Electro-optical liquid crystal system.

摘要

The invention relates to 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 nM and/or in which the quotient of the mass of the liquid crystal mixture and of the mass of the optically transparent medium is 1.5 or more and, which, independently of the polarization of the incident light, has a reduced transmission in one of the two switch states compared to the other state and whose liquid crystal mixture contains one or more compounds of the formula I <CHEM> in which Q<1> is <CHEM> <CHEM> are independently of one another trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene and one of A<1> and, if present, A<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<1> and Z<2> are independently of one another a single bond -CH2CH2-, -COO-, -OCO-, -C=C-, -CH2O- or any desired combinations of these bridge groups, Y and X are independently of one another H or F, and one of X and Y is also Cl, W is -CN, -Cl, -F, -CF3, -OCF3 or -NCS R<1> is alkyl having 1-12 C atoms, in which one or 2 non-adjacent CH2 groups can also be replaced by -O- or -HC=CH-, and m is 0, 1 or 2, with the proviso that at least one of X and Y is F and/or at least one of A<1> and A<2> is 2-fluoro-, 3-fluoro- or 3,5-difluoro-1,4-phenylene. a