Liquid-crystal medium

1. A liquid-crystal medium having a negative dielectric anisotropy and comprising

one or more compounds of formula I in a total amount of 0.25% by weight to 3% by weight

in which

R 1 denotes a straight-chain alkenyl radical having 2 to 15 C atoms or a branched alkenyl radical having 4 to 15 C atoms, where one or more CH 2 groups may each be replaced, independently of one another, by

 —C≡C—, —CF 2 O—, —OCF 2 —, —O—, —CO—O— or —O—CO— in such a way that 0 atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen,

R 2 denotes H, a straight-chain alkyl radical having 1 to 15 C atoms or a branched alkyl radical having 4 to 15 C atoms, where one or more CH 2 groups may each be replaced, independently of one another, by

 —C≡C—, —CF 2 O—, —OCF 2 —, —CH═CH—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen, and

Y 1 denotes H, F, Cl or CH 3 ;

and

one or more compounds of formula III

in which

R 11 and R 12 each, independently of one another, denote H, an alkyl or alkoxy radical having 1 to 15 C atoms, where one or more CH 2 groups may each be replaced, independently of one another, by

 —C≡C—, —CF 2 O—, —OCF 2 —, —CH═CH—, —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen,

A 1 on each occurrence, independently of one another, denotes

a) a 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which one or two non-adjacent CH 2 groups may be replaced by —O— or —S—,

b) a 1,4-phenylene radical, in which one or two CH groups may be replaced by N, or

c) a radical selected from the group consisting of spiro[3.3]heptane-2,6-diyl, 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl,

where the radicals in a), b) and c) may be mono- or polysubstituted by halogen atoms,

n is 0, 1 or 2,

Z 1 on each occurrence, independently of one another, denotes —CO—O—, —O—CO—, —CF 2 O—, —OCF 2 —, —CH 2 O—, —OCH 2 —, —CH 2 —, —CH 2 CH 2 —, —(CH 2 ) 4 —, —CH═CH—CH 2 O—, —C 2 F 4 —, —CH 2 CF 2 —, —CF 2 CH 2 —, —CF═CF—, —CH═CF—, —CF═CH—, —CH═CH—, —C≡C— or a single bond,

L 11 and L 12 each, independently of one another, denote F, Cl, CF 3 or CHF 2 , and

W denotes O or S;

and

one or more stabilisers.

2. The liquid-crystal medium according to claim 1 , further comprising one or more compounds selected from the group consisting of compounds of formulae IIA, IIB, IIC and IID

in which

R 2A , R 2B , R 2C

and R 2D each, independently of one another, denote H, or an alkyl radical having 1 to 15 C atoms or an alkenyl radical having 2 to 15 C atoms, which is un-substituted, monosubstituted by CN or CF 3 or at least monosubstituted by halogen, where one or more CH 2 groups may be replaced by —O—, —S—,

 —C≡C—, —CF 2 O—, —OCF 2 —, —OC—O— or —O—CO— in such a way that O atoms are not linked directly to one another,

L 1 to L 4 each, independently of one another, denote F, Cl, CF 3 or CH F 2 ,

Y denotes H, F, Cl, CF 3 , CHF 2 or CH 3 ,

Z 2 , Z 2B and Z 2D each, independently of one another, denote a single bond, —CH 2 CH 2 —, —CH═CH—, —CF 2 O—, —OCF 2 —, —CH 2 O—, —OCH 2 —, —COO—, —OCO—, —C 2 F 4 —, —CF═CF— or —CH═CHCH 2 O—,

p denotes 0, 1 or 2,

q denotes 0 or 1, and

v denotes 1, 2, 3, 4, 5 or 6.

3. The medium according to claim 1 , wherein the one or more stabilisers are selected from the group consisting of

in which

R ST denotes H, an alkyl or alkoxy radical having 1 to 15 C atoms, wherein one or more CH 2 groups may each be replaced, independently of one another, by —C≡C—, —CF 2 O—, —OCF 2 —, —CH═CH—,

 —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen,

 denotes

Z ST each, independently of one another, denote —CO—O—, —O—CO—, —CF 2 O—, —OCF 2 —, —CH 2 O—, —OCH 2 —, —CH 2 —, —CH 2 CH 2 —, —(CH 2 ) 4 —, —CH═CH—CH 2 O—, —C 2 F 4 —, —CH 2 CF 2 —, —CF 2 CH 2 —, —CF═CF—, —CH═CF—, —CF═CH—, —CH═CH—, —C≡C— or a single bond,

L 1 and L 2 each, independently of one another, denote F, Cl, CF 3 or CHF 2 ,

p denotes 1 or 2, and

q denotes 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

4. The medium according to claim 1 , further comprising one or more compounds of formula IV

in which

R 41 denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to 7 C atoms, and

R 42 denotes alkyl having 1 to 7 C atoms or alkoxy having 1 to 6 C atoms or alkenyl having 2 to 7 C atoms.

5. The medium according to claim 1 , further comprising one or more compounds selected from the group consisting of compounds of the following formulae

6. The medium according to claim 1 , further comprising one or more compounds of formulae IVb-1 to IVb-3

in which

alkyl and alkyl* each, independently of one another, denote alkyl having 1 to 6 C atoms, and

alkenyl and alkenyl* each, independently of one another, denote alkenyl having 2 to 6 C atoms.

7. The medium according to claim 1 , further comprising one or more compounds of formula V

in which

R 51 and R 52 each, independently of one another, denote alkyl having 1 to 7 C atoms, alkoxy having 1 to 7 C atoms or alkoxyalkyl, alkenyl or alkenyloxy having 2 to 7 C atoms,

 and

 identically or differently, denote

Z 51 and Z 52 each, independently of one another, denote —CH 2 —CH 2 —, —CH 2 —O—, —CH═CH—, —C≡C—, —COO— or a single bond, and

n is 1 or 2.

