Liquid crystals derivatives

Synthesis of the first mesoionic nematic and smectic A liquid crystals derived from sydnones has been described and their self-organization into liquid crystal phases has been studied by optical, calorimetric, and powder X-ray diffraction methods <2005CC1552>. 

It was quickly recognized that chirality would play an important role in discotic liquid crystals, not only for the possibility of creating cholesteric and ferroelectric liquid crystals but also as a tool for studying the self-assembly of these molecules as a whole, both in solution and in the solid state. However, initial studies revealed that expression of chirality in discotic liquid crystals was not as straightforward as for liquid crystals derived from calamitic molecules. More recently, with the increase in interest in self-assembly and molecular recognition, considerably more attention has been directed to the study of chiral discotics and their assemblies in solution. The objective of this chapter is... 

Discotic liquid crystals based on carbohydrates are intrinsically chiral due to the chiral nature of their core.49,50 Numerous discotic liquid crystals derived from these mesogens have been reported however, the expression of chirality in the subsequent mesophases has only rarely been seen. An example of the latter is the a-anomer of penta- O -decanoylglucopyranosc (47), which forms a discotic mesophase in which the molecules pack helically in the columns... 

Investigators of cellulosic liquid crystals have two main motivations to study mesophase formation primarily from a scientific viewpoint or a technolomcsd vie oint. The main focus of the latter has been on the potential of preparing high strength/high modulus regenerated cellulose fibers. Another potentim use of cellulosic liquid crystal derivatives is as chiroptical filters (S,lfi). 

TABLE 1. Physical Properties of Selected Liquid-Crystal Derivatives Derived Using Optical Anisotropic Materials"... 

Kaida et al. (1,2) prepared optically anisotropic polymerizable liquid-crystal derivatives, (I) and (II), respectively, containing internal esters that were used in optical disc applications. 

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. 

Naphthyl p-quinone liquid crystals derivatives have been prepared and are described (3). 

Liquid crystals derive both their beauty and their usefulness from their ordered, yet liquid, state. At rest, they possess at least some orientational order at rest, but lack the full three-dimensional positional order of solid crystals. Orientational order implies that the molecules tend to point in the same direction, while positional order implies that the molecules centers of mass tend to lie on lattice points. Spherically symmetric molecules, for example, can have positional order, but no orientational order. Thus, when one heats a simple positionally ordered crystalline solid to its melting point, all of its positional order is destroyed in a single step, producing an isotropic liquid. Orientational order is, however, possible for rod-like or disk-like molecules. Crystalline solids made of such molecules can melt into isotropic liquids in multiple steps at intermediate stages of melting, there can be orientational order with no, or only partial, positional order. That is, the molecules might tend to be aligned in a common direction, but the centers of mass of the molecules take on random positions. Such intermediate phases are liquid crystals.------------------------... 

The arrangement of chiral molecules in thermotropic liquid crystals is more complex, since entire volumes of space - rather than the bounded twisted ribbons discussed above - must be ed subject the constraint of a preferred twist between neighbouring molecules. The simplest examples of such mesophases are the cholesteric liquid crystals, discovered last century, (c/. section 5.1.8). This class of thermotropic liquid crystals derives its generic name from chiral cholesterol derivatives (shown below), which were found a century ago to exhibit peculiar optical changes as they were heated. 

Kranz, H., Vill, V. and Meyer, B. (1996). Prediction of Material Properties from Chemical Structures. The Clearing Temperature of Nematic Liquid Crystal Derived from their Chemical Structures by Artificial Neural Networks. J.Chem.Inf.Comput.Sci, 36,1173-1177. 

Table 4.10 Examples for the most commonly used dielectrically negative liquid crystals deriving their dipole moment from lateral difluorination. The virtual clearing points TNi.vin are extrapolated from the Merck mixture ZLI-4792, Af from ZLI-2857 [41].

Tsiourvas D, Felekis T, Sideratou Z et al (2004) Ionic liquid crystals derived from the protonation of poly(propylene imine) dendrimers with a cholesterol-based carboxylic acid. Liq Cryst 31 739-744... 

C.J. Booth, J.W. Goodby, J.P. Hardy, O.C. Lettington, K.J. Toyne, Fluorosubstituted chiral liquid crystals derived from (R)-2-(4-Hydroxyphenoxy)propan-l-ol. J. Mater. Chem. 3, 935-941 (1993)... 

Gesekus, G. Dierking, L Gerber, S. Wulf, M. Vill, V. Chiral banana liquid crystals derived from sugars. Liq. Cryst. 2004, 31, 145-152. 

Dingemans, T. J. Samulski, E. T. Non-linear boomerang-shaped liquid crystals derived from 2,5-bis(p-hydroxyphenyl)-l,3,4-oxadiazole. L/. Cryst. 2000, 27, 131-136. 

Liquid crystals derived from rod- or lathshaped molecules, forming calamitic phases, have been the most comprehensively studied. Although no exact theory has been developed up to now, which relates the structure of molecules to their specific liquid-crystalline behavior, rules of thumb have been formulated based on the very large number of compounds [4] known, and the related physical data. 

A side-chain liquid crystal polymer is a polymer where on each monomer is grafted a mesogenic molecule, A good example is given by the liquid crystal derived from poly(methyl methacrylate) ... 

For further examples of the Ferrier rearrangement as applied at the start of a synthesis of a thromboxane 62 precursor or of highly oxygenated m-decalinic structures derived from carbohydrates, see Chapter 24. The same reaction applied to the preparation of carbohydrate-based liquid crystals derived from a boronate ester is mentioned in Chapter 17. 

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