Liquid-crystalline medium

A liquid-crystalline medium comprising a mixture of polar compounds of negative dielectric anisotropy, which comprises at least one compound of the formula I

• in which
• R11 is an alkyl or alkenyl radical having 1 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or monosubstituted to perhalo-substituted by halogen, where one or more CH2 groups in these radicals are optionally replaced by —O—, —S—,
• —C≡C—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another,
• A1
• a) is a 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which one or two non-adjacent CH2 groups are optionally replaced by —O— or —S—,
• b) a 1,4-phenylene radical, in which one or two CH groups are optionally replaced by N,
• c) a radical selected from the group consisting of piperidine-1,4-diyl, 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl,
• where the radicals a), b) and c) are optionally monosubstituted or polysubstituted by halogen atoms,
• Z1 is —CO—O—, —O—CO—, —CF2O—, —OCF2—, —CH2O—, —OCH2—, —CH2CH2—, —(CH2)4—, —C2F4—, —CH2CF2—, —CF2CH2—, —CH═CF—, —CF═CH—, —CF═CF—, —CH═CH—, —C≡C— or a single bond,
• R12 is alkenyl having 2-7 carbon atoms, and
• m is 0, 1 or 2.