Heterocyclic compound, crystalline medium method of its stabilization and Fküssigkristallanzeige

The invention relates to liquid crystal (LC) display containing an LC cell consisting of two substrates, at least one substrate is transparent to light and at least one substrate having a planar orientation layer as well as control electrodes, and a layer of an LC medium disposed between the substrates with negative dielectric anisotropy, characterized in that the LC display, a compound of formula includes, as well as optionally a) one or more compounds of the formula II and / or b) one or more compounds selected from the group of compounds of formulas III and IV includes wherein the parameters have the respective meanings given in claim 1, as well as the use of compounds of formula I for the stabilization of a liquid-crystalline medium containing one or more compounds of the formulas II and / or III and / or IV.