Discotic liquid crystal phases

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 liquid-crystal phase, 13 371 Discotic liquid crystals, 15 96 Discotic mesogens, 20 79 Discounted cash flow return rate (DCFRR), 9 544-545... 

The simplest discotic liquid crystal phase is the nematic discotic phase, Nd, in which the normals of the molecular discs tend to align with respect to a preferred direction, i.e., the director, but the mass centers of molecules do not have any positional order. The discs in Figure 1.11 represent the disclike molecules, the molecules are packed in the way a pile of coins is packed randomly. The discotic nematic phase has its chiral counterpart, i.e., the... 

Benzene-hexa-n-hexanoate (n = 5 in Fig. 5.5) has no discotic liquid crystal phase, but three condis states (phases III, II, I) The thermodynamic transition parameters are listed in Table 5.5. According to Eq. (1), one expects for fusion of the rigid crystal (phase IV) besides the ASp and 24 conformational contributions... 

Figure 1 General structures of calamitic and discotic thermotropic liquid crystals. (A) Layered calamitic smectic liquid crystal. The structures of the various types depend on the local packing of the molecules, the extent of the packing, and the orientation of the long axes with respect to the layers. (B) Calamitic nematic liquid crystal. The molecules have no long-range order, and are only orientationally ordered. (C) Ordered columnar discotic liquid crystal. Disk-like molecules form ordered or disordered columns different column packings give rise to various mesophase structures. (D) Nematic-discotic liquid crystal phase. The disk-like molecules are only orientationally ordered.

Some partially (2,3,5,6-) acylated derivatives of hexahydroxybenzene have also been found to exhibit discotic liquid crystal phases, as have the related tetraesters of 2,3,5,6-tetrahydroxy-l,4-benzoquinone [11]. Their synthesis, shown in Scheme 2, is relatively straightforward. 2,3,5,6-Tetra-hydroxy-l,4-benzoquinone [12] is acylated with an excess of the acid chloride in refluxing pyridine. Neutral work-up yields the quinone, whereas the hydroquinone is iso-... 

Two general series of naphthalene derivatives are known to give discotic liquid crystal phases, the multiynes [27, 33] and the p-alkoxyphenoxymethyl derivatives [28]. The multiynes are synthesized through... 

This group has a characteristically flat disk shape, which is responsible for the discotic liquid crystal phase. The nickel bis (dithiolene) core has high thermal and photochemical stability. The substituted R groups impart the solubility in nonpolar solvents. Also, if the R groups are sufficiently long, they can form a nematic liquid crystal, as shown in Figure 5 and 6. 

When the disks have no long-range translational order, an analog of the nematic phase, identified as N, is formed. Very few compounds exhibit an Ng phase. It is not entirely miscible with the nematic phase formed by calamitic systems. If a chiral center is incorporated into a nematic discogen, the material usually exhibits a chiral nematic discotic phase. Figure 2.12 shows disk-shaped molecules exhibiting discotic liquid crystal phases between the solid and isotropic liquid phases. 

Figure 2.12 A crystal composed of disk-shaped molecules can melt via coiumnar and nematic discotic liquid crystal phases.

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