Engineering Photo‐Controlled Dynamic Conjugation Switching in Azine‐Linked Covalent Organic Frameworks for Boosted Photocatalysis

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.