Tuning Photocatalytic Activity in Porphyrin–Based Metal–Organic Frameworks by Controlling Charge Recombination Pathways

Porphyrin–based metal–organic frameworks (MOFs) are promising photocatalysts, but their efficiency is often limited by rapid charge recombination. Herein, we enhance photocatalytic performance by incorporating an electron acceptor, phenyl–C 61 –butyric acid (PCBA), into the porphyrinic framework PCN–222 and its metalated analogues (M = Co, Ni, Cu) via a solvent–assisted ligand incorporation (SALI) method. The free–base composite PCBA@PCN–222(H 2 ) exhibited outstanding photocatalytic activity for aerobic thioanisole oxidation (>99% conversion), far outperforming PCBA@PCN–222(Cu) (23%), PCBA@PCN–222(Ni) (3%), and PCBA@PCN–222(Co) (2%). Electrochemical and picosecond time–resolved photoluminescence (TRPL) studies revealed that this superior activity originates from a remarkably long–lived charge–transfer (CT) state (τ CR = 1.72 ns) in the free–base system. In contrast, the metalated MOFs exhibited intrinsic metal–associated quenching of the porphyrin units that competes with exciton migration within the MOF, and the CT states formed from a fraction of Q–state populations underwent ultrafast charge recombination (τ CR = 70 ∼ 100 ps), which severely limited their efficiency. These findings provide a clear correlation between the lifetime of the photo–induced CT state and catalytic performance, highlighting the importance of the porphyrin’s core electronic nature in designing efficient donor–acceptor photocatalysts.