The invention relates to a liquid-crystalline medium which comprises one or more compounds of the formula I,

in which

R ¹¹ and R ¹² each, independently of one another, denote H, an alkyl or alkoxy radical having 1 to 15 C atoms, where, in addition, one or more CFh groups in these radicals may each be replaced, independently of one another, by -CºC-, -CF2O-, -OCF2-

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

A ¹ in each occurrence independently of one another denotes a) a 1 ,4-cyclohexenylene or 1 ,4-cyclohexylene radical, in which one or two non-adjacent CFh groups may be replaced by -O- or -S-, b) a 1 ,4-phenylene radical, in which one or two CFI groups may be replaced by N, c) a radical from the group piperidine-1 ,4-diyl, 1 ,4-bicyclo[2.2.2]- octylene, naphthalene-2, 6-diyl, decahydronaphthalene-2,6- diyl, 1 ,2,3, 4-tetrahydronaphthalene-2, 6-diyl, phenanthrene- 2,7-diyl and fluorene-2,7-diyl, where the radicals a), b) and c) may be mono- or polysubstituted by halogen atoms, Z ¹ in each occurrence independently of one another

denotes -C0-0-, -0-C0-, -CF2O-, -OCF2-, -CFI2O-, -OCFI2-, -CFI2-, -CH2CH2-, -(CH ₂ ) ₄ -, -CH=CH-CH ₂ 0-, -C ₂ F ₄ -, -CH2CF2-, -CF ₂ CH ₂ -, -CF=CF-, -CH=CF-, -CF=CH-, -CH=CH-, -CºC- or a single bond, and

L ¹¹ and L ¹² each, independently of one another, denote F, Cl, CF3 or

CFIF ₂ , preferably FI or F, most preferably F, and one or more compounds selected from the group of compounds of formulae IIA, MB and IIC

in which

R ^2A , R ^2B and R ^2C 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 CH2 groups in these radicals may be replaced by -O-, -S-,

CO- in such a way that O atoms are not linked directly to one another,

L ¹ to L ⁴ each, independently of one another, denote F, Cl,

CFs or CHF ₂ ,

Z ² and Z ^2’ each, independently of one another, denote a single

bond, -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH ₂ O-, -OCH2-, -COO-, -OCO-, -C ₂ F ₄ -, -CF=CF-, - CH=CHCH ₂ 0-,

P denotes 0, 1 or 2 q denotes 0 or 1 , and v denotes 1 to 6.

Media of this type can be used, in particular, for electro-optical displays having active-matrix addressing based on the ECB effect and for IPS (in-plane switching) displays or FFS (fringe field switching) displays.

The principle of electrically controlled birefringence, the ECB effect or also DAP (deformation of aligned phases) effect, was described for the first time in 1971 (M.F. Schieckel and K. Fahrenschon, "Deformation of nematic liquid crystals with vertical orientation in electrical fields", Appl. Phys. Lett. 19 (1971 ), 3912). This was followed by papers by J.F. Kahn (Appl. Phys. Lett. 20 (1972), 1 193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869). The papers by J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982), 244) showed that liquid-crystalline phases must have high values for the ratio of the elastic constants K3/K1 , high values for the optical anisotropy Dh and values for the dielectric anisotropy of De < -0.5 in order to be suitable for use in high-information display ele- ments based on the ECB effect. Electro-optical display elements based on the ECB effect have a homeotropic edge alignment (VA technology = erti- cally aligned). Dielectrically negative liquid-crystal media can also be used in displays which use the so-called IPS or FFS effect.

Displays which use the ECB effect, as so-called VAN (vertically aligned nematic) displays, for example in the MVA (multi-domain vertical align- ment, for example: Yoshide, H. et al., paper 3.1 : "MVA LCD for Notebook or Mobile PCs ...", SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book I, pp. 6 to 9, and Liu, C.T. et al., paper 15.1 : "A 46-inch TFT-LCD HDTV Technology ...", SID 2004 International Sympo- sium, Digest of Technical Papers, XXXV, Book II, pp. 750 to 753), PVA (patterned vertical alignment, for example: Kim, Sang Soo, paper 15.4:

"Super PVA Sets New State-of-the-Art for LCD-TV", SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 760 to 763), ASV (advanced super view, for example: Shigeta, Mitzuhiro and Fukuoka, Hirofumi, paper 15.2: "Development of High Quality LCDTV", SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 754 to 757) modes, have established themselves as one of the three more recent types of liquid-crystal display that are currently the most important, in particular for television applications, besides IPS (in-plane switching) displays (for example: Yeo, S.D., paper 15.3: "An LC Display for the TV Application", SID 2004 International Symposium, Digest of Technical

Papers, XXXV, Book II, pp. 758 & 759) and the long-known TN (twisted nematic) displays. The technologies are compared in general form, for example, in Souk, Jun, SID Seminar 2004, seminar M-6: "Recent

Advances in LCD Technology", Seminar Lecture Notes, M-6/1 to M-6/26, and Miller, Ian, SID Seminar 2004, seminar M-7: "LCD-Television", Semi- nar Lecture Notes, M-7/1 to M-7/32. Although the response times of mod- ern ECB displays have already been significantly improved by addressing methods with overdrive, for example: Kim, Hyeon Kyeong et al., paper 9.1 : "A 57-in. Wide UXGA TFT-LCD for HDTV Application", SID 2004 Interna- tional Symposium, Digest of Technical Papers, XXXV, Book I, pp. 106 to 109, the achievement of video-compatible response times, in particular on switching of grey shades, is still a problem which has not yet been satis- factorily solved.

Industrial application of this effect in electro-optical display elements requires LC phases, which have to satisfy a multiplicity of requirements. Particularly important here are chemical resistance to moisture, air and physical influences, such as heat, infrared, visible and ultraviolet radiation and direct and alternating electric fields. Furthermore, industrially usable LC phases are required to have a liquid- crystalline mesophase in a suitable temperature range and low viscosity.

None of the hitherto-disclosed series of compounds having a liquid-crystal- line mesophase includes a single compound which meets all these require- ments. Mixtures of two to 25, preferably three to 18, compounds are there- fore generally prepared in order to obtain substances which can be used as LC phases. However, it has not been possible to prepare optimum phases easily in this way since no liquid-crystal materials having signifi cantly negative dielectric anisotropy and adequate long-term stability were hitherto available.

