Liquid-crystalline medium

1. A liquid-crystal medium, comprising

a) at least one compound of each of formulae I-1, at least one compound of formula I-2f-1, and optionally at least one compound of formula I-2, which is different from the compound of formula I-2f-1,

in which

R 1 denotes H, alkyl or alkoxy having 1 to 12 C atoms, or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 12 C atoms, in which one or more CH 2 -groups may be replaced by

 and in all of which one or more H atoms may be replaced by fluorine,

 on each occurrence, independently of one another, denotes

 has one of the meanings given for

 and alternatively denotes

L 11 and L 12 , independently of one another, denote H or F,

L 14 and L 15 independently of one another, denote H or F,

X 1 denotes F, Cl, CN, CF 3 or OCF 3 ,

in which X 1 is F, and L 11 , L 12 , L 13 and L 14 are each independently H or F,

and

b) one or more compounds of formula II-3

in which

R 21 and R 22 denotes H, alkyl or alkoxy having 1 to 12 C atoms, or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 12 C atoms, in which one or more CH 2 -groups may be replaced by

 and in which one or more H atoms may be replaced by fluorine,

L 21 to L 23 independently of one another denote H or F, and

c) one or more compounds of formula D

in which

one of

 denotes

 and

the other of

 denotes

R D denotes H, alkyl or alkoxy having 1 to 12 C atoms, or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 12 C atoms, in which one or more CH 2 -groups may be replaced by

 and in which one or more H atoms may be replaced by fluorine,

X D denotes F, CF 3 or OCF 3 , and

Y D denotes H or F.

2. The liquid-crystal medium according to claim 1 , wherein the medium comprises one or more compounds of formula V

in which

 denotes

R 5 is alkyl having 1 to 20 C atoms, which is straight chain or branched, is non-substituted, mono- or poly-substituted by F, Cl or CN, and in which one or more CH 2 groups are optionally replaced, in each case independently from one another, by —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O—,

—S—CO—, —CO—S—, —CH═CH— or —C≡C— in such a manner that O and/or S atoms are not linked directly to one another,

X 5 is halogen, CF 3 or OCF 3 , and

i is 0 or 1.

3. The liquid-crystal medium according to claim 1 , wherein the medium comprises one or more compounds of formulae II-1 or II-2

in which the occurring groups have the meanings given in claim 1 .

4. The liquid-crystal medium according to claim 1 , wherein the medium comprises one or more compounds of formula III

in which

R 31 , R 32 is alkyl having 1 to 20 C atoms, which is straight chain or branched, is non-substituted, mono- or poly-substituted by F, Cl or CN, and in which one or more CH 2 groups are optionally replaced, in each case independently from one another, by —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O—,

—S—CO—, —CO—S—, —CH═CH— or —C≡C— in such a manner that O and/or S atoms are not linked directly to one another,

 to

 are independently of each other

Z 31 and Z 32 on each occurrence, identically or differently, denote —CH 2 CH 2 —, —CF 2 CF 2 —, —CF 2 CH 2 —, —COO—, trans- —CH═CH—, trans- —CF═CF—, —CH 2 O—, —CF 2 O—, —C≡C— or a single bond

p is 0, 1 or 2.

5. The liquid-crystal medium according to claim 4 , wherein the medium comprises a compound of formula III-3

in which the occurring groups have the meanings given for formula III in claim 4 .

6. The liquid-crystal medium according to claim 1 , wherein the medium has a clearing temperature of 90° C. or more.

7. The liquid-crystal medium according to claim 1 , wherein the medium has a dielectric anisotropy in the range of from 2 to 20, measured at 1 kHz and 20° C.

8. A process for the preparation of a liquid-crystal medium according claim 1 , wherein one or more compounds of formula I-1, one or more compounds of formula I-2f-1, and optionally one or more compounds of formula I-2 different from formula I-2f-1, one or more compounds of formula II-3, and one or more compounds of formula D are mixed with one or more further compounds and/or with one or more additives.

9. A 3D lens, containing a liquid-crystal medium according to claim 1 .

10. A liquid crystal display comprising one or more 3D lenses according to claim 9 .

11. A process for operating a 3D liquid crystal display by addressing one or more 3D lenses according to claim 9 .