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.