Matrix liquid-crystal displays (MLC displays) are known. Non-linear ele- ments which can be used for individual switching of the individual pixels are, for example, active elements (i.e. transistors). The term“active matrix” is then used, where a distinction can be made between two types:

1. MOS (metal oxide semiconductor) transistors on a silicon wafer as substrate 2. thin-film transistors (TFTs) on a glass plate as substrate. In the case of type 1 , the electro-optical effect used is usually dynamic scattering or the guest-host effect. The use of single-crystal silicon as sub- strate material restricts the display size, since even modular assembly of various part-displays results in problems at the joints.

In the case of the more promising type 2, which is preferred, the electro- optical effect used is usually the TN effect. A distinction is made between two technologies: TFTs comprising corn- pound semiconductors, such as, for example, CdSe, or TFTs based on polycrystalline or amorphous silicon. The latter technology is being worked on intensively worldwide. The TFT matrix is applied to the inside of one glass plate of the display, while the other glass plate carries the transparent counter electrode on its inside. Compared with the size of the pixel electrode, the TFT is very small and has virtually no adverse effect on the image. This technology can also be extended to fully colour-capable displays, in which a mosaic of red, green and blue filters is arranged in such a way that a filter element is opposite each switchable pixel.

The term MLC displays here covers any matrix display with integrated non- linear elements, i.e. besides the active matrix, also displays with passive elements, such as varistors or diodes (MIM = metal-insulator-metal).

MLC displays of this type are particularly suitable for TV applications (for example pocket TVs) or for high-information displays in automobile or air- craft construction. Besides problems regarding the angle dependence of the contrast and the response times, difficulties also arise in MLC displays due to insufficiently high specific resistance of the liquid-crystal mixtures [TOGASHI, S„ SEKIGUCHI, K„ TANABE, H„ YAMAMOTO, E„ SORI- MACHI, K„ TAJIMA, E„ WATANABE, H„ SHIMIZU, H„ Proc. Eurodisplay 84, Sept. 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, pp. 141 ff., Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, pp. 145 ff., Paris]. With decreasing resistance, the con- trast of an MLC display deteriorates. Since the specific resistance of the liquid-crystal mixture generally drops over the life of an MLC display owing to interaction with the inside surfaces of the display, a high (initial) resis- tance is very important for displays that have to have acceptable resistance values over a long operating period.

There is thus still a great demand for MLC displays having very high spe- cific resistance at the same time as a large working-temperature range, short response times and a low threshold voltage, with the aid of which various grey shades can be generated.

The disadvantage of the MLC-TN displays frequently used is due to their comparatively low contrast, the relatively high viewing-angle dependence and the difficulty of generating grey shades in these displays.

The market for VA, PS-VA, IPS, FFS and UB-FFS applications is looking for LC mixtures having fast response times and very high reliability. One approach for achieving fast response times is the identification of highly polar LC materials having low rotational viscosities, whose use in LC mixtures facilitates the desired effect. However, the use of highly polar LC materials of this type has an adverse effect on the reliability parameters, in particular after exposure to light.

The invention is based on the object of providing liquid-crystal mixtures, in particular for monitor and TV applications, based on the ECB, UB-FFS, IPS or FFS effect, which do not have the disadvantages indicated above, or only do so to a reduced extent. In particular, it must be ensured for moni- tors and televisions that they also work at extremely high and extremely low temperatures and at the same time have very short response times and at the same time have an improved reliability behaviour, in particular exhibit no or significantly reduced image sticking after long operating times. Compounds of the general formula

are mentioned as constituents of liquid crystalline media in European

Patent application No. EP 17161352.4. There also formulae

are disclosed. Flowever, only the one single compound

wherein n is 2 and m is 5 is used in the media of that document.

The invention thus relates to a liquid-crystalline medium which comprises at least one compound of the formula I and one or more compounds selected from the group of compounds of formulae IIA, MB and MC. These media are particularly well suitable in order to achieve liquid crystal displays that exhibit a fast response time and a good voltage holding ratio and also an excellent stability funder storage at deep temperatures sufficient for many applications.

The mixtures according to the invention preferably exhibit very broad nematic phase ranges with clearing points > 70°C, preferably > 75°C, in particular > 80°C, very favourable values of the capacitive threshold, rela- tively high values of the holding ratio and at the same time very good low- temperature stabilities at -20°C and -30°C, as well as very low rotational viscosity values and short response times. The mixtures according to the invention are furthermore distinguished by the fact that, in addition to the improvement in the rotational viscosity gi, relatively high values of the elas- tic constants K33 for improving the response times can be observed. The use of the compounds of the formula I in LC mixtures, preferably having negative dielectric anisotropy, the ratio of rotational viscosity gi and elastic constants K, is reduced.

Some preferred embodiments of the mixtures according to the invention are indicated below.

In the compounds of the formula I, R ¹¹ and R ¹² preferably each, independ- ently of one another, denote straight-chain alkyl, in particular CH3, n-C ₂ Hs , n-CsFl·, n-C ₄ H9, n-CsHn, n-C6Hi3- or n- C7H15, straight-chain alkoxy, in particular CH3-O, n-C ₂ Hs-0 , n-CsFF-O, n-C ₄ H9-0, n-CsHn-0 or n-C6Hi3-0, furthermore alkenyl, in particular CH3=CH, CH3CH=CH, CH3CH=CHCH ₂ or CH3CH2CH=CH, branched alkoxy, in particular (CH3)2CH(CH2)30, and alkenyloxy, in particular CH ₂ =CHO, CH ₂ =CH ₂ CHO, CH3CH ₂ =CHCHO or O CH ₂ CH ₂ CH=CHCH ₂ 0. R ¹¹ particularly preferably denotes straight-chain alkyl having 1 to 7 C atoms and R ¹² particularly preferably denotes straight-chain alkoxy having 1 to 6 C atoms, in particular methoxy, ethoxy, propoxy, butoxy, pentoxy or hexoxy. L ¹¹ and L ¹² in formula I preferably both denote F.

Preferred compounds of the formula I present in the media are the compounds of the formulae 1-1 to I-3, preferably of formula I-2 ,

in which the parameters have the meanings given above, R ¹¹ denotes straight-chain alkyl and R ¹² preferably denotes alkoxy and L ¹¹ and L ¹² preferably both denote F.

In a preferred embodiment the media comprise one or more compounds of the formula I selected from the group of compounds of formulae 1-0-1 to I- 0-3, preferably of formula I-0-2

in which the parameters have the meanings given above

In another preferred embodiment the media comprise one or more compounds of the formula I selected from the group of compounds of formulae l-S-1 to l-S-3, preferably of formula l-S-2, in which the parameters have the meanings given above.

