Conjugation Lock-In Reinforced Sulfur-Heteropolycyclic Covalent Organic Frameworks with Asymmetric Electron Distribution for Photocatalytic Aerobic Oxidation Reactions.

The development of robust heterogeneous photocatalysts capable of operating under harsh chemical conditions remains a critical yet challenging goal in materials science. Here, we present a postcyclization strategy based on conjugation lock-in reinforcement to construct sulfur-heteropolycyclic covalent organic frameworks (COFs) with asymmetric electron distribution for superior photocatalytic reactions, which is achieved through a consecutive thionation-cyclization-oxidation transformation of N-acylhydrazone precursors using Lawesson's reagent. Systematic characterization reveals that sulfur incorporation endows the framework with enhanced chemical stability, localized asymmetric electron density, rapid charge carrier migration, efficient exciton dissociation, extended π-conjugation, and a well-defined donor-acceptor architecture, collectively leading to significantly improved photocatalytic activity and durability compared to the original hydrazone-linked COF. Consequently, the modified COF exhibits a H₂O₂ evolution rate of 5270 μmol g⁻¹ h⁻¹ in pure water, representing a 3-fold enhancement over the precursor COF (1878 μmol g⁻¹ h⁻¹) and surpassing most reported organic and inorganic competitors. Moreover, it achieves complete conversion of benzylamine within 1 h under mild blue light-emitting diode irradiation, demonstrating high efficiency in aerobic oxidation catalysis. These findings establish the lock-in reinforcement strategy coupled with electronic structure modulation as a versatile route to designing durable and highly active photocatalysts for demanding synthetic and energy-conversion applications.