Spectroscopic Analysis of Solvatochromic Properties in Some Deep Eutectic Solvents and Their Aqueous Mixtures

To study the polarity scale of three deep eutectic solvents (DESs), i.e. choline chloride + glycerol (1:2), choline chloride + ethylene glycol (1:2) and choline chloride + lactic acid (1:2), and their mixtures with water (in the whole mole fraction range), Kamlet-Taft solvent parameters (α, β, and π*), Dimroth-Reichardt’s ET(30) parameter were experimentally measured at constant temperature 298.15±0.1 K. These parameters were obtained based on UV–Vis absorbance of some solvatochromic probes. The spectral changes of these indicators were interpreted in terms of specifc and nonspecifc dye–solvent interactions. The parameter ET(30) was obtained from electronic absorbance of the betaine dye within the mixtures. It was found that the polarity, polarizability and acidity of the co-solvent mixtures decreases by increasing the mole fraction of DESs in the system, while basicity of the media increases with mole fraction of DESs.