Liquid crystal medium

1. A liquid crystal medium comprising

1-30% by weight of one or more compounds of formula IA,

1-10% by weight of one or more compounds of formula IB,

0-9% by weight of one or more compounds of formula IC,

wherein

R 1 and R 2 are each, independently of one another, an alkyl radical having 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CF 3 or at least monosubstituted by halogen, wherein one or more CH 2 groups are optionally, in each case independently of one another, replaced by —O—, —S—,

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

Y 1 is H or F,

X is F, Cl or a halogenated alkyl, alkenyl, alkoxy or alkenyloxy radical having up to 6 carbon atoms, and

r is 1 or 2,

and wherein the medium has a birefringence at 20° C. that is lower than 0.08, and wherein the medium does not contain a compound comprising a cyano group.

2. A medium according to claim 1 , comprising one or more compounds of the following formulae

wherein R 1 is an alkyl radical having 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CF 3 or at least monosubstituted by halogen, wherein one or more CH 2 groups are optionally, in each case independently of one another, replaced by —O—, —S—,

 —CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another.

3. A medium according to claim 1 , further comprising one or more compounds selected from compounds of formulae II, III, IV, V, VI and VII

wherein

R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms,

X 0 is F, Cl, halogenated alkyl, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy having 1 to 6 carbon atoms,

Z 0 is —C 2 H 4 —, —(CH 2 ) 4 —, —CH═CH—, —CF═CF—, —C 2 F 4 —, —CH 2 CF 2 —, —CF 2 CH 2 —, —CH 2 O—, —OCH 2 —, —COO—, —OCF 2 — or —CF 2 O—,

Y 1 to Y 4 are each, independently of one another, H or F, and

r is 0 or 1,

with the proviso that if Z 0 in formula VII is —CF 2 O—, then at least one of Y 1 to Y 4 in formula VII is H.

4. A medium according to claim 1 , further comprising one or more compounds of the following formulae

wherein R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms.

5. A medium according to claim 1 , further comprising one or more compounds of the following formulae

wherein R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms.

6. A medium according to claim 1 , further comprising one or more compounds of the following formulae

wherein

X 0 is F, Cl, halogenated alkyl, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy having 1 to 6 carbon atoms, and

R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms.

7. A medium according to claim 1 , further comprising one or more compounds of the following formula

R 1 and R 2 are each, independently of one another, an alkyl radical having 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CF 3 or at least mono substituted by halogen, wherein one or more CH 2 groups are optionally, in each case independently of one another, replaced by —O—, —S—,

 —CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another.

8. A medium according to claim 1 , comprising one or more compounds of formulae IA, IB, IC,

of IIa,

wherein R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms,

of VIa,

wherein R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms,

and of VIII,

R 1 and R 2 are each, independently of one another, an alkyl radical having 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CF 3 or at least mono substituted by halogen, wherein one or more CH 2 groups are optionally, in each case independently of one another, replaced by —O—, —S—,

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

and optionally one or more compounds of formula IVa,

wherein

X 0 is F, Cl, halogenated alkyl, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy having 1 to 6 carbon atoms, and

R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms,

of VIb,

wherein R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms,

and of XIX,

R 1 and R 2 are each, independently of one another, an alkyl radical having 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CF 3 or at least monosubstituted by halogen, wherein one or more CH 2 groups are optionally, in each case independently of one another, replaced by —O—, —S—,

 —CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another.

9. A medium according to claim 3 , comprising

1-30% by weight of compounds of formula IA,

1-10% by weight of compounds of formula IB,

1-9% by weight of compounds of formula IC,

10-50% by weight of compounds of formula II,

10-50% by weight of compounds of formula VI.

10. A medium according to claim 6 , wherein X 0 is F or OCF 3 .

11. A medium according to claim 1 , wherein R 1 and R 2 in formulae IA, IB and/or IC are straight-chain alkyl or alkoxy with 1 to 12 C-atoms.

12. A medium according to claim 1 , wherein the medium has a birefringence at 20° C. that is lower than 0.075.

13. A medium according to claim 1 , wherein the medium has a birefringence at 20° C. that is from 0.06 to 0.074.

14. A medium according to claim 1 , wherein the medium has a birefringence at 20° C. that is from 0.07 to 0.073.

15. An electro-optical liquid crystal display containing a liquid crystal medium according to claim 1 .

16. A process of preparing a medium according to claim 1 , comprising mixing one or more compounds of formula IA and IB and optionally IC.

17. A liquid crystal medium consisting essentially of

1-30% by weight of one or more compounds of formula IA,

1-10% by weight of one or more compounds of formula IB,

0-9% by weight of one or more compounds of formula IC,

wherein

R 1 and R 2 are each, independently of one another, an alkyl radical having 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CN or CF 3 or at least monosubstituted by halogen, wherein one or more CH 2 groups are optionally, in each case independently of one another, replaced by —O—, —S—,

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

Y 1 is H or F,

X is F, Cl or a halogenated alkyl, alkenyl, alkoxy or alkenyloxy radical having up to 6 carbon atoms, and

r is 1 or 2,

and wherein the medium has a birefringence at 20° C. that is lower than 0.08,

and

compounds selected from the group consisting of compounds of formulae II to XXIX

wherein in compounds of formulae II to VII

R 0 is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms,

X 0 is F, Cl, halogenated alkyl, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy having from 1 to 6 carbon atoms,

Z 0 is —C 2 H 4 —, —(CH 2 ) 4 —, —CH═CH—, —CF═CF—, —C 2 F 4 —, —CH 2 CF 2 —, —CF 2 CH 2 —, —CH 2 O—, —OCH 2 —, —COO—, —OCF 2 — or —CF 2 O—,

Y 1 to Y 4 are, each independently of one another, H or F, with the proviso that if Z 0 in formula VII is —CF 2 O—, then at least one of Y 1 to Y 4 in formula VII is H, and

r is 0 or 1;

wherein in compounds of formulae VIII

R 1 and R 2 are as defined in formula IB;

wherein in compounds of formulae IX to XVI

R 0 ,X 0 and Y 1-4 are each, independently of one another, as defined in formulae II-VII;

wherein in compounds of formulae XVII

R 1 and R 2 are as defined in formula IB, and

Y 1 is as defined in formula II;

wherein in compounds of formulae XVIII and XIX

R 1 and R 2 are as defined in formula IB;

wherein in compounds of formulae XX

A is 1,4-phenylene or trans-1,4-cyclohexylene,

a is 0 or 1,

R 3 is an alkenyl group having from 2 to 9 carbon atoms, and

R 4 is as defined for R 1 in formula IA;

wherein in compounds of formulae XXI

R 3 is an alkenyl group with 2 to 7 carbon atoms,

Q is CF 2 , OCF 2 , CFH, OCFH or a single bond,

Y is F or Cl, and

L 1 and L 2 are independently of each other H or F;

wherein in compounds of formulae XXII to XXV

R 0 , X 0 and Y 1-4 are each, independently of one another, as defined in formulae II-VII, and the 1,4-phenylene rings may be substituted by CN, chlorine or fluorine;

wherein in compounds of formulae XXVI to XXIX

R 0 is as defined in formulae II-VII,

d is 0, 1 or 2, and

‘alkyl’ and ‘alkyl*’ are each, independently of one another, a straight-chain or branched alkyl radical having 1-9 carbon atoms.

18. A medium according to claim 17 , wherein the medium has a birefringence at 20° C. that is lower than 0.075.

19. A medium according to claim 17 , wherein the medium has a birefringence at 20° C. that is from 0.06 to 0.074.

20. An electro-optical liquid crystal display containing a liquid crystal medium according to claim 17 .