James McCusker

There has been considerable renewed interest in the photophysical properties of first-row transition metal complexes, driven in part by a long-standing desire to shift to earth-abundant materials for use in a variety of photolytic applications. A significant challenge to achieving this goal is the fundamental difference in the excited-state properties of first-row metal complexes as compared to their second- and third-row congeners following light absorption.1,2 Our group has been working on understanding the origins of this difference to develop design principles that will assist in overcoming these intrinsic challenges and develop new paradigms for the creation of photo-active first-row chromophores for use in a broad range of settings. This presentation will provide a brief survey of the work we have been engaged in over the past several years employing a combination of synthetic chemistry, ultrafast spectroscopy, and theory.3 Topics to be covered include the application of semi-classical Marcus theory for understanding the photophysics of this class of chromophores, which in turn has led to insights relevant for photoredox catalysis that underscore advantages when operating in the so-called inverted region4-6 versus possible limitations that must be considered when those dynamics are occurring in the normal region.7 The role of spin-state and reorganization energy – which become significant when leveraging reactivity from metal-centered, ligand-field excited states8 – as well as recent work9 suggesting the possibility of accessing reactivity from excited states other than the lowest-energy excited state of a given compound will also be discussed.

References
1.    McCusker, J.K. Science 2019, 363, 484-488.
2.   For an excellent survey of work on d6-based systems, see: Sinha, N.; Wenger, O. J. Am. Chem. Soc. 2023, 145, 4503-4520.
3.   For a recent overview of our work in this area as it applies to photoredox catalysis, see: Alowakennu, M.M.; Bowers, B.E.; Pfund, B.; McCusker, J.K. Acc. Chem. Res. 2026, 59, 2462-2473.
4.   Alowakennu, M.M.; Ghosh, A.; McCusker, J.K. J. Am. Chem. Soc. 2023, 145, 20786-20791.
5.   Ghosh, A.; Yarranton, J.T.; McCusker, J.K. Nat. Chem. 2024, 16, 1665-1672.
6.   Chan, A.Y.; Ghosh, A.; Yarranton, J.T.; Twilton, J.; Jin, J.; Arias-Rotondo, D.M.; Sakai, H.A.; McCusker, J.K.; MacMillan, D.W.C. Science2023, 382, 191-197.
7.   Bowers, B.E.; McCusker, J.K., Nat. Chem., submitted for publication.
8.   Bowers, B.E.; Pfund, B.; Beissel, H.F.; Ghosh, A.; McCusker, J.K. J. Am. Chem. Soc. 2025, 147, 39898-39911.
9.   Ghosh, A.; Pfund, B.; Yarranton, J.T.; Lien, Y.-J.; McCusker, J.K. J. Am. Chem. Soc. 2026, 148, 23879-23890.