Acceptor Strength Modulates Keto‐Enol Tautomerism in Donor–Acceptor COFs for Enhanced Photocatalytic Aerobic Oxidation

Abstract

Abstract Donor–acceptor (D–A) covalent organic frameworks (COFs) have shown significant potential for photocatalytic applications; however, their performance is often hindered by limited charge separation efficiency. In this work, this challenge was addressed through dynamic modulation of keto–enol tautomerism in COFs by employing an acceptor‐strength tuning approach. Three D–A COFs (B‐COF, S‐COF, and dimethylsulfone DS‐COF) were synthesized using triformylphloroglucinol (TP) combined with systematically tuned diamine acceptors containing benzidine (B), sulfone (S), and dimethyl S groups. Both experimental and theoretical investigations reveal that the strongly electron‐withdrawing S group in S‐COF shifts the tautomeric equilibrium toward the keto form (O═C─C═C─N), thereby enhancing π‐conjugation and promoting more efficient charge separation. As a result, S‐COF exhibits a prolonged exciton lifetime of 2.4 ns and a reduced charge‐transfer resistance, delivering superior catalytic performance compared to B‐COF and DS‐COF in four distinct aerobic transformation reactions. Notably, S‐COF achieves up to 95% isolated yield in aldoxime dehydration. Mechanistic studies further confirm that keto‐form predominance, induced by the acceptor group, plays a pivotal role in generating reactive oxygen species (ROS). This work demonstrates a dynamic structural modulation strategy for optimizing D–A COFs and provides valuable insight for the rational design of next‐generation photocatalytic materials.