How the π bridge in donor-π-acceptor type covalent triazine frameworks influenced their photocatalytic hydrogen evolution performance

Covalent triazine frameworks (CTFs) have recently emerged as promising organic semiconductor materials for use in hydrogen evolution reactions (HERs) under visible light radiations. Nevertheless, how to favorably tune the CTF structure and optimize the photo-induced electron transfer pathway for highly efficient HERs still remains a challenge. Herein, we designed a thiophene-bridged electron-donating triphenylamine moiety-based donor-pi-acceptor (D-pi-A) type CTF, SCTF, which is found to be a more feasible photocatalyst for HER in comparison with the benzene-bridged one, BCTF. The HER rate by using SCTF could reach 977.1 mu mol h(-1), which is 6.81 times that by BCTF. Further studies on the thermodynamics and kinetics of charge separation in resulted CTFs suggested that the employment of thiophene pi bridge in SCTF rather than benzene in BCTF could lead to the broader light absorption, optimize charge transfer pathway in crystalline CTFs and enhance the built-in electric field to dramatically accelerate charge separation and transfer. The in-depth exploration of the photocatalytic process has further revealed the role of thiophene bridge in promoting the photocatalytic HER efficiency for D pi-A type CTFs. Overall, we have offered a promising strategy to finely tune CTF structure and the photogenerated carriers transfer pathway for efficient CTF-based photocatalytic HER catalysts.