Ionic liquid crystals

Binnemans, K. (2005) Ionic Liquid Crystals. Chemical Reviews, 105, 4148-4204. 

Dobbs, W., Suisse, J.-M., Douce, L. and Welter, R. (2006) Electrodeposition of Silver Partides and Gold Nanopartides from Ionic Liquid-Crystal Precursors. Angewandte Chemie (International Edition in English), 45, 4179-4182. 

Holbrey, J. D. Seddon, K. R. The phase behaviour of l-alkyl-3-methylimidazolium tetrafluoroborates ionic liquids and ionic liquid crystals, J. Chem. Soc., Dalton Trans., 1999, 2133-2139. 

Cordon, C.M. et al., Ionic liquid crystals hexafluorophosphate salts, /. Mater. Chem., 8, 2627, 1998. 

Scheme 51 Piperazine-based ionic liquid crystals 103 and the effects of anion exchange...

Prominent exceptions are studies on the liquid crystal phase formation and self-assembly of two-dimensional disc- or sheet-like nanomaterials such as the organization of nanodiscs or nanoplatelets into nematic, smectic, or columnar morphologies [263-270] (see Fig. 2 for an example of the self-assembly of nanoclay in aqueous suspensions) or the synthesis of CuCl nanoplatelets from ionic liquid crystal precursors as described by Taubert and co-workers [271-273]. 

Cook, A. G., Baumeister, U., Tschierske, C., Supramolecular dendrimers Unusual mesophases of ionic liquid crystals derived from protonation of DAB dendrimers with facial amphiphilic carboxylic acids. J. Mater. Chem. 2005, 15, 1708-1721. 

Mimaya T.A., Volkov S.V. Ionic Liquid Crystals as Universal Matrices (Solvents).- Green industrial applications of ionic liquids. NATO Science Series, II Mathematics, Physics and Chemistry. Kluwer Academic Publ., 2003. P. 439-456. 

Evans et al. also showed that the 1 1 mixture of BAN and (3, y-distearoyl-phos-photidylcholine (DSPC) gives a smectic A texture in the temperature range of 57.3 to 100°C [21]. This is the first notice of lyotropic lamellar liquid crystals formed in the ionic medium. Additionally, Seddon et al. [28] and Neve et al. [29] have described the long-chained A-alkylpyridinium or l-methyl-3-alkylimidazolium ions to display smectic liquid-crystalline phases above their melting points, when Cl or tetrachloro-metal anions like CoCl " and CuCl " are used as the counter ions. Lin et al. have also noted the liquid crystal behavior of 1-alkylimidazolium salts and the effect on the stereoselectivity of Diels-Alder reactions [30]. However, liquid crystals are classified as ionic liquid crystals (ILCs), and they are distinguished from liquid crystals that are dispersed in ionic liquids. Although the formation of micelles and liquid crystal phases in ionic liquids have been thus reported, there has been no mention of the self-assembly of developed nano-assemblies that are stably dispersed in ionic liquids. In the next section the formation of bilayer membranes and vesicles in ionic liquids is discussed. 

Ionic liquid crystals are liquid crystals containing ionic moieties. Ionic hquid crystals having ammonium and pyridinium salts were reported to show stable thermotropic liquid crystalline behavior [35 0]. Seddon, Bruce, and coworkers showed that some imidazolium and pyridinium salts exhibit low melting points and liquid crystalline behavior [41]. Ionic liquid crystals with lower temperature mesophase ranges are called hquid crystalline ionic liquids. A large variety of thermotropic liquid crystaUine ionic liquids exhibiting anisotropic fluid states were prepared. In particular, the ionic liquid crystals based on imidazolium salts 1 [42-46], 2... 

Figure 25.1 Molecular structures of ionic liquid crystals.

Metal-based ionic liquid crystals containing a tetrahedral tetrahalometalate ion (MX X = Cl, Br, I M = Co, Ni, Cu, Pd, etc.) 7 [41, 54] and 8 [55-57] were studied (Figure 25.1). They provide various coordination geometries. For example, Al-aUcylpyridinium salts 8 often denoted as [C Py]2[CuCl4] (n= 12-18) show a variety of liquid crystalline phases from smectic to columnar or even cubic phases... 

