Host-guest engineering in a two-dimensional anionic porphyrinic metal-organic framework via cationic bodipy encapsulation for boosting photocatalytic H₂ evolution

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. A 2D anionic porphyrinic MOF host undergoes post-synthetic cation exchange, replacing inert [BMI] + with photoactive Bodipy cations. The favorable energy-level alignment drives intramolecular electron transfer from the porphyrin linker (donor) to the Bodipy guest (acceptor), achieving spatial charge separation. This, combined with broadened light absorption, leads to significantly enhanced photocatalytic H₂ evolution. Download: Download high-res image (140KB) Download: Download full-size image