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A ferroelectric liquid crystal mixture having a negative value of .DELTA.e and allowing a high speed response and a low voltage driving, as well as a liquid crystal display devise using the crystal mixture of the invention. The ferroelectric liquid crystal mixture according to the invention comprise

A ferroelectric liquid crystal mixture having a negative value of .DELTA.e and allowing a high speed response and a low voltage driving, as well as a liquid crystal display devise using the crystal mixture of the invention. The ferroelectric liquid crystal mixture according to the invention comprises two or more compounds from at least two different of the following classes of compounds: A. thiadiazoles, B. phenanthrenes, C. 2-fluoropyridines, D. difluorobenzenes, E. meta-substituted aromatic compounds.

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[ We claim:] [1.] A ferroelectric liquid crystal mixture comprising at least two compounds selected from at least two different of the following groups of compounds including two more compounds from at least groups B and C: (1,3,4)-Thiadiazole derivatives of the formula (I): [ STR 73 ] rein the symb

[ We claim:] [1.] A ferroelectric liquid crystal mixture comprising at least two compounds selected from at least two different of the following groups of compounds including two more compounds from at least groups B and C: (1,3,4)-Thiadiazole derivatives of the formula (I): [ STR 73 ] rein the symbols and indices have the following meanings:R.sup.1 and R.sup.2 independently of one another, are(a) a hydrogen atom,(b) a straight-chain or branched-chain alkyl group, with or without an asymmetric carbon atom, having from 2 to 16 carbon atoms, in which one or two --CH.sub.2 -- groups may be replaced by --O--, --S--, --CO--, --CO--O--, --O--CO--, --CH.dbd.CH--, --C.tbd.C--, --Si(CH.sub.3).sub.2 --, 1,4-cyclohexylene, 1,4-phenylene, cyclopropane-1,2-diyl or --O--CO--O--, with the proviso that --O-- and/or --S-- atoms must not be directly bonded to one another; one or more hydrogen atoms of the alkyl group may be substituted by F, Cl, CN and/or CF.sub.3 ; or(c) any one of the following chiral groups: [ STR 74 ]wherein R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7, independently of one another, are a straight-chain or branched-chain alkyl group having from 1 to 16 carbon atoms (with or without an asymmetrical carbon atom), where one or more --CH.sub.2 -- groups may also be replaced by --O-- or --CH.dbd.CH--, with the proviso that oxygen atoms must not be bonded directly to one another; one or more hydrogen atoms of the alkyl group may be substituted by --F or --Cl; or R.sup.4 and R.sup.5 may also together be --(CH.sub.2).sub.4 -- or --(CH.sub.2).sub.5 -- if they are bonded to an oxirane, dioxolane or tetrahydrofuran system;Q is --CH.sub.2 --O--, --CO--O-- or a single bond;Z.sup.1, Z.sup.2 and Z.sup.3 independently of one another, are a single bond, --O--, --CO--O-- or --O--CO--; with the proviso that, when R.sup.1 is (c), then Z.sup.1 is not a single bond, and that, when R.sup.2 is (c), then Z.sup.2 is not a single bond;A.sup.1 and A.sup.2 are identical or different and are 1,4-phenylene, in which one or more H atoms may be replaced by F, pyridine-2,5-diyl, in which one H atom may be replaced by F, pyrimidine-2,5-diyl or trans-1,4-cyclohexylene;a and b are 0 or 1 and a+b is 0 or 1;X.sup.1 and X.sup.2 independently of one another, are --N--, --CF-- or --CH--; Phenanthrene derivatives of the formula (II), [ STR 75 ] which the symbols and indices have the following meanings:E.sup.1, E.sup.2, E.sup.3, E.sup.4, E.sup.5 and E.sup.6 are --N--, --CF-- or --CH--, with the following provisos:if E.sup.1 (E.sup.4) is --N-- or --CF--, E.sup.2 and E.sup.3 (E.sup.5 and E.sup.6) must be --CH--;if E.sup.2 and/or E.sup.3 (E.sup.5 and/or E.sup.6) are --CF--, E.sup.1 (E.sup.4) must be --CH--;if E.sup.2 (E.sup.5) is --N--, E.sup.1 (E.sup.4) must be --CH--, while E.sup.3 (E.sup.6) can be --CH-- or --CF--; andat least one of E.sup.1 to E.sup.6 must be --N-- or --CF--;G is --CH.sub.2 CH.sub.2 -- or --CH.dbd.CH--;R.sup.1 and R.sup.2, independently of one another, are hydrogen or a straight-chain or branched-chain alkyl group having from 1 to 20 carbon atoms (with or without an asymmetrical carbon atom), in which one or more --CH.sub.2 -- groups may be replaced by --O--, --CO--O--, --O--CO--, --O--CO--O--, --CH.dbd.CH--, --C.tbd.C--, cyclopropane-1,2-diyl, --Si(CH.sub.3).sub.2 --, 1,4-phenylene, trans-1,4-cyclohexylene or trans-1,3-cyclopentylene, with the proviso that oxygen atoms and/or sulfur atoms must not be bonded directly to one another; one or more hydrogen atoms of the alkyl group may be substituted by --F, --Cl, --Br, --CF.sub.3, --CN or --OR.sup.3 ; or R.sup.1, R.sup.2 are one of the following chiral groups: [ STR 76 ]wherein R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7, independently of one another, are a straight-chain or branched-chain alkyl group having from 1 to 6 carbon atoms (with or without an asymmetrical carbon atom), where one or more --CH.sub.2 -- groups may also be substituted by --O-- or --CH.dbd.CH--, with the proviso that oxygen atoms must not be bonded directly to one another; one or more hydrogen atoms of the alkyl group may be substituted by --F or --Cl; or R.sup.4 and R.sup.5 may also together be --(CH.sub.2).sub.4 -- or --(CH.sub.2).sub.5 -- if they are bonded to an oxirane, dioxolane or tetrahydrofuran system;Q is --CH.sub.2 --O--, --CO--O-- or a single bond;M.sup.1 and M.sup.2, independently of one another, are --CO--O--, --O--CO--, --CH.sub.2 --O--, --O--CH.sub.2 --, --CH.sub.2 --CH.sub.2 --, --C.tbd.C-- or a single bond;A.sup.1 and A.sup.2, independently of one another, are 1,4-phenylene in which one or more hydrogen atoms may be substituted by F, Cl and/or CN, pyrazine-2,5-diyl pyridazine-3,6-diyl, pyridine-2,5-diyl in which one or more hydrogen atoms may be substituted by F, pyrimidine-2,5-diyl, trans-1,4-cyclohexylene in which one or two hydrogen atoms may be substituted with CN and/or CH.sub.3 ;n and m are 0 or 1, and the sum of n+m is 0 or 1; 2-Fluoropyridine derivatives of the formula (III), [ STR 77 ] which the symbols and indices have the following meanings:R.sup.1 and R.sup.2, independently of one another, are hydrogen or a straight-chain or branched-chain alkyl group having from 1 to 16 carbon atoms (with or without an asymmetrical carbon atom), in which one or two non-adjacent --CH.sub.2 -- groups may be replaced by --O--, --CO--, --CO--O--, --O--CO--, --O--CO--O--, --CH.dbd.CH--, --C.tbd.C--, cyclopropane-1,2-diyl or --Si(CH.sub.3).sub.2 --; one or more hydrogen atoms of the alkyl group may be substituted by F, Cl, CN and/or CF.sub.3 ; or R.sup.1, R.sup.2 are one of the following chiral groups: [ STR 78 ]wherein R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7, independently of one another, are a straight-chain or branched-chain alkyl group having from 1 to 16 carbon atoms (with or without an asymmetrical carbon atom), where one or more --CH.sub.2 -- groups may also be substituted by --O-- or --CH.dbd.CH--, with the proviso that oxygen atoms must not be bonded directly to one another; one or more hydrogen atoms of the alkyl group may be substituted by --F or --Cl; or R.sup.4 and R.sup.5 may also together be --(CH.sub.2).sub.4 -- or --(CH.sub.2).sub.5 -- if they are bonded to an oxirane, dioxolane or tetrahydrofuran system;Q is --CH.sub.2 --O--, --CO--O-- or a single bond;A.sup.1, A.sup.2, A.sup.3 and A.sup.4, independently of one another, are 1,4-phenylene in which one or two hydrogen atoms may be substituted by F, or pyrazine-2,5-diyl, pyridazine-3,6-diyl, pyridine-2,5-diyl or pyrimidine-2,5-diyl, trans-1,4-cyclohexylene in which one or two hydrogen atoms may