Metal-containing ionic liquids and ionic liquid crystals based on imidazolium moiety

Ionic liquids and ionic liquid crystals of imidazolium salts composed of various transition and main group metals have been reviewed. Ionic metal complexes of imidazoles and N-heterocyclic carbenes possess the similar properties were also included. These types of ILs and ILCs have been realized as potential solvents, catalysts, catalyst precursors and reagents for many organic transformations and provide ecofriendly protocols. They have also been found to play key roles in material science. Many of these IL systems are air- and moisture stable and are considered as alternatives for air- and moisture sensitive chloroaluminate-based ILs.     

Self‐Assembly of Imidazolium‐Based Rodlike Ionic Liquid Crystals: Transition from Lamellar to Micellar Organization

By using aryl‐amination chemistry, a series of rodlike 1‐phenyl‐1H‐imidazole‐based liquid crystals (LCs) and related imidazolium‐based ionic liquid crystals (ILCs) has been prepared. The number and length of the C‐terminal chains (at the noncharged end of the rodlike core) and the length of the N‐terminal chain (on the imidazolium unit in the ILCs) were modified and the influence of these structural parameters on the mode of self‐assembly in LC phases was investigated by polarizing microscopy, differential scanning calorimetry, and X‐ray diffraction. For the single‐chain imidazole derivatives nematic phases (N) and bilayer SmA₂ phases were found, but upon increasing the number of alkyl chains the LC phases were lost. For the related imidazolium salts LC phases were preserved upon increasing the number and length of the C‐terminal chains and in this series it leads to the phase sequence SmA–columnar (Col)–micellar cubic (Cub_I/Pm3n). Elongation of the N‐terminal chain gives the reversed sequence. Short N‐terminal chains prefer an end‐to‐end packing of the mesogens in which these chains are separated from the C‐terminal chains. Elongation of the N‐terminal chain leads to a mixing of N‐ and C‐terminal chains, which is accompanied by complete intercalation of the aromatic cores. In the smectic phases this gives rise to a transition from bilayer (SmA₂) to monolayer smectic (SmA) phases. For the columnar and cubic phases the segregated end‐to‐end packing leads to core–shell aggregates. In this case, elongation of the N‐terminal chains distorts core–shell formation and removes Cub_I and Col phases in favor of single‐layer SmA phases. Hence, by tailoring the length of the N‐terminal chain, a crossover from taper‐shaped to polycatenar LC tectons was achieved, which provides a powerful tool for control of self‐assembly in ILCs.     

Surface-functionalized ionic liquid crystal-supported ionic liquid phase materials: ionic liquid crystals in mesopores

The influence of confinement on the ionic liquid crystal (ILC) [C(18)C(1)Im][OTf] is studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The ILC studied is supported on Si-based powders and glasses with pore sizes ranging from 11 to 50 nm. The temperature of the solid-to-liquid-crystalline phase transition seems mostly unaffected by the confinement, whereas the temperature of the liquid-crystalline-to-liquid phase transition is depressed for smaller pore sizes. A contact layer with a thickness in the order of 2 nm is identified. The contact layer exhibits a phase transition at a temperature 30 K lower than the solid-to-liquid-crystalline phase transition observed for the neat ILC. For applications within the "supported ionic liquid phase (SILP)" concept, the experiments show that in pores of diameter 50 nm a pore filling of α>0.4 is sufficient to reproduce the phase transitions of the neat ILC.     

Adjusting the chromatographic properties of poly(ionic liquid)‐modified stationary phases by substitution on the imidazolium cation

Poly(ionic liquid)‐modified stationary phases can have multiple interactions with solutes. However, in most stationary phases, separation selectivity is adjusted by changing the poly(ionic liquid) anions. In this work, two poly(ionic liquid)‐modified silica stationary phases were prepared by introducing the cyano or tetrazolyl group on the pendant imidazolium cation on the polymer chains. Various analytes were selected to investigate their mechanism of retention in the stationary phases using different mobile phases. Two poly(ionic liquid)‐modified stationary phases can provide various interactions toward solutes. Compared to the cyano‐functionalized poly(ionic liquid) stationary phase, the tetrazolyl‐functionalized poly(ionic liquid) stationary phase provides additional cation‐exchange and π‐π interactions, resulting in different separation selectivity toward analytes. Finally, applicability of the developed stationary phases was demonstrated by the efficient separation of nonsteroidal anti‐inflammatory drugs.     

Discotic ionic liquid crystals of triphenylene as dispersants for orienting single-walled carbon nanotubes

Orient and conduct: Triphenylene-based discotic ionic liquid crystals (ILCs) with six imidazolium ion pendants can disperse pristine single-walled carbon nanotubes (SWNTs). When the ILC is columnarly assembled, doping with SWNTs results in macroscopic homeotropic columnar orientation. Combination of shear and annealing treatments gives rise to three different orientation states, which determine the anisotropy of electrical conduction.     

