A Light-Harvesting/Charge-Separation Model with Energy Gradient Made of Assemblies of meta-pyridyl Zinc Porphyrins.

Self-assembly of porphyrins is a fascinating topic not only for mimicking chlorophyll assemblies in photosynthetic organisms but also for the potential of creating molecular-level devices. Herein we have prepared zinc porphyrin derivatives bearing a meta-pyridyl group at the meso-position and studied their assemblies in chloroform. Among porphyrins studied, one with a carbamoylpyridyl moiety (ZnPPyC) gave distinct 1H NMR spectrum in CDCl3, which allowed us to probe the supramolecular structure in solution in detail. Ring-current induced chemical shift changes in 1H NMR, together with vapor pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer in a triangular cone structure. Further incorporation of a directly-linked porphyrin-ferrocene dyads with the same assembling properties in the assemblies lead to a rare light-harvesting/charge-separation model, in which an energy gradient is incorporated and reductive quenching occurs.