Improving the photocatalytic performance of conjugated polyelectrolytes via substituent optimization

Donor-acceptor linear conjugated polyelectrolytes (D-A linear CPEs) have been considered as a type of potential organic photocatalyst for photocatalytic hydrogen evolution. However, most of the organic photocatalysts suffer from an unfavorable hydrogen evolution rate, primarily originating from unsuitable photoelectric properties for photocatalysis. The quest for a universal and easy method to turn the photoelectric characteristics of organic photocatalysts is significant for photocatalytic hydrogen evolution. Herein, we present two series of D-A linear CPEs (PFBBr and PBBBr series). Compared to the PFBBr series polyelectrolytes, the PBBBr series shows obvious extended absorption spectra. Moreover, we employed a facile substituent optimization strategy to fine-turn the photoelectric properties and realized an optimized photocatalytic hydrogen evolution efficiency. Compared to the methoxy group, chlorine atom modified PBBBr, i.e. PBBBr-Cl, achieved a high hydrogen evolution rate of over 1.90 mmol g(-1) h(-1) (4.3 times than that of PBBBr-OMe and 8.5 times than that of PFBBr-OMe). The CPEs with strong electron withdrawing substituents (-F and -Cl) present a reduced exciton binding energy, a smaller absolute value of hydrogen adsorption energy, and an enhanced molecular dipole. Moreover, efficient charge transfer to Pt cocatalysts was observed in -F/-Cl modified CPEs through femtosecond transient absorption spectroscopy. Our results reveal the great potential of substituent optimization in high-performance organic photocatalytic hydrogen evolution.