The results of a study of the effect of pH on the photophysics and photochemistry of di‐sulphonated aluminum phthalocyanine (AlPcS2) in aqueous solution are presented. The pH dependence of the triplet quantum yield, fluorescence quantum yield, singlet‐oxygen quantum yield, triplet lifetime, fluorescence lifetime and apparent dimerization constants is investigated and the results interpreted in terms of the pH dependence of the nature of the axial ligands. Evidence that the aluminum–axial ligand bond strength, rather than dimer binding energy that determines the extent of dimerization is provided by semi‐empirical and ab initio calculations. Possible dimer structures obtained using ab initio calculations are discussed.

Confocal fluorescence microscopy, using a newly constructed laser line-scanning confocal microscope, was applied to an investigation of the early stages of photoinduced destruction of V79-4 Chinese hamster fibroblasts using aluminum and zinc phthalocyanines as photosensitizers. Results obtained in this work show that aluminum and zinc phthalocyanines, once internalized, localize in perinuclear sites that are disrupted upon light exposure resulting in fluorescence redistribution. The combination of laser-line scanning with charge-coupled device detection used in the confocal microscope developed in this work can enable rapid high-resolution sequential imaging, which is ideal for studying photoinduced intracellular fluorescence dynamics.