Improving charge separation by adjusting the planarity of tetrathiophene-based donor-acceptor conjugated polymers for enhanced photocatalytic hydrogen evolution

Conjugated polymers (CPs) are being intensively investigated as promising organic photocactalysts for photo- catalytic hydrogen evolution. Herein, three tetrathiophenes with different molecular planarity as electron-donor units were copolymerized with the electron-acceptor unit, dibenzothiophene-S,S-dioxide by a facile Suzuki reaction to generate donor-acceptor (D-A) typed CPs, fl-TTE-DBTO 2 , sl-TTE-DBTO 2 and TTE-DBTO2. The photo- catalytic hydrogen performance of the CPs is remarkably increased by improving the planarity of tetrathiophene unit, owing to improve charge separation and prolong charge lifetime. As a result, fl-TTE-DBTO 2 with full-locked tetrathiophene unit shows the largest hydrogen evolution rate of 27.97 mmol center dot g- 1 center dot h- 1 under visible light irradiation, with an apparent quantum yield of 9.55 % at 420 nm, which is 7.1 times higher than that of sl-TTE- DBTO2 with simi-locked tetrathiophene unit (3.94 mmol center dot g- 1 center dot h- 1 ) and 87.4 times higher than that of TTE-DBTO2 with no locked of tetrathiophene unit (0.32 mmol center dot g- 1 center dot h- 1 ). This work demonstrates the significance of planarity of tetrathiophene unit in D-A structural CPs for achieving high charge separation and photocatalytic efficiency.