Time-resolved fluorescence quenching study of aqueous solutions of perfluorinated surfactants with the use of protiated luminophore and quencher

Application of fluorescence methods to study micellar solutions of perfluor inated surfactants is very scarce because good probes and quenchers could n ot be found; polycyclic aromatic compounds, the most popular fluorescent pr obes, are difficult to solubilize into fluorinated surfactant micelles. We have found that the incompatibility of protiated probes with perfluorinated chains of surfactant host may be counterbalanced by positive electrostatic interactions. We present the use of a cationic derivative of pyrene,1-pyre nebutyltrimethylammonium bromide, as a luminophore and cationic quenchers, 1-trimethylammonium-2,2,6,6-tetramethyl-piperidine-1-oxyl iodide (nitroxide radical known as CAT1) and 1,1'-dimethyl-4,4'bipyridinium dichloride (meth yl viologen), to examine aqueous solutions of two anionic fluorinated surfa ctants, ammonium perfluorooctanoate (APFO) and tetraethylammonium perfluoro octyl sulfonate (TEAPFOS). On the basis of the Infelta-Tachiya model, we ha ve determined from time-resolved fluorescence quenching data the micellar a ggregation numbers, the rate constants of intramicellar quenching, and the rate constants of the quencher exit from the aggregates. The results indica te formation of ellipsoidal micelles in APFO solution, with the aggregation numbers increasing versus surfactant concentration (from 33 at 0.06 M APFO to 109 at 0.5 M APFO), and threadlike micelles in TEAPFOS solution, which consist of interconnected spherical units each containing at least 52 surfa ctant molecules.