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 R<sub>h</sub>, 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 R<sub>h</sub>. It has been found that with the growth of R<sub>h</sub>, 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 µ<sub>e</sub>/µ<sub>g</sub> 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 R<sub>h</sub>, 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.