmap)](PF6) (Re6) were investigated in parallel to appropriately model the photophysical properties exhibited in the bichromophores. The excited state processes of all molecules in this study were elucidated using a combination of transient absorption spectroscopy and time-resolved photoluminescence (PL) spectroscopy, revealing the kinetics of the energy transfer processes occurring between the appended chromophores. The spectroscopic analysis was further supported by electronic structure calculations which identified the origin of many of the experimentally observed electronic transitions.}, number={35}, journal={The Journal of Physical Chemistry B}, publisher={American Chemical Society (ACS)}, author={Yarnell, James E. and Wells, Kaylee A. and Palmer, Jonathan R. and Breaux, Josué M. and Castellano, Felix N.}, year={2019}, month={Aug}, pages={7611–7627} }
 @article{abdel‐latif_epps_kerr_papa_castellano_abolhasani_2019, title={Facile Room‐Temperature Anion Exchange Reactions of Inorganic Perovskite Quantum Dots Enabled by a Modular Microfluidic Platform}, volume={29}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.201900712}, DOI={10.1002/adfm.201900712}, abstractNote={AbstractIn an effort to produce the materials of next‐generation photoelectronic devices, postsynthesis halide exchange reactions of perovskite quantum dots are explored to achieve enhanced bandgap tunability. However, comprehensive understanding of the multifaceted halide exchange reactions is inhibited by their vast relevant parameter space and complex reaction network. In this work, a facile room‐temperature strategy is presented for rapid halide exchange of inorganic perovskite quantum dots. A comprehensive understanding of the halide exchange reactions is provided by isolating reaction kinetics from precursor mixing rates utilizing a modular microfluidic platform, Quantum Dot Exchanger (QDExer). The effects of ligand composition and halide salt source on the rate and extent of the halide exchange reactions are illustrated. This fluidic platform offers a unique time‐ and material‐efficient approach for studies of solution phase‐processed colloidal nanocrystals beyond those studied here and may accelerate the discovery and optimization of next‐generation materials for energy technologies.}, number={23}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Abdel‐Latif, Kameel and Epps, Robert W. and Kerr, Corwin B. and Papa, Christopher M. and Castellano, Felix N. and Abolhasani, Milad}, year={2019}, month={Mar}, pages={1900712} }
 @article{hany_yang_zhou_sun_gundogdu_seyitliyev_danilov_castellano_sun_vetter_et al._2019, title={Low temperature cathodoluminescence study of Fe-doped β-Ga2O3}, volume={257}, ISSN={0167-577X}, url={http://dx.doi.org/10.1016/j.matlet.2019.126744}, DOI={10.1016/j.matlet.2019.126744}, abstractNote={Optical and electrical properties along the b-axis of Fe-doped β-Ga2O3 were studied using low temperature cathodoluminescence (CL) spectroscopy, optical absorption spectroscopy and current-voltage (IV) measurements. The optical absorption spectroscopy showed an absorption edge without near edge shoulder and the corresponding optical bandgap was calculated to be 4.45 eV using direct band gap treatment. The temperature dependent CL measurements exhibited a strong blue to ultraviolet (UV) band composed of multiple low intensity peaks in the blue range, a main blue peak, a main UV peak, and a weak UV band from the as-grown Fe-doped β-Ga2O3. After a controlled annealing in air, the emissions changed to a red to near infrared (R-NIR) band with two sharp peaks and an UV band that is resolved at room temperature to three UV broad peaks. The R-NIR sharp peaks from the air-annealed sample were ascribed to incorporation of nitrogen during air annealing.}, journal={Materials Letters}, publisher={Elsevier BV}, author={Hany, Ibrahim and Yang, Ge and Zhou, Chuanzhen Elaine and Sun, Cheng and Gundogdu, Kenan and Seyitliyev, Dovletgeldi and Danilov, Evgeny O. and Castellano, Felix N. and Sun, Dali and Vetter, Eric and et al.}, year={2019}, month={Dec}, pages={126744} }
 @article{favale_danilov_yarnell_castellano_2019, title={Photophysical Processes in Rhenium(I) Diiminetricarbonyl Arylisocyanides Featuring Three Interacting Triplet Excited States}, volume={58}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.9b01155}, DOI={10.1021/acs.inorgchem.9b01155}, abstractNote={We present a series of four transition-metal complexes based on the rhenium(I) tricarbonyl 1,10-phenanthroline (phen) template, with a lone ancillary arylisocyanide (CNAr) ligand to yield metal-organic chromophores of the generic molecular formula [Re(phen)(CO)3(CNAr)]+ [CNAr = 2,6-diisopropylphenyl isocyanide (1), 4-phenyl-2,6-diisopropylphenyl isocyanide (2), 4-phenylethynyl-2,6-diisopropylphenyl isocyanide (3), and 4-biphenyl-2,6-diisopropylphenyl isocyanide (4)]. This particular series features varied degrees of π-conjugation length in the CNAr moiety, resulting in significant modulation in the resultant photophysical properties. All molecules possess long-lived [8-700 μs at room temperature (RT)], strongly blue-green photoluminescent and highly energetic excited states (λmax,em = 500-518 nm; Φ = 14-64%). Each of these chromophores has been photophysically investigated using static and dynamic spectroscopic techniques, the latter probed from ultrafast to supra-nanosecond time scales using transient absorption and photoluminescence (PL). Time-resolved PL intensity decays recorded as a function of the temperature were consistent with the presence of at least two emissive states lying closely spaced in energy with a third nonemissive state lying much higher in energy and likely ligand-field in character. The combined experimental evidence, along with the aid of electronic structure calculations (density functional theory and time-dependent density functional theory performed at the M06/Def2-SVP/SDD level), illustrates that the CNAr ligand is actively engaged in manipulating the excited-state decay in three of these molecules (2-4), wherein the triplet metal-to-ligand charge-transfer (3MLCT) state along with two distinct triplet ligand-centered (3LC) excited-state configurations (phen and CNAr) conspire to produce the resultant photophysical properties. Because the π conjugation within the CNAr ligand was extended, an interesting shift in the dominant photophysical processes was observed. When the CNAr conjugation length is short, as in 1, the phenanthroline 3LC state dominates, resulting in a configurationally mixed triplet excited state of both LC and MLCT character. With more extended π conjugation in the CNAr subunit (2-4), the initially generated 3LC(phen)/3MLCT excited state ultimately migrates to the CNAr 3LC state on the order of tens of picoseconds. Molecules 3 and 4 in this series also feature unique examples of inorganic excimer formation, as evidenced by dynamic self-quenching in the corresponding PL intensity decays accompanied by the observation of a short-lived low-energy emission feature.}, number={13}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Favale, Joseph M., Jr. and Danilov, Evgeny O. and Yarnell, James E. and Castellano, Felix N.}, year={2019}, month={Jun}, pages={8750–8762} }
 @article{salehi_dong_shin_zhu_papa_thy bui_castellano_so_2019, title={Realization of high-efficiency fluorescent organic light-emitting diodes with low driving voltage}, volume={10}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-019-10260-7}, DOI={10.1038/s41467-019-10260-7}, abstractNote={AbstractIt is commonly accepted that a full bandgap voltage is required to achieving efficient electroluminescence (EL) in organic light-emitting diodes. In this work, we demonstrated organic molecules with a large singlet-triplet splitting can achieve efficient EL at voltages below the bandgap voltage. The EL originates from delayed fluorescence due to triplet fusion. Finally, in spite of a lower quantum efficiency, a blue fluorescent organic light-emitting diode having a power efficiency higher than some of the best thermally activated delayed fluorescent and phosphorescent blue organic light-emitting diodes is demonstrated. The current findings suggest that leveraging triplet fusion from purely organic molecules in organic light-emitting diode materials offers an alternative route to achieve stable and high efficiency blue organic light-emitting diodes.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Salehi, Amin and Dong, Chen and Shin, Dong-Hun and Zhu, Liping and Papa, Christopher and Thy Bui, Anh and Castellano, Felix N. and So, Franky}, year={2019}, month={May} }
 @article{valentine_radler_mills_kim_castellano_chen_li_2019, title={Resolving the ultrafast intersystem crossing in a bimetallic platinum complex}, volume={151}, ISSN={0021-9606 1089-7690}, url={http://dx.doi.org/10.1063/1.5115169}, DOI={10.1063/1.5115169}, abstractNote={Bimetallic platinum complexes have interesting luminescent properties and feature long-lasting vibrational coherence and ultrafast intersystem crossing (ISC) after photoexcitation. Ultrafast triplet formation is driven by very strong spin-orbit coupling in these platinum (II) systems, where relativistic theoretical approaches beyond first-order perturbation theory are desirable. Using a fully variational relativistic theoretical method recently developed by the authors, we investigate the origins of ultrafast ISC in the [Pt(ppy) (μ-tBu2pz)]2 complex (ppy = phenylpyridine, pz = pyrazolate). Spin-orbit coupling values, evaluated along a Born-Oppenheimer molecular dynamics trajectory, are used to propagate electronic populations in time. Using this technique, we estimate ultrafast ISC rates of 15–134 fs in this species for the possible ISC pathways into the three low-lying triplet states.}, number={11}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={Valentine, Andrew J. S. and Radler, Joseph J. and Mills, Alexis and Kim, Pyosang and Castellano, Felix N. and Chen, Lin X. and Li, Xiaosong}, year={2019}, month={Sep}, pages={114303} }
 @article{karki_paul_rajan_belfore_poudel_rockett_danilov_castellano_arehart_marsillac_2019, title={Analysis of Recombination Mechanisms in RbF-Treated CIGS Solar Cells}, volume={9}, ISSN={["2156-3403"]}, url={https://doi.org/10.1109/JPHOTOV.2018.2877596}, DOI={10.1109/JPHOTOV.2018.2877596}, abstractNote={In this paper, we studied the effect of rubidium fluoride (RbF) post-deposition treatment (PDT) on the properties of Cu(In,Ga)Se<sub>2</sub> (CIGS) solar cells. Specifically, the recombination mechanisms were analyzed by a series of characterizations including thermal and optical defect spectroscopies, temperature dependent current density–voltage measurements, and time resolved photoluminescence. It was found that the main effect of RbF PDT on the solar cell was an increase of the open circuit-voltage, <inline-formula><tex-math notation="LaTeX">$V_{{\text{oc}}}$</tex-math></inline-formula>, by 30 mV due to a decrease of the values of the diode quality factor and reverse saturation current. Recombination mechanisms were identified as being in the CIGS space charge region, likely at the grain boundaries and near the CIGS surface. Breakdown of contributions to the <inline-formula><tex-math notation="LaTeX">$V_{{\text{oc}}}$</tex-math></inline-formula> increase showed that part of it is due to an increase of the majority carrier concentration (16 mV) and another to the increase in the minority carrier lifetime (1 mV). The latest is mostly due to a reduction in the E<sub>V</sub>+0.99 eV deep-level trap density. An additional CIGS surface modification (contributing 13 mV), observed by the secondary ion mass spectrometry, is essential to explain the full change in <inline-formula><tex-math notation="LaTeX">$V_{{\text{oc}}}$</tex-math></inline-formula>.}, number={1}, journal={IEEE JOURNAL OF PHOTOVOLTAICS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Karki, Shankar and Paul, Pran and Rajan, Grace and Belfore, Benjamin and Poudel, Deewakar and Rockett, Angus and Danilov, Evgeny and Castellano, Felix and Arehart, Aaron and Marsillac, Sylvain}, year={2019}, month={Jan}, pages={313–318} }
 @article{mcgoorty_singh_deaton_peterson_taliaferro_yingling_castellano_2018, title={Bathophenanthroline Disulfonate Ligand-Induced Self-Assembly of Ir(III) Complexes in Water: An Intriguing Class of Photoluminescent Soft Materials}, volume={3}, ISSN={2470-1343 2470-1343}, url={http://dx.doi.org/10.1021/acsomega.8b02034}, DOI={10.1021/acsomega.8b02034}, abstractNote={Strong evidence of concentration-induced and dissolved electrolyte-induced chromophore aggregation has been universally observed in numerous water soluble bis-cyclometalated Ir(III) photosensitizers bearing the sulfonated diimine ligands bathophenanthroline disulfonate and bathocuproine disulfonate. This new class of aqueous-based soft materials was highly photoluminescent in their aggregated state where detailed spectroscopic investigations of this phenomenon revealed significant blue shifts of their respective photoluminescence emission spectra with concomitant increases in excited-state lifetimes and quantum yields initiating even at micromolar chromophore concentrations in water or upon the addition of a strong electrolyte. A combination of nanoscale particle characterization techniques, static and dynamic photoluminescence spectroscopic studies, along with atomistic molecular dynamics (MD) simulations of these soft materials suggests the formation of small, heterogeneous nanoaggregate structures, wherein the sulfonated diimine ancillary ligand serves as a pro-aggregating subunit in all instances. Importantly, the experimental and MD findings suggest the likelihood of discovering similar aqueous aggregation phenomena occurring in all transition-metal complexes bearing these water-solubilizing diimine ligands.}, number={10}, journal={ACS Omega}, publisher={American Chemical Society (ACS)}, author={McGoorty, Michelle M. and Singh, Abhishek and Deaton, Thomas A. and Peterson, Benjamin and Taliaferro, Chelsea M. and Yingling, Yaroslava G. and Castellano, Felix N.}, year={2018}, month={Oct}, pages={14027–14038} }
 @article{kim_kelley_chakraborty_wong_van duyne_schatz_castellano_chen_2018, title={Coherent Vibrational Wavepacket Dynamics in Platinum(II) Dimers and Their Implications}, volume={122}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/acs.jpcc.8b01636}, DOI={10.1021/acs.jpcc.8b01636}, abstractNote={Vibrational coherence in the metal–metal-to-ligand-charge transfer (MMLCT) excited state of cyclometalated platinum dimers with a pseudo C2 symmetry was investigated where two nearly degenerate transitions from the highest occupied molecular orbital (metal–metal σ* orbital) to higher energy ligand π* orbitals could be simultaneously induced. We observed oscillatory features in femtosecond degenerate transient absorption (TA) signals from complexes [(ppy)Pt(μ-tBu2pz)]2 (1) and anti-[(ppy)Pt(μ-pyt)]2 (2), which are attributed to coherent nuclear motions that modulate the HOMO (antibonding σ*) energy level, and hence, the energy for the MMLCT transition. The characteristics of such coherent nuclear motions, such as the oscillatory frequency and the dephasing time, differ between 1 and 2 and are explained by mainly two structural factors that could influence the vibrational coherence: the Pt–Pt distance (2.97 A for 1 vs 2.85 A for 2) and molecular shape (1 in an “A” frame vs 2 in an “H” frame). Because the el...}, number={25}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Kim, Pyosang and Kelley, Matthew S. and Chakraborty, Arnab and Wong, Nolan L. and Van Duyne, Richard P. and Schatz, George C. and Castellano, Felix N. and Chen, Lin X.}, year={2018}, month={Apr}, pages={14195–14204} }
 @article{boice_garakyaraghi_patrick_sanz_castellano_hicks_2018, title={Diastereomerically Differentiated Excited State Behavior in Ruthenium(II) Hexafluoroacetylacetonate Complexes of Diphenyl Thioindigo Diimine}, volume={57}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.7b02803}, DOI={10.1021/acs.inorgchem.7b02803}, abstractNote={Mono- and diruthenium hexafluoroacetylacetonate (hfac) complexes of the thioindigo-N,N'-diphenyldiimine chelating ligand 3 have been prepared. The thioindigo diimine ligand binds to ruthenium in a bidentate fashion in the mononuclear compound 2 and serves as a bidentate chelating bridging ligand in the diruthenium complexes 1a and 1b. Compound 2 was isolated as a racemic mixture while the diruthenium complexes were isolated as the meso (ΔΛ) 1a and rac (ΔΔ and ΛΛ) 1b diastereomers. In-depth structural characterization of the compounds was performed, including X-ray crystallography, 1H, 13C, and 19F nuclear magnetic resonance (NMR) spectroscopy, and 2D NMR correlation experiments. Electrochemical properties were evaluated utilizing cyclic voltammetry. Ground state optical properties of the complexes were examined using UV-visible spectroscopy and spectroelectrochemistry. The excited state dynamics of the series were investigated by ultrafast transient absorption spectroscopy. Variable temperature NMR experiments demonstrated that the rac diruthenium compound 1b undergoes conformational exchange with a rate constant of 8700 s-1 at 298 K, a behavior that is not observed in the meso diastereomer 1a. The series of complexes possess metal-to-ligand charge transfer (MLCT) absorption bands in the near-infrared (λmax 689-783 nm). The compounds do not display photoluminescence in room temperature solution-phase experiments or in experiments at 77 K. Transient absorption spectroscopy measurements revealed excited states with picosecond lifetimes for 1a, 1b, and 2, and spectroelectrochemical experiments confirmed assignment of the transient species as arising from MLCT transitions. Unexpectedly, the transient absorption measurements revealed disparate time constants for the excited state decay of diastereomers 1a and 1b.}, number={3}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Boice, Geneviève N. and Garakyaraghi, Sofia and Patrick, Brian O. and Sanz, Corey A. and Castellano, Felix N. and Hicks, Robin G.}, year={2018}, month={Jan}, pages={1386–1397} }
 @article{chen_liu_guo_peng_garakyaraghi_papa_castellano_zhao_ma_2018, title={Energy Transfer Dynamics in Triplet–Triplet Annihilation Upconversion Using a Bichromophoric Heavy-Atom-Free Sensitizer}, volume={122}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/acs.jpca.8b05901}, DOI={10.1021/acs.jpca.8b05901}, abstractNote={A heavy-atom-free triplet sensitizer suitable for triplet-triplet annihilation-based photon upconversion was developed from the thermally activated delayed fluorescence (TADF) molecule 4CzPN by covalently tethering a pyrene derivative (DBP) as a triplet acceptor. The triplet exciton produced by 4CzPN is captured by the intramolecular pyrenyl acceptor and subsequently transferred via intermolecular triplet-triplet energy transfer (TTET) to freely diffusing pyrenyl acceptors in toluene. Transient absorption and time-resolved photoluminescence spectroscopy were employed to examine the dynamics of both the intra- and intermolecular TTET processes, and the results indicate that the intramolecular energy transfer from 4CzPN to DBP is swift, quantitative, and nearly irreversible. The reverse intersystem crossing is suppressed while intersystem crossing remains efficient, achieving high triplet yield and long triplet lifetime simultaneously. The ultralong excited state lifetime characteristic of the DBP triplet was shown to be crucial for enhancing the intermolecular TTET efficiency and the subsequent triplet-triplet annihilation photochemistry. It was also demonstrated that with the long triplet lifetime of the tethered DBP, TTET was enabled under low free acceptor concentrations and/or with sluggish molecular diffusion in polymer matrixes.}, number={33}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Chen, Qi and Liu, Yiming and Guo, Xinyan and Peng, Jiang and Garakyaraghi, Sofia and Papa, Christopher M. and Castellano, Felix N. and Zhao, Dahui and Ma, Yuguo}, year={2018}, month={Jul}, pages={6673–6682} }
 @article{garakyaraghi_mccusker_khan_koutnik_bui_castellano_2018, title={Enhancing the Visible-Light Absorption and Excited-State Properties of Cu(I) MLCT Excited States}, volume={57}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.7b03169}, DOI={10.1021/acs.inorgchem.7b03169}, abstractNote={A computationally inspired Cu(I) metal-to-ligand charge transfer (MLCT) chromophore, [Cu(sbmpep)2]+ (sbmpep = 2,9-di(sec-butyl)-3,8-dimethyl-4,7-di(phenylethynyl)-1,10-phenanthroline), was synthesized in seven total steps, prepared from either dichloro- or dibromophenanthroline precursors. Complete synthesis, structural characterization, and electrochemistry, in addition to static and dynamic photophysical properties of [Cu(sbmpep)2]+, are reported on all relevant time scales. UV-Vis absorption spectroscopy revealed significant increases in oscillator strength along with a concomitant bathochromic shift in the MLCT absorption bands with respect to structurally related model complexes (ε = 16 500 M-1 cm-1 at 491 nm). Strong red photoluminescence (Φ = 2.7%, λmax = 687 nm) was observed from [Cu(sbmpep)2]+, which featured an average excited-state lifetime of 1.4 μs in deaerated dichloromethane. Cyclic and differential pulse voltammetry revealed ∼300 mV positive shifts in the measured one-electron reversible reduction and oxidation waves in relation to a Cu(I) model complex possessing identical structural elements without the π-conjugated 4,7-substituents. The excited-state redox potential of [Cu(sbmpep)2]+ was estimated to be -1.36 V, a notably powerful reductant for driving photoredox chemistry. The combination of conventional and ultrafast transient  absorption and luminescence spectroscopy successfully map the excited-state dynamics of [Cu(sbmpep)2]+ from initial photoexcitation to the formation of the lowest-energy MLCT excited state and ultimately its relaxation to the ground state. This newly conceived molecule appears poised for photosensitization reactions involving energy and electron-transfer processes relevant to photochemical upconversion, photoredox catalysis, and solar fuels photochemistry.}, number={4}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Garakyaraghi, Sofia and McCusker, Catherine E. and Khan, Saba and Koutnik, Petr and Bui, Anh Thy and Castellano, Felix N.}, year={2018}, month={Feb}, pages={2296–2307} }
 @article{chakraborty_yarnell_sommer_roy_castellano_2018, title={Excited-State Processes of Cyclometalated Platinum(II) Charge-Transfer Dimers Bridged by Hydroxypyridines}, volume={57}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.7b02736}, DOI={10.1021/acs.inorgchem.7b02736}, abstractNote={A series of four anti-disposed dinuclear platinum(II) complexes featuring metal-metal-to-ligand charge-transfer (MMLCT) excited states, bridged by either 2-hydroxy-6-methylpyridine or 2-hydroxy-6-phenylpyridine and cyclometalated with 7,8-benzoquinoline or 2-phenylpyridine, are presented. The 2-hydroxypyridine bridging ligands control intramolecular d8-d8 metal-metal σ interactions, affecting the frontier orbitals' electronic structure, resulting in marked changes to the ground- and excited-state properties of these complexes. Three of these molecules possess reversible one-electron oxidations in cyclic voltammetry experiments as a result of strong intramolecular metallophilic interactions. In this series of molecules, X-ray crystallography revealed Pt-Pt distances ranging between 2.815 and 2.878 Å; the former represents the shortest reported metal-metal distance for platinum(II) dimers possessing low-energy MMLCT transitions. All four molecules reported here display visible absorption bands beyond 500 nm and feature MMLCT-based red photoluminescence (PL) above 700 nm at room temperature with high PL quantum yields (up to 4%) and long excited-state lifetimes (up to 341 ns). The latter were recorded using both transient PL and transient absorption experiments that self-consistently yielded quantitatively identical excited-state lifetimes. The energy-gap law was successfully applied to this series of chromophores, documenting this behavior for the first time in molecules possessing MMLCT excited states. The combined data illustrate that entirely new classes of MMLCT chromophores can be envisioned using bridging pyridyl hydroxides in cooperation with various C^N cyclometalates to achieve photophysical properties suitable for excited-state electron- and energy-transfer chemistry.}, number={3}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Chakraborty, Arnab and Yarnell, James E. and Sommer, Roger D. and Roy, Subhangi and Castellano, Felix N.}, year={2018}, month={Jan}, pages={1298–1310} }
 @article{deaton_taliaferro_pitman_czerwieniec_jakubikova_miller_castellano_2018, title={Excited-State Switching between Ligand-Centered and Charge Transfer Modulated by Metal–Carbon Bonds in Cyclopentadienyl Iridium Complexes}, volume={57}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.8b02753}, DOI={10.1021/acs.inorgchem.8b02753}, abstractNote={Three series of pentamethylcyclopentadienyl (Cp*) Ir(III) complexes with different bidentate ligands were synthesized and structurally characterized, [Cp*Ir(tpy)L] n+ (tpy = 2-tolylpyridinato; n = 0 or 1), [Cp*Ir(piq)L] n+ (piq = 1-phenylisoquinolinato; n = 0 or 1), and [Cp*Ir(bpy)L] m+ (bpy = 2,2'-bipyridine; m = 1 or 2), featuring a range of monodentate carbon-donor ligands within each series [L = 2,6-dimethylphenylisocyanide; 3,5-dimethylimidazol-2-ylidene (NHC); methyl)]. The spectroscopic and photophysical properties of these molecules and those of the photocatalyst [Cp*Ir(bpy)H]+ were examined to establish electronic structure-photophysical property relationships that engender productive photochemical reactivity of this hydride and its methyl analogue. The Ir(III) chromophores containing ancillary CNAr ligands exhibited features anticipated for predominantly ligand-centered (LC) excited states, and analogues bearing the NHC ancillary exhibited properties consistent with LC excited states containing a small admixture of metal-to-ligand charge-transfer (MLCT) character. However, the molecules featuring anionic and strongly σ-donating methyl or hydride ligands exhibited photophysical properties consistent with a high degree of CT character. Density functional theory calculations suggest that the lowest energy triplet states in these complexes are composed of a mixture of MLCT and ligand-to-ligand CT originating from both the Cp* and methyl or hydride ancillary ligands. The high degree of CT character in the triplet excited states of methyliridium complexes bearing C^N-cyclometalated ligands offer a striking contrast to the photophysical properties of pseudo-octahedral structures fac-Ir(C^N)3 or Ir(C^N)2(acac) that have lowest-energy triplet excited states characterized as primarily LC character with a more moderate MLCT admixture.}, number={24}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Deaton, Joseph C. and Taliaferro, Chelsea M. and Pitman, Catherine L. and Czerwieniec, Rafał and Jakubikova, Elena and Miller, Alexander J. M. and Castellano, Felix N.}, year={2018}, month={Dec}, pages={15445–15461} }
 @article{yarnell_chakraborty_myahkostupov_wright_castellano_2018, title={Long-lived triplet excited state in a platinum(ii) perylene monoimide complex}, volume={47}, ISSN={["1477-9234"]}, url={https://doi.org/10.1039/C8DT02496K}, DOI={10.1039/c8dt02496k}, abstractNote={We report the synthesis and solution based photophysical properties of a new Pt(ii)-terpyridine complex coupled to a perylene monoimide (PMI) chromophoric unit through an acetylene linkage.}, number={42}, journal={DALTON TRANSACTIONS}, publisher={Royal Society of Chemistry (RSC)}, author={Yarnell, James E. and Chakraborty, Arnab and Myahkostupov, Mykhaylo and Wright, Katherine M. and Castellano, Felix N.}, year={2018}, month={Nov}, pages={15071–15081} }
 @article{garakyaraghi_castellano_2018, title={Nanocrystals for Triplet Sensitization: Molecular Behavior from Quantum-Confined Materials}, volume={57}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.7b03219}, DOI={10.1021/acs.inorgchem.7b03219}, abstractNote={ Inorganic semiconductor quantum dot-molecular constructs represent an emerging class of materials functioning as triplet photosensitizers. Fundamental investigations into the exciton transfer/transduction processes at the interface of these hybrid materials have revealed parallels in the operable mechanisms to those established in purely molecular systems. The similarities in the governing energy migration mechanisms in these quantum-confined materials permit conventional photophysical strategies to be implemented in future research endeavors. This Viewpoint provides a perspective on this emerging field of inorganic quantum dots as photosensitizers, in particular the transfer of triplet excitons at the molecule-nanomaterial interface. The current state-of-the-art will be explored while highlighting areas of potential growth toward exploiting these materials in photofunctional solar energy conversion schemes.}, number={5}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Garakyaraghi, Sofia and Castellano, Felix N.}, year={2018}, month={Feb}, pages={2351–2359} }
 @article{yarnell_davydenko_dorovatovskii_khrustalev_timofeeva_castellano_marder_risko_barlow_2018, title={Positional Effects from σ-Bonded Platinum(II) on Intersystem Crossing Rates in Perylenediimide Complexes: Synthesis, Structures, and Photophysical Properties}, volume={122}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/acs.jpcc.8b01003}, DOI={10.1021/acs.jpcc.8b01003}, abstractNote={In this investigation, the synthesis and photophysical properties of a series of new chromophores featuring Pt(II) σ-bonded to perylenediimide (PDI) cores are reported. A Pt(PPh3)2X (X = Cl, Br) moiety was attached to PDI in either the ortho or the bay position (2- or 1-positions respectively) or a Pt(PPh3)2 subunit was used to bridge two bay positions (1- and 12-positions) forming a Pt(II) cyclometalate. Through a combination of steady-state and transient absorption and photoluminescence spectroscopy, the excited-state dynamics of these molecules were revealed, indicating that the Pt atom location on the PDI has a substantial impact on observed intersystem crossing (ISC) rates. The ISC time constants for the bay-substituted and cyclometalated PDIs are between 2.67 and 1.29 ns, respectively, determined by the singlet fluorescence decays from the initially populated singlet excited states. In the case of the ortho-substituted PDI, ISC to the triplet state occurs on the ultrafast time scale with a time cons...}, number={25}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Yarnell, James E. and Davydenko, Iryna and Dorovatovskii, Pavel V. and Khrustalev, Victor N. and Timofeeva, Tatiana V. and Castellano, Felix N. and Marder, Seth R. and Risko, Chad and Barlow, Stephen}, year={2018}, month={Feb}, pages={13848–13862} }
 @article{radler_lingerfelt_castellano_chen_li_2018, title={Role of Vibrational Dynamics on Excited-State Electronic Coherence in a Binuclear Platinum Complex}, volume={122}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/acs.jpca.8b01352}, DOI={10.1021/acs.jpca.8b01352}, abstractNote={Long-lived quantum coherence between excited electronic states can enable highly efficient energy and charge transport processes in chemical systems. Recent pump-probe experiments on binuclear platinum complexes identified persistent, periodic beating of transient absorption anisotropy signals, indicating long excited-state coherence lifetimes. Our previous simulations of the electronic dynamics of these complexes indicate that coherence lifetimes are sensitive to the balance between competitive electronic couplings. The complexes with shorter Pt-Pt distances underwent no appreciable dephasing in the limit of static nuclei, motivating the inclusion of nuclear motion into our simulations. The tert-butyl-substituted complex is studied in this work using the Ehrenfest method for mixed quantum-classical dynamics to investigate the role of vibrational dynamics on a complex shown to support long coherence lifetimes. Results indicate that the inclusion of excited-state vibrations drives a rapid collapse of the two-state coherence prior to the experimentally determined intersystem crossing. This further suggests singlet excited-state coherences may not be prerequisites for long-lived triplet coherences.}, number={23}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Radler, Joseph J. and Lingerfelt, David B. and Castellano, Felix N. and Chen, Lin X. and Li, Xiaosong}, year={2018}, month={Apr}, pages={5071–5077} }
 @article{deaton_chakraborty_czerwieniec_yersin_castellano_2018, title={Temperature dependence of photophysical properties of a dinuclear CCN-cyclometalated Pt(II) complex with an intimate Pt-Pt contact. Zero-field splitting and sub-state decay rates of the lowest triplet}, volume={20}, ISSN={["1463-9084"]}, url={https://doi.org/10.1039/C8CP05213A}, DOI={10.1039/c8cp05213a}, abstractNote={A dinuclear Pt(ii) complexes exhibits an unusually large zero field splitting in its metal–metal-to-ligand charge transfer triplet excited state.}, number={38}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, publisher={Royal Society of Chemistry (RSC)}, author={Deaton, Joseph C. and Chakraborty, Arnab and Czerwieniec, Rafal and Yersin, Hartmut and Castellano, Felix N.}, year={2018}, month={Oct}, pages={25096–25104} }
 @article{taliaferro_danilov_castellano_2018, title={Ultrafast Dynamics of the Metal-to-Ligand Charge Transfer Excited States of Ir(III) Proteo and Deutero Dihydrides}, volume={122}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/acs.jpca.8b02266}, DOI={10.1021/acs.jpca.8b02266}, abstractNote={For decades, transition metal hydrides have been at the forefront of numerous photocatalytic reactions leveraging either photoacid or photohydride generation. Of upmost importance is the nature of the M-H bond itself, which is typically the major site of photochemical reactivity, particularly in Ir(III) hydrides featuring metal-to-ligand charge transfer (MLCT) excited states. As a departure point for understanding the fundamental spectroscopy and photophysics of the MLCT excited states of Ir(III) diimine hydrides, cis-[Ir(bpy)2H2]+ (bpy = 2,2'-bipyridine) and its deuterated analogue cis-[Ir(bpy)2D2]+ were prepared and investigated. The robust nature of these molecules enabled detailed solution-based photophysical studies using ultrafast transient absorption and infrared spectroscopy, executed without the generation of permanent photoproducts. Static Fourier transform infrared and Raman spectra (λex = 785 nm) of these two molecules revealed weak but measurable Ir-H and Ir-D stretching vibrations centered at 2120 and 1510 cm-1, respectively. Short-lived (τ = 25 ps) MLCT excited states were observed for both cis-[Ir(bpy)2H2]+ and cis-[Ir(bpy)2D2]+ following femtosecond pulsed laser excitation at 480 nm in visible and near-IR transient absorption experiments. A similar time constant was measured for the in-phase and out-of-phase Ir-H stretching modes of the triplet excited state between 1900 and 2200 cm-1 using transient IR spectroscopy. The Ir-D stretching modes in the MLCT excited state were masked by bpy-localized vibrations rendering quantitative evaluation of these modes difficult. The time-resolved infrared data were consistent with density functional theory calculated mid-IR difference spectra in both of these molecules, yielding quantitative matches to the measured IR difference spectra. The information presented here provides valuable insight for understanding the primary photophysical events and transient absorption and IR spectroscopic signatures likely to be encountered throughout metal hydride photochemistry.}, number={18}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Taliaferro, Chelsea M. and Danilov, Evgeny O. and Castellano, Felix N.}, year={2018}, month={Apr}, pages={4430–4436} }
 @inbook{deaton_castellano_2017, title={Archetypal Iridium(III) Compounds for Optoelectronic and Photonic Applications}, ISBN={9781119007166 9781119007135}, url={http://dx.doi.org/10.1002/9781119007166.ch1}, DOI={10.1002/9781119007166.ch1}, abstractNote={This chapter presents the photophysical properties and synthesis of the archetypal complexes suitable for the applications of iridium (Ir) complexes. Ir(III) complexes bearing C^N and C^C: cyclometalated ligands possess impressive photophysical properties that make these compounds highly desirable for the optoelectronic and photonic applications. The cyclometalated Ir(III) compounds are highly emissive because the lowest energy excited states are a mixture of metal-to-ligand charge transfer (MLCT) and ligand-centered (LC) Π-Π* states, not the non-radiative d-d states. Phosphorescent Ir(III) complexes have a d6 configuration at the metal center and MLCT or LC excited states instead of MC states as the lowest energy states. Among phosphorescent compounds, cyclometalated complexes of Ir(III) emit from triplet excited states with extraordinary quantum yields and radiative rates. The chapter summarizes synthetic methods for homo- and heteroleptic complexes that comprising tridentate ligands having one or two C-donors.}, booktitle={Iridium(III) in Optoelectronic and Photonics Applications}, publisher={John Wiley & Sons, Ltd}, author={Deaton, Joseph C. and Castellano, Felix N.}, year={2017}, month={Mar}, pages={1–69} }
 @article{lingerfelt_lestrange_radler_brown-xu_kim_castellano_chen_li_2017, title={Can Excited State Electronic Coherence Be Tuned via Molecular Structural Modification? A First-Principles Quantum Electronic Dynamics Study of Pyrazolate-Bridged Pt(II) Dimers}, volume={121}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/acs.jpca.6b12099}, DOI={10.1021/acs.jpca.6b12099}, abstractNote={Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a binuclear platinum complex, where a persistent periodic beating in the transient absorption signal's anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of binuclear platinum complexes exhibiting a range of interplatinum distances. Results suggest that the long-lived coherence can only result when competitive electronic couplings are in balance. At longer Pt-Pt distances, the electronic couplings between the two halves of the binuclear system weaken, and exciton localization and recombination is favored on short time scales. For short Pt-Pt distances, electronic couplings between the states in the coherent superposition are stronger than the coupling with other excitonic states, leading to long-lived coherence.}, number={9}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Lingerfelt, David B. and Lestrange, Patrick J. and Radler, Joseph J. and Brown-Xu, Samantha E. and Kim, Pyosang and Castellano, Felix N. and Chen, Lin X. and Li, Xiaosong}, year={2017}, month={Feb}, pages={1932–1939} }
 @article{koch_myahkostupov_oblinsky_wang_garakyaraghi_castellano_scholes_2017, title={Charge Localization after Ultrafast Photoexcitation of a Rigid Perylene Perylenediimide Dyad Visualized by Transient Stark Effect}, volume={139}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.7b01630}, DOI={10.1021/jacs.7b01630}, abstractNote={The intramolecular charge-transfer (CT) dynamics of a rigid and strongly conjugated perylenediimide-bridge-perylene dyad (PDIPe) has been investigated in dichloromethane using ultrafast transient electronic absorption spectroscopy and quantum chemical calculations. The strong electronic coupling between the dyad units gives rise to a CT band. Its photoexcitation forms a delocalized CT state with well-preserved ion bands despite the strong coupling. In the dyad, the electronic transition dipole moment of the electron donor perylene is aligned along the axis of the electric field vector with respect to the CT species. This alignment makes the donor sensitive to the Stark effect and thus charge density fluctuations in the CT state. Charge localization on the picosecond time scale manifests as a time-dependent Stark shift in the visible region. Quantum chemical calculations reveal a twist around the acetylene bridging unit to be the responsible mechanism generating a partial to an almost complete CT state. An estimate of the electric field strength in the CT state yields approximately 25 MV/cm, which increases to around 31 MV/cm during charge localization. Furthermore, the calculations illustrate the complexity of electronic structure in this strongly delocalized superchromophore and reflect the complications in the interpretation of transient absorption results when compared to steady-state approaches such as spectroelectrochemistry and model chromophore experiments such as photoinduced bimolecular charge transfer.}, number={15}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Koch, Marius and Myahkostupov, Mykhaylo and Oblinsky, Daniel G. and Wang, Siwei and Garakyaraghi, Sofia and Castellano, Felix N. and Scholes, Gregory D.}, year={2017}, month={Apr}, pages={5530–5537} }
 @article{garakyaraghi_mongin_granger_anthony_castellano_2017, title={Delayed Molecular Triplet Generation from Energized Lead Sulfide Quantum Dots}, volume={8}, ISSN={1948-7185}, url={http://dx.doi.org/10.1021/acs.jpclett.7b00546}, DOI={10.1021/acs.jpclett.7b00546}, abstractNote={The generation and transfer of triplet excitons across the molecular-semiconductor interface represents an important technological breakthrough featuring numerous fundamental scientific questions. This contribution demonstrates curious delayed formation of TIPS-pentacene molecular triplet excitons bound on the surface of PbS nanocrystals mediated through the initial production of a proposed charge transfer intermediate following selective excitation of the PbS quantum dots. Ultrafast UV-vis and near-IR transient absorption spectroscopy was used to track the dynamics of the initial PbS exciton quenching as well as time scale of the formation of molecular triplet excited states that persisted for 10 μs on the PbS surface, enabling subsequent energy and electron transfer reactivity. These results provide the pivotal proof-of-concept that PbS nanocrystals absorbing near-IR radiation can ultimately generate molecular triplets on their surfaces through processes distinct from direct Dexter triplet energy transfer. More broadly, this work establishes that small metal chalcogenide semiconductor nanocrystals interfaced with molecular chromophores exhibit behavior reminiscent of supramolecular chemical systems, a potentially impactful concept for nanoscience.}, number={7}, journal={The Journal of Physical Chemistry Letters}, publisher={American Chemical Society (ACS)}, author={Garakyaraghi, Sofia and Mongin, Cédric and Granger, Devin B. and Anthony, John E. and Castellano, Felix N.}, year={2017}, month={Mar}, pages={1458–1463} }
 @article{constantinou_yi_shewmon_klump_peng_garakyaraghi_lo_reynolds_castellano_so_2017, title={Effect of Polymer-Fullerene Interaction on the Dielectric Properties of the Blend}, volume={7}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/AENM.201601947}, DOI={10.1002/AENM.201601947}, abstractNote={It is commonly believed that large dielectric constants are required for efficient charge separation in polymer photovoltaic devices. However, many polymers used in high‐performance solar cells do not possess high dielectric constants. In this work, the effect of polymer–fullerene interactions on the dielectric environment of the active layer blend and the device performance for several donor–acceptor conjugated polymer systems is investigated. It is found that, while none of the high‐performing polymers studied has a dielectric constant value larger than 3, all polymer–fullerene blends have a significantly larger dielectric constant compared to their pristine constituents. Additionally, it is found that the blend dielectric constant reaches a maximum value in fully optimized devices. Using PTB7:PC71BM blends as an example, it is showed that, in addition to a small increase in the dielectric constant, devices fabricated using the optimum processing additive concentration exhibit almost 3X larger excited state polarizability. This large increase in excited state polarizability results in a substantial difference in short‐circuit current and ultimately device performance. The results show that the excited state polarizability critically depends on polymer–fullerene interactions, and can be a leading indicator of device performance for a given material system.}, number={13}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Constantinou, Iordania and Yi, Xueping and Shewmon, Nathan T. and Klump, Erik D. and Peng, Cheng and Garakyaraghi, Sofia and Lo, Chi Kin and Reynolds, John R. and Castellano, Felix N. and So, Franky}, year={2017}, month={Feb}, pages={1601947} }
