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 closed 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.

Singlet excited state deactivation of a zinc phthalocyanine (ZnPc), porphycene (Po) and tetrapropyl‐porphycene (PrPo) by anionic tryptophan (Trp−) were investigated in cetyltrimethylammonium chloride (CTAC) micelles at pH 9.2 ± 0.1, regulated by a Tris buffer. Data obtained from steady‐state experiments over a wide range of detergent and added NaCl concentrations were analyzed by using a pseudophase ion‐exchange model (Abuin et al., J. Phys. Chem. 87, 5166–5172, 1983). The model was applied to derive singlet quenching rate constants for ZnPc and the porphycenes by Trp− and the selectivity coefficient for Trp/Cl exchange at the micellar surface. The results point to an electron transfer quenching. Neutral tryptophan also quenches efficiently ZnPc fluorescence in CTAC without added buffer and Trp− does not deactivate the triplet state of these dyes. By flash photolysis, only the absorption of the triplet species was detected.