Conformers substituted mesogens

Willow-like cascade construction was facilitated by the preparation of the AB2-type building blocks, e.g., 6-bromo-l-(4-hydroxy-4 -biphenylyl)-2-(4-hydroxyphenyl)hexane (40 Scheme 6.12), 13-bromo-l-(4-hydroxyphenyl)-2-[4-(6-hydroxy-2-naphthalenylyl)-phenyljtridecane (41), and 13-bromo-l-(4-hydroxyphenyl)-2-(4-hydroxy-4"-p-terpheny-lyl)tridecane (42). Scheme 6.12 illustrates the monomer preparative strategy for the incorporation of the monomeric mesogenic moieties predicated on conformational (gauche versus anti) isomerism. Thus, one equivalent of 4-hydroxybiphenyl was allowed to react with 1,4-dibromobutane to yield the monobromide 43, which was converted under Finkelstein conditions to the corresponding iodide 44. Treatment of the latter with ketone 45 under phase transfer conditions afforded the a-substituted ketone 46. Reduc-... 

The NMR technique has provided useful information regarding the orientational characteristics of nematic liquid crystals [96]. In many examples, the order parameters of the mesogenic core comprising a linear array of aromatic nuclei have been accurately determined from the observed dipolar (Dhd) and quadrupolar (Av) splittings by using deuterium-substituted samples. An attempt was made to elucidate the nematic conformation of the polymethylene-type spacer involved in dimer compounds, o, ct)-bis(4-cyanobiphenyl-4 -yloxy)alkanes (CBA- , with = 9,10), by the combined use of NMR and RIS analysis. The chemical structures and the phase transition data obtained by differential scanning calorimetry (DSC) are shown in... 

Thus, supermolecular liquid crystals with a cyclotriphosphazene dendritic core and polycatenar mesogenic units (144) were obtained in three steps by the conventional sequence of substitution (i), derivatization (ii and iii) methods from [N3P3CI6] (Scheme 9). Due to the microsegregation of the alkyl chains and the aromatic central cores and the space-filling properties, compounds (144) adopt a discotic conformation assembled in a columnar mesophase and illustrate the possibilities of using cyclotriphosphazenes for the design of columnar assemblies at room temperature, in the mesophase or in a vitrified solid state with interest for applications in material science. Similarly, the new family of solution processable, photoluminescent, monodisperse nanocomposite dendrimers (145) (Tg > 165 °C, > 465 °C)... 

This general property of 10- and 12-vertex clusters is illustrated in Figure 14.6 with a series of carboxylic acids substituted with a propyl group. The conformations in Figure 14.6 are consistent with experimental molecular structures of mesogenic derivatives and relative stability of the mesophase in isostructural derivatives. 

Recently, Hoffmann et al. [12] have described the molecular and crystalline solid structure of 2-n-nonyl-1,4-phenylene bis(4-n-octyloxybenzoate), as estimated using X-ray diffraction [12]. The observed structure deviates from the model for the nematic phase in the crystalline solid state, as the lateral chains exist in -trans conformation. The type of link between the lateral hydrocarbon chain and the mesogenic core influences the course of the clearing points. A comparison performed for the 2-alkyl, acyl and alkyloxycarbonyl substituted derivatives 2a-2c in Table 1 showed a break in the clearing-point curve at 2b and 2c for five single units (including the -CO- or -CO-0 groups) within the lateral chains. The lower the transition temperatures the more pronounced the break in the curve [13, 15]. 

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