Enhanced photocatalytic hydrogen evolution activity: cross-linking density and π linker modulation of pyrene and triazine based conjugated porous polymers

• PyThTz and PyPhTz were synthesized from tetrasubstituted pyrene and triazine derivatives. • PyThTz, featuring thiophene as the π-linker, achieved a HER of 33.52mmol g −1 h −1 under full-arc light. • PyThTz showed significantly higher photocatalytic activity than PyPhTz, which uses benzene as the π-linker. • π-linker enables electron transfer along polymer chain by facilitating HOMO and LUMO orbital overlap. • Increased cross-linking density reduces the band gap and enhances charge carrier separation and transport. Donor-π-acceptor (D-π-A) type conjugated porous polymers (CPPs) are widely used for photocatalytic hydrogen evolution (PHE), and the choice of electron donor/acceptor and π linker units is key to enhance their photocatalytic performance. In this research, two D-π-A type CPPs including PyThTz and PyPhTz were synthesized by copolymerizing 1,3,6,8-tetrasubstituted pyrene (as the donor) with 1,3,5-triazines derivatives (as the acceptor) containing thiophene and benzene respectively, as π linker units. Small variations in the structure of the π linker significantly affect PHE activity of the two CPPs. It is found that PyThTz exhibits hydrogen evolution rates (HER) of 33.52mmol g −1 h −1 under full-spectrum light and 28.79mmol g −1 h −1 under visible-light, both markedly greater than the HER rates of PyPhTz (7.15 and 2.24mmol g −1 h −1 under full-spectrum light and visible-light, respectively) free of co-catalyst. The superior performance of PyThTz can be assigned to its stronger light absorption, narrower band gap, and reduced photogenerated carrier recombination due to adoption of thiophene as the π linker unit. The enhanced cross-linking density also explains the improved PHE activity compared with our previous work (ThPy-CPP). These findings underscore the critical role of adopting suitable π linker unit in optimizing the PHE performance of triazine based CPPs.