be substituted by CN, or naphthalene-2,6-diyl; M.sup.1, M.sup.2, M.sup.3 and M.sup.4, independently of one another, are --O--, --S--, --CO--, --CO--O--, --O--CO--, --O--CO--O--, --CH.sub.2 --O--, --O--CH.sub.2 --, --CH.sub.2 --CH.sub.2 --, --CH.dbd.CH-- or --C.tbd.C-- with the proviso that two M groups must not be directly bonded to one another; k, l, m, n, o, p, q and r are 0 or 1, with the proviso that the sum of k+m+p+r is more than 0 and less than 4; Phenylene derivatives of the formula (IV), [ STR 79 ]wherein R.sup.1 and R.sup.2, independently of one another, are hydrogen or a straight-chain or branched-chain alkyl group having from 1 to 16 carbon atoms (with or without an asymmetrical carbon atom), in which one or two non-adjacent --CH.sub.2 -- groups may be replaced by --O--, --CO--, --CO--O--, --O--CO--, --O--CO--O--, --CH.dbd.CH--, --C.tbd.C--, cyclopropane-1,2-diyl, 1,4-phenylene, 1,4-Cyclohexylene or --Si(CH.sub.3).sub.2 --; and one or more hydrogen atoms of the alkyl group may be substituted with F, Cl, CN and/or CF.sub.3 ; or R.sup.1, R.sup.2 are one of the following chiral groups: [ STR 80 ]wherein R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7, independently of one another, are a straight-chain or branched-chain alkyl group having from 1 to 16 carbon atoms (with or without an asymmetrical carbon atom), where one or more --CH.sub.2 -- groups may also be substituted by --O-- or --CH.dbd.CH--, with the proviso that oxygen atoms must not be bonded directly to one another; one or more hydrogen atoms of the alkyl group may be substituted by --F or --Cl; or R.sup.4 and R.sup.5 may also together be --(CH.sub.2).sub.4 -- or --(CH.sub.2).sub.5 -- if they are bonded to an oxirane, dioxolane, or tetrahydrofuran system;Q is --CH.sub.2 --O--, --CO--O-- or a single bond;A.sup.1, A.sup.2, A.sup.3 are, independently of one another, 1,4-phenylene in which one two H-atoms may be substituted by F, pyridin-2,5-diyl, pyrimidin-2,5-diyl, pyrazine-2,5-diyl, pyridazin-3,6-diyl, naphthalene-2,6-diyl, 1,2,3,4-tetrahydronapthalene-2,6-diyl or 1,4-cyclohexylene in which one or two hydrogenatoms may be substituted by CN and/or CH.sub.3 groups;X.sup.1 and X.sup.2 are selected from hydrogen, F, Cl, CF.sub.3 and CN; with the proviso that X.sup.1 and X.sup.2 are not simultaneously hydrogen;each of Z.sup.1 and Z.sup.2 are --CO--O--, --O--CO--, --CH.sub.2 CH.sub.2 --, --O--CH.sub.2 --, --CH.sub.2 --O--, --C.tbd.C-- or a single bond;each k, m and n are 0, 1 or 2, and (k,m+n) is 1 or 2; and Meta-substituted aromatic compounds of the formula (V), [ STR 81 ]wherein X.sup.3 is F, Cl, Br, CN, CF.sub.3 or an alkyl group having from 1 to 12 carbon atoms, in which one or two CH.sub.2 -group may be replaced by --O--, --CO--O-- or --O--CO--, and in which one or more hydrogen atoms in the alkyl group may be substituted by F, Cl or CN;R.sup.1 is hydrogen or a straight-chain or branched-chain alkyl group having from 1 to 16 carbon atoms (with or without an asymmetrical carbon atom), in which one or more hydrogen atoms may be substituted by F, Cl, CN and/or CF.sub.3 ;A.sup.1, A.sup.2 and A.sup.3, independently of one another, are 1,4-phenylene in which one or two hydrogen atoms may be substituted by F, or pyrazine-2,5-diyl, pyridazine-3,6-diyl, pyridine-2,5-diyl or pyrimidine-2,5-diyl, trans-1,4-cyclohexylene in which one or two hydrogen atoms may be substituted by CN, or 1,3,4-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, naphthalene-2,6-diyl, or 1,3-thiazole-2,4(5)-diyl;M.sup.1, M.sup.2, M.sup.3 and M.sup.4, independently of one another, are --O--, --S--, --CO--, --CO--O--, --O--CO--, --O--CO--O--, --CH.sub.2 --O--, --O--CH.sub.2 --, --CH.sub.2 --CH.sub.2 --, --CH.dbd.CH-- or --C.tbd.C--, with the proviso that two M groups must not be bonded directly to one another;k, l, m, n, o, p and q are 0 or 1, with the proviso that the sum of l+n+p is more than 0 and less than 4.