Photostable liquid-crystalline medium

A liquid-crystalline medium comprising

• at least one compound of formula I
• and
• at least one compound of formula II
• in which
• L1, L2, L3 and L4 are each, independently of one another, H or F;
• R11 is H, a halogenated or unsubstituted alkyl radical having from 1 to 15 carbon atoms, where, in addition, one or more CH2 groups in these radicals may each be replaced, independently of one another, by —C≡C—, —CH═CH—, —O—, —CO—O—or —O—CO— in such a way that O atoms are not linked directly to one another;
• R21 and R22 are each, independently of one another, H, Cl, F, CN, SF5, SCN, NCS, a halogenated or unsubstituted alkyl radical having from 1 to 15 carbon atoms, where, in addition, one or more CH2 groups in these radicals may each be replaced, independently of one another, by —C≡C—, —CH═CH—, —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another;
• Y11 is F, Cl, CN, SF5, SCN, NCS, a halogenated alkyl radical, a halogenated alkenyl radical, a halogenated alkoxy radical or a halogenated alkenyloxy radical, each having up to 6 carbon atoms;
• Z11 is a single bond,
• a, is 1;
• b, c, d and e are each, independently of one another, 0, 1 or 2;
• f is 1;