Host-guest engineering in a two-dimensional anionic porphyrinic metal-organic framework via cationic bodipy...

The development of efficient and stable photocatalysts for solar-driven hydrogen production remains a significant challenge, primarily limited by inadequate light harvesting and rapid charge recombination. This work addresses these issues through the rational design of a host-guest system within a metal-organic framework (MOF). We report a novel two-dimensional anionic porphyrinic MOF (1) synthesized using 1-butyl-3-methylimidazolium (BMI) as a structure-directing agent, and replaced the inert BMI guests with photoactive 4,4-Difluoro-8-(1-methylpyridin-4-ium-4-yl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (Bodipy)-based cations by cationic exchange strategy, yielding the composite Bodipy@1. The Bodipy units act as complementary antennas, broadening the visible-light absorption range, while the favorable energy-level alignment between the porphyrinic host (donor) and the Bodipy guest (acceptor) establishes an efficient intramolecular charge-transfer pathway. Density functional theory calculations and spectroscopic studies confirm a spatial separation of frontier orbitals, with the highest occupied crystal orbital localized on the porphyrin linker and the lowest unoccupied crystal orbital on the Bodipy cation, which effectively suppresses charge-carrier recombination. Consequently, Bodipy@1 exhibits a remarkable enhancement in photocatalytic hydrogen evolution activity (∼2.5 mmol·g^-1·h^-1), outperforming the pristine MOF 1. This work highlights a potent strategy of energy-level engineering via host-guest assembly, demonstrating that precise post-synthetic modification of anionic MOFs with functional cations is a powerful avenue for designing advanced, stable photocatalysts for solar fuel production.