This paper describes a new conceptual design for enhancement of photocatalytic CO2 reduction of a rhenium(I) complex by light harvesting of periodic mesoporous organosilica (PMO). Mesoporous biphenyl-silica (Bp-PMO) anchoring fac-[ReI(bpy)(CO)3(PPh3)]+(OTf)− (bpy =2,2′-bipyridine; OTf = CF3SO3) in the mesochannels was synthesized by co-condensation of two organosilane precursors, 4,4′-bis(triethoxysilyl)biphenyl and 4-[4-{3-(trimethoxysilyl)propylsulfanyl}butyl]-4′-methyl-2,2′-bipyridine in the presence of a template surfactant, followed by coordination of a rhenium precursor, [ReI(CO)5(PPh3)]+(OTf)− to the bipyridine ligand in the mesochannels. The 280 nm light was effectively absorbed by the biphenyl groups in Bp-PMO, and the excited energy was funneled into the Re complex by resonance energy transfer, which enhanced photocatalytic CO evolution from CO2 by a factor of 4.4 compared with direct excitation of the Re complex. Bp-PMO had an additional merit to protect the Re complex against a decomposition by UV irradiation. These results demonstrate the potential of PMOs as a light-harvesting antenna for designing various photoreaction systems, mimicking the natural photosynthesis.
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