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

Photocatalytic HO 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 HO production activity exhibiting a negative correlation to the Hammett parameters (σ) of the -R groups. Notably, the COF-OH and COF-OMe, bearing the strong electron-donating group, achieve a remarkable HO 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 HO production and advances the development of sustainable photocatalytic materials.