Solvent effects on molecular aggregation of highly water-soluble phthalocyanines

Abstract

Molecular aggregation phenomena of a highly water-soluble, metal-free phthalocyanine, H[Formula: see text]Pc, and its copper complex, Cu(Pc); where Pc denotes tetrakis{(2[Formula: see text],6[Formula: see text]-dimethyl-4[Formula: see text]-sulfonic acid)phenoxy}phthalocyaninate) in water, ethanol, and their mixed solvent systems have been investigated by spectroscopic approach In both aqueous and ethanolic solutions, H[Formula: see text]Pc molecules aggregate in a slipped-cofacial manner, although very weakly in ethanol. On the other hand, Cu(Pc) molecules aggregate in a cofacial manner in water while aligning in a slipped-cofacial manner in ethanol. Magnetic circular dichroism spectroscopy was undertaken to investigate aggregation behaviors of Cu(Pc) in water and ethanol. Presence of 4-phenylpyridine in ethanol effectively inhibited aggregation of Cu(Pc) molecules, although little affected the spectra of the monomers. In a mixed solvent system, where water/ethanol [Formula: see text] 10/90 (v/v), Cu(Pc) is free from aggregation up to almost 10[Formula: see text] M. Driving forces of this molecular aggregation are discussed on the basis of [Formula: see text]–[Formula: see text] interaction and coordination chemistry involving copper ions.