Multi‐electron transfer reactions and exciton interactions in fibrous porphyrin and metalloporphyrin assemblies

Non‐covalent porphyrin and metalloporphyrin fibers of bimolecular thinness in bulk aqueous media are compared with the well‐known H‐ and J‐aggregates of cyanines. The J‐aggregates of cyanines fluoresce and are useful as photographic sensitizers. The J‐aggregates of porphyrins show light‐induced charge separation and the corresponding metal complexes produce stable radical dimers. The distance between the metalloporphyrin centers is calculated from circular dichroism spectra to be 8 Å in the J‐aggregates and about 4 Å in the H‐aggregates. Multi‐electron reactions of the fibers in the ground and excited states can therefore occur in the fibrous porphyrin assemblies. In amphiphilic tetraphenylporphyrins (“octopus porphyrin”), on the other hand, the porphyrin–porphyrin distance is much larger and the fiber dissolves electron‐accepting compounds, e.g. quinones, which also allow for multiple charge separation within such a fiber.