Recent progress on phenothiazine organophotoredox catalysis

Photoredox catalysis has garnered significant attention in recent years due to its broad applicability in visible-light-induced organic transformations. While significant progress has been made in the development of highly oxidizing catalysts, such as acridinium catalysts, there remains a notable shortage of strongly reducing organophotoredox catalysts. Phenothiazines are widely used as photoredox catalysts owing to their unique redox potentials, particularly their low excited-state oxidation potentials (Eox* = −1.35 V to −3.51 V vs. SCE). Thus, they can be applied to a variety of photoredox reactions with oxidative-quenching cycles, and effectively reduce various organic molecules, such as aryl and alkyl halides, alkenes, malonyl peroxides, cobalt complexes, and redox-active esters. Due to their unique properties, this review focuses on the recent advances in phenothiazine organophotoredox catalysis.