In a preferred embodiment of the present invention the media comprise one or more compounds selected from the group of compounds of formulae 1-0-1 to I-0-3 and one or more compounds selected from the group of compounds of formulae l-S-1 to l-S-3.

The compounds of the formula I can be prepared, for example, as described in US 2005/0258399 or WO 02/055463 A1.

The media according to the invention preferably comprise one, two, three, four or more, preferably one, two or three, compounds of the formula I.

The compounds of the formula I are preferably employed in the liquid- crystalline medium in amounts of > 1 %, preferably > 3 % by weight, based on the mixture as a whole. Particular preference is given to liquid- crystalline media which comprise 1 to 40% by weight, very particularly preferably 2 to 30 % by weight, of one or more compounds of the formula I. Preferred embodiments of the liquid-crystalline medium according to the invention are indicated below: a) Liquid-crystalline medium which additionally comprises one or more compounds selected from the group of the compounds of the forrnu- lae 11 A, MB and IIC,

In the compounds of the formulae IIA and MB, Z ² may have identical or different meanings. In the compounds of the formula MB, Z ² and Z ^2' may have identical or different meanings. In the compounds of the formulae IIA, MB and IIC, R ^2A , R ^2B and R ^2C each preferably denote alkyl having 1 to 6 C atoms, in particular CH3, C2H5, n-C3H7, n-C ₄ Hg, n-CsHn .

In the compounds of the formulae IIA and MB, L ¹ , L ² , L ³ and L ⁴ pref- erably denote L ¹ = L ² = F and L ³ = L ⁴ = F, furthermore L ¹ = F and L ² = Cl, L ¹ = Cl and L ² = F, L ³ = F and L ⁴ = Cl, L ³ = Cl and L ⁴ = F. Z ² and Z ² ' in the formulae IIA and MB preferably each, independently of one another, denote a single bond, furthermore a -C2H ₄ - bridge.

If, in the formula MB, Z ² = -C ₂ H ₄ - or -CH ₂ O-, Z ^2' is preferably a single bond or, if Z ^2' = -C ₂ H ₄ - or -CH ₂ O-, Z ² is preferably a single bond. In the compounds of the formulae IIA and MB, (0)C _V H2 _V+ I preferably denotes OCvFhv _+i , furthermore CvFhv _+i . In the compounds of the for- mula IIC, (0)C _v H2v _+i preferably denotes CvFhv+i . In the compounds of the formula IIC, L ³ and L ⁴ preferably each denote F.

Preferred compounds of the formulae IIA, MB and IIC are indicated below:

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1 to 6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2 to 6 C atoms.

Particularly preferred mixtures according to the invention comprise one or more compounds of the formulae IIA-2, IIA-8, IIA-14, IIA-26, II-28, IIA-33, IIA-39, IIA-45, IIA-46, IIA-47, IIA-50, IIB-2, IIB-11 , IIB-16 and IIC-1.

The proportion of compounds of the formulae IIA and/or MB in the mixture as a whole is preferably at least 20 % by weight.

Particularly preferred media according to the invention comprise at least one compound of the formula IIC-1 ,

in which alkyl and alkyl ^* have the meanings indicated above, prefera- bly in amounts of > 3 % by weight, in particular > 5 % by weight and particularly preferably 5 to 25 % by weight. b) Liquid-crystalline medium which additionally comprises one or more compounds of the formula III, in which

R ³¹ and R ³² each, independently of one another, denote a straight- chain alkyl, alkoxy, alkenyl, alkoxyalkyl or alkoxy radical having up to 12 C atoms, and

Z ³ denotes a single

bond, -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -O CH ₂ -, -COO-, -OCO-, -C ₂ F ₄ -, -C ₄ H ₈ -, -CF=CF-.

Preferred compounds of the formula III are indicated below:

in which alkyl and

alkyl* each, independently of one another, denote a straight- chain alkyl radical having 1 to 6 C atoms. The medium according to the invention preferably comprises at least one compound of the formula Ilia and/or formula lllb.

The proportion of compounds of the formula III in the mixture as a whole is preferably at least 5 % by weight c) Liquid-crystalline medium additionally comprising a compound of the formula

preferably in total amounts of > 5 % by weight, in particular > 10 % by

weight.

Preference is furthermore given to mixtures according to the invention comprising the compound (acronym: CC-3-V1 ) preferably in amounts of 2 to 15 % by weight.

Preferred mixtures comprise 5 to 60 % by weight, preferably 10 to 55 % by weight, in particular 20 to 50 % by weight, of the compound of the formula (acronym: CC-3-V) Preference is furthermore given to mixtures which comprise a com pound of the formula (acronym: CC-3-V) and a compound of the formula (acronym: CC-3-V1 ) preferably in amounts of 10 to 60 % by weight. d) Liquid-crystalline medium which additionally comprises one or more tetracyclic compounds of the formulae

in which

R ^7-10 each, independently of one another, have one of the meanings indicated for R ^2A in Claim 5, and w and x each, independently of one another, denote 1 to 6.

Particular preference is given to mixtures comprising at least one compound of the formula V-9. e) Liquid-crystalline medium which additionally comprises one or more compounds of the formulae Y-1 to Y-6,

in which R ¹⁴ -R ¹⁹ each, independently of one another, denote an alkyl or alkoxy radical having 1 to 6 C atoms; z and m each, independently of one another, denote 1 to 6; x denotes 0, 1 , 2 or 3.

The medium according to the invention particularly preferably corn- prises one or more compounds of the formulae Y-1 to Y-6, preferably in amounts of > 5 % by weight. f) Liquid-crystalline medium additionally comprising one or more fluori- nated terphenyls of the formulae T-1 to T-21 ,

in which

R denotes a straight-chain alkyl or alkoxy radical having 1 to 6 C atoms, and m = 0, 1 , 2, 3, 4, 5 or 6 and n denotes 0, 1 , 2, 3 or 4.

R preferably denotes methyl, ethyl, propyl, butyl, pentyl, hexyl, meth- oxy, ethoxy, propoxy, butoxy, pentoxy.

The medium according to the invention preferably comprises the ter- phenyls of the formulae T-1 to T-21 in amounts of 2 to 30 % by weight, in particular 5 to 20 % by weight.

Particular preference is given to compounds of the formulae T-1 , T-2, T-4, T-20 and T-21. In these compounds, R preferably denotes alkyl, furthermore alkoxy, each having 1 to 5 C atoms. In the compounds of the formula T-20, R preferably denotes alkyl or alkenyl, in particular alkyl. In the compound of the formula T-21 , R preferably denotes alkyl.

