Micellar fibers of octopus porphyrin, photoinduced electron transfer reactions in aqueous media

Abstract

Symmetrical tetraresorcinolporphyrin with eight alkylphosphocholine side chains (octopus porphyrin) and its zinc(II) complex were dispersed in aqueous media to give a stable colloidal solution. Electron microscopy showed either planar monolayers or micellar fibers with a uniform thickness of 7 nm. A unique spherical arrangement of eight methyl groups on each side of the porphyrin center provides fat droplet like centers which align in a string of pearls in an extremely open fiber structure. Exciton calculations on the basis of a long wavelength shift of the Soret bands (7-8 nm), line broadening, and electron micrographs indicated a tilt stacking arrangement with a porphyrin separation of 11 Angstrom. The octopus porphyrin fibers fluoresced strongly, and laser flash photolysis lead to electron transfer from the porphyrin to hydrophobic phenyl-p-benzoquinone as well as to hydrophilic 1,2-naphtoquinone-4-sulfonate and dimethylviologen acceptors. The fibers were also active as photocatalysts in the reduction of dimethylviologen to the corresponding radical by amines.

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