Maximizing Photon-to-Electron\nConversion for Atom\nEfficient Photoredox Catalysis

Photoredox catalysis is a powerful tool to access challenging\nand\ndiverse syntheses. Absorption of visible light forms the excited state\ncatalyst (*PC) but photons may be wasted if one of several unproductive\npathways occur. Facile dissociation of the charge-separated encounter\ncomplex [PC<sup>•–</sup>:D<sup>•+</sup>], also\nknown as (solvent) cage escape, is required for productive chemistry\nand directly governs availability of the critical PC<sup>•–</sup> intermediate. Competitive charge recombination, either inside or\noutside the solvent cage, may limit the overall efficiency of a photochemical\nreaction or internal quantum yield (defined as the moles of product\nformed per mole of photons absorbed by PC). Measuring the cage escape\nefficiency (ϕ<sub>CE</sub>) typically requires time-resolved\nspectroscopy; however, we demonstrate how to estimate ϕ<sub>CE</sub> using steady-state techniques that measure the efficiency\nof PC<sup>•–</sup> formation (ϕ<sub>PC</sub>).\nOur results show that choice of electron donor critically impacts\nϕ<sub>PC</sub>, which directly correlates to improved synthetic\nand internal quantum yields. Furthermore, we demonstrate how modest\nstructural differences between photocatalysts may afford a sizable\neffect on reactivity due to changes in ϕ<sub>PC</sub>, and by\nextension ϕ<sub>CE</sub>. Optimizing experimental conditions\nfor cage escape provides photochemical reactions with improved atom\neconomy and energy input, paving the way for sustainable design of\nphotocatalytic systems.