Ultrahigh photocatalytic hydrogen evolution of linear conjugated terpolymers enabled by an ultra-low ratio of the benzothiadiazole monomer

Abstract

Conjugated terpolymers bearing three kinds of π-monomers have been regarded as a promising platform for photocatalytic hydrogen production (PHP). However, the high-performance terpolymers reported so far typically involve large portions (≥20 mol%) of the third monomer. Efficiently modulating the terpolymer by utilizing minimum content of the third component remains a critical challenge. Herein, we report a donor–acceptor linear terpolymer prepared by atom-economical C–H/C–Br coupling with an ultra-low ratio (0.5 mol%) of benzothiadiazole (BT) as the third monomer, which can efficiently modulate properties and afford a hydrogen evolution rate of up to 222.28 mmol h⁻¹ g⁻¹ with an apparent quantum yield of 24.35% at 475 nm wavelength in the absence of a Pt co-catalyst. Systematic spectroscopic studies reveal that even a minimal amount of the BT monomer can effectively tune the light absorption and frontier molecular orbitals of the resulting terpolymers. Compared to the BT-free BSO₂–EDOT bi-polymer, the terpolymer BSED–BT_0.5% involving 0.5 mol% of BT has a much faster electron transfer (5.76 vs. 1.13 ns) and much lower exciton binding energy (61.35 vs. 32.03 meV), showcasing an important discovery that the BT building block even with an ultra-low ratio enables the effective modulations of terpolymers with ultra-high PHP performance.