Thiophene π-Bridge Engineering for Boosting Photocatalytic H2 Evolution of Dioxythiophene-Based D-A-π-A Conjugated Polymers Without Extraneous Noble Metal Loading.

Conjugated polymers featuring donor-acceptor (D-A) architectures have emerged as promising candidates for visible-light-driven hydrogen evolution, owing to their tunable optoelectronic properties. However, achieving high photocatalytic activity without noble-metal cocatalysts remains challenging. Herein, we report a series of D-A type conjugated polymers based on dibenzothiophene sulfone (BTDO) as an electron acceptor and 3,4-ethylenedioxythiophene (EDOT) as an electron donor, synthesized via Suzuki polycondensation. By optimizing the donor/acceptor feed ratio, the optimal copolymer, EDOT-BTDO-5, delivers a hydrogen evolution rate (HER) as high as 87.5 mmol h-1 g-1 was achieved under visible-light irradiation (λ > 420 nm) without any Pt cocatalyst. To further boost the charge separation efficiency, a thiophene π-bridge was introduced, yielding a D-A-π-A ternary copolymer, EDOT-BTDO-T, which exhibits a significantly enhanced HER of 103.45 mmol h-1 g-1, along with remarkable operational stability, retaining ~69% of its initial activity after 20 h of continuous illumination. Comprehensive characterization, including photoelectrochemical analysis and density functional theory (DFT) calculations, reveals that the incorporation of EDOT broadens the visible-light absorption range, while the thiophene π-bridge extends π-conjugation, and facilitates efficiency. This work demonstrates a molecular engineering strategy to construct high-performance, metal-free organic photocatalysts by tailoring D-A and D-A-π-A architectures, providing valuable insights for sustainable photochemical energy conversion.