Fluoroalkylethnyl- and difluoroalkylethynylbenzenes, and their u

Details Fluoroalkylethnyl- and difluoroalkylethynylbenzenes, and their u Fluoroalkylethnyl- and difluoroalkylethynylbenzenes, and their u

1996-11-18

1998-10-13

Kelly, C. H.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

2522996, 25229961, 25229962, 25229965, 25229966, 25229967, 560100, 560102, 560108, 544298, 546339, 546342, 570128, 570129, 570144, 548136, C09K 1930, C09K 1934, C09K 1912, C07C 1908

Patent

active

058207856

DESCRIPTION:

BRIEF SUMMARY
The unusual combination of anisotropic and fluid behavior of liquid crystals has resulted in their use in electro-optical switching and display devices, where their electrical, magnetic, elastic and/or thermal properties can be utilized for changes in alignment. Optical effects can be achieved, for example, with the aid of birefringence, of the inclusion of dichroic dye molecules (guest host mode), or of light scattering.
The requirements of practice are constantly rising, not least also owing to the constantly increasing number of types of light valve (TN, STN, DSTN, TFT, ECB, DECB, DS, GH, PDLC, NCAP, SSFLC, DHF, SBF, etc.). Besides thermodynamic and electro-optical parameters, such as phase sequence and phase temperature range, refractive index, birefringence and dielectric anisotropy, response time, threshold voltage, steepness of the electro-optical characteristic line, elastic constants, electrical resistance, multiplexability or pitch and/or polarization in chiral phases, the stability of the liquid crystals to moisture, gases, temperature and electromagnetic radiation and to the materials with which they are in contact during and after the production process (for example alignment layers) is of considerable importance. Toxicological and ecological acceptability and price are constantly increasing in importance.
A broad review of the field of liquid crystals is offered, for example, by the literature below and the references cited therein: 1980; Breach, Philadelphia, 1980; Physik, Berlin 30, 10, 1982, 507-582; Singapore, 1990; 1992-1993 and and Applications, Gordon Breach, Philadelphia, 1991.
WO 90/13610, EP 0 480 217 and DE-A-40 27 458 describe derivatives of trifluoromethylethynyl-, fluoroethynyl- and chloroethynylbenzene for use in liquid-crystal mixtures.
Since, however, individual compounds have hitherto been unable to satisfy simultaneously the many different requirements of liquid crystals, some of which are mentioned above, there is a constant demand for novel improved liquid-crystal mixtures and thus for a multiplicity of mesogenic and non-mesogenic compounds of different structure which enable the mixtures to be adapted to a very wide variety of applications. This applies both to the areas in which nematic LC phases are used in light valves and to those having smectic phases.
Surprisingly, it has now been found that derivatives of fluoroalkylethynyl- and difluoroalkylethynylbenzene are particularly suitable for use in nematic liquid-crystal mixtures.
The invention thus relates to novel fluoroalkylethynyl- and difluoroalkylethynylbenzenes of the general formula (I) ##STR1## in which the symbols and indices have the following meanings: R.sup.1 is H, a straight-chain or branched (with or without an asymmetric carbon atom) alkyl group having 1 to 15 carbon atoms, in which, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by --O--, --S--, --CO--, --CO--O--, --O--CO--, --CO--S--, --S--CO--, --O--CO--O--, --CH.dbd.CH--, --C.tbd.C--, cyclopropane-1,2-diyl or --Si(CH.sub.3).sub.2 --, and in which, in addition, one or more H atoms in the alkyl radical may be substituted by F, Cl or CN; 1,4-phenylene, pyrazine-2,5-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, in which one or two H atoms may be replaced by F, trans-1,4-cyclohexylene, 1,3,4-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl, CH.sub.2 --, --CH.dbd.CH--, --C.tbd.C--, --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 --, --CH.sub.2 CH.sub.2 CH.sub.2 --O--, --O--CH.sub.2 CH.sub.2 CH.sub.2 --, --CH.sub.2 CH.sub.2 --CO--O--, --O--CO--CH.sub.2 CH.sub.2 --, --CH.sub.2 --O--, --O--CH.sub.2 --, --CO--O-- or --O--CO--; greater than zero; F or Cl;
The novel compounds of the general formula (I) are chemically and photochemically stable. They have low melting points and generally have broad liquid-crystalline phases, in particular broad nematic phases.
In particular, the novel compounds have very high anisotropy of the refractive index and of the dielectric constant, which makes them particularly suitable for use in TFT-TN and

REFERENCES:
patent: 5171473 (1992-12-01), Buchecker et al.
patent: 5264149 (1993-11-01), Buchecker et al.
patent: 5308537 (1994-05-01), Coates et al.
patent: 5447657 (1995-09-01), Schadt et al.

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