A Carboxylate‐based Hydrophilic Organic Photovoltaic Catalyst with a Large Molecular Dipole Moment for High‐Performance Photocatalytic Hydrogen Evolution

Achieving ultrafast dissociation of photogenerated excitons and efficient charge transport within the photocatalyst is a fundamental issue. Additionally, enhancing the interaction between semiconductors and water is crucial for efficient photocatalytic water splitting. Herein, we synthesized a carboxylate-based hydrophilic polymer, hPTB7-Th. Exposed carboxylates enhance semiconductor-water interfacial compatibility, reducing contact resistance and accelerating charge transfer kinetics. Furthermore, the carboxylate substitution shifts polarity centers, amplifying the molecular dipole moment by 10-fold. This induces a giant built-in electric field, enabling ultrafast electron-transfer process (ca. 0.31 ps) in the hPTB7-Th:PCBM bulk heterojunction. Consequently, the hPTB7-Th:PCBM-based bulk heterojunction nanoparticles exhibit excellent photocatalytic activity, achieving an optimal hydrogen evolution rate of 111.5 mmol g^-1 h^-1, four times over the ester-based counterpart (PTB7-Th:PCBM). Moreover, the electrostatic stability imparted by the carboxylates endows hPTB7-Th:PCBM with outstanding operational stability, maintaining 81% of its initial hydrogen evolution rate after 100 h operation. This result places it among the state-of-the-art organic photovoltaic bulk heterojunction photocatalysts in terms of stability. This work establishes a molecular engineering strategy for high-performance bulk heterojunction photocatalysts, emphasizing synergistic optimization of hydrophilicity, dipole engineering, and interfacial dynamics.