Two consecutive post-synthetic modifications of benzothiadiazole-based conjugated polymers for enhanced photocatalytic H2 evolution: the significance of the sulfinyl group

Abstract

Donor/acceptor (D–A) conjugated polymers represent a promising platform for photocatalytic H₂ evolution, and a variety of methods have been developed to expand the library of conjugated polymer-based candidates. However, strategies to facilely modulate the electronic structures are still a challenge. Herein, we demonstrate that the replacement of electron-withdrawing fluorine (F) in the F-substituted benzothiadiazole (BT)-based conjugated polymers with more electron-withdrawing methylsulfinyl (CH₃SO) groups significantly increases the photocatalytic H₂ evolution rate (HER). To overcome the failure of direct polymerization, an approach involving two consecutive post-synthetic modifications (PSM) was innovatively adopted. F-substituted B-FBT-1,3,5-E was first converted into the electron-donating group methylthio (CH₃S)-modified B-SBT-1,3,5-Evia the S_NAr reaction, and the subsequent oxidation afforded the CH₃SO-substituted B-SOBT-1,3,5-E. Photocatalytic H₂ evolution experiment results revealed that the HER of B-FBT-1,3,5-E, B-SBT-1,3,5-E and B-SOBT-1,3,5-E were 155.2 μmol h⁻¹, 92.4 μmol h⁻¹ and 280.0 μmol h⁻¹, respectively, and the best performance of B-SOBT-1,3,5-E was attributed to the more electron-withdrawing and hydrophilic properties of the CH₃SO-group. This protocol can also be extended to three more series of BT-based conjugated polymers with benzene replaced, highlighting the excellent property of the sulfinyl group for designing polymer-based photocatalysts toward solar-to-chemical energy conversion in the near future.