Micro-Environment Programmable Quinoline COFs for High-Performance Photocatalytic H2O2 Generation and Benzylamine Coupling

Photocatalytic H₂O₂ synthesis from water and oxygen by covalent organic frameworks (COFs) has attracted much attention currently. However, conventional COFs often suffer from insufficient stability and activity due to the unclear structure-activity relationship mechanisms. Herein, a series of quinoline-linked COFs-R (-R = -OH, -OMe, -H, -Br, -CN) synthesized via multi-component reactions (MCRs) is reported to systematically modulate their pore microenvironments and enhance photocatalytic performance. Experimental results reveal that the electron-donating capacity of substituents significantly enhances charge separation efficiency, with H₂O₂ production activity exhibiting a negative correlation to the Hammett parameters (σ_p) of the -R groups. Notably, the COF-OH and COF-OMe, bearing the strong electron-donating group, achieve a remarkable H₂O₂ generation rate of 4458 and 4138 µmol g⁻¹ h⁻¹ in the pure water system. Theoretical calculations confirm that substituents optimize the collective donor structure within the π-conjugated triazine framework, boosting photocatalytic activity. Furthermore, the universal Hammett relationship observed in benzylamine coupling reactions establishes a critical structure-activity model for rational COF design. This work provides fundamental insights into the microenvironment engineering of COFs for efficient H₂O₂ production and advances the development of sustainable photocatalytic materials.