WO2019179962A1

WO2019179962A1 - Liquid-crystalline medium

Info

Publication number: WO2019179962A1
Application number: PCT/EP2019/056741
Authority: WO
Inventors: Martin Engel; Simon SIEMIANOWSKI; Sven Christian Laut
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2018-03-22
Filing date: 2019-03-19
Publication date: 2019-09-26
Anticipated expiration: 2020-09-22
Also published as: TWI802666B; TW201940674A

Abstract

The present invention relates to liquid-crystal media comprising one or more compounds of formulae (Y-1, Y-2, Y-3, Y-4) in which the occurring groups and parameters have the meanings defined in claim 1, and a bimesogen as defined in claim 1,to the use of these liquid-crystal media in liquid-crystal displays, and to these liquid-crystal displays, particularly liquid-crystal displays which use the fringe field switching (FFS) effect with dielectrically negative liquid crystals.

Description

Liquid-crystalline medium

The present invention relates to liquid-crystal media, to the use of these liquid-crystal media in liquid-crystal displays, and to these liquid-crystal dis- plays, particularly liquid-crystal displays which use the fringe field switching (FFS) effect with dielectrically negative liquid crystals.

In conventional liquid-crystal displays for example of the TN (twisted nematic) type the electric fields for re-alignment are generated essentially perpendicular to the liquid-crystal layer.

International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electric signals are generated in such a way that the electric fields have a significant component parallel to the liquid-crystal layer (IPS, in-plane switching). The principles of operating such a display are described, for example, by R.A. Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468 (1974).

IPS displays contain an LC layer between two substrates with planar orientation, where the two electrodes are arranged on only one of the two substrates and preferably have interdig itated, comb-shaped structures. On application of a voltage to the electrodes an electric field with a significant component parallel to the LC layer is generated between them. This causes realignment of the LC molecules in the layer plane.

EP 0 588 568, for example, discloses various possibilities for the design of the electrodes and for addressing an IPS display. DE 198 24 137 likewise describes various embodiments of such IPS displays.

Liquid-crystalline materials for IPS displays of this type are described, for example, in DE 195 28 104.

Furthermore, so-called FFS (“fringe-field switching”) displays have been reported (see, inter alia, S.H. Jung et al., Jpn. J. Appl. Phys., Volume 43, No. 3, 2004, 1028), which contain two electrodes on the same substrate, one of which is structured in a comb-shaped manner and the other is unstructured. A strong, so-called "fringe field" is thereby generated, i.e. a strong electric field close to the edge of the electrodes, and, throughout the cell, an electric field which has both a strong vertical component and also a strong horizontal component. FFS displays have a low viewing-angle dependence of the contrast. FFS displays usually contain an LC medium with positive dielectric anisotropy, and an alignment layer, usually of polyimide, which provides planar alignment to the molecules of the LC medium. Furthermore, FFS displays have been disclosed (see S.H. Lee et al., Appl. Phys. Lett. 73(20), 1998, 2882-2883 and S.H. Lee et al., Liquid Crystals 39(9), 2012, 1141-1148), which have similar electrode design and layer thickness as said FFS displays, but comprise a layer of an LC medium with negative dielectric anisotropy instead of an LC medium with positive dielectric anisotropy. The LC medium with negative dielectric anisotropy shows a more favourable director orientation that has less tilt and more twist orientation compared to the LC medium with positive dielectric anisotropy, as a result of which these displays have a higher transmission. FFS displays can be operated as active-matrix or passive-matrix displays. In the case of active-matrix displays, individual pixels are usually addressed by integrated, non-linear active elements, such as, for example, transistors (for example thin-film transistors ("TFTs")), while in the case of passive-matrix displays, individual pixels are usually addressed by the multiplex method, as known from the prior art.

Typical applications of in-plane switching (IPS) and fringe field switching (FFS) technologies are monitors, notebooks, televisions, mobile tele- phones, tablet PCs, etc.

Both the IPS and the FFS technology have certain advantages over other LCD technologies, such as, for example, the vertical alignment (VA) technology, e.g. a broad viewing angle dependency of the contrast. A further improvement has been achieved by the so-called UB-FFS mode, discussed e.g. in Engel, Martin et al., (2015) 43.1 : Invited Paper. UB-FFS: New Materials for Advanced Mobile Applications, SID Symposium Digest of Technical Papers, 46, doi: 10.1002/sdtp.10235. One of the unique features of UB-FFS in contrast to the traditional FFS technology is that it enables higher transmittance, which allows operation of the panel with less energy consumption.

Also UB-FFS is known for having a lower flicker compared to FFS. Low flicker enables further energy saving by decreasing the panel driving frequency. Hence any further improvement of reducing flicker is a key requirement for UB-FFS mixtures. As a root cause the flexo electric effect is considered to generate flicker. So far it is extremely difficult to identify LC materials that reduce flicker.

The flicker phenomenon is well-known for occurring at low frequencies for every panel technology if the voltage decreases over time, leading to a decrease of transmittance and a sudden increase in transmittance by refreshing the voltage. In contrast to this, in the case of UB-FFS flicker is understood as the variation of transmittance depending on the polarity of the applied voltage.

The provision of further liquid-crystalline media and the use thereof in a display having high transmission, a good black state and a high contrast ratio is a central challenge for modern IPS and FFS applications. In addition, modern applications also require good low-temperature stability and fast addressing times.

It is an object of the present invention to provide liquid-crystal media which show at least some of the advantageous properties mentioned above and additionally enable IPS or FFS displays with reduced flicker.

This object is achieved in accordance with the invention by the liquid- crystal medium set forth below.

The invention relates to a liquid-crystal medium comprising one or more compounds selected from the group of compounds of the formulae Y-1 to

in which

R^Y1 and R^Y2 each, independently of one another, denote FI, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, where, in addition, one or more CFI2 groups in these radicals may be replaced by -0-, -S-,

-O-CO- in such a way that O atoms are not linked directly to one another, and m, n and o each, independently of one another, are 0 or 1 and one or more bimesogenic compounds selected from the group of

compounds of the formulae I, II, III, IV, V, VI and VII: R¹¹_A¹¹(-Z¹¹-A¹²-)_P -X¹¹-Sp¹¹-Xⁱ² -(A¹³-Z¹²-)_q A¹⁴-R¹² I

R²¹-A²¹-A²²-(CH₂)_a-A²³-A²⁴-R²² II

R³¹ -A³¹ -A³²-(A³³)_b-Z³¹ -(CH₂)_C-Z³²-A³⁴-A³⁵-A³⁶- R³² III

R⁴¹-A⁴¹-A⁴²-Z⁴¹-(CH₂)_d-Z⁴²-A⁴³-A⁴⁴-R⁴² IV

R51._A51._Z51.(_{C H 2})_e.Z52._A52.(A53)_{f. R}52 y

R⁶¹ -A⁶¹ -A⁶²-(CH₂)_g-Z⁶¹ -A⁶³-A⁶⁴-(A⁶⁵)_h-R⁶² VI

R⁷¹-A⁷¹-Z⁷¹-A⁷²-(Z⁷²-A⁷³)i-(CH₂)_j-(A⁷⁴-Z⁷³-)_k-A⁷⁵-Z⁷⁴-A⁷⁶-R⁷² VII in which

R^{1 1} denotes a straight-chain or branched alkyl group, in which one or more non-adjacent and non-terminal CH₂ groups may be replaced, in each occurrence independently from one another, by -0-,

-S-, -NH-, -N(CH₃)-, -CO-, -COO-, -OCO-, -0-C0-0-, -S-CO-, -CO-S-, -CH=CH-, -CH=CF-, -CF=CF- or -CºC- in such a manner that oxygen atoms are not linked directly to one another,

R¹² denotes F, Cl, CN, NCS, or a straight-chain or branched alkyl group, which may be unsubstituted, mono- or polysubstituted by halogen or CN and in which one or more non-adjacent and non-terminal CFI₂ groups may be replaced, in each occurrence independently from one another, by -0-, -S-, -NH-, -N(CH₃)-, -CO-, -COO-,

-OCO-, -0-C0-0-, -S-CO-, -CO-S-, -CH=CH-, -CH=CF-, -CF=CF- or -CºC- in such a manner that oxygen atoms are not linked directly to one another, preferably F, Cl, CN, a straight-chain or branched alkyl, alkenyl or alkoxy group which may be unsubstituted, mono- or polysubstituted by halogen or CN,

more preferably F or OCF3,

A¹¹ denotes 1 ,4-cyclohexylene, A¹² to A¹⁴ each independently in each occurrence denote, 1 ,4- phenylene, wherein in addition one or more CFI groups may be replaced by N, trans-1 , 4-cyclo-hexylene in which, in addition, one or two non-adjacent CFI2 groups may be replaced by O and/or S, 1 ,4-cyclohexylene, naphthalene-2, 6-diyl, decahydro-naphthalene-2,6-diyl,

1 ,2,3,4-tetrahydro-naphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups, wherein one or more FI atoms may be substituted by F or Cl,

preferably each independently in each occurrence 1 ,4- phenylene, wherein in addition one or more CFI groups may be replaced by N or trans-1 ,4-cyclo-hexylene in which, in addition, one or two non-adjacent CFI2 groups may be replaced by O and/or S, it being possible for both ring groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups, wherein one or more FI atoms may be substituted by F or Cl,

Z¹¹ and Z¹² are, independently of each other in each occurrence, a single bond, -COO-, -OCO-, -O-CO-O-, -OCFI2-,

-CH2O-, -OCF2-, -CF2O-, -CH2CH2-, -(CH₂)₄-, -CF2CF2-, - CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or - CºC-, optionally substituted with one or more of F, S and/or Si, preferably a single bond p and q is each and independently 0, 1 , 2, 3 or 4, preferably 0, 1 ,

2 or 3 and, most preferably 1 or 2.

Sp^{1 1} is a spacer group comprising 1 , 3 or 5 to 40 C atoms, wherein one or more non-adjacent and non-terminal CFI2 groups may also be replaced by -O-, -S-, -NH-, -N(CH₃)-, -CO-, -O-CO-, -S-CO-, -O-COO-, -CO-S-, -CO-O-, -CF2-, -CF2O-, -OCF2- -C(OH)-, -CH(alkyl)-, -CH(alkenyl)-,-CH(alkoxyl)-, -CH(oxaalkyl)-, -CH=CH- or -CºC-, however in such a way that no two O-atoms are adjacent to one another and no two groups selected from -O-CO-, -S-CO-, -O-COO-, -CO-S-,

-CO-O- and -CFI=CFI- are adjacent to each other, preferably -(CFhj_n-, with n 1 , 3 or an integer from 5 to 15, more preferably from 7 to 1 1 , most preferably an odd integer (i.e. 7, 9 or 1 1 ), X^{1 1} and X¹² are independently from one another selected from a single bond, -C0-0-, -0-C0-, -O-COO-, -0-,

-CH=CH-, -CºC-, -CF2-O-, -O-CF2-, -CF2-CF2-,

-CH2-O-, -O-CH2-, -CO-S-, -S-CO-, -CS-S-, -S-CS-, -S- CSS- and -S-, wherein in -X^{1 1}-Sp¹-X¹²- respectively two O atoms, two -CFI=CFI- groups and two groups selected from -O-CO-, -S-CO-, -O-COO-, -CO-S- and

-CO-O- are not linked directly to one another;

R²¹ and R²² denote independently FI, F, Cl, CN, NCS or a straight- chain or branched alkyl group, which may be

unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CFI2 groups to be replaced, in each occurrence independently from one another, by -0-, -S-,

-NH-, -N(CH₃)-, -CO-, -COO-, -OCO-, -O-CO-O-, -S-CO-, -CO-S-, -CH=CH-, -CH=CF-, -CF=CF- or -CºC- in such a manner that oxygen atoms are not linked directly to one another,

preferably F, a straight-chain or branched alkyl or alkoxy group which may be unsubstituted, mono- or

polysubstituted by halogen or CN,

more preferably F or OCF3,

A²¹ to A²⁴ denote independently in each occurrence a aryl-,

heteroaryl-, and heterocyclic group, preferably 1 ,4- phenylene, wherein in addition one or more CFI groups may be replaced by N, 1 ,4-bicyclo-(2,2,2)-octylene, naphthalene-2, 6-diyl, decahydro-naphthalene-2,6-diyl,

1 .2.3.4-tetrahydro-naphthalene-2,6-diyl, cyclobutane- 1 ,3-diyl, spiro[3.3]heptane-2, 6-diyl or dispiro[3.1 .3.1 ] decane-2, 8-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or

alkoxycarbonyl groups, wherein one or more FI atoms may be substituted by F or Cl,

more preferably each independently in each occurrence

1 .4-phenylene, wherein in addition one or more CFI groups may be replaced by N or trans-1 ,4- cyclohexylene in which, in addition, one or two non- adjacent CFI2 groups may be replaced by O and/or S, it being possible for both ring groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups, wherein one or more FI atoms may be substituted by F or Cl, a denotes an integer from 1 to 15, preferably an odd (i.e.

uneven) integer and, more preferably 3, 5, 7, 9 or 1 1 .

