Electronic Trap State Engineered Covalent Organic Frameworks for Programmable Selectivity of Photocatalytic Molecular...

Covalent organic frameworks (COFs) with ordered π skeletons and aligned nanopores could be ideal photocatalytic materials for molecular oxygen activation. Achieving selective generation of specific reactive oxygen species (ROS), such as superoxide radicals (O₂^•-) and singlet oxygen (¹O₂), has remained a challenge in precision photocatalysis. Herein, we report an electronic trap engineering strategy to control ROS selectivity in COFs. It was found that perturbation of the density of carbonyl groups and the partial linkage tautomerization can systematically tune the energy depth of electron traps. Based on this finding, a series of topologically analogous COFs have been designed and synthesized. Among these COFs, COF-HNU60, featuring shallow traps, facilitates stepwise charge separation that enables a sequential redox process to ¹O₂. By contrast, the deep traps in COF-HNU70 and COF-HNU80 stabilize photogenerated electrons and promote selective accumulation of O₂^•-̅ by halting further oxidation. A series of advanced photocatalytic oxidation reactions highlight distinct ROS pathways correlated with trap energy level. Mechanistic studies reveal that the energy depth of electron traps mainly dictates charge separation kinetics and carrier lifetime, thereby governing the selective evolution of O₂^•-̅ and ¹O₂. This work provides a new design principle for COF-based photocatalysts by highlighting the role of trap energy levels in tuning ROS selectivity.