Activating Triplet Excitons in COFs via Layer-Bridging Co Single Atoms for Photocatalytic H2O2 Production and Tandem C─N Coupling.

Covalent organic frameworks (COFs) are promising photocatalysts for solar energy conversion in energy and environmental applications. However, their performance is intrinsically limited by weak spin-orbit coupling (SOC) arising from van der Waals interlayer interactions, thereby suppressing intersystem crossing and triplet-exciton utilization. In this study, we demonstrate that layer-bridging Co single atoms activate triplet excitons in COFs by synergistically enhancing SOC and inducing energy-level splitting via Co─N coordination. This layer-bridging Co coordination markedly promotes singlet-to-triplet conversion, enabling efficient O2 activation and substantially boosting the generation of both 1O2 and O2 •-. Consequently, the Co-bridged COF achieves highly efficient photocatalytic H2O2 production and tandem C─N coupling. This work establishes layer-bridging single-atom coordination as a promising strategy for regulating triplet-state reactivity in COFs, offering new opportunities for reactive oxygen species (ROS)-mediated photocatalysis and tandem organic transformations.