Physical Properties of Novel Fluorinated Ethers and Ether Mixtures for Actively-Addressed, Twisted Nematic Liquid Crystal Displays

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Abstract
Several new classes of low polar, low viscous and optically weak anisotropic two- and three-ring fluorinated liquid crystals (LCs) with ether terminal groups are presented. Their material properties are investigated and compared with those of fluorinated LCs with alkenyl terminal groups. The 4-fluoro-phenylbicyclohexane ethers were found to exhibit dielectric anisotropies Δεwhich are similar to those of the corresponding alkenyls with 1-propenyl and 3-pentenyl group, whereas the alkenyls with 4-pentenyl group exhibit considerably lower Δε-values. The optical and dielectric anisotropies of difluoro-ethers with odd numbers n of the methylene groups separating the ether oxygen from the rigid cores of the molecules are comparable, whereas compounds with odd n′s were found to exhibit lower vis-coelastic ratios γ/K and therefore shorter response times in twisted nematic liquid crystal displays (TN-LCDs) than their even counterparts. In mixtures designed for thin film transistor (TFT)-addressed TN-LCDs the new compounds are shown to exhibit very large voltage holding ratios HR > 98% which are maintained after extended exposure to high temperatures (80°C) and/or high light intensities.