R³¹ and R³² have each and independently from another one of the meanings as given for R²¹ and R²² under formula II, A³¹ to A³⁶ have each and independently from another one of the meanings as given for A²¹ to A²⁴ under formula II, Z³¹ and Z³² are each independently in each occurrence,

-COO-, -OCO-, -0-C0-0-, -OCH2-, -CH2O-, -CH2CH2-, -(CH₂)₄-, -CF2CF2-, -CH=CH-, -CF=CF-,

-CH=CH-COO-, -OCO-CH=CH- or -CºC-, optionally substituted with one or more of F, S and/or Si, preferably -COO-, -OCO- or -O-CO-O-,

more preferably -COO- or -OCO-, b denotes an integer from 1 to 15, preferably an odd (i.e.

uneven) integer and, more preferably 3, 5, 7 or 9 and c denotes 0 or 1 , preferably 0;

R⁴¹ and R⁴² have each and independently one of the meanings as given above for R²¹ under formula II,

A⁴¹ to A⁴⁴ have each and independently one of the meanings as given above for A²¹ under formula II,

Z⁴¹ and Z⁴² are each independently in each occurrence,

-COO-, -OCO-, -O-CO-O-, -OCH2-, -CH2O-, -CH2CH2-, -(CH₂)₄-, -CF2CF2-, -CH=CH-, -CF=CF-,

more preferably -COO- or -OCO-. d denotes an integer from 1 to 15, preferably an odd (i.e.

uneven) integer and, more preferably 3, 5, 7 or 9. - I Q -

R⁵¹ and R⁵² have each and independently one of the meanings as given above for R²¹ under formula II,

A⁵¹ to A⁵³ have each and independently one of the meanings as given above for A²¹ under formula II,

Z⁵¹ and Z⁵² are each independently in each occurrence,

-COO-, -OCO-, -0-C0-0-, -OCH₂-, -CH₂O-, -CH₂CH₂-, -(CH₂)₄-, -CF₂CF₂-, -CH=CH-, -CF=CF-,

-CH=CH-COO-, -OCO-CH=CH- or -CºC-, optionally substituted with one or more of F, S and/or Si, preferably -COO-, -OCO- or -0-C0-0-, more preferably -COO- or -OCO-, denotes an integer from 1 to 15, preferably an odd (i.e. uneven) integer and, more preferably 3, 5, 7 or 9 and f denotes 0 or 1 ;

R⁶¹ and R⁶² have each and independently one of the meanings as given above for R²¹ under formula II,

A⁶¹ to A⁶⁴ have each and independently one of the meanings as given above for A²¹ under formula II,

Z⁶¹ denotes -0-, -COO-, -OCO-, -0-C0-0-, -OCH₂-, -CH₂0,

-CH₂CH₂-, -(CH₂)₄-, -CF₂CF₂-, -CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or -CºC-, optionally substituted with one or more of F, S and/or Si, preferably -0-, -COO-, -OCO- or -0-C0-0-,

more preferably -0-, -COO- or -OCO-, most preferably -

COO- or -0C0-, h denotes 0 or 1 and g denotes an integer from 1 to 15, preferably an odd (i.e. uneven) integer and, more preferably 3, 5, 7 or 9;

R⁷¹ and R⁷² have each and independently one of the meanings as given above for R²¹ under formula II,

A⁷¹ to A⁷⁶ have each and independently one of the meanings as given above for A²¹ under formula II,

Z⁷¹ to Z⁷⁴ each and independently denotes -COO-, -OCO-,

-0-C0-0-, -OCH2-, -CH2O-, -OCF2-, -CF2O-, -CH2CH2-, -(CH₂)₄-,-CF₂CF₂-, -CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CFI=CFI- or -CºC-, optionally substituted with one or more of F, S and/or Si or a single bond,

preferably -COO-, -OCO-, -O-CO-O-, -OCF2-, -CF2O- or a single bond

more preferably -COO-, -OCO-, -OCF2-, -CF2O- or a single bond,

with the proviso that at least one of Z⁷¹ to Z⁷⁴ is not a single bond, j denotes an integer from 1 to 15, preferably an odd (i.e.

uneven) integer and, more preferably 3, 5, 7 or 9 and i and k each and independently denotes 0 or 1 .

The present invention also relates to electro-optical displays or electro- optical components which contain liquid-crystalline media according to the invention. Preference is given to electro-optical displays which are based on the FFS effect and in particular those which are addressed by means of an active-matrix addressing device. The present invention further relates to the use of a liquid-crystalline medium according to the invention in an electro-optical display or in an electro-optical component, and to a process for the preparation of the liquid-crystalline media according to the invention, characterised in that one or more compounds of the formula Y-1 and/or Y-2 and/or Y-3 and/or Y-4 are mixed with one or more compounds selected from the group of compounds of the formulae I, II, III, IV, V, VI and VII, and preferably with one or more further compounds, preferably selected from the group of the compounds of the formulae C and/or P defined below.

The media according to the invention enable displays, in particular FFS displays, which exhibit advantageously low flicker.

The term "liquid crystal", "mesomorphic compound” or "mesogenic compound" (also shortly referred to as "mesogen") means a compound that under suitable conditions of temperature, pressure and concentration can exist as a mesophase (nematic, smectic, etc.) or in particular as a LC phase. Non-amphiphilic mesogenic compounds comprise for example one or more calamitic, banana-shaped or discotic mesogenic groups.

The term "mesogenic group" means in this context, a group with the ability to induce liquid crystal (LC) phase behaviour. The compounds comprising mesogenic groups do not necessarily have to exhibit an LC phase themselves. It is also possible that they show LC phase behaviour only in mixtures with other compounds. For the sake of simplicity, the term "liquid crystal" is used hereinafter for both mesogenic and LC materials.

Throughout the application, unless stated explicitly otherwise, the term “aryl and heteroaryl groups” encompass groups, which can be monocyclic or polycyclic, i.e. they can have one ring (such as, for example, phenyl) or two or more rings, which may also be fused (such as, for example, naphthyl) or covalently linked (such as, for example, biphenyl) or contain a combination of fused and linked rings.

Heteroaryl groups contain one or more heteroatoms, preferably selected from O, N, S and Se. Particular preference is given to mono-, bi- or tricyclic aryl groups having 6 to 25 C atoms and mono-, bi- or tricyclic heteroaryl groups having 2 to 25 C atoms, which optionally contain fused rings and which are optionally substituted. Preference is furthermore given to 5 , 6 or 7-membered aryl and heteroaryl groups, in which, in addition, one or more CH groups may be replaced by N, S or O in such a way that O atoms and/or S atoms are not linked directly to one another. Preferred aryl groups are, for example, phenyl, biphenyl, terphenyl, [1 ,1 ':3',1"]terphenyl-2'-yl, naphthyl, anthracene, binaphthyl, phenanthrene, pyrene, dihydropyrene, chrysene, perylene, tetracene, pentacene, benzopyrene, fluorene, indene, indenofluorene, spirobifluorene, more preferably 1 ,4- phenylene, 4,4’- biphenylene, 1 , 4-tephenylene.

Preferred heteroaryl groups are, for example, 5 membered rings, such as pyrrole, pyrazole, imidazole, 1 ,2,3-triazole, 1 ,2,4-triazole, tetrazole, furan, thiophene, selenophene, oxazole, isoxazole, 1 ,2 thiazole, 1 ,3-thiazole, 1 ,2,3-oxadiazole, 1 ,2,4 oxadiazole, 1 ,2,5-oxadiazole, 1 ,3,4-oxadiazole, 1 ,2,3-thiadiazole, 1 ,2,4-thiadiazole, 1 ,2,5-thiadiazole, 1 ,3,4-thiadiazole, 6 membered rings, such as pyridine, pyridazine, pyrimidine, pyrazine, 1 ,3,5- triazine, 1 ,2,4-triazine, 1 ,2,3-triazine, 1 ,2,4,5-tetrazine, 1 ,2,3,4-tetrazine,

1 ,2,3,5-tetrazine or condensed groups, such as indole, iso-indole, indolizine, indazole, benzimidazole, benzotriazole, purine, naphth- imidazole, phenanthrimidazole, pyridimidazole, pyrazinimidazole, quinoxalinimidazole, benzoxazole, naphthoxazole, anthroxazole, phen- anthroxazole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5, 6-quinoline, benzo-6,7-quino 1ine, benzo-7, 8-quinoline, benzoisoquinoline, acridine, phenothiazine, phenoxazine, benzopyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarboline, phenanthridine, phenanthroline, thieno[2,3b]thiophene, thieno[3,2b]- thiophene, dithienothiophene, isobenzothiophene, dibenzothiophene, benzothiadiazothiophene or combinations of these groups. The heteroaryl groups may also be substituted by alkyl, alkoxy, thioalkyl, fluorine, fluoroalkyl or further aryl or heteroaryl groups.

In the context of this application, the term“(non-aromatic) alicyclic and heterocyclic groups” encompass both saturated rings, i.e. those that contain exclusively single bonds and partially unsaturated rings, i.e. those that may also contain multiple bonds. Heterocyclic rings contain one or more heteroatoms, preferably selected from Si, O, N, S and Se. The (non- aromatic) alicyclic and heterocyclic groups can be monocyclic, i.e. contain only one ring (such as, for example, cyclohexane) or polycyclic, i.e. contain a plurality of rings (such as, for example, decahydro-naphthalene or bicyclooctane). Particular preference is given to saturated groups.

Preference is furthermore given to mono-, bi- or tricyclic groups having 3 to 25 C atoms, which optionally contain fused rings and that are optionally substituted. Preference is furthermore given to 5-, 6-, 7- or 8-membered carbocyclic groups in which, in addition, one or more C atoms may be replaced by Si and/or one or more CH groups may be replaced by N and/or one or more non-adjacent CFh groups may be replaced by -O- and/or -S-. Preferred alicyclic and heterocyclic groups are, for example, 5-membered groups, such as cyclopentane, tetrahydrofuran, tetrahydrothiophene, pyrrolidine, 6-membered groups, such as cyclohexane, silinane,

cyclohexene, tetrahydropyran, tetrahydrothiopyran, 1 ,3-dioxane, 1 ,3- dithiane, piperidine, 7-membered groups, such as cycloheptane and fused groups, such as tetrahydronaphthalene, decahydronaphthalene, indane, bicyclo[1.1.IJ-'pentane-l ,3-diyl, bicyclo[2.2.2]octane-1 ,4-diyl,

spiro[3.3]heptane-2,6-diyl, octahydro-4,7-methanoindane-2,5-diyl, more preferably 1 ,4-cyclohexylene 4,4’- bicyclohexylene, 3,17-hexadecahydro- cyclopenta[a]phenanthrene, optionally being substituted by one or more identical or different groups L. Especially preferred aryl-, heteroaryl-, alicyclic- and heterocyclic groups are 1 ,4-phenylene, 4,4’-biphenylene, 1 , 4-terphenylene, 1 ,4-cyclohexylene, 4,4’- bicyclohexylene and 3,17- hexadecahydro-cyclopenta[a]-phenanthrene, optionally being substituted by one or more identical or different groups L.

Preferred substituents of the above-mentioned aryl-, heteroaryl-, alicyclic- and heterocyclic groups (L) are, for example, solubility-promoting groups, such as alkyl or alkoxy and electron-withdrawing groups, such as fluorine, nitro or nitrile.

Particularly preferred substituents are, for example, halogen, CN, NO2,

CHs, C2H5, OCHs, OC2H5, COCH3, COC2H5, COOCHs, COOC2H5, CFs, OCFs, OCHF2 or OC2F5. Above and below "halogen" denotes F, Cl, Br or I.

Above and below, the terms "alkyl", "aryl", "heteroaryl", etc., also encompass polyvalent groups, for example alkylene, arylene,

heteroarylene, etc.

The term "aryl" denotes an aromatic carbon group or a group derived there from. The term "heteroaryl" denotes "aryl" in accordance with the above definition containing one or more heteroatoms.

Preferred alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methylbutyl, n-pentyl, s-pentyl, cyclo- pentyl, n-hexyl, cyclohexyl, 2-ethylhexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, dodecanyl, trifluoro- methyl, peril uoro-n-butyl, 2,2,2-trifluoroethyl, peril uorooctyl, perfluoro- hexyl, etc. Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxy- ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2- methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n- decoxy, n-undecoxy, n-dodecoxy. Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl, cyclooctenyl.

Preferred alkynyl groups are, for example, ethynyl, propynyl, butynyl, pentynyl, hexynyl, octynyl.

Oxaalkyl, i.e. where one CFte group is replaced by -0-, is preferably straight-chain 2-oxapropyl (= methoxymethyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5- oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, for example.

Preferred amino groups are, for example, dimethylamino, methylamino, methylphenylamino, phenylamino.

The term“chiral” in general is used to describe an object that is non- superimposable on its mirror image. “Achiral” (non- chiral) objects are objects that are identical to their mirror image.

The terms“chiral nematic” and“cholesteric” are used synonymously in this application, unless explicitly stated otherwise.

The term“bimesogenic compound” or“bimesogen” relates to compounds comprising two mesogenic groups in the molecule. Just like normal mesogens, they can form many mesophases, depending on their structure. In particular, bimesogenic compound may induce a second nematic phase, when added to a nematic liquid crystal medium. Bimesogenic compounds are also known as“dimeric liquid crystals”.

Bimesogens are disclosed in for example WO 2015/002114 A1 ,

WO2015/036079 A1 , WO 2014/005672 A1 , WO 2013/174478 A1 , and WO 2013/004333 A1 , in particular compounds of the formulae I, II, III, IV,

V, VI and VII, which can be synthesised according to methods described therein.

The term "director" is known in prior art and means the preferred

orientation direction of the long molecular axes (in case of calamitic compounds) or short molecular axes (in case of discotic compounds) of the liquid-crystalline molecules. In case of uniaxial ordering of such anisotropic molecules, the director is the axis of anisotropy. The term“alignment” or“orientation” relates to alignment (orientation ordering) of anisotropic units of material such as small molecules or fragments of big molecules in a common direction named“alignment direction”. In an aligned layer of liquid-crystalline material, the liquid- crystalline director coincides with the alignment direction so that the alignment direction corresponds to the direction of the anisotropy axis of the material.

The term "planar orientation/alignment", for example in a layer of an liquid- crystalline material, means that the long molecular axes (in case of calamitic compounds) or the short molecular axes (in case of discotic compounds) of a proportion of the liquid-crystalline molecules are oriented substantially parallel (about 180°) to the plane of the layer.

The term "homeotropic orientation/alignment", for example in a layer of a liquid-crystalline material, means that the long molecular axes (in case of calamitic compounds) or the short molecular axes (in case of discotic compounds) of a proportion of the liquid-crystalline molecules are oriented at an angle Q ("tilt angle") between about 80° to 90° relative to the plane of the layer. The terms "uniform orientation" or "uniform alignment" of an liquid- crystalline material, for example in a layer of the material, mean that the long molecular axes (in case of calamitic compounds) or the short molecular axes (in case of discotic compounds) of the liquid-crystalline molecules are oriented substantially in the same direction. In other words, the lines of liquid-crystalline director are parallel.

