Steady-state spectroscopy and time-resolved solvation dynamics have been used to investigate the effects the addition of alkanol has on the location of coumarin 343 (C343) in cetyltrimethylammonium bromide (CTAB)/1-pentanol/cyclohexane/water, CTAB/1-heptanol/cyclohexane/water, and sodium dodecyl sulfate/1-heptanol/cyclohexane/water reverse micelles. Steady-state spectroscopy showed that the probe molecule is not sensitive to alkanol chain lengths or water loading. Instead, C343 is sensitive to the surfactant used to form the reverse micelles. Solvation dynamics measurements utilizing ultrafast time-resolved fluorescence-upconversion spectroscopy revealed two solvation reorganization times regardless of the micellar system studied or hydration level. A hundreds of picosecond time component is attributed to collective motion of the interface. Time-zero analysis reveals a substantial relaxation component occurring on the femtosecond time scale.

A wide variety of probe molecules have been used to characterize the environment found within reverse micelles. This manuscript reports on results from steady-state and time-resolved spectroscopies of the probe molecule Coumarin 343. The steady-state spectra for the probe molecule in ternary and quaternary systems are nearly identical. However, the time-resolved studies clearly indicate substantial differences in the probe sensed by the probe molecule. Implications of these results for the interpretation of spectroscopy of probe molecules in confined media are discussed.