Solvatochromic Parameters of Deep Eutectic Solvents Based on Choline Chloride and Carboxylic Acids

The solvatochromic parameters (Nile red solvation energy ENR, Kamlet–Taft polarizability π*, basicity β, and acidity α) of deep eutectic solvents (DESs) based on choline chloride as a hydrogen bond acceptor and carboxylic acids (formic, acetic, lactic, oxalic, malonic, malic) as hydrogen bond donors have been determined by UV-visible spectroscopy. A modified technique for determining the solvation energy in acidic media using Nile Red was proposed, and the β values obtained using different dyes were correlated with one another. The effects of the structure and physicochemical properties of the hydrogen bond donor (carboxylic acid) and the hydrogen bond donor/acceptor molar ratio on the solvatochromic parameters of DESs was studied.