 @article{yarnell_de la torre_castellano_2017, title={Efficient Phosphorescence from Naphthalenebenzimidizole-Coordinated Iridium(III) Chromophores}, volume={2017}, ISSN={1434-1948}, url={http://dx.doi.org/10.1002/EJIC.201700669}, DOI={10.1002/EJIC.201700669}, abstractNote={The electronic structure and photophysical properties of two phosphorescent iridium(III) cyclometalated complexes are presented. The molecules were synthesized by cyclometalating the ligand 1,8‐naphthalenebenzimidizole (NBI), to an iridium(III) metal center. Two NBI ligands were covalently attached along with a 1,10‐phenanthroline (phen) ligand producing the [Ir(NBI)2(phen)](PF6) complex and three NBI ligands were used to prepare the corresponding tris‐cyclometalate fac‐Ir(NBI)3. The optical properties of these new IrIII molecules were investigated using DFT calculations, photoluminescence spectroscopy, and transient absorption spectroscopy. The molecules at the heart of this study were found to contain long‐lived ligand‐localized triplet excited states on the NBI species, featuring energies suitable for bimolecular photochemical reactions. Both iridium(III) chromophores possess excellent light absorptivity in the visible region of the spectrum with high photoluminescence quantum efficiencies approaching 30 %.}, number={44}, journal={European Journal of Inorganic Chemistry}, publisher={Wiley}, author={Yarnell, James E. and De La Torre, Patricia and Castellano, Felix N.}, year={2017}, month={Sep}, pages={5238–5245} }
 @article{younts_duan_gautam_saparov_liu_mongin_castellano_mitzi_gundogdu_2017, title={Efficient generation of long-lived triplet excitons in 2D hybrid perovskite}, volume={29}, number={9}, journal={Advanced Materials}, author={Younts, R. and Duan, H. S. and Gautam, B. and Saparov, B. and Liu, J. and Mongin, C. and Castellano, F. N. and Mitzi, D. B. and Gundogdu, K.}, year={2017} }
 @article{castellano_2017, title={Inorganic chemistry making iron glow}, volume={543}, number={7647}, journal={Nature}, author={Castellano, F. N.}, year={2017}, pages={627–628} }
 @article{castellano_2017, title={Making iron glow}, volume={543}, ISSN={0028-0836 1476-4687}, url={http://dx.doi.org/10.1038/543627A}, DOI={10.1038/543627A}, abstractNote={An iron complex has been made that has a long-lived excited state and emits light at room temperature as a result of a charge-transfer process. This breakthrough might allow the production of cheap solar cells. See Letter p.695 Transition-metal complexes are used as photosensitizers and photocatalysts, and in light-emitting devices. For these uses, the complexes need to be excited from their ground state to a charge-transfer state, which generally needs to be long-lived to ensure efficient performance. This has made it challenging to replace the scarce but high-performing precious metals used in these complexes with Earth-abundant metals that are cheaper and less toxic. Pavel Chábera et al. now show that a design strategy that utilizes ligands with superior electronic properties yields iron complexes with unprecedented long-lived charge-transfer states. With further development, the approach could deliver iron-based materials for use as light emitters and photosensitizers in solar energy devices.}, number={7647}, journal={Nature}, publisher={Springer Science and Business Media LLC}, author={Castellano, Felix N.}, year={2017}, month={Mar}, pages={627–628} }
 @article{el roz_castellano_2017, title={Photochemical upconversion in water}, volume={53}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/c7cc07188d}, DOI={10.1039/c7cc07188d}, abstractNote={The current investigation achieves photochemical upconversion in pure water using combinations of water soluble Ru(ii) metal-to-ligand charge transfer (MLCT) sensitizers in concert with 9-anthracenecarboxylate (AnCO2−) and 1-pyrenecarboxylate (PyCO2−).}, number={85}, journal={Chem. Commun.}, publisher={Royal Society of Chemistry (RSC)}, author={El Roz, Karim A. and Castellano, Felix N.}, year={2017}, pages={11705–11708} }
 @article{garakyaraghi_koutnik_castellano_2017, title={Photoinduced structural distortions and singlet–triplet intersystem crossing in Cu(i) MLCT excited states monitored by optically gated fluorescence spectroscopy}, volume={19}, ISSN={1463-9076 1463-9084}, url={http://dx.doi.org/10.1039/c7cp03343e}, DOI={10.1039/c7cp03343e}, abstractNote={Comprehensive analysis of the photo-induced structural distortions and singlet–triplet intersystem crossing dynamics of a series of Cu(i) phenanthroline chromophores.}, number={25}, journal={Physical Chemistry Chemical Physics}, publisher={Royal Society of Chemistry (RSC)}, author={Garakyaraghi, Sofia and Koutnik, Petr and Castellano, Felix N.}, year={2017}, pages={16662–16668} }
 @article{razgoniaev_mccusker_castellano_ostrowski_2017, title={Restricted Photoinduced Conformational Change in the Cu(I) Complex for Sensing Mechanical Properties}, volume={6}, ISSN={2161-1653 2161-1653}, url={http://dx.doi.org/10.1021/ACSMACROLETT.7B00465}, DOI={10.1021/ACSMACROLETT.7B00465}, abstractNote={When designing photoresponsive materials, the impact of a polymer host matrix on the photophysical and photochemical properties of chromophores can be dramatic and advantageous for correlating macromolecular properties. Some compounds possess changes in their photophysical response with variation in the surrounding media (e.g., crystalline glass vs solution). This study demonstrates how changes in the excited state dynamics of [Cu(dmp)2]+, where dmp = 2,9-dimethyl-1,10-phenanthroline, are used to quantitatively probe the viscosity of the surrounding polymer matrix. A correlation of both excited state lifetime and photoluminescence emission wavelength on viscosity was observed in different supramolecular materials containing [Cu(dmp)2]+. These effects were attributed to restricted photoinduced structural distortion of the Cu(I) complex as the polymer matrix hardened. This photoluminescence sensor features a greater dynamic range for viscosity sensing (6 orders of magnitude) and displayed larger changes in lifetime response with respect to typical organometallic mechanosensitive probes.}, number={9}, journal={ACS Macro Letters}, publisher={American Chemical Society (ACS)}, author={Razgoniaev, Anton O. and McCusker, Catherine E. and Castellano, Felix N. and Ostrowski, Alexis D.}, year={2017}, month={Aug}, pages={920–924} }
 @article{mongin_moroz_zamkov_castellano_2017, title={Thermally activated delayed photoluminescence from pyrenyl-functionalized CdSe quantum dots}, volume={10}, ISSN={1755-4330 1755-4349}, url={http://dx.doi.org/10.1038/NCHEM.2906}, DOI={10.1038/nchem.2906}, abstractNote={The generation and transfer of triplet excitons across semiconductor nanomaterial–molecular interfaces will play an important role in emerging photonic and optoelectronic technologies, and understanding the rules that govern such phenomena is essential. The ability to cooperatively merge the photophysical properties of semiconductor quantum dots with those of well-understood and inexpensive molecular chromophores is therefore paramount. Here we show that 1-pyrenecarboxylic acid-functionalized CdSe quantum dots undergo thermally activated delayed photoluminescence. This phenomenon results from a near quantitative triplet–triplet energy transfer from the nanocrystals to 1-pyrenecarboxylic acid, producing a molecular triplet-state ‘reservoir’ that thermally repopulates the photoluminescent state of CdSe through endothermic reverse triplet–triplet energy transfer. The photoluminescence properties are systematically and predictably tuned through variation of the quantum dot–molecule energy gap, temperature and the triplet-excited-state lifetime of the molecular adsorbate. The concepts developed are likely to be applicable to semiconductor nanocrystals interfaced with molecular chromophores, enabling potential applications of their combined excited states. The ability to merge the photophysical properties of semiconductor quantum dots with those of well-understood and inexpensive molecular chromophores is important for the development of various emerging photonic and optoelectronic technologies. Now, 1-pyrenecarboxylic acid-functionalized CdSe quantum dots have been shown to undergo thermally activated delayed photoluminescence and display tunable photophysical properties.}, number={2}, journal={Nature Chemistry}, publisher={Springer Science and Business Media LLC}, author={Mongin, Cédric and Moroz, Pavel and Zamkov, Mikhail and Castellano, Felix N.}, year={2017}, month={Dec}, pages={225–230} }
 @article{wang_deloach_jiang_papa_myahkostupov_castellano_liu_dougherty_2017, title={Tuning interfacial spin filters from metallic to resistive within a single organic semiconductor family}, volume={95}, ISSN={2469-9950 2469-9969}, url={http://dx.doi.org/10.1103/PhysRevB.95.241410}, DOI={10.1103/physrevb.95.241410}, abstractNote={Jingying Wang,1 Andrew Deloach,1 Wei Jiang,2 Christopher M. Papa,3 Mykhaylo Myahkostupov,3 Felix N. Castellano,3 Feng Liu,2 and Daniel B. Dougherty1,* 1Department of Physics, North Carolina State University, Raleigh, North Carolina 27695-8202, USA 2Department of Material Science and Engineering, University of Utah, Salt Lake City, Utah 84112, USA 3Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA (Received 6 January 2017; revised manuscript received 26 May 2017; published 30 June 2017)}, number={24}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Wang, Jingying and Deloach, Andrew and Jiang, Wei and Papa, Christopher M. and Myahkostupov, Mykhaylo and Castellano, Felix N. and Liu, Feng and Dougherty, Daniel B.}, year={2017}, month={Jun} }
 @article{hirai_myahkostupov_castellano_gabbai_2016, title={1-Pyrenyl- and 3-Perylenyl-antimony(V) Derivatives for the Fluorescence Turn-On Sensing of Fluoride Ions in Water at Sub-ppm Concentrations}, volume={35}, ISSN={["1520-6041"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84974696668&partnerID=MN8TOARS}, DOI={10.1021/acs.organomet.6b00233}, abstractNote={In the context of our work on main group-based anion sensors, we have synthesized the bromide salts of a series of tetraarylstibonium cations of general formula [ArSbPh3]+ with Ar = 9-phenanthryl ([1]+), 1-pyrenyl- ([2]+), and 3-perylenyl ([3]+). While [1]+ is not stable in water, we found that [2]+ and [3]+ can be used as sensors for the sub-ppm detection of fluoride anions in aqueous solutions consisting of 9/1 (v/v) H2O/DMSO (pH 4.8). Fluoride sensing, which rests on the formation of the fluorostiboranes 2–F and 3–F, is accompanied by a distinct turn-on fluorescence response. This response is especially marked upon conversion of [3]+ into 3–F, with a fluorescence intensity enhancement by ∼8 fold and a quantum yield of 59.2% for 3–F. The relevance of this study is established by demonstrating that [3]+ can be used as a selective fluoride sensor for bottle or tap water.}, number={11}, journal={ORGANOMETALLICS}, author={Hirai, Masato and Myahkostupov, Mykhaylo and Castellano, Felix N. and Gabbai, Francois P.}, year={2016}, month={Jun}, pages={1854–1860} }
 @article{haldrup_dohn_shelby_mara_stickrath_harpham_huang_zhang_moller_chakraborty_et al._2016, title={Butterfly Deformation Modes in a Photoexcited Pyrazolate-Bridged Pt Complex Measured by Time-Resolved X-Ray Scattering in Solution}, volume={120}, ISSN={["1089-5639"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84989246403&partnerID=MN8TOARS}, DOI={10.1021/acs.jpca.6b07728}, abstractNote={Pyrazolate-bridged dinuclear Pt(II) complexes represent a series of molecules with tunable absorption and emission properties that can be directly modulated by structural factors, such as the Pt-Pt distance. However, direct experimental information regarding the structure of the emissive triplet excited state has remained scarce. Using time-resolved wide-angle X-ray scattering (WAXS), the excited triplet state molecular structure of [Pt(ppy)(μ-t-Bu2pz)]2 (ppy = 2-phenylpyridine; t-Bu2pz = 3,5-di-tert-butylpyrazolate), complex 1, was obtained in a dilute (0.5 mM) toluene solution utilizing the monochromatic X-ray pulses at Beamline 11IDD of the Advanced Photon Source. The excited-state structural analysis of 1 was performed based on the results from both transient WAXS measurements and density functional theory calculations to shed light on the primary structural changes in its triplet metal-metal-to-ligand charge-transfer (MMLCT) state, in particular, the Pt-Pt distance and ligand rotation. We found a pronounced Pt-Pt distance contraction accompanied by rotational motions of ppy ligands toward one another in the MMLCT state of 1. Our results suggest that the contraction is larger than what has previously been reported, but they are in good agreement with recent theoretical efforts and suggest the ppy moieties as targets for rational synthesis aimed at tuning the excited-state structure and properties.}, number={38}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Haldrup, Kristoffer and Dohn, Asmus O. and Shelby, Megan L. and Mara, Michael W. and Stickrath, Andrew B. and Harpham, Michael R. and Huang, Jier and Zhang, Xiaoyi and Moller, Klaus B. and Chakraborty, Arnab and et al.}, year={2016}, month={Sep}, pages={7475–7483} }
 @article{khnayzer_olaiya_el roz_castellano_2016, title={Cover Picture: Homogeneous Photocatalytic H2
 Production Using a RuII
 Bathophenanthroline Metal-to-Ligand Charge-Transfer Photosensitizer (ChemPlusChem 10/2016)}, volume={81}, ISSN={2192-6506}, url={http://dx.doi.org/10.1002/CPLU.201600423}, DOI={10.1002/cplu.201600423}, abstractNote={The cover picture shows a representation of photocatalytic hydrogen production from water using a new homogeneous composition. The figure illustrates the absorption of visible light by a chromophore followed by electron transfer processes that lead to the reduction of protons into hydrogen gas. The mechanistic details of an optimized system composed of a ruthenium(II) tris-bathophenanthroline chromophore, N,N-dimethyl-p-toluidine electron donor, and a Co-based molecular catalyst are reported. Details are given in the Full Paper by R. S. Khnayzer et al. on page 1098 in Issue 10, 2016 (DOI: 10.1002/cplu.201600227).}, number={10}, journal={ChemPlusChem}, publisher={Wiley}, author={Khnayzer, Rony S. and Olaiya, Babatunde S. and El Roz, Karim A. and Castellano, Felix N.}, year={2016}, month={Oct}, pages={1015–1015} }
 @article{garakyaraghi_crapps_mccusker_castellano_2016, title={Cuprous Phenanthroline MLCT Chromophore Featuring Synthetically Tailored Photophysics}, volume={55}, ISSN={["1520-510X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84992163171&partnerID=MN8TOARS}, DOI={10.1021/acs.inorgchem.6b01880}, abstractNote={In the interest of expanding the inventory of available long lifetime, photochemically robust, and strongly reducing Cu(I) MLCT sensitizers, we present detailed structural, photophysical, and electrochemical characterization of [Cu(dipp)2]+, dipp = 2,9-diisopropyl-1,10-phenanthroline, and its sterically encumbered tetramethyl analogue [Cu(diptmp)2]+, diptmp = 2,9-diisopropyl-3,4,7,8-tetramethyl-1,10-phenanthroline. The achiral isopropyl substituents enable similar steric bulk effects to the previously investigated sec-butyl substituents while eliminating the complex NMR structural analyses associated with the presence of two chiral centers in the latter. The photophysical properties of [Cu(diptmp)2]+ are impressive, possessing a 2.3 μs lifetime in deaerated CH2Cl2 and a photoluminescence quantum yield of 4.7%, which were slightly attenuated in coordinating tetrahydrofuran (THF) solutions. Nanosecond transient absorption spectroscopy results matched the transient photoluminescence kinetics enabling complete characterization of MLCT excited-state decay in these molecules. The calculated excited-state potential for the Cu2+/Cu+* couple (E = -1.74 V vs Fc+/0) indicated that [Cu(diptmp)2]+* is a strong photoreductant potentially useful for myriad applications. Ultrafast transient absorption measurements performed in THF solutions are also reported, yielding the relative time scales for both the pseudo-Jahn-Teller distortion (0.4-0.8 ps in [Cu(dipp)2]+ and 0.12-0.5 ps in [Cu(diptmp)2]+) and singlet-triplet intersystem crossing (6.4-10.1 ps for [Cu(dipp)2]+ and 3.5-5.4 ps for [Cu(diptmp)2]+) within these molecules. The disparity in the time scales of pseudo-Jahn-Teller distortion and intersystem crossing between two complexes with different anticipated excited-state geometries suggests that strongly impeded structural distortion in the MLCT excited state (i.e., [Cu(diptmp)2]+) enables more rapid surface crossings in the initial deactivation dynamics.}, number={20}, journal={INORGANIC CHEMISTRY}, author={Garakyaraghi, Sofia and Crapps, Peter D. and McCusker, Catherine E. and Castellano, Felix N.}, year={2016}, month={Oct}, pages={10628–10636} }
 @article{mongin_garakyaraghi_razgoniaeva_zamkov_castellano_2016, title={Direct observation of triplet energy transfer from semiconductor nanocrystals}, volume={351}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84961377145&partnerID=MN8TOARS}, DOI={10.1126/science.aad6378}, abstractNote={A different way to put triplets in play
          
            Most molecules adopt a singlet spin configuration: All their electrons are arranged in pairs. Unpaired triplet states engage in a variety of useful reactions but are hard to produce. Quantum mechanics dictates that photo-excitation from singlet to triplet states is inefficient. Instead, chemists rely on sensitizers, which populate the triplet states of their neighbors through energy transfer after absorbing light themselves. Mongin
            et al.
            now show that certain nanoparticles can act as triplet sensitizers.
          
          
            Science
            , this issue p.
            369
          }, number={6271}, journal={Science}, author={Mongin, C. and Garakyaraghi, S. and Razgoniaeva, N. and Zamkov, M. and Castellano, F.N.}, year={2016}, pages={369–372} }
 @article{castellano_2016, title={Editorial for the ACS Select Virtual Issue on Emerging Investigators in Inorganic Photochemistry and Photophysics}, volume={55}, ISSN={["1520-510X"]}, url={https://doi.org/10.1021/acs.inorgchem.6b02830}, DOI={10.1021/acs.inorgchem.6b02830}, abstractNote={ADVERTISEMENT RETURN TO ISSUEEditorialNEXTEditorial for the ACS Select Virtual Issue on Emerging Investigators in Inorganic Photochemistry and PhotophysicsFelix N. Castellano*View Author Information Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States*E-mail: [email protected]Cite this: Inorg. Chem. 2016, 55, 24, 12483–12487Publication Date (Web):December 19, 2016Publication History Published online19 December 2016Published inissue 19 December 2016https://pubs.acs.org/doi/10.1021/acs.inorgchem.6b02830https://doi.org/10.1021/acs.inorgchem.6b02830editorialACS PublicationsCopyright © 2016 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views1130Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (224 KB) Get e-AlertscloseSUBJECTS:Chromophores,Ligands,Metal to ligand charge transfer,Photochemistry,Photoluminescence Get e-Alerts}, number={24}, journal={INORGANIC CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Castellano, Felix N.}, year={2016}, month={Dec}, pages={12483–12487} }
 @article{younts_duan_gautam_saparov_liu_mongin_castellano_mitzi_gundogdu_2016, title={Efficient Generation of Long-Lived Triplet Excitons in 2D Hybrid Perovskite}, volume={29}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201604278}, DOI={10.1002/ADMA.201604278}, abstractNote={Triplet excitons form in quasi-2D hybrid inorganic-organic perovskites and diffuse over 100 nm before radiating with >11% photoluminescence quantum efficiency (PLQE) at low temperatures.}, number={9}, journal={Advanced Materials}, publisher={Wiley}, author={Younts, Robert and Duan, Hsin-Sheng and Gautam, Bhoj and Saparov, Bayrammurad and Liu, Jie and Mongin, Cedric and Castellano, Felix N. and Mitzi, David B. and Gundogdu, Kenan}, year={2016}, month={Dec}, pages={1604278} }
 @article{mcgoorty_khnayzer_castellano_2016, title={Enhanced photophysics from self-assembled cyclometalated Ir(III) complexes in water}, volume={52}, ISSN={["1364-548X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84975148045&partnerID=MN8TOARS}, DOI={10.1039/c6cc03932d}, abstractNote={Two water-soluble anionic cyclometalated Ir(iii) complexes, Ir(ppy)2BPS [1] and Ir(F-mppy)2BPS [2] have been synthesized and display clear evidence of self-assembly in water.}, number={50}, journal={CHEMICAL COMMUNICATIONS}, author={McGoorty, Michelle M. and Khnayzer, Rony S. and Castellano, Felix N.}, year={2016}, pages={7846–7849} }
 @article{yarnell_mccusker_leeds_breaux_castellano_2016, title={Exposing the Excited-State Equilibrium in an Ir-III Bichromophore: A Combined Time Resolved Spectroscopy and Computational Study}, volume={2016}, ISSN={["1099-0682"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84962833574&partnerID=MN8TOARS}, DOI={10.1002/ejic.201600194}, abstractNote={AbstractThe electronic structure and photophysical properties of a luminescent IrIII bis‐cyclometalated complex covalently attached to one 4‐piperidinyl‐1,8‐naphthalimide (PNI) chromophore through a coordinated 1,10‐phenanthroline, [Ir(ppy)2(phen‐PNI)](PF6), is presented. This bichromophore represents a new class of visible light‐harvesting IrIII complexes that exhibit markedly enhanced room‐temperature excited‐state lifetimes (τ = 8.8 ms) as a result of intervening ligand‐centered triplet states present on the pendant naphthalimide chromophore. In this IrIII complex, the intense singlet fluorescence of the pendant PNI chromophore is nearly quantitatively quenched and was found to sensitize the IrIII metal/ligand‐to‐ligand charge‐transfer (MLLCT) excited state. The excited state ultimately returns to the PNI chromophore as a long‐lived excited triplet that disposes of its energy by equilibrating with the photoluminescent IrIII MLLCT excited state. Evidence of the excited‐state equilibrium is provided through static and dynamic photoluminescence spectroscopy, transient absorption spectroscopy, and time‐dependent density functional theory calculations.}, number={12}, journal={EUROPEAN JOURNAL OF INORGANIC CHEMISTRY}, author={Yarnell, James E. and McCusker, Catherine E. and Leeds, Alexander J. and Breaux, Josue M. and Castellano, Felix N.}, year={2016}, month={Apr}, pages={1808–1818} }
 @article{khnayzer_olaiya_el roz_castellano_2016, title={Homogeneous Photocatalytic H-2 Production Using a Ru-II Bathophenanthroline Metal-to-Ligand Charge-Transfer Photosensitizer}, volume={81}, ISSN={["2192-6506"]}, url={https://doi.org/10.1002/cplu.201600227}, DOI={10.1002/cplu.201600227}, abstractNote={AbstractThe prototypical [Ru(bpy)3]2+ (bpy=2,2′‐bipyridine) photosensitizer has been previously demonstrated to be labile in aqueous photocatalytic solutions, especially in the presence of coordinating electron donors. Here, an alternative RuII molecular sensitizer, [Ru(dpp)3]2+ (dpp=4,7‐diphenyl‐1,10‐phenanthroline or bathophenanthroline), is described, which is considerably more stable than its bpy congener, allowing enhanced photocatalysis metrics in conjunction with a cobalt glyoxime ([Co(dmgH)2pyCl], dmgH=dimethylglyoxime, py=pyridine) water reduction catalyst and N,N‐dimethyl‐p‐toluidine (DMT) as the sacrificial donor in a 1:1 mixture of CH3CN/H2O. Photoluminescence studies revealed that DMT reductively quenches the excited state of [Ru(dpp)3]2+ with a bimolecular rate constant of kq=4.9×109 m−1 s−1. The rate constant measured for electron transfer from the reduced sensitizer to the [Co(dmgH)2pyCl] was found to be near the diffusion limit, kCo=2.4×109 m−1 s−1. H2 production by photocatalysis was independently monitored by using a high‐throughput photochemical reactor equipped with pressure transducers, gas chromatogram, and a mass spectrometer for detection; this illustrated that the composition yields high turnover numbers (TONs), approaching 10 000 (H2/Ru) with respect to the sensitizer and deuteration studies using D2O confirmed that H2 is primarily produced from protons derived from water in these systems.}, number={10}, journal={CHEMPLUSCHEM}, publisher={Wiley-Blackwell}, author={Khnayzer, Rony S. and Olaiya, Babatunde S. and El Roz, Karim A. and Castellano, Felix N.}, year={2016}, month={Oct}, pages={1090–1097} }
 @article{khnayzer_olaiya_el roz_castellano_2016, title={Homogeneous Photocatalytic H2
 Production Using a RuII
 Bathophenanthroline Metal-to-Ligand Charge-Transfer Photosensitizer}, volume={81}, ISSN={2192-6506}, url={http://dx.doi.org/10.1002/CPLU.201600424}, DOI={10.1002/cplu.201600424}, abstractNote={AbstractInvited for this month's cover are the research groups of Prof. Rony S. Khnayzer at Lebanese American University and Prof. Felix (Phil) N. Castellano at North Carolina State University. The cover picture illustrates the absorption of visible light by a ruthenium bathophenanthroline MLCT chromophore followed by a sequence of electron transfer steps that ultimately leads to the efficient production of hydrogen gas from water. Read the full text of the article at 10.1002/cplu.201600227.}, number={10}, journal={ChemPlusChem}, publisher={Wiley}, author={Khnayzer, Rony S. and Olaiya, Babatunde S. and El Roz, Karim A. and Castellano, Felix N.}, year={2016}, month={Oct}, pages={1016–1016} }
 @article{mongin_golden_castellano_2016, title={Liquid PEG Polymers Containing Antioxidants: A Versatile Platform for Studying Oxygen-Sensitive Photochemical Processes}, volume={8}, ISSN={["1944-8252"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84987858776&partnerID=MN8TOARS}, DOI={10.1021/acsami.6b05697}, abstractNote={This article proposes the exploitation of widely available, inexpensive, innocuous "green" liquid polyethylene glycol (PEG) polymers containing the oxygen scavenger oleic acid (OA) as promising media for studying oxygen-sensitive photochemical processes. Here we report the successful application of this media to detailed investigations of triplet-sensitized photochemical upconversion, previously established as being readily poisoned by dissolved oxygen. Three different PEG materials were investigated with increasing molecular weight from 200 to 600 g/mol, coded as PEG-200, PEG-400, and PEG-600. These fluidic polymers facilitate an oxygen-depleted environment in comparison to commonly employed organic solvents while providing high solubility and diffusion for the dissolved chromophores. Moreover, the low oxygen permeation afforded by these PEG solvents allows them to remain deoxygenated in open containers under ambient conditions for extended time periods. OA, 9,10-dimethylanthracene (DMA), and 2,5-dimethylfuran (DMF) are shown to efficiently and quantitatively consume dissolved oxygen in the PEG environment in the presence of the photoactivated triplet sensitizer platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP). Oxygen consumption was directly correlated with systematically increasing sensitizer excited-state lifetimes that eventually reach the same plateau as achieved through extensive N2 sparging. Diffusion-controlled bimolecular triplet-triplet energy transfer quenching between PtTPBP and the acceptor/annihilator 9,10-bisphenylethynylanthracene (BPEA) was observed in all three PEG formulations investigated. Subsequent triplet-triplet annihilation, between triplet excited BPEA acceptors, achieves bright and stable upconverted singlet fluorescence from BPEA with no decrease in intensity over 20 h under ambient conditions. In the champion composition (PEG 200), the upconversion quantum efficiency reached 31% under conditions where triplet-triplet annihilation was maximized. This is in stark contrast for the same upconverting pair measured in toluene under ambient conditions, which rapidly decomposes upon exposure to visible light. To illustrate that these PEG compositions could be translated into a suitable solid-state format, these viscous solutions were embedded in a transparent polyurethane polymer shell yielding a flexible and long-term stable upconverting cell that can be manipulated for possible real-world applications. Although the current investigation focused on photochemical upconversion, the oxygen-depleted environments developed here can be utilized to study a plethora of oxygen-intolerant photochemical reactions.}, number={36}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Mongin, Cedric and Golden, Jessica H. and Castellano, Felix N.}, year={2016}, month={Sep}, pages={24038–24048} }
 @misc{mccusker_castellano_2016, title={Materials Integrating Photochemical Upconversion}, volume={374}, ISSN={["2364-8961"]}, url={https://doi.org/10.1007/s41061-016-0021-7}, DOI={10.1007/s41061-016-0021-7}, abstractNote={This review features recent experimental work focused on the preparation and characterization of materials that integrate photochemical upconversion derived from sensitized triplet-triplet annihilation, resulting in the conversion of low energy photons to higher energy light, thereby enabling numerous wavelength-shifting applications. Recent topical developments in upconversion include encapsulating or rigidifying fluid solutions to give them mechanical strength, adapting inert host materials to enable upconversion, and using photoactive materials that incorporate the sensitizer and/or the acceptor. The driving force behind translating photochemical upconversion from solution into hard and soft materials is the incorporation of upconversion into devices and other applications. At present, some of the most promising applications of upconversion materials include imaging and fluorescence microscopy, photoelectrochemical devices, water disinfection, and solar cell enhancement.}, number={2}, journal={TOPICS IN CURRENT CHEMISTRY}, publisher={Springer Science and Business Media LLC}, author={McCusker, Catherine E. and Castellano, Felix N.}, year={2016}, month={Apr} }
 @article{brown-xu_kelley_fransted_chalcraborty_schatz_castellano_chen_2016, title={Tunable Excited-State Properties and Dynamics as a Function of Pt-Pt Distance in Pyrazolate-Bridged Pt(II) Dimers}, volume={120}, ISSN={["1520-5215"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84957060153&partnerID=MN8TOARS}, DOI={10.1021/acs.jpca.5b11233}, abstractNote={The influence of molecular structure on excited-state properties and dynamics of a series of cyclometalated platinum dimers was investigated through a combined experimental and theoretical approach using femtosecond transient absorption (fs TA) spectroscopy and density functional theory (DFT) calculations. The molecules have the general formula [Pt(ppy)(μ-R2pz)]2, where ppy = 2-phenylpyridine, pz = pyrazolate, and R = H, Me, Ph, or (t)Bu, and are strongly photoluminescent at room temperature. The distance between the platinum centers in this A-frame geometry can be varied depending on the steric bulk of the bridging pyrazolate ligands that exert structural constraints and compress the Pt-Pt distance. At large Pt-Pt distances there is little interaction between the subunits, and the chromophore behaves similar to a monomer with excited states described as mixtures of ligand-centered and metal-to-ligand charge transfer (LC/MLCT) transitions. When the Pt(II) centers are brought closer together with bulky bridging ligands, they interact through their dz(2) orbitals and the S1 and T1 states are best characterized as metal-metal-to-ligand charge transfer (MMLCT) in character. The results of the femtoseconds TA experiments reveal that intersystem crossing (ISC) occurs on ultrafast time scales (τS1 < 200 fs), while there are two relaxation processes occurring within the triplet manifold, τ1 = 0.5-3.2 ps and τ2 = 20-70 ps; the longer time constants correspond to the presence of bulkier bridging ligands. DFT calculations illustrate that the Pt-Pt distances further contract in the T1 (3)MMLCT states; therefore, slower relaxation may be related to a larger structural reorganization. Subsequent investigations using faster time resolution are planned to measure the ISC process as well as to identify any potential coherent interaction(s) between the platinum centers that may occur.}, number={4}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Brown-Xu, Samantha E. and Kelley, Matthew S. J. and Fransted, Kelly A. and Chalcraborty, Arnab and Schatz, George C. and Castellano, Felix N. and Chen, Lin X.}, year={2016}, month={Feb}, pages={543–550} }
 @misc{castellano_2015, title={Altering Molecular Photophysics by Merging Organic and Inorganic Chromophores}, volume={48}, ISSN={["1520-4898"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84925398223&partnerID=MN8TOARS}, DOI={10.1021/ar500385e}, abstractNote={Photofunctional molecules and assemblies lie at the heart of many important fundamental processes in nature, and researchers have generated multitudes of artificial chromophores intended to mimic these naturally occurring systems. As dynamic spectroscopic techniques are becoming more widely available, ultrafast techniques in particular, substantial insight continues to be gleaned from the initial photon stimulation event through internal conversion, structural rearrangements, intersystem crossing, energy migration, electron transfer events, and ultimately regeneration of the ground state chromophores in both naturally occurring and inspired chromophores. This Account details research endeavors motivated by the concept that merging organic and inorganic chromophores can lead to new molecules exhibiting novel excited state properties. Moreover, these excited state properties can be fundamentally understood using combinations of static and dynamic spectroscopic tools, yielding systematic improvements to molecules poised for application in diverse research areas including light-harvesting, lifetime engineering, photocatalysis, and photochemical upconversion. Initial explorations focused on utilizing Förster energy transfer processes in Ru(II)-based metal-organic chromophores for solar light-harvesting while maintaining long excited state lifetimes. This eventually led to molecules exhibiting triplet-triplet energy transfer between energetically proximate triplet states featuring thermally activated photoluminescence from the upper charge transfer excited state with markedly extended lifetimes. Interest in systematically producing long-lived excited states with concomitant large Stokes shifts inspired the development of numerous Pt(II) bipyridyl and terpyridyl acetylide charge transfer chromophores featuring ultrafast intramolecular energy migration, high quantum yield ligand-localized phosphorescence at room temperature, and synthetically tunable excited state absorption properties. This structural motif also made it possible to access the triplet excited states of perylenediimide chromophores, permitting quantitative examination of internal conversion and intersystem crossing processes in these complex molecules. The generation of new metal-organic structures featuring unique photophysics appears limitless and simply requires the continued ingenuity of researchers.}, number={3}, journal={ACCOUNTS OF CHEMICAL RESEARCH}, author={Castellano, Felix N.}, year={2015}, month={Mar}, pages={828–839} }
 @article{jurss_khnayzer_panetier_el roz_nichols_head-gordon_long_castellano_chang_2015, title={Bioinspired design of redox-active ligands for multielectron catalysis: effects of positioning pyrazine reservoirs on cobalt for electro- and photocatalytic generation of hydrogen from water}, volume={6}, ISSN={["2041-6539"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84937232650&partnerID=MN8TOARS}, DOI={10.1039/c5sc01414j}, abstractNote={We report the effects of installing redox-active pyrazines at distinct positions in a series of isostructural Co catalysts.}, number={8}, journal={CHEMICAL SCIENCE}, author={Jurss, Jonah W. and Khnayzer, Rony S. and Panetier, Julien A. and El Roz, Karim A. and Nichols, Eva M. and Head-Gordon, Martin and Long, Jeffrey R. and Castellano, Felix N. and Chang, Christopher J.}, year={2015}, pages={4954–4972} }
 @article{mccusker_castellano_2015, title={Efficient Visible to Near-UV Photochemical Upconversion Sensitized by a Long Lifetime Cu(I) MLCT Complex}, volume={54}, ISSN={["1520-510X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84935843196&partnerID=MN8TOARS}, DOI={10.1021/acs.inorgchem.5b00907}, abstractNote={The current investigation compares the photochemical upconversion sensitization properties of two long lifetime Cu(I) metal-to-ligand charge transfer (MLCT) chromophores to 3 distinct anthryl-based triplet acceptors. The sensitizers [Cu(dsbtmp)2](PF6) (1, dsbtmp = 2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline) and [Cu(dsbp)2](PF6) (2, dsbp = 2,9-di(sec-butyl-1,10-phenanthroline) were selectively excited in the presence of anthracene, 9,10-diphenylanthracene (DPA), and 9,10-dimethylanthracene (DMA) in degassed dichloromethane solutions. In all instances, triplet energy transfer was observed from selective excitation of the Cu(I) MLCT chromophore to each respective anthryl species. The bimolecular triplet-triplet energy transfer quenching rate constants were extracted from dynamic Stern-Volmer analyses in each case, yielding values below the diffusion limit in dichloromethane. However, the Stern-Volmer quenching constants (KSV's) were sizable enough (up to ∼2300 M(-1) with 1 as a sensitizer) to support efficient photochemical upconversion. As such, visible to near-UV photochemical upconversion was observed in every instance, along with the anticipated quadratic-to-linear incident light power dependence when pumping at 488 nm. The latter verified that it is indeed sensitized triplet-triplet annihilation responsible for the generation of the anthryl-based singlet fluorescence. Photochemical upconversion quantum efficiencies were evaluated using a relative actinometric method as both a function of incident light power density as well as anthryl acceptor/annihilator concentration. When 1 was used as the sensitizer, upconversion quantum yields as large as 9.2% and 17.8% were observed for DMA and DPA, respectively. Finally, the combination of 1 with DMA was shown to be quite robust, showing no obvious signs of decomposition during 12 h of continuous 488 nm photolysis.}, number={12}, journal={INORGANIC CHEMISTRY}, author={McCusker, Catherine E. and Castellano, Felix N.}, year={2015}, month={Jun}, pages={6035–6042} }
 @article{castellano_mccusker_2015, title={MLCT sensitizers in photochemical upconversion: past, present, and potential future directions}, volume={44}, ISSN={["1477-9234"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84944184428&partnerID=MN8TOARS}, DOI={10.1039/c5dt03212a}, abstractNote={This frontier presentation highlights the historical development of MLCT sensitizers in photochemical upconversion while indentifying current state-of-the-art and exciting opportunities in this arena moving towards the future.}, number={41}, journal={DALTON TRANSACTIONS}, author={Castellano, Felix N. and McCusker, Catherine E.}, year={2015}, pages={17906–17910} }
 @article{olivier_bai_uh_yoo_therien_castellano_2015, title={Near-Infrared-to-Visible Photon Upconversion Enabled by Conjugated Porphyrinic Sensitizers under Low-Power Noncoherent Illumination}, volume={119}, ISSN={["1520-5215"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84930644572&partnerID=MN8TOARS}, DOI={10.1021/acs.jpca.5b03199}, abstractNote={We report four supermolecular chromophores based on (porphinato)zinc(II) (PZn) and (polypyridyl)metal units bridged via ethyne connectivity (Pyr1RuPZn2, Pyr1RuPZnRuPyr1, Pyr1RuPZn2RuPyr1, and OsPZn2Os) that fulfill critical sensitizer requirements for NIR-to-vis triplet-triplet annihilation upconversion (TTA-UC) photochemistry. These NIR sensitizers feature: (i) broad, high oscillator strength NIR absorptivity (700 nm < λ(max(NIR)) < 770 nm; 6 × 10(4) M(-1) cm(-1) < extinction coefficient (λ(max(NIR))) < 1.6 × 10(5) M(-1) cm(-1); 820 cm(-1) < fwhm < 1700 cm(-1)); (ii) substantial intersystem crossing quantum yields; (iii) long, microsecond time scale T1 state lifetimes; and (iv) triplet states that are energetically poised for exergonic energy transfer to the molecular annihilator (rubrene). Using low-power noncoherent illumination at power densities (1-10 mW cm(-2)) similar to that of terrestrial solar photon illumination conditions, we demonstrate that Pyr1RuPZn2, Pyr1RuPZn2RuPyr1, and Pyr1RuPZnRuPyr1 sensitizers can be used in combination with the rubrene acceptor/annihilator to achieve TTA-UC: these studies represent the first examples whereby a low-power noncoherent NIR light source drives NIR-to-visible upconverted fluorescence centered in a spectral window within the bandgap of amorphous silicon.}, number={22}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Olivier, Jean-Hubert and Bai, Yusong and Uh, Hyounsoo and Yoo, Hyejin and Therien, Michael J. and Castellano, Felix N.}, year={2015}, month={Jun}, pages={5642–5649} }
 @article{khnayzer_martin_codding_castellano_2015, title={Parallelization of photocatalytic gas-producing reactions}, volume={86}, ISSN={0034-6748 1089-7623}, url={http://dx.doi.org/10.1063/1.4915349}, DOI={10.1063/1.4915349}, abstractNote={High-throughput screening has been widely utilized in the pharmaceutical and manufacturing industry targeting the development of new molecules and materials for numerous applications. To enable more rapid progress in photocatalytic water-splitting reactions, the construction of high-throughput combinatorial photoreactors enabling the parallel optimization of relevant compositions under varieties of experimental conditions seems appropriate. This contribution describes a 16-photoreactor apparatus permitting the kinetic evaluation of photocatalytic gas-producing reactions using head-space pressure, gas chromatography, and mass spectrometry operating in parallel, illustrated with molecular-based homogeneous photocatalytic H2-generating compositions.}, number={3}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Khnayzer, Rony S. and Martin, Douglas R. and Codding, Charles L. and Castellano, Felix N.}, year={2015}, month={Mar}, pages={034101} }
 @article{deng_francis_weare_castellano_2015, title={Photochemical upconversion and triplet annihilation limit from a boron dipyrromethene emitter}, volume={14}, ISSN={["1474-9092"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84934293936&partnerID=MN8TOARS}, DOI={10.1039/c5pp00106d}, abstractNote={Non-coherent sensitized red-to-green upconversion has been achieved utilizing platinum(II) tetraphenyltetrabenzoporphyrin (PtTPTBP) as the triplet sensitizer and a nearly quantitatively fluorescent meso -(2,6-dichloropyridyl)-substituted boron dipyrromethene (Cl2PyBODIPY) chromophore ( Φ = 0.99 in toluene) as the energy acceptor/annihilator in deoxygenated toluene. Dynamic Stern–Volmer analysis revealed that PtTPTBP phosphorescence as quenched by C_l2PyBODIPY occurs with a K _SV of 108 000 M−1, yielding a triplet–triplet energy transfer rate constant of 2.3 × 109 M−1 s−1. Using a non-coherent red light-emitting diode excitation source centered at 626 nm, the incident power dependence responsible for generating singlet BODIPY fluorescence in the green was shown to traverse quadratic to linear regimes, the latter being achieved near 60 mW cm−2. These data were consistent with a photochemical upconversion mechanism being responsible for generating singlet fluorescence from the C_l2PyBODIPY chromophores through sensitized triplet–triplet annihilation (TTA). Integrated delayed fluorescence transients were utilized to reveal the TTA efficiency for the C_l2PyBODIPY chromophore and saturated near 46%, representing the lower limit for the TTA process. Kinetic modelling of the delayed fluorescence transient produced from 1.5 mJ laser pulses (λ_ex = 615 nm) revealed a maximum limiting TTA efficiency of 64% for this upconverting composition, implying that this is indeed an extremely relevant acceptor/annihilator composition for photochemical upconversion.}, number={7}, journal={PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES}, author={Deng, F. and Francis, A. J. and Weare, W. W. and Castellano, F. N.}, year={2015}, pages={1265–1270} }
 @article{deng_lazorski_castellano_2015, title={Photon upconversion sensitized by a Ru(II)-pyrenyl chromophore}, volume={373}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84995605686&partnerID=MN8TOARS}, DOI={10.1098/rsta.2014.0322}, abstractNote={
            The near-visible-to-blue singlet fluorescence of anthracene sensitized by a ruthenium chromophore with a long-lived triplet-excited state, [Ru(5-pyrenyl-1,10-phenanthroline)
            3
            ](PF
            6
            )
            2
            , in acetonitrile was investigated. Low intensity non-coherent green light was used to selectively excite the sensitizer in the presence of micromolar concentrations of anthracene generating anti-Stokes, singlet fluorescence in the latter, even with incident power densities below 500 μW cm
            −2
            . The resultant data are consistent with photon upconversion proceeding from sensitized triplet–triplet annihilation (TTA) of the anthracene acceptor molecules, confirmed through transient absorption spectroscopy as well as static and dynamic photoluminescence experiments. Additionally, quadratic-to-linear incident power regimes for the upconversion process were identified for this composition under monochromatic 488 nm excitation, consistent with a sensitized TTA mechanism ultimately producing the anti-Stokes emission characteristic of anthracene singlet fluorescence.
