Smectogen

Detailed x-ray diffraction studies on polar liquid crystals have demonstrated tire existence of multiple smectic A and smectic C phases [M, 15 and 16]. The first evidence for a smectic A-smectic A phase transition was provided by tire optical microscopy observations of Sigaud etal [17] on binary mixtures of two smectogens. Different stmctures exist due to tire competing effects of dipolar interactions (which can lead to alternating head-tail or interdigitated stmctures) and steric effects (which lead to a layer period equal to tire molecular lengtli). These... 

In order for dipole—dipole and dipole-iaduced dipole iateractioas to be effective, the molecule must coataia polar groups and/or be highly polarizable. Ease of electronic distortion is favored by the presence of aromatic groups and double or triple bonds. These groups frequently are found ia the molecular stmcture of Hquid crystal compouads. The most common nematogenic and smectogenic molecules are of the type shown ia Table 2. 

This equation only accounts for the high cutoff frequency a> c (colc = Knqjc/1)), and diverges as co— -O. When the high- (ft>() and low-frequency (ft)/) cutoffs are taken into account, one obtains for smectogens... 

Note 1 When the type of mesophase formed is known, more precisely qualifying terminology can be used, e.g., nematogen, smectogen and chiral nematogen. 

A Cu2+ containing linear polymer [77] exhibiting smectogenic behaviour is obtained by a polycondensation technique (Fig. 27). A homologous set of polycondensates of 4,4 -[l,12 dodecanediyl bisfoxy)] bis benzoic acid with bis[AT-[[2,4 dihydrophenyl]methylene]-alkylamino] Cu(II) exhibits monotropic liquid crystalline behaviour with 4—13 carbon atoms in the alkylamino group [78]. 

Copolymerization of two mesogenic monomers is, at the present time, the only pathway to obtain polymers with cholesteric mesophase (see Part 4.4). On the other hand, only by copolymerizing smectogenic and nematogenic monomers and investigating the properties of copolymers in a broad interval of compositions, is it possible to establish the principles of formation of each type of mesophase. We demonstrate... 

A large number of low molecular weight smectogens have been prepared and studied by X-ray diffraction methods At this time relatively few smectic polymers have been prepared and identified, and the smectic D, G, and H phases have not, as yet, been reported in polymers. 

Dobbs W, Douce L, Heinrich B (2009) l-(4-aIkyloxybenzyl)-3-methyl-lH-imidazol-3-ium organic backbone a versatile smectogenic moiety. Beilstein J Org Chem 5(1) 51... 

Unsymmetrically 1,1 -disubstituted ferrocenes 43 ( = 11-16) were synthesized by combining the organic substituents used to prepare 41 (n) and 42 ( ). Introduction of dissymmetry had two effects on the thermal and mesomorphic properties. First, a depression in the melting points was observed. Second, the smectogenic character of the materials was enhanced. Indeed, with the exception of 43 ( = 11), which showed only a SmA phase, all the members of the series showed both SmC and SmA phases. In view of the mesomorphic properties obtained for 43 ( ) in comparison with those of 41 ( ) and 42 ( ), one can anticipate that the combination of very different substituents (e.g., chiral with non-chiral moieties, hydrocarbon with fluorocarbon motifs) should lead to ferrocenes showing rich mesomorphism. 

Bryan RF, Hartley P, Miller RW, Shen M-S(1980)AnX-ray study of the p-n-alkoxybenzoicacids. Part VI. Isotypic crystal structures of four smectogenic acids having seven, e t, nine, and 10 alkyl chain atoms. Mol. Cryst. Liq. Cryst., 62 281... 

LC copolymers containing both nemato-genic (or smectogenic) and NLO active side groups, and... 

LC Copolymers Containing Both Nematogenic (or Smectogenic) and Active Side Groups... 

A number of copolymers having nemat-ogenic (or smectogenic) and NLO active groups have been synthesized [155, 173-181]. Table 15 lists a number of chemical groups that have been used for their mesogenic properties. As can be seen from their formulas, highly polar terminal substituents... 

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