Crystallization engineering of imine-linked covalent organic frameworks via amine/aldehyde dual regulation for photocatalytic hydrogen evolution.

Crystallization control offers an effective yet underexplored route to regulate charge-transfer dynamics in covalent organic framework (COF) photocatalysts. Herein, an amine/aldehyde dual-regulator strategy is developed to promote imine exchange and framework rearrangement in a triazine-based COF without altering its parent skeleton. Compared with the pristine and single-regulated analogues, the benzaldehyde and aniline dual-regulated COF (COF-Bz-An) shows enhanced in-plane crystallinity, more ordered π-stacking, and higher pore accessibility. Because light absorption and band energetics are largely preserved, the enhanced photocatalysis is primarily attributed to improved charge-transfer kinetics arising from framework ordering. Mechanistic analyses reveal that the ordered framework reduces defect-associated carrier loss and promotes charge separation and migration. Consequently, COF-Bz-An produces 4.5 times more H2 than the pristine framework and outperforms aniline-regulated COF (COF-An) and benzaldehyde-regulated COF (COF-Bz) by 2.1 and 1.2 times, respectively, while maintaining stable activity over 25 h. This work highlights an effective dual-regulator crystallization engineering for optimizing COF photocatalysts.