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