Cyanobiphenyl compounds

In some cases a cyano-phenyl overlapping of type II was found in the solid phase of the cyanobiphenyl compounds (Fig. 30). 

In addition, these materials have very good thermal stabihties and nearly room temperature mesomorphic range and are serious candidates to compete with the famous commercial cyanobiphenyl compounds, and despite their high molecular weight, their physical properties are closer to those of low molecular mass materials than to polymers or dendrimers. 

The 4-alkyl-4 -cyanobiphenyl compounds, originally synthesized by Gray and coworkers [20], were responsible for the mass industrial development of liquid crystal... 

Fig. 21. Electro-optic response times for a twisted nematic device as a function of polymer concentration. The polymer was a polysiloxane backbone system (as in Figs 19 and 20) dissolved in a nematic cyanobiphenyl compound. Ihe applied voltage was 5Vn, , the cell thickness was 12jum and data are...

It is well known that for liquid crystalline molecules like the cyanobiphenyl compounds, physical properties such as the clearing points change regularly depending on whether the number of carbon atoms of the alkyl chain is odd or even. This phenomenon has been explained by the molecular linearity for odd or even carbon numbers of the alkyl chains. A similar phenomenon is observed in the case of polyimide (1) with the alkyl chain structures shown in Fig. 5.2.3 [16,17]. 

The vast majority of molecules that build up liquid crystal phases are polar or even strongly polar. As an example we may take the cyanobiphenyl compound 8CB (Merck Ltd) with the formula... 

We investigated the effect of alkyl chain length of cyanobiphenyl compounds that had a primary alcohol end group (compounds I-n, where n is the number of carbon atoms of the alcohol) on the growth inhibition of A549 cells [198]. In addition, a compound bearing a secondary alcohol was synthesized (compound n ) for comparison. Figure 11.31 shows the structure ofthe compounds, and their phase transition temperatures are shown in Table 11.2. AU compounds except I-l and II-4 show an enantiotropic nematic phase [199-201] I-l and II-4 are monotropic nematic. 

Guo JB, Shi Y, Han X, Jin OY, Wei J, Yang H. StabUizing blue phases of a simple cyanobiphenyl compound by addition of achiral mesogen monomer with a branched end group and chiral hydrogen-bonded assemblies. J Mater Chem C 2013 1 947-57. 

Cyanobiphenyl compounds are well-known for their widespread practical utility in displays. The data in TABLE 2 are based on pVT measurements which provide estimates of the volume discontinuity at the nematic-isotropic transition as well as the pressure and temperature points of phase equilibrium. The general range of AV is from 0.2 to 1.0 cm /mol. The fitting constants presented in TABLE 3 were evaluated by a least squares fit to the second order polynomial defined above. The constant term is approximately the room pressure transition temperature. The data fit the polynomial well showing a mild curvature which increases at higher pressures. No obvious trends are apparent from the magnitudes and signs of the parameters. 

The first report on the liquid crystalline properties of these compounds was published by Gray and Mosley [44] in 1976. The series of 4 -n-alkyl-4-cyanobiphenyls (CBn) have been widely studied by different methods due to their readily accessible nematic ranges around room temperature. The compounds have the phase sequences crystal-nematic-isotropic for CBS, CBIO, and monotropic nematic for CBS, CB4 crystal-smectic A-nematic-isotropic for CB9 crystal-smectic A-isotropic for CBll. The lower homologous CB2 is nonmesogenic. The general chemical structure of the compounds CBn is presented in Fig. 1. 

The crystal structure of the mesogenic compound 4 -(4-hydroxy-1-n-butoxy)-4-cyanobiphenyl (CB0(CH2)40H) was described by Gehring et al. [59]. In... 

From the X-ray data of single crystals, it is possible to obtain information about the intermolecular interactions and the overlapping between the polar groups of neighbouring molecules. In Sects. 2.1.1, 2.1.2 and 2.1.3 the crystal structures of cyanobiphenyls were described. No cyano-phenyl overlapping of type 1 can be observed in the solid state of the compounds. 

Each of these couplings is inversely proportional to the cube of the distance between the atoms concerned, and all the dipolar couplings depend on the degree of orientation of the molecules. The ratios of couplings thus depend on the ratios of distances in the molecule, and from them the entire molecular structure, except for the overall size, may be determined. Studies of silyl compounds dissolved in cyanobiphenyl liquid crystals have yielded the following HSiH angles ... 

The Tfj-symmetrical hexaaddition pattern also represents an attractive core tecton for dendrimer chemistry [26, 31, 63-67]. Examples for such dendrimers, involving a core branching multiplicity of 12, are 38 and 39 [63, 64], Addition of six mesotropic cyanobiphenyl malonate addends produced the spherical thermotropic liquid crystal 40 [65], DSC and POM investigations revealed a smectic A phase between 80 and 133 °C. Interestingly, this spherical and highly symmetrical compound gives rise to liquid crystallinity despite the absence of molecular anisotropy. 

One alternative approach is to use photoisomerisable chiral compounds where the E and Z isomers have different helical twisting powers, e.g. menthone derivatives. By incorporating co-polymers, prepared from menthone containing monomers and cyano esters (5.5), as dopants into nematic LC mixtures materials, e.g. a mixture of cyanobiphenyls and cyanoterphenyls (E7 available from Merck), colour change can be effected by irradiating with UV light (365 nm). The colour obtained is dependent... 

Unactivated nitriles only react with azides when the two functions are incorporated into the same molecule. Thus 7-azidobutyronitrile and 5-azidocapronitrile (101) undergo an acid-catalyzed cyclization to the corresponding 1,5-disubsti-tuted tetrazoles (102) 17 and thermal cyclization of 2-azido-2 -cyanobiphenyl (103) yields tetrazolophenanthridine (104), a stable compound which decomposes only at 300° into a black... 

Derivatives of Biphenyl. By coupling diazo compounds and N-nitrosoacetyl derivatives obtained from substituted anilines with benzene, a large variety of biphenyl derivatives can be prepared in which only one of the rings is substituted. In this manner, the isomeric monosubstituted biphenyls, RCel CeHs, have been prepared in which R = Br, Cl, CH3, OCH3, NO2, CN, etc. The meta derivatives, such as 3-brQmobiphenyl (I), 3-nitrobiphenyl (II), and 3-cyanobiphenyl (III), are of particular interest because they cannot be prepared readily from biphenyl. The usefulness of the methods for the preparation of compounds of definite... 

Similar cyclization at the hydroxylamine may also take place in the presence of a cyano group.154-156 In the hydrogenation of 2-nitro-2 -cyanobiphenyl (27) over platinum oxide in ethanol, 6-aminophenanthridine A-oxide (28) was the sole compound produced. Compound 28, which was suggested to be in equilibrium with 29, was obtained in 90% yield in the hydrogenation in tetrahydrofuran in which 27 was more soluble than in ethanol (eq. 9.65).154... 

However, smectic phases are, by far, the most abundant kind of mesophases reported for ionic systems. Analogous compounds with only one cyanobiphenyl group or one or two pendant cholesterol units, 2, 3, and 4, with Br, Tf N", and Eu(tta) (tta =2-thenoyltrifluoroacetonate) only showed SmA or chiral SmA. 

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