The enhancement of photocatalytic hydrogen evolution in imine-linked pyrene-based covalent organic frameworks through the regulation of active site distances

Photocatalytic hydrogen (H₂) evolution represents an effective strategy to alleviate the increasingly serious energy shortage and environmental pollution. Recently, covalent organic frameworks (COFs) have gradually attracted attention in designing advanced polymeric photocatalysts and exhibited great potential in the field of photocatalytic H₂ evolution. Herein, four pyrene-based COFs were prepared with nitrogen active sites featuring a gradually increased distance in the imine bonds and their photocatalytic H₂ production performance was then investigated. The results showed that an appropriate distance between the active sites in pyrene-based COFs is conducive to significantly enhancing charge separation efficiency and improving photocatalytic H₂ production performance. Through the synergistic effect of protonation and the optimum active site distance, the optimal Py-COF-3 (AC) demonstrated a remarkable H₂ evolution rate of 19.6 mmol g⁻¹ h⁻¹ for at least 12 hours. This study provides a molecular-structure design to regulate the nitrogen active site distance and presents an effective method to enhance the catalytic performance of COF-based photocatalysts.