The wavelength of light generally referred to in this application is 550 nm, unless explicitly specified otherwise.

The birefringence Dh herein is defined by the following equation

D^h = n_e - n₀ wherein n_e is the extraordinary refractive index and n₀ is the ordinary refractive index and the effective average refractive index n_av. is given by the following equation n_av. = [(2 n₀ ² + n_e ²)/3]^1/2

The extraordinary refractive index n_e and the ordinary refractive index n₀ can be measured using an Abbe refractometer.

In the present application the term“dielectrically positive” is used for compounds or components with De > 3.0,“dielectrically neutral” with -1 .5 < De < 3.0 and“dielectrically negative” with De < -1 .5. De is determined at a frequency of 1 kHz and at 20°C. The dielectric anisotropy of the respective compound is determined from the results of a solution of 10 % of the respective individual compound in a nematic host mixture. In case the solubility of the respective compound in the host medium is less than 10 % its concentration is reduced by a factor of 2 until the resultant medium is stable enough at least to allow the determination of its properties.

Preferably, the concentration is kept at least at 5 %, however, in order to keep the significance of the results a high as possible. The capacitance of the test mixtures are determined both in a cell with homeotropic and with homogeneous alignment. The cell gap of both types of cells is

approximately 20 pm. The voltage applied is a rectangular wave with a frequency of 1 kHz and a root mean square value typically of 0.5 V to 1 .0 V; however, it is always selected to be below the capacitive threshold of the respective test mixture.

De is defined as (e | | - e±), whereas e_3n. is (e 1 1 + 2 e±) / 3. The dielectric permittivity of the compounds is determined from the change of the respective values of a host medium upon addition of the compounds of interest. The values are extrapolated to a concentration of the compounds of interest of 100 %. A typical host medium is ZLI-4792 or BL-087 both commercially available from Merck, Darmstadt.

For the present invention

denote trans-1 ,4-cyclohexylene

denote 1 ,4-phenylene.

Furthermore, the definitions as given in C. Tschierske, G. Pelzl and S. Diele, Angew. Chem. 2004, 116, 6340-6368 shall apply to non-defined terms related to liquid crystal materials in the instant application.

A smaller group of preferred groups -A¹¹(-Z¹¹-A¹²-)_P or MG-11 comprising only 6-membered rings is listed below. For reasons of simplicity, Phe in these groups is 1 ,4-phenylene, PheL is a 1 ,4-phenylene group which is substituted by 1 to 4 groups L, with L being preferably F, Cl, CN, OFI, NO2 or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, very preferably F, Cl, CN, OFI, NO2, CFI3, C2FI5, OCFI3, OC2FI5, COCHs, COC2H5, COOCHs, COOC2H5, CFs, OCFs, OCHF2, OC2F5, in particular F, Cl, CN, CFI3, C2FI5, OCFI3, COCFI3 and OCF3, most preferably F, Cl, CFI3, OCFI3 and COCFIs and Cyc is 1 ,4-cyclohexylene. This list comprises the subformulae shown below,

-Cyc- MG-11 -1

-Cyc-Cyc- MG-11 -2

-Cyc-Phe- MG-11 -3

-Cyc-Phel MG-11 -4

-Cyc-Phe-Cyc- MG-11 -5

-Cyc-PheL-Cyc- MG-11 -6

-Cyc-Cyc-Cyc- MG-11 -7

-Cyc-Phe-Phe- MG-11 -8

-Cyc-Phe-PheL- MG-11 -9

-Cyc-PheL-Phe- MG-11 -10

-Cyc-PheL-PheL- MG-11 -11

-Cyc-Cyc-Phe- MG-11 -12

-Cyc-Cyc-PheL- MG-11 -13 -Cyc-Z-Cyc- MG-11-14

-Cyc-Z-Phe- MG-11-15

-Cyc-Z-PheL- MG-11-16

-Cyc-Z-Phe-Cyc- MG-11-17

-Cyc-Z-PheL-Cyc- MG-11-18

-Cyc-Z-Cyc-Cyc- MG-11-19

-Cyc-Z-Phe-Phe- MG-11-20

-Cyc-Z-Phe-PheL- MG-11-21

-Cyc-Z-PheL-Phe- MG-11-22

-Cyc-Z-PheL-PheL- MG-11-23

-Cyc-Z-Cyc-Phe- MG-11-24

-Cyc-Z-Cyc-PheL- MG-11-25

-Cyc-Phe-Z-Cyc- MG-11-26

-Cyc-PheL-Z-Cyc- MG-11-27

-Cyc-Cyc-Z-Cyc- MG-11-28

-Cyc-Phe-Z-Phe- MG-11-29

-Cyc-Phe-Z-PheL- MG-11-30

-Cyc-PheL-Z-Phe- MG-11-31

-Cyc-PheL-Z-PheL- MG-11-32

-Cyc-Cyc-Z-Phe- MG-11-33

-Cyc-Cyc-Z-PheL- MG-11-34

-Cyc-Z-Phe-Z-Cyc- MG-11-35

-Cyc-Z-PheL-Z-Cyc- MG-11-36

-Cyc-Z-Cyc-Z-Cyc- MG-11-37

-Cyc-Z-Phe-Z-Phe- MG-11-38

-Cyc-Z-Phe-Z-PheL- MG-11-39

-Cyc-Z-PheL-Z-Phe- MG-11-40

-Cyc-Z-PheL-Z-PheL- MG-11-41

-Cyc-Z-Cyc-Z-Phe- MG-11-42

-Cyc-Z-Cyc-Z-PheL- MG-11-43 wherein

Cyc is 1 ,4-cyclohexlene, preferably trans-1 ,4-cyclohexlene,

Phe is 1 ,4-phenylene, PheL is 1 ,4-phenylene, which is substituted by one, two or three fluorine atoms, by one or two Cl atoms or by one Cl atom and one F atom and

Z has one of the meanings of Z¹¹ as given under formula I and if present twice, at least one is preferably selected from -CºC-, -C=C-, -COO-, -OCO-, -O-CO-O-, -OCH2-, -CH2O-, -OCF2- or -CF2O-.

Particularly preferred are the sub-formulae, wherein Z in each case independently has one of the meanings of Z¹¹ as given under formula I and if present twice, preferably one of Z is -COO-, -OCO-, -CH2-O-, -O-CH2-, - CF2-O- or -O-CF2-.

Preferably MG-1 1 is selected from the sub-formulae not containing two groups Z, more preferably from MG-1 1 -2 to MG-1 1 -13, even more preferably from MG-1 1 -2 or MG-1 1 -3.

A smaller group of preferred groups -(A¹³-Z¹²-)_q A¹⁴- or MG-12 comprising only 6-membered rings is listed below. For reasons of simplicity, Phe in these groups is 1 ,4-phenylene, PheL is a 1 ,4-phenylene group which is substituted by 1 to 4 groups L, with L being preferably F, Cl, CN, OFI, NO₂ or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, very preferably F, Cl, CN, OH, NO2, CH3, C2H5, OCH3, OC2H5, COCH3, COC2H5, COOCHs, COOC2H5, CFs, OCFs, OCHF2, OC2F5, in particular F, Cl, CN, CH3, C₂H₅, OCH3, COCH3 and OCF3, most preferably F, Cl, CH3, OCH3 and COCHs and Cyc is 1 ,4-cyclohexylene. This list comprises the subformulae shown below,

-Cyc- MG-12-1 -Phe- MG-12-2

-PheL- MG-12-3

-Cyc-Cyc- MG-12-4

-Cyc-Phe- MG-12-5

-Cyc-PheL- MG-12-6

-Phe-Cyc- MG-12-7 -PheL-Cyc- MG-12-8

-Phe-Phe- MG-12-9

-PheL-PheL- MG-12-10

-PheL-Phe- MG-12-11 -Phe-PheL- MG-12-12

-Cyc-Phe-Phe- MG-12-13 -Cyc-Phe-PheL- MG-12-14 -Cyc-PheL-Phe- MG-12-15 -Cyc-PheL-PheL- MG-12-16 -Phe-Cyc-Phe- MG-12-17 -PheL-Cyc-Phe- MG-12-18 -Phe-Cyc-PheL- MG-12-19 -PheL-Cyc-PheL- MG-12-20 -Phe-Phe-Cyc- MG-12-21 -Phe-PheL-Cyc- MG-12-22 -PheL-Phe-Cyc- MG-12-23 -PheL-PheL-Cyc- MG-12-24 -Cyc-Phe-Cyc- MG-12-25 -Cyc-PheL-Cyc- MG-12-26

-Cyc-Cyc-PheL- MG-12-27 -Cyc-Cyc-Phe- MG-12-28 -PheL-Cyc-Cyc- MG-12-29 -Phe-Cyc-Cyc- MG-12-30 -Cyc-Cyc-Cyc- MG-12-31

-Phe-Phe-Phe- MG-12-32 -Phe-Phe-PheL- MG-12-33 -Phe-PheL-Phe- MG-12-34 -PheL-Phe-Phe- MG-12-35 -PheL-PheL-Phe- MG-12-36

-Phe-PheL-PheL- MG-12-37 -PheL-PheL-PheL- MG-12-38

Cyc-Z-Cyc- MG-12-39

Cyc-Z-Phe- MG-12-40

Cyc-Z-PheL- MG-12-41 -Phe-Z-Cyc- MG-12-42 -PheL-Z-Cyc- MG-12-43 -Phe-Z-Phe- MG-12-44 -PheL-Z-PheL- MG-12-45 -PheL-Z-Phe- MG-12-46

-Phe-Z-PheL- MG-12-47 -Cyc-Z-Phe-Phe- MG-12-48 -Cyc-Z-Phe-PheL- MG-12-49 -Cyc-Z-PheL-Phe- MG-12-50 -Cyc-Z-PheL-PheL- MG-12-51

-Phe-Z-Cyc-Phe- MG-12-52 -PheL-Z-Cyc-Phe- MG-12-53 -Phe-Z-Cyc-PheL- MG-12-54 -PheL-Z-Cyc-PheL- MG-12-55 -Phe-Z-Phe-Cyc- MG-12-56

-Phe-Z-PheL-Cyc- MG-12-57 -PheL-Z-Phe-Cyc- MG-12-58 -PheL-Z-PheL-Cyc- MG-12-59 -Cyc-Z-Phe-Cyc- MG-12-60 -Cyc-Z-PheL-Cyc- MG-12-61

-Cyc-Z-Cyc-PheL- MG-12-62 -Cyc-Z-Cyc-Phe- MG-12-63 -PheL-Z-Cyc-Cyc- MG-12-64 -Phe-Z-Cyc-Cyc- MG-12-65 -Cyc-Z-Cyc-Cyc- MG-12-66

-Phe-Z-Phe-Phe- MG-12-67 -Phe-Z-Phe-PheL- MG-12-68 -Phe-Z-PheL-Phe- MG-12-69 -PheL-Z-Phe-Phe- MG-12-70 -PheL-Z-PheL-Phe- MG-12-71

-Phe-Z-PheL-PheL- MG-12-72 -PheL-Z-PheL-PheL- MG-12-73

-Cyc-Phe-Z-Phe- MG-12-74

-Cyc-Phe-Z-PheL- MG-12-75

-Cyc-PheL-Z-Phe- MG-12-76 -Cyc-PheL-Z-PheL- MG-12-77 -Phe-Cyc-Z-Phe- MG-12-78 -PheL-Cyc-Z-Phe- MG-12-79 -Phe-Cyc-Z-PheL- MG-12-80 -PheL-Cyc-Z-PheL- MG-12-81

-Phe-Phe-Z-Cyc- MG-12-82 -Phe-PheL-Z-Cyc- MG-12-83 -PheL-Phe-Z-Cyc- MG-12-84 -PheL-PheL-Z-Cyc- MG-12-85 -Cyc-Phe-Z-Cyc- MG-12-86

-Cyc-PheL-Z-Cyc- MG-12-87 -Cyc-Cyc-Z-PheL- MG-12-88 -Cyc-Cyc-Z-Phe- MG-12-89 -PheL-Cyc-Z-Cyc- MG-12-90 -Phe-Cyc-Z-Cyc- MG-12-91

-Cyc-Cyc-Z-Cyc- MG-12-92 -Phe-Phe-Z-Phe- MG-12-93 -Phe-Phe-Z-PheL- MG-12-94 -Phe-PheL-Z-Phe- MG-12-95 -PheL-Phe-Z-Phe- MG-12-96

-PheL-PheL-Z-Phe- MG-12-97 -Phe-PheL-Z-PheL- MG-12-98 -PheL-PheL-Z-PheL- MG-12-99 -Cyc-Z-Phe-Z-Phe- MG-1 2-100

-Cyc-Z-Phe-Z-PheL- MG-1 2-101 -Cyc-Z-PheL-Z-Phe- MG-1 2-102 -Cyc-Z-PheL-Z-PheL- MG-1 2-103 -Phe-Z-Cyc-Z-Phe- MG-1 2-104 -PheL-Z-Cyc-Z-Phe- MG-1 2-105

-Phe-Z-Cyc-Z-PheL- MG-1 2-106 -PheL-Z-Cyc-Z-PheL- MG-1 2-107 -Phe-Z-Phe-Z-Cyc- MG-1 2-108 -Phe-Z-PheL-Z-Cyc- MG-1 2-109 -PheL-Z-Phe-Z-Cyc- MG-1 2-1 10 -PheL-Z-PheL-Z-Cyc- MG-1 2-1 1 1 -Cyc-Z-Phe-Z-Cyc- MG-12-1 12 -Cyc-Z-PheL-Z-Cyc- MG-12-1 13 -Cyc-Z-Cyc-Z-PheL- MG-12-1 14 -Cyc-Z-Cyc-Z-Phe- MG-12-1 15 -Phe-Z-Cyc-Z-Cyc- MG-12-1 16

-Phe-Z-Cyc-Z-Cyc- MG-12-1 17 -Cyc-Z-Cyc-Z-Cyc- MG-12-1 18 -Phe-Z-Phe-Z-Phe- MG-12-1 19 -Phe-Z-Phe-Z-PheL- MG-12-1 20 -Phe-Z-PheL-Z-Phe- MG-12-1 21

-PheL-Z-Phe-Z-Phe- MG-12-1 22 -PheL-PheL-Z-Phe- MG-12-1 23 -Phe-PheL-Z-PheL- MG-12-1 24 -PheL-PheL-Z-PheL- MG-12-1 25 wherein

Cyc is 1 ,4-cyclohexlene, preferably trans-1 ,4-cyclohexlene,

Phe is 1 ,4-phenylene,

PheL is 1 ,4-phenylene, which is substituted by one, two or three fluorine atoms, by one or two Cl atoms or by one Cl atom and one F atom and

Z has one of the meanings of Z¹¹ as given under partial formula II and if present twice, at least one is preferably selected from -CºC-, -C=C-, -COO-, -OCO-, -0-C0-0-, - OCH2-, -CH2O-, -OCF2- or -CF2O-.

