Synthesis and optical properties of novel covalent and non-covalent porphyrin dimers

Abstract

A new series of porphyrin dimers in different geometry have been synthesized. The reductive amination of dicarbonyl compounds, especially 2,5-hexadione and isophthaldhyde, with porphyrin monomers, α,α,α,α-5-(p-aminophenyl)-10,15,20-tris-(4-tolyl)porphyrin, α,α,α,α- and α,α,β,β-5,10,15,20-tetrakis-(o-aminophenyl)porphyrin in the presence of excess of NaBH 3 CN , afforded novel dimeric single and double bridged dimers of free base porphyrins, covalently linked through aliphatic or aromatic spacers. All the synthesized compounds were characterized by NMR, IR, UV-vis, and MS spectroscopy. Significant spectral changes occurred in the absorption spectra of these covalent porphyrin dimers comparing with that of the reference monomers, indicating strong electronic interaction between the adjacent porphyrin units. The UV-vis spectra showed the presence of another kind of non-covalent aggregation, which was observed at pH = 2.5-3 for some of these synthesized dimers. A similar behavior of association was also detected when α,β,α,β-5,10,15,20-tetrakis-(o-aminophenyl)porphyrin was measured at pH = 3.5 in acetone.