Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1989-06-05
1991-10-08
Maples, John S.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
25229963, 25229901, 2522996, 359104, C09K 1934
Patent
active
050552210
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the use of compounds of the formula I atoms, in which one or more non-neighbouring CH.sub.2 groups may also be replaced by --O--, --CO--, --O--CO--, --O--COO--, --CO--O--and/or --CH=CH--, or one of the radicals R.sub.1 and R.sub.2 is also H, F, Cl, Br or CN, pyrimidin-2,5-diyl, pyridin-2,5-diyl, pyrazin-2,5-diyl or pyridazin-3,6-diyl, F and/or Cl atoms and/or CH.sub.3 and/or CN groups, 1,4-phenylene, which is unsubstituted or substituted by one or two F and/or Cl atoms and/or CH.sub.3 and/or CN groups, in which one or more CH groups may also be replaced by N, --OCH.sub.2 --, --O--CH.sub.2 -- or a single bond, and
And also smectic liquid-crystalline phases, particularly chiral tilted smectic phases, containing compounds of the formula I.
Chiral tilted smectic liquid-crystalline phases having ferroelectric properties can be prepared by adding one or more tilted smectic phases havng a suitable chiral doping substance to the basic mixtures (L. A. Beresnev et al., Mol. Cryst. Liq. Cryst. 89, 327 (1982); H. R. Brand et al., J. Physique 44 (lett.), L-771 (1983). Such phases can be used as dielectrics for rapidly switching displays, which are 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) based on the ferroelectric properties of the chirally tilted phase. In this phase, the elongated molecules are arranged in layers, the molecules having a tilt angle to the layer perpendiculars. When proceeding from layer to layer, the tilt direction changes through a small angle relative to an axis which is perpendicular to the layers, so that a helical structure is formed. In displays which are 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 spacing of the plates (about 1-2 .mu.m). The longitudinal axes of the molecules are thereby forced to align themselves in a plane parallel to the plates of the cell, two distinct tilt orientations being produced. Switching to and fro between these two states can be accomplished in the liquid-crystalline phase, which has a spontaneous polarization, by applying a suitable electrical alternating field. This switching process is significantly faster than the conventional twisted cells (TN-LCDs), which are based on nematic liquid crystals.
The low chemical, thermal and light stability of the currently available materials having chirally tilted smectic phases (such as, for example, Sc*) is a great disadvantage for many applications. A further disadvantageous property of displays based on the currently available chirally tilted smectic mixtures is that the spontaneous polarization has values which are too small, so that the switching time behaviour of the displays is unfavourably influenced and/or the pitch and the tilt of the phases do not correspond to the requirements of display technology. In addition, the temperature range of the ferroelectric phases is usually too small and is mainly at temperatures which are too high.
It has now been found that the use of compounds of the formula I as components of chirally tilted smectic mixtures can essentially reduce the disadvantages mentioned. The compounds of the formula I are thus extremely suitable as components of chirally tilted smectic liquid-crystalline phases. In particular, especially chemically stable chirally tilted smectic liquid-crystalline phases having favourable ferroelectric phase regions, particularly having broad Sc.sup.* phase regions, excellent supercool-ability to temperatures well below 0.degree. C. without crystallization occurring (even phases according to the invention having a melting point above 0.degree. C. can generally be supercooled to well below 0.degree. C.), favourable degree of pitch, and values for the spontaneous polarization which are high for such phases can be prepared with their aid. P is the spontaneous pol
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Bofinger Klaus
Eidenschink Rudolf
Hopf Reinhard
Krause Joachim
Pausch Axel
Maples John S.
Merck Patent Gesellschaft mit beschrankter Haftung
Treanor Richard
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