In the above given preferred subformulae of formula MG-1 1 and MG-12,

PheL preferably denotes the group furthermore

or

wherein L is preferably F, Cl, CFb, OCH3 and COCH3_.

Preferably MG-12 is selected from the sub-formulae not containing two groups Z, more preferably from MG-12-1 to MG-12-38, even more preferably from MG-12-4 or MG-12-38, in particular, from MG-12-9 to MG- 12-12 or MG-12-32 to MG-12-38.

Preferably the compounds of formula I are unsymmetric compounds, which comprise different mesogenic groups MG-11 and MG-12_.

Especially preferred are compounds of formula I wherein the respective pairs of mesogenic groups MG-11 and MG-12 each comprise two or three six-atomic rings, more preferably MG-11 and MG-12 each comprise two six-atomic rings or MG-11 comprises two six-atomic rings and MG-12 comprises three six-atomic rings.

Further preferred are compounds of formula I wherein

Sp¹¹ denotes -(CFh , where n is an integer from 1 to 15, wherein one or more -CFI₂- groups may be replaced by -CO-, preferably an uneven integer, more preferably 7, 9, 11 or 13, Further preferred compounds of formula I are those wherein -X^{1 1}-Sp^{1 1}-Xi2. is -Sp¹¹-, -Sp¹¹-0-, -Sp¹¹-C0-0-, -Sp¹¹-0-C0-, -0,0-0- Sp¹¹, -O-CO-Sp¹¹ ,-O-Sp¹¹-, -0-Sp¹¹-C0-0-, -0-Sp¹¹-0- CO-, -O-CO-Sp¹¹-0-, -O-CO-Sp¹¹-0-CO-,

-C0-0-Sp¹¹-0- or -C0-0-Sp¹¹-C0-0-, however under the condition that in -X¹¹-Sp¹¹-X¹²- no two O-atoms are adjacent to one another, no two -CH=CH- groups are adjacent to each other and no two groups selected from -0-C0-, -S-CO-, -0-C00-, -CO-S-, -CO-O- and -CH=CH- are adjacent to each other.

Further preferred compounds of formula I are selected from the following substructure,

wherein

L denotes each and independently in each occurrence F, Cl,

CH3, OCH3 and COCH3, preferably F, r denotes an integer between 0 and 4, preferably 0, 1 or 2

R^{1 1} denotes an alkyl or alkoxy radical, which may be straight chain or branched having 2, 3, 4, 5, 6, 7 or 8 carbon atoms R¹² denotes CN, NO₂, F, OCFI3, OCN, COR^x, COOR^x or a mono- oligo- or polyfluorinated alkyl or alkoxy group with 1 to 4 C atoms, preferably F,

R^x is optionally fluorinated alkyl with 1 to 4, preferably 1 to 3 C atoms, and

n denotes 7, 9, 1 1 or 13.

R^{1 1} denotes alkyl, which may be straight chain or branched

having 2, 3, 4, 5, 6, 7 or 8 carbon atoms, preferably straight chain alkyl having 3, 4, or 5 carbon atoms,

R¹² denotes CN, F, CF3 or OCF3, preferably F, CF3 or OCF3, more preferably F, and n denotes 7, 9 or 1 1 .

Preferred compounds of formula II are selected from compounds in which the groups (-A²¹-A²²-) and (-A²³-A²⁴-) are each and independently selected from the following groups

-Phe-Phe- MG1

-PheL-PheL- MG2 -Phe-PheL- MG3

-PheL-Phe- MG4 wherein

Phe in these groups is 1 ,4-phenylene,

PheL is a 1 ,4-phenylene group which is substituted by 1 to 4

groups L, with L being preferably F, Cl, CN, OH, NO2 or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, very preferably F, Cl, CN, OH, NO2, CH3, C2H5, OCHs, OC2H5, COCH3, COC2H5, COOCHs, COOC2H5, CFs, OCF3, OCHF2, OC2F5, in particular F, Cl, CN, CH3, C2H5, OCH3, COCH3 and OCF3, most preferably F, Cl, CH3, OCH3 and COCHs and

Cyc is 1 ,4-cyclohexylene.

Preferred are compounds of formula II wherein the groups (R²¹-A²¹-A²²-) and (-A²³-A²⁴-R²²) in formula II are identical or mirror images.

Likewise preferred are compounds of formula II wherein (R²¹-A²¹-A²²-) and (_A²³-A²⁴-R²²) in formula II are different.

Preferred compounds of formula II are indicated below:

wherein

n denotes an integer from 1 to 15, preferably an odd (i.e.

uneven) integer and, more preferably 3, 5, 7, 9 or 1 1 .

Preferred compounds of formula III are selected from compounds in which c denotes 0 and the group (-A³¹-A³²-) is selected from the groups MG1 to MG4 as given above.

Further preferred compounds of formula III are selected from compounds in which c denotes 1 and the groups (-A²⁴-A²⁵-A²⁶-) and (-A²¹-A²²-A²³-) are each and independently selected from the following groups

-Phe-Phe-Phe- MG5

-Phe-Phe-PheL- MG6

-Phe-PheL-Phe- MG7

-PheL-Phe-Phe- MG8

-PheL-Phe-PheL- MG9

-PheL-PheL-Phe- MG10

-PheL-PheL-PheL- MG1 1 wherein

Phe, PheL an L have one of the meanings given above for the groups MG- 1 to MG-4.

Further preferred compounds of formula III are selected from compounds in which c denotes 0 and the group (-A²¹-A²²-) is selected from the groups MG1 to MG4 as given above and in which the group (-A²⁴-A²⁵-A²⁶-) is selected from the groups MG5 to MG1 1 .

Especially preferred compounds of formula III are selected from the group of compounds of the following formulae,

Preferred compounds of formula IV are selected from compounds in which the groups (-A⁴¹-A⁴²-) and (-A⁴³-A⁴⁴-) are each and independently selected from the groups of MG1 to MG4 as given above.

Especially preferred compounds of formula IV are selected from the group of compounds of the following formulae: symmetrical ones (IVa and IVb):

- non-symmetrical ones (IVc):

Especially preferred are compounds of formula V wherein the A⁵¹ is selected from the following group of formulae Va’ to Vf and the mirror images of formulae Va’, Vd’ and Ve’

Ve’

Vf

Preferably R⁵¹ and R⁵² in formula V are selected of H, F, Cl, CN, NO2,

OCHs, COCHs, COC2H5, COOCHs, COOC2H5, CFs, C2F5, OCFs, OCHF2 and OC2F₅, in particular of H, F, Cl, CN, OCFI3 and OCF3, especially of H, F, CN and OCF_3. Preferred compounds of formula V are selected from the group of compounds of formulae VA to VD, preferably of formulae VA and/or VC, most preferably of formula VC,

wherein

LG⁵¹ is Z⁵¹-(CH₂)_Z-Z⁵²,

(F)o denotes FI and

(F)i denotes F. and the other parameters have the respective meanings given above including the preferred meanings. Preferably Z⁵¹-(CH₂)_z-Z⁵² denotes -0-C0-(CH₂)_n-C0-0-, -0-(CH₂)_n-0- or - (CH₂)_n -, more preferably -0-C0-(CFI₂)_n-C0-0-, wherein n denotes 3, 5, 7 or 9,

Particularly preferred compounds of formula VA are selected from the group of compounds of formulae VA-1 to VA-3

wherein the parameters have the respective meanings given above including the preferred meanings.

Particularly preferred compounds of formula VB are selected from the group of compounds of formulae VB-1 to VB-3

Compounds of formula VC are very much preferred. And of these particularly preferred compounds are selected from the group of compounds of formulae VC-1 to VC-3

Preferred compounds of formula VI are selected from compounds in which the groups (-A⁶¹-A⁶²-) and (-A⁶³-A⁶⁴-) are each and independently selected from the groups of MG1 to MG4 as given above.

Further preferred are compounds of formula VI wherein h denotes 0 and the groups (-A⁶¹-A⁶²-) and (-A⁶³-A⁶⁴-(A⁶⁵)h) in formula VI are not identical or not mirror images or wherein h denotes 1

In particular preferred compounds of formula VI are selected from the group of compounds of the following formulae,

Preferred compounds of formula VII are selected from compounds in which at least one of the groups -A⁷¹-Z⁷¹-A⁷²-(Z⁷²-A⁷³),-,

-(A⁷⁴-Z⁷³-)k-A⁷⁵-Z⁷⁴-A⁷⁶- are is selected from the groups of MGa to MGn and their mirror images

wherein wherein L is in each occurrence independently of each other preferably F, Cl, CN or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, very preferably F, Cl, CN, CFb, C2FI5, OCFI3, OC2FI5, COCFI3, COC2H5, COOCH3, COOC2H5, CF3, OCF3, OCHF2, OC2F5, in particular F, Cl, CN, CFI3, C2FI5, OCFI3, COCFI3 and OCF3, most preferably F, Cl, CFI3, OCH3 and COCH3 and r is in each occurrence independently of each other 0, 1 , 2, 3 or 4, preferably 0, 1 or 2.

or

wherein L is preferably F, Cl, CH3, OCH3 and COCH3_.

Further preferred are compounds of formula VII wherein the groups -A⁷¹- Z⁷¹-A⁷²-(Z⁷²-A⁷³)i- and -(A⁷⁴-Z⁷³-)k-A⁷⁵-Z⁷⁴-A⁷⁶- in formula VII are identical or mirror images with the proviso that at least one of Z⁷¹ to Z⁷⁴ is not a single bond.

Further preferred are compounds of formula VII, wherein i and k both denote 1 , more preferably one of i and k denotes 0 and the other 1 , most preferably i and k both denote 0.

Especially preferred compounds of formula VII are selected from the group of compounds of the following formulae

wherein R⁷¹ and R⁷², each and independently denote F or CN, preferably F.

Preferably, the medium according to the invention comprises one or more compounds of formula Y-5

in which

R^Y1 has the meaning defined above for formulae Y-1 to Y-4, and

R^Y3 denotes alkyl or alkenyl having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, and preferably

R^Y1 denotes an unsubstituted alkyl radical having 1 to 7 C

atoms, particularly preferably an n-alkyl radical, very preferably having 2 to 5 C atoms, or an unsubstituted alkenyl radical having 2 to 7 C atoms, particularly preferably a straight-chain alkenyl radical, very preferably having 2 to 5 C atoms, R^Y3 denotes an unsubstituted alkyl radical having 1 to 7 C atoms, particularly preferably having 2 to 5 C atoms.

In a preferred embodiment, the media according to the invention comprise one or more compounds of the formula Y-1 , preferably one or more compounds selected from the group of the compounds of the formulae Y-1 -1 and Y-1 -2,

in which the occurring groups have the meaning given above for formula Y-1 and preferably

R^Y1 on each occurrence, identically or differently, denotes an unsubstituted alkyl radical having 1 to 7 C atoms, preferably an n-alkyl radical, particularly preferably having 2 to 5 C atoms, or

an unsubstituted alkenyl radical having 2 to 7 C atoms, preferably a straight-chain alkenyl radical, particularly preferably having 2 to 5 C atoms,

R^Y2 on each occurrence, identically or differently, denotes an unsubstituted alkyl radical having 1 to 7 C atoms, preferably having 2 to 5 C atoms, or an unsubstituted alkoxy radical having 1 to 6 C atoms, preferably having 2, 3 or 4 C atoms.

In a preferred embodiment, the media according to the invention comprise one or more compounds of the formula Y-2, preferably one or more compounds selected from the group of compounds of the formulae Y-2-1 and Y-2-2,

in which the parameters have the meaning given above for formula Y-2 and preferably

R^Y1 denotes an alkyl radical having 2 to 5 C atoms, preferably having 3 to 5 C atoms, and

R^Y2 denotes an alkyl or alkoxy radical having 2 to 5 C atoms, preferably an alkoxy radical having 2 to 4 C atoms, or an alkenyloxy radical having 2 to 4 C atoms.

In a particularly preferred embodiment, the media according to the invention comprise one or more compounds of the formula Y-3, preferably one or more compounds selected from the group of the compounds of the formulae Y-3-1 and Y-3-2, very particularly preferably of the formula Y-3-2,

in which the parameters have the meaning given above formula Y-3 and preferably

In a further preferred embodiment, the medium comprises one or more compounds of the formula Y-4, preferably of the formula Y-4-1 ,

in which alkyl and alkyl’, independently of one another, denote alkyl having 1 to 7 C atoms, preferably having 2 to 5 C atoms.

Preferably, the liquid-crystal medium according to the invention comprises one or more compounds selected from the group of compounds of the formulae B and BS, preferably BS,

in which

R^B1, R^B2, independently of one another, denote an unsubstituted alkyl radical having 1 to 7 C atoms, preferably an n-alkyl radical, particularly preferably having 2 to 5 C atoms, or an unsubstituted alkenyl or alkoxy radical having 2 to 7 C atoms, particularly preferably having 2 to 5 C atoms, where preferably at least one of the radicals R^B1 and R^B2 denotes alkoxy.

Particularly preferably, the medium comprises one or more compounds of compound BS, preferably selected from the compounds of the formula BS-

in which alkoxy and alkoxy’ denote n-alkyloxy having 2 to 5 C atoms.

