Pressure effect on water solvation dynamics in micellar media

Solvation dynamics of a fluorescent probe in micellar environment has been studied as a function of pressure using picosecond time-dependent fluorescence spectroscopy. Steady-state and time-dependent fluorescence spectra of coumarin 153 (C153) solubilized in two kinds of aqueous surfactant micellar solutions, i.e. neutral micelle; triton-X100 (TX100) and ionic micelle; sodium dodecylsulfate (SDS) have been measured at high pressures. Both steady-state and time-dependent spectra exhibit opposite pressure dependence. For the steady-state spectra, with increasing pressure, the peak maximum shifts toward blue in the TX100 medium, while it shifts toward red in the SDS medium. The solvation time decreases for TX100, while it increases for SDS. The results suggest the different hydration structure surrounding micelles.