Solvatochromic and preferential solvation of fluorescein in some water-alcoholic mixed solvents

It is known that the hydrogen bonding has a significant effect on the spectral properties of fluorescein, however its relevance to solution behavior and preferential solvation of fluorescein is unclear in mixed solvents. In this work, absorption spectra of fluorescein dianion have been investigated in pure water, methanol, ethanol, 1-propanol, 2-propanol, dimethylsulfoxide, N,N-dimethylformamide, acetonitrile and in binary mixtures of water with the mentioned alcohols at 298.15 K. Spectral changes were interpreted in terms of specific and nonspecific solute-solvent interactions. The energy of electronic transition in maximum absorption (ET) was calculated in each binary mixture. The extent and importance of each of solute-solvent interactions to ET were analyzed in the framework of the linear solvation energy relationships. Preferential solvation was detected as a nonideal behavior of ET curve respective to the analytical mole fraction of alcohols in all binary mixtures. The ET values were fitted to a solvent exchange model to calculate the preferential solvation parameters. The preference of fluorescein dianion to be solvated by one of the solvating species relative to others was discussed in terms of solvent-solvent and solute-solvent interactions.