Unprecedented Flux-Mediated Synthesis of Crystalline Polyimide Covalent Organic Frameworks Using the 4-Dimethylaminopyridine (DMAP)-Type Nucleophilic Catalyst for Use in Efficient Photosynthesis of HO.

Photocatalytic HO production from water and O represents a sustainable approach for clean chemical synthesis, but developing efficient and stable photocatalysts remains challenging. Herein, we report a novel 4-dimethylaminopyridine (DMAP)-type nucleophilic catalyst-mediated flux synthesis strategy to prepare crystalline polyimide covalent organic frameworks (PI-COFs) as efficient photocatalysts for HO generation. Interestingly, by introducing molten DMAP as the reaction medium, we achieved three PI-COFs (DMAP-BNCOFs, DMAP-BBCOFs, and DMAP-NNCOFs) with significantly enhanced crystallinity and porosity compared to those obtained in conventional solvothermal synthesis. The optimized PI-COFs showed excellent photocatalytic activity, among which DMAP-BNCOFs could achieve a HO production rate of 8051.4 μmol h g without the presence of any sacrificial agents under visible-light irradiation, representing the most efficient polymeric/framework photocatalysts ever reported. The photocatalyst demonstrated remarkable stability over 90 h of continuous operation with no activity loss. DMAP-BNCOFs exhibited a lower exciton binding energy and longer excited-state lifetime compared with those of DMAP-BBCOFs and DMAP-NNCOFs. Experimental and theoretical studies revealed that enhanced performance stems from the optimal electronic structure, efficient charge separation, and accelerated O activation. This work provides new insights into the flux synthesis approach and rational design of PI-COF photocatalysts and establishes an effective strategy for sustainable HO production.