          }, number={2044}, journal={Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences}, publisher={The Royal Society}, author={Deng, Fan and Lazorski, Megan S. and Castellano, Felix N.}, year={2015}, pages={20140322} }
 @article{mosca_khnayzer_lazorski_danilov_castellano_anzenbacher_2015, title={Sensing of 2,4,6-Trinitrotoluene (TNT) and 2,4-Dinitrotoluene (2,4-DNT) in the Solid State with Photoluminescent Ru-II and Ir-III Complexes}, volume={21}, ISSN={["1521-3765"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84929926404&partnerID=MN8TOARS}, DOI={10.1002/chem.201405717}, abstractNote={AbstractA series of metal–organic chromophores containing RuII or IrIII were studied for the luminometric detection of nitroaromatic compounds, including trinitrotoluene (TNT). These complexes display long‐lived, intense photoluminescence in the visible region and are demonstrated to serve as luminescent sensors for nitroaromatics. The solution‐based behavior of these photoluminescent molecules has been studied in detail in order to identify the mechanism responsible for metal‐to‐ligand charge‐transfer (MLCT) excited state quenching upon addition of TNT and 2,4‐dinitrotoluene (2,4‐DNT). A combination of static and dynamic spectroscopic measurements unequivocally confirmed that the quenching was due to a photoinduced electron transfer (PET) process. Ultrafast transient absorption experiments confirmed the formation of the TNT radical anion product following excited state electron transfer from these metal complexes. Reported for the first time, photoluminescence quenching realized through ink‐jet printing and solid‐state titrations was used for the solid‐state detection of TNT; achieving a limit‐of‐quantitation (LOQ) as low as 5.6 ng cm−2. The combined effect of a long‐lived excited state and an energetically favorable driving force for the PET process makes the RuII and IrIII MLCT complexes discussed here particularly appealing for the detection of nitroaromatic volatiles and related high‐energy compounds.}, number={10}, journal={CHEMISTRY-A EUROPEAN JOURNAL}, author={Mosca, Lorenzo and Khnayzer, Rony S. and Lazorski, Megan S. and Danilov, Evgeny O. and Castellano, Felix N. and Anzenbacher, Pavel, Jr.}, year={2015}, month={Mar}, pages={4056–4064} }
 @article{myahkostupov_castellano_2015, title={Tetrahedral rigid core antenna chromophores bearing bay-substituted perylenediimides}, volume={71}, ISSN={["0040-4020"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84947996715&partnerID=MN8TOARS}, DOI={10.1016/j.tet.2015.10.083}, abstractNote={Two new representative methane- and adamantane-centered 'antenna' tetramers bearing bay-substituted π-conjugated phenylethynyl-perylenediimides (PDICCPh) as chromophoric subunits, tetrakis-[1-(4-ethynylphenyl)-N,N′-bis(1-hexylheptyl)-perylene-3,4:9,10-tetracarboxylic diimide]-methane (1) and tetrakis-1,3,5,7-[1-(4-ethynylphenyl)-N,N′-bis(1-hexylheptyl)-perylene-3,4:9,10-tetracarboxylic diimide]-adamantane (2), have been synthesized and their structural aspects have been thoroughly investigated by NMR spectroscopy. These PDI tetramers (1 and 2) represent the first successful example of incorporating the bay-substituted phenylethynyl-perylenediimides into the large rigid core tetrahedral frameworks. In these PDI tetramers, dynamic NMR experiments revealed the existence of perylene-centered conformational dynamic equilibrium (ΔG≠=15−17 kcal/mol), the primary cause of the observed spectral broadening in conventional 1H NMR spectra (295 K). In addition, PDI tetramers 1 and 2 were found to possess exceptional (photo)chemical stability, and their corresponding photophysical properties (ɛmax∼180,000; τFL=6.9 ns; ΦFL∼60%) make them viable candidates for various photonic applications and are in good agreement with other related multichromophoric PDI-based systems.}, number={51}, journal={TETRAHEDRON}, author={Myahkostupov, Mykhaylo and Castellano, Felix N.}, year={2015}, month={Dec}, pages={9519–9527} }
 @article{garakyaraghi_danilov_mccusker_castellano_2015, title={Transient Absorption Dynamics of Sterically Congested Cu(I) MLCT Excited States}, volume={119}, ISSN={["1089-5639"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84926435446&partnerID=MN8TOARS}, DOI={10.1021/acs.jpca.5b00901}, abstractNote={Subpicosecond through supra-nanosecond transient absorption dynamics of the homoleptic Cu(I) metal-to-ligand charge transfer (MLCT) photosensitizers including the benchmark [Cu(dmp)2](+) (dmp =2,9-dimethyl-1,10-phenanthroline) chromophore, as well as [Cu(dsbp)2](+) (dsbp =2,9-di(sec-butyl)-1,10-phenanthroline and [Cu(dsbtmp)2](+) (dsbtmp =2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline) were investigated in dichloromethane and tetrahydrofuran solutions. Visible and near-IR spectroelectrochemical measurements of the singly reduced [Cu(dsbp)2](+) and [Cu(dsbtmp)2](+) species were determined in tetrahydrofuran, allowing for the identification of redox-specific phenanthroline-based radical anion spectroscopic signatures prevalent in the respective transient absorption experiments. This study utilized four different excitation wavelengths (418, 470, 500, and 530 nm) to elucidate dynamics on ultrafast times scales spanning probe wavelengths ranging from the UV to the near-IR (350 to 1450 nm). With the current time resolution of ∼150 fs, initial excited state decay in all three compounds was found to be independent of excitation wavelength. Not surprisingly, there was little to no observed influence of solvent in the initial stages of excited state decay in any of these molecules including [Cu(dmp)2](+), consistent with results from previous investigators. The combined experimental data revealed two ranges of time constants observed on short time scales in all three MLCT chromophores and both components lengthen as a function of structure in the following manner: [Cu(dsbtmp)2](+) < [Cu(dsbp)2](+) < [Cu(dmp)2](+). The molecule with the most inhibited potential for distortion, [Cu(dsbtmp)2](+), possessed the fastest ultrafast dynamics as well as the longest excited state lifetimes in both solvents. These results are consistent with a small degree of excited state distortion, rapid intersystem crossing, and weak vibronic coupling to the ground state. The concomitant systematic variation in both initial time constants, assigned to pseudo-Jahn-Teller distortion and intersystem crossing, suggest that both processes are intimately coupled in all molecules in the series. The variability in these time scales illustrate that strongly impeded structural distortion in Cu(I) MLCT excited state enables more rapid surface crossings in the initial deactivation dynamics.}, number={13}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Garakyaraghi, Sofia and Danilov, Evgeny O. and McCusker, Catherine E. and Castellano, Felix N.}, year={2015}, month={Apr}, pages={3181–3193} }
 @article{lazorski_castellano_2014, title={Advances in the light conversion properties of Cu(I)-based photosensitizers}, volume={82}, ISSN={["0277-5387"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84907906041&partnerID=MN8TOARS}, DOI={10.1016/j.poly.2014.04.060}, abstractNote={The need to develop low-cost, sustainable, earth abundant fuel sources is becoming paramount as the rate of global energy consumption continues to increase. Toward this goal, solar energy conversion is an obvious choice, yet the current molecular based technologies still rely heavily on expensive, non-earth abundant photosensitizers, which limits the net benefits of these systems. Complexes of copper(I) have been recognized for decades as viable low-cost, earth abundant alternative photosensitizers in solar energy conversion technologies; however, when used in solution based applications, issues such as geometrical distortions associated with photoexcitation and ligand lability has frustrated numerous research efforts. Fortunately, these investigations have not been in vain, and many investigations have successfully circumvented the aforementioned issues. Recent reports on Cu(I) based photosensitizers demonstrate that they are beginning to rival the performance metrics of the more costly, less earth abundant species typically used in solution-based solar energy conversion schemes. Therefore, this minireview focuses on the most recent and influential advances made in the field of Cu(I) based photosensitizers.}, journal={POLYHEDRON}, author={Lazorski, Megan S. and Castellano, Felix N.}, year={2014}, month={Nov}, pages={57–70} }
 @article{mccusker_chakraborty_castellano_2014, title={Excited State Equilibrium Induced Lifetime Extension in a Dinuclear Platinum(II) Complex}, volume={118}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/JP503827E}, DOI={10.1021/JP503827E}, abstractNote={Covalently linking two square planar platinum(II) centers using two pyrazolate bridging ligands allows the filled dz(2) orbitals on each Pt center to overlap, producing a Pt-Pt σ interaction and new low energy dσ* → π* metal-metal-to-ligand charge transfer (MMLCT) transitions terminating on an appropriate π-acceptor ligand such as 2-phenylpyridine (ppy). In an effort to extend the lifetime of the associated MMLCT excited state, we decided to append piperidinyl naphthalimide (PNI) chromophores to the 2-phenylpyridine charge transfer ligands. This structural modification introduces low-lying PNI-based triplet states serving as long-lived triplet population reservoirs, thermally capable of repopulating the charge transfer state at room temperature (RT), thereby extending its excited state lifetime. Specifically, [Pt(PNI-ppy)(μ-Ph2pz)]2 (1), where PNI-ppy is N-(2-phenylpyridine)-4-(1-piperidinyl)naphthalene-1,8-dicarboximide and Ph2pz is 3,5-diphenylpyrazolate, was synthesized and structurally characterized. The static and dynamic photophysical behavior of 1 was directly compared to the MMLCT complex [Pt(ppy)(μ-Ph2pz)]2 (2), lacking the PNI substituents, as well as the naked PNI-ppy ligand 3, intended to independently model the MMLCT and NI excited state properties, respectively. Ultimately, experimental evidence for the presence of both the (3)PNI and (3)MMLCT excited states in 1 were revealed at RT in nanosecond transient absorbance and time-resolved photoluminescence spectroscopy, respectively. Temperature-dependent transient absorption spectroscopy permitted the extraction of an energy gap of 1740 cm(-1) between the MMLCT and PNI triplet states in 1 along with the time constants associated with the interconversions between the various excited states resident on this complex chromophore, ultimately decaying back to the ground state with a time constant of 65 μs at RT.}, number={45}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={McCusker, Catherine E. and Chakraborty, Arnab and Castellano, Felix N.}, year={2014}, month={Jun}, pages={10391–10399} }
 @article{jumper_anna_stradomska_schins_myahkostupov_prusakova_oblinsky_castellano_knoester_scholes_2014, title={Intramolecular radiationless transitions dominate exciton relaxation dynamics}, volume={599}, ISSN={["1873-4448"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84897401500&partnerID=MN8TOARS}, DOI={10.1016/j.cplett.2014.03.007}, abstractNote={Reports of long-lived exciton coherences have lead researchers to expect that model dimer systems inevitably generate exciton superposition states observable by two-dimensional electronic spectroscopy. Here we report a careful photophysical characterization of a model dimer system, a diacetylene-linked perylenediimide dimer to examine that issue. The absorption spectrum of the dimer shows molecular exciton splitting, indicating that excitation is delocalized. The assignment of exciton states was supported by other photophysical measurements as well as theoretical calculations. Ultrafast two-dimensional electronic spectroscopy was employed to identify and characterize excitonic and vibrational features, as they evolve over time. Population transfer between the two exciton states is found to happen in <50 fs, thus preventing the sustainment of exciton coherences. We show that such fast radiationless relaxation cannot be explained by coupling to a solvent spectral density and is therefore missed by standard approaches such as Redfield theory and the hierarchical equations of motion.}, journal={CHEMICAL PHYSICS LETTERS}, author={Jumper, Chanelle C. and Anna, Jessica M. and Stradomska, Anna and Schins, Juleon and Myahkostupov, Mykhaylo and Prusakova, Valentina and Oblinsky, Daniel G. and Castellano, Felix N. and Knoester, Jasper and Scholes, Gregory D.}, year={2014}, month={Apr}, pages={23–33} }
 @article{bartelmess_francis_el roz_castellano_weare_sommer_2014, title={Light-Driven Hydrogen Evolution by BODIPY-Sensitized Cobaloxime Catalysts}, volume={53}, ISSN={["1520-510X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84899787366&partnerID=MN8TOARS}, DOI={10.1021/ic500218q}, abstractNote={We report four photocatalytically active cobaloxime complexes for light-driven hydrogen evolution. The cobaloxime catalysts are sensitized by different meso-pyridyl boron dipyrromethene (BODIPY) chromophores, bearing either two bromo- or iodo-substituents on the BODIPY core. The pyridine linker between the BODIPY and cobaloxime is further modified by a methyl substituent on the pyridine, influencing the stability and electronic properties of the cobaloxime catalyst and thus the photocatalytic efficiency of each system. Four cobaloxime catalyst complexes and three novel BODIPY chromophores are synthesized and characterized by absorption, fluorescence, infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and electrochemistry. Crystal structures for the BODIPY-cobaloxime complexes 2 and 3 are presented. In contrast to the photocatalytically inactive, nonhalogenated reference complex 1, the four newly reported molecules are active for photocatalytic hydrogen evolution, with a maximum turnover number (TON) of 30.9 mol equiv of H2 per catalyst for the meso-methylpyridyl 2,6-diiodo BODIPY-sensitized cobaloxime complex 5. We conclude that accessing the photoexcited triplet state of the BODIPY chromophore by introducing heavy atoms (i.e., bromine or iodine) is necessary for efficient electron transfer in this system, enabling catalytic hydrogen generation. In addition, relatively electron-donating pyridyl linkers improve the stability of the complex, increasing the overall TON for hydrogen production.}, number={9}, journal={INORGANIC CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Bartelmess, Juergen and Francis, Aaron J. and El Roz, Karim A. and Castellano, Felix N. and Weare, Walter W. and Sommer, Roger D.}, year={2014}, month={May}, pages={4527–4534} }
 @article{schmidt_castellano_2014, title={Photochemical Upconversion: The Primacy of Kinetics}, volume={5}, ISSN={["1948-7185"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84912528809&partnerID=MN8TOARS}, DOI={10.1021/jz501799m}, abstractNote={Incoherent photochemical upconversion is a process by which low-energy light can be converted into a higher-energy form with promising applications in solar energy conversion and storage, photocatalysis, biological imaging, and photochemical drug activation. Despite intensive research in recent years, there remains an underappreciation of the chemical kinetics that controls the efficiency of the upconversion process. Here, we provide a brief overview of research into photochemical upconversion and provide a tutorial to guide the design of efficient upconversion compositions. We further provide our perspective on where this area of research is heading and how very efficient systems will be developed.}, number={22}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, author={Schmidt, Timothy W. and Castellano, Felix N.}, year={2014}, month={Nov}, pages={4062–4072} }
 @article{castellano_mccusker_2015, title={Preface}, volume={282-283}, ISSN={0010-8545}, url={http://dx.doi.org/10.1016/J.CCR.2014.06.027}, DOI={10.1016/J.CCR.2014.06.027}, abstractNote={Substituent effects may tune and alter the optical and electronic properties of ligands and the complexes which they comprise. We review the effect of electron-withdrawing and -donating groups on the dipyridophenazine (dppz) framework. The observation of selected modulation of the properties associated with the phenazine or phenanthroline MOs is observed and reflected in the electrochemical and optical properties. The effect of donor groups that can give rise to ligand-centred charge-transfer optical transitions is also discussed. The effect of substituents on complexes with triazole ligands is examined; in stark contrast to the findings for dppz systems, and virtually regardless of the type of triazole ligand, substituents have only a muted effect on optical and electrochemical properties.}, journal={Coordination Chemistry Reviews}, publisher={Elsevier BV}, author={Castellano, Felix N. and McCusker, James K.}, year={2015}, month={Jan}, pages={1} }
 @article{kim_deng_castellano_kim_2014, title={Red-to-Blue/Cyan/Green Upconverting Microcapsules for Aqueous- and Dry-Phase Color Tuning and Magnetic Sorting}, volume={1}, ISSN={["2330-4022"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84906701246&partnerID=MN8TOARS}, DOI={10.1021/ph500036m}, abstractNote={Microcapsules that achieve multicolor triplet–triplet annihilation (TTA)-based upconversion (UC) in both aqueous and dry phases without deoxygenation are presented for the first time. Platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP) was used as a sensitizer and perylene, 9,10-bis(phenylethynyl)anthracene (BPEA), and a boron dipyrromethene derivative (BD-2) were employed as acceptors for red to blue, cyan, and green UC, respectively. Additional color tuning was introduced into microcapsules by embedding rose bengal onto the microcapsule shell, resulting in UC-mediated excitation of a distal fluorophore through a trivial process. Microcapsules were further modified to host superparamagnetic nanoparticles for magnetic-induced collection, which permitted sorting and color separation potentially instrumental for various photonics-based applications.}, number={4}, journal={ACS PHOTONICS}, author={Kim, Jae-Hyuk and Deng, Fan and Castellano, Felix N. and Kim, Jae-Hong}, year={2014}, month={Apr}, pages={382–388} }
 @article{deng_sun_castellano_2014, title={Texaphyrin sensitized near-IR-to-visible photon upconversion}, volume={13}, ISSN={["1474-9092"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84898786350&partnerID=MN8TOARS}, DOI={10.1039/c4pp00037d}, abstractNote={Near-IR (NIR) absorption from a Cd( ii ) texaphyrin (TXP) has been successfully coupled with rubrene triplet acceptors/annihilators in vacuum degassed dichloromethane to upconvert NIR (670–800 nm) incident photons into yellow fluorescence through sensitized triplet–triplet annihilation. Stern–Volmer analysis of dynamic energy transfer quenching of TXP by rubrene using transient absorption spectroscopy revealed Stern–Volmer and bimolecular quenching constants of 21?000 M^−1 and 5.7 × 10^8 M^−1 s^−1 respectively, for the triplet–triplet energy transfer process. The upconverted emission intensity with respect to the incident excitation power density at 750 nm was shown to vary between quadratic and linear, illustrating the expected kinetic limits for the light producing photochemistry under continuous wave illumination. Furthermore, with increasing TXP sensitizer concentration, the characteristic quadratic-to-linear crossover point shifted to lower incident photon power density. This is consistent with the notion that stronger photon capture in the sensitizer leads to experimental conditions promoting upconversion under milder excitation conditions. The maximum quantum yield of the TXP-sensitized rubrene upconverted fluorescence was 1.54 ± 0.04% under dilute conditions determined relative to [Os(phen)_3](PF_6)_2 under continuous wave excitation conditions. This saturating quantum efficiency was realized when the incident light power dependence reached the quadratic-to-linear crossover point and was constant over the region where the composition displayed linear response to incident light power density. In pulsed laser experiments at higher sensitizer concentrations, the triplet–triplet annihilation quantum yield was determined to saturate at approximately 13%, corresponding to an upconversion yield of ∼10%, suggesting that the dichloromethane solvent either lowers the T_2 state of the rubrene acceptor or is somehow attenuating the annihilation reaction between excited rubrene triplets.}, number={5}, journal={PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES}, author={Deng, Fan and Sun, Wenfang and Castellano, Felix N.}, year={2014}, pages={813–819} }
 @article{khnayzer_thoi_nippe_king_jurss_el roz_long_chang_castellano_2014, title={Towards a comprehensive understanding of visible-light photogeneration of hydrogen from water using cobalt(ii) polypyridyl catalysts}, volume={7}, ISSN={1754-5692 1754-5706}, url={http://dx.doi.org/10.1039/C3EE43982H}, DOI={10.1039/C3EE43982H}, abstractNote={Numerous visible-light absorbing homogeneous photocatalytic compositions are shown to produce copious amounts of hydrogen gas from pure water.}, number={4}, journal={Energy Environ. Sci.}, publisher={Royal Society of Chemistry (RSC)}, author={Khnayzer, R. S. and Thoi, V. S. and Nippe, M. and King, A. E. and Jurss, J. W. and El Roz, K. A. and Long, J. R. and Chang, C. J. and Castellano, F. N.}, year={2014}, pages={1477–1488} }
 @article{mccusker_hablot_ziessel_castellano_2014, title={Triplet State Formation in Homo- and Heterometallic Diketopyrrolopyrrole Chromophores}, volume={53}, ISSN={["1520-510X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84914165949&partnerID=MN8TOARS}, DOI={10.1021/ic502169a}, abstractNote={The synthesis, structural characterization, and excited-state dynamics of series of diketopyrrolopyrrole (DPP) bridged homodinuclear Ir(III) and heterodinuclear Ir(III)/Pt(II) complexes is described. Steady-state and time-resolved photoluminescence along with transient absorption measurements were used to probe the nature of the emissive and long-lived excited states. Upon excitation into the (1)DPP ligand-localized excited state in the presence of coordinated Ir(III) or Pt(II) metal centers, the intersystem crossing is enhanced, leading to a quenching of the (1)DPP fluorescence and the formation of the long-lived (τ ≈ 30-40 μs) (3)DPP excited state in all instances.}, number={23}, journal={INORGANIC CHEMISTRY}, author={McCusker, Catherine E. and Hablot, Delphine and Ziessel, Raymond and Castellano, Felix N.}, year={2014}, month={Dec}, pages={12564–12571} }
 @article{deng_blumhoff_castellano_2013, title={Annihilation Limit of a Visible-to-UV Photon Upconversion Composition Ascertained from Transient Absorption Kinetics}, volume={117}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/JP4022618}, DOI={10.1021/JP4022618}, abstractNote={Noncoherent sensitized green-to-near-visible upconversion has been achieved utilizing palladium(II) octaethylporphyrin (PdOEP) as the triplet sensitizer and anthracene as the energy acceptor/annihilator in vacuum degassed toluene. Selective 547 nm excitation of PdOEP with incident irradiance as low as 600 μW/cm(2) results in the observation of anthryl fluorescence at higher energy. Stern-Volmer analysis of the dynamic phosphorescence quenching of PdOEP by anthracene possesses an extremely large K(SV) of 810,000 M(-1), yielding a triplet-triplet energy transfer quenching constant of 3.3 × 10(9) M(-1) s(-1). Clear evidence for the subsequent triplet-triplet annihilation (TTA) of anthracene was afforded by numerous experiments, one of the most compelling was an excitation scan illustrating that the Q-band absorption features of PdOEP are solely responsible for sensitizing the anti-Stokes fluorescence. The upconverted emission intensity with respect to the excitation power was shown to vary between quadratic and linear using either coherent or noncoherent light sources, illustrating the expected kinetic limits for the light producing photochemistry under continuous wave illumination. Time-resolved experiments directly comparing the total integrated anthracene intensity/time fluorescence data produced through upconversion (λ(ex) = 547 nm, delayed signal) and with direct excitation (λ(ex) = 355 nm, prompt signal) under conditions where the laser pulse is completely absorbed by the sample reveal annihilation efficiencies of approximately 40%. Similarly, the delayed fluorescence kinetic analysis reported by Schmidt and co-workers (J. Phys. Chem. Lett. 2010, 1, 1795-1799) was used to reveal the maximum possible efficiency from a model red-to-yellow upconverting composition and this treatment was applied to the anthryl triplet absorption decay transients of anthracene measured for the PdOEP/anthracene composition at 430 nm. From this analysis approximately 50% of the anthryl triplets that decay by TTA produce singlet fluorescence, consistent with the notion that annihilation spin statistics does not impose efficiency limits on upconversion photochemistry.}, number={21}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Deng, Fan and Blumhoff, Jörg and Castellano, Felix N.}, year={2013}, month={May}, pages={4412–4419} }
 @article{nippe_khnayzer_panetier_zee_olaiya_head-gordon_chang_castellano_long_2013, title={Catalytic proton reduction with transition metal complexes of the redox-active ligand bpy2PYMe}, volume={4}, ISSN={2041-6520 2041-6539}, url={http://dx.doi.org/10.1039/C3SC51660A}, DOI={10.1039/C3SC51660A}, abstractNote={A new pentadentate, redox-active ligand bpy2PYMe has been synthesized and its corresponding transition metal complexes of Fe2+ (1), Co2+ (2), Ni2+ (3), Cu2+ (4), and Zn2+ (5) have been investigated for electro- and photo-catalytic proton reduction in acetonitrile and water, respectively. Under weak acid conditions, the Co complex displays catalytic onset at potentials similar to those of the ligand centered reductions in the absence of acid. Related Co complexes devoid of ligand redox activity catalyze H2 evolution under similar conditions at significantly higher overpotentials, showcasing the beneficial effect of combining ligand-centered redox activity with a redox-active Co center. Furthermore, turnover numbers as high as 1630 could be obtained under aqueous photocatalytic conditions using [Ru(bpy)3]2+ as a photosensitizer. Under those conditions catalytic hydrogen production was solely limited by photosensitizer stability. Introduction of an electron withdrawing CF3 group into the pyridine moiety of the ligand as in bpy2PYMe-CF3 renders its corresponding Co complex 6 less active for proton reduction in electro- and photocatalytic experiments. This surprising effect of ligand substitution was investigated by means of density functional theory calculations which suggest the importance of electronic communication between Co1+ and the redox-active ligand. Taken together, the results provide a path forward in the design of robust molecular catalysts in aqueous media with minimized overpotential by exploiting the synergy between redox-active metal and ligand components.}, number={10}, journal={Chemical Science}, publisher={Royal Society of Chemistry (RSC)}, author={Nippe, Michael and Khnayzer, Rony S. and Panetier, Julien A. and Zee, David Z. and Olaiya, Babatunde S. and Head-Gordon, Martin and Chang, Christopher J. and Castellano, Felix N. and Long, Jeffrey R.}, year={2013}, pages={3934} }
 @article{chakraborty_deaton_haefele_castellano_2013, title={Charge-Transfer and Ligand-Localized Photophysics in Luminescent Cyclometalated Pyrazolate-Bridged Dinuclear Platinum(II) Complexes}, volume={32}, ISSN={0276-7333 1520-6041}, url={http://dx.doi.org/10.1021/OM400276V}, DOI={10.1021/OM400276V}, abstractNote={We present the synthesis, photophysical characterization, and electrochemistry of three series of cyclometalated binuclear platinum(II) complexes, each bridged by two 3,5-disubstituted pyrazolate ligands (μ-R2pz). These neutral compounds have the general formula [C∧NPt(μ-R2pz)]2, where C∧N is a cyclometalating ligand corresponding to 2-(2′-thienyl)pyridine (thpy), 1-phenylisoquinoline (piq), or 7,8-benzoquinoline (bzq) with R = H, Me, iPr, Ph, corresponding to series I–III dimers, respectively. Systematic variation of the cyclometalating ligands in addition to the bridging pyrazolates renders colorful structures exhibiting a range of electrochemical and spectroscopic behavior with absorption and photoluminescence properties tuned over a wide portion of the visible spectrum. Steric bulk introduced into the 3,5-positions on the pz bridges readily modulates intramolecular d8–d8 metal–metal σ interactions strongly affecting the frontier orbitals’ electronic structure, manifested by changes in absorption and e...}, number={14}, journal={Organometallics}, publisher={American Chemical Society (ACS)}, author={Chakraborty, Arnab and Deaton, Joseph C. and Haefele, Alexandre and Castellano, Felix N.}, year={2013}, month={Jul}, pages={3819–3829} }
 @article{mccusker_castellano_2013, place={McCusker, C.E}, title={Design of a Long-Lifetime, Earth-Abundant, Aqueous Compatible Cu(I) Photosensitizer Using Cooperative Steric Effects}, volume={52}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/IC401213P}, DOI={10.1021/IC401213P}, abstractNote={A new homoleptic Cu(I) photosensitizer, [Cu(dsbtmp)2](+) (dsbtmp = 2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline), designed to exhibit cooperative steric hindrance, unexpectedly produced strong photoluminescence (Φ = 1.9-6.3%) and long excited state lifetimes (τ = 1.2-2.8 μs) in a broad range of coordinating and noncoordinating solvents. The combination of the 2,9-sec-butyl substituents with the neighboring 3,8-methyl groups led to a Cu(I) complex with small degrees of ground and excited state distortion ultimately producing a molecule with robust metal-to-ligand charge transfer photophysics largely insulated from solvent interactions, reversible redox chemistry serving as a strong excited state reductant, along with impressive thermodynamic and photochemical stability in solution.}, number={14}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={McCusker, Catherine E. and Castellano, Felix N.}, year={2013}, month={Jul}, pages={8114–8120} }
 @article{el-ballouli_khnayzer_khalife_fonari_hallal_timofeeva_patra_castellano_wex_kaafarani_2013, title={Diarylpyrenes vs. diaryltetrahydropyrenes: Crystal structures, fluorescence, and upconversion photochemistry}, volume={272}, ISSN={["1010-6030"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84884505475&partnerID=MN8TOARS}, DOI={10.1016/j.jphotochem.2013.07.018}, abstractNote={Abstract The synthesis of two series of substituted 2,7-diaryl-4,5,9,10-tetrahydropyrenes ( 1a – c ) and 2,7-diarylpyrenes ( 2a – c ) is reported; the opposing phenyl tips being terminated with t Bu (a), OCH 3 (b), or F ( c ) to impart variation in electronic properties. X-ray crystallographic analysis of the six compounds revealed edge-to-face packing predominately due to van der Waals forces in the solid state in all instances. The photophysical properties of these compounds were investigated in solution and in solid state/thin films. Since the 2,7-bis(4- tert -butylphenyl)tetrahydropyrene 1a possesses unity fluorescence quantum efficiency, it was successfully employed as the emitter in a low power upconversion scheme featuring fac -Ir(ppy) 3 [ppy = 2-phenylpyridine] as the photosensitizer.}, journal={JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY}, author={El-Ballouli, Ala'a O. and Khnayzer, Rony S. and Khalife, Jihane C. and Fonari, Alexandr and Hallal, Kassem M. and Timofeeva, Tatiana V. and Patra, Digambara and Castellano, Felix N. and Wex, Brigitte and Kaafarani, Bilal R.}, year={2013}, month={Nov}, pages={49–57} }
 @article{khon_lambright_khnayzer_moroz_perera_butaeva_lambright_castellano_zamkov_2013, title={Improving the Catalytic Activity of Semiconductor Nanocrystals through Selective Domain Etching}, volume={13}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/NL400715N}, DOI={10.1021/NL400715N}, abstractNote={Colloidal chemistry offers an assortment of synthetic tools for tuning the shape of semiconductor nanocrystals. While many nanocrystal architectures can be obtained directly via colloidal growth, other nanoparticle morphologies require alternative processing strategies. Here, we show that chemical etching of colloidal nanoparticles can facilitate the realization of nanocrystal shapes that are topologically inaccessible by hot-injection techniques alone. The present methodology is demonstrated by synthesizing a two-component CdSe/CdS nanoparticle dimer, constructed in a way that both CdSe and CdS semiconductor domains are exposed to the external environment. This structural morphology is highly desirable for catalytic applications as it enables both reductive and oxidative reactions to occur simultaneously on dissimilar nanoparticle surfaces. Hydrogen production tests confirmed the improved catalytic activity of CdSe/CdS dimers, which was enhanced 3-4 times upon etching treatment. We expect that the demonstrated application of etching to shaping of colloidal heteronanocrystals can become a common methodology in the synthesis of charge-separating nanocrystals, leading to advanced nanoparticles architectures for applications in areas of photocatalysis, photovoltaics, and light detection.}, number={5}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Khon, Elena and Lambright, Kelly and Khnayzer, Rony S. and Moroz, Pavel and Perera, Dimuthu and Butaeva, Evgeniia and Lambright, Scott and Castellano, Felix N. and Zamkov, Mikhail}, year={2013}, month={Apr}, pages={2016–2023} }
 @book{castellano_2013, title={LOW POWER UPCONVERSION FOR SOLAR FUELS PHOTOCHEMISTRY}, DOI={10.2172/1089302}, abstractNote={Earth abundant copper(I) diimine complexes represent a renewable and economically feasible alternative to commonly used heavy metal containing chromophores. In the metal-to-ligand charge transfer (MLCT) excited state, copper(I) diimine complexes typically undergo a significant structural rearrangement, leading to molecules with large Stokes shifts and very short excited state lifetimes, thereby limiting their usefulness as sensitizers in bimolecular electron and triplet energy transfer reactions. Strategically placed bulky substituents on the coordinating phenanthroline ligands have proven useful in restricting the transiently produced excited state Jahn-Teller distortion, leading to longer-lived excited states. By combining bulky sec-butyl groups in the 2- and 9- positions with methyl groups in the 3-,4-, 7-, and 8- positions, a remarkably long-lived (2.8 μs in DCM) copper(I) bis-phenanthroline complex, [Cu(dsbtmp)2]+, has been synthesized and characterized. Unlike other copper(I) diimine complexes, [Cu(dsbtmp)2]+ also retains a μs lifetime in coordinating solvents such as acetonitrile and water as a result of the cooperative sterics inherent in the molecular design. Preliminary results on the use of this complex in hydrogen-forming homogeneous photocatalysis is presented. Photon upconversion based on sensitized triplet-triplet annihilation (TTA) represents a photochemical means to generate high-energy photons (or high-energy chemical products) from low-energy excitation, having potential applications in solar energy more » conversion and solar fuels producing devices. For the first time, synthetically facile and earth abundant Cu(I) MLCT sensitizers have been successfully incorporated into two distinct photochemical upconversion schemes, affording both red-to-green and orange-to-blue wavelength conversions. Preliminary results on aqueous-based photochemical upconversion as well as intramolecular Sn(IV) porphyrins containing axially coordinated aromatic hydrocarbon chromophores poised for upconversion photochemistry are also presented. « less}, institution={Office of Scientific and Technical Information (OSTI)}, author={Castellano, Felix}, year={2013}, month={Aug} }
 @article{donato_mccusker_castellano_zysman-colman_2013, title={Mono- and Dinuclear Cationic Iridium(III) Complexes Bearing a 2,5-Dipyridylpyrazine (2,5-dpp) Ligand}, volume={52}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/IC400478D}, DOI={10.1021/IC400478D}, abstractNote={The synthesis, X-ray structures, photophysical, and electrochemical characterization of mono- (1) and dinuclear (2) cationic iridium(III) complexes bearing a 2,5-dipyridylpyrazine (2,5-dpp) ancillary ligand are reported. Upon the complexation of a first equivalent of iridium, the photoluminescence shifts markedly into the deep red (λem = 710 nm, ΦPL = 0.9%) compared to other cationic iridium complexes such as [Ir(ppy)2(bpy)]PF6. With the coordination of a second equivalent of iridium, room temperature luminescence is completely quenched. Both 1 and 2 are luminescent at low temperatures but with distinct excited state decay kinetics; the emission of 2 is significantly red-shifted compared to 1. Emission both at 298 and 77 K results from a mixed charge-transfer state. Density functional theory (DFT) calculations and electrochemical behavior point to an electronic communication between the two iridium complexes.}, number={15}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Donato, Loïc and McCusker, Catherine E. and Castellano, Felix N. and Zysman-Colman, Eli}, year={2013}, month={Jul}, pages={8495–8504} }
 @article{deng_sommer_myahkostupov_schanze_castellano_2013, title={Near-IR phosphorescent metalloporphyrin as a photochemical upconversion sensitizer}, volume={49}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/C3CC44479A}, DOI={10.1039/C3CC44479A}, abstractNote={The phosphorescent metalloporphyrin sensitizer PtTPTNP (TPTNP = tetraphenyltetranaphtho[2,3]porphyrin) has been successfully coupled with perylenediimide (PDI) or rubrene utilized as triplet acceptors/annihilators to upconvert 690 nm incident photons into yellow fluorescence through sensitized triplet-triplet annihilation at overall efficiencies in the 6-7% range while exhibiting exceptional photostability.}, number={67}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Deng, Fan and Sommer, Jonathan R. and Myahkostupov, Mykhaylo and Schanze, Kirk S. and Castellano, Felix N.}, year={2013}, pages={7406} }
 @article{mccusker_castellano_2013, title={Orange-to-blue and red-to-green photon upconversion with a broadband absorbing copper(i) MLCT sensitizer}, volume={49}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/C3CC40778K}, DOI={10.1039/C3CC40778K}, abstractNote={A synthetically facile and earth abundant Cu(I) metal-to-ligand charge transfer sensitizer was successfully incorporated into two distinct photochemical upconversion schemes, affording red-to-green and orange-to-blue wavelength conversions.}, number={34}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={McCusker, Catherine E. and Castellano, Felix N.}, year={2013}, pages={3537} }
