Intrinsically Inhibiting Singlet Quenching of Organic Sensitizers for Enhanced CO₂ Photoreduction

High-performance, precious-metal-free photosensitizers (PSs) are crucial for driving photocatalytic CO₂ reduction (PCO₂R) in an efficient and sustainable manner. Organic PSs exhibiting thermally activated delayed fluorescence (TADF) are particularly promising owing to their ideal photophysics and well-understood electron-transfer mechanisms. However, rational improvement via structural design remains elusive. In this study, we present a comparative study on three TADF-type PSs for precious-metal-free PCO₂R. Our results reveal that the kinetic competition between intersystem crossing (ISC) and singlet excited-state quenching determines the utilization efficiency of the long-lived triplet state, a key species to enable high cage-escape yield and eventually the PCO₂R performance. Guided by this principle, we have developed a Br-substituted PS derived from 1,3-dicyano-2,4,5,6-tetrakis(diphenylamino)-benzene, in which the heavy-atom effect ensures rapid ISC while avoids reinforcing singlet quenching. Such strong steering toward triplet utilizations has led to record-high quantum yields near 50% for complete CO production with a cobalt catalyst, significantly surpassing the performances of precious-metal benchmarks (Ru and Ir-based) and most documented organic PS-driven systems.