Solvatochromic probe behavior within choline chloride-based deep eutectic solvents: effect of temperature and water

Area of Science:

• Green Chemistry
• Physical Chemistry
• Solvent Science

Background:

• Deep eutectic solvents (DESs) are emerging as sustainable alternatives to traditional solvents.
• DES properties are tunable by altering their constituent hydrogen bond donors and salts.
• Temperature and water content significantly influence DES physicochemical characteristics.

Purpose of the Study:

• To investigate the impact of temperature and water on the behavior of solvatochromic probes in three distinct DESs.
• To elucidate the changes in DES properties like acidity, basicity, and polarity under varying conditions.
• To understand the solvation dynamics and interactions within aqueous DES mixtures.

Main Methods:

• Utilized solvatochromic probes, including pyrene, to monitor changes in DES microenvironment.
• Employed FTIR absorbance and Raman spectroscopy to analyze intermolecular interactions in aqueous DES mixtures.
• Investigated three DESs: ethaline, glyceline, and reline, formed from choline chloride and different hydrogen bond donors.

Main Results:

• Increased temperature led to decreased H-bond donating acidity and solution polarity, as indicated by probe responses.
• Water addition enhanced dipolarity/polarizability and reduced H-bond accepting basicity.
• Pyrene's response suggested significant preferential solvation by DES in aqueous mixtures, particularly in ethaline and glyceline.
• Spectroscopic data confirmed increased interspecies H-bonding in aqueous ethaline and glyceline compared to reline.

Conclusions:

• Temperature and water content are critical factors modulating DES properties and solvation behavior.
• The hydroxyl functionalities in ethaline and glyceline contribute to stronger interspecies H-bonding with water.
• DESs offer tunable environments for chemical processes, with solvation effects being predictable yet showing specific interactions.