Photophysical study of Zn phthalocyanine in binary solvent mixtures

Photophysical properties of phthalocyanines are important in photodynamic therapy, where these compounds are proposed as photosensitizing agents. We report here some significant solvent effects on the photophysical properties of Zn phthalocyanine (ZnPc) observed in binary solvent mixture dimethyl sulfoxide/water at several ratios of cosolvents. The absorbance of ZnPc at the maximum of Q band has a sharp drop in intensity for a water mass percent in the solvent mixture larger than 40%. The same characteristic shows also the quantum yield of fluorescence. A particular result is the increase of singlet oxygen lifetime for water percentage raise up to 20% in the solvent mixture. The effects are discussed in connection with the particular solvent microenvironment, involving DMSO/water clusters formation and the strong interaction between the solute and the solvent.