@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{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{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{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{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{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{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{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}, number={13}, journal={Advanced Energy Materials}, author={Constantinou, I. and Yi, X. P. and Shewmon, N. T. and Klump, E. D. and Peng, C. and Garakyaraghi, S. and Lo, C. K. and Reynolds, J. R. and Castellano, F. N. and So, F.}, year={2017} }
 @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{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} }