Thiophene vs. benzene: how π-spacer engineering transforms photocatalytic hydrogen evolution

Abstract

Conjugated porous polymers (CPPs) are promising materials for photocatalysis, yet their efficiency is highly dependent on the rational design of molecular frameworks. Here, we synthesized two donor–π–acceptor (D–π–A) type CPPs using spirobifluorene as the donor and triazine as the acceptor, introducing different π-spacer units, benzene and thiophene, to investigate their effect on photocatalytic activity. The incorporation of thiophene as a π-spacer enhances electron delocalization within the triazine acceptor, effectively reducing charge transfer distance and improving the migration rate of photogenerated carriers. Theoretical calculations reveal that the thiophene-linked polymer (ThSF-CPP) exhibits a narrower bandgap, stronger intramolecular charge transfer, and a higher degree of electron localization at the active sites, facilitating efficient hydrogen evolution. Consequently, ThSF-CPP achieves a high hydrogen evolution rate (HER) of 16.75 mmol h⁻¹ g⁻¹ under full-arc irradiation, with an apparent quantum yield of 7.3% at 475 nm. Upon introducing 3 wt% Pt as a cocatalyst, the HER further increases to 34.65 mmol h⁻¹ g⁻¹. These findings underscore the crucial role of π-spacer engineering in optimizing charge separation and transfer, offering a molecular design strategy for high-performance polymer-based photocatalysts.