Fluorophenyl compounds for liquid-crystalline mixtures

A compound of formula I

• in which
• R1 denotes H, F, Cl, Br, a halogenated or unsubstituted alkyl radical having 1 to 15 C atoms, in which one or more CH2 groups are optionally, independently of one another, replaced by —C≡C—, —(CO)O—, —O(CO)—, —(CO)— or —O— in such a way that O atoms are not linked directly to one another,
• A1 denotes
• a) trans-1,4-cyclohexylene or cyclohexenylene, in which one or more non-adjacent CH2 groups are optionally replaced by —O— and/or —S—, and in which H may be substituted by F,
• b) 1,4-phenylene, in which one or two CH groups are optionally replaced by N and in which one or more H atoms are optionally replaced by Br, Cl, F, CN, methyl, methoxy or a mono- or polyfluorinated methyl or methoxy group,
• Z1 denotes a single bond, —CH2O—, —(CO)O—, —CF2O—,
• —CH2CH2CF2O—, —CF2CF2—, —CH2CF2—, —CH2CH2—, —(CH2)4—,
• —CH═CH—, —CH═CF—, —CF═CF— or where an asymmetrical Z1 group may be oriented to either direction in formula I,
• L1 and L2, independently of one another, denote H or F,
• X1 denotes F, Cl, CN, SF5, a halogenated alkyl radical, halogenated alkoxy radical, halogenated alkenyl radical or halogenated alkenyloxy radical, each having up to 7 C atoms, and
• a denotes 0, 1 or 2.