The terphenyls are preferably employed in the mixtures according to the invention if the Dh value of the mixture is to be > 0.1. Preferred mixtures comprise 2 to 20 % by weight of one or more terphenyl corn- pounds selected from the group of the compounds T-1 to T-21. g) Liquid-crystalline medium additionally comprising one or more bi- phenyls of the formulae B-1 to B-3, in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1 to 6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2 to 6 C atoms.

The proportion of the biphenyls of the formulae B-1 to B-3 in the mix- ture as a whole is preferably at least 3 % by weight, in particular > 5 % by weight.

Of the compounds of the formulae B-1 to B-3, the compounds of the formula B-2 are particularly preferred.

Particularly preferred biphenyls are

in which alkyl ^* denotes an alkyl radical having 1 to 6 C atoms. The medium according to the invention particularly preferably comprises one or more compounds of the formulae B-1 a and/or B-2c. h) Liquid-crystalline medium comprising at least one compound of the formulae Z-1 to Z-7,

Z-7 in which R and alkyl have the meanings indicated above. i) Liquid-crystalline medium additionally comprising at least one corn- pound of the formulae 0-1 to 0-18,

in which R ¹ and R ² have the meanings indicated for R ^2A . R ¹ and R ² preferably each, independently of one another, denote straight-chain alkyl or alkenyl. Preferred media comprise one or more compounds of the formulae 0-1 , 0-3, 0-4, 0-6, 0-7, 0-10, 0-1 1 , 0-12, 0-14, 0-15, 0-16 and/or 0-17.

Particularly preferred comprise one or more compounds selected from the group of the compounds of the formula 0-17,

Mixtures according to the invention very particularly preferably corn- prise the compounds of the formula 0-10, 0-12, 0-16 and/or 0-17, in particular in amounts of 5 to 30 %.

Preferred compounds of the formulae 0-10 and 0-17 are indicated below:

The medium according to the invention particularly preferably corn- prises the tricyclic compounds of the formula 0-1 Oa and/or of the for- mula 0-1 Ob in combination with one or more bicyclic compounds of the formulae 0-17a to 0-17d. The total proportion of the compounds of the formulae 0-1 Oa and/or 0-1 Ob in combination with one or more compounds selected from the bicyclic compounds of the formulae 0-17a to 0-17d is 5 to 40 %, very particularly preferably 15 to 35 %. Very particularly preferred mixtures comprise compounds 0-1 Oa and

0-17a:

The compounds 0-1 Oa and 0-17a are preferably present in the mix- ture in a concentration of 15 to 35 %, particularly preferably 15 to 25 % and especially preferably 18 to 22 %, based on the mixture as a whole. Very particularly preferred mixtures comprise the compounds 0-1 Ob and

0-17a:

The compounds 0-1 Ob and 0-17a are preferably present in the mixture in a concentration of 15 to 35 %, particularly preferably 15 to 25 % and especially preferably 18 to 22 %, based on the mixture as a whole. Very particularly preferred mixtures comprise the following three corn- pounds:

The compounds 0-1 Oa, 0-1 Ob and 0-17a are preferably present in the mixture in a concentration of 15 to 35 %, particularly preferably 15 to 25 % and especially preferably 18 to 22 %, based on the mixture as a whole.

Preferred mixtures comprise at least one compound selected from the group of the compounds

7, in which R ¹ and R ² have the meanings indicated above. Preferably in the compounds 0-6, 0-7 and 0-17, R ¹ denotes alkyl or alkenyl hav- ing 1 to 6 or 2 to 6 C atoms respectively and R ² denotes alkenyl hav- ing 2 to 6 C atoms. Preferred mixtures comprise at least one compound of the formulae 0-6a, 0-6b, 0-7a, 0-7b, 0-17e, 0-17f, 0-17g and 0-17h:

in which alkyl denotes an alkyl radical having 1 to 6 C atoms.

The compounds of the formulae 0-6, 0-7 and 0-17e-h are preferably present in the mixtures according to the invention in amounts of 1 to 40 % by weight, preferably 2 to 35 % by weight and very particularly preferably 2 to 30 % by weight. j) Preferred liquid-crystalline media according to the invention comprise one or more substances which contain a tetrahydronaphthyl or naph- thyl unit, such as, for example, the compounds of the formulae N-1 to N-5,

in which R ^{1 N} and R ^2N each, independently of one another, have the meanings indicated for R ^2A , preferably denote straight-chain alkyl, straight-chain alkoxy or straight-chain alkenyl, and

Z ¹ and Z ² each, independently of one another,

denote -C ₂ H ₄ -, -CH=CH-, -(CH ₂ ) ₄ -, -(CH ₂ ) ₃ 0-, -0(CH ₂ ) ₃ -, - CH=CHCH ₂ CH ₂ -, -CH ₂ CH ₂ CH=CH-, -CH ₂ 0-, -OCH ₂ -, -CO

O-, -OCO-, -C ₂ F ₄ -, -CF=CF-, -CF=CH-, -CH=CF-, -CF ₂ O-, -OCF ₂ -, -CH ₂ - or a single bond. k) Preferred mixtures comprise one or more compounds selected from the group of the difluorodibenzochroman compounds of the formula BC, chromans of the formula CR, fluorinated phenanthrenes of the formulae PH-1 and PH-2, fluorinated dibenzofurans of the formula BF-1 and BF-2,

in which

R ^B1 , R ^B2 , R ^CR1 , R ^CR2 , R ¹ , R ² each, independently of one another, have the meaning of R ^2A . c is 0, 1 or 2 and d denotes 1 or 2. R ¹ and R ² preferably, independently of one another, denote alkyl or alkoxy having 1 to 6 C atoms. The compounds of the formulae BF-1 and BF-2 should not be identical to one or more compounds of the for- mula I.

The mixtures according to the invention preferably comprise the corn- pounds of the formulae BC, CR, PH-1 , PH-2 and/or BF in amounts of 3 to 20 % by weight, in particular in amounts of 3 to 15 % by weight.

Particularly preferred compounds of the formulae BC and CR are the compounds BC-1 to BC-7 and CR-1 to CR-5,

in which alkyl and alkyl* each, independently of one another, denote a

straight-chain alkyl radical having 1 to 6 C atoms, and alkenyl and

alkenyl* each, independently of one another, denote a

straight-chain alkenyl radical having 2 to 6 C atoms.

Very particular preference is given to mixtures comprising one, two or three compounds of the formula BC-2, BF-1 and/or BF-2.

