2,3-difluorohydroquinone derivatives

Details 2,3-difluorohydroquinone derivatives 2,3-difluorohydroquinone derivatives

1992-04-21

1993-09-28

Stoll, Robert L.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229967, 560 59, 560 62, 560 63, 568645, 568649, 568656, 359103, C09K 1930, C07C 6976, C07C 4100

Patent

active

052484475

DESCRIPTION:

BRIEF SUMMARY
SUMMARY OF THE INVENTION

The invention relates to 2,3-difluorohydroquinone derivatives of the formula I ##STR2## in which
R.sup.1 and R.sup.2, in each case independently of one another, are alkyl having 1 to 15 C atoms or alkenyl having 3 to 15 C atoms which are unsubstituted, monosubstituted by cyano or at least monosubstituted by fluorine or chlorine, it also being possible for one CH.sub.2 group in these radicals to be replaced by --O--, --CO--, --CO--O--, --O--CO-- or --O--CO--O--,


EXAMPLES

A.sup.1, A.sup.2 and A.sup.3, in each case independently of one another, are CH.sub.2 groups may be replaced by --O-- and/or --S--, replaced by N, or 1,4-bicylo-(2,2,2)octylene (sic), 1,3,4-thiadiazole-2,5-diyl, napththalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl, polysubstituted by F, Cl, CH.sub.3 or CN,
Z.sup.1 is --CO--O--, --O--CO--, --CH.sub.2 --CH.sub.2 --, --OCH.sub.2 --, --CH.sub.2 O--, --C.tbd.C-- or a single bond,
Q.sup.1 and Q.sup.2, in each case independently of one another, arc --CO-- or --CH.sub.2 --,
m and n are each 0, 1 or 2, and
(m+n) is 0, 1 or 2.
For reasons of simplicity, Cyc below is a 1,4-cyclohexylene group and PheF.sub.2 below is a group of the formula ##STR3##
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 deformation of aligned phases or the effect of dynamic scattering.
The compounds of the formula I are distinguished by a clearly negative anisotropy of the dielectric constant and, in an electrical field, are aligned with their longitudinal molecular axes perpendicular to the field direction.
This effect is known and is utilized to control the optical transparency in various liquid-crystal displays, for example in liquid-crystal cells of the light-scattering type (dynamic scattering), of the so-called DAP type (deformation of aligned phases) or ECB type (electrically controlled birefrigence) or of the guest/host type (guest/host interaction).
The compounds of the formula I are also suitable as components of nematic or chirally nematic liquid-crystalline media having a dielectric anisotropy which is positive overall. The purpose of the compounds of the formula I here is to increase .epsilon..sub.195. The negative dielectric anisotropy of the compounds according to the invention is overcompensated here by addition of components which are highly positive dielectrically. Such media are used for TN displays having a 90.degree. twist or, in particular, for more highly twisted TN cells since they result here in particularly steep characteristic lines.
In addition, compounds of the formula I are suitable as components of chiral tilted smectic media. Chiral tilted smectic liquid-crystalline media having ferroelectric properties can be prepared by adding a suitable chiral dope to base mixtures containing one or more tilted smectic media (L. A. Veresnev et al., Mol. Cryst. Liq. Cryst. 89, 327 (1982); H. R. Brand et al., J. Physique 44 (lett.), L-771 (1983). Such media can be used as dielectrics for rapidly switching displays based on the principle, described by Clark and Lagerwall, of SSFLC technology (N. A. Clark and S. T. Lagerwall, Appl. Phys. Lett. 36, 899 (1980); U.S. Pat. 4,367,924) on the basis of the ferroelectric properties of the chiral tilted medium.
A number of liquid-crystalline compounds having slightly negative dielectric anisotropy have hitherto already been synthesized. In contrast, only relatively few liquid-crystal components having a large negative anisotropy of the dielectric constant are known. In addition, the latter generally have disadvantages, such as, for example, poor solubility in mixtures, high viscosity, high melting points and chemical instability. There is therefore a demand for further compounds having negative dielectric anisotropy which permit the properties of mixtures to be further improved for a very wide variety of electrooptical applications.
Liquid-crystal compounds

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