Effect of electric permittivity of the solvent on aggregation process of the water-soluble sulfonated metal phthalocyanines

Dimerization of sulfonated phthalocyanines of divalent metals (Zn, Cu, and Co) in binary water-alcohol solutions was studied by spectroscopic techniques. The dimerization manifests itself in changes in the absorption spectra and in a decrease of fluorescence intensity. The equilibrium constants of dimerization depend on the electric permittivity of the solvent and on degree of sulfonation. The process can be semi-qualitatively described by a simple model taking into account solvation and electrostatic interactions between phthalocyanine anions. The effect of electric permittivity has not been observed in sulfonated Al and Si phthalocyanines. Experimentally determined fluorescence quantum yields in alcoholic solutions range between 0.74 and 0.015.