@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{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{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{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{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{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} }