Boronium-Based Polythiophene Networks: Synthesis, Characterization, and Photocatalytic Hydrogen Evolution Property

Abstract

The marriage between the boron (B) element and π-conjugated structures endowed organic π-conjugated polymers (OCPs) with intriguing structures and properties. Herein, we report the first example of cationic boronium based polythiophene networks. New boronium monomers were readily accessed by the strong Lewis acid–base coordination between thienylborane and 2,2′-bipyridine. Subsequent counteranion exchange reactions gave the B-monomers various counteranions. Polycondensation between the monomers and distannylated oligothiophenes further afforded cationic B-polythiophene networks. The results showed that the solid-state networks exhibited better controlled and stable chemical structures, in particular the uniform chemical environment of the cationic B-center that was still not addressed in the literature. The theoretical and experimental results further suggested that the nonplanar boronium-bipyridine structures endowed the networks with strong intramolecular charge separation characteristics, which is the advantage of the photocatalytic process. As a proof of concept, the networks were applied as photocatalysts in the application of visible light-driven hydrogen evolution. Compared with the previous polythiophene (HER: 0.1 μmol·h^–1·g^–1) and BN-cross-linked polythiophene network (HER: 11 μmol·h^–1·g^–1), the new boronium networks exhibited higher H₂ evolution rates (HER: 96 μmol·h^–1·g^–1 for P1c, 279 μmol·h^–1·g^–1 for P2c, and 186 μmol·h^–1·g^–1 for P3c) where the HERs are highly dependent on the counteranions. Overall, our studies provided a new design strategy of ionic B-OCPs with intriguing structures and properties.