Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1987-10-09
1989-10-03
Gron, Teddy S.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
25229901, 25229963, 25229967, 25229961, 350350R, 350350S, 558268, 558270, 560 59, 560 73, 560102, 560106, 560107, 560108, 560109, G02F 113, C09K 1930, C07C 6976
Patent
active
048714720
DESCRIPTION:
BRIEF SUMMARY
The invention relates to esters of the formula I ##STR2## wherein R.sup.1 and R.sup.2 each independently of one another are R, OR, OCOR, COOR or OCOOR, are not adjacent and are not linked by O can also be replaced by --O--, --CO--, --O--CO--, --CO--O--, --CH-halogen, --CHCN-- and/or --CH.dbd.CH--, 1,4-phenylene or trans-1,4-cyclohexylene, --OCH.sub.2 --, --CH.sub.2 CH.sub.2 -- or a single bond and Z.sup.2 is --CH.sub.2 CH.sub.2 -- or a single bond and R.sup.2 is an alkyl group, a single bond, A.sup.3 is then 1,4-phenylene, and OCOOR.
The compounds of the formula I are suitable as components of chiral tilted smectic phases which have ferroelectric properties.
Chiral tilted smectic liquid crystal phases with ferroelectric properties can be prepared by adding a suitable chiral doping substance to base mixtures with one or more tilted smectic phases (L. A. Beresnev et al., Mol. Crystl. Liq. Cryst. 89, 327 (1982); and H. R. Brand et al., J. Physique 44 (lett.), L-771 (1983)). Such phases can be used as dielectrics for rapid-switching displays which, for example, 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) and U.S. Pat. No. 4,367,924), on the basis of the ferroelectric properties of the chirally tilted phase. In this phase, the elongated molecules are arranged in layers, the molecules having a tilting angle to the layer perpendicular. On progressing from layer to layer, the tilting direction changes by a small angle in 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 tilting directions of the molecules is suppressed by a very small distance between the plates (about 1-2 .mu.m). The longitudinal axes of the molecules are thereby forced to arrange themselves in a plane parallel to the plates of the cell, which means that two distinct tilting orientations are formed. By applying a suitable alternating electrical field, switching backwards and forwards between these two states can be effected in the liquid crystal phase with spontaneous polarization. This switching operation is considerably faster than in conventional twisted cells (TN-LCD's) based on nematic liquid crystals.
A great disadvantage for many applications of the materials currently available with chirally tilted smectic phases (such as, for example, Sc*) is their low chemical, thermal and light stability. Another adverse property of displays based on chirally tilted smectic mixtures currently available is that the spontaneous polarization has values which are too low, so that the switching time properties of the displays are adversely influenced and/or the pitch and tilt of the phases do not meet the requirements of display technology. Moreover, the temperature range of the ferroelectric phases is usually too small and is predominantly at temperatures which are too high.
It has now been found that as components of chiral tilted smectic mixtures, the compounds of the formula I can substantially reduce the disadvantages mentioned. The compounds of the formula I are thus outstandingly suitable as components of chiral tilted smectic liquid crystal phases. In particular, chiral tilted smectic liquid crystal phases which have a particularly high chemical stability and have favourable ferroelectric phase ranges, especially with wide Sc* phase ranges, are very easy to supercool down to temperatures far below 0.degree. C. without crystallization occurring (even phases according to the invention with a melting point above 0.degree. C. can in general be supercooled to far below 0.degree. C.), and have a favourable pitch height and spontaneous polarization values which are high for such phases, can be prepared with the aid of these compounds. P is the spontaneous polarization in nC/cm.sup.2.
The compounds of the formula I have a wide field of use. Depending on the choic
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Geelhaar Thomas
Krause Joachim
Reiffenrath Volker
Gron Teddy S.
Merck Patent Gesellschaft mit beschrankter Haftung
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