Apolar Nematic Materials for STN-LCDs

Apolar nematic compounds usually possess a low k2,-ilk ratio e.g. 1.0 33/ 1.5), partially due to the absence of molecular dimers. However, they are still essential components of nematic mixtures for STN-LCDs, since they are used to lower the viscosity and melting point of a nematic mixture of polar components as well as improve the multiplexability of the mixture due in part to the reduction in the proportion of molecular dimers of associated polar molecules. Therefore, the synthesis of the first polar alkenyl liquid crystals with high k jku ratios led to the synthesis of a series of apolar alkenyl-substituted compounds with the carbon-carbon double bond in various positions in the terminal chain. Some typical compounds (140-149) are shown in Table 

Based on the evaluation of the results of physical measurements on polar alkenyl compounds described above, the position and configuration of the carbon-carbon double bond found in the apolar compounds is similar to that in the polar compounds, essentially for the same reasons. However, the combination of a low melting point and a high nematic clearing point of the bicyclohexane compounds (142,143 and 145) is remarkable. The birefringence and viscosity of these compounds is remarkably low.  

Fluoro- and methyl-substituted compounds are attractive from a synthetic point of view due to the availability of cheap starting materials in an otherwise complex synthetic procedure. The short methyl group is attractive, as a terminal alkyl chain also contributes to a low viscosity and the suppression of smectic phases. 

The data collated in the Tables 3.14-3.16 reveals that the presence of a trans carbon-carbon double bond in a limited number of specific positions gives rise to a higher clearing point and a higher 33/ 11 ratio than those of the corresponding material without a double bond in the terminal chain. Smectic phases, especially the ordered smectic B phase, are strongly suppressed. This is 

Similar effects have been found for /ra 5-4- -alkylcyclohexyl trans-4-n-alkylcyclohexanoates and the corresponding esters with one or two trans carbon-carbon double bonds in the terminal chain.However, the ester with two terminal alkenyl chains only possesses a nematic phase over a temperature range of Related bicyclohexanes with an additional 

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