Vinylene-linked covalent organic frameworks with manipulated electronic structures for efficient solar-driven photocatalytic hydrogen production

Vinylene-linked covalent organic frameworks (COFs) are promising photocatalysts owing to their fully conjugated skeletons that facilitate charge carrier mobility. Constructing donor-acceptor (D-A) architectures could further enhance photoinduced charge generation and transport, thus promoting photocatalysis. Therefore, three D-A-type vinylene-linked COFs were fabricated via Knoevenagel polymerization for efficient photocatalysis. By varying the donor moieties from phenyl to 2,5-dimethylbenzene and 3,3’-dimethyl-1,1’-biphenyl in the skeletons, the light-harvesting, optical-bandgap, and charge-transfer properties of the COFs were precisely regulated. All three COFs exhibited attractive photocatalytic hydrogen evolution rates (HERs) upon visible-light irradiation, especially that fabricated using 2,4,6-trimethyl-1,3,5-triazine (TM) and 3,3’-dimethyl[1,1’-biphenyl]-4,4’-dicarboxaldehyde (DMA, TM-DMA-COF). TM-DMA-COF exhibited the strongest D-A interactions, excellent charge-carrier separation and transfer kinetics, and a reduced energy barrier for H2 formation. Thus, it afforded the highest HER of 4300 µmol h−1 gcat−1, surpassing those of most state-of-the-art COF photocatalysts. This study provides a simple and effective protocol for modulating the photocatalytic activities of COFs at the molecular level and an interesting insight into the relationship between structural design and photocatalytic performance.