 @article{wilke_castellano_2013, title={Photochemical Upconversion: A Physical or Inorganic Chemistry Experiment for Undergraduates Using a Conventional Fluorimeter}, volume={90}, ISSN={0021-9584 1938-1328}, url={http://dx.doi.org/10.1021/ED300142Z}, DOI={10.1021/ED300142Z}, abstractNote={Photochemical upconversion is a regenerative process that transforms lower-energy photons into higher-energy light through two sequential bimolecular reactions, triplet sensitization of an appropriate acceptor followed by singlet fluorescence producing triplet–triplet annihilation derived from two energized acceptors. This laboratory directly investigates this phenomenon using the facile photo-induced triplet–triplet energy-transfer reaction between the benchmark inorganic chromophore tris(2,2′-bipyridyl)ruthenium(II), [Ru(bpy)3]2+, and 9,10-diphenylanthracene (DPA). Selective green excitation of [Ru(bpy)3]2+ in the presence of DPA results in two observations, the (dynamic) quenching of the [Ru(bpy)3]2+ photoluminescence in the red and the production of upconverted DPA singlet fluorescence in the blue. The quadratic nature of the incident light power dependence for the latter process is easily realized by using the percent transmission characteristics of neutral density filters placed in the excitation be...}, number={6}, journal={Journal of Chemical Education}, publisher={American Chemical Society (ACS)}, author={Wilke, Bryn M. and Castellano, Felix N.}, year={2013}, month={Apr}, pages={786–789} }
 @article{baker_rachford_castellano_baker_2013, title={Ranking Solvent Interactions and Dielectric Constants with [Pt(mesBIAN)(tda)]: A Cautionary Tale for Polarity Determinations in Ionic Liquids}, volume={14}, ISSN={1439-4235}, url={http://dx.doi.org/10.1002/CPHC.201200981}, DOI={10.1002/CPHC.201200981}, abstractNote={AbstractThe solvatochromic properties of [Pt(mesBIAN)(tda)] are studied in traditional molecular solvents and ionic liquids and duly compared along established empirical solvent parameter scales. The charge‐transfer absorption band of [Pt(mesBIAN)(tda)] is determined to be primarily dependent upon solvent acidity and dipolarity. Notably, ionic liquids do not obey the same well‐behaved trend as molecular solvents, highlighting the complexity and domain (nano)segregation inherent to ionic liquids.}, number={5}, journal={ChemPhysChem}, publisher={Wiley}, author={Baker, Gary A. and Rachford, Aaron A. and Castellano, Felix N. and Baker, Sheila N.}, year={2013}, month={Feb}, pages={1025–1030} }
 @article{khnayzer_mccusker_olaiya_castellano_2013, title={Robust Cuprous Phenanthroline Sensitizer for Solar Hydrogen Photocatalysis}, volume={135}, ISSN={["0002-7863"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84884875774&partnerID=MN8TOARS}, DOI={10.1021/ja407816f}, abstractNote={The Cu(I) metal-to-ligand charge-transfer complex, [Cu(dsbtmp)2](+) (dsbtmp = 2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline), exhibits outstanding stability as a visible-light-absorbing photosensitizer in hydrogen-evolving homogeneous photocatalysis. In concert with the Co(dmgH)2(py)Cl water reduction catalyst and N,N-dimethyl-p-toluidine sacrificial donor in 1:1 H2O:CH3CN, this Cu(I) sensitizer remains active even after 5 days of visible-light-pumped (λex = 452 ± 10 nm) hydrogen evolution catalysis. Deuteration studies illustrate that the hydrogen produced from this composition does indeed originate from aqueous protons.}, number={38}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Khnayzer, Rony S. and McCusker, Catherine E. and Olaiya, Babatunde S. and Castellano, Felix N.}, year={2013}, month={Sep}, pages={14068–14070} }
 @article{myahkostupov_prusakova_oblinsky_scholes_castellano_2013, title={Structural Refinement of Ladder-Type Perylenediimide Dimers: A Classical Tale of Conformational Dynamics}, volume={78}, ISSN={["0022-3263"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84883763311&partnerID=MN8TOARS}, DOI={10.1021/jo401348w}, abstractNote={We have synthesized and thoroughly characterized two representative ladder-type acetylene-bridged perylenediimide dimers bearing long alkyl chain solubilizing groups, bis[1-ethynyl-N,N'-bis(1-hexylheptyl)-perylene-3,4:9,10-tetracarboxylic diimide] ([PDICC]2, 1) and 1,1'-ethynyl-bis[N,N'-bis(1-hexylheptyl)-perylene-3,4:9,10-tetracarboxylic diimide] ([PDI]2CC, 2). In these dimeric PDI molecules, NMR-based structural characterization became nontrivial because severe (1)H spectral broadening and greater than expected numbers of observed (13)C resonances substantially complicated the interpretation of traditional 1-D spectra. However, rational two-dimensional NMR approaches based on both homo- and heteronuclear couplings ((1)H-(1)H COSY; (1)H-(13)C HSQC), in conjunction with high-level structural DFT calculations (GIAO/B3LYP/6-31G(d,p)/PCM, chloroform), were readily applied to these structures, producing well-defined analytical characterization, and the associated methodology is described in detail. Furthermore, on the basis of dynamic NMR experiments, both 1 and 2 were found to exist in a perylene-centered conformational dynamic equilibrium (ΔG‡ = 13-17 kcal/mol), which primarily caused the observed ambiguities in conventional 1-D spectra.}, number={17}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Myahkostupov, Mykhaylo and Prusakova, Valentina and Oblinsky, Daniel G. and Scholes, Gregory D. and Castellano, Felix N.}, year={2013}, month={Sep}, pages={8634–8644} }
 @article{yang_walpita_zhou_luk_vyas_khnayzer_tiwari_diri_hadad_castellano_et al._2013, title={Toward Organic Photohydrides: Excited-State Behavior of 10-Methyl-9-phenyl-9,10-dihydroacridine}, volume={117}, ISSN={1520-6106 1520-5207}, url={http://dx.doi.org/10.1021/JP401770E}, DOI={10.1021/JP401770E}, abstractNote={The excited-state hydride release from 10-methyl-9-phenyl-9,10-dihydroacridine (PhAcrH) was investigated using steady-state and time-resolved UV/vis absorption spectroscopy. Upon excitation, PhAcrH is oxidized to the corresponding iminium ion (PhAcr(+)), while the solvent (acetonitrile/water mixture) is reduced (52% of PhAcr(+) and 2.5% of hydrogen is formed). The hydride release occurs from the triplet excited state by a stepwise electron/hydrogen-atom transfer mechanism. To facilitate the search for improved organic photohydrides that exhibit a concerted mechanism, a computational methodology is presented that evaluates the thermodynamic parameters for the hydride ion, hydrogen atom, and electron release from organic hydrides.}, number={49}, journal={The Journal of Physical Chemistry B}, publisher={American Chemical Society (ACS)}, author={Yang, Xin and Walpita, Janitha and Zhou, Dapeng and Luk, Hoi Ling and Vyas, Shubham and Khnayzer, Rony S. and Tiwari, Subodh C. and Diri, Kadir and Hadad, Christopher M. and Castellano, Felix N. and et al.}, year={2013}, month={May}, pages={15290–15296} }
 @article{chirdon_mccusker_castellano_bernhard_2013, title={Tracking of Tuning Effects in Bis-Cyclometalated Iridium Complexes: A Combined Time Resolved Infrared Spectroscopy, Electrochemical, and Computational Study}, volume={52}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/IC401009Q}, DOI={10.1021/IC401009Q}, abstractNote={Electronic structure and photophysical properties have been investigated for a new series of fluorinated iridium complexes with the parent [Ir(ppy)2(deeb)](PF6) (deeb is 4,4'-diethylester-2,2'-bipyridine). Time resolved infrared spectroscopy (TRIR) has been used to observe the long-lived triplet excited state of each complex confirming its mixed charge transfer character. Supplementary evidence of charge transfer in the triplet state is provided via emission spectroscopy, transient absorption spectroscopy, and density functional theory (DFT) calculations. Both computational and spectroscopic assignments reveal consistency in the first excitation throughout the series of complexes. Electrochemical measurements meanwhile show that increasing fluorination still induces expected shifting of frontier orbitals. Excited states beyond the lowest lying triplet are probed for the complexes via UV-vis spectroscopy which reveals three distinct features. These features are assigned via time-dependent DFT (TD-DFT) to build a broader understanding of electronic structure.}, number={15}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Chirdon, Danielle N. and McCusker, Catherine E. and Castellano, Felix N. and Bernhard, Stefan}, year={2013}, month={Jul}, pages={8795–8804} }
 @article{frath_yarnell_ulrich_castellano_ziessel_2013, title={Ultrafast Photoinduced Electron Transfer in Viologen-Linked BODIPY Dyes}, volume={14}, ISSN={1439-4235}, url={http://dx.doi.org/10.1002/CPHC.201300547}, DOI={10.1002/CPHC.201300547}, abstractNote={AbstractNew boron‐dipyrromethene (BODIPY) dyes linked to viologen are prepared and their photophysical and electrochemical properties are investigated. Both synthesized molecules have similar electronic absorption spectra with the absorption maximum localized at 517 and 501 nm for dye 1 and dye 2, respectively. They exhibit well‐defined redox behavior, highlighting the presence of BODIPY and viologen subunits, with little perturbation of the redox potential of both subunits with respect to the parent compounds. Both dyes are heavily quenched by photoinduced electron transfer from the BODIPY to the viologen subunit. The transient absorption technique demonstrates that dye 2 forms the viologen radical within a timeframe of 7.1 ps, and that the charge‐separated species has a lifetime of 59 ps. Sustained irradiation of dye 2 in the presence of a tertiary amine allows for the accumulation of BODIPY–methyl‐4,4′‐bipyridinium (BODIPY–MV+), as observed by its characteristic absorption at 396 and 603 nm. However, dye 2 does not generate catalytic amounts of hydrogen under standard conditions.}, number={14}, journal={ChemPhysChem}, publisher={Wiley}, author={Frath, Denis and Yarnell, James E. and Ulrich, Gilles and Castellano, Felix N. and Ziessel, Raymond}, year={2013}, month={Aug}, pages={3348–3354} }
 @article{schultz_li_mccusker_moorefield_castellano_wesdemiotis_newkome_2012, title={Back Cover: Dondorff Rings: Synthesis, Isolation, and Properties of 60°-Directed Bisterpyridine-Based Folded Tetramers (Chem. Eur. J. 37/2012)}, volume={18}, ISSN={0947-6539}, url={http://dx.doi.org/10.1002/chem.201290162}, DOI={10.1002/chem.201290162}, abstractNote={Taking advantage of the coordination strength of a ruthenium(II) bisterpyridine complex, G. Newkome, C. Wesdemiotis, A. Schultz, and co-workers in their Communication on page 11569 ff. have successfully synthesized a series of novel tetrameric macrocycles based on a 60°-oriented bisterpyridine ligand, resulting in folded architectures. Resembling the graceful giant manta ray, these folded metallomacrocycles, termed Dondorff rings after the first to report these rays, were characterized photophysically, as well as by ESI-TWIM-MS and molecular modeling.}, number={37}, journal={Chemistry - A European Journal}, publisher={Wiley}, author={Schultz, Anthony and Li, Xiaopeng and McCusker, Catherine E. and Moorefield, Charles N. and Castellano, Felix N. and Wesdemiotis, Chrys and Newkome, George R.}, year={2012}, month={Aug}, pages={11840–11840} }
 @article{schultz_li_mccusker_moorefield_castellano_wesdemiotis_newkome_2012, title={Dondorff Rings: Synthesis, Isolation, and Properties of 60°-Directed Bisterpyridine-Based Folded Tetramers}, volume={18}, ISSN={0947-6539}, url={http://dx.doi.org/10.1002/chem.201201796}, DOI={10.1002/chem.201201796}, abstractNote={Square feat: The synthesis, isolation, and characterization of five novel bisterpyridine-based metallomacrocycles, possessing a folded tetrameric configuration is reported (see figure). The initial dimeric building block with the stable linear {tpy-Ru(II)-tpy} connectivity circumvents the formation of the thermodynamically favored molecular triangles.}, number={37}, journal={Chemistry - A European Journal}, publisher={Wiley}, author={Schultz, Anthony and Li, Xiaopeng and McCusker, Catherine E. and Moorefield, Charles N. and Castellano, Felix N. and Wesdemiotis, Chrys and Newkome, George R.}, year={2012}, month={Aug}, pages={11569–11572} }
 @article{haefele_blumhoff_khnayzer_castellano_2012, title={Getting to the (Square) Root of the Problem: How to Make Noncoherent Pumped Upconversion Linear}, volume={3}, ISSN={1948-7185}, url={http://dx.doi.org/10.1021/jz300012u}, DOI={10.1021/jz300012u}, abstractNote={We present experimental data illustrating that photochemical upconversion based on sensitized triplet–triplet annihilation can exhibit anti-Stokes emissions whose intensities with respect to the excitation power can vary between quadratic and linear using a noncoherent polychromatic light source. The benchmark upconverting composition consisting of Pd(II) octaethylporphyrin (PdOEP) sensitizers and 9,10-diphenylanthracene (DPA) acceptors/annihilators in toluene was selected to generate quadratic, intermediate, and linear behavior under both coherent and noncoherent excitation conditions. Each of these power laws was traversed in a single sample in one contiguous experiment through selective pumping of the sensitizer using an Ar+ laser. Wavelength-dependent responses ranging from quadratic to pseudolinear were also recorded from the identical sample composition when excited by Xe lamp/monochromator output in a conventional fluorimeter, where the optical density at λex dictates the observed incident power de...}, number={3}, journal={The Journal of Physical Chemistry Letters}, publisher={American Chemical Society (ACS)}, author={Haefele, Alexandre and Blumhoff, Jörg and Khnayzer, Rony S. and Castellano, Felix N.}, year={2012}, month={Jan}, pages={299–303} }
 @article{kim_deng_castellano_kim_2012, title={High Efficiency Low-Power Upconverting Soft Materials}, volume={24}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/cm3012414}, DOI={10.1021/cm3012414}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTHigh Efficiency Low-Power Upconverting Soft MaterialsJae-Hyuk Kim†, Fan Deng‡, Felix N. Castellano*‡, and Jae-Hong Kim*†View Author Information† School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States ‡ Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, United States *E-mail: [email protected]; [email protected]Cite this: Chem. Mater. 2012, 24, 12, 2250–2252Publication Date (Web):June 7, 2012Publication History Received23 April 2012Revised4 June 2012Published online12 June 2012Published inissue 26 June 2012https://doi.org/10.1021/cm3012414Copyright © 2012 American Chemical SocietyRIGHTS & PERMISSIONSACS AuthorChoiceArticle Views6456Altmetric-Citations177LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Light,Luminescence,Materials,Polymers,Power Get e-Alerts}, number={12}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Kim, Jae-Hyuk and Deng, Fan and Castellano, Felix N. and Kim, Jae-Hong}, year={2012}, month={Jun}, pages={2250–2252} }
 @article{prusakova_mccusker_castellano_2012, title={Ligand-Localized Triplet-State Photophysics in a Platinum(II) Terpyridyl Perylenediimideacetylide}, volume={51}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic301169t}, DOI={10.1021/ic301169t}, abstractNote={The synthesis, electrochemistry, and photophysical behavior of a Pt(II) terpyridyl perylenediimide (PDI) acetylide (1) charge-transfer complex is reported. The title compound exhibits strong (ε ≈ 5 × 10(4) M(-1)cm(-1)) low-energy PDI acetylide-based π-π* absorption bands in the visible range extending to 600 nm, producing highly quenched singlet fluorescence (Φ = 0.014 ± 0.001, τ = 109 ps) with respect to a nonmetalated PDI model chromophore. Nanosecond transient absorption spectroscopy revealed the presence of a long excited-state lifetime (372 ns in 2-methyltetrahydrofuran) with transient features consistent with the PDI-acetylide triplet state, ascertained by direct comparison to a model Pt(II) PDI-acetylide complex lacking low-energy charge-transfer transitions. For the first time, time-resolved step-scan FT-IR spectroscopy was used to characterize the triplet excited state of the PDI-acetylide sensitized in the title compound and its associated model complex. The observed red shifts (∼30-50 cm(-1)) in the C═O and C≡C vibrations of the two Pt(II) complexes in the long-lived excited state are consistent with formation of the (3)PDI acetylide state and found to be in excellent agreement with the expected change in the relevant DFT-calculated IR frequencies in the nonmetalated PDI model chromophore (ground singlet state and lowest triplet excited state). Formation of the PDI triplet excited state in the title chromophore was also supported by sensitization of the singlet oxygen photoluminescence centered at ∼1275 nm in air-saturated acetonitrile solution, Φ((1)O(2)) = 0.52. In terms of light emission, only residual PDI-based red fluorescence could be detected and no corresponding PDI-based phosphorescence was observed in the visible or NIR region at 298 or 77 K in the Pt(II) terpyridyl perylenediimideacetylide.}, number={15}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Prusakova, Valentina and McCusker, Catherine E. and Castellano, Felix N.}, year={2012}, month={Jul}, pages={8589–8598} }
 @article{mccusker_hablot_ziessel_castellano_2012, title={Metal Coordination Induced π-Extension and Triplet State Production in Diketopyrrolopyrrole Chromophores}, volume={51}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic301238e}, DOI={10.1021/ic301238e}, abstractNote={Triplet state photophysics has been generated in two distinct diketopyrrolopyrrole (DPP) chromophores terminated with either phenyl (1) or thienyl (2) spacers, when sandwiched between two Ir(III) complexes using bipyridyl linkers. Upon coordination of the bpy-DPP-bpy subunit resulting in its planarization, the π-conjugation in the DPP chromophore formally extends and was manifested as a substantial red shift in the absorption and fluorescence profiles of 1 and 2. Low energy excitation of these dinuclear metal complexes produced strongly quenched singlet fluorescence, generated quite intense long-lived (τ ∼ 3 μs) absorption transients in the red, sensitized (1)O(2) photoluminescence centered at 1270 nm in aerated solutions, and yielded low temperature near-IR phosphorescence in 1 centered at 950 nm.}, number={15}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={McCusker, Catherine E. and Hablot, Delphine and Ziessel, Raymond and Castellano, Felix N.}, year={2012}, month={Jul}, pages={7957–7959} }
 @article{perera_lorek_khnayzer_moroz_o’connor_khon_diederich_kinder_lambright_castellano_et al._2012, title={Photocatalytic Activity of Core/Shell Semiconductor Nanocrystals Featuring Spatial Separation of Charges}, volume={116}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/jp308921s}, DOI={10.1021/jp308921s}, abstractNote={The present study investigates the photocatalytic activity of ZnSe/CdS core/shell semiconductor nanocrystals. These nanoparticles exhibit a spatial separation of photoinduced charges between the core and the shell domains, which makes them potentially viable for photocatalytic applications. Unfortunately, one of the excited charges remains inside the core semiconductor and thus cannot efficiently react with the external environment. Here, we explore this issue by investigating the mechanisms of hole extraction from the ZnSe core to the surface of the CdS shell. In particular, the effect of shell thickness in ZnSe/CdS core/shell nanocrystals on the ability of core-localized charges to perform oxidative reactions was determined. By using a combination of time-resolved spectroscopy and electrochemical techniques, we demonstrate that the use of hole-scavenging surfactants facilitates an efficient transfer of core-localized holes to the surface even in the case of shells exceeding 7 nm in thickness. These meas...}, number={43}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Perera, Dimuthu and Lorek, Ryan and Khnayzer, Rony S. and Moroz, Pavel and O’Connor, Timothy and Khon, Dmitry and Diederich, Geoffrey and Kinder, Erich and Lambright, Scott and Castellano, Felix N. and et al.}, year={2012}, month={Oct}, pages={22786–22793} }
 @article{spänig_haefele_castellano_2012, title={Photoprocesses of Relevance to Supramolecular Chemistry}, DOI={10.1002/9780470661345.smc089}, abstractNote={Abstract
          This contribution focuses exclusively on the application of photophysical methods that can be applied toward signaling a variety of supramolecular chemistry events using examples from the recent literature. It is not intended to be comprehensive but rather to illustrate how specific photo techniques can be used to glean insight into supramolecular phenomena. Given the widespread availability of fluorescence technologies worldwide, the current study reflects its dominant usage in supramolecular chemistry while exemplifying a range of techniques within the discipline. Nondestructive transient absorption spectroscopy is also discussed in light of how it can be utilized in conjunction with supramolecular photochemistry, specifically in the identification of intermediates that cannot be interrogated otherwise. Relevant aspects of molecular photochemistry and photophysics are briefly introduced below and developed further where necessary. Given the number of comprehensive reviews in the general area of supramolecular photochemistry and photophysics, we attempt to highlight only recent examples using a conceptual framework most relevant to the authors of this contribution, largely involving combinations of metal‐ and organic‐based chromophores.}, journal={Supramolecular Chemistry}, author={Spänig, Fabian and Haefele, Alexandre and Castellano, Felix N.}, year={2012}, month={Mar} }
 @article{muro-small_yarnell_mccusker_castellano_2012, title={Spectroscopy and Photophysics in Cyclometalated RuII-Bis(bipyridyl) Complexes}, volume={2012}, ISSN={1434-1948}, url={http://dx.doi.org/10.1002/ejic.201200460}, DOI={10.1002/ejic.201200460}, abstractNote={AbstractA series of cyclometalated RuII coordination compounds of the general structural formula [Ru(bpy)2(C∧N)]PF6 {C∧N = 2‐phenylpyridine (1), 2‐(2,4‐difluorophenyl)pyridine (2), 2‐(4‐methoxyphenyl)‐5‐methylpyridine (3), benzo[h]quinoline (4); bpy = 2,2′‐bipyridine} have been synthesized, structurally and electrochemically characterized, and examined by using a battery of spectroscopic techniques. The combination of static and dynamic photoluminescence at room temperature and 77 K, resonance Raman spectroscopy, cyclic voltammetry, spectroelectrochemistry, and ultrafast transient absorption spectroscopy reveal that – although the nature of the cyclometalating ligand substantially affects the oxidation potential at the metal center – the lowest‐energy metal‐to‐ligand charge‐transfer excited state always retains pure Ru→bpy character across this series of molecules, and the cyclometalating subunit plays the role of ancillary ligand.}, number={25}, journal={European Journal of Inorganic Chemistry}, publisher={Wiley}, author={Muro-Small, Maria L. and Yarnell, James E. and McCusker, Catherine E. and Castellano, Felix N.}, year={2012}, month={Jul}, pages={4004–4011} }
 @article{ke_myahkostupov_castellano_gabbaï_2012, title={Stibonium Ions for the Fluorescence Turn-On Sensing of F– in Drinking Water at Parts per Million Concentrations}, volume={134}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja308194w}, DOI={10.1021/ja308194w}, abstractNote={The 9-anthryltriphenylstibonium cation, [1](+), has been synthesized and used as a sensor for the toxic fluoride anion in water. This stibonium cation complexes fluoride ions to afford the corresponding fluorostiborane 1-F. This reaction, which occurs at fluoride concentrations in the parts per million range, is accompanied by a drastic fluorescence turn-on response. It is also highly selective and can be used in plain tap water or bottled water to test fluoridation levels.}, number={37}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Ke, Iou-Sheng and Myahkostupov, Mykhaylo and Castellano, Felix N. and Gabbaï, François P.}, year={2012}, month={Sep}, pages={15309–15311} }
 @article{khnayzer_mara_huang_shelby_chen_castellano_2012, title={Structure and Activity of Photochemically Deposited “CoPi” Oxygen Evolving Catalyst on Titania}, volume={2}, ISSN={2155-5435 2155-5435}, url={http://dx.doi.org/10.1021/cs3005192}, DOI={10.1021/cs3005192}, abstractNote={The cobalt phosphate “CoPi” oxygen evolving catalyst (OEC) was photochemically grown on the surface of TiO2 photoanodes short-circuited to a Pt wire under bandgap illumination in the presence of Co(NO3)2 and sodium phosphate (NaPi) buffer. Extended photodeposition (15 h) using a hand-held UV lamp readily permitted quantitative structural and electrochemical characterization of the photochemically deposited CoPi OEC on titania. The formed catalytic material was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy experiments, illustrating the production of easily visualized micrometer scale clusters throughout the titania surface containing both cobalt and phosphate. X-ray absorption fine structure (XAFS) and X-ray absorption near edge structure (XANES) studies indicated that the newly formed material was structurally consistent with the production of molecular cobaltate clusters composed of a cobalt oxide core that is most likely terminated by phosphate ions. ...}, number={10}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Khnayzer, Rony S. and Mara, Michael W. and Huang, Jier and Shelby, Megan L. and Chen, Lin X. and Castellano, Felix N.}, year={2012}, month={Sep}, pages={2150–2160} }
 @article{castellano_2012, title={Transition metal complexes meet the rylenes}, volume={41}, ISSN={1477-9226 1477-9234}, url={http://dx.doi.org/10.1039/c2dt30765k}, DOI={10.1039/c2dt30765k}, abstractNote={This Perspective highlights an emerging area of metal-organic chromophore science related to the photochemistry and photophysics of coordination compounds and organometallic structures covalently tethered to rylene (naphthalene-cored) imide and diimide scaffolds. This combination of molecules renders highly colourful structures producing an array of excited state behaviour and in some instances strongly aggregated self-assembled metal-organic architectures.}, number={28}, journal={Dalton Transactions}, publisher={Royal Society of Chemistry (RSC)}, author={Castellano, Felix N.}, year={2012}, pages={8493–8501} }
 @article{yarnell_deaton_mccusker_castellano_2011, title={Bidirectional “Ping-Pong” Energy Transfer and 3000-Fold Lifetime Enhancement in a Re(I) Charge Transfer Complex}, volume={50}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic200974h}, DOI={10.1021/ic200974h}, abstractNote={The synthesis and photophysics of a new Re(I)-carbonyl diimine complex, Re(PNI-phen)(CO)(3)Cl, where the PNI-phen is N-(1,10-phenanthroline)-4-(1-piperidinyl)naphthalene-1,8-dicarboximide is reported. The metal-to-ligand charge transfer (MLCT) emission lifetime was increased approximately 3000-fold at room temperature with respect to that of the model complex [Re(phen)(CO)(3)Cl] as a result of thermal equilibrium between the emissive (3)MLCT state and a long-lived triplet ligand-centered ((3)LC) state on the PNI chromophore. This represents the longest excited state lifetime (τ = 651 μs) that has ever been observed for a Re(I)-based CT photoluminescence at room temperature. The energy transfer processes and the associated rate constants leading to the establishment of the excited state equilibrium were elucidated by a powerful combination of three techniques (transient visible and infrared (IR) absorption and photoluminescence), each applied from ultrafast to the micro/milliseconds time scale. The MLCT excited state was monitored by transient IR using CO vibrations through time intervals where the corresponding signals obtained in conventional visible transient absorption were completely obscured by overlap with strong transients originating from the pendant PNI chromophore. Following initial excitation of the (1)LC state on the PNI chromophore, energy is transferred to form the MLCT state with a time constant of 45 ps, a value confirmed in all three measurement domains within experimental error. Although transient spectroscopy confirms the production of the (3)MLCT state on ultrafast time scales, Förster resonance energy transfer calculations using the spectral properties of the two chromophores support initial singlet transfer from (1)PNI* to produce the (1)MLCT state by the agreement with the experimentally observed energy transfer time constant and efficiency. Intersystem crossing from the (1)MLCT to the (3)MLCT excited state is believed to be extremely fast and was not resolved with the current experiments. Finally, triplet energy was transferred from the (3)MLCT to the PNI-centered (3)LC state in less than 15 ns, ultimately achieving equilibrium between the two excited states. Subsequent relaxation to the ground state occurred via emission resulting from thermal population of the (3)MLCT state with a resultant lifetime of 651 μs. The title chromophore represents an interesting example of "ping-pong" energy transfer wherein photon excitation first migrates away from the initially prepared (1)PNI* excited state and then ultimately returns to this moiety as a long-lived excited triplet which disposes of its energy by equilibrating with the photoluminescent Re(I) MLCT excited state.}, number={16}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Yarnell, James E. and Deaton, Joseph C. and McCusker, Catherine E. and Castellano, Felix N.}, year={2011}, month={Aug}, pages={7820–7830} }
 @article{onicha_panthi_kinstle_castellano_2011, title={Carbazole donor and carbazole or bithiophene bridged sensitizers for dye-sensitized solar cells}, volume={223}, ISSN={1010-6030}, url={http://dx.doi.org/10.1016/j.jphotochem.2011.08.001}, DOI={10.1016/j.jphotochem.2011.08.001}, abstractNote={Abstract Three metal-free organic sensitizers consisting of carbazole as an electron donor, carbazole or bithiophene as the linker and cyanoacrylic acid as the electron acceptor and anchoring groups were designed and synthesized for use in dye-sensitized solar cells (DSSCs). The sensitizers were characterized by 1 H and 13 C NMR, MALDI-TOF (or HRMS), UV–Vis, photoluminescence, and electrochemistry. The HOMO and LUMO electron distributions of the sensitizers were calculated using density functional theory on a B3LYP level for geometry optimization. The photovoltaic performance of the sensitizers in operational liquid junction-based DSSCs under AM 1.5 G one-sun excitation (100 mW/cm 2 ) indicate that the sensitizers are promising candidates for use in DSSCs. Sensitizers 1 and 2 produce a power conversion efficiency of 2.70% with a maximum IPCE of 75% at 450 nm, while sensitizer 3 has a power conversion efficiency of 2.23% with a maximum IPCE of 66% at 440 nm. The sensitizers thus exhibit excellent photon-to-current conversion efficiencies in the blue region of the spectrum and serve as candidates for further strategic optimization in tandem cells.}, number={1}, journal={Journal of Photochemistry and Photobiology A: Chemistry}, publisher={Elsevier BV}, author={Onicha, Anthony C. and Panthi, Krishna and Kinstle, Thomas H. and Castellano, Felix N.}, year={2011}, month={Sep}, pages={57–64} }
 @article{rowley_ardo_sun_castellano_meyer_2011, title={Charge Recombination to Oxidized Iodide in Dye-Sensitized Solar Cells}, volume={115}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/jp204675p}, DOI={10.1021/jp204675p}, abstractNote={The goal of this study was to determine whether electrons injected into TiO2 in dye-sensitized solar cells (DSSCs) react with di-iodide, I2•–, a known intermediate in sensitized iodide oxidation. The approach was to utilize time-resolved absorption spectroscopy to quantify the yield of I2•– disproportionation under conditions where I2•– reduction by electrons photoinjected into TiO2, TiO2(e–)s, could be competitive. The DSSC was based on [Ru(dtb)2(dcb)]2+, where dtb is 4,4′-(C(CH3)3)2-2,2′-bipyridine and dcb is 4,4′-(COOH)2-2,2′-bipyridine, sensitized mesoporous nanocrystalline TiO2 thin films sintered onto an optically transparent fluorine-doped tin oxide (FTO) conductive substrate. A transparent Pt counter-electrode and a 0.5 M LiI/0.05 M I2/acetonitrile electrolyte completed the DSSC. After pulsed 532 nm laser excitation, the first iodide oxidation product observed spectroscopically was I2•–. Under all conditions studied, there was no direct evidence for the reaction between TiO2(e–) and I2•–, and the ...}, number={41}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Rowley, John G. and Ardo, Shane and Sun, Yali and Castellano, Felix N. and Meyer, Gerald J.}, year={2011}, month={Sep}, pages={20316–20325} }
 @article{cho_mara_wang_lockard_rachford_castellano_chen_2011, title={Coherence in Metal−Metal-to-Ligand-Charge-Transfer Excited States of a Dimetallic Complex Investigated by Ultrafast Transient Absorption Anisotropy}, volume={115}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp109174f}, DOI={10.1021/jp109174f}, abstractNote={Coherence in the metal-metal-to-ligand-charge transfer (MMLCT) excited state of diplatinum molecule [Pt(ppy)(μ-(t)Bu(2)pz)](2) has been investigated through the observed oscillatory features and their corresponding frequencies as well as polarization dependence in the single-wavelength transient absorption (TA) anisotropy signals. Anticorrelated parallel and perpendicular TA signals with respect to the excitation polarization direction were captured, while minimal oscillatory features were observed in the magic angle TA signal. The combined analysis of the experimental results coupled with those previous calculated in the literature maps out a plausible excited state trajectory on the potential energy surface, suggesting that (1) the two energetically close MMLCT excited states due to the symmetry of the molecule may be electronically and coherently coupled with the charge density shifting back and forth between the two phenylpyridine (ppy) ligands, (2) the electronic coupling strength in the (1)MMLCT and (3)MMLCT states may be extracted from the oscillation frequencies of the TA signals to be 160 and 55 cm(-1), respectively, (3) a stepwise intersystem crossing cascades follows (1)MMLCT → (3)MMLCT (T(1b)) → (3)MMLCT (T(1a)), and (4) a possible electronic coherence can be modulated via the Pt-Pt σ-interactions over a picosecond and survive the first step of intersystem crossing. Future experiments are in progress to further investigate the origin of the oscillatory features. These experimental observations may have general implications in design of multimetal center complexes for photoactivated reactions where coherence in the excited states may facilitate directional charge or energy transfer along a certain direction between different parts of a molecule.}, number={16}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Cho, Sung and Mara, Michael W. and Wang, Xianghuai and Lockard, Jenny V. and Rachford, Aaron A. and Castellano, Felix N. and Chen, Lin X.}, year={2011}, month={Apr}, pages={3990–3996} }
 @article{myahkostupov_zamkov_castellano_2011, title={Dye-sensitized photovoltaic properties of hydrothermally prepared TiO2 nanotubes}, volume={4}, ISSN={1754-5692 1754-5706}, url={http://dx.doi.org/10.1039/c0ee00533a}, DOI={10.1039/c0ee00533a}, abstractNote={Hydrothermal synthesis utilizing aqueous alkaline reaction conditions was employed for the preparation of TiO2 nanotubes. The ultimate material morphology was found to be extremely sensitive to the nature of the reaction conditions including the chemical nature of the reactor itself—well-defined TiO2 nanotubes were obtained only when the reaction was carried out in a Teflon reactor/autoclave assembly, as ascertained by electron microscopy imaging. In addition, it was shown that the nanomaterial morphology heavily impacted the performance of dye-sensitized photovoltaic devices based on these materials; devices assembled from well-defined TiO2 nanotubes exhibited marked overall improvement in the power conversion efficiency. Several individual experimental parameters including hydrothermal synthesis temperature, film thickness, TiO2 paste composition, and sintering temperature were shown to affect the photovoltaic properties of the resultant solar cells. Upon sensitization with Ru(dcbpyH2)2(NCS)2, optimized devices showed an average power conversion efficiency of 3.76 ± 0.25% under AM1.5G one sun illumination, seemingly limited by low dye surface coverages.}, number={3}, journal={Energy & Environmental Science}, publisher={Royal Society of Chemistry (RSC)}, author={Myahkostupov, Mykhaylo and Zamkov, Mikhail and Castellano, Felix N.}, year={2011}, pages={998} }
 @article{spaenig_olivier_prusakova_retailleau_ziessel_castellano_2011, title={Excited-State Properties of Heteroleptic Iridium(III) Complexes Bearing Aromatic Hydrocarbons with Extended Cores}, volume={50}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic201397v}, DOI={10.1021/ic201397v}, abstractNote={The synthesis, complete structural characterization, electrochemistry, and excited-state dynamics of a series of four bis-heteroleptic iridium(III) charge-transfer complexes composed of a single acac-functionalized and two ortho-metalated 2-phenylpyridine ligands. The formed iodophenyl complex (2) was used as a metallosynthon to introduce extended-core ethynyltolyl (3), ethynylpyrene (4), and ethynylperylene (5) residues into these structures projecting from the acac ancillary ligand. Static and dynamic photoluminescence along with ultrafast and conventional transient absorption measurements in conjunction with cyclic voltammetry were employed to elucidate the nature of the intramolecular energy-transfer processes occurring in the excited states of polychromophores 4 and 5 and are directly compared with those of model complexes 2 and 3. Upon charge-transfer excitation of these molecules, the long-lived triplet-state metal-to-ligand charge-transfer ((3)MLCT)-based photoluminescence readily observed in 2 and 3 (τ = 1 μs) is nearly quantitatively quenched, resulting from production of the associated triplet intraligand ((3)IL) excited states in 4 and 5 through intramolecular triplet-triplet energy transfer. The respective formation of the extended-core (3)*pyrenyl and (3)*perylenyl-localized excited states in 4 and 5 is confirmed by their ultrafast excited-state evolution, which ultimately generates features associated with these (3)IL excited states and their greatly extended excited-state lifetimes with respect to the parent complexes 2 and 3.}, number={21}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Spaenig, Fabian and Olivier, Jean-Hubert and Prusakova, Valentina and Retailleau, Pascal and Ziessel, Raymond and Castellano, Felix N.}, year={2011}, month={Nov}, pages={10859–10871} }
 @article{wang_goeb sébastien_ji_pogulaichenko_castellano_2011, title={Homogeneous Photocatalytic Hydrogen Production Using π-Conjugated Platinum(II) Arylacetylide Sensitizers}, volume={50}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic101731j}, DOI={10.1021/ic101731j}, abstractNote={Three platinum(II) terpyridylacetylide charge-transfer complexes possessing a lone ancillary ligand systematically varied in phenylacetylide π-conjugation length, [Pt((t)Bu(3)tpy)([C≡CC(6)H(4)](n)H)]ClO(4) (n = 1-3), are evaluated as photosensitizers (PSs) for visible-light-driven (λ > 420 nm) hydrogen production in the presence of a cobaloxime catalyst and the sacrificial electron donor triethanolamine (TEOA). Excited-state reductive quenching of the PS by TEOA produces PS(-) (k(q) scales with the driving force as 1 > 2 > 3), enabling thermal electron transfer to the cobalt catalyst. The initial H(2) evolution is directly proportional to the incident photon flux and visible-light harvesting capacity of the sensitizer, 3 > 2 > 1. The combined data suggest that PSs exhibiting attenuated bimolecular reductive quenching constants with respect to the diffusion limit can overcome this deficiency through improved light absorption in homogeneous H(2)-evolving compositions.}, number={3}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Wang, Xianghuai and Goeb Sébastien and Ji, Zhiqiang and Pogulaichenko, Nadezhda A. and Castellano, Felix N.}, year={2011}, month={Feb}, pages={705–707} }
