Spectral studies of zinc octacarboxyphthalocyanine aggregation

The association of zinc octacarboxyphthalocyanine, was studied using UV–vis absorption and fluorescence emission spectroscopy; the effects of dye concentration, pH and solvents on spectra were discussed. Calculations showed that the dye dimerized in aqueous solutions ranging from 5.0 × 10−7 to 5.0 × 10−5 mol/dm3, at 25 °C. The dimerization constant of 106 dm3/mol and the spectral Q band shift of 1185 cm−1 imparted by dimerization indicated strong π–π interactions between phthalocyanine molecules. Red S1 fluorescence of the dye monomer was observed in various solutions which was quenched owing to molecular association and other factors. The strong influence of pH on both aggregation and fluo…