Alkinyl-derivatives and their use in liquid crystalline mixtures

A liquid crystalline mixture having at least two components, wherein at least one component is compound of the formula ##STR7## wherein rings A and C each individually are trans-1,4-cyclohexylene, 1,4-phenylene, trans-1,3-dioxane-2,5-diyl, pyridine-2,5-diyl or pyrimidine-2,5-diyl, provided that not more than one of rings A and C is pyridine-2,5-diyl or pyrimidine-2,5-diyl, with the proviso that the position of the nitrogen atom in the pyridine-2,5-diyl ring and pyrimidine-2,5-diyl, respectively, is directed only in the direction of the triple bond --C.tbd.C--,

• ring B is 2,3-difluoro-substituted 1,4-phenylene,
• Z.sup.1 or Z.sup.2 is a single covalent bond and Z.sup.2 or Z.sup.1, respectively, is a single covalent bond, ethylene, oxymethylene or methyleneoxy, m and n are each a number 0 to 2, and the sum m+n is 1 or 2,
• R.sup.1 is C.sub.1-10 -alkyl, C.sub.2-9 -alkoxyalkyl or C.sub.1-9 -alkoxy and
• R.sup.2 is C.sub.1-10 -alkyl,
• with the proviso that two 1,4-phenylene rings are linked with each other only by a single covalent bond.