Photophysical processes in molecules of halogenated fluorescein derivatives in anionic reverse micelles

We studied the photophysical processes of halogenated fluorescein derivatives (eosin (E), erythrosine (ER), and Rose Bengal (RB)) in aqueous micellar solutions using dynamic light scattering and stationary and time-resolved fluorescence spectroscopy. The introduction of dye molecules into reverse AOT micelles causes an increase in their hydrodynamic radii $R_{h}$. The kinetics of fluorescence of the studied dye molecules in reverse micelles was investigated. The average time $\langle\tau\rangle$ of the excited state decreases with increasing $R_h$ for eosin, erythrosine, and Rose Bengal, which is associated with an increase in the mobility of water molecules and a weakening of the effect of geometric limitation of dye molecules. The degrees of fluorescence anisotropy $r$ of dye molecules in reverse micelles were measured; the $r$ values in micellar systems are greater than in aqueous solutions and decrease with increasing $R_{h}$. For the studied dye molecules in micellar systems, the rotational correlation time $\theta$ was determined, which decreases for all studied dyes with increasing $R_{h}$, which indicates a decrease in the microviscosity of a limited aqueous medium inside the micelle. It is found that $\theta_{\mathrm{E}}>\theta_{\mathrm{ER}}>\theta_{\mathrm{BR}}$; that is, the effect of the internal heavy atom appears in the value of the rotational correlation time.