Photoredox catalysis relies on light-induced electron transfer leading to a radical pair comprising an oxidized donor and a reduced acceptor in a solvent cage. For productive onward reaction to occur, the oxidized donor and the reduced acceptor must escape from that solvent cage before they undergo spontaneous reverse electron transfer. Here we show the decisive role that cage escape plays in three benchmark photocatalytic reactions, namely, an aerobic hydroxylation, a reductive debromination and an aza-Henry reaction. Using ruthenium(II)- and chromium(III)-based photocatalysts, which provide inherently different cage escape quantum yields, we determined quantitative correlations between the rates of photoredox product formation and the cage escape quantum yields. These findings can be largely rationalized within the framework of Marcus theory for electron transfer.

光氧化还原催化依赖于光诱导的电子转移，导致在溶剂笼中形成包含氧化供体和还原受体的自由基对。为了发生富有成效的后续反应，氧化的供体和还原的受体必须在进行自发反向电子转移之前从溶剂笼中逸出。在这里，我们展示了笼逃逸在三个基准光催化反应中所起的决定性作用，即有氧羟基化、还原脱溴和氮杂亨利反应。使用钌（II）基和铬（III）基光催化剂（它们提供本质上不同的笼逃逸量子产率），我们确定了光氧化还原产物形成速率与笼逃逸量子产率之间的定量相关性。这些发现在很大程度上可以在马库斯电子转移理论的框架内合理化。