Rod-like mesogen

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 ...

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. ... 

Hence, benzoic acids can be more appropriately considered as self-assembled rod-like mesogens with two fluorinated terminal chains (see Sect. 4.4). 

Fig. 27 Comparison of phenylpyrimidine based rod-like mesogens with an alkyl chain at one end and different types of fluorinated chains at the other end (77° C) a observed on heating, all other transitions were observed on cooling [167-170]...

Fig. 29 Comparison of selected examples of rod-like mesogens combining hydrocarbon chains and semiperfluorinated chains (T/° C) indicating the effect of replacing one F by H (I0I/I02 105/ 106) and the effect of RF-chain branching (106a,b) [163, 177-183]...

Fig. 30 Selected examples of chiral rod-like mesogens with one fluorinated chain (77° C) one enantiomer is shown as example (SmCA = antiferroelectric SmC phase SmC = ferroelectric SmC phase SmCpi = ferrielectric SmC phase SmCa = helical SmC phase SmI = chiral tilted low temperature phase) [197-199]...

Fig. 32 Selected examples of rod-like mesogens with semiperfluorinated chains at both ends and additional bulky lateral substituents (77° C) [237-239]...

Hydrogen bonded dimers of 4-RF-substituted benzoic acids [119, 120, 122, 126], /rcyclohexane carboxylic acids [120], and hydrogen bonded complexes of benzoic acids with 4,4 -bipyridine and stilbazole [166, 243-246] can be regarded as supramolecular rod-like mesogens with two fluorinated chains. Figures 33 and 34 show comparisons of selected benzoic acid dimers and their bipyridine and stilbazole complexes. Comparison of the benzoic acid dimers 122 and 123 with -alkyl chains and F-terminated -alkyl chains, respectively, indicates that a single F-atom at the end of the alkyl chain reduces the mesophase stability... 

Fig. 34 Examples of supramolecular rod-like mesogens formed by self assembly of branched fluorinated benzoic acid into dimers and their 4,4 -bipyridine complexes (77° C) [166]...

A combination of fluorinated segments and siloxane groups was used by Mehl et al. for the terminal-terminal and lateral-lateral interconnection of rod-like mesogens (e.g., compound 206). In contrast to the usually observed smectic phases... 

Fig. 1 Rod-like mesogen with terminal crown ether...

Thermotropic liquid crystals come in two types calamitic and discotic. Calamitic phases (from the Greek for tube ) are all those that are caused by rod-like mesogens. The more recently characterised discotic phases are caused by disc-like species. Calamitic phases may be either nematic (from the Greek for thread ), smectic (from the Greek for soap ) or cholesteric (named after the cholesterol derivatives such as 13.4, which exhibit this behaviour). 

Spurred on by discussions on whether the smectic layers of the fluorocarbon-substituted polymers XXIII-m-n are induced by the immiscibility between hydrocarbon and fluorocarbon segments or by the fact that fluorocarbon segments form rod-like mesogenic units by themselves, Pugh et al. synthesized a series of siloxane-terminated monomers XXIV-m-n, with m=l,2 and n=4-S [79]. In these monomers, the rigid fluorocarbon segment was replaced by short polydimethylsiloxane (PDMS) segments that are also immiscible with hydrocarbons but are very flexible (Fig. 15). 

Rzoska, S. J., and Drozd-Rzoska, A. (2002) On the tricritical point of the isotropic - nematic transition in a rod-like mesogen hidden in the negative pressure region, in NATO Sci. Series II, vol. 84, Liquids under negative pressures, eds. lime, A. R., Maris, H. J., and Williams P. R. (Kluwer-Springer, Dordrecht) p. 116... 

Fig. 15 Orientation of attachment of rod-like mesogenic groups to a central scaffold and mesophases formed for supermolecular systems, shown in comparison to the structures of side-chain liquid crystal polymers...

Compound 43 was found to exhibit a chiral nematic phase (see the texture in Fig. 48), hexagonal disordered columnar (see Fig. 49) and rectangular disordered columnar phases, in the sequence g 5.4 Col d 30 Col 102.3 N 107.7 °C Iso Liq [94]. Thus the increase in the number density of the meso-gens bound to the central scaffold transforms the situation from the octamers 41 and 42, which exhibit calamitic phases, to one where the hexadecamer 43 exhibits columnar phases. However, the formation of columnar phases when the dendrimer possesses rod-like mesogenic groups is not easy to vi-... 

Rowan, Mather et al. [63—65] have examined the use of complementary nu-cleobase interactions to allow the formation of supramolecular LC materials of the main type shown in Fig. 3a and b. In these cases, a rod-like mesogen-bis(phenylethynyl)benzene-was functionalized symmetrically (homoditopi-cally) with thymine (T) or N6-anisoyl protected adenine (AAn) using alkoxy spacers of varying length to yield molecules of the type Bp-1-Bp, where Bp depicts the variable nucleobase moiety, AAn or T (Fig. 5). 

Many molecules with rod-like mesogens have been analyzed in the liquid crystalline phase, but only few of the low-temperature pramrsor crystals have been studied. Among them one might find many conformationally disordered crystals A survey... 

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