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

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.