The Effect of Nanoscale Reverse Micelles on the Photophysical Properties of Fluorescein Molecules
Photophysical processes in water-micellar solutions of fluorescein have been studied using the methods of stationary time-resolved fluorescence spectroscopy and dynamic light scattering. It has been found that the introduction of dye molecules into reverse micelles causes an increase in their hydrodynamic radii Rh, proportional to the degree of hydration w. The absorption and fluorescence spectra, the average lifetime of the excited state t, and the degree of fluorescence anisotropy r of the fluorescein molecules are presented for different values of Rh. It has been found that with the growth of Rh, the fraction of the anionic form of the dye in water-micellar solutions increases. In this case, an increase in the ratio of the dipole moments of the fluorescein molecules in the excited and ground states µe/µg is observed, due to the structural reorganization of micelles. It has been experimentally established that the rotational relaxation time θ of dye molecules decreases with growing Rh, which indicates an increase in the microviscosity of the environment of the fluorescein molecules due to the localization of dye molecules in the region of surface water in the micelle.