Conformation mesogens

The various orientations and conformations mesogenic groups can adopt in a layer has been studied extensively for low molar mass smectic materials, and the classification and terminology of smectic systems is entirely based on these studies. However, low molar mass smectic compound or smectic LC-side chain polymers do, of course, not allow one to elucidate the role spacers play in the layer structures of LC-main chain polymers. Therefore, poly(ester-imide)s, po-... 

Scheme 3. Lowest energy conformations for the mesogen 5CB (4-n-pentyl-4 -cyanobiphenyl)...

In 1985, Astheimer et al, [134] described the crystal structure of the mesogenic 4,4 -di(7S0-hexoxybenzalazine, Here, the centrosymmetric molecule is fully elongated with the hexoxy group in an aU-trans conformation and the phenyl rings are exactly coplanar. 

Keywords Smectic liquid crystals, Molecular conformations, polar and steric frustrations, Polyphilic and perfluorinated mesogens. X-ray diffraction... 

Finally, we should mention that the asymmetry of molecular shape, polyphilic effects and conformational constraints are the dominant factors in the stabilization of polar ordering in achiral mesogens. The examples presented above are, therefore, highly significant. They show that many liquid crystalline structures are intrinsically polar and may be effectively stabilized by suitable design of the mesogenic molecules. 

Figure 8.20 Structure and phase sequence of prototypical bent-core mesogen NOBOW (8) are given, along with space-filling model showing one of many conformational minima obtained using MOPAC with AMI force field. With observation by Tokyo Tech group of polar EO switching for B2 smectic phases formed by mesogens of this type, banana LC field was bom. Achiral, polar C2v layer structure, with formation of macroscopic spontaneous helix in polarization field (and concomitant chiral symmetry breaking), was proposed to account for observed EO behavior.

ID and 2D 13C NMR were carried out in a series of novel nematogens by Bayle and co-workers to study the effects on the conformation and order due to the addition of lateral and/or terminal substituents.249 251 For example, lateral flexible substituents are found to adopt a mean conformation more or less parallel to the mesogenic core. As a result, lateral chains are less disordered than terminal chains. Nematogens containing polyoxyethylene ether (POE) chain as a lateral crown ether and terminal chain(s) have been... 

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