Compounds of the formula ##STR1## wherein n stands for the number 0 or 1; R.sup.1 denotes a group R.sup.3 or R.sup.3 --A.sup.3 --Z.sup.2 -- and R.sup.2 denotes a group R.sup.4 or R.sup.4 --A.sup.4 --Z.sup.3 --; ring A.sup.1 is unsubstituted or halogen-, cyano- and/or methylsubstituted 1,4-phenylene in which optionally 1 CH group or 2 CH groups is/are replaced by nitrogen; A.sup.3 A.sup.4 and ring A.sup.2 each independently represent unsubstituted or halogen-, cyano- and/or methyl- -substituted 1,4-phenylene in which optionally 1 CH group or 2 CH groups is/are replaced by nitrogen or trans-1,4-cyclohexylene, trans-1,3-dioxane-2,5-diyl, 1-cyano-trans-1,4-cyclohexylene, bicyclo[2.2.2]octane- -1,4-diyl, naphthalene-2,6-diyl, tetralin-2,6-diyl or trans-decalin-2,6- diyl; Z.sup.1, Z.sup.2 and Z.sup.3 each independently are a single covalent bond, --COO--, --OOC--, --CH.sub.2 O--, --OCH.sub.2 --, --CH.sub.2 CH.sub.2 --, --C.vertline.C--, --(CH.sub.2).sub.3 O--, --O(CH.sub.2).sub.3 --, --(CH.sub.2).sub.4 -- or the trans form of --CH.dbd.CH-- CH.sub.2 O-- or --OCH.sub.2 --CH.dbd.CH--; R.sup.3 and R.sup.4 each independently denote halogen, cyano, --NCS, --CF.sub.3, --OCF.sub.3 or alkyl in which optionally one >CH--CH C.dbd.C