I) Preferred mixtures comprise one or more indane compounds of the formula In,

in which

R ^{1 1} , R ¹² R ¹³ each, independently of one another, denote a straight- chain alkyl, alkoxy, alkoxyalkyl or alkenyl radical having 1 to 6 C atoms,

R ¹² and R ¹³ additionally denote halogen, preferably F,

i denotes 0, 1 or 2. Preferred compounds of the formula In are the compounds of the formulae ln-1 to In-16 indicated below:

Particular preference is given to the compounds of the formulae ln-1 , ln-2, ln-3 and ln-4.

The compounds of the formula In and the sub-formulae ln-1 to In-16 are preferably employed in the mixtures according to the invention in concentrations > 5 % by weight, in particular 5 to 30 % by weight and very particularly preferably 5 to 25 % by weight. m) Preferred mixtures additionally comprise one or more compounds of the formulae L-1 to L-1 1 ,

in which

R, R ¹ and R ² each, independently of one another, have the meanings indicated for R ^2A in Claim 5 and alkyl denotes an alkyl radical having

1 to 6 C atoms s denotes 1 or 2.

Particular preference is given to the compounds of the formulae L-1 and L-4, in particular L-4.

The compounds of the formulae L-1 to L-11 are preferably employed in concentrations of 5 to 50 % by weight, in particular 5 to 40 % by weight and very particularly preferably 10 to 40 % by weight. Particularly preferred mixture concepts are indicated below: (the acronyms used are explained in Table A. n and m here each, independently of one another, denote 1 to 15, preferably 1 to 6).

The mixtures according to the invention preferably comprise

- one or more compounds of the formula I in which L ¹¹ = L ¹² = F, R ¹ = alkyl and R ^1* = alkoxy;

and/or

- CPY-n-Om, in particular CPY-2-02, CPY-3-02 and/or CPY-5-02, pref- erably in concentrations > 5 %, in particular 10 to 30 %, based on the mixture as a whole, and/or - CY-n-Om, preferably CY-3-02, CY-3-04, CY-5-02 and/or CY-5-04, pref- erably in concentrations > 5 %, in particular 15 to 50 %, based on the mixture as a whole, and/or - CCY-n-Om, preferably CCY-4-02, CCY-3-02, CCY-3-03, CCY-3-01 and/or CCY-5-02, preferably in concentrations > 5 %, in particular 10 to 30 %, based on the mixture as a whole, and/or

- CLY-n-Om, preferably CLY-2-04, CLY-3-02 and/or CLY-3-03, preferably in concentrations > 5 %, in particular 10 to 30 %, based on the mixture as a whole.

Preference is furthermore given to mixtures according to the invention which comprise:

(n and m each, independently of one another, denote 1 to 6.)

- the compounds of formula I, preferably of formulae 1-1 to I-3, i.e. of formulae 1-0-1 to I-0-3 and/or l-S-1 to l-S-3, especially LB-3-04 and/or LB(S)-4-03 in a concentration in the range of from 1 to 20 %, more preferably from 2 to 15 %, particularly preferably from 3 to 12 % by weight and very particularly preferably from 4 to 11 % by weight

- CPY-n-Om and CY-n-Om, preferably in concentrations of 10 to 80 %, based on the mixture as a whole, and/or

- CPY-n-Om and CK-n-F, preferably in concentrations of 10 to 70 %, based on the mixture as a whole, and/or

- CPY-n-Om and PY-n-Om, preferably CPY-2-02 and/or CPY-3-02 and PY-3-02, preferably in concentrations of 10 to 45 %, based on the mixture as a whole, and/or - CPY-n-Om and CLY-n-Om, preferably in concentrations of 10 to 80 %, based on the mixture as a whole, and/or

- CCVC-n-V, preferably CCVC-3-V, preferably in concentrations of 2 to10 %, based on the mixture as a whole, and/or

- CCC-n-V, preferably CCC-2-V and/or CCC-3-V, preferably in concentra- tions of 2 to 10 %, based on the mixture as a whole, and/or

- CC-V-V, preferably in concentrations of 5 to 50 %, based on the mixture as a whole. In a particularly preferred embodiment of the present invention the medium comprises the compound B-20-05 in a concentration in the range of from

2 to 8 % and the compound CC-3-V in a concentration in the range of from 25 to 35 % and the compound CC-3-V1 in a concentration in the range of from 8 to 12 %.

The invention furthermore relates to an electro-optical display having active-matrix addressing based on the ECB, VA, PS-VA, PA-VA, IPS, PS- IPS, FFS or PS-FFS effect, characterised in that it contains, as dielectric, a liquid-crystalline medium according to one or more of Claims 1 to 11.

The liquid-crystalline medium according to the invention preferably has a nematic phase from < -20°C to > 70°C, particularly preferably from < -30°C to > 80°C, very particularly preferably from < -40°C to > 90°C. The expression "have a nematic phase" here means on the one hand that no smectic phase and no crystallisation are observed at low temperatures at the corresponding temperature and on the other hand that clearing still does not occur on heating from the nematic phase. The investigation at low temperatures is carried out in a flow viscometer at the corresponding tem- perature and checked by storage in test cells having a layer thickness cor- responding to the electro-optical use 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 referred to as stable at this temperature. At tempera- tures of -30°C and -40°C, the corresponding times are 500 h and 250 h respectively. At high temperatures, the clearing point is measured by con- ventional methods in capillaries.

The liquid-crystal mixture preferably has a nematic phase range of at least 60 K and a flow viscosity V20 of at most 30 mm ² · s ¹ at 20°C. The values of the birefringence Dh in the liquid-crystal mixture are gener- ally between 0.07 and 0.16, preferably between 0.08 and 0.13.

The liquid-crystal mixture according to the invention has a De of -0.5 to -8.0, in particular -2.5 to -6.0, where De denotes the dielectric anisotropy. The rotational viscosity gi at 20°C is preferably < 150 mPa s, in particu- lar < 120 mPa s.

The liquid-crystal media according to the invention have relatively low val- ues for the threshold voltage (Vo). They are preferably in the range from 1.7 V to 3.0 V, particularly preferably < 2.5 V and very particularly prefera- bly < 2.3 V.

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

In addition, the liquid-crystal media according to the invention have high values for the voltage holding ratio in liquid-crystal cells. In general, liquid-crystal media having a low addressing voltage or thresh- old voltage exhibit a lower voltage holding ratio than those having a higher addressing voltage or threshold voltage and vice versa. For the present invention, the term "dielectrically positive compounds" denotes compounds having a De > 1.5, the term "dielectrically neutral com- pounds" denotes those having -1.5 < De < 1.5 and the term "dielectrically negative compounds” denotes those having De < -1.5. The dielectric ani- sotropy of the compounds is determined here by dissolving 10 % of the compounds in a liquid-crystalline host and determining the capacitance of the resultant mixture in at least one test cell in each case having a layer thickness of 20 pm with homeotropic and with homogeneous surface align- ment 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. All temperature values indicated for the present invention are in °C.

