@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{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{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{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{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{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{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{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{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{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{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{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={Abstract}, 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} }