Regulating local polarization in truxenone-based covalent organic frameworks for boosting photocatalytic hydrogen evolution

The high local charge delocalization and strong dipole moment are two key factors that affect the photocatalytic hydrogen evolution over covalent organic frameworks (COFs)-based photocatalysts. However, there is a scarcity of reports that systematically investigate the structure–function relationship of these factors based on precise structural models. Herein, this study proposes a novel strategy for evaluating local charge delocalization using three rationally designed truxenone-based COFs. By controlling the structure and dipole of the monomers at the molecular level, we aim to investigate the structure–function relationship of these COFs concerning local charge delocalization. Among the different truxenone-based COFs evaluated, 1,3,5-tris (p-formyl phenyl) benzene-based COF (TeTpb-COF) exhibits the highest hydrogen evolution rate of 21.6 mmol g−1 h−1, resulting in a 108-fold improvement in photocatalytic hydrogen evolution performance compared with that of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine-based COF (TeTt-COF, 0.2 mmol g−1 h−1). This enhancement can be attributed to the strong intramolecular built-in electric field, which facilitates the efficient separation of photogenerated charges in the donor–acceptor (D–A) block units and increases the photoinduced charge migration distance and separation efficiency. This work highlights the strategy of adjusting the building blocks to enhance the local dipole moment in truxenone-based COFs, thereby significantly improving photocatalytic hydrogen evolution. The regulation of building blocks offers an opportunity to create a novel COF platform for high-efficiency photocatalytic hydrogen evolution.