Porphocyanines: Expanded Aromatic Tetrapyrrolic Macrocycles

Abstract

Porphocyanines are tetrapyrrolic macrocycles containing two dipyrromethene units linked together by two CN−C bridges. The syntheses of 2,3,7,8,14,15,19,20-octaethylporphocyanine, 5,17-diphenylporphocyanine, 2,3,7,8-tetraethyl-17-phenylporphocyanine, and other meso-aryl and β-alkyl, including a tetra-β-propionate, derivatives and metal complexes are described. The physical and chemical properties of porphocyanines show them to be aromatic. The aromaticity is reflected in the large deshielding of the outer β-protons and shielding of the inner pyrrolic protons in their NMR spectra. The optical spectra of these compounds exhibit Soret and Q bands similar to porphyrins but all significantly bathochromically shifted. The ability of porphocyanines to act as catalysts for the generation of singlet molecular oxygen was investigated using a cholesterol oxidation assay.