pH-Dependence of the Absorption and Fluorescent Properties of Fluorone Dyes in Aqueous Solutions

A series of fluorone dyes (fluorescein, eosin Y, erythrosin B) in aqueous solution is investigated by the absorption, fluorescence spectroscopic and time-resolved methods. Based on an analysis of the absorption spectrum amplitude, the fluorescence quantum yield, and the fluorescence lifetime vs. pH, the dissociation constants of the dyes in the ground and excited states are calculated. Quantitative and qualitative differences in the character of ionic equilibrium between fluorescein and its halogenated derivatives - eosin Y and erythrosin B - are revealed. The polarized fluorescence method has shown that the hydrodynamic diameter changes in a series of fluorone dyes due to both the increase of the bond length upon halogenation and the influence of solvation shell upon the change of the dye ionic species.