Fluorobenzene derivatives and liquid-crystalline medium

Details Fluorobenzene derivatives and liquid-crystalline medium Fluorobenzene derivatives and liquid-crystalline medium

1994-04-12

1996-01-30

Geist, Gary L.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229966, C09K 1930, C09K 1912

Patent

active

054878454

DESCRIPTION:

BRIEF SUMMARY
The invention relates to new fluorobenzene derivatives of the formula I ##STR2## in which R is H, an alkyl or alkenyl radical of 1 to 15 carbon atoms which is unsubstituted or monosubstituted by CN or CF.sub.3 or at least monosubstituted by halogen, it being possible for one or more CH.sub.2 groups in these radicals also to be replaced, in each case independently of one another, by ##STR3## in such a manner that O atoms are not linked directly to one another, A.sup.1 and A.sup.2, in each case independently of one another, are a CH.sub.2 groups can also be replaced by --O-- and/or --S--, replaced by N, 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl, fluorine, --CO--O--, --O--CO--, --CH.sub.2 O--, --OCH.sub.2 --, --CH.sub.2 CH.sub.2 --, --CH.dbd.CH--, --C.dbd.C-- or a single bond, one of the radicals Z.sup.1 and Z.sup.2 is also --(CH.sub.2).sub.4 -- or --CH.dbd.CH--CH.sub.2 CH.sub.2 --,
The invention furthermore relates to the use of these compounds as components of liquid-crystalline media and to liquid-crystal and electrooptical display elements containing the liquid-crystalline media according to the invention.
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, the guest-host effect, the effect of the deformation of aligned phases or the effect of dynamic scattering.
The object of the invention was to find new stable liquid-crystalline or mesogenic compounds which are suitable as components of liquid-crystalline media and in particular have simultaneously a comparatively low viscosity and a relatively high dielectric anisotropy.
It has now been found that compounds of the formula I are highly suitable as components of liquid-crystalline media. In particular, they have comparatively low viscosities. By means of them, it is possible to obtain stable liquid-crystalline media having a road mesophase range and advantageous values for optical and dielectric anisotropy. These media furthermore have a very good low-temperature behaviour.
Liquid crystals of the formula ##STR4## have already been disclosed in DE 3,209,179. Compounds of the formulae ##STR5## are disclosed in JP 62/103,057. Finally, compounds of the formula ##STR6## are described in JP 63,216,858. Compounds of the following formulae: ##STR7## are disclosed in German Offenlegungsschriften 3,042,391 and 3,139,130.
Various compounds having liquid-crystalline properties and a terminally-bound CF.sub.3 group are already known (U.S. Pat. No. 4,330,426; U.S. Pat. No. 4,684,476; J. C. Liang and S. Kumar, Mol. Cryst. Liq. Cryst. 1987; Vol. 142, pp. 77-84). However, these compounds often have a strongly smectogenic character and are less suitable for many practical applications.
However, in view of the wide range of applications of these compounds having a high .DELTA..epsilon., it was desirable to have available further compounds of exactly tailor-made properties for the particular applications.
In addition, by providing the compounds of the formula I, the range of liquid-crystalline substances, which in the various aspects of industrial application are suitable for the preparation of liquid-crystalline mixtures, is very generally and significantly broadened.
The compounds of the formula I have a broad range of applications. Depending on the choice of substituents, these compounds can serve as base materials of which liquid-crystalline media are composed for the most part; however, it is also possible to add compounds of the formula I to liquid-crystalline base materials from other classes of compounds, in order, for example, to influence the dielectric and/or optical anisotropy of such a dielectric and/or to optimize its threshold voltage and/or its viscosity.
In the pure state, the compounds of the formula I are colorless and form liquid-crystalline mesophases in a temperature range favored for electrooptical use. They have very good chemical, heat and light

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