The mixtures according to the invention are suitable for all VA-TFT applica- tions, such as, for example, VAN, MVA, (S)-PVA, ASV, PSA (polymer sustained VA) and PS-VA (polymer stabilized VA). They are furthermore suitable for IPS (in-plane switching) and FFS (fringe field switching) appli cations having negative De.

The nematic liquid-crystal mixtures in the displays according to the inven- tion generally comprise two components A and B, which themselves con- sist of one or more individual compounds.

Component A has significantly negative dielectric anisotropy and gives the nematic phase a dielectric anisotropy of < -0.5. Besides one or more corn- pounds of the formula I, it preferably comprises the compounds of the for- mulae IIA, MB and/or IIC, furthermore one or more compounds of the for- mula 0-17.

The proportion of component A is preferably between 45 and 100 %, in particular between 60 and 100 %. For component A, one (or more) individual compound(s) which has (have) a value of De < -0.8 is (are) preferably selected. This value must be more negative, the smaller the proportion A in the mixture as a whole.

Component B has pronounced nematogeneity and a flow viscosity of not greater than 30 mm ² · s ^-1 , preferably not greater than 25 mm ² · s ^-1 , at 20°C.

A multiplicity of suitable materials is known to the person skilled in the art from the literature. Particular preference is given to compounds of the formula 0-17.

Particularly preferred individual compounds in component B are extremely low-viscosity nematic liquid crystals having a flow viscosity of not greater than 18 mm ² · s ^-1 , preferably not greater than 12 mm ² · s ^-1 , at 20°C.

Component B is monotropically or enantiotropically nematic, has no smec- tic phases and is able to prevent the occurrence of smectic phases down to very low temperatures in liquid-crystal mixtures. For example, if various materials of high nematogeneity are added to a smectic liquid-crystal mix- ture, the nematogeneity of these materials can be compared through the degree of suppression of smectic phases that is achieved.

The mixture may optionally also comprise a component C, comprising compounds having a dielectric anisotropy of De >1.5. These so-called posi- tive compounds are generally present in a mixture of negative dielectric anisotropy in amounts of < 20 % by weight, based on the mixture as a whole. Besides one or more compounds of the formula I, the phases preferably comprise 4 to 15, in particular 5 to 12, and particularly preferably < 10, compounds of the formulae IIA, MB and/or IIC and optionally one or more compounds of the formula 0-17. Besides compounds of the formula I and the compounds of the formulae IIA, MB and/or IIC and optionally 0-17, other constituents may also be pre- sent, for example in an amount of up to 45 % of the mixture as a whole, but preferably up to 35 %, in particular up to 10 %.

The other constituents are preferably selected from nematic or nemato- genic substances, in particular known substances, from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl cyclohexanecarboxylates, phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclo- hexylnaphthalenes, 1 ,4-biscyclohexylbiphenyls or cyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolanes and substituted cinnamic acid esters.

The most important compounds which are suitable as constituents of liquid-crystal phases of this type can be characterised by the formula IV

R ²⁰ -L-G-E-R ²¹ IV in which L and E each denote a carbo- or heterocyclic ring system from the group formed by 1 ,4-disubstituted benzene and cyclohexane rings, 4,4’- disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidine and 1 ,3-dioxane rings, 2,6-disubsti- tuted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetra- hydroquinazoline,

G denotes -CFI=CFI- -N(0)=N- -CH=CQ- -CH=N(0)- -CºC- -CH2-CH2- -CO-O- -CH2-O- -CO-S- -CH2-S- -CH=N- -COO-Phe-COO- -CF2O- -CF=CF- -OCF2- -OCH2- -(CH ₂ )4- -(CH ₂ ) ₃ 0- or a C-C single bond, Q denotes halogen, preferably chlorine, or -CN, and R ²⁰ and R ²¹ each denote alkyl, alkenyl, alkoxy, alkoxyalkyl or alkoxycar- bonyloxy having up to 18, preferably up to 8, carbon atoms, or one of these radicals alternatively denotes CN, NC, NO ₂ , NCS, CF3, SF ₅ , OCF3, F, Cl or Br.

In most of these compounds, R ²⁰ and R ²¹ are different from one another, one of these radicals usually being an alkyl or alkoxy group. Other variants of the proposed substituents are also common. Many such substances or also mixtures thereof are commercially available. All these substances can be prepared by methods known from the literature.

It goes without saying for the person skilled in the art that the VA, IPS or FFS mixture according to the invention may also comprise compounds in which, for example, H, N, O, Cl and F have been replaced by the corres- ponding isotopes.

Polymerisable compounds, so-called reactive mesogens (RMs), for exam- pie as disclosed in U.S. 6,861 ,107, may furthermore be added to the mix- tures according to the invention in concentrations of preferably 0.01 to 5 % by weight, particularly preferably 0.2 to 2 % by weight, based on the mixture. These mixtures may optionally also comprise an initiator, as described, for example, in U.S. 6,781 ,665. The initiator, for example lrganox-1076 from BASF, is preferably added to the mixture comprising polymerisable compounds in amounts of 0 to 1 %. Mixtures of this type can be used for so-called polymer-stabilised VA modes (PS-VA) or PSA (polymer sustained VA), in which polymerisation of the reactive mesogens is intended to take place in the liquid-crystalline mixture. The prerequisite for this is that the liquid-crystalline compounds of the LC host do not react under the polymerisation conditions of the reactive mesogens, i.e.

generally on exposure to UV in the wavelength range from 320 to 360 nm. Liquid-crystalline compounds containing an alkenyl side chain, such as, for example, CC-3-V, exhibit no reaction under the polymerisation conditions (UV polymerisation) for the RMs. The mixtures according to the invention may furthermore comprise con- ventional additives, such as, for example, stabilisers, antioxidants, UV absorbers, nanoparticles, microparticles, etc.

The structure of the liquid-crystal displays according to the invention corre- sponds to the usual geometry, as described, for example, in

EP-A 0 240 379.

The following examples are intended to explain the invention without limit ing it. Above and below, per cent data denote per cent by weight; all tem- peratures are indicated in degrees Celsius.