Polymerizable Ionic Liquid Crystals

Polymerizable vinylimidazolium ionic liquids (ILs) that contain mesogenic coumarin and biphenyl units, respectively, have been synthesized. The N‐alkylation of N‐vinylimidazole with bromoalkylated mesogenic units 7‐(6‐bromohexyloxy)coumarin ( 1 ) and 4,4′‐bis(6‐bromohexyloxy)biphenyl ( 2 ) was then carried out. The thermal behavior of the obtained ILs 3 and 4 was investigated by differential scanning calorimetry and polarizing optical microscopy. These measurements showed that the attached mesogenic units induce the self‐assembly of ILs and, therefore, the occurrence of liquid crystalline phases. Subsequently, the ionic liquid crystals (ILCs) 3 and 4 were polymerized by a free‐radical mechanism.

     

Collision-induced dissociation of sulfur-containing imidazolium ionic liquids

A number of 1,2-dimethylimidazole ionic liquids substituted on N(II) with alkyl chains of varying lengths terminated with sulfur-containing groups were investigated by electrospray high-resolution tandem Fourier-transform mass spectrometry. Fragmentation pathways are strongly dependent on the oxidation state of the sulfur and the alkyl chain length. The dissociations detected are rationalized by deuterium labeling, comparisons between homologous compounds and accurate mass data. Several homolytic processes are reported, leading to distonic ions and loss of hydrogen, methyl and other free radicals.     

Ion transport in polymerized lyotropic liquid crystals containing ionic liquid

In this work, we investigate the effect of morphology and segmental dynamics on ion transport in polymerized lyotropic liquid crystals (polyLLCs) containing 1-butyl-3-methylimidazolium tetrafluoroborate as ionic liquid (IL). We demonstrate that two important factors, which affect ion conduction in polyLLCs, are grain size and chain density at the interface. The polyLLC with large grain size (70 nm) shows significant reduction in ion conductivity (one order of magnitude) compared to its homopolymer/IL mixture. However, the polyLLC with small grain size (20 nm) has little difference in ion conductivity compared to its homopolymer/IL mixture. It is observed that decreasing the chain density enhances the interaction of IL with polymer chains and consequently slows the relaxation of polymer chains. In addition, comparing the dynamics of polymer chains in mixtures of homopolymer/IL and templated LLC mesophases shows that the confinement in LLC structure prolongs the relaxation of polymer chains.     

Dendronized supramolecular polymers self‐assembled from dendritic ionic liquids

The synthesis, structural, and retrostructural analysis of a library of self‐assembling dendrons containing triethyl and tripropyl ammonium, pyridinium and 3‐methylimidazolium chloride, tetrafluoroborate, and hexafluorophosphate at their apex are reported. These dendritic ionic liquids self‐assemble into supramolecular columns or spheres which self‐organize into 2D hexagonal or rectangular and 3D cubic or tetragonal liquid crystalline and crystalline lattices. Structural analysis by X‐ray diffraction experiments demonstrated the self‐assembly of supramolecular dendrimers containing columnar and spherical nanoscale ionic liquid reactors segregated in their core. Both in the supramolecular columns and spheres the noncovalent interactions mediated by the ionic liquid provide a supramolecular polymer and therefore, these assemblies represent a new class of dendronized supramolecular polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4165–4193, 2009     

Effects of alkyl chain length on properties of 1-alkyl-3-methylimidazolium fluorohydrogenate ionic liquid crystals

A series of 1‐alkyl‐3‐methylimidazolium fluorohydrogenate salts (C_xMIm(FH)₂F, x=8, 10, 12, 14, 16, and 18) have been characterized by thermal analysis, polarized optical microscopy, IR spectroscopy, X‐ray diffraction, and anisotropic ionic conductivity measurements. Liquid crystalline mesophases with a smectic A interdigitated bilayer structure are observed from C₁₀ to C₁₈, showing a fan‐like or focal conic texture. The temperature range of the mesophase increases with the increase in the alkyl chain length (from 10.1 °C for C₁₀MIm(FH)₂F to 123.1 °C for C₁₈MIm(FH)₂F). The distance between the two layers in the smectic structure gradually increases with increasing alkyl chain length and decreases with increasing temperature. Conductivity parallel to the smectic layers is around 10 mS cm^?1 regardless of the alkyl chain length, whereas that perpendicular to the smectic layers decreases with increasing alkyl chain length because of the thicker insulating sheet with the longer alkyl chain.     

Room temperature imidazolium ionic liquid: a solvent for extraction of carbamates prior to liquid chromatographic analysis

A simple and rapid method for preconcentration of carbamate insecticides, including methomyl, propoxur, carbofuran, carbaryl, isoprocarb, methiocarb and promecarb, has been developed. It was based on a liquid-liquid microextraction using a [C₄MIM][PF₆] room temperature ionic liquid as an extraction solvent prior to analysis by high performance liquid chromatography with UV detection. Experimental parameters affecting the extraction performance, such as the volumes of sample, extractant and dissolving solvent, and extraction time, were studied. Under the selected conditions, the enrichment factors in the range between 10 and 25 could be achieved with the limit of detection in the range of 2-40 μg L⁻¹, and with the relative standard deviations of lower than 0.6 and 10.2% for retention time and peak area, respectively. The proposed method offers advantages in reduction of the exposure danger to toxic solvents used in the conventional liquid-liquid extraction, simplicity of the extraction processes, rapidity, and sensitivity enhancement. The method was demonstrated to apply to the analysis of fruit and natural surface water samples.     

