Engineering Photo-Controlled Dynamic Conjugation Switching in Azine-Linked Covalent Organic Frameworks for Boosted...

Photocatalysis holds transformative potential for addressing energy and environmental challenges. Covalent organic frameworks (COFs), with predesignable structures and exceptional light-harvesting capabilities, are promising photocatalysts; however, their catalytic efficiency is critically limited by rapid electron-hole recombination. Herein, we report a dynamic conjugation-switching strategy in azine-linked COFs by regulating the electronic effects of the building blocks. Specifically, we constructed three azine-based COFs using high electron-affinity triphenyltriazine (TPTA) for COF-TPTA, moderate electron-affinity triphenylbenzene (TPB) for COF-TPB, and low electron-affinity triphenylamine (TPA) for COF-TPA. Ultrafast spectroscopy and theoretical calculations reveal a state-dependent conjugation in COF-TPB, characterized by ground-state π-electron localization and excited-state delocalization, leading to a mismatch in its electron structure between the ground and excited states that suppresses carrier recombination. Capitalizing on its optimal conjugation-switching and favorable oxygen reduction dynamics, COF-TPB delivers an H₂O₂ production rate of 1205 µmol g^-1 h^-1 from O₂ and H₂O, outperforming COF-TPTA and COF-TPA by 6.2 and 1.9 times, respectively. Importantly, the generalizability of this mechanism to other azine-based systems allowed for the development of a photocatalyst with a high rate of 1463 µmol g^-1 h^-1. This work pioneers a dynamic electronic-structure engineering paradigm for photocatalyst optimization, offering transformative insights into photocatalyst design.