Photophysical behaviour of cationic 2-(dimethylamino) ethanethio tetrasubstituted phthalocyanine complexes in the presence of gold nanoparticles

Magnesium and aluminium phthalocyanines tetrasubstituted with 2-(dimethylamino) ethanethiol have been synthesized (complexes 2 and 3). The prepared complexes were converted to water soluble ones by quaternizing with methyl iodide. The quaternized complexes (2Q, 3Q) show monomeric behaviour in organic solvents but show aggregation in water, especially for 2Q. Furthermore the water soluble complexes were conjugated with gold nanoparticles in DMSO to avoid aggregation of the phthalocyanines in water. The phthalocyanines showed a blue shift in their Q bands upon conjugation with gold nanoparticles. Low fluorescence quantum yields and lifetimes were also observed for the conjugates compared to the non-conjugated phthalocyanine molecules. The conjugated complexes showed an increase in the triplet quantum yields with a concomitant decrease in their triplet lifetimes.