 @inproceedings{castellano_2011, title={Making hydrogen photocatalytically from water}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80051896414&partnerID=MN8TOARS}, booktitle={ACS National Meeting Book of Abstracts}, author={Castellano, F.N.}, year={2011} }
 @article{goeb_prusakova_wang_vézinat_sallé_castellano_2011, title={Phosphorescent self-assembled PtII tetranuclear metallocycles}, volume={47}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/c1cc10239g}, DOI={10.1039/c1cc10239g}, abstractNote={A series of rigid Pt(II) diimine diacetylide complexes and their corresponding metallocyclic derivatives were synthesized through coordination-driven self-assembly. The photophysical properties of these complexes have been studied in detail, revealing exceptionally high RT phosphorescence quantum yields and lifetimes when the excited state becomes localized on the π-conjugated bridging-ligand following intramolecular charge-transfer sensitization.}, number={15}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Goeb, Sébastien and Prusakova, Valentina and Wang, Xianghuai and Vézinat, Aurélie and Sallé, Marc and Castellano, Felix N.}, year={2011}, pages={4397} }
 @inproceedings{khnayzer_castellano_2011, title={Photo-assisted catalysts growth and water splitting at the metal oxide/molecule interface}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84861019229&partnerID=MN8TOARS}, booktitle={ACS National Meeting Book of Abstracts}, author={Khnayzer, R.S. and Castellano, F.N.}, year={2011} }
 @article{khnayzer_thompson_zamkov_ardo_meyer_murphy_castellano_2012, title={Photocatalytic Hydrogen Production at Titania-Supported Pt Nanoclusters That Are Derived from Surface-Anchored Molecular Precursors}, volume={116}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/jp206943s}, DOI={10.1021/jp206943s}, abstractNote={Degussa P-25 TiO2 bearing surface-anchored Pt(dcbpy)Cl2 [dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine] prepared with systematically varied surface coverage produced Pt0 nanoparticles under bandgap illumination in the presence of methanol hole scavengers. Energy-dispersive X-ray spectroscopy confirmed the presence of elemental platinum in the newly formed nanoparticles during scanning transmission electron microscopy (STEM) experiments. According to the statistical analysis of numerous STEM images, the Pt0 nanoclusters were distributed in a segregated manner throughout the titania surface, ranging in size from 1 to 3 nm in diameter. The final achieved nanoparticle size and net hydrogen production were determined as a function of the Pt(dcbpy)Cl2 surface coverage as well as other systematically varied experimental parameters. The hybrid Pt/TiO2 nanomaterials obtained upon complete decomposition of the Pt(dcbpy)Cl2 precursor displayed higher photocatalytic activity (300 μmol/h) for hydrogen evolution in aq...}, number={1}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Khnayzer, Rony S. and Thompson, Lucas B. and Zamkov, Mikhail and Ardo, Shane and Meyer, Gerald J. and Murphy, Catherine J. and Castellano, Felix N.}, year={2012}, month={Jan}, pages={1429–1438} }
 @article{singh-rachford_nayak_muro-small_goeb sèbastian_therien_castellano_2011, title={Supermolecular-Chromophore-Sensitized Near-Infrared-to-Visible Photon Upconversion}, volume={133}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja200045y}, DOI={10.1021/ja200045y}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionSupermolecular-Chromophore-Sensitized Near-Infrared-to-Visible Photon UpconversionTanya N. Singh-Rachford, Animesh Nayak, Maria L. Muro-Small, Sèbastian Goeb, Michael J. Therien*, and Felix N. Castellano*Cite this: J. Am. Chem. Soc. 2011, 133, 8, 2791Publication Date (Web):February 2, 2011Publication History Published online2 February 2011Published inissue 2 March 2011https://pubs.acs.org/doi/10.1021/ja200045yhttps://doi.org/10.1021/ja200045ycorrectionACS PublicationsCopyright © 2011 . This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views2047Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (901 KB) Get e-Alertsclose Get e-Alerts}, number={8}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Nayak, Animesh and Muro-Small, Maria L. and Goeb Sèbastian and Therien, Michael J. and Castellano, Felix N.}, year={2011}, month={Mar}, pages={2791–2791} }
 @article{myahkostupov_castellano_2011, title={Synthesis and Characterization of Tris(Heteroleptic) Ru(II) Complexes Bearing Styryl Subunits}, volume={50}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic201618e}, DOI={10.1021/ic201618e}, abstractNote={We have developed and optimized a well-controlled and refined methodology for the synthesis of substituted π-conjugated 4,4'-styryl-2,2'-bipyridine ligands and also adapted the tris(heteroleptic) synthetic approach developed by Mann and co-workers to produce two new representative Ru(II)-based complexes bearing the metal oxide surface-anchoring precursor 4,4'-bis[E-(p-methylcarboxy-styryl)]-2,2'-bipyridine. The two targeted Ru(II) complexes, (4,4'-dimethyl-2,2'-bipyridine)(4,4'-di-tert-butyl-2,2'-bipyridine)(4,4'-bis[E-(p-methylcarboxy-styryl)]-2,2'-bipyridine) ruthenium(II) hexafluorophosphate, [Ru(dmbpy)(dtbbpy)(p-COOMe-styryl-bpy)](PF(6))(2) (1) and (4,4'-dimethyl-2,2'-bipyridine)(4,4'-dinonyl-2,2'-bipyridine)(4,4'-bis[E-(p-methylcarboxy-styryl)]-2,2'-bipyridine) ruthenium(II) hexafluorophosphate, [Ru(dmbpy)(dnbpy)(p-COOMe-styryl-bpy)](PF(6))(2) (2) were obtained as analytically pure compounds in high overall yields (>50% after 5 steps) and were isolated without significant purification effort. In these tris(heteroleptic) molecules, NMR-based structural characterization became nontrivial as the coordinated ligand sets each sense profoundly distinct magnetic environments greatly complicating traditional 1D spectra. However, rational two-dimensional approaches based on both homo- and heteronuclear couplings were readily applied to these structures producing quite definitive analytical characterization and the associated methodology is described in detail. Preliminary photoluminescence and photochemical characterization of 1 and 2 strongly suggests that both molecules are energetically and kinetically suitable to serve as sensitizers in energy-relevant applications.}, number={19}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Myahkostupov, Mykhaylo and Castellano, Felix N.}, year={2011}, month={Oct}, pages={9714–9727} }
 @article{khnayzer_blumhoff_harrington_haefele_deng_castellano_2012, title={Upconversion-powered photoelectrochemistry}, volume={48}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/c1cc16015j}, DOI={10.1039/c1cc16015j}, abstractNote={Upconversion photochemistry occurring between palladium(II) octaethylporphyrin (PdOEP, 1) and 9,10-diphenylanthracene (DPA, 2) in toluene successfully sensitizes nanostructured WO(3) photoanodes (E(g) = 2.7 eV) to sub-bandgap non-coherent green photons at low power density.}, number={2}, journal={Chem. Commun.}, publisher={Royal Society of Chemistry (RSC)}, author={Khnayzer, Rony S. and Blumhoff, Jörg and Harrington, Jordan A. and Haefele, Alexandre and Deng, Fan and Castellano, Felix N.}, year={2012}, pages={209–211} }
 @article{rachford_ziessel_bura_retailleau_castellano_2010, title={Boron Dipyrromethene (Bodipy) Phosphorescence Revealed in [Ir(ppy)2(bpy-C≡C-Bodipy)]+}, volume={49}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic901996u}, DOI={10.1021/ic901996u}, abstractNote={The synthesis, structural characterization, electrochemistry, and molecular photophysics of [Ir(ppy)(2)(bpy-C[triple bond]C-Bodipy)](PF(6)), where ppy is 2-phenylpyridine and bpy-C[triple bond]C-Bodipy is 5-ethynyl-2,2'-bipyridine-8-phenyl-1,3,5,7-tetramethyl-4,4-bis(2,5-dioxaoct-7-ynyl)-4-bora-3a,4a-diaza-s-indacene (4), is presented. Static and dynamic photoluminescence and absorption measurements in conjunction with cyclic voltammetry were employed to elucidate the nature of the intramolecular energy transfer processes occurring in the excited state of the title chromophore. Parallel studies were performed on appropriate model chromophores (2 and 3) intended to represent the photophysics of the isolated molecular subunits, that is, triplet metal-to-ligand-charge-transfer ((3)MLCT) and triplet Bodipy intraligand ((3)IL) excited states, respectively. Upon charge transfer excitation of the title chromophore, the (3)MLCT based phosphorescence readily observed in 2 (Phi(em) = 0.027, tau = 243 ns) is quantitatively quenched resulting from production of the (3)Bodipy excited state through intramolecular triplet-triplet energy transfer. The formation of the (3)Bodipy-localized excited state is confirmed by features in the transient absorption difference spectrum, extended excited-state lifetime (tau = 25 micros), as well the observation of (3)IL Bodipy-based phosphorescence detected at 730 nm at 77 K. The low temperature Bodipy phosphorescence is readily produced in 4 as a result of the internal Ir(III) heavy atom.}, number={8}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Rachford, Aaron A. and Ziessel, Raymond and Bura, Thomas and Retailleau, Pascal and Castellano, Felix N.}, year={2010}, month={Apr}, pages={3730–3736} }
 @article{muro_rachford_wang_castellano_2010, title={ChemInform Abstract: PlatinumII Acetylide Photophysics}, volume={42}, DOI={10.1002/chin.201102276}, abstractNote={AbstractReview: 105 refs.}, number={2}, journal={ChemInform}, publisher={Wiley-Blackwell}, author={Muro, Maria L. and Rachford, Aaron A. and Wang, Xianghuai and Castellano, Felix N.}, year={2010}, pages={no-no} }
 @article{onicha_castellano_2010, title={Electrolyte-Dependent Photovoltaic Responses in Dye-Sensitized Solar Cells Based on an Osmium(II) Dye of Mixed Denticity}, volume={114}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/jp100279e}, DOI={10.1021/jp100279e}, abstractNote={This work focuses upon the effects of electrolyte composition, specifically the role of Li+ and I− ions, on the resultant photovoltaic performance of dye-sensitized solar cells (DSCs) based on a new Os(II) polypyridine complex of mixed denticity, [Os(tBu3tpy)(dcbpyH2)(NCS)]PF6 (1). Photophysical and electrochemical characterization of 1 confirmed the suitability of this dye to serve as a sensitizer for regenerative DSCs on mesoscopic titania films. Device photovoltaic performances were assessed by measuring external quantum efficiencies as a function of wavelength, and current−voltage curves, the latter under simulated AM1.5G one-sun illumination. Varying the concentration of LiI in the redox electrolyte affects the short-circuit photocurrent (JSC), open-circuit voltage (VOC), fill factor (ff), power conversion efficiency (η), and external quantum efficiency (EQE) of the individual devices. Increasing the concentration of LiI results in enormous increases in JSC in the Os(II)-based devices accompanied by ...}, number={14}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Onicha, Anthony C. and Castellano, Felix N.}, year={2010}, month={Mar}, pages={6831–6840} }
 @article{wang_goeb sébastien_ji_castellano_2010, title={Excited State Absorption Properties of Pt(II) Terpyridyl Complexes Bearing π-Conjugated Arylacetylides†}, volume={114}, ISSN={1520-6106 1520-5207}, url={http://dx.doi.org/10.1021/jp101528z}, DOI={10.1021/jp101528z}, abstractNote={The synthesis, photophysics, and excited state absorption properties of three platinum(II) terpyridyl acetylide charge transfer (CT) complexes possessing a lone ancillary ligand systematically varied in phenylacetylide (PA) π-conjugation length, [Pt((t)Bu(3)tpy)([C≡C-C(6)H(4)](n)-H)]ClO(4) (n = 1, 2, 3), are described. Density functional theory (DFT) calculations performed on the ground states of complexes 1, 2, and 3 reveal that their HOMOs reside mainly on the ancillary π-conjugated PA moiety, ranging from 86 to 97%, with LUMOs predominantly centered on the terpyridyl acceptor ligand (91-92%). This electronic structure leads to the production of a triplet ligand-to-ligand CT ((3)LLCT) excited state upon visible light excitation with minor contributions from the corresponding triplet metal-to-ligand CT ((3)MLCT) excited state. Unusually strong red-to-near-IR transient absorptions are produced in the excited states of these molecules following selective long wavelength visible excitation of the low energy CT bands that do not emanate from the terpyridyl radical anion produced in the CT excited state or from an arylacetylide-based triplet intraligand ((3)IL) excited state. The extinction coefficients of these low energy absorption transients were determined using the energy transfer method with anthracene serving as the triplet acceptor. A detailed theoretical investigation using DFT and TDDFT methods reveals that these intense near-IR transient absorptions involve transitions resulting from transient oxidation of the PA subunit. In essence, the production of the (3)LLCT excited state transiently oxidizes the PA moiety by one electron, producing the corresponding highly absorbing radical cation-like species, analogous to that experienced in related intramolecular photoinduced electron transfer reactions. The computational work successfully predicts the oscillator strength and peak wavelength of the measured excited state absorption transients across this series of molecules. In the present effort, there is a convergence of theory and experiment given that the excited state absorption properties of these Pt(II) chromophores are determined by localized transitions that resemble open shell radical cation species.}, number={45}, journal={The Journal of Physical Chemistry B}, publisher={American Chemical Society (ACS)}, author={Wang, Xianghuai and Goeb Sébastien and Ji, Zhiqiang and Castellano, Felix N.}, year={2010}, month={Nov}, pages={14440–14449} }
 @article{ardo_sun_castellano_meyer_2010, title={Excited-State Electron Transfer from Ruthenium-Polypyridyl Compounds to Anatase TiO2 Nanocrystallites: Evidence for a Stark Effect}, volume={114}, ISSN={1520-6106 1520-5207}, url={http://dx.doi.org/10.1021/jp102349m}, DOI={10.1021/jp102349m}, abstractNote={Photophysical studies were performed with [Ru(dtb)(2)(dcb)](PF(6))(2) and cis-Ru(dcb)(dnb)(NCS)(2,) where dtb is 4,4'-(C(CH(3))(3))(2)-2,2'-bipyridine, dcb is 4,4'-(COOH)(2)-2,2'-bipyridine, and dnb is 4,4'-(CH(3)(CH(2))(8))(2)-2,2'-bipyridine), anchored to anatase TiO(2) particles (∼15 nm in diameter) interconnected in a mesoporous, thin film (∼10 μm thick) immersed in Li(+)-containing acetonitrile electrolytes. Pulsed-laser excitation resulted in rapid, nonquantitative excited-state injection into TiO(2) with a rate constant that could not be time-resolved, k(inj) > 10(8) s(-1), to yield an interfacial charge-separated state. Return of this state to ground-state products displayed observation-wavelength-dependent kinetics due to charge recombination and a second process. The second process occurred in parallel and was assigned to a transient Stark effect created by the electric field originating from the electrons in TiO(2) on ruthenium sensitizers that had not undergone excited-state injection. The kinetics for this processes were well modeled by a stretched exponential function. The impact of this field on the metal-to-ligand charge transfer excited-state of Ru(dtb)(2)(dcb)(2+) or the oxidized form of cis-Ru(dcb)(dnb)(NCS)(2) were also investigated. Unambiguous identification of a Stark effect on the excited-state sensitizers was accomplished through fluence-dependent measurements. The possible influence of the electric field on the oxidized sensitizers was at best speculative. The unique relative orientation of the electric field and sensitizer afforded by the nanocrystal geometry resulted in unidirectional shifts in the absorption and photoluminescence spectra of the Ru(II) coordination compounds. On the basis of the magnitude of the shift, it was estimated that a transient field as large as 2.7 MV/cm was generated upon excited-state injection of electrons in TiO(2) at concentrations relevant to an operational dye-sensitized solar cell.}, number={45}, journal={The Journal of Physical Chemistry B}, publisher={American Chemical Society (ACS)}, author={Ardo, Shane and Sun, Yali and Castellano, Felix N. and Meyer, Gerald J.}, year={2010}, month={Nov}, pages={14596–14604} }
 @article{guo_muro-small_ji_zhao_castellano_2010, title={Naphthalimide Phosphorescence Finally Exposed in a Platinum(II) Diimine Complex}, volume={49}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic101107b}, DOI={10.1021/ic101107b}, abstractNote={Room temperature (RT) phosphorescence is observed from a naphthalimide species for the first time in the square-planar chromophore Pt(dbbpy)(C[triple bond]C-NI)(2), where NI = N-butyl-4-ethynylnaphthalimide and dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine. The combination of static and time-resolved absorption and photoluminescence data is uniformly consistent with triplet-state photophysics localized on an appended C[triple bond]C-NI unit following excitation into the low-energy absorption bands. This molecule features rather impressive long-lifetime, high-quantum-efficiency NI-based RT phosphorescence (tau = 124 micros; Phi = 0.215) centered at 621 nm, exemplifying how the platinum acetylide linkage strongly promotes intersystem crossing in the NI subunit, representative of a class of molecules whose excited states are typically dominated by singlet fluorescence.}, number={15}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Guo, Huimin and Muro-Small, Maria L. and Ji, Shaomin and Zhao, Jianzhang and Castellano, Felix N.}, year={2010}, month={Aug}, pages={6802–6804} }
 @inproceedings{castellano_2010, title={New heteroleptic Ru(II) and Os(II) sensitizers for dye-sensitized solar cells based on titania materials}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79951476458&partnerID=MN8TOARS}, booktitle={ACS National Meeting Book of Abstracts}, author={Castellano, F.N.}, year={2010} }
 @article{singh-rachford_castellano_2010, title={Photon upconversion based on sensitized triplet–triplet annihilation}, volume={254}, ISSN={0010-8545}, url={http://dx.doi.org/10.1016/J.CCR.2010.01.003}, DOI={10.1016/J.CCR.2010.01.003}, abstractNote={Photon upconversion, the process wherein light of long wavelength is frequency converted to photons of higher energy, is readily achieved at low incident power through sensitized triplet–triplet annihilation (TTA) in various chromophore combinations spanning the UV to the near-IR. This emerging wavelength-shifting technology truly represents a viable route towards converting low energy terrestrial solar photons into light adequate to drive electron transfer in operational photovoltaics. Generalized molecular design constraints, all operational examples reported to date, and measurement techniques applied to these low power nonlinear processes are reviewed in this contribution. In many instances, direct visualization of this phenomenon is presented in solution and within various polymeric host materials.}, number={21-22}, journal={Coordination Chemistry Reviews}, publisher={Elsevier BV}, author={Singh-Rachford, Tanya N. and Castellano, Felix N.}, year={2010}, month={Nov}, pages={2560–2573} }
 @article{ardo_sun_staniszewski_castellano_meyer_2010, title={Stark Effects after Excited-State Interfacial Electron Transfer at Sensitized TiO2 Nanocrystallites}, volume={132}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja909781g}, DOI={10.1021/ja909781g}, abstractNote={Photophysical studies were performed with [Ru(dtb)(2)(dcb)](PF(6))(2) and cis-Ru(dcb)(dnb)(NCS)(2,) where dtb is 4,4'-(C(CH(3))(3))(2)-2,2'-bipyridine, dcb is 4,4'-(COOH)(2)-2,2'-bipyridine, and dnb is 4,4'-(CH(3)(CH(2))(8))(2)-2,2'-bipyridine), anchored to anatase TiO(2) particles ( approximately 15 nm in diameter) interconnected in a mesoporous, 10 mum thick film immersed in Li(+)-containing CH(3)CN electrolytes with iodide or phenothiazine donors. Pulsed-laser excitation resulted in rapid excited-state injection and donor oxidation to yield TiO(2)(e(-))s and oxidized donors, while the metal-to-ligand charge-transfer (MLCT) absorption spectrum of the Ru(II) coordination compounds differed from that which was initially excited. The spectral data were consistent with an underlying Stark effect and indicated that the surface electric field was not completely screened from the molecular sensitizer. The magnitude of the electric field was estimated to be approximately 270 MV/m from Li(+) titration experiments, corresponding to a approximately 40 mV potential drop. With iodide donors, the amplitude of the Stark effect decreased over time periods where charge recombination was absent, behavior attributed to "screening" of the electric field by interfacial ionic reorganization. The screening kinetics were nonexponential but were well described by the Kohlrausch-Williams-Watts model, from which a characteristic rate constant, tau(o)(-1), of approximately 1.5 x 10(5) s(-1) was abstracted. At least seven other sensitizers and five different cations, as well as on SnO(2) nanoparticle films, exhibited similar transient absorption behavior with iodide donor molecules indicating that the effect was quite general. In the presence of phenothiazine donors (or in the absence of an external donor), there was no clear evidence for screening, and the Stark effect disappeared concurrent with interfacial charge recombination. Complementary spectroelectrochemical studies of these same sensitized films displayed similar absorption spectra when the TiO(2) thin film was partially reduced with a forward bias. Spectral modeling in the absence of donor molecules as well as studies of TiO(2) thin films sensitized with two different Ru(II) compounds demonstrated that the electric field created by excited-state injection from one sensitizer influenced the absorption spectra of other sensitizers that had not undergone photoinduced electron injection.}, number={19}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Ardo, Shane and Sun, Yali and Staniszewski, Aaron and Castellano, Felix N. and Meyer, Gerald J.}, year={2010}, month={May}, pages={6696–6709} }
 @article{singh-rachford_nayak_muro-small_goeb_therien_castellano_2010, title={Supermolecular-Chromophore-Sensitized Near-Infrared-to-Visible Photon Upconversion}, volume={132}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja105510k}, DOI={10.1021/ja105510k}, abstractNote={Selective near-IR (NIR) excitation (780 nm) of the conjugated supermolecule ruthenium(II) [15-(4'-ethynyl-(2,2';6',2''-terpyridinyl))-bis[(5,5',-10,20-di(2',6'-bis(3,3-dimethylbutoxy)phenyl)porphinato)zinc(II)]ethyne][4'-pyrrolidin-1-yl-2,2';6',2''-terpyridine] bis(hexafluorophosphate) (Pyr(1)RuPZn(2)) in solutions containing N,N-bis(ethylpropyl)perylene-3,4,9,10-tetracarboxylicdiimide (PDI) or tetracene gives rise to a substantial anti-Stokes energy gain (PDI, 0.70 eV; tetracene, 0.86 eV). Experimental data clearly demonstrate that this upconverted fluorescence signal is produced via Pyr(1)RuPZn(2)-sensitized triplet-triplet annihilation (TTA) photochemistry. The TTA process was confirmed by the quadratic dependence of the integrated (1)PDI* emission centered at 541 nm derived from 780 nm laser excitation. The T(1)→T(n) excited state absorption decay of Pyr(1)RuPZn(2), monitored at 900 nm as a function of PDI concentration, revealed Stern-Volmer and bimolecular quenching constants of 10 048 M(-1) and 5.9 × 10(8) M(-1) s(-1), respectively, for the PDI triplet sensitization process. The T(1)→T(n) PDI extinction coefficient at 560 nm (ε(T) = 6.6 × 10(4) M(-1) cm(-1)) was determined through the triplet energy transfer method utilizing anthracene as the donor chromophore. (3)PDI* transient triplet absorption dynamics observed as a function of 485 nm incident nanosecond pump laser fluence demonstrate a bimolecular (3)PDI*-(3)PDI* TTA rate constant (k(TT) = 1.0 ± 0.2 × 10(9) M(-1) s(-1)). The maximum quantum yield of the supermolecule-sensitized PDI upconverted emission (Φ(UC) = 0.0075 ± 0.0002) was determined relative to [Os(phen)(3)][PF(6)](2) at an incident laser power of 22 mW at 780 nm. This study successfully demonstrates NIR-to-visible photon upconversion and achieves a new record anti-Stokes shift of 0.86 eV for sensitized TTA, using the supermolecular Pyr(1)RuPZn(2)sensitizer. The stability of the Pyr(1)RuPZn(2)/PDI chromophore combination is readily apparent as continuous irradiation at 780 nm produces 541 nm centered fluorescence with no significant decrease in intensity measured over time domains exceeding several hours. The molecular components of these NIR-to-vis upconverting compositions illustrate that substantial anti-Stokes energy gains via a TTA process can be effortlessly realized.}, number={40}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Nayak, Animesh and Muro-Small, Maria L. and Goeb, Sèbastian and Therien, Michael J. and Castellano, Felix N.}, year={2010}, month={Oct}, pages={14203–14211} }
 @article{lockard_rachford_smolentsev_stickrath_wang_zhang_atenkoffer_jennings_soldatov_rheingold_et al._2010, title={Triplet Excited State Distortions in a Pyrazolate Bridged Platinum Dimer Measured by X-ray Transient Absorption Spectroscopy}, volume={114}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp1088299}, DOI={10.1021/jp1088299}, abstractNote={The excited-state structure of a dinuclear platinum(II) complex with tert-butyl substituted pyrazolate bridging units, [Pt(ppy)(μ-(t)Bu(2)pz)](2) (ppy = 2-phenylpyridine; (t)Bu(2)pz = 3,5-di-tert-butylpyrazolate) is studied by X-ray transient absorption (XTA) spectroscopy to reveal the transient electronic and nuclear geometry. DFT calculations predict that the lowest energy triplet excited state, assigned to a metal-metal-to-ligand charge transfer (MMLCT) transition, has a contraction in the Pt-Pt distance. The Pt-Pt bond length and other structural parameters extracted from fitting the experimental XTA difference spectra from full multiple scattering (FMS) and multidimensional interpolation calculations indicates a metal-metal distance decrease by approximately 0.2 Å in the triplet excited state. The advantages and challenges of this approach in resolving dynamic transient structures of nonbonding or weak-bonding dinuclear metal complexes in solution are discussed.}, number={48}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Lockard, Jenny V. and Rachford, Aaron A. and Smolentsev, Grigory and Stickrath, Andrew B. and Wang, Xianghuai and Zhang, Xiaoyi and Atenkoffer, Klaus and Jennings, Guy and Soldatov, Alexander and Rheingold, Arnold L. and et al.}, year={2010}, month={Dec}, pages={12780–12787} }
 @article{sun_onicha_myahkostupov_castellano_2010, title={Viable Alternative to N719 for Dye-Sensitized Solar Cells}, volume={2}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am100311m}, DOI={10.1021/am100311m}, abstractNote={A new synthetically facile heteroleptic ruthenium(II) sensitizer (NBu(4))[Ru(4,7-dpp)(dcbpyH)(NCS)(2)], coded as YS5, where NBu(4) is tetrabutylammonium, 4,7-dpp is 4,7-diphenyl-1,10-phenanthroline, and dcbpyH is the singly deprotonated surface anchoring derivative of 4,4'-dicarboxy-2,2'-bipyridine (dcbpyH(2)), was designed, synthesized, and incorporated into regenerative mesoscopic titania-based dye-sensitized solar cells. The sensitizer has characteristic broad, high extinction coefficient MLCT bands spanning the visible spectrum. The compound was fully characterized by 1D and 2D (1)H NMR, MALDI-TOF-MS, UV-vis, photoluminescence, Raman, IR, and electrochemistry. YS5 exhibits strong visible absorption properties with a molar extinction coefficient of 1.71 x 10(4) M(-1) cm(-1) at its 522 nm maximum. In operational liquid junction-based DSSCs under simulated AM 1.5G one-sun excitation (100 mW/cm(2)), the photovoltaic performance of YS5 compares almost equally against the current benchmark sensitizer N719 in side-by-side comparisons, producing a power conversion efficiency of 6.05% with a maximum IPCE of 65% at 540 nm. The data presented in this manuscript strongly suggest that YS5 is indeed a viable sensitizer for nanocrystalline TiO(2)-based DSSCs, seemingly poised for widespread adaptation.}, number={7}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Sun, Yali and Onicha, Anthony C. and Myahkostupov, Mykhaylo and Castellano, Felix N.}, year={2010}, month={Jun}, pages={2039–2045} }
 @article{sun_machala_castellano_2010, title={Controlled microwave synthesis of RuII synthons and chromophores relevant to solar energy conversion}, volume={363}, ISSN={0020-1693}, url={http://dx.doi.org/10.1016/j.ica.2009.07.028}, DOI={10.1016/j.ica.2009.07.028}, abstractNote={Here we describe the efficient high yield atmospheric pressure microwave-assisted synthesis for seven distinct RuII coordination complexes relevant to solar energy conversion schemes and dye sensitized solar cells. In all instances, the reaction times have been markedly shortened, concomitant with higher yields with little or no need for subsequent purification and several multi-step reactions proceeded flawlessly in a single pot. Importantly, we observed no evidence for the decarboxylation of the essential metal oxide surface-anchoring 4,4′-diethylester-2,2′-bipyridine or 4,4′-dicarboxy-2,2′-bipyridine ligands as long as open reaction vessel conditions were utilized; these functionalities are not tolerant to sealed microwave reaction (superheated solvent/pressurized) conditions. The combined results suggest that microwave-assisted chemistry is indeed a valuable tool as far as RuII coordination chemistry is concerned and can likely be applied in the combinatorial pursuit of new dyes bearing sensitive functionalities.}, number={1}, journal={Inorganica Chimica Acta}, publisher={Elsevier BV}, author={Sun, Yali and Machala, Michael L. and Castellano, Felix N.}, year={2010}, month={Jan}, pages={283–287} }
 @article{danilov_rachford_goeb sébastien_castellano_2009, title={Evolution of the Triplet Excited State in PtII Perylenediimides}, volume={113}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp9012762}, DOI={10.1021/jp9012762}, abstractNote={Here, we present the ultrafast dynamics of a series of metal complexes developed to permit access to the perylenediimide (PDI) triplet manifold that preserves the desirable colorfastness and visible light-absorption properties associated with these dyes. To this end, three Pt(II) complexes each bearing two PDI moieties tethered to the metal center through acetylide linkages emanating from one of the PDI bay positions have been thoroughly examined by static spectroscopic methods, electrochemistry, laser flash photolysis, and ultrafast transient absorption spectrometry. Upon ligation to the Pt(II) center, the bright singlet-state fluorescence (Phi = 0.91, tau = 4.53 ns) of the free PDI-CCH chromophore is quantitatively quenched, and no long wavelength photoluminescence is observed from any of the Pt(II)-PDI complexes in deaerated solutions. Ultrafast transient measurements reveal that upon ligation of PDI-CCH to the Pt(II) center, picosecond intersystem crossing (tau = 2-4 ps) from the (1)PDI excited state is followed by vibrational cooling (tau = 12-19 ps) of the hot (3)PDI excited state, whereas only singlet-state dynamics, including stimulated emission, were observed in the "free" PDI-CCH moiety. In each of the Pt-PDI chromophores, quantitatively similar transient absorption difference spectra were obtained; the only distinguishing characteristic is in their single-exponential lifetimes (tau = 246 ns, 1.0 mus, and 710 ns). These long-lived (3)PDI excited states are clearly poised for bimolecular electron and energy transfer schemes. In the present case, the latter is demonstrated through bimolecular sensitization of singlet oxygen phosphorescence at approximately 1270 nm in aerated dichloromethane solutions, producing reasonable (1)O(2) quantum yields (Phi(Delta) = 0.40-0.55) across this series of molecules.}, number={19}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Danilov, Evgeny O. and Rachford, Aaron A. and Goeb Sébastien and Castellano, Felix N.}, year={2009}, month={May}, pages={5763–5768} }
 @article{singh-rachford_lott_weder_castellano_2009, title={Influence of Temperature on Low-Power Upconversion in Rubbery Polymer Blends}, volume={131}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja904696n}, DOI={10.1021/ja904696n}, abstractNote={The upconverting properties of a dye cocktail composed of palladium(II) octaethylporphyrin (PdOEP, triplet sensitizer) and 9,10-diphenylanthracene (DPA, triplet acceptor/annihilator) were investigated as a function of temperature in several low glass transition temperature (T(g)) polymer hosts including an ethyleneoxide-epichlorohydrin copolymer (EO-EPI) and the polyurethanes Texin 270, Texin 285, and Tecoflex EG-80A. Selective excitation of PdOEP at 544 nm in the presence of DPA in these materials resulted in anti-Stokes blue emission from DPA, a consequence of sensitized triplet-triplet annihilation (TTA) photochemistry, confirmed by the quadratic dependence of the upconverted fluorescence intensity with respect to incident light power. The upconversion process was completely suppressed by cooling a PdOEP/DPA blend film to below the T(g) of the respective polymer. However, the blue emission was clearly visible by the naked eye upon heating these films to room temperature (290 K). Subsequently, the upconverted emission intensity increased with increasing temperature and was found to be completely reversible upon several heating and cooling cycles provided the temperature remained below 400 K. Heating samples above this temperature resulted in unrecoverable failure of the material to produce upconverted photons. The phosphorescence intensity decay of PdOEP in the polymer host, Tecoflex EG-80A, adequately fits to a sum of two exponential functions as well as the Kohlrausch-Williams-Watts (KWW) stretched exponential model. Increasing the temperature of the film increases the complexity and heterogeneity of the system as evidenced by the lower beta values obtained from the KWW model as the temperature increases.}, number={33}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Lott, Joseph and Weder, Christoph and Castellano, Felix N.}, year={2009}, month={Aug}, pages={12007–12014} }
 @article{singh-rachford_castellano_2009, title={Low Power Visible-to-UV Upconversion}, volume={113}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp9021163}, DOI={10.1021/jp9021163}, abstractNote={Low power visible-to-UV photon upconversion is demonstrated for the first time, achieved from two simple organic chromophores dissolved in benzene. Selective 442 nm excitation of the triplet sensitizer 2,3-butanedione (biacetyl) in the presence of the laser dye 2,5-diphenyloxazole (PPO) results in the observation of singlet fluorescence from the latter in the UV centered at 360 nm, anti-Stokes shifted by a record 0.64 eV with respect to the excitation. All of the experimental data are consistent with the upconverted singlet PPO fluorescence being produced as a result of biacetyl-sensitized triplet-triplet annihilation (TTA) of triplet excited PPO chromophores. Nanosecond laser flash photolysis performed under pseudo-first-order conditions revealed the bimolecular rate constant of triplet-triplet energy transfer between the biacetyl sensitizer and PPO acceptor, k(q) = 9.0 x 10(8) M(-1)s(-1). The TTA process was confirmed by the quadratic dependence of the upconverted integrated PPO emission intensity measured with respect to incident 442 nm light power density. The maximum quantum yield of the upconverted emission (0.0058 +/- 0.0002) was determined relative to 1,8-diphenyl-1,3,5,7-octatetraene, both measured with 0.389 W/cm(2) incident power density. The PPO triplet-triplet annihilation rate constant (k(TT)) was determined from transient absorption decays monitored at the peak of its characteristic triplet-to-triplet excited-state absorption (500 nm) as a function of incident pulsed laser fluence; this process attains the diffusion limit in benzene at room temperature, k(TT) = 1.1 +/- 0.1 x 10(10) M(-1) s(-1).}, number={20}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Castellano, Felix N.}, year={2009}, month={May}, pages={5912–5917} }
 @article{singh-rachford_castellano_2009, title={Nonlinear Photochemistry Squared: Quartic Light Power Dependence Realized in Photon Upconversion}, volume={113}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp906782g}, DOI={10.1021/jp906782g}, abstractNote={Simultaneous two-photon excitation of a solution mixture of [Ru(dmb)3]2+ and 9,10-diphenylanthracene (DPA) using 860 nm light pulses from a Ti:Sapphire laser resulted in triplet energy transfer followed by triplet-triplet annihilation (TTA), ultimately leading to upconverted DPA fluorescence from the sensitized DPA triplets. The photochemistry sequence was confirmed by the unprecedented quartic (x4) incident light power dependence exhibited by this process, which incidentally generated a record anti-Stokes shift of 1.38 eV for sensitized TTA.}, number={33}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Castellano, Felix N.}, year={2009}, month={Aug}, pages={9266–9269} }
 @article{muro_diring stéphane_wang_ziessel_castellano_2009, title={Photophysics in Platinum(II) Bipyridylacetylides}, volume={48}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic901036a}, DOI={10.1021/ic901036a}, abstractNote={The synthesis, structural characterization, photoluminescence, and excited state absorption properties of a series of platinum(II) terpyridyl complexes bearing a bipyridyl acetylide subunit are presented. The [(t)Bu(3)tpyPtC identical withCbpy](+) (1) complex displays a broad and structureless emission profile at room temperature (RT), a lifetime of 5.8 mus, and transient absorption (TA) difference spectra characteristic of a charge transfer (CT) excited state. Upon coordination of Fe(2+) to 1, producing tetranuclear 2, the CT emission was quantitatively quenched presumably through the low-lying iron-based ligand field states present. Surprisingly, the addition of Zn(2+) to solutions of 1 produces a higher energy emissive state with a substantially longer excited state lifetime of 16.1 mus. The combined spectroscopic data measured for the zinc titration product (3) suggests that the overall excited state is dominated by a CT manifold, albeit at higher energy relative to 1. The photophysics of a bis-phosphine complex bearing two trans-disposed bpy-acetylide subunits (4) produced a model chromophore possessing an intraligand triplet excited state with a lifetime of 26 mus at RT. The bipyridyl analogue of 1, (t)Bu(2)bpyPt(C identical withCbpy)(2) (5), was also prepared and its photophysics are consistent with a lowest CT parentage at RT. The 77 K emission spectra measured for complexes 1, 3, 4, and 5 are all consistent with a triplet bpy-acetylide localized excited state; the E(00) energies vary over a modest 344 cm(-1) across the series. However, the shorter 77 K excited state lifetimes observed for 1, 3, and 5 in comparison to 4 suggests that the energetically proximate CT state in the former compounds significantly influences excited state decay at low temperature.}, number={24}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Muro, Maria L. and Diring Stéphane and Wang, Xianghuai and Ziessel, Raymond and Castellano, Felix N.}, year={2009}, month={Dec}, pages={11533–11542} }
