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, zinc porphyrin derivatives bearing a meta-pyridyl group at the meso position were prepared and their assemblies studied in chloroform. Among the porphyrins studied, one with a carbamoylpyridyl moiety gave a distinct H-1 NMR spectrum in CDCl3, which allowed the supramolecular structure in solution to be probed in detail. Ring-current-induced chemical-shift changes in the H-1 NMR spectrum, together with vapor-pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer with a triangular cone structure. Incorporation of a directly linked porphyrin-ferrocene dyad with the same assembling properties in the assemblies led to a rare example of a light-harvesting/charge-separation system in which an energy gradient is incorporated and reductive quenching occurs.

Automated summary

This study focused on the self-assembly of zinc porphyrin derivatives with meta-pyridyl groups in chloroform, revealing a unique trimer structure with a triangular cone shape. Incorporation of a porphyrin-ferrocene dyad into the assemblies led to a rare light-harvesting/charge-separation system with energy gradient and reductive quenching.