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A closer look into deep eutectic solvents: exploring intermolecular interactions using solvatochromic probes

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Abstract

Deep eutectic solvents (DESs) constitute a new class of ionic solvents that has been developing at a fast pace in recent years. Since these solvents are commonly suggested as green alternatives to organic solvents, it is important to understand their physical properties. In particular, polarity plays an important role in solvation phenomena. In this work, the polarity of different families of DESs was studied through solvatochromic responses of UV-vis absorption probes. Kamlet–Taft α, β, π* and ETN parameters were evaluated using different solvatochromic probes, as 2,6-dichloro-4-(2,4,6-triphenyl-N-pyridino)-phenolate (Reichardt's betaine dye 33), 4-nitroaniline, and N,N-diethyl-4-nitroaniline for several families of DESs based on cholinium chloride, DL-menthol and a quaternary ammonium salt ([N4444]Cl). In addition, a study to understand the difference in polarity properties between DESs and the corresponding ILs, namely ILs based on cholinium cation and carboxylic acids as anions ([Ch][Lev], [Ch][Gly] and [Ch][Mal]), was carried out. The chemical structure of the hydrogen bond acceptor (HBA) in a DES clearly controls the dipolarity/polarizability afforded by the DES. Moreover, Kamlet–Taft parameters do not vary much within the family, but they differ among families based on different HBA, either for DESs containing salts ([Ch]Cl or [N4444]Cl) or neutral compounds (DL-menthol). A substitution of the HBD was also found to play an important role in solvatochromic probe behaviour for all the studied systems.

Graphical abstract: A closer look into deep eutectic solvents: exploring intermolecular interactions using solvatochromic probes

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Publication details

The article was received on 21 Sep 2017, accepted on 26 Nov 2017 and first published on 27 Nov 2017


Article type: Paper
DOI: 10.1039/C7CP06471C
Citation: Phys. Chem. Chem. Phys., 2018, Advance Article
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    A closer look into deep eutectic solvents: exploring intermolecular interactions using solvatochromic probes

    C. Florindo, A. J. S. McIntosh, T. Welton, L. C. Branco and I. M. Marrucho, Phys. Chem. Chem. Phys., 2018, Advance Article , DOI: 10.1039/C7CP06471C

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