Polymorphism‐Controlled Exciton Dissociation in Hydrogen‐Bonded Organic Framework Photocatalysts

ABSTRACT Organic photocatalysts have attracted extensive attention, while multiple interrelated factors influence photocatalytic activity, making it challenging to identify the dominant structural features that govern performance. Here, we report two pyrene‐based hydrogen‐bonded organic framework polymorphs, H 4 PTBA‐AA and H 4 PTBA‐ABC, which exhibit nearly identical light absorption, hydrophilicity, and dispersed particle sizes, but they show markedly different excited‐state behaviors. Spectroscopic studies reveal that H 4 PTBA‐AA shows smaller exciton binding energy and preferentially forms a charge‐transfer (CT)‐like state, whereas H 4 PTBA‐ABC is more prone to evolve into an excimer‐like state. As a result, the photocatalytic H 2 evolution rate of H 4 PTBA‐AA is approximately six times higher than that of H 4 PTBA‐ABC. For the first time, through a relatively well‐controlled comparison, this study shows that molecular packing plays an important role in exciton dissociation in HOF frameworks and provides useful insights for the rational design of efficient photocatalytic organic frameworks.