Visible-Light-Driven ROS-Engineered Switchable Photocatalysis: Cross-Coupling versus Homo-Coupling Reactions

Visible-light-driven photocatalysis offers a sustainable platform for promoting challenging chemical transformations under benign reaction conditions; however, both precise control over the generation of reactive oxygen species (ROS) and their reactivity- and selectivity-guided chemistry remain significant challenges. Herein, we report a series of distinct [Co-M3] heterobimetallic coordination complexes (HCCs) (M2+ = Zn, Cd, and Hg) supported by a common Co3+-based metalloligand featuring benzimidazole rings. In this design, a metalloligand acts as a light-harvesting unit, while the secondary metals modulate charge distribution, excited-state dynamics, and catalytic activity. Comprehensive structural, spectroscopic, and electrochemical investigations reveal that systematic variation of the secondary metals tunes the band-edge positions and governs the ROS-generation pathways. The [Co-Zn3] HCC generates both •O2– and •OH, while [Co-Cd3] and [Co-Hg3] HCCs exclusively produce •OH and •O2– radicals, respectively. Metal-dependent ROS generation is supported by both spectral studies and probe-based quantification. The coexistence of •O2– and •OH generated by [Co-Zn3] drives C-S cross-coupling, whereas selective •OH generation by [Co-Cd3] promotes C–C homocoupling, and exclusive •O2– generation in [Co-Hg3] leads to S–S homocoupling. Mechanistic studies establish that the cross-coupling reaction requires the cooperative action of both ROS, whereas the exclusive generation of a single ROS drives the homocoupling selectivity. The photocatalysts’ ability to control ROS generation enables precise switching between distinct transformations under visible-light irradiation, while their excellent stability, recyclability, and heterogeneous behavior further enhance their catalytic performance. Overall, this work demonstrates that rational design enables fine control over excited-state processes and ROS chemistry, providing a powerful strategy for achieving predictable and switchable photocatalysis with earth-abundant metals.