Electrooptical liquid crystal system

An electrooptical liquid crystal system

• which contains a dielectrically positive liquid crystal mixture and a further optically transparent medium between 2 electrodes which are optionally applied to substrate sheets;
• whose liquid crystal molecules in the switched-off state have an irregular orientation,
• in which one of the refractive indices of the liquid crystal mixture essentially agrees with the refractive index of the matrix n.sub.M and/or in which the quotient of the mass of the mass of the liquid crystal mixture and of the mass of the optically transparent medium is 1.5 or more,
• which, independently of the polarization of the incident light, has an electrically switchable transmission
• wherein the liquid crystal mixture contains one or more compounds of the formula I ##STR82## in which Q.sup.1 is ##STR83## are independently of one another trans-1,4-cyclohexylene, 1,4-phenylene,2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene and one of A.sup.1 and, if present, A.sup.2 is also pyridine-2,5-diyl, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl, tetrahydropyran-2,5-diyl or naphthalene-2,6-diyl,
• Z.sup.1 and Z.sup.2 are independently of one another a single bond, --CH.sub.2 CH.sub.2 --, --COO--, --OCO--, --CH.sub.2 O--,
• Y and X are independently of one another H or F, and one of X and Y is also Cl,
• W is --Cl, --CF.sub.3, --OCF.sub.3, or --OCHF.sub.2,
• R.sup.1 alkyl having 1-12 C atoms, in which one or 2 non-adjacent CH.sub.2 groups can also be replaced by --O-- or --CH.dbd.CH--, and
• m is 0, 1 or 2
• with the provisos that (i) the mixture contains less than 15% of terminally cyano-substituted compounds, and (ii) contains at least 50% of compounds of formula I.

An electrooptical liquid crystal system

• which contains a dielectrically positive liquid crystal mixture and a further optically transparent medium between 2 electrodes which are optionally applied to substrate sheets;
• whose liquid crystal molecules in the switched-off state have an irregular orientation,
• in which one of the refractive indices of the liquid crystal mixture essentially agrees with the refractive index of the matrix n.sub.M and/or in which the quotient of the mass of the mass of the liquid crystal mixture and of the mass of the optically transparent medium is 1.5 or more,
• which, independently of the polarization of the incident light, has an electrically switchable transmission
• wherein the liquid crystal mixture contains one or more compounds of the formula I ##STR91## in which Q.sup.1 is ##STR92## are 3-fluoro-1,4-phenylene,
• Z.sup.1 and Z.sup.2 are --COO-- or --OCO--,
• Y and X are independently of one another H or F, and one of X and Y is also Cl,
• W is --OCF.sub.3 or --OCHF.sub.2,
• R.sup.1 is alkyl having 1-12 C atoms, in which one or 2 non-adjacent CH.sub.2 groups can also be replaced by --O-- or --CH.dbd.CH--, and
• m is 0, 1 or 2
• with the proviso that
• the mass ratio of compounds of formula I with respect to the mass of the liquid crystal mixture is at least 50%, and that the mixture contains less than 15% of terminally cyano-substituted components.