Liquid crystal calamitic

Fig. 2. The generic molecular structure of calamitic liquid crystals illustrating the semi-rigid core fragments, the positions of the end-groups (C and A), linking groups (B) and, possibly, laterally substituted groups (L)...

Other more exotic types of calamitic liquid crystal molecules include those having chiral components. This molecular modification leads to the formation of chiral nematic phases in which the director adopts a natural helical twist which may range from sub-micron to macroscopic length scales. Chirality coupled with smectic ordering may also lead to the formation of ferroelectric phases [20]. 

Here the vector rj represents the centre of mass position, and D is usually averaged over several time origins to to improve statistics. Values for D can be resolved parallel and perpendicular to the director to give two components (D//, Dj ), and actual values are summarised for a range of studies in Table 3 of [45]. Most studies have found diffusion coefficients in the 10 m s range with the ratio D///Dj between 1.59 and 3.73 for calamitic liquid crystals. Yakovenko and co-workers have carried out a detailed study of the reorientational motion in the molecule PCH5 [101]. Their results show that conformational molecular flexibility plays an important role in the dynamics of the molecule. They also show that cage models can be used to fit the reorientational correlation functions of the molecule. 

Calamitic liquid crystals generally contain two or more rings, at least one flexible chain and often a small, polar function in some cases, small, lateral groups (normally fluorine) are attached. Some will contain metal... 

Based on a known synthesis of spiro compounds with six-membered rings [63] we succeeded in the stepwise assembly of terminal substituted mono-[64] and dispiranes [65]. Hereby the cyclisation of the dibromide 35 with TOSMIC (Iter. 1) is the keystep of the reaction sequence as the initial ketone functional group (36) is recovered. Four subsequent reactions led to the spirodibromide 40 (Iter. 2). Final spirocyclisation afforded the dispirane 41, representing a precursor for new calamitic liquid crystals (Fig. 16) [66]. 

M Funahashi and JI Hanna, Fast hole transport in a new calamitic liquid crystal of 2-(4 -Heptyloxyphenyl)-6-dodecylthiobenzothiazole, Phys. Rev. Lett., 78 2184-2187, 1997. 

Calamitic liquid crystals consist of rod-like molecules, i.e. a pronounced shape anisotropy with one extended principal axis and two short perpendicular ones. Three main classes can be described as in Figure 2. 

The liquid crystalline properties of 43a-d were interesting as all derivatives showed very stable mesophases with phase widths of 57-109 K. It is remarkable that Schiff bases 43c,d are stable at temperatures above 300 °C. It also strikes that, in contrast to conventional calamitic liquid crystals, the Schiff bases 43c,d possess significantly higher phase transition temperatures compared to azo linked 43a,b. Additionally, the trans compounds tend to possess higher clearing temperatures due to the elongated shape of the molecules. 

Fig. 17 Spindle-like hematite (10) [534] and anatase (11) [533] nanoparticles coated with calamitic liquid crystals...

Table 5.6 Transition temperatures (°C) for the calamitic liquid crystals (22-26)...

Fig. 20. Examples of linking groups used in the construction of calamitic liquid crystal molecules.

Summary Cyclic siloxanes substituted with mesogenic groups, which are connected to the backbone by aliphatic spacers, exhibit liquid crystalline (LC) phases as the classic calamitic liquid crystals. 

Figure 2.3 Typical example of a calamitic liquid crystal and schematic...

Structural Characterization of Inherent Structures of Calamitic Liquid Crystals... 

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