咪唑类离子液体的合成及其在分析化学中的应用

本文介绍了咪唑类离子液体的合成,特别是以BF4-、PF6-为阴离子的咪唑类离子液体的合成,并重点综述了近年来咪唑类离子液体在电化学分析、质谱、光谱、色谱及毛细管电泳等分析化学中的应用.     

Synthesis of a kind of geminal imidazolium ionic liquid with long aliphatic chains

A novel geminal imidazolium ionic liquid with long hydrocarbon group,1,4-bis(3-tetradecylimidazolium-1-yl)butane bromide was synthesized and an efficient synthesized method was introduced detailedly.Its structure was determined by FT-IR,~1H NMR and elemental analysis.     

Thermotropic liquid crystal behaviour of gemini imidazolium-based ionic amphiphiles

Thermotropic ionic liquid crystals (LCs) are useful for a number of applications such as anisotropic ion transport and as organised reaction media/solvents because of their ordered fluid properties and intrinsic charge units. A large number of different ionic LC architectures are known, but only a handful of examples of gemini (i.e. paired or dimeric) ionic LCs have been prepared and studied. In this work, a series of 20 new symmetric, imidazolium-based, gemini cationic LCs containing two bridged imidazolium cations and two pendant alkyl chains was synthesised, and the thermotropic LC behaviours were characterised. The imidazolium unit provides a highly tunable and modular platform for the design and synthesis of gemini cationic LCs which offers excellent structure control. As expected, the thermotropic LC properties of these new amphilphilic, gemini ionic LCs were found to be strongly influenced by the length of the spacer between the imidazolium units, the length of the pendant alkyl tails, and the nature of the anion. Smectic A (SmA) thermotropic LC phases were observed in more than half of the gemini imidazolium LC systems studied.     

Self‐assembly and lower critical solution temperature properties of supramolecular block copolymer/ionic liquid complexes depending on the alkyl chain length of imidazolium rings

We report the liquid crystalline (LC) assembly and lower critical solution temperature (LCST) properties of wedge‐shaped block copolymer (BCP)/1‐alkyl‐3‐methylimidazolium tetrafluoroborate ([C_nMIM][BF₄], n = 2, 4, 6) complexes ( 1 – 3 ) depending on the alkyl chain length of the ionic liquids (ILs). In contrast to the crystalline BCP, all of the ionic samples showed LC phases. 1 with [C₂MIM][BF₄] exhibited a hexagonal columnar phase, and 3 with [C₆MIM][BF₄] exhibited a gyroid phase. Interestingly, a temperature‐dependent transformation from columnar phase to gyroid phase was revealed for 2 with [C₄MIM][BF₄]. The phase difference may be explained by the supramolecular shape change that was dependent on the alkyl chain length of the ILs. The LCST behavior was characterized using the differential scanning calorimetry, turbidity observations, and the X‐ray diffraction techniques. Notably, the primary d‐spacing began to decrease at the clouding temperature (T_c). 3 showed the highest T_c at 130 °C, which is greater than the temperature of the order‐to‐disorder transition. The results demonstrate that the subtle variation in the IL structure affects the morphological and LCST properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3587–3596     

Microwave-accelerated Claisen rearrangement in bicyclic imidazolium [b-3C-im][NTf2] ionic liquid

With microwaves, a chemically stable ionic liquid [b-3C-im][NTf₂] recently developed in our laboratory was used as solvent and successfully applied to accelerate Claisen rearrangement reactions at high temperatures. In the presence of Lewis acid MgCl₂, these thermal rearrangements could be achieved in similar reaction times but at lower temperature. For the microwaved reactions studied in this work, without scarifying isolated yields, the reaction times were significantly reduced from hours (by conventional heating) to ≤3 min. Our result also demonstrated that [b-3C-im][NTf₂] ionic liquid was a useful solvent substitute and could be recycled multiple times for the studied rearrangement reaction at elevated temperatures.     

Sulfur makes the difference: synthesis and mesomorphic properties of novel thioether-functionalized imidazolium ionic liquid crystals

Novel thioether-linked imidazolium ionic liquid crystals were synthesized starting from methyl 2-mercaptoacetate. The mesomorphic properties were determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. All mesogens displayed smectic A mesophase geometries with strongly interdigitated bilayer structures. Comparison of the thioether-linked imidazolium salts with the corresponding amine- and amide-linked imidazolium salts as well as simple N-alkyl-imidazolium salts showed that both mesophase width and stability increased with increasing softness of the linking unit, thus indicating the beneficial effect of sulfur. Additionally, an increase of the length of the linking unit decreased the interdigitation of the alkyl chains.