Liquid-crystalline compounds

Details Liquid-crystalline compounds Liquid-crystalline compounds

1996-08-22

1998-09-08

Wu, Shean C.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229901, 25229961, 25229964, 25229965, 25229966, 25229967, C09K 1934, C09K 1952, C09K 1930, C09K 1920

Patent

active

058040978

DESCRIPTION:

BRIEF SUMMARY
This application is 371 of PCT/EP/03069 filed Sep. 14, 1994.
A large number of liquid-crystalline compounds is known. However, these generally do not solidify in a glass-like manner. Defined compounds having liquid-crystalline properties which do solidify in a glass-like manner are described, for example, in DE-A 37 03 640, DE-A 38 27 603, DE-A 38 30 968 and EP-A-504 660. A common feature of the compounds described in the first three applications is that they readily crystallize even from the glass state, and the orientation in the frozen state is thus unstable. Any mixtures employed in the case of crystallization are also no longer stable, since the requirement of the molecules to build up mixed crystals is very much stronger in the crystal than the requirements for miscibility in an anisotropic fluid.
The compounds described in EP-A-504 660 form stable glasses. They have a high dipole moment parallel to the long axis of the molecules and form nematic or smectic A phases. The dipole moment along the long axis of the molecules means that these materials align parallel thereto in an electric field; they therefore do not have ferroelectric properties, and any helical superstructures present are unstable in the electric field.
Also known are liquid-crystalline systems which have a defined structure and in which mesogenic groups are bonded to a central unit via a spacer (for example DE-A-40 11 811). However, these materials do not solidify in a glass-like manner, but instead crystallize very readily due to their high symmetry. Furthermore, Liquid Crystals 11 (5) (1992), 779, describes ferroelectric liquid crystals which are bonded to a central unit via a spacer. These materials have mesogenic structures which are unstable to heat and also to weak acids or bases and to water.
Desirable compounds for use as liquid-crystalline ferroelectric materials would be those which have a phase behavior in which the phase sequence passed through on cooling is nematic, smectic A and smectic C. Furthermore, the materials should have high flow viscosities in order to prevent the display from being pressure-sensitive, and in particular should be stable to weak acid bases.
A further desired feature is good miscibility with other liquid-crystalline compounds.
It is an object of the present invention to provide, novel liquid-crystalline compounds which solidify in a glass-like manner and which have smectic and nematic phases, are insensitive to variations in temperature and pH and to water and have high flow viscosity.
We have found that this object is achieved by compounds of the formula I --O--, --CONH-- or --CON(R)--, where R is C.sub.1 -- to C.sub.4 -alkyl,
X is preferably trisubstituted phenyl or cyclohexyl, where the substituents are in particular in the meta-position to one another.
Of the radicals Y, particular preference is given to --OCO--, --O-- and --COO--.
Spacers which can be used are all groups known for this purpose; the spacers are usually linked to X via ester or ether groups or via a direct bond. The spacers generally have from 2 to 30, preferably 2 to 12, carbon atoms and can be interrupted in the chain, for example, by O, S, NH or NCH.sub.3. Suitable substituents for the spacer chain are fluorine, chlorine, bromine, cyano, methyl and ethyl. ##STR1## where m is from 1 to 3 and
M can be a known mesogenic group. Particularly suitable are radicals containing aromatic or heteroaromatic groups. In particular, the mesogenic radicals conform to the formula III radical, OCH.sub.2, CH.dbd.N, N.dbd.CH or a direct bond, and
T is generally an aromatic carbocyclic or heterocyclic ring system, which may be substituted by fluorine, chlorine, bromine, cyano, hydroxyl or nitro, conforming, for example, to the following base structures: ##STR2##
Particularly preferred examples of mesogenic groups M are: ##STR3##
Examples of side chains B are C.sub.2 - to C.sub.30 -alkyl or -alkenyl, preferably C.sub.2 - to C.sub.11 -alkyl, where the radicals may be linear or branched, may be interrupted once or more than once by O, OCO, COO, ##S

REFERENCES:
patent: 5417882 (1995-05-01), Bach et al.
Japanese Journal of Applied Physics, vol. 22, No. 10, pp. L661-L663, Oct. 1983, K. Miyasato, et al., "Direct Method with Triangular Waves for Measuring Spontaneous Polarization in Ferroelectric Liquid Crystals".

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