An Oxygen‐Rich Strategy Boosting the Photocatalytic Hydrogen Evolution of Benzodithiophene‐Based Conjugated Polymers

ABSTRACT Oxygen incorporation into conjugated polymers is a proven strategy to boost photocatalytic hydrogen evolution by improving hydrophilicity, tuning band structures, and increasing active sites. However, the impact of backbone oxygen content on performance is not fully understood. To address this, we designed four polymers with varying oxygen levels, denoted PBDT‐2O, PBDT‐4O, PBDT‐6O, and PBDT‐8O, using benzo[1,2‐b:4,5‐b']dithiophene (BDT), its tetraoxide derivative (BDTTO), thiophene (T), and 3,4‐ethylenedioxythiophene (DOT) as building blocks. Compared to PBDT‐2O, the alkoxy side chains in PBDT‐4O enhanced hydrophilicity and planar conjugation. Oxidizing the BDT sulfur atoms to sulfonyl groups in PBDT‐6O created a donor‐acceptor push‐pull effect, resulting in a redshifted absorption and narrower band gap. The synergistic combination of disulfonyl and alkoxy functionalities in PBDT‐8O delivered the best performance, with a hydrogen evolution rate of 55.52 mmol g − 1 h − 1 and an apparent quantum yield of 2.44% at 600 nm. It also maintained high activity (25.8 mmol g − 1 h − 1 ) under natural sunlight. Mechanistic studies using femtosecond transient absorption spectroscopy and DFT calculations revealed that this synergy accelerates exciton dissociation, enhances charge separation, and provides more active sites. This work clarifies the role of oxygen content and offers a rational design strategy for efficient polymer photocatalysts in solar energy conversion.