@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={Photoexcited 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{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{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={In this work, a series of eight similarly structured perinone chromophores were synthesized and photophysically characterized to elucidate the electronic and structural tunability of their excited state properties, including excited state redox potentials and fluorescence lifetimes/quantum yields. Despite their similar structure, these chromophores exhibited a broad range of visible absorption properties, quantum yields, and excited state lifetimes. In conjunction with static and time-resolved spectroscopies from the ultrafast to nanosecond time regimes, time-dependent computational modeling was used to correlate this behavior to the relationship between non-radiative decay and the energy-gap law. Additionally, the ground and excited state redox potentials were calculated and found to be tunable over a range of 1 V depending on the diamine or anhydride used in their synthesis (Ered* = 0.45-1.55 V; Eox* = -0.88 to -1.67 V), which is difficult to achieve with typical photoredox-active transition metal complexes. These diverse chromophores can be easily prepared, and with their range of photophysical tunability, will be valuable for future use in photofunctional applications.}, 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{chakraborty_lahiri_wilson_2020, title={A STATISTICAL ANALYSIS OF NOISY CROWDSOURCED WEATHER DATA}, volume={14}, ISSN={["1932-6157"]}, DOI={10.1214/19-AOAS1290}, abstractNote={Spatial prediction of weather elements like temperature, precipitation, and barometric pressure are generally based on satellite imagery or data collected at ground stations. None of these data provide information at a more granular or "hyperlocal" resolution. On the other hand, crowdsourced weather data, which are captured by sensors installed on mobile devices and gathered by weather-related mobile apps like WeatherSignal and AccuWeather, can serve as potential data sources for analyzing environmental processes at a hyperlocal resolution. However, due to the low quality of the sensors and the nonlaboratory environment, the quality of the observations in crowdsourced data is compromised. This paper describes methods to improve hyperlocal spatial prediction using this varying-quality, noisy crowdsourced information. We introduce a reliability metric, namely Veracity Score (VS), to assess the quality of the crowdsourced observations using a coarser, but high-quality, reference data. A VS-based methodology to analyze noisy spatial data is proposed and evaluated through extensive simulations. The merits of the proposed approach are illustrated through case studies analyzing crowdsourced daily average ambient temperature readings for one day in the contiguous United States.}, number={1}, journal={ANNALS OF APPLIED STATISTICS}, author={Chakraborty, Arnab and Lahiri, Soumendra Nath and Wilson, Alyson}, year={2020}, month={Mar}, pages={116–142} }
 @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 Å for 1 vs 2.85 Å for 2) and molecular shape (1 in an "A" frame vs 2 in an "H" frame). Because the electronic coupling between the two Pt atoms determines the energy splitting of the bonding σ and antibonding σ* orbital, the Pt–Pt stretching mode coupled to the MMLCT transition changes the inter Pt distance from that of the ground state. Interestingly, while 1 shows a single Pt–Pt stretching frequency of 120 cm–1 in the MMLCT state, 2 exhibits multiple downshifted frequencies (80 and 105 cm–1) in the MMLCT state along with a shorter vibrational dephasing time than 1. Based on the ground state optimized structures and Raman calculations, the changes evident in the vibrational wavepacket dynamics in 2 are closely correlated with the "H" framed geometry in 2 compared to the "A" frame in 1, leading to the sharp increase in π–π interaction between ppy ligands. Although the TA experiments do not directly reveal the ultrafast intersystem crossing (ISC) because of a strong coherent spike at early time scales, the dependence of the vibrational wavepacket dynamics on molecular geometry can be understood based on previously proposed potential energy surfaces as a function of Pt–Pt distance, suggesting that the interaction between the cyclometalating ligands can be a key factor in determining the Pt–Pt shortening and the related energy relaxation dynamics in the Pt(II) dimers. Further experiments using femtosecond broadband TA and X-ray scattering spectroscopy are planned to investigate directly the ISC and Pt–Pt contraction to support the relationship between ground state molecular geometry and photoinduced structural changes in the Pt(II) dimers.}, 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{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. This structural arrangement resulted in quantitative quenching of the highly fluorescent PMI chromophore by introducing metal character into the lowest energy singlet state, thereby leading to the formation of a long-lived PMI-ligand localized triplet excited state (τ = 8.4 μs). Even though the phosphorescence from this triplet state was not observed, highly efficient quenching of this excited state by dissolved oxygen and the observation of singlet oxygen photoluminescence in the near-IR at 1270 nm initially pointed towards triplet excited state character. Additionally, the coincidence of the excited state absorbance difference spectra from the sensitized PMI ligand using a triplet donor and the Pt-PMI complex provided strong evidence for this triplet state assignment, which was further supported by TD-DFT calculations.}, 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{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(<sc>ii</sc>) 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{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} }