ESR Studies of the Dynamic Properties of Ion Radicals Captured by Surfactant Micelles

Abstract

Abstract ESR spectra of duroquinone anion radical (DQ−), methyl viologen cation radical (MV+), and 5,10-dimethyl-5,10-dihydrophenazine cation radical (DMPZ+) were measured in various aqueous surfactant solutions. The line width of each peak of the ESR spectra for DQ− in cationic and anionic surfactant solutions showed a quadratic dependence on the total nuclear quantum number, M=Σmi (i=1 to 12), of methyl protons of DQ−. The rotational correlation times, τc, of DQ− determined from these dependences, were 10−9–10−8 s in cationic surfactant (dodecyl-, tetradecyl-, and hexadecyltrimethylammonium bromide) solutions, and 10−10–10−9 s in nonionic surfactant (Triton X-100) solution. ESR spectra of MV+ and DMPZ+ in anionic surfactant (sodium dodecyl sulfate; SDS) solution showed anomalous patterns as not exhibiting the hyperfine splittings due to the nitrogen nucleus. These anomalies were explained by the more significant broadening of the outer peaks due to nitrogen splitting compared with the broadening of the central peaks corresponding to the nuclear quantum number of nitrogen, MN=mN1+mN2=0. From these results, the rotational correlation time for DMPZ+ in SDS solution was estimated as about 10−10 s.