In situ co-assembly-induced strained molecular graphene nanocrystals in hydrogen-bonded organic frameworks for enhanced photocatalytic hydrogen evolution

The integration of carbon nanomaterials with crystalline porous semiconductors represents a promising strategy to boost charge separation and photocatalytic performance. Conventional synthesis of such composites, which relies on pre-formed host frameworks, preserves structural integrity but often requires harsh conditions. Moreover, post-synthetic host-guest assembly typically exhibits weak noncovalent interactions, limiting electronic coupling for electron transfer. Here, we demonstrate, for the first time, the confinement of molecular graphene (coronene) within hydrogen-bonded organic frameworks (HOFs), specifically HOF-101, via rapid in situ co-assembly crystallization. Coronene undergoes confined crystallization within the pores of HOF-101, resulting in strained crystallization of coronene crystals (Cor), which establishes robust host-guest interactions and thereby strong electronic coupling. Compared to HOF-101, Cor/HOF-101 exhibits significantly improved charge transfer and separation, leading to a 4.1-fold increase in photocatalytic hydrogen evolution activity (13.1 mmol·g⁻¹·h⁻¹). In contrast, methyl-group-induced steric hindrance in HOF-101 isoreticular derivative, HOF-101-CH₃, suppresses the confined crystallization of Cor, leading to weak host-guest interactions and negligible photocatalytic enhancement. This work represents the first HOF-based host-guest photocatalyst, providing new mechanistic insight and a general design principle for constructing high-efficiency HOFs-based photocatalysts through enhanced host-guest electronic coupling.