Preferably, the medium further comprises one or more compounds selected from the group of compounds of the formulae C and P

in which

R^C1 denotes an unsubstituted alkyl radical having 1 to 7 C

atoms or an unsubstituted alkenyl radical having 2 to 7 C atoms, preferably an n-alkyl radical, particularly preferably having 2, 3, 4 or 5 C atoms, and

R^C2 denotes an unsubstituted alkyl radical having 1 to 7 C

atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, both preferably having 2 to 5 C atoms, an unsub- stituted alkenyl radical having 2 to 7 C atoms, preferably having 2, 3 or 4 C atoms, more preferably a vinyl radical or a 1 -propenyl radical and in particular a vinyl radical,

R^P1 and R^P2, independently of one another, have one of the meanings given for R²¹ and R²² and preferably denote alkyl having 1 to 7 C atoms, preferably n-alkyl, particularly preferably n- alkyl having 1 to 5 C atoms, alkoxy having 1 to 7 C atoms, preferably n-alkoxy, particularly preferably n-alkoxy having 2 to 5 C atoms, alkoxyalkyl, alkenyl or alkenyloxy having 2 to 7 C atoms, preferably having 2 to 4 C atoms, preferably alkenyloxy,

if present, each, independently of one another, denote

preferably

denotes

and, if present,

preferably denotes Z^P1 to Z^P3 each, independently of one another, denote -CH2-CH2-, -CH2-O-, -CH=CH-, -CºC-, -COO- or a single bond, pref- erably -CH2-CH2-, -CH2-O- or a single bond and particu- larly preferably a single bond, i and j each, independently of one another, denote 0 or 1

(i ⁺ j) preferably denotes 0 or 1.

In a particularly preferred embodiment, the medium comprises one or more compounds of the formula C, preferably selected from the group of the compounds of the formulae C-1 to C-4, preferably selected from the group of the compounds of the formulae C and C-2,

in which alkyl and alkyl’, independently of one another, denote alkyl having 1 to 7 C atoms, preferably having 2 to 5 C atoms, alkenyl denotes an alkenyl radical having 2 to 5 C atoms, prefer- ably having 2 to 4 C atoms, particularly preferably 2 C atoms, alkenyl’ denotes an alkenyl radical having 2 to 5 C atoms, prefer- ably having 2 to 4 C atoms, particularly preferably having 2 to 3 C atoms, and alkoxy denotes alkoxy having 1 to 5 C atoms, preferably having 2 to 4 C atoms.

In a particularly preferred embodiment, the media according to the inven- tion comprise one or more compounds of the formula C-1 and/or one or more compounds of the formula C-2.

In a further preferred embodiment, the medium comprises one or more compounds of the formula C, selected from the group of the compounds of the formulae C-3 and C-4,

in which alkyl and alkyl’, independently of one another, denote alkyl having 1 to 7 C atoms, preferably having 2 to 5 C atoms, alkoxy denotes alkoxy having 1 to 5 C atoms, preferably having 2 to 4 C atoms. In a further preferred embodiment, the medium comprises one or more compounds of the formula P selected from the group of the compounds of the formulae P-1 to P-10, preferably selected from the group of the corn- pounds of the formulae P-1 to P-5,

in which the parameters have the meanings given above under formula P, and

Y^p denotes H or F, and preferably

R^P1 denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to

7 C atoms, and

R^P2 denotes alkyl having 1 to 7 C atoms, alkenyl having 2 to 7

C atoms or alkoxy having 1 to 6 C atoms, preferably alkyl or alkenyl, particularly preferably alkenyl.

In a further preferred embodiment, the medium comprises one or more compounds of the formula P-1 selected from the group of the compounds of the formulae P-1 a and P-1 b, preferably of the formula P-1 b,

in which alkyl and alkyl’, independently of one another, denote alkyl having 1 to 7 C atoms, preferably having 2 to 5 C atoms, alkoxy denotes alkoxy having 1 to 5 C atoms, preferably having 2 to 4 C atoms. In a further preferred embodiment, the medium comprises one or more compounds of the formula P-3 selected from the group of the compounds of the formulae P-3a and P-3b,

in which alkyl and alkyl’, independently of one another, denote alkyl having 1 to 7 C atoms, preferably having 2 to 5 C atoms, and alkenyl denotes alkenyl having 2 to 7 C atoms, preferably having 2 to 5 C atoms.

In a further preferred embodiment, the medium comprises one or more compounds of the formula P-4 selected from the group of the compounds of the formulae P-4a and P-4b,

in which alkyl and alkyl’, independently of one another, denote alkyl having 1 to 7 C atoms, preferably having 2 to 5 C atoms. In addition, the present invention relates to a process for the stabilisation of a liquid-crystalline medium which comprises one or more compounds selected from the group of the compounds of the formulae Y-1 to Y-4 and/or one or more compounds of the formula C and/or one or more corn- pounds of the formula P, characterised in that one or more compounds of the formula I are added to the medium.

The liquid-crystalline media according to the resent invention may corn- prise one or more chiral compounds. In a particularly preferred embodiment of the present invention, the liquid- crystalline media comprise one or more compounds of the formula

in which n denotes 0, 1 , 2, 3, 4, 5 or 6, preferably 2 or 4, particularly pref- erably 2, preferably in a concentration of 0.1 to 5%, particularly preferably of 0.2 to 1 %.

In a particularly preferred embodiment of the present invention, the liquid- crystalline media comprise one or more compounds of the formula Y-5-1

in which n denotes 0, 1 , 2, 3, 4, 5 or 6, preferably 1 , 2, 3 or 4, particularly preferably 1 , and m denotes 1 , 2, 3 or 4, preferably 1 , 2, or 3, particularly preferably 3, in a concentration of 0.1 to 5%, particularly preferably of 0.2 to 2%.

Particularly preferred embodiments of the present invention meet one or more of the following conditions, where the acronyms (abbreviations) are explained in Tables A to C and illustrated by examples in Tables D and E.

The liquid-crystalline medium has a birefringence of 0.060 or more, particularly preferably 0.070 or more.

The liquid-crystalline medium has a birefringence of 0.130 or less, particularly preferably 0.120 or less.

The liquid-crystalline medium has a birefringence in the range of 0.090 to 0.120, preferably of 0.095 to 0.115, particularly preferably of 0.100 to 0.110. iv. The liquid-crystalline medium has a negative dielectric anisotropy having an absolute value of 2.0 or more, particularly preferably 2.5 or more. v. The liquid-crystalline medium has a negative dielectric anisotropy having an absolute value of 7.0 or less, particularly preferably 6.5 or less. vi. The liquid-crystalline medium has a negative dielectric anisotropy having an absolute value in the range of 2.5 to 6.5, preferably of 3.0 to 6.0, particularly preferably of 3.0 to 5.5. vii. The liquid-crystalline medium comprises one or more particularly pre- ferred compounds of the formula C selected from the sub-formulae given below:

in which alkyl has the meaning given above and preferably, in each case independently of one another, denotes alkyl having 1 to 6, pref- erably having 2 to 5, C atoms and particularly preferably n-alkyl. viii. The total concentration of the compounds of the formula C in the mix- ture as a whole is 5% or more, preferably 15% or more, and is pref- erably in the range of from 10% to 60%, particularly preferably in the range of from 10% to 55%, and very particularly preferably in the range of from 15% to 50%. ix. The liquid-crystalline medium comprises one or more compounds of the formula C selected from the group of the compounds of the fol lowing formulae: CC-n-V and/or CC-n-Vm, particularly preferably CC-3-V, preferably in a concentration of 55% or less, particularly preferably 50% or less, and optionally additionally CC-3-V1 , preferably in a concentration of 15% or less, and/or CC-4-V, preferably in a concentration 20% or less, particularly preferably 10% or less. x. The total concentration of the compounds B and/or BS in the mixture as a whole is in the range of from 1 % to 20%, preferably from 2.5% to 17.5%, particularly preferably from 4% to 15%. xi. The total concentration of the compounds of the formula CC-3-V in the mixture as a whole is 10% or more, preferably 15% or more. xii. The proportion of compounds of the formulae Y-1 to Y-4 and

optionally B and/or BS and/or Y-5 in the mixture as a whole is in the range of from 10% to 95%, preferably from 40% to 90% and particularly preferable from 50% to 85%. xiii. The liquid-crystalline medium comprises one or more compounds of the formula C, preferably of the formulae C-1 and/or C-2, preferably in a total concentration of 20% or more, in particular of 25% or more, and very particularly preferably in the range of from 30% to 45%. xiv. The medium comprises one two or three compounds selected from the group of compounds of the formulae I, II, III, IV, V, VI, and VII., preferably I, II, VI and VII, particularly of formula 1-4, lla, VI-6 and VII-21. xv. The total concentration of the compounds of the formulae I, II, III, IV, V, VI, and VII in the medium is in the range of from 0.1 % to 10%, preferably from 0.5% to 8% and particularly preferably from 1 % to 5%.

The medium according to the invention particularly preferably comprises one or more compounds of the formula Y-1 in a total concentration in the range of from 5% to 30% and/or one or more compounds of the formula Y-2 in a total concentration in the range of from 3% to 30% and/or one or more compounds of the formula Y-3 in a total concentration in the range of from 5% to 30% and/or one or more compounds of the formula Y-4 in a total concentration in the range of from 1 % to 30%;

5 - 60% by weight of one or more compounds selected from the group of the compounds of the formulae Y-1 to Y-4 and III, and/or

10 - 60% by weight of one or more compounds selected from the group of the compounds of the formulae Y-1 to Y-4 and/or

10 - 60% by weight of one or more compounds of the formulae C and/or P, where the total content of all compounds in the medium is 100%. The liquid-crystal mixture preferably has a nematic phase range having a width of at least 80 K and a flow viscosity V20 of at most 30 mm² · s ¹ at 20°C. The liquid-crystal mixture according to the invention has a De of -0.5 to -8.0, in particular -1.5 to -6.0, and very particularly preferably -2.0 to -5.0, where De denotes the dielectric anisotropy.

The rotational viscosity gi is preferably 200 mPa s or less, in particular 150 mPa s or less, particularly preferably 120 mPa s or less.

The mixtures according to the invention are suitable for all VA-TFT applica- tions, such as, for example, VAN, MVA, (S)-PVA and ASV. Furthermore, they are particularly suitable for IPS (in-plane switching), FFS (fringe-field switching) and PALC applications having negative De.

The liquid-crystalline media according to the invention preferably comprise 4 to 15, in particular 5 to 12, and particularly preferably 10 or less, corn- pounds. These are preferably selected from the group of the compounds of the formulae I, II, III, IV, V, VI, VII, Y-1 , Y-2, Y-3, Y-4, Y-5 and/or C and/or P.

The liquid-crystalline media according to the invention may optionally also comprise more than 18 compounds. In this case, they preferably comprise 18 to 25 compounds.

Besides compounds of the formulae I, II, III, IV, V, VI, VII, Y-1 , Y-2, Y-3, Y- 4, and/or C and/or P, other constituents may also be present, for example in an amount of up to 45%, but preferably up to 35%, in particular up to 10%, of the mixture as a whole.

The media according to the invention may optionally also comprise a di- electrically positive component, the total concentration of which is preferably 10% or less, based on the entire medium. For the present application it is advantageous for the medium to have a nematic phase from in each case at least -20°C or less to 70°C or more, particularly preferably from -30°C or less to 80°C or more, very particularly preferably from -40°C or less to 85°C or more and most preferably from -40°C or less to 90°C or more.

The expression "have a nematic phase" here means on the one hand that no smectic phase and no crystallisation is observed at low temperatures at the corresponding temperature and on the other hand that no clearing occurs on heating from of the nematic phase. The investigation at low tem- peratures is carried out in a flow viscometer at the corresponding tempera- ture and checked by storage in test cells having a cell thickness corre- sponding to the electro-optical application for at least 100 hours. If the storage stability at a temperature of -20°C in a corresponding test cell is 1000 h or more, the medium is regarded as stable at this temperature. At temperatures of -30°C and -40°C, the corresponding times are 500 h and 250 h respectively. At high temperatures, the clearing point is measured in capillaries by conventional methods. The liquid-crystal media according to the invention have relatively low val- ues for the threshold voltage (Vo) in the range of from 1.4 V to 2.5 V, preferably from 1.5 V to 2.2 V, particularly preferably from 1.6 V to 2.0 V.

In addition, the liquid-crystal media according to the invention have high values for the VHR in liquid-crystal cells.

In freshly filled cells at 20°C in the cells, these are greater than or equal to 95%, preferably greater than or equal to 97%, particularly preferably greater than or equal to 98% and very particularly preferably greater than or equal to 99%, and after 5 minutes in the oven at 100°C in the cells, these are greater than or equal to 80%, preferably greater than or equal to 85%, particularly preferably greater than or equal to 90% and very particu- larly preferably greater than or equal to 95%. In general, liquid-crystal media having a low addressing voltage or thresh- old voltage here have a lower VHR than those having a higher addressing voltage or threshold voltage, and vice versa. These preferred values for the individual physical properties are preferably also in each case maintained by the media according to the invention in combination with one another.

In the present application, the term "compounds", also written as "com- pound(s)", means both one and also a plurality of compounds, unless explicitly indicated otherwise.

Unless indicated otherwise, the individual compounds are generally em- ployed in the mixtures in concentrations in each case from 1 % or more to 30% or less, preferably from 2% or more to 30% or less and particularly preferably from 3% or more to 16% or less.

