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

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 g 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 BSO-EDOT bi-polymer, the terpolymer BSED-BT involving 0.5 mol% of BT has a much faster electron transfer (5.76 1.13 ns) and much lower exciton binding energy (61.35 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.