 @book{muro_rachford_wang_castellano_2010, title={PlatinumII acetylide photophysics}, volume={29}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-72749111391&partnerID=MN8TOARS}, DOI={10.1007/3418_2009_1}, abstractNote={The photophysics of PtII acetylide chromophores represents an important emergent area of research and development. The present review exclusively deals with photophysical processes in square planar PtII complexes of the general formulae: Pt(N^N)(C≡CR)2, [Pt(N^N^N)(C≡CR)]+, Pt(N^N^C)(C≡CR), trans-Pt(PR3)2(C≡CR)2, and cis-Pt(P^P)(C≡CR)2, where N^N is a bidentate 2,2'-bipyridine, N^N^N and N^N^C are tridentate polypyridines, PR3 is a monodentate phosphine and P^P is a bidentate phosphine ligand. These molecules exhibit a range of photophysical attributes depending upon the nature of the lowest electronic triplet excited state(s) which are either charge-transfer, ligand-localized, or an admixture of the two. Under special circumstances, intermolecular interactions further complicate the electronic structures of the ground and excited states and the resulting spectroscopy. Recent computational approaches emphasizing the successful application of DFT and TD-DFT methods towards understanding the absorption and emission processes of these chromophores are also presented.}, journal={Topics in Organometallic Chemistry}, author={Muro, M.L. and Rachford, A.A. and Wang, X. and Castellano, F.N.}, year={2010}, pages={159–191} }
 @article{she_rachford_wang_goeb_el-ballouli_castellano_hupp_2009, title={Solvent-induced configuration mixing and triplet excited-state inversion: insights from transient absorption and transient dc photoconductivity measurements}, volume={11}, ISSN={1463-9076 1463-9084}, url={http://dx.doi.org/10.1039/b908977b}, DOI={10.1039/b908977b}, abstractNote={Solvent-induced excited-state configuration mixing in a Pt(II) diimine chromophore with phenylene ethynylene containing acetylide ligands, [Pt((t)Bu2bpy)(PE3)2] (1), was characterized by nanosecond transient absorption spectroscopy and transient dc photoconductivity (TDCP). The mixing is a result of closely spaced triplet charge transfer (3CT) and intraligand-localized (3IL) triplet energy levels that are finely tuned with solvent polarity as ascertained by their parent model chromophores [Pt((t)Bu2bpy)(PE1)2] (2) and [Pt(P2)(PE3)2] (3), respectively. The absorption difference spectrum of the mixed triplet state is dramatically different from those of the 3CT and 3IL state model chromophores. The 3CT, 3IL and configuration-mixed triplet states led to distinct TDCP signals. The TDCP response is of negative polarity for 3CT excited states but of positive polarity for 3IL excited states. TDCP transients for 1 in mixed solvents are a combination of signals from the 3IL and 3CT states, with the signal magnitude depending on the polarity of solvent composition. The fraction of 3CT state character in the configurationally mixed excited state was quantified by TDCP to be approximately 0.24 in pure benzene, while it decreased to approximately 0.05 in 20 : 80 (v : v) benzene-CH2Cl2. The charge transfer fraction appears to increase slightly to approximately 0.11 in the lower polarity 20 : 80 n-hexane-CH2Cl2 medium. TDCP is shown to be a useful tool for the identification of the lowest excited state in electrically neutral metal-organic chromophores.}, number={38}, journal={Physical Chemistry Chemical Physics}, publisher={Royal Society of Chemistry (RSC)}, author={She, Chunxing and Rachford, Aaron A. and Wang, Xianghuai and Goeb, Sébastien and El-Ballouli, Ala'a O. and Castellano, Felix N. and Hupp, Joseph T.}, year={2009}, pages={8586} }
 @article{singh-rachford_castellano_2009, title={Supra-Nanosecond Dynamics of a Red-to-Blue Photon Upconversion System}, volume={48}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic802114d}, DOI={10.1021/ic802114d}, abstractNote={Blue-green upconverted emission from 2-chloro-bis-phenylethynylanthracene (2CBPEA) sensitized by the red-absorbing platinum(II)tetraphenyltetrabenzoporphyrin (PtTPBP) has been investigated in N,N-dimethylformamide (DMF). The upconverted singlet fluorescence of 2CBPEA resulting from its sensitized triplet-triplet annihilation (TTA) is observed following selective excitation of PtTPBP at 635 +/- 5 nm. Stern-Volmer analysis of the photoluminescence quenching of PtTPBP by 2CBPEA yields a bimolecular quenching constant of 1.62 x 10(9) M(-1) s(-1), slightly below the diffusion limit in DMF at room temperature. The TTA process was confirmed by the quadratic dependence of the integrated upconverted singlet fluorescence emission profile of 2CBPEA measured as a function of 635 nm incident laser power. Time-resolved emission spectra following 630 nm nanosecond laser pulses illustrate the prompt nature of porphyrin phosphorescence quenching and the delayed nature of the upconverted singlet fluorescence from 2CBPEA. Transient absorption decays monitored at the peak of the characteristic 2CBPEA triplet-triplet excited-state absorption (490 nm) measured as a function of incident nanosecond 630 nm pump laser fluence recovered the rate constant for the sensitized TTA process, k(TT) = 5.64 +/- 0.08 x 10(9) M(-1) s(-1). To calculate this rate constant, we determined the triplet-triplet extinction coefficient of 2CBPEA (12,500 M(-1) cm(-1) at 490 nm) utilizing triplet energy transfer from donors with known excited-state extinction coefficients, namely [Ru(bpy)(3)](2+) and 2-acetonaphthone and averaged these values. The current work, to the best of our knowledge, represents the first example of red-to-blue upconversion thus demonstrating another viable sensitized TTA process, as well as providing the first measurements of k(TT) in a photon upconverting scheme. As 2CBPEA is stable under ambient conditions, this chromophore represents an almost ideal candidate for light-producing sensitized TTA in aerated polymeric materials, and we demonstrate successful translation of the present donor-acceptor/annihilator system into a low T(g) polyurethane.}, number={6}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Castellano, Felix N.}, year={2009}, month={Mar}, pages={2541–2548} }
 @article{rachford_castellano_2009, title={Thermochromic Absorption and Photoluminescence in [Pt(ppy)(μ-Ph2pz)]2}, volume={48}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic901156z}, DOI={10.1021/ic901156z}, abstractNote={The temperature effects on the spectral properties and photophysics of a new d(8)-d(8) dinuclear Pt(II) chromophore, [Pt(ppy)(mu-Ph(2)pz)](2) (ppy is 2-phenylpyridine and Ph(2)pz is 3,5-diphenylpyrazolate), have been investigated. The thermochromic shifts are tentatively ascribed to intramolecular sigma interactions between the two pseudocofacial d(z(2)) orbitals. Substantial emission profile changes occur in the solid state, solution, and doped polymer films.}, number={23}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Rachford, Aaron A. and Castellano, Felix N.}, year={2009}, month={Dec}, pages={10865–10867} }
 @inproceedings{singh-rachford_castellano_2009, title={Toward harvesting additional solar inventory through photon upconversion}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78649506348&partnerID=MN8TOARS}, booktitle={ACS National Meeting Book of Abstracts}, author={Singh-Rachford, T.N. and Castellano, F.N.}, year={2009} }
 @article{singh-rachford_castellano_2010, title={Triplet Sensitized Red-to-Blue Photon Upconversion}, volume={1}, ISSN={1948-7185}, url={http://dx.doi.org/10.1021/jz900170m}, DOI={10.1021/jz900170m}, abstractNote={Sensitized red-to-blue upconversion with a record 0.8 eV anti-Stokes shift has been achieved utilizing platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP) as the triplet sensitizer and perylene as the energy acceptor/annihilator in deaerated benzene. Selective 635 nm excitation of PtTPBP results in the observation of perylene fluorescence centered at 451 nm. Stern−Volmer analysis of dynamic phosphorescence quenching of PtTPBP by perylene yields a triplet−triplet energy transfer quenching constant of 4.08 × 109 M−1s−1. Clear evidence for the subsequent triplet−triplet annihilation of 3perylene* was afforded by the quadratic dependence of the integrated perylene fluorescence spectra with respect to incident 635 nm light power. The maximum upconversion quantum yield of perylene fluorescence under our sensitized excitation conditions is 0.0065 ± 0.0001, as ascertained by relative actinometry. The present chromophore combination was successfully translated into the solid state using a low glass transition tem...}, number={1}, journal={The Journal of Physical Chemistry Letters}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Castellano, Felix N.}, year={2010}, month={Jan}, pages={195–200} }
 @article{rachford_hua_adams_castellano_2009, title={[Pt(mesBIAN)(tda)]: A near-infrared emitter and singlet oxygen sensitizer}, ISSN={1477-9226 1477-9234}, url={http://dx.doi.org/10.1039/b818177b}, DOI={10.1039/b818177b}, abstractNote={The synthesis and subsequent photophysical investigation of [Pt(mesBIAN)(tda)], where mesBIAN is bis(mesitylimino)acenaphthene and tda is tolan-2,2'-diacetylide, reveal excited-state characteristics best described as triplet charge transfer ((3)CT) in nature upon visible light excitation. Large ground-state dipole moments are apparent as the absorption spectrum dramatically red-shifts with decreasing solvent polarity. The (3)CT excited state is significantly lower in energy than the ligand-centered (3)tda excited-state, as confirmed by steady-state and time-resolved techniques. Singlet oxygen sensitization studies demonstrate that (1)O(2) production occurs by diffusive quenching from the photo-excited (3)CT state (Phi(Delta) = 0.24, lambda(max) approximately 1270 nm) in oxygen-saturated dichloromethane.}, number={20}, journal={Dalton Transactions}, publisher={Royal Society of Chemistry (RSC)}, author={Rachford, Aaron A. and Hua, Fei and Adams, Christopher J. and Castellano, Felix N.}, year={2009}, pages={3950} }
 @article{rachford_goeb_castellano_2008, title={Accessing the Triplet Excited State in Perylenediimides}, volume={130}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja800333y}, DOI={10.1021/ja800333y}, abstractNote={Here, we present a strategy designed to permit access to the PDI triplet manifold that preserves the desirable colorfastness and visible light-absorption properties associated with these dyes. To this end, three new Pt(II) complexes each bearing two PDI moieties tethered to the metal center via acetylide linkages emanating from one of the PDI bay positions have been synthesized, structurally characterized, and thoroughly examined by nanosecond laser flash photolysis. Upon ligation, the bright singlet-state fluorescence of the PDI chromophore is quantitatively quenched, and no long wavelength photoluminescence is observed from the Pt(II)-PDI complexes in deaerated solutions. In each of the Pt-PDI chromophores, quantitatively similar transient absorption difference spectra were obtained; the only distinguishing characteristic is in their single-exponential lifetimes (tau = 246 ns, 1.0 micros, and 710 ns). Triplet-state sensitization experiments of "free" PDI-CCH using thioxanthone confirmed the PDI triplet state assignments in each of the Pt-PDI structures.}, number={9}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Rachford, Aaron A. and Goeb, Sébastien and Castellano, Felix N.}, year={2008}, month={Mar}, pages={2766–2767} }
 @article{du_schneider_li_zhao_patel_castellano_eisenberg_2008, title={Bi- and Terpyridyl Platinum(II) Chloro Complexes: Molecular Catalysts for the Photogeneration of Hydrogen from Water or Simply Precursors for Colloidal Platinum?}, volume={130}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja711090w}, DOI={10.1021/ja711090w}, abstractNote={Platinum(II) bi- and terpyridyl chloro complexes, Pt(dcbpy)Cl2 and [Pt(ttpy)Cl]+, where dcbpy = 4,4'-dicarboxyl-2,2'-bipyridine and ttpy = 4-tolyl-2,2':6',2''-terpyridine, are used to investigate the nature of the active catalyst for the photocatalytic production of hydrogen from water. In a Pt(II) chloro system that contains a sacrificial electron donor, either MeOH or triethanolamine (TEOA), and titanium dioxide (TiO2) as an electron relay, sizable amounts of H2 can be observed upon UV bandgap irradiation. The quantity of H2 can be significantly reduced in the presence of mercury under the same conditions. Using a known sensitizer, [Pt(ttpy)(phenylacetylide)]+ (1), combined with a Pt(II) chloro complex in a similar system, there is a substantial induction period until the evolution of H2, under visible light (lambda > 410 nm) irradiation. It is suggested that the Pt(II) chloro complexes are simply acting as precursors to Pt colloids that function as the H2 generating catalyst}, number={15}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Du, Pingwu and Schneider, Jacob and Li, Fan and Zhao, Wei and Patel, Upali and Castellano, Felix N. and Eisenberg, Richard}, year={2008}, month={Apr}, pages={5056–5058} }
 @article{singh-rachford_haefele_ziessel_castellano_2008, title={Boron Dipyrromethene Chromophores: Next Generation Triplet Acceptors/Annihilators for Low Power Upconversion Schemes}, volume={130}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja807056a}, DOI={10.1021/ja807056a}, abstractNote={In the present study, the red-light absorbing platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP) was used as a triplet sensitizer in conjunction with two distinct iodophenyl-bearing BODIPY derivatives independently serving as triplet acceptors/annihilators poised for photon upconversion based on triplet-triplet annihilation. In deaerated benzene solutions, extremely stable and high quantum efficiency green (Phi(UC) = 0.0313 +/- 0.0005) and yellow (Phi(UC) = 0.0753 +/- 0.0036) upconverted emissions were observed from selective red excitation of the PtTPBP sensitizer at 635 +/- 5 nm. The current systems represent the first examples of photon upconversion where aromatic hydrocarbons do not serve the role of triplet acceptor/annihilator. Notably, the nature of the current chromophore compositions permitted highly reproducible upconversion quantum efficiency determinations while permitting the evaluation of the triplet-triplet annihilation quantum yields in both instances.}, number={48}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Haefele, Alexandre and Ziessel, Raymond and Castellano, Felix N.}, year={2008}, month={Dec}, pages={16164–16165} }
 @article{rachford_goeb sébastien_ziessel_castellano_2008, title={Ligand Localized Triplet Excited States in Platinum(II) Bipyridyl and Terpyridyl Peryleneacetylides}, volume={47}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic702454k}, DOI={10.1021/ic702454k}, abstractNote={An investigation of the photophysics of two complexes, [Pt((t)Bu3tpy)(C triple bond C-perylene)]BF4 (1) and Pt((t)Bu2bpy)(C triple bond C-perylene)2 (2), where (t)Bu3tpy is 4,4',4''-tri( tert-butyl)-2,2':6',2''-terpyridine, (t)Bu2bpy is 4,4'-di( tert-butyl)-2,2'-bipyridine, and C triple bond C-perylene is 3-ethynylperylene, reveals that they both exhibit perylene-centered ligand localized excited triplet states ((3)IL) upon excitation with visible light. These complexes do not display any significant photoluminescence at room temperature but readily sensitize (1)O2 in aerated CH2Cl2 solutions, as evidenced by its characteristic emission near 1270 nm. The transient absorption difference spectra were compared to bi- and tridentate phosphine peryleneacetylides intended to model the (3)IL peryleneacetylide excited states in addition to the related phenylacetylide-bearing polyimine analogues, with the latter model being the respective triplet charge-transfer ((3)CT) excited states. The transient difference spectra of the two title compounds display excited-state absorptions largely attributable to perylene localized (3)IL states yet exhibit somewhat attenuated excited-state lifetimes relative to those of the phosphine model chromophores. The abbreviated lifetimes in 1 and 2 may suggest the involvement of the energetically proximate (3)CT triplet state exerting an influence on excited-state decay, and the effect appears to be stronger in 1 relative to 2, consistent with the energies of their respective (3)CT states.}, number={10}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Rachford, Aaron A. and Goeb Sébastien and Ziessel, Raymond and Castellano, Felix N.}, year={2008}, month={May}, pages={4348–4355} }
 @inproceedings{islangulov_singh_lott_weder_castellano_2008, title={Low-power upconversion in solid polymer films}, volume={49}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-51849130452&partnerID=MN8TOARS}, number={1}, booktitle={American Chemical Society, Polymer Preprints, Division of Polymer Chemistry}, author={Islangulov, R.R. and Singh, T. and Lott, J. and Weder, C. and Castellano, F.N.}, year={2008}, pages={1028–1029} }
 @article{muro_daws_castellano_2008, title={Microarray pattern recognition based on PtII terpyridyl chloride complexes: vapochromic and vapoluminescent response}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/b812634h}, DOI={10.1039/b812634h}, abstractNote={Eighteen distinct Pt(II) terpyridyl chloride cross-reactive sensor elements incorporated into microarrays with 1000 x 250 microm well dimensions generate distinctive colorimetric and luminometric responses upon exposure to a variety of volatile organic compounds (VOCs).}, number={46}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Muro, Maria L. and Daws, Charles A. and Castellano, Felix N.}, year={2008}, pages={6134} }
 @article{singh-rachford_castellano_2008, title={Pd(II) Phthalocyanine-Sensitized Triplet−Triplet Annihilation from Rubrene}, volume={112}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp7111878}, DOI={10.1021/jp7111878}, abstractNote={Upconverted yellow singlet fluorescence from rubrene (5,6,11,12-tetraphenylnapthacene) was generated from selective excitation (lambdaex = 725 nm) of the red light absorbing triplet sensitizer palladium(II) octabutoxyphthalocyanine, PdPc(OBu)8, in vacuum degassed toluene solutions using a Nd:YAG/OPO laser system in concert with gated iCCD detection. The data are consistent with upconversion proceeding from triplet-triplet annihilation (TTA) of rubrene acceptor molecules. The TTA process was confirmed by the quadratic dependence of the upconverted delayed fluorescence intensity with respect to incident light, measured by integrating the corresponding kinetic traces as a function of the incident excitation power. In vacuum degassed toluene solutions, the red-to-yellow upconversion process is stable under continuous long wavelength irradiation and is readily visualized by the naked eye even at modest laser fluence (0.6 mJ/pulse). In aerated solutions, however, selective excitation of the phthalocyanine sensitizer leads to rapid decomposition of rubrene into its corresponding endoperoxide as evidenced by UV-vis (in toluene), 1H NMR (in d6-benzene), and MALDI-TOF mass spectrometry, consistent with the established reactivity of rubrene with singlet dioxygen. The upconversion process in this triplet sensitizer/acceptor-annihilator combination was preliminarily investigated in solid polymer films composed of a 50:50 mixture of an ethyleneoxide/epichlorohydrin copolymer, P(EO/EP). Films that were prepared under an argon atmosphere and maintained under this inert environment successfully achieve the anticipated quadratic incident power dependence, whereas air exposure causes the film to deviate somewhat from this dependence. To the best of our knowledge, the current study represents the first example of photon upconversion using a phthalocyanine triplet sensitizer, furthering the notion that anti-Stokes light-producing sensitized TTA appears to be a general phenomenon as long as proper energy criteria are met.}, number={16}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Castellano, Felix N.}, year={2008}, month={Apr}, pages={3550–3556} }
 @article{singh-rachford_islangulov_castellano_2008, title={Photochemical Upconversion Approach to Broad-Band Visible Light Generation}, volume={112}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp712165h}, DOI={10.1021/jp712165h}, abstractNote={The sensitized triplet-triplet annihilation (TTA) of 9,10-dimethylanthracene (DMA) upon selective excitation of [Ru(dmb)3]2+ (dmb = 4,4'-dimethyl-2,2'-bipyridine) at 514.5 nm in dimethylformamide (DMF) resulted in upconverted and downconverted DMA excimer photoluminescence. The triplet excited state of [Ru(dmb)3]2+ is efficiently quenched by 11 mM DMA in DMF resulting in photon upconversion but no excimer formation. The bimolecular quenching constant of the dynamic quenching process is 1.4 x 109 M-1 s-1. At 90 mM DMA, both upconversion and downconversion processes are readily observed in aerated DMF solutions. The TTA process was confirmed by the quadratic dependence of the upconverted and downconverted emission emanating from the entire integrated photoluminescence profile (400-800 nm) of DMA measured with respect to incident light power. Time-resolved emission spectra of [Ru(dmb)3]2+ and 90 mM DMA in both aerated and deaerated DMF clearly illustrates the time-delayed nature of both types of singlet-state emission, which interestingly shows similar decay kinetics on the order of 14 mus. The emission quantum yields (Phi) measured using relative actinometry increased with increasing DMA concentrations, reaching a plateau at 3.0 mM DMA (Phi = 4.0%), while at 90 mM DMA, the overall quantum yield diminished to 0.5%. The dominant process occurring at 3.0 mM DMA is upconversion from the singlet excited state of DMA, whereas at 90 mM DMA, both upconversion and excimeric emission are observed in almost equal portions, thereby resulting in an overall broad-band visible light-emission profile.}, number={17}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Singh-Rachford, Tanya N. and Islangulov, Radiy R. and Castellano, Felix N.}, year={2008}, month={May}, pages={3906–3910} }
 @article{muro_diring stéphane_wang_ziessel_castellano_2008, title={Photophysics of the Platinum(II) Terpyridyl Terpyridylacetylide Platform and the Influence of FeII and ZnII Coordination}, volume={47}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic800316x}, DOI={10.1021/ic800316x}, abstractNote={The synthesis, structural characterization, and photoluminescence (PL) properties of the square-planar terpyridylplatinum(II) complex [ ( t )Bu 3tpyPtCCtpy] (+) ( 1) and the octahedral trinuclear Fe (II) and Zn (II) analogues [Fe( ( t )Bu 3tpyPtCCtpy) 2] (4+) ( 2) and [Zn( ( t )Bu 3tpyPtCCtpy) 2] (4+) ( 3) are described. The photophysical properties of the mononuclear Pt (II) complex 1 are consistent with a charge-transfer excited-state parentage producing a large Stokes shift with a concomitant broad, structureless emission profile. The Fe-based ligand-field states in 2 provide an efficient nonradiative deactivation pathway for excited-state decay, resulting in a nonemissive compound at room temperature. Interestingly, upon chelation of 1 with Zn (II), a higher energy charge-transfer emission with a low-energy shoulder and a 215 ns excited-state lifetime is produced in 3. A spectroscopically identical species relative to 3 was produced in control experiments when 1 was reacted with excess protons (HClO 4) as ascertained by UV-vis and static PL spectra measured at room temperature and 77 K. Therefore, the chelation of Zn (II) to 1 is acid-base in nature, and its Lewis acidity renders the highest occupied molecular orbital level in 1 much less electron-rich, which induces a blue shift in both the absorption and emission spectra. At 77 K, complexes 1, 3, and protonated 1 display at least one prevalent vibronic component in the emission profile (1360 cm (-1)) resembling PL emanating from a ligand-localized excited-state, indicating that these emitting states are inverted relative to room temperature. These results are qualitatively confirmed by the application of time-dependent theory using only the 1360 cm (-1) mode to reproduce the low-temperature emission spectra.}, number={15}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Muro, Maria L. and Diring Stéphane and Wang, Xianghuai and Ziessel, Raymond and Castellano, Felix N.}, year={2008}, month={Aug}, pages={6796–6803} }
 @article{staniszewski_ardo_sun_castellano_meyer_2008, title={Slow Cation Transfer Follows Sensitizer Regeneration at Anatase TiO2 Interfaces}, volume={130}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja803668z}, DOI={10.1021/ja803668z}, abstractNote={After rapid photoinduced electron injection into TiO2 and regeneration by a donor, D, such as iodide or phenothiazine, sensitizers are present in an environment distinctly different from that prior to light absorption. Significantly, the absorption spectrum of the Ru(II) sensitizer in this new environment is one that is known to be less favorable for excited-state electron injection. The transient absorption features were found to report on photoinduced variations in the local electronic environment of the Ru(II) sensitizer-TiO2 interface that were induced by ion transfer. The data demonstrate that slow (micros to ms) cation transfer follows regeneration to yield the sensitizer that was initially photoexcited.}, number={35}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Staniszewski, Aaron and Ardo, Shane and Sun, Yali and Castellano, Felix N. and Meyer, Gerald J.}, year={2008}, month={Sep}, pages={11586–11587} }
 @article{glik_kinayyigit_ronayne_towrie_sazanovich_weinstein_castellano_2008, title={Ultrafast Excited State Dynamics of Pt(II) Chromophores Bearing Multiple Infrared Absorbers}, volume={47}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic800578h}, DOI={10.1021/ic800578h}, abstractNote={The paper reports the synthesis, structural characterization, electrochemistry, ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopy associated with two independent d (8) square planar Pt(II) diimine chromophores, Pt(dnpebpy)Cl 2 ( 1) and Pt(dnpebpy)(C[triple bond]Cnaph) 2 ( 2), where dnpebpy = 4,4'-(CO 2CH 2- (t) Bu) 2-2,2'-bipyridine and CCnaph = naphthylacetylide. The neopentyl ester substitutions provided markedly improved complex solubility relative to the corresponding ethyl ester which facilitates synthetic elaboration as well as spectroscopic investigations. Following 400 nm pulsed laser excitation in CH 2Cl 2, the 23 cm (-1) red shift in the nu C=O vibrations in 1 are representative of a complex displaying a lowest charge-transfer-to-diimine (CT) excited state. The decay kinetics in 1 are composed of two time constants assigned to vibrational cooling of the (3)CT excited-state concomitant with its decay to the ground state (tau = 2.2 +/- 0.4 ps), and to cooling of the formed vibrationally hot ground electronic state (tau = 15.5 +/- 4.0 ps); we note that an assignment of the latter to a ligand field state cannot be excluded. Ultrafast TA data quantitatively support these assignments yielding an excited-state lifetime of 2.7 +/- 0.4 ps for the (3)CT excited-state of 1 and could not detect any longer-lived species. The primary intention of this study was to develop a Pt (II) complex ( 2) bearing dual infrared spectroscopic tags (C[triple bond]C attached to the metal and CO (ester) attached to the diimine ligand) to independently track the movement of charge density in different segments of the molecule following pulsed light excitation. Femtosecond laser excitation of 2 in CH 2Cl 2 at 400 nm simultaneously induces a red-shift in both the nu C=O (-30 cm (-1)) and the nu C[triple bond]C (-61 cm (-1)) vibrations. The TRIR data in 2 are consistent with a charge transfer assignment, and the significant decrease of the energy of the nu C[triple bond]C vibration suggests a considerable contribution from the acetylide ligands in the highest occupied molecular orbital. Therefore, we assign the lowest energy optical transitions in 2 as a combination of metal-to-ligand and ligand-to-ligand charge transfers. The excited-state of 2 is emissive at RT, with an emission maximum at 715 nm, quantum yield of 0.0012, and lifetime of 23 ns.}, number={15}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Glik, Elena A. and Kinayyigit, Solen and Ronayne, Kate L. and Towrie, Michael and Sazanovich, Igor V. and Weinstein, Julia A. and Castellano, Felix N.}, year={2008}, month={Aug}, pages={6974–6983} }
 @article{zhao_sun_castellano_2008, title={Visible-Light Induced Water Detoxification Catalyzed by PtII Dye Sensitized Titania}, volume={130}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja803522v}, DOI={10.1021/ja803522v}, abstractNote={A new dye sensitization system incorporating Pt(dcbpy)Cl2 on Degussa P-25 TiO2 for the photomineralization of aqueous organic pollutants under visible light irradiation is described. The representative wastewater pollutant, 4-chlorophenol (4-CP), is readily oxidized (ultimately to CO2) when the PtII dye sensitized TiO2 is exposed to visible light in the presence of dissolved O2, and the reaction is accelerated when the solution is purged with O2 gas at 1 atm. The sensitizer is regenerated during the photocatalysis; therefore, 4-CP effectively reduces the oxidized form of the surface bound dye. The experimental data are consistent with parallel oxidative decomposition pathways for 4-CP, one which operates using conduction band electrons to produce hydroxyl radicals and another where the oxidized sensitizer irreversibly oxidizes 4-CP.}, number={38}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Zhao, Wei and Sun, Yali and Castellano, Felix N.}, year={2008}, month={Sep}, pages={12566–12567} }
 @article{guo_ogawa_kim_danilov_castellano_reynolds_schanze_2007, title={A fulleropyrrolidine end-capped platinum-acetylide triad: the mechanism of photoinduced charge transfer in organometallic photovoltaic cells}, volume={9}, ISSN={1463-9076 1463-9084}, url={http://dx.doi.org/10.1039/b700379j}, DOI={10.1039/b700379j}, abstractNote={The fullerene end-capped platinum acetylide donor-acceptor triad Pt(2)ThC(60) was synthesized and characterized by using photophysical methods and photovoltaic device testing. The triad consists of the platinum acetylide oligomer Ph-[triple bond, length as m-dash]-Pt(PBu3)2-[triple bond, length as m-dash]-Th-[triple bond, length as m-dash]-Pt(PBu3)2-[triple bond, length as m-dash]-Ph (Ph=phenyl and Th=2,5-thienyl, stereochemistry at both Pt centers is trans) that contains fulleropyrrolidine moieties on each of the terminal phenylene units. Electrochemistry of the triad reveals relatively low potential oxidation and reduction waves corresponding, respectively, to oxidation of the platinum acetylide and reduction of the fulleropyrrolidine units. Photoluminescence spectroscopy shows that the singlet and triplet states of the platinum acetylide chromophore are strongly quenched in the triad assembly, both in solution at ambient temperature as well as in a low-temperature solvent glass. The excited state quenching arises due to intramolecular photoinduced electron transfer to produce a charge separated state based on charge transfer from the platinum acetylide (donor) to the fulleropyrrolidine (acceptor). Picosecond time resolved absorption spectroscopy confirms that the charge transfer state is produced within 1 ps of photoexcitation, and it decays by charge recombination within 400 ps. Organic photovoltaic devices fabricated using spin-coated films of Pt2ThC60 as the active material operate with modest efficiency, exhibiting a short circuit photocurrent of 0.51 mA cm(-2) and an open circuit voltage of 0.41 V under 100 mW cm(-2)/AM1.5 illumination. The results are discussed in terms of the relationship between the mechanism of photoinduced electron transfer in the triad and the comparatively efficient photovoltaic response exhibited by the material.}, number={21}, journal={Physical Chemistry Chemical Physics}, publisher={Royal Society of Chemistry (RSC)}, author={Guo, Fengqi and Ogawa, Katsu and Kim, Young-Gi and Danilov, Evgeny O. and Castellano, Felix N. and Reynolds, John R. and Schanze, Kirk S.}, year={2007}, pages={2724} }
 @article{shikhova_danilov_kinayyigit_pomestchenko_tregubov_camerel_retailleau_ziessel_castellano_2007, title={Excited-State Absorption Properties of Platinum(II) Terpyridyl Acetylides}, volume={46}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic0618652}, DOI={10.1021/ic0618652}, abstractNote={A comprehensive photophysical study is presented which compares the ground- and excited-state properties of four platinum(II) terpyridyl acetylide compounds of the general formula [Pt(tBu3tpy)(CCR)]+, where tBu3tpy is 4,4',4' '-tri-tert-butyl-2,2':6',2' '-terpyridine and R is an alkyl or aryl group. [Ru(tBu3tpy)3]2+ and the pivotal synthetic precursor [Pt(tBu3tpy)Cl]+ were also investigated in the current work. The latter two complexes possess short excited-state lifetimes and were investigated using ultrafast spectrometry while the other four compounds were evaluated using conventional nanosecond transient-absorption spectroscopy. The original intention of this study was to comprehend the nature of the impressive excited-state absorptions that emanate from this class of transition-metal chromophores. Transient-absorbance-difference spectra across the series contain the same salient features, which are modulated only slightly in wavelength and markedly in intensity as a function of the appended acetylide ligand. More intense absorption transients are observed in the arylacetylide structures relative to those bearing an alkylacetylide, consistent with transitions coupled to the pi system of the ancillary ligand. Reductive spectroelectrochemical measurements successfully generated the electronic spectrum of the tBu3tpy radical anion in all six complexes at room temperature. These measurements confirm that electronic absorptions associated with the tBu3tpy radical anion simply do not account for the intense optical transitions observed in the excited state of the Pt(II) chromophores. Transient-trapping experiments using the spectroscopically silent reductive quencher DABCO clearly demonstrate the loss of most transient-absorption features in the acetylide complexes throughout the UV, visible, and near-IR regions following bimolecular excited-state electron transfer, suggesting that these features are strongly tied to the photogenerated hole which is delocalized across the Pt center and the ancillary acetylide ligand.}, number={8}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Shikhova, Elena and Danilov, Evgeny O. and Kinayyigit, Solen and Pomestchenko, Irina E. and Tregubov, Alexander D. and Camerel, Frank and Retailleau, Pascal and Ziessel, Raymond and Castellano, Felix N.}, year={2007}, month={Apr}, pages={3038–3048} }
 @inproceedings{sun_castellano_2007, title={Heteroleptic ruthenium(II) terpyridyl complexes for dye-sensitized solar cells}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-37349020070&partnerID=MN8TOARS}, booktitle={ACS National Meeting Book of Abstracts}, author={Sun, Y. and Castellano, F.N.}, year={2007} }
 @article{luman_castellano_2007, title={Lengthening of Fluorescence Lifetimes in Self-organized Metal-Organic Assemblies ¶}, volume={77}, DOI={10.1562/0031-8655(2003)0770510loflis2.0.co2}, abstractNote={Resonance energy transfer from tris(2,2′‐bipyridyl)ruthenium (II) ([Ru(bpy)3]2+) to nile blue A is demonstrated in aqueous solution in the presence of sodium dodecyl sulfate (SDS). At SDS concentrations below the critical micelle concentration, aggregates that permit energy transfer between these dyes at optically dilute (10 μM) concentrations with nearly 100% efficiency are formed. The disparity between the lifetimes of the donor and acceptor results in the lengthening of the photoluminescence lifetime of the sensitized emission observed from nile blue A. Time‐resolved luminescence measurements confirm that the long‐lived components of the emission originate from sensitized acceptor emission.}, number={5}, journal={Photochemistry and Photobiology}, publisher={American Society for Photobiology}, author={Luman, Charles R. and Castellano, Felix N.}, year={2007}, month={May}, pages={510–514} }
 @article{hua_kinayyigit_rachford_shikhova_goeb_cable_adams_kirschbaum_pinkerton_castellano_2007, title={Luminescent Charge-Transfer Platinum(II) Metallacycle}, volume={46}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic701103u}, DOI={10.1021/ic701103u}, abstractNote={The photophysical and electrochemical properties of a platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2'-diacetylide (tda), Pt(dbbpy)(tda) [dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine] (1), are compared with two reference compounds, Pt(dbbpy)(C[triple bond]CPh)(2) (2) and Pt(dppp)tda [dppp = 1,3-bis(diphenylphosphino)propane] (3), respectively. The X-ray crystal structure of 1 is reported, which illustrates the nearly perfect square planarity exhibited by this metallacycle. Chromophore 2 possesses low-lying charge-transfer excited states analogous to 1, whereas structure 3 lacks such excited states but features a low-lying platinum-perturbed tda intraligand triplet manifold. In CH(2)Cl(2), 1 exhibits a broad emission centered at 562 nm at ambient temperature, similar to 2, but with a higher photoluminescence quantum yield and longer excited-state lifetime. In both instances, the photoluminescence is consistent with triplet-charge-transfer excited-state parentage. The rigidity imposed by the cyclic diacetylide ligand in 1 leads to a reduction in nonradiative decay, which enhances its room-temperature photophysical properties. By comparison, 3 radiates highly structured tda-localized triplet-state phosphorescence at room temperature. The 77 K emission spectrum of 1 in 4:1 EtOH/MeOH becomes structured and is quantitatively similar to that measured for 3 under the same conditions. Because the 77 K spectra are nearly identical, the emissions are assigned as (3)tda in nature, implying that the charge-transfer states are raised in energy, relative to the (3)tda levels in 1 in the low-temperature glass. Nanosecond transient absorption spectrometry and ultrafast difference spectra were determined for 1-3 in CH(2)Cl(2) and DMF at ambient temperature. In 1 and 2, the major absorption transients are consistent with the one-electron reduced complexes, corroborated by reductive spectroelectrochemical measurements performed at room temperature. As 3 does not possess any charge-transfer character, excitation into the pipi* transitions of the tda ligand generated transient absorptions in the relaxed excited state assigned to the ligand-localized triplet state. In all three cases, the excited-state lifetimes measured by transient absorption are similar to those measured by time-resolved photoluminescence, suggesting that the same excited states giving rise to the photoluminescence are responsible for the absorption transients. ESR spectroscopy of the anions 1- and 2- and reductive spectroelectrochemistry of 1 and 2 revealed a LUMO based largely on the pi* orbital of the dbbpy ligand. Time-dependent density functional theory calculations performed on 1-3 both in vacuum and in a CH(2)Cl(2) continuum revealed the molecular orbitals, energies, dipole moments, and oscillator strengths for the various electronic transitions in these molecules. A DeltaSCF-method-derived shift applied to the calculated transition energies in the solvent continuum yielded good agreement between theory and experiment for each molecule in this study.}, number={21}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Hua, Fei and Kinayyigit, Solen and Rachford, Aaron A. and Shikhova, Elena A. and Goeb, Sébastien and Cable, John R. and Adams, Christopher J. and Kirschbaum, Kristin and Pinkerton, A. Alan and Castellano, Felix N.}, year={2007}, month={Oct}, pages={8771–8783} }
