Liquid crystal discotic

The liquid-crystalline state has been known for more than a century, as the so-called mesophase. It has a finite viscosity and at the same time anisotropic physical properties. Mesogenic systems do not lose all their long-range order suddenly above their melting points instead, as their temperature is increased, the positional long- 

Disc-like molecules may also exhibit the liquid crystal phase, de Gennes predicted this possibility in his famous book The Physics of Liquid Crystals  

Present interest in disc-like aromatic molecules results mainly from their application as ID charge carrier materials for use in photoconductors, light emitting devices, organic transistors, and photovoltaic applications [265]. 

Investigation of symmetric and non-symmetric triphenylenes combining three fluorinated and three non-fhiorinated chains (compounds 149 and 150 in Fig. 40) has shown that these compounds can possess a higher stability of the columnar phases compared to those with all chains semiperfluorinated (compound 148), whereas the distribution of the fluorinated chains (symmetric vs. non-symmetric) does not play a significant role [272], 

Disc-like molecules with a pentakis(phenylethynyl)phenoxy core commonly form nematic phases which can be strongly stabilized by the presence of only one 

Introduction of perfluorinated chains into the periphery of other disc-like or board-like Ji-conjugated aromatics [251, 252], such as coronene diimides [279], perylene diimides [280-282], naphthalene tetracarboxylic diimides [283-286], 

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Figure C2.2.7. Schematic illustrating tire classification and nomenclature of discotic liquid crystal phases. For tire columnar phases, tire subscripts are usually used in combination witli each otlier. For example, denotes a rectangular lattice of columns in which tire molecules are stacked in a disordered manner (after [33])...

Discotic blue phases Discotic liquid crystals Discover Disc Tube... 

Fig. 12. Molecular structure and phases of a typical discotic liquid crystal.

The reaction was extended to PhCH2X (X = Cl or Br) which gives the hexa(phenyl-ethyl)benzene complex. The new free aromatic ligand is easily disengaged by photolysis in acetonitrile [76a] Eq. (20). This line of research is now offering us the perspective of making new discotic liquid crystals using suitably substituted... 

The prime requirement for the formation of a thermotropic liquid crystal is an anisotropy in the molecular shape. It is to be expected, therefore, that disc-like molecules as well as rod-like molecules should exhibit liquid crystal behaviour. Indeed this possibility was appreciated many years ago by Vorlander [56] although it was not until relatively recently that the first examples of discotic liquid crystals were reported by Chandrasekhar et al. [57]. It is now recognised that discotic molecules can form a variety of columnar mesophases as well as nematic and chiral nematic phases [58]. 

There have been several simulations of discotic liquid crystals based on hard ellipsoids [41], infinitely thin platelets [59, 60] and cut-spheres [40]. The Gay-Berne potential model was then used to simulate the behaviour of discotic systems by Emerson et al. [16] in order to introduce anisotropic attractive forces. In this model the scaled and shifted separation R (see Eq. 5) was given by... 

To date, the crystal structures of more than 200 mesogenic compounds are known. In this review, we wish to present a general overview of the crystal structures of mesogenic compounds up to the end of 1997. Unfortunately, it is not possible to consider the crystal structure determinations of carbohydrate liquid crystals [13, 14], metallomesogens [15-18], phasmid and biforked mesogens [19-22], perfluorinated mesogenic compounds [23-27], benzoic acids [6, 28-31], cinnamic acids [7, 32, 33], dicarboxylic acids [34, 35], cinnamate compounds [8, 36-40], and discotic liquid crystals [41-43] due to the lack of space. 

Since the discovery of discotic liquid crystals [121], the mesophases formed by rod-like and disc-like molecules have been considered as belonging to different liquid crystalline classes. Indeed, the conventional rod-like and disc-... 

Coco, S Espinet, P Marb n-Alvarez, J.M. and Levelut, A.M. (1997) Effects of Isonitrile Substituents on Mesogenic Properties of Halogoldiisonitrile Complexes Calamitic and Discotic Liquid Crystals. Journal of Materials Chemistry, 7, 19-23. 

Discotic liquid crystals on the other hand are based around a fairly flat core structure and are generally surrounded by six or eight peripheral alkyl(oxy) chains. Examples are given in Fig. 3. 

Chiral Lyotropic Discotic Liquid Crystals and Self-Assembly of Chiral Discotics in Dilute Solution... 

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... 

To understand how chirality is expressed, it is important to first describe the different thermotropic mesophase assemblies which can be formed by chiral discotics. Even though expression of chirality has been observed in thermotropic mesophases, the chiral expression occurs in a rather uncontrolled manner, and systems which are suitable for applications, for example, easily switchable columns/ferroelectric discotic liquid crystals, consequently have not yet been developed. Hence, the assembly of discotics in solution has received considerable attention. Supramolecular assemblies of discotic molecules in solution are still in their infancy and have not yet found commercial application, but they are of fundamental importance since they allow a detailed and focused investigation of the specific interactions that are required to express chirality at higher levels of organization. As such, the fundamental knowledge acquired from supramolecular assemblies in solution might formulate the design criteria for thermotropic chiral discotic mesophases and provide the necessary tools for the creation of functional systems. 

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... 

CHIRAL LYOTROPIC DISCOTIC LIQUID CRYSTALS AND SELF-ASSEMBLY OF CHIRAL DISCOTICS IN DILUTE SOLUTION... 

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