Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1990-10-22
1993-03-23
Stoll, Robert L.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
546301, 359104, C09K 1934, C07D21172, G02F 113
Patent
active
051961415
DESCRIPTION:
BRIEF SUMMARY
The invention relates to 5-oxy-2-phenylpyridines of the formula I ##STR3## in which m and n, independently of one another, are each from 1 to 18, and ##STR4## or a single bond, with the provisos that a) in the case where Q.sup.1 =Q.sup.2 =a single bond, the sum of m+n.gtoreq.11, and b) in the case where Q.sup.2 =CO, the radical C.sub.n H.sub.2n+1 is straight-chain, and to ferroelectric liquid-crystalline media containing these compounds.
Chiral, tilted, smectic, liquid-crystalline media 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). Media of this type can be used as dielectrics for rapidly 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. 4,367,924) on the basis of the ferroelectric properties of the chiral, tilted medium. In these media, the long molecules are arranged in layers, the molecules having a tilt angle to the layer perpendiculars. On moving from layer to layer, the tilt direction changes by a small angle with respect to an axis perpendicular to the layers, thus forming a helical structure. 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). The longitudinal axes of the molecules are therefore forced to arrange themselves in a plane parallel to the plates of the cell, thus causing two preferred tilt orientations. By applying a suitable electrical alternating field, it is possible to switch back and forth between these two states in the liquid-crystalline phase exhibiting spontaneous polarization. This switching process is considerably faster than in customary twisted cells (TN-LCDs) based on nematic liquid crystals.
A great disadvantage for many applications of the currently available materials having chiral, tilted, smectic phases (such as, for example, Sc*, but also S.sub.H *, S.sub.I *, S.sub.J *, S.sub.K *, S.sub.G *, S.sub.F *) is their low chemical, thermal and photostability. A further disadvantageous property of displays based on currently available chiral, tilted, smectic media is that the values for the spontaneous polarization are too low, which means that the switching time behaviour of the displays is adversely affected and/or the pitch and/or the tilt and/or the viscosity of the media does not conform to the requirements of display technology. In addition, the temperature range of the ferroelectric media is usually too small and is predominantly at excessively high temperatures.
It has now been found that the use of compounds of the formula I as components of chiral, tilted, smectic media can essentially reduce the disadvantages mentioned. The compounds of the formula I are thus preeminently suitable as components of chiral, tilted, smectic liquid-crystalline media. In particular, they can be used to prepare chiral, tilted, smectic liquid-crystalline media which are particularly stable chemically and have favourable ferroelectric phase ranges, favourable values for the viscosity, in particular having broad Sc* phase ranges, excellent supercoolability down to temperatures of less than 0.degree. C. without crystallization occurring, and spontaneous polarization values which are high for phases of this type. P is the spontaneous polarization in nC/cm.sup.2. However, the compounds of the formula I are also suitable for liquid-crystalline media for the electroclinic effect.
The compounds of the formula I have a broad field of application. Depending on the choice of substituents, these compounds can be used as base materials from which liquid-crystalline, smectic media are predominantly composed; however, it is also possible to add compounds of
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Geelhaar Thomas
Hittich Reinhard
Poetsch Eike
Reiffenrath Volker
Wachtler Andreas
Merck Patent Gesellschaft mit beschrankter Haftung
Stoll Robert L.
Tucker Philip
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