Trifluorinated liquid crystals for TFT displays

3,4,5-tri-fluorobenzene derivatives with different core structures have been synthesized and their physical properties have been determined. Most of the compounds are nematic with broad existence regions. The materials have large dielectric anisotropy, low viscosity, low optical anisotropy and very good voltage holding ratio and high chemical stability and are valuable components for mixtures to be used in TFT displays. The good voltage holding ratio of the compounds is related to their high electrical resistivity. In order to reproduce the dependence of the resistivity on the dielectric constant, we derived a general formula. Its derivation is based on the interaction of the impurity ions with the induced and permanent dipoles of the liquid crystal molecules. We are able to show, that ion/ion interactions in highly purified liquid crystals may be neglected.