Construction of a flexible D-A covalent organic framework for enhanced photocatalytic activity

[Display omitted] •A novel flexible D-A catalyst was synthesized through solvothermal method.•Presented excellent catalytic performance in the photosynthesis of benzimidazole.•Exhibited good stability after recycling experiments.•A possible catalytic mechanism was speculated. Covalent organic frameworks (COFs) are promising crystalline materials for photocatalytic organic transformations. It has been reported that the donor–acceptor (D-A) structure is favorable for the separation of photogenerated carriers, while the impact of flexible monomers on the optoelectronic performance and photocatalytic property of D-A COF remains unclear. Accordingly, a novel flexible D-A COF was synthesized by the Schiff-base condensation reaction of thieno [3,2-b] thiophene-2,5-dicarboxaldehyde (TTDC) with 2,4,6-tri (4-aminophenoxy)-1,3,5-triazine (TPT), named as TPT-COF. While the rigid D-A COF was constructed by the condensation reaction of TTDC with 2,4,6-tris (4-aminophenyl)-1,3,5-triazine (TAPT), named as TTT-COF. Compared with TTT-COF, TPT-COF showed much better catalytic performance for the photosynthesis of benzimidazole. It might be due to its larger interlayer distance and more efficient photogenerated carrier separation and migration. Notably, this newly designed COF also exhibited outstanding stability and tolerance for diverse substrates. This study might provide a rational inspiration for developing efficient COF photocatalysts through the molecular design strategy.