Esters

A liquid crystalline mixture comprising at least two components wherein at least one of the components is a compound of the formula ##STR28## wherein X.sup.2 is a single covalent bond or --COO--;

• X.sup.1 is a single covalent bond, --COO--, or --CH.sub.2 CH.sub.2 --;
• ring A is a benzene ring or trans-1,4-cyclohexylene;
• ring B is a benzene ring or when X.sup.2 is --COO--, ring B also can be trans-1,4-cyclohexylene;
• Z.sup.1, Z.sup.2 and Z.sup.3 individually are hydrogen or when positioned on a benzene ring which is not linked directly with a further ring via a single covalent bond, Z.sup.1, Z.sup.2 and Z.sup.3 also can be halogen, cyano or methyl;
• Y.sup.2 is cyano, nitro, 2,2-dicyanovinyl or when Y.sup.1 is hydrogen Y.sup.2 also can be 2,2-dicyano-1-methylvinyl;
• Y.sup.1 is halogen, cyano, C.sub.1 -C.sub.3 -alkyl or when X.sup.1 is --COO-- or Y.sup.2 is nitro or at least one of Z.sup.1 and Z.sup.2 is other than hydrogen, Y.sup.1 also can be hydrogen;
• and R.sup.1 is C.sub.1 -C.sub.12 -alkyl or when positioned on a benzene ring R.sup.1 also can be C.sub.1 -C.sub.12 -alkoxy.

An electro-optical cell comprising:

• (a) two plate means;
• (b) liquid crystal means disposed between the two plate means and including a compound of the formula ##STR29## wherein X.sup.2 is a single covalent bond or --COO--;
• X.sup.1 is a single covalent bond, --COO--, or --CH.sub.2 CH.sub.2 --;
• ring A is a benzene ring or trans-1,4-cyclohexylene;
• ring B is a benzene ring or when X.sup.2 is --COO--, ring B also can be trans-1,4-cyclohexylene;
• Z.sup.1, Z.sup.2 and Z.sup.3 individually are hydrogen or when positioned on a benzene ring which is not linked directly with a further ring via a single covalent bond, Z.sup.1, Z.sup.2 and Z.sup.3 also can be halogen, cyano or methyl;
• Y.sup.2 is cyano, nitro, 2,2-dicyanovinyl or when Y.sup.1 is hydrogen Y.sup.2 also can be 2,2-dicyano-1-methylvinyl;
• Y.sup.1 is halogen, cyano, C.sub.1 -C.sub.3 -alkyl or when X.sup.1 is --COO-- or Y.sup.2 is nitro or at least one of Z.sup.1 and Z.sup.2 is other than hydrogen, Y.sup.1 also can be hydrogen;
• and R.sup.1 is C.sub.1 -C.sub.12 -alkyl or when R.sup.1 is positioned on a benzene ring R.sup.1 also can be C.sub.1 -C.sub.12 -alkoxy;
• and
• (c) means for applying an electrical potential to said plate means.