Time-resolved spectroscopic studies of sulphonated aluminium phthalocyanine triplet states

摘要

The photophysical and photochemical properties of sulphonated aluminum and zinc phthalocyanines have been investigated in a range of solvents and model biological systems. Anomalous effects are observed upon deuteration of the solvent and addition of fluoride ions. In D$-2$/O the excited singlet and triplet state lifetimes and quantum yields of fluorescence and triplet state formation are increased relative to H$-2$/O. No solvent isotope effect is observed between CH$-3$/OH and CH$-3$/OD. It is proposed that relaxation of the excited state involves a tunnelling type interaction in which the phthalocyanine's highly energetic metal-axial ligand stretching vibrations are coupled to the HO-H or DO-D stretching vibrations. A significant increase in triplet lifetimes of phthalocyanine sensitizers bound to protein substrates is observed which is a function of the degree of sulphonation. The implications of these results to the determination of the quantum yields of singlet oxygen formation in D$-2$/O and lipophilic environments are discussed.