Liquid-crystalline medium

Liquid-crystalline medium based on a mixture of polar compounds having negative dielectric anisotropy, characterised in that it comprises at least one compound of the formula I

• in which
• R0 and R1 each, independently of one another, denote H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, where, in addition, one or more CH2 groups in these radicals may be replaced by —O—, —S—,
• —C≡C—, —OC—O— or —O—CO— in such a way that O atoms are not linked directly to one another,
• A1 a) denotes a 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which one or two non-adjacent CH2 groups may be replaced by —O— or —S—,
• b) denotes a 1,4-phenylene radical, in which one or two CH groups may be replaced by N,
• c) denotes a radical 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-tetrahydro-naphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl, where the radicals a), b) and c) may be mono- or polysubstituted by halogen atoms,
• Z1 denotes —CO—O—, —O—CO—, —CF2O—, —OCF2—, —CH2O—, —OCH2—, —CH2CH2—, —(CH2)4—, —C2F4—, —CH2CF2—, —CF2CH2—, —CF═CF—, —CH═CF—, —CF═CH—, —CH═CH—, —C≡C— or a single bond, and
• m denotes 0, 1 or 2.