Synergistic Enhancement of Photoredox Catalysis Beyond the Singlet Bottleneck Through Triplet Charge Recombination and Magnetic Field Effects

Abstract Organic photosensitizers with redox‐active excited states have revitalized photoredox catalysis, but their efficiency is often hindered by spontaneous back electron transfer (BET), particularly in singlet‐driven pathways. Enhancing triplet utilization is therefore critical for improving catalytic performance but remains challenging, especially without structural modifications to the catalyst. Here, using phenothiazine‐type photosensitizers as a model system, we demonstrate a synergistic strategy that enhances reaction efficiency by almost 300%. Triplet charge recombination (TCR) is shown to be significantly promoted within the nonpolar micellar core, enhancing triplet generation and facilitating efficient triplet‐substrate interactions. Furthermore, an external magnetic field is introduced along the triplet pathway to depress BET by inhibiting spin conversion of radical‐ion‐pair intermediates from triplet to singlet. The developed kinetic modeling provides quantitative insights and mechanistic validation of the magnetic field effect. This work establishes a powerful synergistic strategy to control photoredox mechanisms, offering a new framework for advancing catalytic performance.