Abstract
The halide-sensitive fluorescence probe, 6-methoxy-N-alkylquinolinium, was prepared to investigate the behavior of counterion dissociation in micellar aqueous solution. Fluorescence was quenched by halide ions based on linear Stern-Volmer plots. The plots indicated a distinct break at cmc of cationic surfactants containing halide counterions. The slope of Stern-Volmer for 6-methoxy-N-ethylquinolinium (MEQ) decreased beyond cmc owing to micellar counterion binding. The quenching efficiency of 6-methoxy-N-dodecylquinolinium (C12MQ) increased significantly beyond cmc with surfactant concentration. The fluorescence of micellar solubilized C12MQ would thus appear to be quenched effectively by halide ions at the micellar surface. These ions were found to function effectively as a quencher in cationic micelle systems, but to have no effect on amphiphilic probe fluorescence in the presence of anionic micelles. Repulsive electrostatic interactions are thus shown to occur between halide ions and anionic micelles containing probes.
