Aromatic compounds, and their use in liquid-crystalline mixtures

A ferroelectric liquid crystal mixture, comprising one or more aromatic compounds of the formula (I)

• R.sup.1 (--A.sup.1).sub.a (--M.sup.1).sub.b (--A.sup.2).sub.c (--M.sup.2).sub.d --B(13 M.sup.3).sub.c (--A.sup.3).sub.f (--M.sup.4).sub.g (--A.sup.4).sub.h --R.sup.2 (I)
• in which the symbols and indices have the following meanings:
• B is ##STR56## R.sup.1 and R.sup.2 are identical or different and are hydrogen, or a straight-chain or branched alkyl radical having 1 to 20 carbon atoms (with or without an asymmetrical carbon atom), where one or more --CH.sub.2 -- groups may also be replaced by --O--, --S--, --CO--, --CS--, --CH.dbd.CH--, --C.tbd.C--, , --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 sulfur atoms must not be bonded directly to one another, and/or one or more H atoms of the alkyl radical may be substituted by --F, --Cl, or --OR.sup.2, or are alternatively one of the following chiral groups:
• ##STR57## R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are identical or different and are hydrogen or a straight-chain or branched alkyl radical having 1-16 carbon atoms (with or without an asymmetrical carbon atom), where one or more --CH.sub.2 -- groups may also be replaced by --O-- with the proviso that oxygen atoms must not be bonded directly to one another, and/or one or more H atoms of the alkyl radical may be substituted by --F or --Cl;
• 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.sup.1 and Q2 are identical or different and are CH.sub.2, CF.sub.2, or O;
• P.sup.1, P.sup.2 and P.sup.3 are identical or different and are C--H, C--F or N;
• M.sup.1, M.sup.2, M.sup.3 and M.sup.4 are identical or different and are --CO--O--, --O--CO--, --CH.sub.2 --O--, --O--CH.sub.2 --, --CH.dbd.CH--, --C.tbd.C--, --O--CO--CH.dbd.CH--, --CH.dbd.CH--COO--, --O--CO--CH.sub.2 --CH.sub.2 --, --CH.sub.2 --CH.sub.2 --COO--, --O--CH.sub.2 --CH.sub.2 --CH.sub.2 --, --CH.sub.2 --CH.sub.2 --CH.sub.2 --O-- or a single bond;
• A.sup.1, A.sup.2, A.sup.3 and A.sup.4 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 or more H atoms may be replaced by F, pyrimidine-2,5-diyl, in which one or two H atoms may be replaced by F, trans-1,4-cyclohexylene, in which one or two H atoms may be replaced by CN and/or CH.sub.3, 1,3,4-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, 1,3-thiazole-2,4-diyl, in which one H atom may be replaced by F, 1,3-thiazole-2,5-diyl, in which one H atom may be replaced by F, thiophene-2,4-diyl, in which one H atom may be replaced by F, thiophene-2,5-diyl, in which one or two H atoms may be replaced by F, naphthalene-2,6-diyl, in which one or more H atoms may be replaced by F;
• a, b, c, d, e, f, g and h are zero or one;
• with the following proviso:
• if the group B is ##STR58## at least one of the radicals R.sup.1 must comprise an --Si(CH.sub.3).sub.2 -- and/or ##STR59## group and/or be one of the following chiral groups:
• ##STR60##