@article{d0cd7a7bf20340da86ac859a3fd50e63,
title = "Ion-pair reorganization regulates reactivity in photoredox catalysts",
abstract = "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 (BArF4−). 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. These results suggest that ion pairing could be an underappreciated factor that modulates reactivity in ionic photoredox catalysts. [Figure not available: see fulltext.].",
author = "Earley, {J. D.} and A. Zieleniewska and Ripberger, {H. H.} and Shin, {N. Y.} and Lazorski, {M. S.} and Mast, {Z. J.} and Sayre, {H. J.} and McCusker, {J. K.} and Scholes, {G. D.} and Knowles, {R. R.} and Reid, {O. G.} and G. Rumbles",
note = "Funding Information: This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the US Department of Energy (DOE) under contract number DE-AC36-08GO28308. Funding was provided by the US Department of Energy, Office of Science, as part of BioLEC EFRC under grant DE-SC0019370. The views expressed in the article do not necessarily represent the views of the DOE or the US Government. The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for US Government purposes. This article is submitted in fond memory of the late John Warman (TU Delft, Netherlands, 1939–2020), whose seminal research laid the foundation for transient microwave spectroscopy, and the dielectric loss spectroscopy that is described here. Funding Information: This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the US Department of Energy (DOE) under contract number DE-AC36-08GO28308. Funding was provided by the US Department of Energy, Office of Science, as part of BioLEC EFRC under grant DE-SC0019370. The views expressed in the article do not necessarily represent the views of the DOE or the US Government. The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for US Government purposes. This article is submitted in fond memory of the late John Warman (TU Delft, Netherlands, 1939–2020), whose seminal research laid the foundation for transient microwave spectroscopy, and the dielectric loss spectroscopy that is described here. Publisher Copyright: {\textcopyright} 2022, The Author(s), under exclusive licence to Springer Nature Limited.",
year = "2022",
month = jul,
doi = "10.1038/s41557-022-00911-6",
language = "English (US)",
volume = "14",
pages = "746--753",
journal = "Nature Chemistry",
issn = "1755-4330",
publisher = "Nature Publishing Group",
number = "7",
}