Carboxylated Zinc‐phthalocyanine, Influence of Dimerization on the Spectroscopic Properties. An Absorption, Emission, and Thermal Lensing Study

Monomer and dimer absorption and emission spectra, and dimerization constants are reported for the diamide of the zinc‐tetracarboxyphthalocyanine in pure dimethylformamide (DMF) and in H 2 O/DMF mixtures at room temperature. The dimerization constant increases steadily with the water content. The monomer absorption Q‐band is insensitive to the solvent composition, whereas dimer spectra show great variations with the water content. Stationary emission measurements show that fluorescence originates exclusively from the monomers. The fluorescence spectrum as well as its absolute fluorescence quantum yield, measured by steady‐state thermal lensing, are also insensitive to the solvent composition. The thermal lensing method is discussed for the case of two absorbing species in equilibrium.