Efficient Photocatalytic Hydrogen and Oxygen Evolution by Side‐Group Engineered Benzodiimidazole Oligomers with Strong Built‐in Electric Fields and Short‐Range Crystallinity

The insufficient charge separation and sluggish exciton transport severely limit the utilization of polymeric photocatalysts. To resolve the above issues, we incorporate bountiful carboxyl substituents within a novel benzodiimidazole oligomer and assemble it into a crystalline semiconductor. The photocatalyst is polar, hydrophilic, short‐range crystalline, and capable of both hydrogen and oxygen evolution. The introduction of carboxyl side‐groups adds asymmetry to the local structure and increases the built‐in electric field. Further, accelerated carrier transfer is enabled via the short‐range crystallinity. The superior hydrogen and oxygen production rates of 18.63 and 2.87 mmol g−1 h−1 represent one of the best performances ever reported among dual‐functional polymeric photocatalysts. Our work initiates studies on high‐performance oligomer photocatalysts, opening a new frontier to produce solar fuel. Carboxyl‐rich benzodiimidazole oligomers (BDO‐HC) are obtained through a side‐group assisted self‐assembly. The carboxyl‐based strong built‐in electric field promotes charge separation, and the nano‐range crystals provide short channels for charge transfer. The photocatalyst is capable of efficient hydrogen and oxygen evolution.