The effect of pH on the photophysics and photochemistry of di-sulphonated aluminum phthalocyanine

The results of a study of the effect of pH on the photophysics and photoche mistry of di-sulphonated aluminum phthalocyanine (AIPcS(2)) in aqueous solu tion are presented, The pH dependence of the triplet quantum yield, fluores cence quantum yield, singlet-oxygen quantum yield, triplet lifetime, fluore scence lifetime and apparent dimerization constants is investigated and the results interpreted in terms of the pH dependence of the nature of the axi al ligands, Evidence that the aluminum-axial ligand bond strength, rather t han dimer binding energy that determines the extent of dimerization is prov ided by semi-empirical and ab initio calculations. Possible dimer structure s obtained using ab initio calculations are discussed.