Linker\nLength Engineering toward Enhanced Photocatalytic\nAerobic Oxidation in Benzothiadiazole-Based Covalent Organic Frameworks

The intrinsic structural advantages and tunability of\ncovalent\norganic frameworks (COFs) have made them promising photocatalysts\nfor various photocatalytic reactions. However, it remains a great\nchallenge to systematically tune the linker lengths and to build a\nlinker-length-dependent structure-performance relationship of COFs-based\nphotocatalysts. Herein, five isoreticular COFs with sql underlying\nnets have been successfully synthesized using benzothiadiazole-based\nditopic aldehydes with varied linker lengths and 1,3,6,8-tetrakis(4-aminophenyl)pyrene\nas organic building units. The five obtained COFs exhibit significantly\ndifferent activities toward photocatalytic aerobic oxidation. Remarkably,\nthe COF-containing vinyl group, HIAM-0020, exhibited the best photocatalytic\nperformance with near-unity conversion and selectivity for photocatalytic\noxidative benzylamine coupling within 2 h. The experimental and theoretical\ninvestigations indicate that HIAM-0020 exhibits faster charge separation\nability and lower charge migration resistance compared with the other\nfour COFs. This work represents promising guidance for the rational\ndesign and synthesis of COF-based photocatalysts to achieve efficient\norganic transformation.