Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1990-11-15
1994-05-03
Wu, Shean C.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
570129, 359103, C09K 1930, C07C 2513, G02F 113
Patent
active
053085418
DESCRIPTION:
BRIEF SUMMARY
The invention relates to novel halogenated benzene derivatives of the formula I ##STR2## in which n is 1 to 10, the rings A and B are each trans-1,4-cyclohexylene, or one of the rings A and B is alternatively 1,4-phenylene or 3-fluoro-1,4-phenylene, X is F, Cl, --CHF.sub.2, --CF.sub.3, --CN, --OCF.sub.3 or --OCHF.sub.2, Y and Z are each, independently of one another, H or F, r=1 or, in the case where s=1, B=trans-1,4-cyclohexylene and simultaneously X=--CHF.sub.2, --CF.sub.3, --OCF.sub.3 or --OCHF.sub.2, r is alternatively 0, and s=1 or, in the case where B=1,4-phenylene or 3-fluoro-1,4-phenylene, s is alternatively 0, and liquid-crystalline media containing these compounds.
DESCRIPTION OF THE ART
EP-A 0 205 998 and 0 291 949 disclose liquid crystals of the formula A1 ##STR3## in which A is F or CN, and R is alkyl having 1 to 7 carbon atoms.
However, the compounds where A=F have only moderate dielectric anisotropy, which frequently results in relatively high threshold voltages in mixtures.
In addition, the miscibility of the compounds A1 with other liquid-crystal compounds is in some cases inadequate.
Further, similar nitrile compounds are known: ##STR4##
EP-A 0 280 902 discloses liquid crystals of the formula A2 ##STR5## in which A is H, F, Cl, Br or CN.
EP-A 0 272 580 discloses liquid crystals of the formula B ##STR6## in which R.sup.1 is C.sub.2 H.sub.5 or C.sub.4 H.sub.7.
However, the compounds A2 are either not up to the high demands regarding electrical resistance (A=CN), as required, for example, for displays having an active matrix, or they have only moderate dielectric anisotropy, which frequently results in relatively high threshold voltages in mixtures (A=H, F, Cl or Br). By contrast, the compounds B have extremely high melting points and relatively unfavorable miscibility with other liquid-crystal compounds. In addition, their dielectric anisotropy is extremely low.
Like similar compounds, for example those disclosed in German Offenlegungsschrift 33 17 597, the compounds of the formula I can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell.
All the substances employed hitherto for this purpose have certain disadvantages, for example excessively high melting points, excessively low clear points, inadequate stability to heat, light or electrical fields, inadequate electrical resistance, excessive temperature dependence of the threshold voltage, induction of smectic phases at low temperatures and/or inadequate solubility at low temperatures.
In particular in the case of displays of the supertwist type (STN) having twist angles of considerably more than 220.degree. or in the case of displays having an active matrix, the materials employed hitherto have disadvantages.
SUMMARY OF THE INVENTION
The invention had the object of finding novel liquid-crystalline compounds which are suitable as components of liquid-crystalline media, in particular for nematic media having positive dielectric anisotropy, and which do not have the disadvantages of the known compounds, or only do so to a small extent. This object has been achieved by the provision of the novel compounds of the formula I.
It has been found that the compounds of the formula I are pre-eminently suitable as components of liquid-crystalline media. They can be used, in particular, to obtain liquid-crystalline media having broad nematic ranges, high clear point, excellent nematogeneity down to low temperatures, excellent chemical stability, a pronounced .epsilon..perp. with a positive dielectric anisotropy, low temperature dependence of the threshold voltage and/or low optical anisotropy. The novel compounds also exhibit good solubility for or in other components of media of this type and a high positive dielectric anisotropy at the same time as favorable viscosity.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The nitriles of the formula I (X=CN) [in particular those of the formulae Iaa (s is preferably 1), Iac, Ib, Ibd (Y is preferably F), Ibf and Ibg] exhibit, for high-cl
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Coates David
Hittich Reinhard
Plach Herbert
Poetsch Eike
Reiffenrath Volker
Merck Patent Gesellschaft mit beschrankter Haftung
Wu Shean C.
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