Ion-pair reorganization regulates reactivity in photoredox catalysts

Earley, J. D.; Zieleniewska, A.; Ripberger, H. H.; Shin, N. Y.; Lazorski, M. S.; Mast, Z. J.; Sayre, H. J.; McCusker, J. K.; Scholes, G. D.; Knowles, R. R.; Reid, Obadiah G.; Rumbles, Garry

doi:10.1038/s41557-022-00911-6

Ion-pair reorganization regulates reactivity in photoredox catalysts

Journal Article · Thu Apr 14 00:00:00 EDT 2022 · Nature Chemistry

DOI:https://doi.org/10.1038/s41557-022-00911-6· OSTI ID:1863582

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National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Colorado, Boulder, CO (United States); National Renewable Energy Laboratory
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Princeton Univ., NJ (United States)
National Renewable Energy Lab. (NREL), Golden, CO (United States); Metropolitan State Univ. of Denver, CO (United States)
Michigan State Univ., East Lansing, MI (United States)
National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Colorado, Boulder, CO (United States)

Cyclometalated and polypyridyl complexes of d₆ metals are promising photoredox catalysts, using light to drive reactions with high kinetic or thermodynamic barriers via the generation of reactive radical intermediates. However, while tuning of their redox potentials, absorption energy, excited-state lifetime and quantum yield are well-known criteria for modifying activity, other factors could be important. Here we show that dynamic ion-pair reorganization controls the reactivity of a photoredox catalyst, [Ir[dF(CF₃)ppy]₂(dtbpy)]X. Time-resolved dielectric-loss experiments show how counter-ion identity influences excited-state charge distribution, evincing large differences in both the ground- and excited-state dipole moment depending on whether X is a small associating anion (PF₆^–) that forms a contact-ion pair versus a large one that either dissociates or forms a solvent-separated pair (BAr^F₄^–). These differences correlate with the reactivity of the photocatalyst toward both reductive and oxidative electron transfer, amounting to a 4-fold change in selectivity toward oxidation versus reduction. Furthermore, these results suggest that ion pairing could be an underappreciated factor that modulates reactivity in ionic photoredox catalysts.

View Accepted Manuscript (DOE)

Research Organization:: Energy Frontier Research Centers (EFRC) (United States).Bio-inspired Light-Escalated Chemistry (BioLEC); National Renewable Energy Laboratory (NREL), Golden, CO (United States); Princeton Univ., NJ (United States)

Sponsoring Organization:: USDOE Office of Science (SC)

Grant/Contract Number:: AC36-08GO28308; SC0019370

OSTI ID:: 1863582

Alternate ID(s):: OSTI ID: 1865121

Journal Information:: Nature Chemistry, Journal Name: Nature Chemistry Vol. 14; ISSN 1755-4330

Publisher:: Nature Publishing GroupCopyright Statement

Country of Publication:: United States

Language:: English

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