3,6-disubstituted 2-halopyridines

Details 3,6-disubstituted 2-halopyridines 3,6-disubstituted 2-halopyridines

1992-02-11

1995-02-14

Wu, Shean

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229901, 359103, 359104, C09K 1934, G02F 113

Patent

active

053892917

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to 3,6-disubstituted 2-halopyridines of the formula I ##STR2## where R.sup.1 and R.sup.2 are each, independently of one another, an alkyl or alkenyl radical having up to 15 carbon atoms which is unsubstituted or monosubstituted by CN, halogen or CF.sub.3, it also being possible for one or more CH.sub.2 groups in these radicals to be replaced, in each case independently of one another, by --S--, --O--, --CO--,--CO--O--,--O--CO-- or --O--CO--O-- in such a manner that S and/or O atoms are not linked directly to one another, and one of the radicals R.sup.1 and R.sup.2 is alternatively halogen, --CF.sub.3, --OCF.sub.3 or OCHF.sub.2, non-adjacent CH.sub.2 groups may be replaced by --O-- and/or --S--, be replaced by N, 1,3-bicyclo[1.1.1]pentylene, 1,4-cylohexenylene [sic], 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, halogen, --CH.sub.2 --, --C--C--, --CH.sub.2 O--, --OCH.sub.2 --, --CO--O--, --O--CO--, --CH.dbd.N--, --CH.sub.2 S--, --SCH.sub.2 --, a single bond or an alkylene group having 3 to 6 carbon atoms in which, in addition, one CH.sub.2 group may be replaced by --O--,--CO--O--, --O--CO--, --CH-halogen- or --CHCN--, OCHF.sub.2 or alkoxy, n is 1 or 2, and/or single bond.


BACKGROUND OF THE INVENTION

Chiral tilted smectic liquid-crystalline phases having ferroelectric properties can be prepared by adding a suitable chiral dope to base mixtures having one or more tilted smectic phases (L. A. Beresnev et al., Mol. Cryst. Liq. Cryst. 89, 327 (1982); H. R. Brand et al., J. Physique 44 (lett.), L 771 (1983). Phases of this type can be used as dielectrics for fast-switching displays based on the principle of SSFLC technology described by Clark and Lagerwall (N. A. Clark and S. T. Lagerwall, Appl. Phys. Lett. 36, 899 (1980); U.S. Pat. No. 4,367,924) on the basis of the ferroelectric properties of the chirally [sic] tilted phase. The elongate molecules in this phase are arranged in layers, the molecules having a tilt angle to the layer normals. On moving from layer to layer, the tilt direction changes by a small angle with respect to an axis perpendicular to the layers, so that a helical structure is formed. In displays based on the principle of SSFLC technology, the smectic layers are arranged perpendicular to the plates of the cell. The helical arrangement of the tilt directions of the molecules is suppressed by a very small separation of the plates (about 1-2 .mu.m). This forces the longitudinal axes of the molecules to line up in a plane parallel to the plates of the cell, which causes two preferential tilt alignments to be formed. Application of a suitable alternating electrical field allows switching back and forth between these two states in the liquid-crystalline phase having spontaneous polarization. This switching operation is significantly faster than in conventional twisted cells (TN-LCDs), which are based on nematic liquid crystals.
The currently available materials having chirally [sic] tilted smectic phases (such as, for example, Sc* [sic ], but also S.sub.H *, S.sub.I *, S.sub.J *, S.sub.K *, S.sub.G * and S.sub.F *) has the great disadvantage for many applications of low chemical, thermal and photostability. A further disadvantageous property of displays based on currently available chirally [sic] tilted smectic mixtures is that the spontaneous polarization has values which are too low, so that the response time behavior of the displays is adversely affected and/or the pitch and/or the tilt and/or the viscosity of the phases does not meet the requirements of display technology. In addition, the temperature range of the ferroelectric phases is usually too small and is predominantly at excessively high temperatures.


SUMMARY OF THE INVENTION

It has now been found that the use of compounds of the formula I as components of chirally [sic] tilted smectic mixtures can significantly reduce said disadvantages. The compounds of the formula I are thus eminently

REFERENCES:
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patent: 5160662 (1992-11-01), Satoh et al.
patent: 5204477 (1993-04-01), Reiffenrath et al.
patent: 5205962 (1993-04-01), Coates et al.

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