In a preferred embodiment, the liquid-crystalline media according to the invention comprise one or more compounds selected from the group of compounds of the formulae I, II, III, IV, V, VI, VII, one or more compounds of the formula C, preferably selected from the group of the compounds of the formulae CC-n-V and CC-n-Vm, preferably CC-3-V, CC-3-V1 , CC-4-V and CC-5-V, particularly preferably selected from the group of the compounds CC-3-V, CC-3-V1 and CC-4-V, very par- ticularly preferably the compound CC-3-V, and optionally additionally the compound(s) CC-4-V and/or CC-3-V1 , one or more compounds of the formula Y-1 -1 , preferably of the formula CY-n-Om, selected from the group of the compounds of the formulae CY-3-02, CY-3-04, CY-5-02 and CY-5-04, one or more compounds of the formula Y-1 -2, preferably selected from the group of the compounds of the formulae CCY-n-m and CCY-n-Om, prefer- ably of the formula CCY-n-Om, preferably selected from the group of the compounds of the formulae CCY-3-02, CCY-2-02, CCY-3-01 , CCY-3-03, CCY-4-02, CCY-3-02 and CCY-5-02, optionally, preferably obligatorily, one or more compounds of the formula Y-2-2, preferably of the formula CLY-n-Om, preferably selected from the group of the compounds of the formulae CLY-2-04, CLY-3-02, CLY-3-03, one or more compounds of the formula Y-3-2, preferably of the formula CPY-n-Om, preferably selected from the group of the compounds of the formulae CPY-2-02 and CPY-3-02, CPY-4-02 and CPY-5-02, one or more compounds of the formula Y-4, preferably of the formula PYP-n-m, preferably selected from the group of the compounds of the formulae PYP-2-3 and PYP-2-4, one or more compounds of the formula BS, preferably the compound of the formula B(S)-20-05. The compounds of the formula I according to the invention are known to the person skilled in the art or can be prepared analogously by conven- tional processes known from the literature from commercially available 4- hydroxy-2,2,6,6-tetramethyl-1 -piperidinyl N-oxide (CAS No. 2226-96-2) (see, for example, Houben Weyl, Methoden der Organischen Chemie

[Methods of Organic Chemistry], Thieme-Verlag, Stuttgart).

For the present invention, the expression "dielectrically positive corn- pounds" means compounds having a De of > 1.5, the expression "dielectri- cally neutral compounds" means those where -1.5 < De < 1.5 and the ex- pression "dielectrically negative compounds” means those where De < -1.5. The dielectric anisotropy of the compounds is determined here by dissolv- ing 10% of the compounds in a liquid-crystalline host and determining the capacitance of the resultant mixture in each case in at least one test cell having a cell thickness of 20 pm with homeotropic and with homogeneous surface alignment at 1 kHz. The measurement voltage is typically 0.5 V to 1.0 V, but is always lower than the capacitive threshold of the respective liquid-crystal mixture investigated.

The host mixture used for dielectrically positive and dielectrically neutral compounds is ZLI-4792 and that used for dielectrically negative corn- pounds is ZLI-2857, both from Merck KGaA, Germany. The values for the respective compounds to be investigated are obtained from the change in the dielectric constant of the host mixture after addition of the compound to be investigated and extrapolation to 100% of the compound employed. The compound to be investigated is dissolved in the host mixture in an amount of 10%. If the solubility of the substance is too low for this purpose, the concentration is halved in steps until the investigation can be carried out at the desired temperature. The liquid-crystal media according to the invention may, if necessary, also comprise further additives, such as, for example, stabilisers and/or pleo- chroic dyes and/or chiral dopants in the usual amounts. The amount of these additives employed is preferably in total 0% or more to 10% or less, based on the amount of the entire mixture, particularly preferably 0.1 % or more to 6% or less. The concentration of the individual compounds em- ployed is preferably 0.1 % or more to 3% or less. The concentration of these and similar additives is generally not taken into account when speci- fying the concentrations and concentration ranges of the liquid-crystal compounds in the liquid-crystal media.

In a preferred embodiment, the liquid-crystal media according to the inven- tion comprise a polymer precursor which comprises one or more reactive compounds, preferably reactive mesogens, and, if necessary, also further additives, such as, for example, polymerisation initiators and/or polymeri- sation moderators, in the usual amounts. The amount of these additives employed is in total 0% or more to 10% or less, based on the amount of the entire mixture, preferably 0.1 % or more to 2% or less. The concentra- tion of these and similar additives is not taken into account when specifying the concentrations and concentration ranges of the liquid-crystal com- pounds in the liquid-crystal media. The compositions consist of a plurality of compounds, preferably 3 or more to 30 or fewer, particularly preferably 6 or more to 20 or fewer and very particularly preferably 10 or more to 16 or fewer compounds, which are mixed in a conventional manner. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent of the mixture. This is advantageously carried out at elevated temperature. If the selected temperature is above the clear- ing point of the principal constituent, completion of the dissolution operation is particularly easy to observe. However, it is also possible to prepare the liquid-crystal mixtures in other conventional ways, for example using pre- mixes or from a so-called "multibottle system".

The mixtures according to the invention exhibit very broad nematic phase ranges having clearing points of 65°C or more, very favourable values for the capacitive threshold, relatively high values for the holding ratio and at the same time very good low-temperature stabilities at -30°C and -40°C. Furthermore, the mixtures according to the invention are distinguished by low rotational viscosities gi. It goes without saying to the person skilled in the art that the media accord- ing to the invention for use in VA, IPS, FFS or PALC displays may also comprise compounds in which, for example, H, N, O, Cl, F have been replaced by the corresponding isotopes. The structure of the liquid-crystal displays according to the invention corre- sponds to the usual geometry, as described, for example, in

EP 0 240 379 A1.

The liquid-crystal phases according to the invention can be modified by means of suitable additives in such a way that they can be employed in any type of, for example, ECB, VAN, IPS, GH or ASM-VA LCD display that has been disclosed to date.

Table E below indicates possible dopants which can be added to the mix- tures according to the invention. If the mixtures comprise one or more dopants, it is (they are) employed in amounts of 0.01 to 4%, preferably 0.1 to 1.0%.

Stabilisers which can be added, for example, to the mixtures according to the invention, preferably in amounts of 0.01 to 6%, in particular 0.1 to 3%, are shown below in Table F.

For the purposes of the present invention, all concentrations are, unless explicitly noted otherwise, indicated in per cent by weight and relate to the corresponding mixture or mixture component, unless explicitly indicated otherwise.

All temperature values indicated in the present application, such as, for example, the melting point T(C,N), the smectic (S) to nematic (N) phase transition T(S,N) and the clearing point T(N,I), are indicated in degrees Celsius (°C) and all temperature differences are correspondingly indicated in differential degrees (° or degrees), unless explicitly indicated otherwise.

For the present invention, the term "threshold voltage" relates to the capa- citive threshold (Vo), also known as the Freedericks threshold, unless explicitly indicated otherwise.

All physical properties are and have been determined in accordance with "Merck Liquid Crystals, Physical Properties of Liquid Crystals", status Nov. 1997, Merck KGaA, Germany, and apply for a temperature of 20°C, and Dh is determined at 589 nm and De at 1 kFIz, unless explicitly indicated other- wise in each case.

The threshold voltages, as well as all other electro-optical properties, are determined using test cells produced at Merck. The test cells for the determination of De have a cell thickness of approximately 20 pm. The electrode is a circular ITO electrode having an area of 1.13 cm² and a guard ring. The orientation layers are SE-1211 from Nissan Chemicals, Japan, for homeotropic orientation (e| | ) and polyimide AL-1054 from JSR, Japan, for homogeneous orientation (e_±). The capacitances are determined using a Solatron 1260 frequency response analyser using a sine wave with a voltage of 0.3 V_rms. The light used in the electro-optical measurements is white light. A set-up using a commercially available DMS instrument from Autronic-Melchers, Germany, is used here. The characteristic voltages have been determined under perpendicular observation. The threshold (V10), mid-grey (V50) and saturation (V90) voltages have been determined for 10%, 50% and 90% relative contrast, respectively.

Unless indicated otherwise, a chiral dopant is not added to the liquid- crystal mixtures used, but the latter are also particularly suitable for appli- cations in which doping of this type is necessary.

The VHR is determined in test cells produced at Merck Japan. The test cells have alkali-free glass substrates and are provided with polyimide alignment layers with a layer thickness of 50 nm, which result in planar alignment of the liquid crystals. The layer gap is a uniform 3.0 pm or 6.0 pm. The surface area of the transparent ITO electrodes is 1 cm².

Unless indicated otherwise, the VHR is determined at 20°C (VHR20) and after 5 minutes in an oven at 100°C (VHR100) in a commercially available instrument from Autronic Melchers, Germany. The voltage used has a frequency of in a range from 1 Hz to 60 Hz, unless indicated more pre- cisely.

The stability to UV irradiation is investigated in a "Suntest CPS", a com- mercial instrument from Heraeus, Germany. The sealed test cells are irra- diated for between 30 min and 2.0 hours, unless explicitly indicated, with- out additional heating. The irradiation power in the wavelength range from 300 nm to 800 nm is 765 W/m² V. A UV "cut-off" filter having an edge wavelength of 310 nm is used in order to simulate the so-called window glass mode. In each series of experiments, at least four test cells are investigated for each condition, and the respective results are indicated as averages of the corresponding individual measurements.

The decrease in the voltage holding ratio (AVHR) usually caused by the exposure, for example by UV irradiation by LCD backlighting, is determined in accordance with the following equation (1 ): AVHR(t) = VHR(t ) - VHR(t = 0) (1) .

The rotational viscosity is determined using the rotating permanent magnet method and the flow viscosity in a modified Ubbelohde viscometer. For liquid-crystal mixtures ZLI-2293, ZLI-4792 and MLC-6608, all products from Merck KGaA, Darmstadt, Germany, the rotational viscosity values determined at 20°C are 161 mPa s, 133 mPa s and 186 mPa s respec- tively, and the flow viscosity values (v) are 21 mm²-s ¹, 14 mm²-s ¹ and 27 mm²-s ¹ respectively.

Flicker is defined as the difference between the maximum and the minimum transmittance divided by the average transmittance for a given frequency period, i.e. from the time of applying the positive polarity to the end of applying the negative polarity of the electric field.

Flicker is measured by using standard UB-FFS electro-optical (e/o) test cells, described above, applying an A/C voltage of L16, L127, L255 and/or V100, where L refers to the corresponding gray level and V100 to the voltage corresponding to 100% transmittance with 1 Flz to 30 Flz at a temperature of 20°C, 25 °C and or 60 °C.

D/C offset controlled adaptively in order to get the minimum flicker value with typical values of the D/C offset between 0 mV and +- 100 mV.

Flicker is measured at V100 (L255) which is the voltage maximum of the voltage-transmittance curve (V/T curve).

Gray level flicker is measured at a gray level of L127. The following symbols are used, unless explicitly indicated otherwise:

Vo threshold voltage, capacitive [V] at 20°C,

n_e extraordinary refractive index measured at 20°C and 589 nm, n₀ ordinary refractive index measured at 20°C and 589 nm,

Dh optical anisotropy measured at 20°C and 589 nm, e_± dielectric susceptibility perpendicular to the director at 20°C and 1 kHz,

e 1 1 dielectric susceptibility parallel to the director at 20°C and

1 kHz,

De dielectric anisotropy at 20°C and 1 kHz,

cl.p. or

T(N,I) clearing point [°C],

v flow viscosity measured at 20°C [mm²-s ¹],

gi rotational viscosity measured at 20°C [nnPa-s],

Ki elastic constant, "splay" deformation at 20°C [pN],

K₂ elastic constant, "twist" deformation at 20°C [pN],

K₃ elastic constant, "bend" deformation at 20°C [pN], and LTS low-temperature stability of the phase, determined in test cells,

VHR voltage holding ratio,

AVHR decrease in the voltage holding ratio,

Srel relative stability of the VHR.

The following examples explain the present invention without limiting it. However, they show the person skilled in the art preferred mixture con- cepts with compounds preferably to be employed and the respective con- centrations thereof and combinations thereof with one another. In addition, the examples illustrate the properties and property combinations that are accessible.

For the present invention and in the following examples, the structures of the liquid-crystal compounds are indicated by means of acronyms, with the transformation into chemical formulae taking place in accordance with Tables A to C below. All radicals C_nH_2n+i, C_mH_2m+1 and C1H21+1 or C_nH_2n, C_mH_2m and CiH2i are straight-chain alkyl radicals or alkylene radicals, in each case having n, m and I C atoms respectively. Table A shows the codes for the ring elements of the nuclei of the compound, Table B lists the bridging units, and Table C lists the meanings of the symbols for the left- and right-hand end groups of the molecules. The acronyms are composed of the codes for the ring elements with optional linking groups, followed by a first hyphen and the codes for the left-hand end group, and a second hyphen and the codes for the right-hand end group. Table D shows illustra tive structures of compounds together with their respective abbreviations.

Table A: Ring elements

Table B: Bridging members

Table C: End groups

On the left individually or in combiOn the right individually or in comnation bination

On the left only in combination On the right only in combination

-...n...- -C_nH2n- -...n... -CnFten-

-...M...- -CFH- -...M... -CFH-

-...D...- -CF₂- -...D... -CF₂-

-...V...- -CH=CH- -...V... -CH=CH-

-...Z...- -CO-O- -...Z... -CO-O-

-...Zl...- -O-CO- -...Zl... -O-CO-

-...K...- -CO- -...K... -CO-

-...W...- -CF=CF- -...W... -CF=CF- in which n and m are each integers, and the three dots are place- holders for other abbreviations from this table.

Table D

Table D shows exemplary compounds of formulae I to VII.

In this table n is an integer selected from 3 and 5 to 15, preferably from 3, 5, 7 and 9, unless explicitly defined otherwise.

F-PGI-O-n-O-PP-N

N-PZIGI-n-GZP-N

F-GIZIGI-n-GZG-F

N-P01 GI-n-G01 P-N

TO-GIGI-ZI-n-Z-GG-OT

TO-GIP-O-n-O-PP-N

N-PP-ZI-n-PP-N

F-GIP-SCO-n-COS-PP-N

N-PGI-S-n-S-GP-N wherein n is an integer from 12 to 15, preferably an even integer.

Further preferred compounds of formula I according to the present application are those abbreviated by the following acronyms:

m-P-O-n-O-PP-k

m-PY-ZI-n-Z-PP-N

m-CPGI-O-n-O-GPP-k wherein m and k are independently of each other an integer from 1 to 9 preferably from 1 to 7, more preferably from 3 to 5 and n is an integer from 1 to 15, preferably an odd integer from 3 to 9.

Table E

CC-n-mVI

PP-n-Om

CGP-n-m

CY-V-n

PY-V-n

CPY-V-n

CY-n-m

CCY-n-m

PYP-n-m

The following abbreviations are used:

(n, m and z are, independently of one another, each an integer, preferably 1 to 6) Table F shows chiral dopants which are preferably employed in the mix- tures according to the invention.