Throughout the patent application, 1 ,4-cyclohexylene rings and 1 ,4- phenylene rings are depicted as follows:

The cyclohexylene rings are trans-1 ,4-cyclohexylene rings, unless explicitly mentioned otherwise.

Throughout the patent application and in the working examples, the struc- tures of the liquid-crystal compounds are indicated by means of acronyms. Unless indicated otherwise, the transformation into chemical formulae is carried out in accordance with Tables 1 to 3. All radicals C _n H _2n+i , C _m H _2m+1 and C _m H _{2m +1} or C _n H _2n and C _m H _2m are straight-chain alkyl radicals or alkylene radicals respectively in each case having n, m, m‘ or z C atoms respectively n, m, m‘, z each denote, independently of one another, 1 , 2,

3, 4, 5, 6, 7, 8, 9, 10, 1 1 or 12, preferably 1 , 2, 3, 4, 5 or 6. In Table 1 the ring elements of the respective compound are coded, in Table 2 the bridging members are listed and in Table 3 the meanings of the symbols for the left-hand or right-hand side chains of the compounds are indicated. Table 1: Ring elements

Table 3: Side chains

Left-hand side chain Right-hand side chain

Besides one or more compounds of the formula I, the mixtures according to the invention preferably comprise one or more compounds of the corn- pounds mentioned below from Table A.

Table A

The following abbreviations are used:

(n, m, m’, z: each, independently of one another, 1 , 2, 3, 4, 5 or 6;

(0)C _m H _2m+i means OCmF m+i or CmFhm+i)

B(S)-nO-Om

PB-n-m

CPP-n-m

CCY-n-Om

CCY-n-OmV

CC-n-mV1

CY-V-On

ccvc-v-v

CCOChrom-n-Om

CETNaph-n-Om

CZY-n-Om

PGP-n-2V1

The liquid-crystal mixtures which can be used in accordance with the invention are prepared in a manner which is conventional per se. In gen- eral, the desired amount of the components used in lesser amount is dis- solved in the components making up the principal constituent, advanta- geously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing.

By means of suitable additives, the liquid-crystal phases according to the invention can be modified 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.

The dielectrics may also comprise further additives known to the person skilled in the art and described in the literature, such as, for example, UV absorbers, antioxidants, nanoparticles and free-radical scavengers. For example, 0 to 15 % of pleochroic dyes, stabilisers, such as, for example, phenols, HALS (hindered amine light stabilisers), or chiral dopants may be added. Suitable stabilisers for the mixtures according to the invention are, in particular, those listed in Table C.

For example, 0 to 15 % of pleochroic dyes may be added, furthermore con- ductive salts, preferably ethyldimethyldodecylammonium 4-hexoxybenzo- ate, tetrabutylammonium tetraphenylboranate or complex salts of crown ethers (cf., for example, Haller et al., Mol. Cryst. Liq. Cryst, Volume 24, pages 249-258 (1973)), may be added in order to improve the conductivity or substances may be added in order to modify the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Substances of this type are described, for example, in DE-A 22 09 127, 22 40 864,

23 21 632, 23 38 281 , 24 50 088, 26 37 430 and 28 53 728. Table B

Table B indicates possible dopants which can be added to the mixtures according to the invention. If the mixtures comprise a dopant, it is added in amounts of 0.01 to 4 % by weight, preferably 0.01 to 3 % by weight.

R/S-2011 R/S-3011

R/S-1011

The mixtures according to the invention comprise at least one stabiliser from Table C given below.

Table C

Stabilisers, which can be added, for example, to the mixtures according to the invention in amounts of 0 to 10 % by weight, preferably 0.001 to 5 % by weight, in particular 0.001 to 1 % by weight, are indicated below.

35

Working examples:

The following examples are intended to explain the invention without limit- ing it. In the examples, m.p. denotes the melting point and C denotes the clearing point of a liquid-crystalline substance in degrees Celsius; boiling temperatures are denoted by m.p. Furthermore: C denotes crystalline solid state, S denotes smectic phase (the index denotes the phase type), N denotes nematic state, Ch denotes cholesteric phase, I denotes isotropic phase, T _g denotes glass-transition temperature. The number between two symbols indicates the conversion temperature in degrees Celsius an.

The host mixture used for determination of the optical anisotropy Dh of the compounds of the formula I is the commercial mixture ZLI-4792 (Merck KGaA). The dielectric anisotropy De is determined using commercial mix- ture ZLI-2857. The physical data of the compound to be investigated are obtained from the change in the dielectric constants of the host mixture after addition of the compound to be investigated and extrapolation to 100 % of the compound employed. In general, 10 % of the compound to be investigated are dissolved in the host mixture, depending on the solubility.

Unless indicated otherwise, parts or per cent data denote parts by weight or per cent by weight. Above and below:

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

n _e denotes extraordinary refractive index at 20°C and 589 nm, n ₀ denotes ordinary refractive index at 20°C and 589 nm,

Dh denotes optical anisotropy at 20°C and 589 nm,

e± denotes dielectric permittivity perpendicular to the director at

20°C and 1 kHz,

denotes dielectric permittivity parallel to the director at 20°C and 1 kHz,

De denotes dielectric anisotropy at 20°C and 1 kHz,

cl.p., T(N,l) denotes clearing point [°C], gi denotes rotational viscosity measured at 20°C [nnPa-s], deter- mined by the rotation method in a magnetic field,

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

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

K3 denotes elastic constant, "bend" deformation at 20°C [pN], and

LTS denotes low-temperature stability (nematic phase), deter- mined in test cells or in the bulk, as specified.

Unless explicitly noted otherwise, all values indicated in the present appli cation for temperatures, such as, for example, the melting point T(C,N), the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T(N,I) or cl.p., are indicated in degrees Celsius (°C). M.p. denotes melting point . Furthermore, Tg = glass state, C = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The numbers between these symbols represent the transition temperatures.

The term "threshold voltage" for the present invention relates to the capacitive threshold (Vo), also called the Freedericksz threshold, unless explicitly indicated otherwise. In the examples, as is generally usual, the optical threshold can also be indicated for 10 % relative contrast (V10).

The display used for measurement of the capacitive threshold voltage con- sists of two plane-parallel glass outer plates at a separation of 20 pm, which each have on the insides an electrode layer and an unrubbed poly- imide alignment layer on top, which cause a homeotropic edge alignment of the liquid-crystal molecules. The display or test cell used for measurement of the tilt angle consists of two plane-parallel glass outer plates at a separation of 4 pm, which each have on the insides an electrode layer and a polyimide alignment layer on top, where the two polyimide layers are rubbed antiparallel to one another and cause a homeotropic edge alignment of the liquid-crystal molecules.

