| Abstract: | Ionic equilibria and fluorescence decay of rhodamine B were studied in micellar solutions of sodium n-dodecyl sulfate (SDS) with various additives (NaCl, pentanol-1, crown ether, and tetra-n-butyl ammonium salt), and five nonionic surfactants (Brij 35, nonyl phenol 12, Triton X-100, Triton X-305, Tween 80), as well as in  -cyclodextrin solutions. The apparent dissociation constants,
, of rhodamine B (HR+  R + H+) were obtained. The distribution of the dye species HR+ and R in the ultramicroheterogeneous systems was studied using absorption and emission spectra, fluorescence life-times,  , and the plots of p
versus surfactant concentration. The p
values under conditions of complete binding, p
, were found to be markedly higher than that in water
. The medium effects,
, in organized solutions studied are in accord with the charge type of the acid-base couple +/±, confirming the zwitterionic nature of rhodamine B neutral species. Both and
a values of the dye were shown to sense the changes in the micellar microenvironments, and the possibility of using rhodamine B as an interfacial acid-base indicator, for example, for monitoring of surface potentials and of bulk ionic strength, were demonstrated. |
