experimental study on the solvation behavior in aqueous choline chloride-based deep eutectic solutions by solvatochromic dyes

The preferential solvation behavior of three solvatochromic indicators (4-nitroaniline, n, n-dimethyl-4-nitroaniline, and 2,6-diphenyl-4-(2,4,6-tri phenyl pyridinium-1-yl)phenolate in some deep eutectic solvents (dess) including choline chloride + glycerol (1:2), choline chloride + ethylene glycol (1:2) and choline chloride + lactic acid (1:2), and their mixtures with water was investigated at constant temperature 298.15±0.1 k by using uv–vis absorption measurements. the solvent exchange model was successfully utilized to analyze the spectral shifts of these dyes to make a description of the preferential solvation behavior of the solute in mixed solvents under study. it was found that the solvation shell of the dyes is mainly affected by the solvent-solvent and solvent-solute interactions, especially hydrogen bonding. the preferential solvation parameter shows that in all aqueous mixtures of des, the order of preferential solvation for the solvatochromic dyes is as des > (water-des) complex > water. the contribution of water to the preferential solvation of dyes is low. this is probably due to the great affinity of water molecules for the self-association and the strong interaction between des and the dyes.