Excited-State Identification of a Nickel-Bipyridine Photocatalyst by Time-Resolved X-ray Absorption Spectroscopy

Rachel F. Wallick, Sagnik Chakrabarti, John H. Burke, Richard Gnewkow, Ju Byeong Chae, Thomas C. Rossi, Ioanna Mantouvalou, Birgit Kanngießer, Mattis Fondell, Sebastian Eckert, Conner Dykstra, Laura E. Smith, Josh Vura-Weis, Liviu M. Mirica, Renske M. van der Veen

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)4976-4982
Number of pages7
JournalJournal of Physical Chemistry Letters
Issue number18
StatePublished - May 9 2024

ASJC Scopus subject areas

  • General Materials Science
  • Physical and Theoretical Chemistry


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