Effect of Controlling Thiophene Rings on D-A Polymer Photocatalysts Accessed via Direct Arylation for Hydrogen Production

Conjugated polymer photocatalysts for hydrogen production have the advantages of an adjustable structure, strong response in the visible light region, adjustable energy levels, and easy functionalization. Using an atom- and step-economic direct C-H arylation method, dibromocyanostilbene was polymerized with thiophene, dithiophene, terthiophene, and fused thienothiophene and dithienothiophene, respectively, to produce donor-acceptor (D-A)-type linear conjugated polymers containing different thiophene derivatives with different conjugation lengths. Among them, the D-A polymer photocatalyst constructed from dithienothiophene could significantly broaden the spectral response, with a hydrogen evolution rate up to 12.15 mmol h(-1) g(-1). The results showed that the increase in the number of fused rings on thiophene building blocks was beneficial to the photocatalytic hydrogen production of cyanostyrylphene-based linear polymers. For the unfused dithiophene and terthiophene, the increase in the number of thiophene rings enabled more rotation freedom between the thiophene rings and reduced the intrinsic charge mobility, resulting in lower hydrogen production performance accordingly. This study provides a suitable process for the design of electron donors for D-A polymer photocatalysts.

Automated summary

Conjugated polymer photocatalysts for hydrogen production have adjustable structures, strong response to visible light, adjustable energy levels, and easy functionalization. A direct C-H arylation method was used to polymerize dibromocyanostilbene with thiophene, dithiophene, terthiophene, and fused thienothiophene and dithienothiophene, resulting in donor-acceptor (D-A)-type linear conjugated polymers with different thiophene derivatives and conjugation lengths. The D-A polymer photocatalyst made from dithienothiophene showed a significantly broadened spectral response and a hydrogen evolution rate of up to 12.15 mmol h(-1) g(-1). Increasing the number of fused rings on the thiophene building blocks was found to enhance the photocatalytic hydrogen production of cyanostyrylphene-based linear polymers. On the other hand, increasing the number of thiophene rings in unfused dithiophene and terthiophene resulted in reduced intrinsic charge mobility and lower hydrogen production performance. This study provides a suitable process for designing electron donors for D-A polymer photocatalysts.