Quenching of pyrene fluorescence by amphiphilic nitroxide radicals embedded in cationic micelles

Steady-state and nanosecond time-resolved studies have been carried out on the fluorescence quenching of excited pyrene by n-doxylstearic methyl esters (n-DSE, n = 5, 10, 12) in an aqueous solution of cationic micelles of hexadecyltrimethylammonium chloride (HTAC, 0.1 M). The aggregation number (N = 114 ± 6) and the rate constants of intramicellar quenching (1.4 × 107, 1.3 × 107 and 1.05 × 107 s−1 for 5-, 10- and 12-DSE respectively) have been determined. The results are discussed in terms of the average location of the luminophore and the quencher molecules in the aggregates, considering previous findings of electron spin echo modulation studies of n-doxylstearic acid spin probes in micellar systems.