Rod-like mesogens

The structures of polymers that form liquid crystals are illustrated schematically in fig. 1.1.9. The basic monomer units are low molar mass mesogens, rod-like or disc-like, which are attached to the polymer backbone in the main chain itself (fig. 1.1.9(a)), or as side groups (fig. 1 1 9 ( ))- nature of the mesophase depends rather sensitively on the... 

FIGURE 3 Mesophases exhibited by calamitic mesogens (rod-like shape) versus mesophases exhibited by discotic mesogens (disk-Uke shape). 

Most polymeric Hquid crystals are based on stiff rod-like molecular units which are called calamitic mesogens. There are some unusual polymers (which are not discussed here) that contain flat disk-like molecular units called discotic mesogens in which the disks form columnar arrays like stacks of poker chips. 

It is not possible to predict from the related crystal structure alone whether the compound will melt to a liquid crystalline phase or not, because the anisotropic molecules (calamitic and discotic ones) form in favourable anisotropic packing. As a rule long shaped rod-like molecules quite often possess a layered arrangement in the solid state regardless of whether the compound is mesogenic or not. 

Fig, 18a,b, The polymorphic behaviour of the phasmidic-like mesogens a molecular model with six terminal chains b phase diagram for the binary mixture of double swallow-tailed compound (I) with conventional rod-like mesogen (II) (adapted from Letko et al. [123])... 

Figure 8.1 Typical shapes (a) rod-like mesogenic molecule ...

There are now three major shape classifications of low molar mass liquid crystals - rod-like (calamitic), disc-like (discotic) and bent-core. The last of these is the most recent, and while examples of bent mesogens have been known for some years, it is only since the mid-1990s that the area has attracted widespread attention [2],... 

Mesogen composed of rod-like or lath-like molecules. Note Examples are ... 

Mesogen composed of rod-like molecules with large lateral branehes such as alkyl, alkoxy or ring-containing moieties. 

Note 5 If the mesogenic side-groups are rod-like (calamitic) in nature, the resulting polymer may, depending upon its detailed structure, exhibit any of the common types of calamitic mesophases nematic, chiral nematic or smectic. Side-on fixed SGPLC, however, are predominantly nematic or chiral nematic in character. Similarly, disc-shaped side-groups tend to promote discotic nematic or columnar mesophases while amphiphilic side-chains tend to promote amphiphilic or lyotropic mesophases. 

Rod-like chain of a MCPLC with direct links between the mesogenic groups for which the persistence length is at least comparable with the contour length and much greater than the diameter. 

Note 2 The mesogenic groups ean be, e.g., rod-like or dise-like, and can be attached laterally or longitudinally to the flexible spacers. 

The term mesophase is used in reference to the liquid crystalline phase, and the molecular (sub)structures that give rise to this phase are termed mesogens. Macromolecules with rod-like or a flat, disc-like geometries tend to form such... 

Approaches used to the development of LC materials with valuable luminescent properties include the synthesis of rod-like mesogens from fluorescent moieties, e.g. benzopyrans, " and discotic LCs with a fluorescent polyaromatic core. ... 

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