Polarity Behaviour and Specific Interactions of Imidazolium-Based Ionic Liquids in Ethylene Glycol

Effect of Mixture Composition on the Photophysics of Indoline Dyes in Imidazolium Ionic Liquid-Molecular Solvent Mixtures: A Femtosecond Transient Absorption Study

We conducted a study on the photophysics of three indoline dyes, D102, D149, and D205, in binary mixtures of ionic liquids (IL) and polar aprotic molecular solvents (MS). Specifically, we examined the behavior of these dyes in IL-MS mixtures containing four different imidazolium-based ILs and three different polar aprotic MSs. Our investigation involved several techniques, including stationary absorption and emission measurements, as well as femtosecond transient absorption (TA) spectroscopy. Through our analysis, we discovered a peculiar behavior of several photophysical properties at low IL mole fractions (0 < XIL < 0.2). Indeed, in this range of mixture composition, the absorption maximum wavelength decreases noticeably, while the emission maximum wavelength and the Stokes shift, expressed in wavenumbers, reach a maximum. while a minimum occurs in the relative quantum yield and the excited state lifetime. These results indicate that the solvation of dye undergoes a large change in this range of mixture composition. We found that, at high ionic liquid content, the excited relaxation times are correlated with the high viscosity, while at low content, it is the polarity of the solvent that influences the behavior of the excited relaxation times. At a mixture composition of around 0.10, the behavior of the photophysical properties of the studied IL-MS mixtures indicates a crossover between situations where the solvation is dominated by that of ions and that dominated by the solvent.

Liquid crystalline microspheres of azobenzene amphiphiles formed by thermally induced pH changes in binary water-hydrolytic ionic liquid media

Anionic azobenzene-containing bilayered membranes dispersed in binary water-ionic liquid (IL) media undergo proton-responsive transformation into liquid crystalline microspheres (LCMs). This transformation was induced by protons released by the heat-induced hydrolysis of tetrafluoroborate ions in the ILs. This work demonstrates the first beneficial use of hydrolysis-susceptible ILs in chemistry.

Transport properties and intermolecular interactions in binary mixtures based on the protic ionic liquid ethylimidazolium triflate and ethylene glycol

The binary mixture based on the protic ionic liquid (PIL) ethylimidazolium triflate (C2HImTfO) and the diol compound ethylene glycol (EG) has been investigated in the whole composition range from pure PIL to pure EG. At 30 °C the addition of EG increases both the ionic conductivity and the self-diffusivity of the ions. These quantities, however, change at different rates suggesting that the ionicity of the system is composition dependent. This behaviour is explained by means of new intermolecular forces established when a second compound like EG is introduced into the ionic network. More specifically, a complex H-bonded network is formed that involves the -NH group of the cation, the -OH group of EG and the -SO3 group of the anion. This configuration may increase the fluidity of the mixture but not necessarily the ionic dissociation. Moreover, diffusion NMR results indicate the occurrence of local proton dynamics, which arise from a proton exchange between the -NH of the cation and the -OH of EG, providing the requisite for a long-range Grotthuss mechanism of proton transport.

Nicotine-based surface active ionic liquids: Synthesis, self-assembly and cytotoxicity studies

New ester-functionalized surface active ionic liquids (SAILs) based on nicotine, [C_nENic][Br] (n=8, 10 and 12), with bromide counterions have been synthesized, characterized and investigated for their self-assembly behavior in aqueous medium. Conductivity measurements in aqueous solutions of the investigated SAILs have provided information about their critical micelle concentration (cmc), and degree of counterion binding (β), where cmc was found to be 2-3-fold lower than homologous SAILs or conventional cationic surfactants. The inherent fluorescence of SAILs in the absence of any external fluorescent probe have shed light on cmc as well as interactions prevailing between the monomers in micelle at molecular level. The thermodynamic parameters related to micellization have been deduced from isothermal titration calorimetry (ITC) and conductivity measurements. ¹H NMR, spin-lattice (T₁) relaxation time and 2D ¹H-^IH ROESY measurements have been exploited to get detailed account of internal structure of micelle. The size and shape of the micelles have been explored using dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. The synthesized SAILs have been found to be non-cytotoxic towards C6-Glioma cell line, which adds to the possible utility of these SAILs for diverse biological applications.

Vibrational Spectroscopy of Ionic Liquids

Vibrational spectroscopy has continued use as a powerful tool to characterize ionic liquids since the literature on room temperature molten salts experienced the rapid increase in number of publications in the 1990's. In the past years, infrared (IR) and Raman spectroscopies have provided insights on ionic interactions and the resulting liquid structure in ionic liquids. A large body of information is now available concerning vibrational spectra of ionic liquids made of many different combinations of anions and cations, but reviews on this literature are scarce. This review is an attempt at filling this gap. Some basic care needed while recording IR or Raman spectra of ionic liquids is explained. We have reviewed the conceptual basis of theoretical frameworks which have been used to interpret vibrational spectra of ionic liquids, helping the reader to distinguish the scope of application of different methods of calculation. Vibrational frequencies observed in IR and Raman spectra of ionic liquids based on different anions and cations are discussed and eventual disagreements between different sources are critically reviewed. The aim is that the reader can use this information while assigning vibrational spectra of an ionic liquid containing another particular combination of anions and cations. Different applications of IR and Raman spectroscopies are given for both pure ionic liquids and solutions. Further issues addressed in this review are the intermolecular vibrations that are more directly probed by the low-frequency range of IR and Raman spectra and the applications of vibrational spectroscopy in studying phase transitions of ionic liquids.

