Side chain engineering for modulating hydrophilicity of benzobisthiazole-based linear conjugated polymer to improve the photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution through water splitting using conjugated polymer catalysts presents a promising prospect for sustainable energy production, however, challenges in charge carrier dynamics and interfacial reactivity limit practical implementation of conjugated polymers. This study systematically investigates the role of hydrophilic side-chain engineering in optimizing photocatalytic performance by designing structurally homologous benzobisthiazole-based linear conjugated polymers, B-PBT (butyl side chains) and O-PBT (oligoethylene glycol side chains), with matched light absorption spectra and morphologies. Structural characterization confirmed identical conjugated backbones and semi-crystalline features, while morphological analysis revealed analogous flake-like architectures for both polymers. Despite comparable light absorption ranges, O-PBT exhibited a 7-fold higher hydrogen evolution rate than B-PBT under visible light, attributed to hydrophilic modulation. Contact angle measurements (34.0° for O-PBT v.s. 59.5° for B-PBT) and photoelectrochemical analyses demonstrated enhanced interfacial water affinity, suppressed charge recombination and reduced charge-transfer resistance in O-PBT. This work decouples hydrophilicity effects from light-absorptive and morphological factors, establishing side-chain engineering as a critical strategy for optimizing interfacial reactivity and charge dynamics in organic photocatalysts.