Table F

CM 45

R-5011 / S-5011 In a preferred embodiment of the present invention, the media according to the invention comprise one or more compounds selected from the group of the compounds from Table F.

Table G shows stabilisers which can be employed in the mixtures accord- ing to the invention in addition to the compounds of the formula I. The parameter n here denotes an integer in the range from 1 to 12. In particu- lar, the phenol derivatives shown can be employed as additional stabilisers since they act as antioxidants.

Table G Stabilisers which can be added, for example, to the mixtures according to the invention in amounts of 0-10% by weight are mentioned below.

n = 1 , 2, 3, 4, 5, 6 or 7

 In a preferred embodiment of the present invention, the media according to the invention comprise one or more compounds selected from the group of the compounds from Table G. Examples

The following examples explain the present invention without restricting it.

The physical properties make it clear to the person skilled in the art what

properties can be achieved and in what ranges they can be modified. In

particular, the combination of the various properties which can preferably

be achieved is thus well defined for the person skilled in the art.

Example Mixtures are prepared using the following compounds of the

formulae I, II and VII, respectively:

-1

1 -1

Mixture Example M1

0 CCY-3-01 7.0 % T₍N,i). [°C]: 80.5

CCY-4-02 7.0 % Dh (20°C, 589.3 nm): 0.1058

CCY-3-02 4.0 % n_e (20°C, 589.3 nm): 1 .5918

CPY-2-02 3.0 % De (20°C, 1 kHz): -5.2

, _c CLY-2-04 5.0 % si (20°C, 1 kHz): 9.6

CLY-3-03 4.5 % Ki (20°C) [pN] : 14.0

CLY-3-02 4.0 % K₃ (20°C) [pN]: 13.5

B(S)-20-05 6.0 % _g1 (20°C) [mPa s] 138

B(S)-20-04 6.0 % Vo (20°C) [V] 1 .70

0

CC-3-V 30.5 %

CY-3-02 17.0 %

PGIY-2-04 1 .5 %

PYP-2-3 1 .5 %

5 lla-1 -1 3.0 %

Mixture Example M2

CCY-3-01 6.5 % T₍N,i). [°C]: 80.5

CCY-4-02 5.5 % Dh (20°C, 589.3 nm): 0.1081

0

CCY-3-02 3.0 % n_e (20°C, 589.3 nm): 1 .5940

CPY-2-02 3.0 % De (20°C, 1 kHz): -5.4

CLY-2-04 6.0 % si (20°C, 1 kHz): 9.5

CLY-3-03 6.0 % Ki (20°C) [pN] : 14.3

5

CLY-3-02 4.0 % K₃ (20°C) [pN]: 13.9 B(S)-20-05 6.0 % g1 (20°C) [mPa s] 137

B(S)-20-04 6.0 % Vo (20°C) [V] 1.70

CC-3-V 30.5 %

CY-3-02 15.5 %

PGIY-2-04 2.5 %

PYP-2-3 2.5 %

VII-b-1 3.0 %

Mixture Example M3

CCY-3-01 5.0 % T₍N,i). [°C]: 81.0

CCY-4-02 5.5 % Dh (20°C, 589.3 nm): 0.1068

CCY-3-02 2.5 % n_e (20°C, 589.3 nm): 1.5919

CPY-2-02 2.5 % De (20°C, 1 kHz): -5.2

CLY-2-04 6.0 % si (20°C, 1 kHz): 9.4

CLY-3-03 6.0 % Ki (20°C) [pN] : 14.6

CLY-3-02 5.5 % K₃ (20°C) [pN]: 14.1

B(S)-20-05 6.0 % g1 (20°C) [mPa s] 146

B(S)-20-04 6.0 % Vo (20°C) [V] 1.74

CC-3-V 30.5 %

CY-3-02 17.5 %

PGIY-2-04 1.5 %

PYP-2-3 2.5 %

I -4-2-1 3.0 %

Mixture Example M4

CCY-3-01 6.5 % T₍N,i). [°C]: 81.5

CCY-4-02 5.0 % Dh (20°C, 589.3 nm): 0.1077

CCY-3-02 3.0 % n_e (20°C, 589.3 nm): 1.5931

CPY-2-02 3.0 % De (20°C, 1 kHz): -5.3

CLY-2-04 6.0 % si (20°C, 1 kHz): 9.4

CLY-3-03 6.0 % Ki (20°C) [pN] : 14.6 CLY-3-02 4.0 % K₃ (20°C) [pN]: 14.5

B(S)-20-05 6.0 % g1 (20°C) [mPa s] 129

B(S)-20-04 6.0 % Vo (20°C) [V] 1.74

CC-3-V 32.0 %

CY-3-02 16.0 %

PGIY-2-04 2.5 %

PYP-2-3 3.0 %

VI 1-21 -1 1.0 %

The comparative mixture example C-1 , which, apart from the bimesogen, comprises the same compounds and has the same birefringence as the Mixture Examples M1 to M4, is prepared as follows:

Comparative Mixture Example C1

CCY-3-01 7.0 % T(N,I). [°C]: 80

CCY-4-02 6.0 % Dh (20°C, 589.3 nm): 0.1069

CCY-3-02 3.0 % n_e (20°C, 589.3 nm): 1.5914

CPY-2-02 8.5 % De (20°C, 1 kHz): -5.2

CLY-2-04 5.0 % si (20°C, 1 kHz): 9.2

CLY-3-03 5.0 % Ki (20°C) [pN] : 14.1

B(S)-20-05 6.0 % K₃ (20°C) [pN]: 14.1

B(S)-20-04 6.0 % g1 (20°C) [mPa s] 116

CC-3-V 33.5 % Vo (20°C) [V] 1.73

CY-3-02 15.0 %

PGIY-2-04 5.0 % - l i e -

The mixtures M1 to M4 are investigated concerning flicker in test displays as described above. The following results are obtained:

All mixtures M1 to M4 according to the invention show advantageously low flicker resulting in superior image qualities of a displays comprising these mixtures.

All mixtures M1 to M4 according to the invention show less flicker compared to the mixture C1 which does not contain a bimesogenic additive.

Claims

Patent Claims

1 . A liquid-crystalline medium, characterised in that it comprises

a) one or more compounds selected from the group of compounds of the formulae Y-1 to Y-4

in which

-O-CO- in such a way that O atoms are not linked directly to one another, and m, n and o each, independently of one another, are 0 or 1 , and b) one or more bimesogenic compounds selected from the group of compounds of the formulae I, II, III, IV, V, VI and VII: R¹¹_A¹¹(-Z¹¹-A¹²-)_P -X¹¹-Sp¹¹-Xⁱ² -(A¹³-Z¹²-)_q A¹⁴-R¹² I

R²¹-A²¹-A²²-(CH₂)_a-A²³-A²⁴-R²² II

R⁴¹-A⁴¹-A⁴²-Z⁴¹-(CH₂)_d-Z⁴²-A⁴³-A⁴⁴-R⁴² IV

R51._A51._Z51.(_{C H 2})_e.Z52._A52.(A53)_{f. R}52 y

R⁶¹ -A⁶¹ -A⁶²-(CH₂)_g-Z⁶¹ -A⁶³-A⁶⁴-(A⁶⁵)_h-R⁶² VI

R¹¹ denotes a straight-chain or branched alkyl group, in which one or more non-adjacent and non-terminal CH₂ groups may be replaced, in each occurrence independently from one another, by -0-, -S-, -NH-, -N(CH3)-, -CO-, -COO-, -OCO-, -0-C0-0-, -S-CO-, -CO-S-, -CH=CH-, -CH=CF-, -CF=CF- or -CºC- in such a manner that oxygen atoms are not linked directly to one another,

R¹² denotes F, Cl, CN, NCS, or a straight-chain or branched alkyl group, which may be unsubstituted, mono- or polysubstituted by halogen or CN and in which one or more non-adjacent and non-terminal CFI₂ groups may be replaced, in each occurrence independently from one another, by -0-, -S-, -NH-, -N(CH₃)-, -CO-, -COO-, -OCO-, -0-C0-0-, -S-CO-, -CO-S-, -CH=CH-,

-CH=CF-, -CF=CF- or -CºC- in such a manner that oxygen atoms are not linked directly to one another, preferably F, Cl, CN, a straight-chain or branched alkyl, alkenyl or alkoxy group which may be unsubstituted, mono- or polysubstituted by halogen or CN, more preferably F or OCF3,

A¹¹ denotes 1 ,4-cyclohexylene,

A¹² to A¹⁴ each independently in each occurrence denote, 1 ,4- phenylene, wherein in addition one or more CFI groups may be replaced by N, trans-1 ,4-cyclo-hexylene in which, in addition, one or two non-adjacent CFI2 groups may be replaced by O and/or S, 1 ,4-cyclohexylene, naphthalene-2, 6-diyl, decahydro-naphthalene-2,6-diyl, 1 ,2,3,4-tetrahydro-naphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups, wherein one or more FI atoms may be substituted by F or Cl,

-CH2O-, -OCF2-, -CF2O-, -CH2CH2-, -(CH₂)₄-, -CF2CF2-, -CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or -CºC-, optionally substituted with one or more of F, S and/or Si, p and q is each and independently 0, 1 , 2, 3 or 4,

Sp¹¹ is a spacer group comprising 1 , 3 or 5 to 40 C atoms, wherein one or more non-adjacent and non-terminal CFte groups may also be replaced by -0-, -S-, -NH-, -N(CH₃)-, -CO-, -0-C0-, -S-CO-, -0-C00-, -CO-S-, -C0-0-, -CF₂-, -CF2O-, -OCF2- -C(OH)-, -CH(alkyl)-, -CH(alkenyl)-,-CH(alkoxyl)-, -CH(oxaalkyl)-, -CH=CH- or -CºC-, in such a way that no two O-atoms are adjacent to one another and no two groups selected from

-O-CO-, -S-CO-, -O-COO-, -CO-S-, -CO-O- and

-CFI=CFI- are adjacent to each other, preferably

-(CFhj_n-, with n 1 , 3 or an integer from 5 to 15, more preferably from 7 to 11 , most preferably an odd integer (i.e. 7, 9 or 11 ),

X¹¹ and X¹² are independently from one another selected from a single bond, -CO-O-, -O-CO-, -O-COO-, -0-,

-CH=CH-, -CºC-, -CF2-O-, -O-CF2-, -CF2-CF2-,

-CH2-O-, -O-CH2-, -CO-S-, -S-CO-, -CS-S-, -S-CS-, -S-CSS- and -S-, wherein in -X^{1 1}-Sp¹-X¹²-, two O atoms, two -CFI=CFI-, groups and two groups selected from -O- CO-, -S-CO-, -O-COO-, -CO-S- and -CO-O-, respectively are not linked directly to one another;

R²¹ and R²² denote independently FI, F, Cl, CN, NCS or a straight- chain or branched alkyl group, which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CFI2 groups to be replaced, in each occurrence independently from one another, by -0-, -S-,

preferably F, a straight-chain or branched alkyl or alkoxy group which may be unsubstituted, mono- or polysubstituted by halogen or CN,

more preferably F or OCF3,

A²¹ to A²⁴ denote independently in each occurrence a aryl-,

1 ,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-

1 .3-diyl, spiro[3.3]heptane-2, 6-diyl or dispiro[3.1 .3.1 ] decane-2, 8-diyl, it being possible for all these groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups, wherein one or more FI atoms may be substituted by F or Cl,

more preferably each independently in each occurrence

1 .4-phenylene, wherein in addition one or more CFI groups may be replaced by N or trans-1 ,4- cyclohexylene in which, in addition, one or two non- adjacent CFI2 groups may be replaced by O and/or S, it being possible for both ring groups to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl groups, wherein one or more FI atoms may be substituted by F or Cl, a is an integer from 1 to 15, preferably an odd (i.e.

uneven) integer and, more preferably 3, 5, 7, 9 or 1 1 .

R³¹ and R³² have each and independently from another one of the meanings as given for R²¹ and R²² under formula II, A³¹ to A³⁶ have each and independently from another one of the meanings as given for A²¹ to A²⁴ under formula II,

Z³¹ and Z³² are each independently in each occurrence,

-COO-, -OCO-, -0-C0-0-, -OCH2-, -CH2O-, -CH2CH2-, -(CH₂)₄-, -CF2CF2-, -CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or -CºC-, optionally substituted with one or more of F, S and/or Si, preferably -COO-, -OCO- or -O-CO-O-, more preferably -COO- or -OCO-, is an integer from 1 to 15, preferably an odd (i.e.

uneven) integer and, more preferably 3, 5, 7 or 9 and is 0 or 1 , preferably 0;

Z⁴¹ and Z⁴² are each independently in each occurrence,

-COO-, -OCO-, -O-CO-O-, -OCH2-, -CH2O-, -CH2CH2-, -(CH₂)₄-, -CF2CF2-, -CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or -CºC-, optionally substituted with one or more of F, S and/or Si, preferably -COO-, -OCO- or -O-CO-O-, more preferably -COO- or -OCO-. denotes an integer from 1 to 15, preferably an odd (i.e. uneven) integer and, more preferably 3, 5, 7 or 9. R⁵¹ and R⁵² have each and independently one of the meanings as given above for R²¹ under formula II,

Z⁵¹ and Z⁵² are each independently in each occurrence,

more preferably -COO- or -OCO-, e denotes an integer from 1 to 15, preferably an odd (i.e.

uneven) integer and, more preferably 3, 5, 7 or 9 and f is 0 or 1 ;

Z⁶¹ denotes -0-, -COO-, -OCO-, -O-CO-O-, -OCH2-, -CH₂0,

-CH2CH2-, -(CH₂)₄-, -CF2CF2-, -CH=CH-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or -CºC-, optionally substituted with one or more of F, S and/or Si, preferably -0-, -COO-, -OCO- or -O-CO-O-, more preferably -0-, -COO- or -OCO-, most preferably - COO- or -0C0-, h denotes 0 or 1 and g denotes an integer from 1 to 15, preferably an odd (i.e. uneven) integer and, more preferably 3, 5, 7 or 9;

Z⁷¹ to Z⁷⁴ each and independently denotes -COO-, -OCO-,

preferably -COO-, -OCO-, -O-CO-O-, -OCF2-, -CF2O- or a single bond

more preferably -COO-, -OCO-, -OCF2-, -CF2O- or a single bond,

uneven) integer and, more preferably 3, 5, 7 or 9 and i and k each and independently denotes 0 or 1.

