2,3-Difluoro-5-(trifluoromethyl)benzenes, and the use thereof in liquid-crystal mixtures

摘要

2,3-Difluoro-5-(trifluoromethyl)benzenes of the formula (I) <IMAGE> in which the symbols have the following meaning: R<1> is H, a straight-chain or branched (with or without an asymmetrical carbon atom) alkyl having 1 to 15 carbon atoms, in which, in addition, one or two non-adjacent CH2 groups may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -CO-S-, -S-CO-, -O-CO-O-, -CH=CH-, -C IDENTICAL C-, <IMAGE> or -Si(CH3)2-, and in which, in addition, one or more H atoms of the alkyl radical may be substituted by F, Cl or CN; A<1>, A<2> and A<3> are identical or different and are 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 or naphthalene-2,6-diyl, bicyclo[2.2.2]octane-1,4-diyl or 1,3-dixaborinane-2,5-diyl; M<1>, M<2> and M<3> are identical or different and are -CH2CH2-, -CH=CH-, -C IDENTICAL C-, -CH2CH2CH2CH2-, -CH2CH2CH2-O-, -O-CH2CH 2CH2-, -CH2CH2CO-O-, -OCO-CH2CH2-, -CH2O-, -OCH2-, -CO-O- or -O-CO-; k, l, m, n, o and p are zero or one, with the proviso that the sum k + m + o is greater than zero. The novel compounds of the formula (I) are chemically and photochemically stable. They have low melting points and generally broad liquid-crystalline phases, in particular broad nematic phases.