Reaction of zinc phthalocyanine excited states with amines in cationic micelles

Excited state deactivation of a zinc phthalocyanine (ZnPc) by amines was studied in micelles of hexadecyltrimethylammonium chloride. The singlet state deactivation was studied by fluorescence quenching. This technique allows us to determine equilibrium constants for the distribution of the amines between the aqueous and the micellar phases. It could be established that amines associate to the micelles in two different ways: with a greater affinity to a saturable number of sites, that we will term binding sites, and with a lower affinity by a partitioning mechanism. Equilibrium constants could be determined for aliphatic and aromatic amines. A kinetic scheme taking into account the simultaneous quenching of ZnPc fluorescence by the two types of micellized amines could be successfully applied to derive singlet quenching rate constants, under the assumption that micelles behave like dosed compartments during the singlet deactivation. Aromatic amines are more efficient than aliphatic ones, and partitioned quenchers are more effective than bound quenchers. Aromatic amines also deactivate the triplet state of ZnPc. By flash photolysis, the absorption of the anion radical of ZnPc was detected. This species originates on singlet and triplet quenching, indicating that both proceed by electron transfer.