A Specific Interaction between Ionic Liquids’ Cations and Reichardt’s Dye

Abstract

Solvatochromic probes are often used to understand solvation environments at the molecular scale. In the case of ionic liquids constituted by an anion and a cation, which are designed and paired in order to obtain a low melting point and other desirable physicochemical properties, these two indivisible components can interact in a very different way with the probe. This is the case with one of the most common probes: Reichardt’s Dye. In the cases where the positive charge of the cation is delocalized on an aromatic ring such as imidazolium, the antibonding orbitals of the positively charged aromatic system are very similar in nature and energy to the LUMO of Reichardt’s Dye. This leads to an interesting, specific cation-probe interaction that can be used to elucidate the nature of the ionic liquids’ cations. Parallel computational and experimental investigations have been conducted to elucidate the nature of this interaction with respect to the molecular structure of the cation.

Recent Advances in the Synthesis and Applications of Ionic Liquids Derived from Natural Products

“…Somers and co-workers exploited 95 other well-known aromatic molecules derived from lignin, namely 4-hydroxy-3-methoxybenzoic (vanillic) acid, 3,4,5-trihydroxybenzoic (gallic) acid, and 4-hydroxy-3,5-dimethoxybenzoic (syringic) acid, to prepare the already described 96 salts 239a-c, as well as the new ILs 240a-c and 241a-c, respectively (Figure 15). These compounds were easily obtained in quantitative yield by mixing the above-mentioned acids with the com-mercially available aqueous solution of choline hydroxide or a methanolic solution of 1-ethyl-3-methylimidazolium methyl carbonate or pure 1,5-diazabicyclo[5.4.0]undec-7ene (DBU).…”

A Combined Experimental/Computational Study of Dicationic Ionic Liquids with Bromide and Tungstate Anions

“…Imidazolium systems have been chosen for this study due to their great popularity, thus making possible a more direct comparison with structurally related DILs. Furthermore, the possibility of C2-H hydrogens forming hydrogen bonds with the anions considered in this work as well as with other molecules makes imidazolium DILs interesting both from the point of view of structural investigation and catalytic activity assessment [61]. The structures of the double-charged cations considered are reported in Figure 1.…”

Polarity of Organic Solvent/Water Mixtures Measured with Reichardt’s B30 and Related Solvatochromic Probes—A Critical Review

“…However, this approach is only partially justified, as we have recently shown [43]. The concept of determining HBD parameters works quite well for ionic liquids (ILs) and other salts due to the electrostatic interaction between the B30 phenolate anion and the constituent cation of the IL [41,[44][45][46]. However, due to some contradictions between theory and experimental results, the phenomenon is still under investigation [46].…”

“…The concept of determining HBD parameters works quite well for ionic liquids (ILs) and other salts due to the electrostatic interaction between the B30 phenolate anion and the constituent cation of the IL [41,[44][45][46]. However, due to some contradictions between theory and experimental results, the phenomenon is still under investigation [46]. B30 in particular is routinely used as a polarity indicator for binary solvent mixtures [2,[6][7][8][9][13][14][15][16][17][18][19][20][21].…”