Choline Fluoride-Ethylene glycol deep eutectic solvent mixture - Synthesis and physicochemical properties

A critical factor in achieving tunability in DESs is varying the type of hydrogen bond acceptors (HBAs) and donors (HBDs). Choline halides (ChX), such as ChCl and ChBr, have been studied to investigate the effect of the choline anion on DESs. However, ChF-based DESs have been underrepresented in scientific research. ChF has excellent potential, such as high electron affinity, ionization potential, and strong hydrogen bond interactions. Moreover, ChF-based DES can lead to a deeper understanding of DESs due to the NMR-active F-19 nuclear spin nature. We report the first synthesis and characterization of choline fluoride-EG (1:2, ChF:EG) DES, which we named EthalineF. We studied this mixture using various spectroscopic techniques, including NMR, FT-IR, Raman, and UV-vis spectroscopies. Polarity, density, viscosity, and conductivity measurements were collected as well. Transient absorption spectroscopy (TAS) was used to study the solvation dynamics of EthalineF. F-19 NMR indicated that some fluoride anions (similar to 15%) are coordinated to the choline cation. In EthalineF, the new type of observed fluoride anions is proposed to be a tight-binding choline-fluoride ion pair. Further, EthalineF has a larger solvodynamic radius than Ethaline. This can explain the lower conductivity for EthalineF compared to Ethaline despite the higher fluidity and solvation dynamics for EthalineF.

Automated summary

A critical factor in achieving tunability in DESs is the variation of HBAs and HBDs. Choline fluoride-based DESs, such as EthalineF, were synthesized and characterized for the first time. Various spectroscopic techniques were used to study EthalineF, and measurements of polarity, density, viscosity, and conductivity were collected. The results showed that EthalineF has a larger solvodynamic radius compared to Ethaline, explaining the lower conductivity despite higher fluidity and solvation dynamics.