 @article{islangulov_lott_weder_castellano_2007, title={Noncoherent Low-Power Upconversion in Solid Polymer Films}, volume={129}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja075014k}, DOI={10.1021/ja075014k}, abstractNote={Noncoherent low-power photon upconversion has been realized in solid thin films composed of an ethyleneoxide/epichlorohydrin copolymer doped with palladium octaethylporphyrin (PdOEP) and 9,10-diphenylanthracene (DPA). Selective excitation of PdOEP at 544 nm generates easily visualized DPA fluorescence in the blue with noncoherent light sources under ambient laboratory conditions. The incident excitation power dependence is quadratic in nature, exemplifying that sequential one-photon absorption by PdOEP leads to the sensitization of two triplet DPA chromophores, which in turn annihilate to produce the upconverted singlet DPA fluorescence. Time-resolved emission experiments confirm that the solid host facilitates these sequential bimolecular reactions leading to delayed DPA fluorescence; however, these processes are notably slower than the analogous photochemistry in fluid solution.}, number={42}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Islangulov, Radiy R. and Lott, Joseph and Weder, Christoph and Castellano, Felix N.}, year={2007}, month={Oct}, pages={12652–12653} }
 @inproceedings{kinayyigit_castellano_2007, title={Platinum(II) alkoxyterpyridine salts as vapochromic sensors: Synthesis, photophysics and sensing properties}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-37349089754&partnerID=MN8TOARS}, booktitle={ACS National Meeting Book of Abstracts}, author={Kinayyigit, S. and Castellano, F.N.}, year={2007} }
 @article{muro_castellano_2007, title={Room temperature photoluminescence from [Pt(4′-CCR-tpy)Cl]+ complexes}, ISSN={1477-9226 1477-9234}, url={http://dx.doi.org/10.1039/b709886c}, DOI={10.1039/b709886c}, abstractNote={The synthesis, photophysics, electronic structure, and electrochemical characterization of 4'-tert-butylacetylene-2,2':6',2''-terpyridineplatinum(II) chloride (1), 4'-phenylacetylene-2,2':6',2''-terpyridineplatinum(II) chloride (2), and their Zn(II) analogs are described. The Pt(II) complexes display interesting photophysical properties, showing vibronically resolved emission spectra at room temperature in CH(2)Cl(2), resembling a ligand localized emission profile. The photophysics and (1)O2 sensitization experiments support a triplet state assignment for these emissions which are best described as an admixture of charge transfer and ligand localized components, which decay symmetrically with time as evidenced by time resolved emission spectra. Room temperature ligand-localized fluorescence emission is observed from the zinc complexes whereas phosphorescence emission from the (3)pi-pi* manifold was obtained at 77 K in 4 : 1 EtOH/MeOH matrices doped with 10% ethyliodide. Compounds 1 and 2 display long-lived emission at room temperature, the latter possessing a longer lifetime, higher quantum yield, and longer wavelength emission. Lowering the temperature from 298 K to 77 K induces an increase in the excited state lifetime of both platinum systems together with a blue shift in their respective emission maxima, concomitant with more pronounced vibronic structure. The data are consistent with configurationally mixed triplet excited states at room temperature which persists in 77 K glasses. The corresponding Zn(II) complexes display significantly higher energy ligand-localized phosphorescence at 77 K. This latter result suggests that the nature of the metal and/or coordination environment imparts a significant electronic pertubation into the ligand-localized triplet states of these conjugated terpyridyl structures.}, number={41}, journal={Dalton Transactions}, publisher={Royal Society of Chemistry (RSC)}, author={Muro, Maria L. and Castellano, Felix N.}, year={2007}, pages={4659} }
 @article{goeb_rachford_castellano_2008, title={Solvent-induced configuration mixing and triplet excited state inversion exemplified in a Pt(ii) complex}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/b713285a}, DOI={10.1039/b713285a}, abstractNote={The present study provides clear-cut experimental evidence for solvent-induced configuration mixing and complete triplet state inversion at room temperature in a Pt(ii) charge transfer complex bearing a combination of energetically proximate charge transfer and intraligand triplet excited states.}, number={7}, journal={Chem. Commun.}, publisher={Royal Society of Chemistry (RSC)}, author={Goeb, Sébastien and Rachford, Aaron A. and Castellano, Felix N.}, year={2008}, pages={814–816} }
 @article{polyansky_danilov_castellano_2006, title={Observation of Triplet Intraligand Excited States through Nanosecond Step-Scan Fourier Transform Infrared Spectroscopy}, volume={45}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic0518374}, DOI={10.1021/ic0518374}, abstractNote={Nanosecond step-scan Fourier transform infrared spectroscopy permits the observation of triplet intraligand ((3)IL) character in the excited states of [Ru(bpy)2(PNI-phen)]2+ and [Ru(PNI-phen)3]2+ where PNI is 4-piperidinyl-1,8-naphthalimide. After pulsed 355-nm laser excitation, the two ground-state imide C=O bands in each compound are bleached and two substantially lower energy vibrations are produced; the lower energy feature appears as two distinct bands split by an overlapping transient bleach. Model studies confirm that the time-resolved vibrational data are consistent with photoinduced sensitization of the 3IL excited state. Density functional theory calculations also support these assignments because localization of triplet electron density on the PNI moiety is expected to lead to red-shifted C=O vibrations of magnitude similar to those measured experimentally. The current results illustrate that triplet electron density can be directly tracked by time-resolved infrared measurements in metal-organic chromophores and that frequency shifts comparable to those observed in charge-transfer systems can be realized.}, number={6}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Polyansky, Dmitry E. and Danilov, Evgeny O. and Castellano, Felix N.}, year={2006}, month={Mar}, pages={2370–2372} }
 @article{anula_myshkin_guliaev_luman_danilov_castellano_bullerjahn_rodgers_2006, title={Photo Processes on Self-Associated Cationic Porphyrins and Plastocyanin Complexes 1. Ligation of Plastocyanin Tyrosine 83 onto Metalloporphyrins and Electron-Transfer Fluorescence Quenching}, volume={110}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp054712t}, DOI={10.1021/jp054712t}, abstractNote={The spectroscopic properties of the self-associated complexes formed between the anionic surface docking site of spinach plastocyanin and the cationic metalloporphyrins, in which the tyrosine 83 (Y83) moiety is placed just below the docking site, tetrakis(N-methyl-4-pyridyl)porphyrin (Pd(II)TMPyP(4+) and Zn(II)TMPyP(4+)), have been studied and reported herein. The fluorescence quenching phenomenon of the self-assembled complex of Zn(II)TMPyP(4+)/plastocyanin has also been discovered. The observed red-shifting of the Soret and Q-bands of the UV-visible spectra, ca. 9 nm for Pd(II)TMPyP(4+)/plastocyanin and ca. 6 nm for the Zn(II)TMPyP(4+)/plastocyanin complexes, was explained in terms of exciton theory coupled with the Gouterman model. Thus, the hydroxyphenyl terminus of the Y83 residue of the self-associated plastocyanin/cationic porphyrin complexes was implicated in the charge-transfer ligation with the central metal atoms of these metalloporphyrins. Moreover, ground-state spectrometric-binding studies between Pd(II)TMPyP(4+) and the Y83 mutant plastocyanin (Y83F-PC) system proved that Y83 moiety of plastocyanin played a critical role in the formation of such ion-pair complexes. Difference absorption spectra and the Job's plots showed that the electrostatic attractions between the cationic porphyrins and the anionic patch of plastocyanin, bearing the nearby Y83 residue, led to the predominant formation of a self-associated 1:1 complex in the ground-state with significantly high binding constants (K = (8.0 +/- 1.1) x 10(5) M(-1) and (2.7 +/- 0.8) x 10(6) M(-1) for Pd(II)TMPyP(4+) and zinc variant, respectively) in low ionic strength buffer, 1 mM KCl and 1 mM phosphate buffer (pH 7.4). Molecular modeling calculations supported the formation of a 1:1 self-associated complex between the porphyrin and plastocyanin with an average distance of ca. 9 A between the centers of mass of the porphyrin and Y83 positioned just behind the anionic surface docking site on the protein surface. The photoexcited singlet state of Zn(II)TMPyP(4+) was quenched by the Y83 residue of the self-associated plastocyanin in a static mechanism as evidenced by steady-state and time-resolved fluorescence experiments. Even when all the porphyrin was complexed (more than 97%), significant residual fluorescence from the complex was observed such that the amplitude of quenching of the singlet state of uncomplexed species was enormously obscured.}, number={7}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Anula, Hewa M. and Myshkin, Eugene and Guliaev, Anton and Luman, Charles and Danilov, Evgeny O. and Castellano, Felix N. and Bullerjahn, George S. and Rodgers, Michael A. J.}, year={2006}, month={Feb}, pages={2545–2559} }
 @article{islangulov_castellano_2006, title={Photochemical Upconversion: Anthracene Dimerization Sensitized to Visible Light by a RuII Chromophore}, volume={45}, ISSN={1433-7851 1521-3773}, url={http://dx.doi.org/10.1002/anie.200601615}, DOI={10.1002/anie.200601615}, abstractNote={Double up: Photochemical upconversion by MLCT-sensitized triplet–triplet annihilation is demonstrated (MLCT=metal-to-ligand charge transfer). Selective visible excitation of [Ru(dmb)3]2+ (dmb=4,4′-dimethyl-2,2′-bipyridine) in the presence of anthracene efficiently produces the [4+4] cycloaddition product. This transformation traditionally requires ultraviolet light. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2006/z601615_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={36}, journal={Angewandte Chemie International Edition}, publisher={Wiley}, author={Islangulov, Radiy R. and Castellano, Felix N.}, year={2006}, month={Sep}, pages={5957–5959} }
 @article{islangulov_castellano_2006, title={Photochemical Upconversion: Anthracene Dimerization Sensitized to Visible Light by a RuII Chromophore}, volume={118}, DOI={10.1002/ange.200601615}, abstractNote={Verdoppelt: Photochemische Upconversion durch MLCT-sensibilisierte Triplett-Triplett-Aufhebung wird gezeigt (MLCT=Metall-Ligand-Charge-Transfer). Die selektive Anregung von [Ru(dmb)3]2+ (dmb=4,4′-Dimethyl-2,2′-bipyridin) in Gegenwart von Anthracen mit sichtbarem Licht führt effizient zum [4+4]-Cycloaddukt. Bisher wurde für diese Umwandlung ultraviolette Strahlung benötigt. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2006/z601615_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={36}, journal={Angew. Chem.}, publisher={Wiley-Blackwell}, author={Islangulov, Radiy R. and Castellano, Felix N.}, year={2006}, month={Sep}, pages={6103–6105} }
 @article{castellano_pomestchenko_shikhova_hua_muro_rajapakse_2006, title={Photophysics in bipyridyl and terpyridyl platinum(II) acetylides}, volume={250}, ISSN={0010-8545}, url={http://dx.doi.org/10.1016/J.CCR.2006.03.007}, DOI={10.1016/J.CCR.2006.03.007}, abstractNote={The photophysical properties of mononuclear PtII chromophores of the general structural formulae: Pt(LL)(CCR)2 and [Pt(LLL)(CCR)]+ (LL = substituted or unsubstituted 2,2′-bipyridine; LLL = substituted or unsubstituted 2,2′:6′,2″-terpyridine; R = aryl or alkyl) are described. Topics related to their preparation, spectroscopy, photochemistry, and photophysics are reviewed.}, number={13-14}, journal={Coordination Chemistry Reviews}, publisher={Elsevier BV}, author={Castellano, Felix N. and Pomestchenko, Irina E. and Shikhova, Elena and Hua, Fei and Muro, Maria L. and Rajapakse, Nepali}, year={2006}, month={Jul}, pages={1819–1828} }
 @article{hua_kinayyigit_cable_castellano_2006, title={Platinum(II) Diimine Diacetylides:  Metallacyclization Enhances Photophysical Properties}, volume={45}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic060102b}, DOI={10.1021/ic060102b}, abstractNote={The synthesis, structural characterization, and photoluminescence properties of a new platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2'-diacetylide (tda), Pt(dbbpy)(tda) [dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine], are described. In CH2Cl2, Pt(dbbpy)(tda) exhibits a strong visible charge-transfer absorption and broad emission centered at 562 nm. The photoluminescence quantum yield and excited-state lifetime are 0.52 and 2.56 mus, respectively, at room temperature. These parameters indicate that the planarization and rigidity introduced by the cyclic diacetylide leads to a lower-energy-absorbing species displaying enhanced photophysics relative to the analogous Pt(dbbpy)(CCPh)2. Time-dependent density functional theory calculations, which include solvation by CH2Cl2 via the polarizable continuum model, are used to reveal the nature of the excited states in these molecules that are responsible for the charge-transfer transitions. The 77 K emission spectra of the two compounds in EtOH/MeOH glasses are compared, uncovering tda-based ligand-localized phosphorescence in the title compound.}, number={11}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Hua, Fei and Kinayyigit, Solen and Cable, John R. and Castellano, Felix N.}, year={2006}, month={May}, pages={4304–4306} }
 @article{zhao_castellano_2006, title={Upconverted Emission from Pyrene and Di-tert-butylpyrene Using Ir(ppy)3 as Triplet Sensitizer}, volume={110}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp064261s}, DOI={10.1021/jp064261s}, abstractNote={Metal-to-ligand charge-transfer sensitized upconverted fluorescence in noncovalent triplet energy transfer assemblies is investigated using Ir(ppy)3 as the sensitizer (ppy=2-phenylpyridine) and pyrene or 3,8-di-tert-butylpyrene as the triplet acceptor/annihilator. Upconverted singlet fluorescence from pyrene or 3,8-di-tert-butylpyrene resulting from triplet-triplet annihilation (TTA) is observed following selective excitation of Ir(ppy)3 in deaerated dichloromethane solutions using 450-nm laser pulses. In both systems, the TTA process is confirmed by the near quadratic dependence of the upconverted fluorescence intensity on incident light power, measured by integrating the upconverted delayed fluorescence kinetic traces as a function of incident excitation power. At the relatively high concentrations of pyrene that were utilized, pyrene excimer formation was detected by its characteristic broad emission centered near 470 nm. In essence, selective excitation of Ir(ppy)3 ultimately resulted in the simultaneous sensitization of both singlet pyrene and pyrene excimers, and the latter degrades the energy stored in the pyrene singlet excited state. Furthermore, in the case of di-tert-butylpyrene/Ir(ppy)3, the formation of excimers is successfully blocked because of the presence of the sterically hindering tert-butyl groups. The current work demonstrates that sensitized TTA is indeed accessible to chromophore systems beyond those previously reported, suggesting the generality of the approach.}, number={40}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Zhao, Wei and Castellano, Felix N.}, year={2006}, month={Oct}, pages={11440–11445} }
 @article{hua_kinayyigit_cable_castellano_2005, title={Green Photoluminescence from Platinum(II) Complexes Bearing Silylacetylide Ligands}, volume={44}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic048498j}, DOI={10.1021/ic048498j}, abstractNote={The synthesis, structural characterization, photoluminescence properties, and density functional theory analysis of three Pt(II) diimine complexes, Pt(dbbpy)(C triple bond CR)2 [dbbpy = 4,4'-di(tert-butyl-2,2'-bipyridine; R = -SiMe3, -CC-SiMe3, or -t-Bu], are presented. The Pt(dbbpy)(C triple bond C-tBu)2 complex serves as a carbon-based ligand structure for which the photophysical properties of the two silicon-bearing complexes are compared in dichloromethane. Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-C triple bond C-SiMe3)2 display visible absorptions with strong green emission (lambda(emmax) = 526 and 524 nm, respectively) while Pt(dbbpy)(C triple bond C-t-Bu)2 displays efficient, long-lived yellow emission (lambda(emmax) = 557 nm). Direct side by side comparisons of Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-t-Bu)2 suggest that the difference in excited state energy results from the relative sigma-donor strength of the acetylide ligands.}, number={3}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Hua, Fei and Kinayyigit, Solen and Cable, John R. and Castellano, Felix N.}, year={2005}, month={Feb}, pages={471–473} }
 @article{pomestchenko_polyansky_castellano_2005, title={Influence of a Gold(I)−Acetylide Subunit on the Photophysics of Re(Phen)(CO)3Cl}, volume={44}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/ic048376r}, DOI={10.1021/ic048376r}, abstractNote={The synthesis and photophysical properties of two new Re(I) complexes are reported: fac-Re(phenC triple-bond CH)(CO)(3)Cl (where phenC triple bond CH is 5-ethynyl-1,10-phenanthroline) and its Au(I)-acetylide analogue (fac-Re(phenC triple-bond CAuPPh(3))(CO)(3)Cl). Also reported are the photophysical measurements obtained for the benchmark fac-Re(phen)(CO)(3)Cl chromophore, as well as the phenC triple-bond CAuPPh(3) and phenC triple-bond CH ligands. The unstable nature of the precursor gold-containing ligand illustrates the advantage of using the "chemistry on the complex" approach, which facilitated preparation of the Re-Au binuclear complex. Where possible, all compounds were studied by static and transient absorption (TA), as well as steady-state and time-resolved photoluminescence (TRPL), at room temperature (RT) and 77 K, as well as nanosecond time-resolved infrared (TRIR) spectroscopy. The spectroscopic information provided by these techniques enabled a thorough evaluation of excited-state decay in most cases. In fac-Re(phenC triple bond CH)(CO)(3)Cl, the RT excited-state decay is most consistent with a metal-to-ligand charge transfer (MLCT) assignment, whereas at 77 K, the lowest excited state is dominated by the triplet intraligand ((3)IL) state, localized within the diimine ligand. The lowest excited state in fac-Re(phenC triple-bond CAuPPh(3))(CO)(3)Cl seems to result from an admixture of Re-based MLCT and (3)IL states resident on the phenC triple-bond CAuPPh(3) moiety. TA and TRIR methods indicate that these excited states are thermally equilibrated at room temperature. At 77 K, the MLCT energy of fac-Re(phenC triple-bond CAuPPh(3))(CO)(3)Cl is increased as a result of the glassy medium and the resulting excited state can be considered to be ligand-localized.}, number={10}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Pomestchenko, Irina E. and Polyansky, Dmitry E. and Castellano, Felix N.}, year={2005}, month={May}, pages={3412–3421} }
 @article{islangulov_kozlov_castellano_2005, title={Low power upconversion using MLCT sensitizers}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/b506575e}, DOI={10.1039/b506575e}, abstractNote={Selective low energy excitation of the metal-to-ligand charge transfer (MLCT) transition in [Ru(dmb)(3)](2+)(dmb = 4,4'-dimethyl-2,2'-bipyridine) in the presence of anthracene or 9,10-diphenylanthracene yields easily visualized upconverted singlet fluorescence resulting from triplet-triplet annihilation at low excitation power.}, number={30}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Islangulov, Radiy R. and Kozlov, Denis V. and Castellano, Felix N.}, year={2005}, pages={3776} }
 @article{danilov_pomestchenko_kinayyigit_gentili_hissler_ziessel_castellano_2005, title={Ultrafast energy migration in platinum(II) diimine complexes bearing pyrenylacetylide chromophores}, volume={109}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-15744395865&partnerID=MN8TOARS}, DOI={10.1021/jp045269}, abstractNote={The ultrafast excited-state dynamics of three structurally related platinum(II) complexes has been investigated using femtosecond transient absorption spectrometry in 2-methyltetrahydrofuran (MTHF). Previous work has shown that Pt(dbbpy)(C[triple bond]C-Ph)2 (dbbpy is 4,4'-di(tert-butyl)-2,2'-bipyridine and C[triple bond]C-Ph is ethynylbenzene) has a lowest metal-to-ligand charge transfer (3MLCT) excited state, while the multichromophoric Pt(dbbpy)(C[triple bond]C-pyrene)2 (CC-pyrene is 1-ethynylpyrene) contains the MLCT state, but possesses a lowest intraligand (3IL) excited state localized on one of the CC-pyrenyl units (Pomestchenko, I. E.; Luman, C. R.; Hissler, M.; Ziessel, R.; Castellano, F. N. Inorg. Chem. 2003, 42, 1394-96). trans-Pt(PBu3)2(C[triple bond]C-pyrene)2 serves as a model system that provides a good representation of the CC-pyrene-localized 3IL state in a Pt(II) complex lacking the MLCT excited state. Following 400 nm excitation, the formation of the 3MLCT excited state in Pt(dbbpy)(C[triple bond]C-Ph)2 is complete within 200 +/- 40 fs, and intersystem crossing to the 3IL excited state in trans-Pt(PBu3)2(C[triple bond]C-pyrene)2 occurs with a time constant of 5.4 +/- 0.2 ps. Selective excitation into the low-energy MLCT bands in Pt(dbbpy)(C[triple bond]C-pyrene)2 (lambda(ex) = 480 nm) leads to the formation of the 3IL excited state in 240 +/- 40 fs, suggesting ultrafast wire-like energy migration in this molecule. The kinetic data suggest that the presence of the MLCT states in Pt(dbbpy)(C[triple bond]C-pyrene)2 markedly accelerates the formation of the triplet state of the pendant pyrenylacetylide ligand. In essence, the triplet sensitization process is kinetically faster than pure intersystem crossing in trans-Pt(PBu3)2(CC-pyrene)2 as well as vibrational relaxation in the MLCT excited state of Pt(dbbpy)(C[triple bond]C-Ph)2. These results are potentially important for the design of chromophores intended to reach their lowest excited state on subpicosecond time scales and advocate the likelihood of wire-like behavior in triplet-triplet energy transfer.}, number={11}, journal={Journal of Physical Chemistry A}, author={Danilov, E.O. and Pomestchenko, I.E. and Kinayyigit, S. and Gentili, P.L. and Hissler, M. and Ziessel, R. and Castellano, F.N.}, year={2005}, pages={2465–2471} }
 @article{kozlov_castellano_2004, title={Anti-Stokes delayed fluorescence from metal–organic bichromophores}, ISSN={1359-7345 1364-548X}, url={http://dx.doi.org/10.1039/b412681e}, DOI={10.1039/b412681e}, abstractNote={Long wavelength excitation of [Ru(dmb)(2)(bpy-An)](2+) (dmb is 4,4'-dimethyl-2,2'-bipyridine and bpy-An is 4-methyl-4'-(9-anthrylethyl)-2,2'-bipyridine) in CH(3)CN solution produces upconverted delayed singlet anthracene fluorescence via bimolecular triplet-triplet annihilation.}, number={24}, journal={Chem. Commun.}, publisher={Royal Society of Chemistry (RSC)}, author={Kozlov, Denis V. and Castellano, Felix N.}, year={2004}, pages={2860–2861} }
 @article{ferri_scoponi_bignozzi_tyson_castellano_doyle_redmond_2004, title={Near-Field Optical Addressing of Luminescent Photoswitchable Supramolecular Systems Embedded in Inert Polymer Matrices}, volume={4}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl049770p}, DOI={10.1021/nl049770p}, abstractNote={Optical recording and luminescence readout of novel covalently linked photochrome/luminophore supramolecular complexes has been demonstrated by near-field scanning optical microscopy (NSOM). Localized UV irradiation of these complexes dispersed in polymeric matrices resulted in photoinduced state switching and a concomitant increase in emission intensity. Subsequent luminescence imaging showed well-resolved luminescent data bit arrays with good signal-to-noise ratios. Spatially resolved emission spectra of the luminescent data bits confirmed the switching mechanism.}, number={5}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Ferri, Violetta and Scoponi, Marco and Bignozzi, Carlo A. and Tyson, Daniel S. and Castellano, Felix N. and Doyle, Hugh and Redmond, Gareth}, year={2004}, month={May}, pages={835–839} }
 @article{kozlov_castellano_2004, title={Photochemically Reversible Luminescence Lifetime Switching in Metal−Organic Systems}, volume={108}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp045818b}, DOI={10.1021/jp045818b}, abstractNote={We use a diarylethene with solution-stable open and closed forms (1,2-bis(2-methylbenzo[b]thiophen-3-yl) hexafluorocyclopentene), BTF6, as a photochromic energy transfer quencher of the metal-to-ligand charge-transfer (MLCT) based luminescence in [Ru(dpp)3]2+, dpp = 4,7-diphenyl-1,10-phenanthroline. As only the closed form of BTF6 serves as a quencher for the MLCT luminescence, and the read (390 nm), write (λ 500 nm) wavelengths are well-separated, this system potentially represents an economic alternative to covalent systems. For the first time, we demonstrate the concept of using luminescence lifetimes to transduce the photochromic binary state of the quencher as opposed to the intensity-based readout schemes that are traditionally employed. The luminescence quenching process is described in terms of Forster-type resonance energy transfer (RET) enhanced by diffusion.}, number={48}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Kozlov, Denis V. and Castellano, Felix N.}, year={2004}, month={Dec}, pages={10619–10622} }
 @article{kozlov_tyson_goze_ziessel_castellano_2004, title={Room temperature phosphorescence from Ruthenium(II) complexes bearing conjugated pyrenylethynylene subunits}, volume={43}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-4644352861&partnerID=MN8TOARS}, DOI={10.1021/ic049288+}, abstractNote={We describe the synthesis, electrochemistry, and photophysical properties of several Ru(II) complexes bearing different numbers of pyrenylethynylene substituents in either the 5- or 5,5'-positions of 2,2'-bipyridine, along with the appropriate Ru(II) model complexes bearing either bromo- or ethynyltoluene functionalities. In addition, we prepared and studied the photophysical behavior of the diimine ligands 5-pyrenylethynylene-2,2'-bipyridine and 5,5'-dipyrenylethynylene-2,2'-bipyridine. Static and dynamic absorption and luminescence measurements reveal the nature of the lowest excited states in each molecule. All model Ru(II) complexes are photoluminescent at room temperature and exhibit excited-state behavior consistent with metal-to-ligand charge transfer (MLCT) characteristics. In the three Ru(II) molecules bearing multiple pyrenylethynylene substituents, there is clear evidence that the lowest excited state is triplet intraligand (3IL)-based, yielding long-lived room temperature phosphorescence in the red and near IR. This phosphorescence emanates from either 5-pyrenylethynylene-2,2'-bipyridine or 5,5'-dipyrenylethynylene-2,2'-bipyridine, depending upon the composition of the coordination compound. In the former case, the excited-state absorption difference spectra that were measured for the free ligand are easily superimposed with those obtained for the metal complexes coordinated to either one or two of these species. The latter instance is slightly complicated since coordination of the 5,5'-ligand to the Ru(II) center planarizes the diimine structure, leading to an extended conjugation on the long axis with a concomitant red shift of the singlet pi-pi absorption transitions and the observed room temperature phosphorescence. As a result, transient absorption measurements obtained using free 5,5'-dipyrenylethynylene-2,2'-bipyridine show a marked blue shift relative to its Ru(II) complex, and this extended pi-conjugation effect was confirmed by coordinating this ligand to Zn(II) at room temperature. In essence, all three pyrenylethynylene-containing Ru(II) complexes are unique in this genre of chromophores since the lowest excited state is 3IL-based at room temperature and at 77 K, and there is no compelling evidence of interacting or equilibrated excited states.}, number={19}, journal={Inorganic Chemistry}, author={Kozlov, D.V. and Tyson, D.S. and Goze, C. and Ziessel, R. and Castellano, F.N.}, year={2004}, pages={6083–6092} }
 @article{pomestchenko_castellano_2004, title={Solvent Switching between Charge Transfer and Intraligand Excited States in a Multichromophoric Platinum(II) Complex}, volume={108}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/jp049641x}, DOI={10.1021/jp049641x}, abstractNote={The photophysical properties of a new multichromophoric platinum(II) complex, Pt(dbbpy)(C≡C−nap)2 (1) (dbbpy = 4,4‘-(di-tert-butyl)-2,2‘-bipyridine; C≡C−nap = 1-ethynylnaphthalene), is reported in four different solvent systems of varying polarity:  toluene, 2-methyltetrahydrofuran, dichloromethane, and acetonitrile. Since the low-energy dπ Pt → π* dbbpy metal-to-ligand charge transfer (MLCT) transitions in this chromophore are negative solvatochromic in nature, increasing solvent polarity raises the energy of the MLCT state. At the same time, the low-lying, metal-perturbed π,π* triplet intraligand (3IL) state present within the molecule on the −C≡C−nap fragments are largely invariant to solvent polarity as evidenced by the absorption and emission properties of the model chromophore lacking the low-energy charge transfer state, Pt(dppe)(C≡C−nap)2 (2) (dppe = 1,2-bis(diphenylphosphino)ethane). In solvents of low polarity, the static and dynamic absorption and luminescence spectroscopy of 1 are largely cons...}, number={16}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Pomestchenko, Irina E. and Castellano, Felix N.}, year={2004}, month={Apr}, pages={3485–3492} }
 @article{trouts_tyson_pohl_kozlov_waldron_castellano_2003, title={Dinuclear metal-organic material for binary optical recording}, volume={13}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0037799267&partnerID=MN8TOARS}, DOI={10.1002/adfm.200304352}, abstractNote={AbstractA diimine ligand tethered to anthracene in the 9‐position, 4′‐(9‐anthrylethyl)‐4‐methyl‐2,2′‐bipyridine (bpy‐An), was dimerized through cycloaddition photochemistry. The resultant head‐to‐tail photodimer (bpy‐PD) was used as a bridging ligand in the preparation of a new dinuclear RuII complex, [Ru(dmb)2(bpy‐PD)Ru(dmb)2]4+ (dmb = 4,4′dimethyl‐2,2′‐bipyridine). The corresponding mononuclear species containing anthracene ([Ru(dmb)2(bpy‐An)]2+ was also synthesized and serves as a model compound in this study. UV photolysis (λ < 300 nm) of the strongly luminescent RuII dinuclear complex results in cycloreversion, generating two anthracene‐containing mononuclear species, [Ru(dmb)2(bpy‐An)]2+, whose emission is largely quenched as a result of nonradiative triplet–triplet energy transfer. The photophysical and photochemical properties of the dinuclear system have been studied in CH3CN solutions and in solid polyvinyl alcohol (PVA) thin films. The “on”–“off” luminescence switching characteristics and concomitant non‐destructive readout properties suggested that these molecules could be useful in read‐only memory (ROM) applications. In the solid state, micrometer‐sized objects were imaged using visible light, taking advantage of the luminescence contrast generated from the UV photochemical reaction. These written images were stable for at least 6 months, indicating that long‐term binary data storage is indeed feasible in these ROM metal–organic materials.}, number={5}, journal={Advanced Functional Materials}, author={Trouts, T.D. and Tyson, D.S. and Pohl, R. and Kozlov, D.V. and Waldron, A.G. and Castellano, F.N.}, year={2003}, pages={398–402} }
 @article{lee_luman_castellano_lin_2003, title={Directed assembly of chiral organometallic squares that exhibit dual luminescence}, volume={9}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0042736331&partnerID=MN8TOARS}, number={17}, journal={Chemical Communications}, author={Lee, S.J. and Luman, C.R. and Castellano, F.N. and Lin, W.}, year={2003}, pages={2124–2125} }
 @article{luman_castellano_2003, title={Lengthening of Fluorescence Lifetimes in Self-organized Metal-Organic Assemblies}, volume={77}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0037590273&partnerID=MN8TOARS}, DOI={10.1562/0031-8655(2003)077<0510:LOFLIS>2.0.CO;2}, abstractNote={Abstract Resonance energy transfer from tris(2,2′-bipyridyl)ruthenium (II) ([Ru(bpy)3]2+) to nile blue A is demonstrated in aqueous solution in the presence of sodium dodecyl sulfate (SDS). At SDS concentrations below the critical micelle concentration, aggregates that permit energy transfer between these dyes at optically dilute (10 μM) concentrations with nearly 100% efficiency are formed. The disparity between the lifetimes of the donor and acceptor results in the lengthening of the photoluminescence lifetime of the sensitized emission observed from nile blue A. Time-resolved luminescence measurements confirm that the long-lived components of the emission originate from sensitized acceptor emission.}, number={5}, journal={Photochemistry and Photobiology}, author={Luman, C.R. and Castellano, F.N.}, year={2003}, pages={510–514} }
 @book{luman_castellano_2004, title={Phenanthroline Ligands}, volume={1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84902415875&partnerID=MN8TOARS}, DOI={10.1016/B0-08-043748-6/01202-0}, journal={Comprehensive Coordination Chemistry II}, author={Luman, C.R. and Castellano, F.N.}, year={2004}, pages={25–39} }
 @article{pomestchenko_luman_hissler_ziessel_castellano_2003, title={Room temperature phosphorescence from a platinum(II) diimine bis(pyrenylacetylide) complex}, volume={42}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0037430188&partnerID=MN8TOARS}, DOI={10.1021/ic0261631}, abstractNote={Room temperature phosphorescence has been observed in a synthetically facile Pt(II) complex, Pt(dbbpy)(CtriplebondC-pyrene)(2) (dbbpy = 4,4'-di(tert-butyl)-2,2'-bipyridine; CtriplebondC-pyrene = 1-ethynylpyrene), in fluid solution. The static and time-resolved absorption and luminescence data are consistent with phosphorescence emerging from the appended CtriplebondC-pyrenyl units following excitation into the low energy dpi Pt --> pi* dbbpy metal-to-ligand charge transfer absorption bands.}, number={5}, journal={Inorganic Chemistry}, author={Pomestchenko, I.E. and Luman, C.R. and Hissler, M. and Ziessel, R. and Castellano, F.N.}, year={2003}, pages={1394–1396} }
 @article{goze_kozlov_tyson_ziessel_castellano_2003, title={Synthesis and photophysics of ruthenium(II) complexes with multiple pyrenylethynylene subunits}, volume={27}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-1642456622&partnerID=MN8TOARS}, DOI={10.1039/b307327k}, abstractNote={We describe the synthesis and photophysical properties of new Ru(II) complexes bearing different numbers of pyrenylethynylene substituents in either the 5 or 5,5′ positions of 2,2′-bipyridine. Static and dynamic absorption and luminescence measurements reveal the nature of the lowest excited states in each molecule. The 5-substituted complexes display behavior dominated by triplet intraligand π,π* excited states, generating long-lived room temperature phosphorescence in the red. While the photophysical properties in the 5,5′-substituted case are still largely influenced by triplet intraligand π,π* excited states, the data suggest the possibility of an excited state manifold composed of “mixed” intraligand and charge transfer character.}, number={12}, journal={New Journal of Chemistry}, author={Goze, C. and Kozlov, D.V. and Tyson, D.S. and Ziessel, R. and Castellano, F.N.}, year={2003}, pages={1679–1683} }
 @article{goze_kozlov_castellano_suffert_ziessel_2003, title={Synthesis of bipyridine and terpyridine based ruthenium metallosynthons for grafting of multiple pyrene auxiliaries}, volume={44}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0142153446&partnerID=MN8TOARS}, DOI={10.1016/j.tetlet.2003.09.127}, abstractNote={The synthesis of novel ruthenium(II) bipyridine or terpyridine complexes bearing an increasing number of pyrene or toluyl moieties is described. The ruthenium complexes are constructed in a first step with ligands bearing the required bromine functions, followed in a second step by stepwise grafting of 1-ethynylpyrene or 4-ethynyltoluene promoted by Pd(0). A complex bearing a protected triethylsilylacetylene function was also prepared. In situ deprotection of this function with K2CO3 and cross-coupling with 1-bromopyrene afforded a soluble complex in which two pyrene moieties are linearly linked via ethynyl spacers to one of the bipyridine ligands. These highly coloured complexes exhibit well defined absorption and emission properties in solution at both rt and 77 K.}, number={48}, journal={Tetrahedron Letters}, author={Goze, C. and Kozlov, D.V. and Castellano, F.N. and Suffert, J. and Ziessel, R.}, year={2003}, pages={8713–8716} }
 @article{luminescence lifetime-based sensor for cyanide and related anions_2002, volume={124}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0037024174&partnerID=MN8TOARS}, DOI={10.1021/ja0259180}, abstractNote={A new Ru(II) complex is described which serves as a luminescence lifetime-based sensor for fluoride and cyanide anions (KF = 640 000 mol-1, KCN = 430 000 mol-1). This chromophore displays observable changes in its UV-vis and steady-state luminescence spectra upon cyanide binding. Prior to cyanide addition, this complex exhibits a single-exponential lifetime (tau = 377 +/- 20 ns). With increasing cyanide concentrations, the intensity decays are composed of two exponentials: long tau (320-370 ns) and short tau (13-17 ns). The average lifetimes shorten as a function of cyanide concentration since the fractional intensity shifts from an initial dominant long lifetime component to the short lifetime component. This work represents the first example of a direct method for the luminescence lifetime-based sensing of anions.}, number={22}, journal={Journal of the American Chemical Society}, year={2002}, pages={6232–6233} }
 @article{tyson_bignozzi_castellano_2002, title={Metal-organic approach to binary optical memory}, volume={124}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036571242&partnerID=MN8TOARS}, DOI={10.1021/ja0255608}, abstractNote={Two new Ru(II) diimine chromophores, each containing a single photochromic dianthryl unit, have been prepared and characterized. The photoluminescence from the Ru(II) complexes is modulated by the photochromic action of the dianthryl species, which serves as a triplet energy transfer quencher in one photochromic state. The coupling of the dianthryl photochromic action to the Ru(II) complex emission permits nondestructive photoluminescence readout of binary information photochemically recorded on the molecular level. Luminescent images stored on polystyrene films that contain these molecules maintained their integrity for periods of months with no apparent degradation or variation in the image resolution, suggesting their durability for long-term storage in read-only memory applications.}, number={17}, journal={Journal of the American Chemical Society}, author={Tyson, D.S. and Bignozzi, C.A. and Castellano, F.N.}, year={2002}, pages={4562–4563} }