Modulating the mixed micellization of CTAB and an ionic liquid 1-hexadecyl-3-methylimidazollium bromide via varying physical states of ionic liquid

The physical nature of [C₁₆mim][Br] as monomers/micelles led to different IL–CTAB mixed self-assembled structures.

Greener synthetic route for superparamagnetic and luminescent α-Fe2O3 nanoparticles in binary mixtures of ionic liquid and ethylene glycol

The composition of IL and EG binary solvent mixture affects the structural, morphological, luminescent and magnetic properties of α-Fe₂O₃ nanoparticles.

Probing structural patterns of ion association and solvation in mixtures of imidazolium ionic liquids with acetonitrile by means of relative1H and13C NMR chemical shifts

Competition between ion solvation and association in mixtures of imidazolium ionic liquids and molecular solvents can be systematically addressed by the analysis of relative chemical shift variation with mixture composition.

A novel colloidal suspension of TBA+BF4−–EG and its applications as a soft solid electrolyte

A novel ionically conducting colloidal suspension was prepared from a quaternary ammonium salt and ethylene glycol.

Ionic and Molecular Liquids: Working Together for Robust Engineering

Because of their outstanding versatility, room-temperature ionic liquids (RTILs) are utilized in an ever increasing number of novel and fascinating applications, making them the Holy Grail of modern materials science. In this Perspective, we address the fundamental research and prospective applications of RTILs in combination with molecular liquids, concentrating on three significant areas: (1) the use of molecular liquids to decrease the viscosity of RTILs; (2) the role of RTIL micelle formation in water and organic solvents; and (3) the ability of RTILs to adsorb pollutant gases. Current achievements are examined, and future directions for the potential uses of RTILs are outlined.

Ether- and alcohol-functionalized task-specific ionic liquids: attractive properties and applications

In recent years, the designer nature of ionic liquids (ILs) has driven their exploration and exploitation in countless fields among the physical and chemical sciences. A fair measure of the tremendous attention placed on these fluids has been attributed to their inherent designer nature. And yet, there are relatively few examples of reviews that emphasize this vital aspect in an exhaustive or meaningful way. In this critical review, we systematically survey the physicochemical properties of the collective library of ether- and alcohol-functionalized ILs, highlighting the impact of ionic structure on features such as viscosity, phase behavior/transitions, density, thermostability, electrochemical properties, and polarity (e.g. hydrophilicity, hydrogen bonding capability). In the latter portions of this review, we emphasize the attractive applications of these functionalized ILs across a range of disciplines, including their use as electrolytes or functional fluids for electrochemistry, extractions, biphasic systems, gas separations, carbon capture, carbohydrate dissolution (particularly, the (ligno)celluloses), polymer chemistry, antimicrobial and antielectrostatic agents, organic synthesis, biomolecular stabilization and activation, and nanoscience. Finally, this review discusses anion-functionalized ILs, including sulfur- and oxygen-functionalized analogs, as well as choline-based deep eutectic solvents (DESs), an emerging class of fluids which can be sensibly categorized as semi-molecular cousins to the IL. Finally, the toxicity and biodegradability of ether- and alcohol-functionalized ILs are discussed and cautiously evaluated in light of recent reports. By carefully summarizing literature examples on the properties and applications of oxy-functional designer ILs up till now, it is our intent that this review offers a barometer for gauging future advances in the field as well as a trigger to spur further contemplation of these seemingly inexhaustible and--relative to their potential--virtually untouched fluids. It is abundantly clear that these remarkable fluidic materials are here to stay, just as certain design rules are slowly beginning to emerge. However, in fairness, serendipity also still plays an undeniable role, highlighting the need for both expanded in silico studies and a beacon to attract bright, young researchers to the field (406 references).

Insight into the interactions that control the phase behaviour of new aqueous biphasic systems composed of polyethylene glycol polymers and ionic liquids

New polyethylene glycol (PEG)/ionic liquid aqueous biphasic systems (ABS) are presented. Distinct pairs of PEG polymers and ionic liquids can induce phase separation in aqueous media when dissolved at appropriate concentrations. Phase diagrams have been determined for a large array of systems at 298, 308 and 323 K. A comparison of the binodal curves allowed the analysis of the tunable structural features of the ionic liquid (i.e., anionic nature, cationic core, cationic alkyl side chain length and functionalisation, and number of alkyl substituents in the cation) and the influence of the molecular weight of the PEG polymer on the ability of these solutes to induce an ABS. It was observed that contrary to typical ABS based on ionic liquids and inorganic salts, in which the phase behaviour is dominated by the formation of the hydration complexes of the ions, the interactions between the PEG polymers and ionic liquids control the phase demixing in the polymer-type ABS studied herein. It is shown that both the ionic liquids and PEG polymers can act as the salting-out species; that is, it is an occurrence that is dependent on the structural features of the ionic liquid. For the first time, PEG/ionic liquid ABS are reported and insight into the major interactions that govern the polymer/ionic liquid phase behaviour in aqueous media are provided. The use of two different nonvolatile and tunable species (i.e., ionic liquids and PEG polymers) to form ABS allows the polarities of the phases to be tailored. Hence, the development of environmentally friendly separation processes that make use of these novel systems is envisaged.