@article{3dab4ba4da1543d7a5e8eaef2508b0c8,
title = "Excited-State Identification of a Nickel-Bipyridine Photocatalyst by Time-Resolved X-ray Absorption Spectroscopy",
abstract = "Photoassisted catalysis using Ni complexes is an emerging field for cross-coupling reactions in organic synthesis. However, the mechanism by which light enables and enhances the reactivity of these complexes often remains elusive. Although optical techniques have been widely used to study the ground and excited states of photocatalysts, they lack the specificity to interrogate the electronic and structural changes at specific atoms. Herein, we report metal-specific studies using transient Ni L- and K-edge X-ray absorption spectroscopy of a prototypical Ni photocatalyst, (dtbbpy)Ni(o-tol)Cl (dtb = 4,4′-di-tert-butyl, bpy = bipyridine, o-tol = ortho-tolyl), in solution. We unambiguously confirm via direct experimental evidence that the long-lived (∼5 ns) excited state is a tetrahedral metal-centered triplet state. These results demonstrate the power of ultrafast X-ray spectroscopies to unambiguously elucidate the nature of excited states in important transition-metal-based photocatalytic systems.",
author = "Wallick, {Rachel F.} and Sagnik Chakrabarti and Burke, {John H.} and Richard Gnewkow and Chae, {Ju Byeong} and Rossi, {Thomas C.} and Ioanna Mantouvalou and Birgit Kanngie{\ss}er and Mattis Fondell and Sebastian Eckert and Conner Dykstra and Smith, {Laura E.} and Josh Vura-Weis and Mirica, {Liviu M.} and {van der Veen}, {Renske M.}",
note = "This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Numbers DE-SC0018904 (J.V.W., L.M.M., R.F.W.) and DE-SC0021062 (C.D.). This work was supported by a Packard Fellowship in Science and Engineering from the David and Lucile Packard Foundation (R.M.v.d.V., R.F.W.) and by NSF CHE-2155160 (L.M.M., S.C., J.B.C.). J.H.B. acknowledges support by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE21-46756 and the Robert C. and Carolyn J. Springborn Endowment for Student Support Program. Solid-state NEXAFS spectroscopy was carried out with the support of Diamond Light Source, beamline B07-C (proposal cm31118-3). The authors acknowledge assistance from Frank de Groot and Matthijs van Spronsen with this measurement. Solution-phase L-edge measurements were carried out at the UE52_SGM beamline, nmTransmission NEXAFS end station at the BESSY II electron storage ring operated by the Helmholtz-Zentrum Berlin fu\u0308r Materialien und Energie GmbH. We would like to thank Robby Bu\u0308chner for assistance during the experiment. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We would like to thank Xiaoyi Zhang, Rick Spence, Burak Guzelturk, and Jin Yu for assistance during the experiment.",
year = "2024",
month = may,
day = "9",
doi = "10.1021/acs.jpclett.4c00226",
language = "English (US)",
volume = "15",
pages = "4976--4982",
journal = "Journal of Physical Chemistry Letters",
issn = "1948-7185",
publisher = "American Chemical Society",
number = "18",
}