Rapid Exciton Migration and Amplified Funneling Effects of Multi-Porphyrin Arrays in a Re(I)/Porphyrinic MOF Hybrid for Photocatalytic CO2 Reduction

A porphyrinic metal–organic framework (PMOF) known as PCN-222­(Zn) was chemically doped with a molecular Re­(I) catalyst-bearing carboxylate anchoring group to form a new type of metal–organic framework (MOF)–Re­(I) hybrid photocatalyst. The porphyrinic MOF-sensitized hybrid (PMOF/Re) was prepared with an archetypical CO2 reduction catalyst, (L)­ReI(CO)3Cl (Re­(I); L = 4,4′-dicarboxylic-2,2′-bipyridine), in the presence of 3 vol % water produced CO with no leveling-off tendency for 59 h to give a turnover number of ≥1893 [1070 ± 80 μmol h–1 (g MOF)−1]. The high catalytic activity arises mainly from efficient exciton migration and funneling from photoexcited porphyrin linkers to the peripheral Re­(I) catalytic sites, which is in accordance with the observed fast exciton (energy) migration (≈1 ps) in highly ordered porphyrin photoreceptors and the effective funneling into Re­(I) catalytic centers in the Re­(I)-doped PMOF sample. Enhanced catalytic performance is convincingly supported by serial photophysical measurements including decisive Stern–Volmer interpretation.