8. The medium according to claim 1 , further comprising a chiral dopant.

9. The medium according to claim 1 , further comprising one or more polymerisable compounds of formula P

P-Sp-A 1 -(Z 1 -A 2 ) z -R  P

in which

P denotes a polymerisable group,

Sp denotes a spacer group or a single bond,

A 1 and A 2 identically or differently, denote an aromatic, heteroaromatic, alicyclic or heterocyclic group, which may contain fused rings, and which is unsubstituted, or mono- or polysubstituted by L,

L denotes F, Cl, —CN, P-Sp- or a straight-chain alkyl having 1 to 25 C atoms or a branched alkyl having 4 to 25 C atoms or a cyclic alkyl having 3 to 25 C atoms, wherein one or more non-adjacent CH 2 groups are optionally replaced by —O—, —S—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a manner that O and/or S atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by P-Sp-, F or Cl,

Z 1 denotes —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —OCH 2 —, —CH 2 O—, —SCH 2 —, —CH 2 S—, —CF 2 O—, —OCF 2 —, —CF 2 S—, —SCF 2 —, —(CH 2 ) n1 —, —CF 2 CH 2 —, —CH 2 CF 2 —, —(CF 2 ) n1 —, —CH═CH—, —CF═CF—, —CH═CF—, —CF═CH—, —C≡C—, —CH═CH—CO—O—, —O—CO-CH═CH—, —CH 2 —CH 2 —CO—O—, —O—CO—CH 2 —CH 2 —, —CR 0 R 00 — or a single bond,

R 0 and R 00 identically or differently, denote H or alkyl having 1 to 12 C atoms,

R denotes H, L, or P-Sp-,

z is 0, 1, 2 or 3, and

n1 is 1, 2, 3 or 4.

10. The medium according to claim 9 , wherein the one or more polymerisable compounds of formula P are polymerised.

11. A liquid-crystal display, comprising the medium according to claim 1 .

12. The display according to claim 11 , which is a PSA display.

13. The display according to claim 12 , which is a PS-VA, PS-IPS, PS-FFS, PS-UB-FFS, polymer stabilised SA-VA or polymer stabilised SA-FFS display.

14. The display according to claim 11 , wherein the display is a VA, IPS, U-IPS, FFS, UB-FFS, SA-FFS or SA-VA display.

15. An electro-optical display, comprising the medium according to claim 1 .

16. The medium according to claim 1 , exhibiting a dielectric anisotropy Δε of −6 to −2.

17. The medium according to claim 1 , exhibiting an optical anisotropy Δn of 0.08 to 0.13.

18. The medium according to claim 1 , wherein the compound of formula I is a compound of one of formulae I-1 and I-2

in which R 1 and R 2 have the meanings given for formula I.

19. The medium according to claim 1 , wherein the compound of formula I is a compound of one of formulae I-a to I-f

in which R 2 has the meaning given for formula I.

20. The medium according to claim 1 , wherein the compound of formula I is a compound of one of formulae I-a-1 or I-a-2

21. A liquid-crystal medium having a negative dielectric anisotropy and comprising one or more compounds of formulae I-3 to I-10

in which

R 1 denotes a straight-chain alkenyl radical having 2 to 15 C atoms or a branched alkenyl radical having 4 to 15 C atoms, where one or more CH 2 groups may each be replaced, independently of one another, by

 —C≡C—, —CF 2 O—, —OCF 2 —, —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen.

22. A liquid-crystal medium having a negative dielectric anisotropy and comprising

one or more compounds of formula I-3 to I-10

in which

R 1 denotes a straight-chain alkenyl radical having 2 to 15 C atoms or a branched alkenyl radical having 4 to 15 C atoms, where one or more CH 2 groups may each be replaced, independently of one another, by

 —C≡C—, —CF 2 O—, —OCF 2 —, —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen;

and

one or more compounds of formula III

in which

R 11 and R 12 each, independently of one another, denote H, an alkyl or alkoxy radical having 1 to 15 C atoms, where one or more CH 2 groups may each be replaced, independently of one another, by

 —C≡C—, —CF 2 O—, —OCF 2 —, —CH═CH—, —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen,

A 1 on each occurrence, independently of one another, denotes

a) a 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which one or two non-adjacent CH 2 groups may be replaced by —O— or —S—,

b) a 1,4-phenylene radical, in which one or two CH groups may be replaced by N, or

c) a radical selected from the group consisting of spiro[3.3]heptane-2,6-diyl, 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl,

where the radicals in a), b) and c) may be mono- or polysubstituted by halogen atoms,

n is 0, 1 or 2,

Z 1 on each occurrence, independently of one another, denotes —CO—O—, —O—CO—, —CF 2 O—, —OCF 2 —, —CH 2 O—, —OCH 2 —, —CH 2 —, —CH 2 CH 2 —, —(CH 2 ) 4 —, —CH═CH—CH 2 O—, —C 2 F 4 —, —CH 2 CF 2 —, —CF 2 CH 2 —, —CF═CF—, —CH═CF—, —CF═CH—, —CH═CH—, —C≡C— or a single bond,

L 11 and L 12 each, independently of one another, denote F, Cl, CF 3 or CHF 2 , and

W denotes O or S;

and

one or more stabilisers.

23. The liquid-crystal medium according to claim 1 , wherein the one or more compounds of formula I are present in the liquid-crystal medium in a total amount of 0.25% by weight to 2% by weight.

24. The liquid-crystal medium according to claim 1 , wherein the one or more compounds of formula I are present in the liquid-crystal medium in a total amount of 0.25% by weight to 1% by weight.