Tuning Protonation Microenvironments via Edge-Linker Design in One-Dimensional Imine-Linked Covalent Organic Frameworks for Enhanced Photocatalytic Hydrogen Evolution

Protonated covalent organic frameworks (COFs) have attracted considerable attention as promising photocatalysts for hydrogen evolution. Despite significant progress, prior investigations have predominantly targeted protonation at imine linkages, overlooking the broader influence of other structural motifs on the photocatalytic performance. Herein, we propose an “edge-linker engineering” strategy to tune the protonation microenvironment and electronic structure of one-dimensional (1D) imine-linked COFs by incorporating distinct edge linkers: −CH₂–, −O–, and −S–, yielding COF-MDA, COF-ODA, and COF-SDA, respectively. While protonation primarily occurs at imine bonds, the nature of the edge linker profoundly influences the electronic structure of the framework. Notably, the sulfur-containing a −S– linker in COF-SDA significantly enhances charge delocalization and facilitates the hydrogen reduction process. As a result, COF-SDA exhibits the highest hydrogen evolution rate under visible-light irradiation, using ascorbic acid as the protonation reagent, outperforming its analogs. Density functional theory calculations elucidate that the COF-SDA exhibits enhanced hydrogen binding affinity and a reduced energy for proton reduction, highlighting the critical role of edge-linker-mediated electronic modulation. This study establishes a comprehensive structure–function relationship among edge-site design, protonation behavior, and photocatalytic activity in 1D COFs, providing a molecular design paradigm for developing polymer photocatalysts for solar-to-hydrogen conversion.