Linker Length Engineering toward Enhanced Photocatalytic Aerobic Oxidation in Benzothiadiazole-Based Covalent Organic Frameworks

The intrinsic structural advantages and tunability of covalent organic frameworks (COFs) have made them promising photocatalysts for various photocatalytic reactions. However, it remains a great challenge to systematically tune the linker lengths and to build a linker-length-dependent structure-performance relationship of COFs-based photocatalysts. Herein, five isoreticular COFs with sql underlying nets have been successfully synthesized using benzothiadiazole-based ditopic aldehydes with varied linker lengths and 1,3,6,8-tetrakis(4-aminophenyl)pyrene as organic building units. The five obtained COFs exhibit significantly different activities toward photocatalytic aerobic oxidation. Remarkably, the COF-containing vinyl group, HIAM-0020, exhibited the best photocatalytic performance with near-unity conversion and selectivity for photocatalytic oxidative benzylamine coupling within 2 h. The experimental and theoretical investigations indicate that HIAM-0020 exhibits faster charge separation ability and lower charge migration resistance compared with the other four COFs. This work represents promising guidance for the rational design and synthesis of COF-based photocatalysts to achieve efficient organic transformation.