Polymorphism-Controlled Exciton Dissociation in Hydrogen-Bonded Organic Framework Photocatalysts.

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, H4PTBA-AA and H4PTBA-ABC, which exhibit nearly identical light absorption, hydrophilicity, and dispersed particle sizes, but they show markedly different excited-state behaviors. Spectroscopic studies reveal that H4PTBA-AA shows smaller exciton binding energy and preferentially forms a charge-transfer (CT)-like state, whereas H4PTBA-ABC is more prone to evolve into an excimer-like state. As a result, the photocatalytic H2 evolution rate of H4PTBA-AA is approximately six times higher than that of H4PTBA-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.