2. The liquid-crystalline medium according to claim 1 , wherein the total concentration of the one or more bimesogenic compounds selected from the group of compounds of the formulae I, II, III, IV, V, VI and VII in the medium is in the range of from 0.1 % to 10% by weight.

3. The liquid-crystalline medium according to claim 1 or 2, wherein the

medium comprises one or more compounds selected from the group of compounds of the formulae B and BS,

in which

R^B1, R^B2, independently of one another, denote an alkyl radical

having 1 to 7 C atoms, or an alkenyl or alkoxy radical having 2 to 7 C atoms.

4. The liquid-crystalline medium according to one or more of claims 1 to 3, wherein the medium comprises one or more compounds of formula Y-5

in which

R^Y1 has the meaning defined in claim 1 for formulae Y-1 to Y-4, and

R^Y3 denotes alkyl or alkenyl having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen.

5. The liquid-crystalline medium according to one or more of claims 1 to 4, wherein the medium comprises one or more compounds selected from the group of compounds of formulae C and P

in which

R^C1 denotes an unsubstituted alkyl radical having 1 to 7 C

atoms or an unsubstituted alkenyl radical having 2 to 7 C atoms,

R^C2 denotes an unsubstituted alkyl radical having 1 to 7 C

atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, an unsubstituted alkenyl radical having 2 to 7 C atoms,

R^P1 and R^P2, independently of one another, have one of the meanings given for R²¹ and R²² in claim 1 ,

.independently of one another, denote

Z^P1 to Z^P3 independently of one another, denote -CH2-CH2-, -CH2-O-,

-CH=CH-, -CºC-, -COO- or a single bond, i and j independently of one another, are 0 or 1.

6. The medium according to claim 5, wherein the compounds of

formula C are selected from the group of compounds of formulae C-1 to C-4,

in which alkyl and alkyl’ independently of one another, denote alkyl having

1 to 7 C atoms, alkenyl denotes an alkenyl radical having 2 to 5 C atoms, , alkenyl’ denotes an alkenyl radical having 2 to 5 C atoms, and alkoxy denotes alkoxy having 1 to 5 C atoms.

7. The medium according to one or more of claims 1 to 6, wherein the medium comprises one or more compounds of formula I of claim 1 , in which the group -A¹¹(-Z¹¹-A¹²-)_p- is selected from the groups MG-11-1 to MG-11-43 and in which the group -(A¹³-Z¹²-)_q A¹⁴- is selected from the groups MG-12-1 to MG-12-125:

-Cyc- MG-11-1 -Cyc-Cyc- MG-11-2 -Cyc-Phe- MG-11-3 -Cyc-Phel MG-11-4 -Cyc-Phe-Cyc- MG-11-5 -Cyc-PheL-Cyc- MG-11-6

-Cyc-Cyc-Cyc- MG-11-7 -Cyc-Phe-Phe- MG-11-8 -Cyc-Phe-PheL- MG-11-9 -Cyc-PheL-Phe- MG-11-10 -Cyc-PheL-PheL- MG-11-11

-Cyc-Cyc-Phe- MG-11-12 -Cyc-Cyc-PheL- MG-11-13 -Cyc-Z-Cyc- MG-11-14 -Cyc-Z-Phe- MG-11-15 -Cyc-Z-PheL- MG-11-16

-Cyc-Z-Phe-Cyc- MG-11-17 -Cyc-Z-PheL-Cyc- MG-11-18 -Cyc-Z-Cyc-Cyc- MG-11-19 -Cyc-Z-Phe-Phe- MG-11-20 -Cyc-Z-Phe-PheL- MG-11-21 -Cyc-Z-PheL-Phe- MG-11-22 -Cyc-Z-PheL-PheL- MG-11-23 -Cyc-Z-Cyc-Phe- MG-11-24 -Cyc-Z-Cyc-PheL- MG-11-25 -Cyc-Phe-Z-Cyc- MG-11-26 -Cyc-PheL-Z-Cyc- MG-11-27

-Cyc-Cyc-Z-Cyc- MG-11-28 -Cyc-Phe-Z-Phe- MG-11-29 -Cyc-Phe-Z-PheL- MG-11-30 -Cyc-PheL-Z-Phe- MG-11-31 -Cyc-PheL-Z-PheL- MG-11-32

-Cyc-Cyc-Z-Phe- MG-11-33 -Cyc-Cyc-Z-PheL- MG-11-34 -Cyc-Z-Phe-Z-Cyc- MG-11-35 -Cyc-Z-PheL-Z-Cyc- MG-11-36 -Cyc-Z-Cyc-Z-Cyc- MG-11-37

-Cyc-Z-Phe-Z-Phe- MG-11-38 -Cyc-Z-Phe-Z-PheL- MG-11-39 -Cyc-Z-PheL-Z-Phe- MG-11-40 -Cyc-Z-PheL-Z-PheL- MG-11-41 -Cyc-Z-Cyc-Z-Phe- MG-11-42

-Cyc-Z-Cyc-Z-PheL- MG-11-43

-Cyc- MG-12-1

-Phe- MG-12-2 -PheL- MG-12-3

-Cyc-Cyc- MG-12-4

-Cyc-Phe- MG-12-5

-Cyc-PheL- MG-12-6 -Phe-Cyc- MG-12-7

-PheL-Cyc- MG-12-8 -Phe-Phe- MG-12-9 -PheL-PheL- MG-12-10 -PheL-Phe- MG-12-11 -Phe-PheL- MG-12-12 -Cyc-Phe-Phe- MG-12-13 -Cyc-Phe-PheL- MG-12-14 -Cyc-PheL-Phe- MG-12-15 -Cyc-PheL-PheL- MG-12-16 -Phe-Cyc-Phe- MG-12-17 -PheL-Cyc-Phe- MG-12-18

-Phe-Cyc-PheL- MG-12-19 -PheL-Cyc-PheL- MG-12-20 -Phe-Phe-Cyc- MG-12-21 -Phe-PheL-Cyc- MG-12-22 -PheL-Phe-Cyc- MG-12-23

-PheL-PheL-Cyc- MG-12-24 -Cyc-Phe-Cyc- MG-12-25 -Cyc-PheL-Cyc- MG-12-26 -Cyc-Cyc-PheL- MG-12-27 -Cyc-Cyc-Phe- MG-12-28

-PheL-Cyc-Cyc- MG-12-29 -Phe-Cyc-Cyc- MG-12-30 -Cyc-Cyc-Cyc- MG-12-31 -Phe-Phe-Phe- MG-12-32 -Phe-Phe-PheL- MG-12-33

-Phe-PheL-Phe- MG-12-34 -PheL-Phe-Phe- MG-12-35 -PheL-PheL-Phe- MG-12-36 -Phe-PheL-PheL- MG-12-37 -PheL-PheL-PheL- MG-12-38

-Cyc-Z-Cyc- MG-12-39 -Cyc-Z-Phe- MG-12-40 -Cyc-Z-PheL- MG-12-41 -Phe-Z-Cyc- MG-12-42

-PheL-Z-Cyc- MG-12-43 -Phe-Z-Phe- MG-12-44 -PheL-Z-PheL- MG-12-45 -PheL-Z-Phe- MG-12-46 -Phe-Z-PheL- MG-12-47 -Cyc-Z-Phe-Phe- MG-12-48 -Cyc-Z-Phe-PheL- MG-12-49 -Cyc-Z-PheL-Phe- MG-12-50 -Cyc-Z-PheL-PheL- MG-12-51 -Phe-Z-Cyc-Phe- MG-12-52 -PheL-Z-Cyc-Phe- MG-12-53

-Phe-Z-Cyc-PheL- MG-12-54 -PheL-Z-Cyc-PheL- MG-12-55 -Phe-Z-Phe-Cyc- MG-12-56 -Phe-Z-PheL-Cyc- MG-12-57 -PheL-Z-Phe-Cyc- MG-12-58

-PheL-Z-PheL-Cyc- MG-12-59 -Cyc-Z-Phe-Cyc- MG-12-60 -Cyc-Z-PheL-Cyc- MG-12-61 -Cyc-Z-Cyc-PheL- MG-12-62 -Cyc-Z-Cyc-Phe- MG-12-63

-PheL-Z-Cyc-Cyc- MG-12-64 -Phe-Z-Cyc-Cyc- MG-12-65 -Cyc-Z-Cyc-Cyc- MG-12-66 -Phe-Z-Phe-Phe- MG-12-67 -Phe-Z-Phe-PheL- MG-12-68

-Phe-Z-PheL-Phe- MG-12-69 -PheL-Z-Phe-Phe- MG-12-70 -PheL-Z-PheL-Phe- MG-12-71 -Phe-Z-PheL-PheL- MG-12-72 -PheL-Z-PheL-PheL- MG-12-73

-Cyc-Phe-Z-Phe- MG-12-74 -Cyc-Phe-Z-PheL- MG-12-75 -Cyc-PheL-Z-Phe- MG-12-76 -Cyc-PheL-Z-PheL- MG-12-77

-Phe-Cyc-Z-Phe- MG-12-78 -PheL-Cyc-Z-Phe- MG-12-79 -Phe-Cyc-Z-PheL- MG-12-80 -PheL-Cyc-Z-PheL- MG-12-81 -Phe-Phe-Z-Cyc- MG-12-82 -Phe-PheL-Z-Cyc- MG-12-83 -PheL-Phe-Z-Cyc- MG-12-84 -PheL-PheL-Z-Cyc- MG-12-85 -Cyc-Phe-Z-Cyc- MG-12-86 -Cyc-PheL-Z-Cyc- MG-12-87 -Cyc-Cyc-Z-PheL- MG-12-88

-Cyc-Cyc-Z-Phe- MG-12-89 -PheL-Cyc-Z-Cyc- MG-12-90 -Phe-Cyc-Z-Cyc- MG-12-91 -Cyc-Cyc-Z-Cyc- MG-12-92 -Phe-Phe-Z-Phe- MG-12-93

-Phe-Phe-Z-PheL- MG-12-94 -Phe-PheL-Z-Phe- MG-12-95 -PheL-Phe-Z-Phe- MG-12-96 -PheL-PheL-Z-Phe- MG-12-97 -Phe-PheL-Z-PheL- MG-12-98

-PheL-PheL-Z-PheL- MG-12-99

-Cyc-Z-Phe-Z-Phe- MG-1 2-100 -Cyc-Z-Phe-Z-PheL- MG-1 2-101 -Cyc-Z-PheL-Z-Phe- MG-1 2-102

-Cyc-Z-PheL-Z-PheL- MG-1 2-103 -Phe-Z-Cyc-Z-Phe- MG-1 2-104 -PheL-Z-Cyc-Z-Phe- MG-1 2-105 -Phe-Z-Cyc-Z-PheL- MG-1 2-106 -PheL-Z-Cyc-Z-PheL- MG-1 2-107

-Phe-Z-Phe-Z-Cyc- MG-1 2-108 -Phe-Z-PheL-Z-Cyc- MG-1 2-109 -PheL-Z-Phe-Z-Cyc- MG-1 2-1 10 -PheL-Z-PheL-Z-Cyc- MG-1 2-1 1 1 -Cyc-Z-Phe-Z-Cyc- MG-1 2-1 12

-Cyc-Z-PheL-Z-Cyc- MG-1 2-113 -Cyc-Z-Cyc-Z-PheL- MG-1 2-114 -Cyc-Z-Cyc-Z-Phe- MG-1 2-115 -Phe-Z-Cyc-Z-Cyc- MG-1 2-116 -Phe-Z-Cyc-Z-Cyc- MG-1 2-117 -Cyc-Z-Cyc-Z-Cyc- MG-1 2-118 -Phe-Z-Phe-Z-Phe- MG-12-119

-Phe-Z-Phe-Z-PheL- MG-12-120

-Phe-Z-PheL-Z-Phe- MG-12-121

-PheL-Z-Phe-Z-Phe- MG-12-122

-PheL-PheL-Z-Phe- MG-12-123

-Phe-PheL-Z-PheL- MG-12-124

-PheL-PheL-Z-PheL- MG-12-125 in which

Phe denotes 1 ,4-phenylene

PheL denotes a 1 ,4-phenylene group, which is substituted by 1 to 4 groups L, with L being F, Cl, CN, OH, NO2 or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, and

Cyc denotes 1 ,4-cyclohexylene.

8. The medium according to one or more of claims 1 to 6, wherein the medium comprises a compound of formula II of claim 1 , in which the groups (-A²¹-A²²-) and (-A²³-A²⁴-) are each and independently selected from the following groups -Phe-Phe-

-PheL-PheL-

-Phe-PheL-

-PheL-Phe- in which Phe, PheL and Cyc have the meanings given in claim 6.

9. The medium according to one or more of claims 1 to 6, wherein the medium comprises a compound of formula VII of claim 1 in which at least one of the groups -A⁷¹-Z⁷¹-A⁷²-(Z⁷²-A⁷³),- and

-(A⁷⁴-Z⁷³-)k-A⁷⁵-Z⁷⁴-A⁷⁶- is selected from the groups of MGa to MGn and their mirror images

in which

L on each occurrence, independently of each other, denotes F, Cl, CN or an optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, r on each occurrence independently of each other

is 0, 1 , 2, 3 or 4.

10. An Electro-optical display, characterised in that it comprises the liquid- crystalline medium according to one or more of claims 1 to 9.

11.The display according to claim 10, wherein the display is an FFS

display.

12. Use of the liquid-crystalline medium according to one or more of claims 1 to 9 in an electro-optical display.

13. Process for the preparation of the liquid-crystalline medium according to one or more of claims 1 to 9, characterised in that one or more corn- pounds of the formula Y-1 and/or Y-2 and/or Y-3 and/or Y-4 are mixed with one or more compounds selected from the group of compounds of the formulae I, II, III, IV, V, VI and VII.