Liquid crystal properties 4,4 -disubstituted

The thermal characteristics exhibited by the series 11 [18] and 14 [20] proved that interesting liquid crystal properties can be obtained with symmetrically 1,T-disubstituted ferrocene derivatives. The structure of the organic unit, which is combined with the ferrocenyl moiety, must be carefully chosen. 

We designed and studied [27] a family of unsymmetrically l,l -disubstituted ferrocene derivatives obtained by combining the organic units A and B (above), used to prepare the families 13 and 14, respectively within the same molecular framework. Structures 25 (Fig. 9-21) led to remarkable mesomorphic properties. All derivatives exhibited liquid crystal properties. Compound 25 (n = 11) gave rise to an enantiotropic smectic A phase. Complex 25 (n = 12) showed an enantiotropic... 

Special thiol carboxylic esters (29) were prepared from aroyl halides and arcne thiolates. These 4,4 -disubstituted S-aryl arenecarbothioates might gain importance from a practical point of view, since they exhibit liquid crystal properties and could be useful as components of a display cell. Another thiocarboxylic ester (30), which was obtained from a zinc thiochelate and benzoyl chloride (equation 19), ° might be potentially useful as a precursor for organic conductors. 

It is interesting to note that several long-chain dipolar Schiff bases have physical properties which impart to them liquid crystal behavior [2a, b]. Most of these imines are disubstituted 7V-benzyIideneanilines (structure I) which... 

Ferrocene-containing co-polyesters, preparation, 12, 350 Ferrocene-containing liquid crystals dendrimers, 12, 235 disubstituted ferrocenes, 12, 227 hydrogen-bonded ferrocene derivatives, 12, 234 monosubstituted ferrocenes, 12, 222 polycatenar ferrocenes, 12, 234 properties, 12, 221... 

Detailed analyses of intramolecular structures are possible. Comparison of NMR and fluorescence data shows meso- and racemic diastereoisomers are found from 2,4-di(2-pyrenyl)pentane 24 jhe polarization of monomer and excimer of 4,9, disubstituted pyrenes have been measured in nematic liquid crystals 25 Quenching of pyrene fluorescence by alcohols in cyclodextrin inclusion complexes has also been studied in detail 26 Solvent effects on the photophysical properties of pyrene-3-carboxylic acid has been used to measure the pJJ, in different solvents 27 Geminate recombination in excited state proton transfer reactions has been studied with... 

Several 1,2-disubstituted Fc derivatives 48 ( = 6, 12) were prepared, but none of the compounds showed liquid-crystalline properties. " From our systematic investigations on disubstituted ferrocenes, we could clearly establish the following liquid-crystal tendency 1,3-> , -> 1,2-isomeric structures. This sequence can be explained in terms of structural features (i) the 1,3-disubstituted ferrocenes possess the highest molecular anisotropy among the isomeric structures, (ii) the substituents located at the 1,1 -positions generate a step in the structure (S- or U-shape), which results in a reduction of the molecular anisotropy and a loss of colinearity of the mesogenic substituents, and (iii) the substituents located at the 1,2-positions give rise to a hairpin structure which lacks molecular anisotropy. 

The data obtained for 58 ( ) and 59 further emphasize the influence of the substitution pattern on mesomorphic properties. Whereas a two-aromatic ring system (plus the Cp nucleus) was found to be non-mesomorphic for 1,3-disubstitution,introduction of an additional substituent on the second Cp ring gave monotropic liquid crystals 58 ( ). This result indicated that the repulsive interactions induced by the Fc core are compensated, at least in part, by the third substituent. This allows both substituted Cp rings to interact favorably, which results in mesomorphism promotion. In a structure such as 59, the depth (bulkiness) of Fc (about 3.3 A) is, in a way, hidden by the substituents anchored on the two Cp nuclei. Therefore, the 1,1 -3-trisubstitution pattern is a stronger mesomorphic promoter than the 1,3-disubstitution one (for identical substituents). This is supported by the fact that 46( =16), the 1,3-disubstituted counterpart of 59, gave a much narrower liquid-crystalline range (42 °C) than 59. 

Disubstituted imidazo[2,l-f)][l,3,4]thiadiazoles (56 R, R, R = H, alkyl, cycloalkyl, aryl) are liquid crystals, and various properties of these compounds have been investigated <88ZORl92, 88ZOR199, 88ZOR1306, 90LC475>. 

ILs used in self-assembly systems can be divided in two categories protic ionic liquids (PILs, solvent properties are similar to water) and aprotic ionic liquids (AILs, largest group most of them derived from disubstituted imidazolium cations). Many surfactant ILs have thermotropic properties, forming liquid crystal phases with no additional solvent present. The solvophobic interaction between PILs and... 

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