 @article{tyson_luman_castellano_2002, title={Photodriven electron and energy transfer from a light-harvesting metallodendrimer}, volume={41}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036644319&partnerID=MN8TOARS}, DOI={10.1021/ic011298c}, abstractNote={Intermolecular electron and energy transfer from a light-harvesting metallodendrimer [Ru[bpy(C-450)(4)](3)](2+), where bpy(C-450)(4) is a 2,2'-bipyridine derivative containing 4 coumarin-450 units connected together through aryl ether linkages, is observed in acetonitrile solutions at room temperature. The model complex [Ru(dmb)(3)](2+), where dmb is 4,4'-dimethyl-2,2'-bipyridine, is included for quantitative comparison. The excited states of both compounds are metal-to-ligand charge transfer in nature and participate in excited-state electron and triplet energy transfer processes. Quenching constants were determined from luminescence and time-resolved absorption experiments at constant ionic strength. [Ru[bpy(C-450)(4)](3)](2+) displays significantly slower quenching rates to molecular oxygen and methyl viologen relative to the other processes investigated. Triplet energy transfer from [Ru[bpy(C-450)(4)](3)](2+) to 9-methylanthracene is quantitatively indistinguishable from [Ru(dmb)(3)](2+) while reductive electron transfer from phenothiazine was slightly faster in the former. With the exception of dioxygen quenching, our results indicate that the current dendritic structure is ineffective in shielding the core from bimolecular electron and triplet energy transfer reactions. Electrochemical measurements of [Ru[bpy(C-450)(4)](3)](2+) reveal irreversible oxidative processes at potentials slightly negative to the Ru(III/II) potential that are assigned to oxidations in the dendritic structure. Excited-state oxidative electron-transfer reactions facilitate this process resulting in the reduction of ground-state Ru(III) to Ru(II) and the trapping of the methyl viologen radical cation (MV(*+)) when methyl viologen serves as the quencher. This process generates a minimum of 9 MV(*+)'s for every [Ru[bpy(C-450)(4)](3)](2+) molecule and disassembles the metallodendrimer, resulting in the production of a [Ru(dmb)(3)](2+)-like species and "free" C-450-like dyes.}, number={13}, journal={Inorganic Chemistry}, author={Tyson, D.S. and Luman, C.R. and Castellano, F.N.}, year={2002}, pages={3578–3586} }
 @article{tyson_henbest_bialecki_castellano_2001, title={Excited state processes in ruthenium(II)/pyrenyl complexes displaying extended lifetimes}, volume={105}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035818134&partnerID=MN8TOARS}, DOI={10.1021/jp011770f}, abstractNote={The synthesis and photophysical properties of two Ru(II) diimine complexes bearing one (dyad) and three (tetrad) pyrenyl units, respectively, are presented. The pyrene chromophore in each metal complex is tethered through a single C−C bond in the 5-position of 1,10-phenanthroline (py-phen). Both Ru(II) complexes display increased absorption cross sections near 340 nm largely due to the presence of the pyrenyl chromophore(s). Excitation from 300 to 540 nm results exclusively in the observation of metal-to-ligand charge transfer (MLCT) based emission that is exceptionally long lived, 23.7 μs and 148 μs in deaerated CH3CN, respectively. This luminescence was analyzed using steady-state and time-resolved techniques at room temperature and 77 K. The tetrad complex, [Ru(py-phen)3]2+, displays a dynamic self-quenching reaction at room temperature in dilute CH3CN solutions that is well modeled by a Stern−Volmer expression. The excited-state processes occurring between the MLCT core and the pyrenyl units were furt...}, number={35}, journal={Journal of Physical Chemistry A}, author={Tyson, D.S. and Henbest, K.B. and Bialecki, J. and Castellano, F.N.}, year={2001}, pages={8154–8161} }
 @article{tyson_luman_zhou_castellano_2001, title={New Ru(II) chromophores with extended excited-state lifetimes}, volume={40}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035973695&partnerID=MN8TOARS}, DOI={10.1021/ic010287g}, abstractNote={We describe the synthesis, electrochemical, and photophysical properties of two new luminescent Ru(II) diimine complexes covalently attached to one and three 4-piperidinyl-1,8-naphthalimide (PNI) chromophores, [Ru(bpy)(2)(PNI-phen)](PF(6))(2) and [Ru(PNI-phen)(3)](PF(6))(2), respectively. These compounds represent a new class of visible light-harvesting Ru(II) chromophores that exhibit greatly enhanced room-temperature metal-to-ligand charge transfer (MLCT) emission lifetimes as a result of intervening intraligand triplet states ((3)IL) present on the pendant naphthalimide chromophore(s). In both Ru(II) complexes, the intense singlet fluorescence of the pendant PNI chromophore(s) is nearly quantitatively quenched and was found to sensitize the MLCT-based photoluminescence. Excitation into either the (1)IL or (1)MLCT absorption bands results in the formation of both (3)MLCT and (3)IL excited states, conveniently monitored by transient absorption and fluorescence spectroscopy. The relative energy ordering of these triplet states was determined using time-resolved emission spectra at 77 K in an EtOH/MeOH glass where dual emission from both Ru(II) complexes was observed. Here, the shorter-lived higher energy emission has a spectral profile consistent with that typically observed from (3)MLCT excited states, whereas the millisecond lifetime lower energy band was attributed to (3)IL phosphorescence of the PNI chromophore. At room temperature the data are consistent with an excited-state equilibrium between the higher energy (3)MLCT states and the lower energy (3)PNI states. Both complexes display MLCT-based emission with room-temperature lifetimes that range from 16 to 115 micros depending upon solvent and the number of PNI chromophores present. At 77 K it is apparent that the two triplet states are no longer in thermal equilibrium and independently decay to the ground state.}, number={16}, journal={Inorganic Chemistry}, author={Tyson, D.S. and Luman, C.R. and Zhou, X. and Castellano, F.N.}, year={2001}, pages={4063–4071} }
 @article{zhou_tyson_castellano_2000, title={First Generation Light-Harvesting Dendrimers with a [Ru(bpy) 3 ] 2+ Core and Aryl Ether Ligands Functionalized with Coumarin 450}, volume={39}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0034605906&partnerID=MN8TOARS}, DOI={10.1002/1521-3773(20001201)39:23<4301::AID-ANIE4301>3.0.CO;2-9}, abstractNote={Angewandte Chemie International EditionVolume 39, Issue 23 p. 4301-4305 Communication First Generation Light-Harvesting Dendrimers with a [Ru(bpy)3]2+ Core and Aryl Ether Ligands Functionalized with Coumarin 450 Xiaoli Zhou, Xiaoli Zhou Department of Chemistry and Center for Photochemical Sciences Bowling Green State University Bowling Green, OH 43403, USA, Fax: (+1) 419-372-9809Search for more papers by this authorDaniel S. Tyson, Daniel S. Tyson Department of Chemistry and Center for Photochemical Sciences Bowling Green State University Bowling Green, OH 43403, USA, Fax: (+1) 419-372-9809Search for more papers by this authorFelix N. Castellano Prof., Felix N. Castellano Prof. castell@bgnet.bgsu.edu Department of Chemistry and Center for Photochemical Sciences Bowling Green State University Bowling Green, OH 43403, USA, Fax: (+1) 419-372-9809Search for more papers by this author Xiaoli Zhou, Xiaoli Zhou Department of Chemistry and Center for Photochemical Sciences Bowling Green State University Bowling Green, OH 43403, USA, Fax: (+1) 419-372-9809Search for more papers by this authorDaniel S. Tyson, Daniel S. Tyson Department of Chemistry and Center for Photochemical Sciences Bowling Green State University Bowling Green, OH 43403, USA, Fax: (+1) 419-372-9809Search for more papers by this authorFelix N. Castellano Prof., Felix N. Castellano Prof. castell@bgnet.bgsu.edu Department of Chemistry and Center for Photochemical Sciences Bowling Green State University Bowling Green, OH 43403, USA, Fax: (+1) 419-372-9809Search for more papers by this author First published: 01 December 2000 https://doi.org/10.1002/1521-3773(20001201)39:23<4301::AID-ANIE4301>3.0.CO;2-9Citations: 56Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract A new class of light-harvesting dendrimers based on metal–organic hybrids (see picture) is described, including the synthesis and photophysical characterization. The inorganic core displays sensitized emission with decay times on the microsecond timescale, which is beneficial for fluorescence lifetime-based technologies. Citing Literature Supporting Information Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2000/z15388_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. Volume39, Issue23December 1, 2000Pages 4301-4305 RelatedInformation}, number={23}, journal={Angewandte Chemie}, author={Zhou, X. and Tyson, D.S. and Castellano, F.N.}, year={2000}, month={Dec}, pages={4301–4305} }
 @article{tyson_gryczynski_castellano_2000, title={Long-range resonance energy transfer to [Ru(bpy)3]2+}, volume={104}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0001437001&partnerID=MN8TOARS}, number={13}, journal={Journal of Physical Chemistry A}, author={Tyson, D.S. and Gryczynski, I. and Castellano, F.N.}, year={2000}, pages={2919–2924} }
 @article{tyson_bialecki_castellano_2000, title={Ruthenium(II) complex with a notably long excited state lifetime}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0034620012&partnerID=MN8TOARS}, DOI={10.1039/b007336i}, abstractNote={A new Ru(II) diimine complex, 
[Ru(5-pyrenyl-1,10-phenanthroline)]3(PF6)2 
([Ru(py-phen)3]2+), possesses a room temperature 
excited state lifetime of 148 ± 8 μs.}, number={23}, journal={Chem. Commun.}, publisher={Royal Society of Chemistry (RSC)}, author={Tyson, Daniel S. and Bialecki, Jason and Castellano, Felix N.}, year={2000}, pages={2355–2356} }
 @article{lakowicz_gryczynski_tolosa_dattelbaum_castellano_li_rao_1999, title={Advances in Fluorescence Spectroscopy: Multi-Photon Excitation, Engineered Proteins, Modulation Sensing and Microsecond Rhenium Metal-Ligand Complexes}, volume={95}, ISSN={0587-4246 1898-794X}, url={http://dx.doi.org/10.12693/aphyspola.95.179}, DOI={10.12693/aphyspola.95.179}, abstractNote={The technology and applications of fluorescence spectroscopy are rapidly advancing. In this overview presentation we summarize some recent developments from this laboratory. Two and three-photon excitation have been observed for a wide variety of intrinsic and extrinsic fluorophores, including tryptophan, tyrosine, DNA stains, membrane probes, and even alkanes. It has been possible to observe multi-photon excitation of biopolymers without obvious photochemical or photo-thermal effects. Although not de-scribed in our lecture, another area of increasing interest is the use of engineered proteins for chemical and clinical sensing. We show results for the glucose-galactose binding protein from E. coli. The labeled protein shows spectral changes in response to micromolar concentrations of glucose. This protein was used with a novel sensing method based on the modulated emission of the labeled proteins and a long lifetime reference fluorophore. And finally, we describe a recently developed rhenium complex which displays a lifetime near 3 µs in oxygenated aqueous solution. Such long life-time probes allow detection of microsecond dynamic processes, bypassing the usual nanosecond timescale limit of fluorescence. The result of these developments in protein engineering, sensing methods, and metal-ligand probe chemistry will be the increased use of fluorescence in clinical chemistry and point-of-care analyses.}, number={1}, journal={Acta Physica Polonica A}, publisher={Institute of Physics, Polish Academy of Sciences}, author={Lakowicz, J.R. and Gryczynski, I. and Tolosa, L. and Dattelbaum, J.D. and Castellano, F.N. and Li, L. and Rao, G.}, year={1999}, month={Jan}, pages={179–196} }
 @article{tolosa_gryczynski_eichhorn_dattelbaum_castellano_rao_lakowicz_1999, title={Glucose sensor for low-cost lifetime-based sensing using a genetically engineered protein}, volume={267}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0033081688&partnerID=MN8TOARS}, DOI={10.1006/abio.1998.2974}, abstractNote={We describe a glucose sensor based on a mutant glucose/galactose binding protein (GGBP) and phase-modulation fluorometry. The GGBP from Escherichia coli was mutated to contain a single cysteine residue at position 26. When labeled with a sulfhydryl-reactive probe 2-(4'-iodoacetamidoanilino)naphthalene-6-sulfonic acid, the labeled protein displayed a twofold decrease in intensity in response to glucose, with a dissociation constant near 1 microM glucose. The ANS-labeled protein displayed only a modest change in lifetime, precluding lifetime-based sensing of glucose. A modulation sensor was created by combining ANS26-GGBP with a long-lifetime ruthenium (Ru) metal-ligand complex on the surface of the cuvette. Binding of glucose changed the relative intensity of ANS26-GGBP and the Ru complex, resulting in a dramatic change in modulation at a low frequency of 2.1 MHz. Modulation measurements at 2.1 MHz were shown to accurately determine the glucose concentration. These results suggest an approach to glucose sensing with simple devices.}, number={1}, journal={Analytical Biochemistry}, author={Tolosa, L. and Gryczynski, I. and Eichhorn, L.R. and Dattelbaum, J.D. and Castellano, F.N. and Rao, G. and Lakowicz, J.R.}, year={1999}, pages={114–120} }
 @article{tyson_castellano_1999, title={Intramolecular singlet and triplet energy transfer in a ruthenium(II) diimine complex containing multiple pyrenyl chromophores}, volume={103}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0001549018&partnerID=MN8TOARS}, number={50}, journal={Journal of Physical Chemistry A}, author={Tyson, D.S. and Castellano, F.N.}, year={1999}, pages={10955–10960} }
 @article{tyson_castellano_1999, title={Light-Harvesting Arrays with Coumarin Donors and MLCT Acceptors}, volume={38}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0001445634&partnerID=MN8TOARS}, DOI={10.1021/ic9905300}, abstractNote={We present a light-harvesting strategy that utilizes organic donor molecules to achieve sensitized metal-to-ligand charge transfer (MLCT) based emission. In this scheme, coumarin dye molecules are covalently linked to the periphery of diimine ligands in Ru(II) inorganic complexes that display MLCT excited states. Our findings suggest that the singlet−singlet energy transfer strategies traditionally employed in artificial light-harvesting arrays can be adapted to incorporate MLCT excited states.}, number={20}, journal={Inorg. Chem.}, publisher={American Chemical Society (ACS)}, author={Tyson, Daniel S. and Castellano, Felix N.}, year={1999}, month={Oct}, pages={4382–4383} }
 @article{li_castellano_gryczynski_lakowicz_1999, title={Long-lifetime lipid rhenium metal-ligand complex for probing membrane dynamics on the microsecond timescale}, volume={99}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032933714&partnerID=MN8TOARS}, DOI={10.1016/S0009-3084(99)00002-X}, abstractNote={We report the luminescence and spectral properties of a phospholipid analogue containing a long-lifetime luminescent rhenium metal–ligand complex (MLC) covalently linked to the amino group of phosphatidyl ethanolamine. When incorporated into synthetic membranes, this lipid probe displays intensity decay times near 3 μs. Importantly, the probe displays highly polarized emission with a maximal fundamental anisotropy of 0.33. This probe is expected to have numerous applications for studies of microsecond diffusion and dynamics of membranes.}, number={1}, journal={Chemistry and Physics of Lipids}, author={Li, L. and Castellano, F.N. and Gryczynski, I. and Lakowicz, J.R.}, year={1999}, pages={1–9} }
 @article{lakowicz_castellano_gryczynski_gryczynski_dattelbaum_1999, title={Two-photon excitation of rhenium metal-ligand complexes}, volume={122}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0011578262&partnerID=MN8TOARS}, number={2}, journal={Journal of Photochemistry and Photobiology A: Chemistry}, author={Lakowicz, J.R. and Castellano, F.N. and Gryczynski, I. and Gryczynski, Z. and Dattelbaum, J.D.}, year={1999}, pages={95–101} }
 @article{castellano_lakowicz_2008, title={A Water-Soluble Luminescence Oxygen Sensor}, volume={67}, DOI={10.1111/j.1751-1097.1998.tb05184.x}, abstractNote={ABSTRACTWe developed a water‐soluble luminescent probe for dissolved oxygen. This probe is based on (Ru[dpp(SO3Na)2]3) Cl2, which is a sulfonated analogue of the well‐known oxygen probe (Ru[dpp]3)Cl2. The compound dpp is 4,7‐diphenyl‐1,10‐phenanthroline and dpp(SO3Na)2 is a disulfonated derivative of the same ligand. In aqueous solution in the absence of oxygen (Ru[dpp(SO3Na)2]3)Cl2 displays a lifetime of 3.7 μs that decreases to 930 ns on equilibrium with air and 227 ns on equilibrium with 100% oxygen. The Stern–Vohner quenching constant is 11330 M−1. This high oxygen‐quenching constant means that the photoluminescence of Ru(dpp[SO3Na]2)3Cl2 is 10% quenched at an oxygen concentration of 8.8 x 10−6M, or equilibration with 5.4 torr of oxygen. The oxygen probe dissolved in water displays minimal interactions with lipid vesicles composed of dipalmityl‐L‐α‐phosphatidyl glycerol but does appear to interact with human serum albumin. The absorption maximum near 480 nm, long lifetime and large Stokes’shift allow this probe to be used with simple instrumentation based on a light‐emitting diode light source, allowing low‐cost oxygen sensing in aqueous solutions. To the best of our knowledge this is the first practical water‐soluble oxygen sensor.}, number={2}, journal={Photochemistry and Photobiology}, publisher={Wiley-Blackwell}, author={Castellano, Felix N. and Lakowicz, Joseph R.}, year={2008}, month={Jan}, pages={179–183} }
 @article{castellano_lakowicz_1998, title={A Water-Soluble Luminescence Oxygen Sensor}, volume={67}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031989216&partnerID=MN8TOARS}, number={2}, journal={Photochemistry and Photobiology}, author={Castellano, F.N. and Lakowicz, J.R.}, year={1998}, pages={179–183} }
 @article{guo_castellano_li_lakowicz_1998, title={A long-lifetime Ru(II)metal-ligand complex as a membrane probe}, volume={71}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032579936&partnerID=MN8TOARS}, DOI={10.1016/S0301-4622(97)00135-X}, abstractNote={A luminescent metal-ligand complex, [Ru(bpy)2(dppz)]2+, (where dppz is dipyrido[3,2-a:2',3'-c] phenazine), was used as a photoluminescence probe for investigating submicrosecond lipid dynamics in a dipalmitoyl-L-alpha-phosphotidylglycerol (DPPG) model bilayer system. The luminescence of [Ru(bpy)2(dppz)]2+ in buffer is completely quenched but becomes luminescent when intercalated into DPPG vesicles. The experimental results show that the emission intensity of [Ru(bpy)2(dppz)]2+ intercalated into DPPG vesicles increases dramatically as temperature is increased towards the lipid phase transition temperature. This effect is abolished in bilayers containing a high concentration (> 30 mol%) of cholesterol, suggesting this probe is sensitive to the membrane composition. Frequency-domain emission intensity decays, measured as a function of increasing temperature towards the lipid phase transition temperature (2 to 57 degrees C), display two major lifetime components. The short lifetime disappears at temperatures well above the phase transition temperature. A comparison of oxygen quenching with iodide quenching suggests the heterogeneity of probe location at temperatures well below the lipid phase transition temperature and the homogeneity of probe location at temperature well above the lipid phase transition temperature. [Ru(bpy)2(dppz)]2+ displays polarized emission, enabling the study of membrane dynamics. The long decay time displayed by this probe allows measurement of the overall rotational correlation time of lipid vesicles on the microsecond time-scale. Because of the long lifetime, polarized emission, and background free nature of the photoluminescence measurements, [Ru(bpy)2(dppz)]2+ has numerous applications in the biophysical studies of membranes.}, number={1}, journal={Biophysical Chemistry}, author={Guo, X.-Q. and Castellano, F.N. and Li, L. and Lakowicz, J.R.}, year={1998}, pages={51–62} }
 @inproceedings{castellano_guo_li_szmacinski_sipior_lakowicz_1998, title={A long-lived, highly luminescent rhenium (I) metal-ligand complex as a probe of biomolecules}, volume={3256}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032225971&partnerID=MN8TOARS}, DOI={10.1117/12.307064}, abstractNote={A luminescent rhenium(I) metal-ligand complex, [Re(bcp)(CO)3(4-COOHPy)](ClO4), where bcp is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline and 4-COOHPy is isonicotinic acid, has been synthesized and characterized. This complex displays high quantum yields and long excited- state lifetimes (0.3 - 10 microseconds) in fluid solution at room temperature. The metal-to-ligand charge transfer (MLCT) emission from this compound exhibits sensitivity to micro- environment. [Re(bcp)(CO)3(4-COOHPy)]+ displays highly polarized emission with a maximum anisotropy near 0.3 in the absence of rotational diffusion. This Re(I) MLCT complex was conjugated to several biomolecules, including the proteins human serum albumin (HSA) and bovine immunoglobulin G(IgG) as well as an amine containing lipid. When bound to a protein or lipid, the decay time is near 3 microseconds and the quantum yield is approximately 0.12 in aqueous air-equilibrated solution at room temperature. The unique spectral properties and reactive carboxylic acid functionality of [Re(bcp)(CO)3(4-COOHPy)]+, allowed utilization of this probe in numerous biophysical and biomedical applications.}, booktitle={Proceedings of SPIE - The International Society for Optical Engineering}, author={Castellano, F.N. and Guo, X.-Q. and Li, L. and Szmacinski, H. and Sipior, J. and Lakowicz, J.R.}, year={1998}, pages={223–233} }
 @article{ruthkosky_kelly_castellano_meyer_1998, title={Electron and energy transfer from CuI MLCT excited states}, volume={171}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032049755&partnerID=MN8TOARS}, number={1}, journal={Coordination Chemistry Reviews}, author={Ruthkosky, M. and Kelly, C.A. and Castellano, F.N. and Meyer, G.J.}, year={1998}, pages={309–322} }
 @article{castellano_dattelbaum_lakowicz_1998, title={Long-lifetime Ru(II) complexes as labeling reagents for sulfhydryl groups}, volume={255}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032518578&partnerID=MN8TOARS}, DOI={10.1006/abio.1997.2468}, abstractNote={We report the synthesis and spectral properties of two long-lifetime highly luminescent Ru(II) complexes containing either a sulfhydryl reactive iodoacetamido group or a less reactive choloroacetamido group, [Ru(bpy)2(5-iodoacetamido-1,10-phenanthroline)] (PF6)2 and [Ru(bpy)2(5-chloroacetamido-1,10-phenanthroline)](PF6) 2, respectively, where bpy is 2,2'-bipyridine. Ru(bpy)2(phen-IA)](PF6)2 was covalently linked to human serum albumin (HSA) and human immunoglobulin G (IgG). The photoluminescence lifetime of protein-bound probes approaches 1 microsecond under ambient conditions. In the absence of rotational motions, this probe displayed an anisotropy of 0.18 for excitation at 472 nm. Anisotropy decay data were used to determine the overall rotational correlation times of HSA and IgG. These long-lifetime sulfhydryl-reactive probes can be used to recover microsecond rotational motions and/or domain motions of proteins and/or macromolecular complexes.}, number={2}, journal={Analytical Biochemistry}, author={Castellano, F.N. and Dattelbaum, J.D. and Lakowicz, J.R.}, year={1998}, pages={165–170} }
 @article{szmacinski_castellano_terpetschnig_dattelbaum_lakowicz_meyer_1998, title={Long-lifetime Ru(II) complexes for the measurement of high molecular weight protein hydrodynamics}, volume={1383}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032478239&partnerID=MN8TOARS}, DOI={10.1016/S0167-4838(97)00196-9}, abstractNote={We describe the synthesis and characterization of two asymmetrical ruthenium(II) complexes, [Ru(dpp)2(dcbpy)]2+ and [Ru(dpp)2(mcbpy)]2+, as well as the water soluble sulfonated derivatives [Ru(dpp(SO3Na)2)2(dcbpy)]2+ and [Ru(dpp(SO3Na)2)2(mcbpy)]2+ (dpp is 4,7-diphenyl-1,10-phenanthroline, dcbpy is 4,4′-dicarboxylic acid-2,2′-bipyridine, mcbpy is 4-methyl,4′-carboxylic acid-2,2′-bipyridine, and dpp(SO3Na)2 is the disulfonated derivative of dpp) as probes for the measurement of the rotational motions of proteins. The spectral (absorption, emission, and anisotropy) and photophysical (time-resolved intensity and anisotropy decays) properties of these metal–ligand complexes were determined in solution, in both the presence and absence of human serum albumin (HSA). These complexes display lifetimes ranging from 345 ns to 3.8 μs in deoxygenated aqueous solutions under a variety of conditions. The carboxylic acid groups on these complexes were activated to form N-hydroxysuccinimide (NHS) esters which were used to covalently label HSA, and were characterized spectroscopically in the same manner as above. Time-resolved anisotropy measurements were performed to demonstrate the utility of these complexes in measuring long rotational correlation times of bioconjugates between HSA and antibody to HSA. The potential usefulness of these probes in fluorescence polarization immunoassays was demonstrated by an association assay of the Ru(II)-labeled HSA with polyclonal antibody.}, number={1}, journal={Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology}, author={Szmacinski, H. and Castellano, F.N. and Terpetschnig, E. and Dattelbaum, J.D. and Lakowicz, J.R. and Meyer, G.J.}, year={1998}, pages={151–159} }
 @article{lakowicz_castellano_dattelbaum_tolosa_rao_gryczynski_1998, title={Low-frequency modulation sensors using nanosecond fluorophores}, volume={70}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032535150&partnerID=MN8TOARS}, DOI={10.1021/ac980876c}, abstractNote={We describe a new approach to fluorescence sensing based on a mixture of fluorophores, one of which is sensitive to the desired analyte. If a long-lifetime analyte-insensitive fluorophore is mixed with a short-lifetime analyte-sensitive fluorophore, the modulation of the emission at conveniently low frequencies becomes equal to the fractional fluorescence intensity of the sensing fluorophore. Under these conditions, the modulation can be used to determine the analyte concentration. This can be used with any fluorophore that changes intensity in response to analyte and does not require the sensing fluorophore to display a change in lifetime. The feasibility of modulation-based sensing was demonstrated using mixtures of 6-carboxyfluorescein and [Ru 2,2'-(bipyridyl)3]2+ as a pH sensor and of the calcium probe Fluo-3 and [Ru 2,2'-(bipyridyl)3]2+ as a calcium sensor.}, number={24}, journal={Analytical Chemistry}, author={Lakowicz, J.R. and Castellano, F.N. and Dattelbaum, J.D. and Tolosa, L. and Rao, G. and Gryczynski, I.}, year={1998}, pages={5115–5121} }
 @inbook{lakowicz_gryczynski_szmacinski_malak_castellano_murtaza_guo_li_lin_dattelbaum_1998, place={Netherlands}, series={NATO ASI series. Partnership sub-series 3, High technology}, title={Recent Developments in Fluorescence Spectroscopy: Three-Photon Excitation, Two-Color Two-Photon Excitation, Light Quenching, and Development of Long-Lifetime Probes for Biophysics and Clinical Chemistry}, ISBN={9780792351016}, booktitle={Near-Infrared Dyes for High Technology Applications}, publisher={Kluwer Academic Publishers}, author={Lakowicz, J.R. and Gryczynski, I. and Szmacinski, H. and Malak, H. and Castellano, F.N. and Murtaza, Z. and Guo, X.Q. and Li, L. and Lin, H. and Dattelbaum, J.D.}, editor={Daehne, Siegfried and Resch-Genger, Ute and Wolfbeis, Otto S.Editors}, year={1998}, pages={3–19}, collection={NATO ASI series. Partnership sub-series 3, High technology} }
 @article{guo_castellano_li_lakowicz_1998, title={Use of a Long-Lifetime Re(I) Complex in Fluorescence Polarization Immunoassays of High-Molecular-Weight Analytes}, volume={70}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031989268&partnerID=MN8TOARS}, number={3}, journal={Analytical Chemistry}, author={Guo, X.-Q. and Castellano, F.N. and Li, L. and Lakowicz, J.R.}, year={1998}, pages={632–637} }
 @article{guo_castellano_li_szmacinski_lakowicz_sipior_1997, title={A long-lived, highly luminescent Re(I) metal-ligand complex as a biomolecular probe}, volume={254}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031574366&partnerID=MN8TOARS}, DOI={10.1006/abio.1997.2413}, abstractNote={A highly luminescent rhenium (I) metal-ligand complex [Re(bcp)(CO)3(4-COOHPy)](ClO4), where bcp is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline and 4-COOHPy is isonicotinic acid, has been synthesized and characterized. High quantum yields (> 0.5) and long excited-state lifetimes (0.3-10 micronseconds) in fluid solutions at room temperature were found for this complex, with remarkable emission sensitivity to microenvironment. This compound also displays highly polarized emission with a maximum anisotropy near 0.3 in the absence of rotational diffusion. This Re complex was conjugated to several biomolecules, including the proteins human serum albumin and bovine immunoglobulin G, as well as an amine-containing lipid. When bound to a protein or lipid, the decay time is near 3 microseconds and the quantum yield is approximately 0.12 in aqueous oxygenated solution at room temperature. This compound's unique spectral properties along with its conjugatability allowed us to utilize it as biomolecular probe in a variety of environments.}, number={2}, journal={Analytical Biochemistry}, author={Guo, X.-Q. and Castellano, F.N. and Li, L. and Szmacinski, H. and Lakowicz, J.R. and Sipior, J.}, year={1997}, pages={179–186} }
 @article{castellano_malak_gryczynski_lakowicz_1997, title={Creation of Metal-to-Ligand Charge Transfer Excited States with Two-Photon Excitation}, volume={36}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0001280450&partnerID=MN8TOARS}, number={24}, journal={Inorganic Chemistry}, author={Castellano, F.N. and Malak, H. and Gryczynski, I. and Lakowicz, J.R.}, year={1997}, pages={5548–5551} }
 @article{stipkala_castellano_heimer_kelly_livi_meyer_1997, title={Light-Induced Charge Separation at Sensitized Sol-Gel Processed Semiconductors}, volume={9}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0001223767&partnerID=MN8TOARS}, number={11}, journal={Chemistry of Materials}, author={Stipkala, J.M. and Castellano, F.N. and Heimer, T.A. and Kelly, C.A. and Livi, K.J.T. and Meyer, G.J.}, year={1997}, pages={2341–2353} }
 @article{argazzi_bignozzi_heimer_castellano_meyer_1997, title={Light-induced charge separation across Ru(II)-modified nanocrystalline TiO2 interfaces with phenothiazine donors}, volume={101}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0000519579&partnerID=MN8TOARS}, number={14}, journal={Journal of Physical Chemistry B}, author={Argazzi, R. and Bignozzi, C.A. and Heimer, T.A. and Castellano, F.N. and Meyer, G.J.}, year={1997}, pages={2591–2597} }
 @article{malak_gryczynski_lakowicz_meyers_castellano_1997, title={Long-lifetime metal-ligand complexes as luminescent probes for DNA}, volume={7}, ISSN={1053-0509 1573-4994}, url={http://dx.doi.org/10.1007/bf02760501}, DOI={10.1007/bf02760501}, abstractNote={We examined the intensity and anisotropy decays of DNA labeled with two ruthenium metal-ligand complexes, [Ru(bpy)2(dppz)]2+ and [Ru(phe)2(dppz)]2+. Both complexes display high emission anisotropies in the absence of rotational diffusion, making them suitable probes for rotational motions. When bound to DNA, these complexes display decay times as long as 294 ns, providing long-lived probes of DNA dynamics. The decay times of both complexes were rather insensitive to dissolved oxygen. We examined anisotropy decays of these complexes bound to B-form DNA. The anisotropy decays revealed correlation times near 10, 50, and several hundred nanoseconds, suggesting that these probes are sensitive to a wide range of DNA motions. The use of metal-ligand complexes should allow resolution of both the torsional and bending motions of DNA, the latter of which has been mostly inaccessible using shorter-lived fluorescent probes bound to DNA.}, number={2}, journal={Journal of Fluorescence}, publisher={Springer Science and Business Media LLC}, author={Malak, Henryk and Gryczynski, Ignacy and Lakowicz, Joseph R. and Meyers, Gerald J. and Castellano, Felix N.}, year={1997}, month={Jun}, pages={107–112} }
 @article{malak_castellano_gryczynski_lakowicz_1997, title={Two-photon excitation of ethidium bromide labeled DNA}, volume={67}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0030831009&partnerID=MN8TOARS}, DOI={10.1016/S0301-4622(97)00017-3}, abstractNote={We examined the steady state and time-resolved emission of DNA stained with ethidium bromide (EB) when excited with 90 fs pulses from a mode-locked titanium sapphire laser. Over the wavelength range from 840 to 880 nm EB-DNA was found to display two-photon excitation, with a cross-section near 7 x 10(-50) cm4s/photon. Frequency-domain intensity decay measurements revealed similar multi-exponential intensity decays for one- and two-photon excitation. Time-resolved anisotropy decay measurements revealed similar correlation times, but different amplitudes as has been observed previously for two- versus one-photon excitation. These results indicate that two-photon excitation of EB-DNA can be accomplished with the fundamental output of a Ti:sapphire laser without obvious heating or perturbation of the DNA.}, number={1-3}, journal={Biophysical Chemistry}, author={Malak, H. and Castellano, F.N. and Gryczynski, I. and Lakowicz, J.R.}, year={1997}, pages={35–41} }
 @article{castellano_meyer, title={Light-Induced Processes in Molecular Gel Materials}, DOI={10.1002/9780470166451.ch4}, abstractNote={This chapter contains sections titled: Introduction Sol-Gel Materials Sol-Gel Optics Artificial Photosynthetic Gel Materials Future Directions}, journal={Progress in Inorganic Chemistry}, publisher={Wiley-Blackwell}, author={Castellano, Felix N. and Meyer, Gerald J.}, pages={167–208} }
 @book{castellano_meyer_1996, title={Light-induced processes in molecular gel materials}, volume={44}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-53249100834&partnerID=MN8TOARS}, journal={Progress in Inorganic Chemistry}, author={Castellano, F.N. and Meyer, G.J.}, year={1996}, pages={167–208} }
 @article{ruthkosky_castellano_meyer_1996, title={Photodriven Electron and Energy Transfer from Copper Phenanthroline Excited States}, volume={35}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0000482638&partnerID=MN8TOARS}, number={22}, journal={Inorganic Chemistry}, author={Ruthkosky, M. and Castellano, F.N. and Meyer, G.J.}, year={1996}, pages={6406–6412} }
 @article{lakowicz_malak_gryczynski_castellano_meyer_1995, title={DNA Dynamics Observed With Long-Lifetime Metal-Ligand Complexes}, volume={1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84984260086&partnerID=MN8TOARS}, DOI={10.1002/bspy.350010302}, abstractNote={AbstractMeasurements of DNA dynamics are typically limited to the nanosecond timescale because of the nanosecond decay times of commonly used fluorophores such as ethidium bromide and acridine derivatives. We show that the time‐resolved anisotropy measurements can be extended to the submicrosecond timescale using metal‐ligand complexes. The ruthenium complex [Ru(2,2′,‐bipyridine)2(dipyrido[3,2‐a : 2′,3′‐c]phenazine)]2+, or [Ru(bpy)2(dppz)]2+, was found to display high anisotropy near 0.2, at −60°C in 100% glycerol, when excited in its long‐wavelength absorption bands. The decay time of [Ru(bpy)2(dppz)]2+ when bound to DNA is over 100 ns, allowing intensity to be measured to over 400 ns. Other Ru complexes display still longer lifetimes to 750 ns when bound to DNA. This class of fluorophores should enable measurement of DNA dynamics over a wide range of times (from 1 ns to several μs), which were previously inaccessible using time‐resolved fluorescence. © 1995 John Wiley & Sons, Inc.}, number={3}, journal={Biospectroscopy}, author={Lakowicz, J.R. and Malak, H. and Gryczynski, I. and Castellano, F.N. and Meyer, G.J.}, year={1995}, pages={163–168} }
 @article{castellano_meyer_1995, title={Dynamic electron transfer in aquo- and alco-SiO2 gels}, volume={99}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33751155534&partnerID=MN8TOARS}, number={40}, journal={Journal of Physical Chemistry}, author={Castellano, F.N. and Meyer, G.J.}, year={1995}, pages={14742–14748} }
 @article{argazzi_bignozzi_heimer_castellano_meyer_1995, title={Long-lived photoinduced charge separation across nanocrystalline TiO2 interfaces}, volume={117}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-1542797788&partnerID=MN8TOARS}, number={47}, journal={Journal of the American Chemical Society}, author={Argazzi, R. and Bignozzi, C.A. and Heimer, T.A. and Castellano, F.N. and Meyer, G.J.}, year={1995}, pages={11815–11816} }
 @article{castellano_ruthkosky_meyer_1995, title={Photodriven energy transfer from cuprous phenanthroline derivatives}, volume={34}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0002294960&partnerID=MN8TOARS}, number={1}, journal={Inorganic Chemistry}, author={Castellano, F.N. and Ruthkosky, M. and Meyer, G.J.}, year={1995}, pages={3–4} }
 @article{argazzi_bignozzi_heimer_castellano_meyer_1994, title={Enhanced spectral sensitivity from ruthenium(II) polypyridyl based photovoltaic devices}, volume={33}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33751158856&partnerID=MN8TOARS}, number={25}, journal={Inorganic Chemistry}, author={Argazzi, R. and Bignozzi, C.A. and Heimer, T.A. and Castellano, F.N. and Meyer, G.J.}, year={1994}, pages={5741–5749} }
 @article{castellano_heimer_tandhasetti_meyer_1994, title={Photophysical properties of ruthenium polypyridyl photonic SiO2 gels}, volume={6}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0000082516&partnerID=MN8TOARS}, number={7}, journal={Chemistry of Materials}, author={Castellano, F.N. and Heimer, T.A. and Tandhasetti, M.T. and Meyer, G.J.}, year={1994}, pages={1041–1048} }
 @article{castellano_stipkala_friedman_meyer_1994, title={Spectroscopic and excited-state properties of titanium dioxide gels}, volume={6}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0001039521&partnerID=MN8TOARS}, number={11}, journal={Chemistry of Materials}, author={Castellano, F.N. and Stipkala, J.M. and Friedman, L.A. and Meyer, G.J.}, year={1994}, pages={2123–2129} }
 @article{castellano_he_greenaway_1993, title={Hydroxyl radical production in the reactions of copper-containing amine oxidases with substrates}, volume={1157}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0027270510&partnerID=MN8TOARS}, DOI={10.1016/0304-4165(93)90060-L}, abstractNote={Solutions of porcine kidney diamine oxidase, PKDAO, and bovine plasma amine oxidase, BPAO, were saturated with the spin-trapping agent alpha-phenyl-N-t-butylnitrone, PBN, and incubated with cadaverine or benzylamine substrate, respectively, under aerobic conditions. EPR spectra due to trapped hydroxyl radicals were obtained for both enzymes with no evidence of superoxide formation. Under anaerobic conditions, hydroxyl radicals were formed only when H2O2 was present as well as substrate. Catalase prevented hydroxyl radical formation by PKDAO but not BPAO. The results indicate that hydroxyl radical is produced in the reaction of the product H2O2 with the reduced enzymes and therefore may be important in turnover-related enzyme degradation, but is not a true reaction intermediate.}, number={3}, journal={BBA - General Subjects}, author={Castellano, F.N. and He, Z. and Greenaway, F.T.}, year={1993}, pages={162–166} }