Liquid-crystalline medium

Liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, characterized in that it comprises one or more compounds of the general formula I,

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• in which
• R is H, an alkyl or alkenyl radical having 1 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, it also being possible for one or more. CH2 groups in these radicals to be replaced, in each case independently of one another, by —O—,
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• —CO—, —CO—O—, —O—CO— —S—, or —O—CO—O— in such a way that O atoms are not linked directly to one another,
• A1 (a) is a trns-1,4-cyclohexylene radical in which, in addition, one or more non-adjacent CH2 groups may have been replaced by —O— and/or —S—, or a 1,4-cyclohexenylene radical,
• (b) is a 1,4-phenylene radical, in which, in addition, one or two CH groups may have been replaced by N,
• (c) is a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydro-naphthalene-2,6-diyl and 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, where the radicals (a) and (b) may be mono-substituted or polysubstituted by CN, CH3 or F,
• Z1 is —CO—O—, —O—CO—, —CH2O—, —OCH2—, CH2CH2—, —CF2O—, —OCF2 —CH═CH—, —C∝C—, —(CH2)4—, —CH═CH—CH2CH2— or a single bond,
• Y is F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 carbon atoms
• L1 is H or F, and
• m is 0 or 1.