Liquid-crystal medium

1. A liquid crystal display comprising:

two substrates, at least one which is transparent to light;

an electrode provided on each substrate or two electrodes provided on only one of the substrates; and

located between the substrates a layer of a liquid-crystal medium;

the liquid-crystal medium comprising:

a liquid-crystalline host containing a liquid crystal component, and

an optically active component,

wherein the liquid crystal component comprises one or more compounds of formula CPY-n-Om, one or more compounds of formula PY-n-Om and one or more compounds of formula PYP-n-m in a total concentration in the range of from 45 to 70%:

wherein m and n are each, independently of each other, an integer from 1 to 12,

wherein the liquid crystal medium has negative dielectric anisotropy and the molecules in the layer of the liquid crystal medium in the switched-off state are aligned perpendicular to the electrode surfaces or have a tilted homeotropic alignment, the liquid-crystalline host has a chiral pitch, p, in the range of from 8 to 30 μm, the liquid crystal component has a birefringence Δn in the range of from 0.110 to 0.150;

wherein the display has a cell gap and the thickness, d, of the cell gap is in the range of from 3 μm to 5 μm; and

wherein the ratio d/p between the thickness of the cell gap d and the chiral pitch p is 0.1 to 1.

2. The liquid crystal display according to claim 1 , wherein the optically active component comprises one or more compounds selected from the formulae

in which

R a11 , R a12 and R b12 , independently of one another, denote alkyl having 1 to 15 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may each be replaced, independently of one another, by —C(R z )═C(R z )—, —C≡C—, —O—, —S—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by F, Cl, Br, I or CN, with the proviso that R a12 is different from R b12 ,

R a21 and R a22 , independently of one another, denote alkyl having 1 to 15 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may each be replaced, independently of one another, by —C(R z )═C(R z )—, —C≡C—, —O—, —S—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by F, Cl, Br, I or CN,

R a31 , R a31 and R b32 , independently of one another, denote straight-chain alkyl having 1 to 15 C atoms or branched alkyl having 3 to 15 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may each be replaced, independently of one another, by —C(R z )═C(R z )—, —C≡C—, —O—, —S—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by F, Cl, Br, I or CN, with the proviso that R a32 is different from R b32 ,

R z denotes H, CH 3 , F, Cl, or CN,

R 8 denotes alkyl having 1 to 15 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may each be replaced, independently of one another, by —C(R z )═C(R z )—, —C≡C—, —O—, —S—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by F, Cl, Br, I or CN,

Z 8 denotes —C(O)O—, —CH 2 O—, —CF 2 O— or a single bond,

A 11 is defined as A 12 below, or alternatively denotes

A 12 denotes

L 11 denotes F, Cl, —CN, P-Sp-, or straight chain alkyl having 1 to 25 C atoms, branched alkyl having 3 to 25 C atoms, or cyclic alkyl having 3 to 25 C atoms, wherein in said alkyl groups one or more non-adjacent CH 2 — groups are each 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,

A 21 denotes

A 22 has one of the meanings given for A 12

A 31 has one of the meanings given for A 11 ,

alternatively denotes

A 32 has one of the meanings given for A 12 ,

n2 on each occurrence, identically or differently, is 0, 1 or 2, and

n3 is 1, 2 or 3.

3. The liquid crystal display according to claim 1 , wherein the liquid-crystalline host further comprises one or more compounds of the formulae

in which

R 11 and R 12 each, independently of one another, denote alkyl having 1 to 12 C atoms, where one or two non-adjacent CH 2 groups may each be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another,

L denotes F,

b denotes 0 or 1, and

r denotes 1, 2 or 3.

4. The liquid crystal display according to claim 1 , wherein the liquid-crystalline host additionally comprises one or more compounds of the following formulae:

in which

alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and

alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 C atoms.

5. The liquid crystal display according to claim 1 , wherein the liquid-crystalline host additionally comprises one or more compounds of the following formula:

in which

R 5 and R 6 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH 2 groups may each be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another,

each, independently of one another, denote

in which L 5 denotes F or Cl, and L 6 denotes F, Cl, OCF 3 , CF 3 , CH 3 , CH 2 F or CHF 2 .

6. The liquid crystal display according to claim 1 , wherein the liquid-crystalline host further comprises one or more compounds of the following formula:

in which the individual radicals have the following meanings:

R 3 and R 4 each, independently of one another, denote alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adjacent CH 2 groups may each be replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O— in such a way that O atoms are not linked directly to one another, and

Z y denotes —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 a single bond.

