4-Alkyl-4 -cyanobiphenyl compounds

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

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]. 

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. 

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 compounds which first found applications in display devices were the 4-alkyl-4 -cyanobiphenyls 17 and the 4-alkoxy-4 -cyanobiphenyls 18 (Gray and colleagues, 1973) . It has subsequently proved possible to incorporate other structural features and thereby modify the liquid crystal characteristics in interesting and sometimes useful ways. For... 

In 1975 Cladis discovered the sequence of phases nematic, smectic, and again nematic at atmospheric pressure. The lower-temperature nematic phase was designated as the re-entrant nematic phase (N ). By 1977 Cladis [68] was successful in giving evidence of a pressure-induced re-entrant nematic phase (Fig. 2). The investigated compounds were cyano Schiff bases and cyanobiphenyls with terminal n-alkyl or... 

The alkyl and alkoxy cyanobiphenyls (n-CB and n-OCB) derivatives synthesized by Gray and coworkers and the bicyclohexyl derivatives (PCH- and CCH-n), 4, bind rapidly to a variety of metals. The Sheffield Liquid Crystal group [12] used these compounds for the synthesis of metallomesogens with a linear geometry M = Pd, Pt, Rh. 

For a mesophase to obtain, it is generally necessary that the terminal groups of the molecules contain permanent dipoles. For example, the N-I transition of 4-octyloxybenzoic acid is some 40° higher than that of 4-nonylbenzoic acid despite the essentially equivalent size of the two molecules. Similarly, the 4-alkoxy-4 -cyanobiphenyls form substantially more stable mesophases than 4-alkyl-4 -cyanobiphenyls. Polarity of the termini, however, frequently gives rise to very strong intermolecular attractions. In such cases, the melting points of the compound may be raised so high that the mesophase cannot survive. 

Earlier methods of preparation of 4-alkyl-4 -cyanobiphenyls, which have found applications as liquid crystals, have led only to low yields, a problem which has recently been overcome with a newly described preparation of 4-alkyl-4 -bromobiphenyls (261) and their conversion into the cyano-compounds. The series of compounds (261) are formed by decomposition of the hydrazones (262) with KOBu. ... 

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