Ultrahigh photocatalytic hydrogen evolution of linear conjugated terpolymer enabled by an ultra-low ratio of 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 third component remains a critical challenge. Herein, we report a donor-acceptor linear terpolymer prepared by the atom-economical C−H/C−Br coupling with an ultra-low ratio (0.5 mol%) of benzothiadiazole (BT) as the third monomer, which can effectively modulate properties with a hydrogen evolution rate up to 222.28 mmol h-1 g-1 in the absence of Pt co-catalyst with an apparent quantum yield of 22.73% at 500 nm wavelength. Systematic spectroscopic studies reveal that even a minimal ratio of 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-BT0.5% 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 BT building block even with an ultra-low ratio enables the effective modulations of the terpolymers with ultra-high PHP performance.