7. The liquid crystal display according to claim 1 , wherein the liquid crystal medium additionally comprises one or more self-alignment additives of formula SA

MES-R A   SA

in which

MES denotes a mesogenic group comprising one or more rings, and optionally one or more polymerizable groups, and

R A is a polar anchor group.

8. The liquid crystal display according to claim 7 , wherein the one or more self-alignment additives of formula SA are selected from the compounds of formula SAa

R 1 -[A 2 -Z 2 ] m -A 1 -R a   SAa

in which

A 1 , A 2 each, independently of one another, denote an aromatic, hetero-aromatic, alicyclic or heterocyclic group, which may also contain fused rings, and which may also be mono- or polysubstituted by any of groups L and -Sp-P,

L in each case, independently of one another, denotes H, F, Cl, Br, I, —CN, —NO 2 , —NCO, —NCS, —OCN, —SCN, —C(═O)N(R 0 ) 2 , —C(═O)R 0 , optionally substituted silyl, optionally substituted aryl or cycloalkyl having 3 to 20 C atoms, or straight-chain alkyl having 1 to 25 C atoms, branched alkyl having 3 to 25 C atoms, alkoxy having 1 to 25 C atoms, branched alkoxy having 3 to 25 C atoms, alkylcarbonyl having 2 to 25 C atoms, branched alkylcarbonyl having 4 to 25 atoms, alkoxycarbonyl having 2 to 25 C atoms, branched alkoxycarbonyl having 4 to 25 C atoms, alkyl-carbonyloxy having 2 to 25 C atoms, branched alkylcarbonyloxy having 4 to 25 C atoms, alkoxycarbonyloxy having 2 to 25 C atoms, or branched alkoxycarbonyloxy having 4 to 25 C atoms, in which, in addition, one or more H atoms may each be replaced by F or Cl,

P denotes a polymerizable group,

Sp denotes a spacer group or a single bond,

Z 2 in each case, independently of one another, denotes a single bond, —O—, —S—, —CO—, —CO—O—, —OCO—, —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—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH—, —(CR 0 R 00 ) n1 —, —CH(-Sp-P)—, —CH 2 CH(-Sp-P)—, —CH(-Sp-P)CH(-Sp-P)—,

n1 denotes 1, 2, 3 or 4,

m denotes 1, 2, 3, 4, 5 or 6,

R 0 in each case, independently of one another, denotes alkyl having 1 to 12 C atoms,

R 00 in each case, independently of one another, denotes H or alkyl having 1 to 12 C atoms,

R 1 independently of one another, denotes H, halogen, or straight-chain alkyl having 1 to 25 C atoms or, branched alkyl having 3 to 25 C atoms, or cyclic alkyl having 3 to 25 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may each be replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another and in which, in addition, one or more H atoms may each be replaced by F or Cl,

or a group -Sp-P, and

R a denotes a polar anchor group having at least one group selected from —OH, —NH 2 , NHR 11 , —SH, C(O)OH and —CHO, in which R 11 denotes alkyl having 1 to 12 C atoms.

9. The liquid crystal display according to claim 7 , wherein the polar anchor group R a or R A of the self-alignment additive is of the formulae

in which

p denotes 1 or 2,

q denotes 2 or 3,

 denotes a substituted or unsubstituted ring system or condensed ring system,

Y, on each occurrence, identically or differently, denotes —O—, —S—, —C(O)—, —C(O)O—, —OC(O)—, —NR 11 — or a single bond,

denotes 0 or 1,

X 1 , on each occurrence, identically or differently, denotes H, alkyl, fluoroalkyl, OH, NH 2 , NHR 11 , NR 11 2 , —SH, OR 11 , C(O)OH, —CHO, where at least one group X 1 denotes a radical selected from —OH, —NH 2 , NHR 11 , —SH, C(O)OH and —CHO,

R 11 denotes alkyl having 1 to 12 C atoms,

Sp a , Sp c , Sp d each, independently of one another, denote a spacer group or a single bond, and

Sp b denotes a tri- or tetravalent group.

10. The liquid crystal display according to claim 1 , wherein the liquid crystal medium additionally comprises a polymerizable component comprising one or more polymerizable compounds.

