Solvent effect in the theoretical absorption and emission spectra of fluorescein dyes

Fluorescein and its halogenated derivatives representing a family of homologous dyes with the gradual substitution of halogen atoms for hydrogen ones are widely used in biomedicine as fluorescent probes. This stimulates the intense experimental and theoretical studies of their fluorescent properties in aqueous solutions. However, the theoretical calculations are complicated by the necessity of taking into account the effect of a solvent (water) in the explicit form and the need for effective basic sets. This is especially important for the dyes that contain heavy atoms. In this study, the quantum-chemical investigations of the dianionic form of fluorescein and its Br- and I-substituted derivatives (eosin Y and erythrosin B) have been carried out using the time-dependent density functional theory (B3LYP functional) implemented in the GAMESS software suite. The effect of a solvent has been considered in the framework of the modified Thomas polarizable continuum model. The calculations have been made for vertical (absorption and emission) excitations in the adiabatic approximation and at the nonequilibrium solvation. The results obtained for the nonequilibrium solvation are in excellent agreement with the experimental data for fluorescein and its halogenated derivatives.