Comparison of the photophysics of an aggregating and non-aggregating aluminium phthalocyanine system incorporated into unilamellar vesicles

The hydrophobic sensitizer, aluminium phthalocyanine chloride (AIPcCI), and the amphiphilic sensitizer, cis-disulphonated aluminium phthalocyanine (cis-AIPcS₂), were incorporated into small unilamellar vesicles (SUVs) and large unilamellar vesicles (LUVs). AIPcCI exhibits aggregation, which increases with increasing sensitizer concentration, whereas cis-AlPcS₂ is monomeric at all concentrations studied. Complex fluorescence decays are observed, showing decay time distributions which broaden with increasing phthalocyanine concentration. The phthalocyanine aggregate, although non-fluorescent, influences the overall photophysical behaviour of the phthalocyanine-vesicle system. The effect of aggregation on the resulting photophysics of phthalocyanines was investigated by comparing aggregated and non-aggregated phthalocyanine systems. The implications for photodynamic therapy (PDT) are briefly discussed.