11. The liquid crystal display according to claim 10 , wherein the one or more polymerizable compounds are of formula R

P-Sp-A 1 -(Z 1 -A 2 ) z -R  R

in which the individual radicals, independently of each other and on each occurrence identically or differently, have the following meanings:

P a polymerizable group,

Sp a spacer group or a single bond,

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

Z 1 —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 ,R 00 H or alkyl having 1 to 12 C atoms,

R H, L, or P-Sp-,

L F, Cl, —CN, P-Sp-, or straight chain alkyl having 1 to 25 C atoms, branched alkyl having 3 to 25 C atoms, or cyclic alkyl having 3 to 25 C atoms, wherein one or more non-adjacent CH 2 -groups are each 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 0, 1, 2 or 3, and

n1 1, 2, 3 or 4.

12. The liquid crystal display according to claim 10 , where the one or more polymerizable compounds are of formulae M1 to M31:

in which

P 1 , P 2 and P 3 each, independently of one another, denote an acrylate or methacrylate group,

Sp 1 , Sp 2 and Sp 3 each, independently of one another, denote a single bond or a spacer group having one of the meanings indicated above and below for Sp, where, in addition, one or more of the radicals P 1 -Sp 1 -, P 1 -Sp 2 - and P 3 -Sp 3 - may denote R aa , with the proviso that at least one of the radicals P 1 -Sp 1 -, P 2 -Sp 2 and P 3 -Sp 3 - present is different from R aa ,

R aa denotes H, F, Cl, CN, or straight-chain alkyl having 1 to 25 C atoms or branched alkyl having 3 to 25 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may each be replaced, independently of one another, by C(R 0 )═C(R 00 )—, —C≡C—, —N(R 0 )—, —O—, —S—, —CO—, —CO—O—, —O—CO—, or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by F, Cl, CN or

R 0 , R 00 each, independently of one another and identically or differently on each occurrence, denote H or alkyl having 1 to 12 C atoms,

R y and R z each, independently of one another, denote H, F, CH 3 or CF 3 ,

X 1 , X 2 and X 3 each, independently of one another, denote —CO—O—, —O—CO— or a single bond,

Z 1 denotes —O—, —CO—, —C(R y R z )— or —CF 2 CF 2 —,

Z 2 and Z 3 each, independently of one another, denote —CO—O—, —O—CO—, —CH 2 O—, —OCH 2 —, —CF 2 O—, —OCF 2 — or —(CH 2 ) n —, where n is 2, 3 or 4,

L on each occurrence, identically or differently, denotes F, Cl, CN, or straight-chain, optionally mono- or polyfluorinated alkyl having 1 to 12 C atoms, branched alkyl having 3 to 12 C atoms, alkoxy having 1 to 12 C atoms, branched alkoxy having 3 to 12 C atoms, alkenyl having 2 to 12 C atoms, branched alkenyl having 3 to 12 C atoms, alkynyl having 2 to 12 C atoms, branched alkynyl having 4 to 12 C atoms, alkylcarbonyl having 2 to 12 C atoms, branched alkylcarbonyl having 4 to 12 C atoms, alkoxycarbonyl having 2 to 12 C atoms, branched alkoxycarbonyl having 4 to 12 C atoms alkylcarbonyloxy having 2 to 12 C atoms, branched alkylcarbonyloxy having 4 to 12 C atoms, alkoxycarbonyloxy having 2 to 12 C atoms, or branched alkoxycarbonyloxy having 4 to 12 C atoms,

L′ and L″ each, independently of one another, denote H, F or Cl,

r denotes 0, 1, 2, 3 or 4,

s denotes 0, 1, 2 or 3,

t denotes 0, 1 or 2, and

x denotes 0 or 1.

13. The liquid crystal display according to claim 10 , wherein the polymerizable compounds are polymerized.

14. The liquid crystal display of claim 1 , wherein the display is a VA display.

15. The liquid crystal display according to claim 7 , wherein the display is a SA-VA display.

16. The liquid crystal display according to claim 10 , wherein the display is a PS-VA or a polymer stabilized SA-VA display.

17. A process for the production of a liquid crystal display according to claim 13 , comprising: providing the liquid crystal medium between the substrates of the display, and polymerizing the polymerizable compounds.

18. The liquid crystal display of claim 1 , wherein the display is a VA display, a PS-VA display, an SA-VA display, or a polymer stabilized SA-VA display.