Bipyridinium cation 9 [58], phosphonium [59-62], guanidinium [63], and vina-midinium [64] cations were used to form thermotropic ionic liquid crystals. For example, the mixture of diheptyl and dioctyl viologens 9 (20 80 by wt%) with TFSI anion forms a smectic A phase between 22° and 132°C. It was reported that the viologens show fluorescence in both non-polar and polar organic solvents, which can be useful for the development of biological and chemical sensors [65]. 

ANISOTROPIC IONIC CONDUCTIVITIES OF IONIC LIQUID CRYSTALS... 

In this chapter we have described the mesomorphic behavior and ionic conductivities of ionic liquid-based liquid crystalline materials. These ion-active anisotropic materials have great potentials for applications not only as electrolytes that anisotropically transport ions at the nanometer scale but also as ordered solvents for reactions. Ionic liquid crystals have also been studied for uses as diverse as nonliner optoelectronic materials [61, 62], photoluminescent materials [78], structuredirecting reagents for mesoporous materials [79, 80] and ordered solvents for organic reactions [47, 81]. Approaches to self-organization of ionic liquids may open a new avenue in the field of material science and supramolecular chemistry. 

Fig. 1 Diagrams depicting a a layer of a cubic sodium chloride crystal b a monoclinic 1,3-dimethylimidazolium chloride ionic-liquid crystal c two radial distribution functions (RDFs) in liquid l-dodecyl-3-methylimidazolium hexafluorophosphate. Anions and cations are depicted in red and blue. In the cases of b and c the blue circles represent the centroid of the imidazolium rings of the cations. The alternating sequences of red and blue circles in a and b as well as the two curves in phase opposition in c clearly indicate the existence and nature of the polar networks in ionic condensed phases...

Yamanaka N, Kawano R, Kubo W et al. (2007) Dye-sensitized Ti02 solar cells using imida-zolium-type ionic liquid crystal systems as effective electrolytes. J Phys Chem B 111 4763—4769... 

Gordon CM, Holbrey JD, Kennedy AR et al. (1998) Ionic liquid crystals hexafluorophos-phate salts. J Mat Chem 8 2627-2636... 

Ionic liquids with anions containing transition metal complexes were among the earliest developed room temperature ionic liquids [60], Transition metal based ionic liquids have been synthesized either by reaction of phosphonium or imidazolium halides with the corresponding metal halides, or by metathesis with alkali salts of the metal-based anions. Among the metal containing ionic liquids, ionic liquid-crystals are excluded in this section as they were reviewed thoroughly in 2005 [61], Synthesis of metal based salts can be divided in to three groups (1) transition metal salts, (2) p-block metal salts and (3)/-block metal salts. 

Abstract Ionic liquid crystals (ILCs) are emerging as interesting materials since they are expected to combine together the technological properties of ionic liquids (ILs) and liquid crystals (LCs). In this chapter, we will present a survey of the literature of the last 5 years, from 2005 to mid-2010 concerning ILCs. The chapter is divided into four sections ILCs based on organic cations (and anions), metal-based ILCs and polymeric ILCs, and applications of ILCs. 

Liquid crystal phases, or mesophases, are characterized by a partial order, intermediate between the full orientational and translational disorder of the isotropic liquid phase and the full orientational and translational order of the crystalline phase. Thermotropic liquid-crystal phases are obtained for a given compound (or possibly a mixture) as a function of temperature, while the so-called lyotropic liquid-crystal phases are obtained as a function of the concentration of a given solute in a solvent Typical examples of the latter systems are the various types of aggregates formed by amphiphilic molecules either in water or in organic solvents. In this chapter we will be interested only in thermotropic systems. An interesting review on lyotropic ionic liquid crystals can be found in Ref. [2],... 

Ionic Liquid Crystals Based on Organic Cations and Anions... 

Pyridinium and Bipyridinium-Based Ionic Liquid Crystals... 

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