Unless indicated otherwise, the VFIR is determined at 20°C (VFIR20) and after 5 minutes in an oven at 100°C (VFIR100) in a commercially available instrument Model 6254 from TOYO Corporation, Japan. The voltage used has a frequency of in a range from 1 Hz to 60 Hz, unless indicated more precisely.

The accuracy of the VHR measurement values depends on the respective value of the VHR. The accuracy decreases with decreasing values. The deviations generally observed in the case of values in the various magni- tude ranges are compiled in their order of magnitude in the following table.

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/m ² 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 or by LCD backlighting, is deter- mined in accordance with the following equation (1 ):

AVHR (t) = VHR (t) - VHR (t = 0)

In order to investigate the low-temperature stability, also known as "LTS", i.e. the stability of the LC mixture in the bulk against spontaneous crystallisation of individual components at low temperatures or the occurrence of smectic phases, as the case may be, several sealed bottles, each containing about 1 g of the material, are stored at one or more given temperatures, typically of -10°C, -20°C, -30°C and/or -40°C and it is inspected at regular intervals visually, whether a phase transition is observed or not. As soon as the first one of the samples at a given temperature shows a change time is noted. The time until the last inspection, at which no change has been observed, is noted as the respective LTS. The ion density from which the resistivity is calculated is measured using the commercially available LC Material Characteristics Measurement System Model 6254 from Toyo Corporation, Japan, using VHR test cells with AL16301 Polyimide (JSR Corp., Japan) having a 3.2pm cell gap. The measurement is performed after 5 min of storage in an oven at 60 °C or 100 °C.

The so-called ΉTR" denotes the helical twisting power of an optically active or chiral substance in an LC medium (in pm). Unless indicated otherwise, the HTP is measured in the commercially available nematic LC host mixture MLD-6260 (Merck KGaA) at a temperature of 20°C.

Unless explicitly noted otherwise, all concentrations in the present applica- tion are indicated in per cent by weight and relate to the corresponding mixture as a whole, comprising all solid or liquid-crystalline components, without solvents. All physical properties are determined in accordance with "Merck Liquid Crystals, Physical Properties of Liquid Crystals", Status November 1997, Merck KGaA, Germany, and apply for a temperature of 20°C, unless explicitly indicated otherwise. The following mixture examples having negative dielectric anisotropy are suitable, in particular, for liquid-crystal displays which have at least one planar alignment layer, such as, for example, IPS and FFS displays, in particular UB-FFS ( = ultra-bright FFS), and for VA displays.

Mixture examples and Comparative Examples

Comparative Mixture C1 is prepared as follows:

CY-3-04 20.0 % Clearing point /°C: 86.5

CCY-3-02 8.0 % Dh (589 nm, 20°C): 0.1089

CCY-3-03 6.0 % n _e (589 nm, 20°C): 1.5917

CCY-4-02 8.0 % De (1 kHz, 20°C): -4.3 CLY-3-02 5.0 % si (1 kHz, 20°C]: 8.0

CLY-3-03 5.0 % Ki (pN, 20°C): 14.6

CLY-2-042 6.0 % K ₃ (pN, 20°C): 15.1

PYP-2-3 10.0 % Vo (20°C)/ V: 1.99

CC-3-V 26.0 % gi (20°C)/ mPa s: 151 PGIY-2-04 6.0 % LTSbuik (-20°C) / h: > 336 å 100.0 % LTSbuik (-30°C) / h: > 144

This mixture has a rather poor response times, but good VHR values Comparative Mixture C2 is prepared as follows:

B(S)-20-05 6.0 %

CY-3-04 14.0 % Clearing point /°C: 86.0

CCY-3-02 6.0 % Dh (589 nm, 20°C): 0.1118 CCY-3-03 6.0 % n _e (589 nm, 20°C): 1.5968

CCY-4-02 6.0 % De (1 kHz, 20°C): -4.3

CLY-3-02 4.5 % si (1 kHz, 20°C]: 8.0

CLY-3-03 5.0 % Ki (pN, 20°C): 14.9

CLY-2-042 6.0 % K ₃ (pN, 20°C): 14.8 PYP-2-3 9.0 % Vo (20°C)/ V: 1.96

PGIY-2-04 6.0 % gi (20°C)/ mPa s: 132

CC-3-V 31.5 %

å 100.0 %

This mixture shows improved response times compared to that of the comparative example 1 , mainly due to it’s reduced gi, but a lower VHR. Mixture M1 is prepared as follows:

LB-3-04 10.0 % Clearing point /°C: 86.0

CY-3-04 14.0 % Dh (589 nm, 20°C): 0.1114

CCY-3-02 7.0 % n _e (589 nm, 20°C): 1.5954

CCY-3-03 4.0 % De (1 kHz, 20°C): -4.3

CCY-4-02 4.0 % si (1 kHz, 20°C]: 7.9

CLY-3-02 6.0 % Ki (pN, 20°C): 15.0 CLY-3-03 6.0 % K ₃ (pN, 20°C): 15.1

CLY-2-042 4.0 % Vo (20°C)/ V: 1.99

PYP-2-3 7.0 % gi (20°C)/ mPa s: 137

PGIY-2-04 4.0 % LTSbuik (-20°C) / h: > 1.000

CC-3-V 32.0 % LTSbuik (-30°C) / h: 312 å 100.0 %

Mixture M2 is prepared as follows:

LB(S)-4-03 10.0 % Clearing point /°C: 86.4 CY-3-04 20.0 % Dh (589 nm, 20°C): 0.1114

CCY-3-02 7.0 % n _e (589 nm, 20°C): 1.5964

CCY-3-03 3.0 % De (1 kHz, 20°C): -4.3

CCY-4-02 3.0 % si (1 kHz, 20°C]: 8.0

CLY-3-02 6.0 % Ki (pN, 20°C): 14.9 CLY-3-03 6.0 % K ₃ (pN, 20°C): 15.0

CLY-2-042 3.0 % Vo (20°C)/ V: 1.98

PYP-2-3 7.0 % gi (20°C)/ mPa-s: 137

PGIY-2-04 5.0 % LTSbuik (-20°C) / h: > 624

CC-3-V 31.0 % LTSbuik (-30°C) / h: > 768 å 100.0 %

Storage tests at deep temperatures are performed with the above mixtures in test cell having an appropriate thickness. Good VHR and, at the same time improved response time mainly due to it’s good value of (gi/ Ki) compared to CM1 as compiled in the following table. Table 1 : VHR values

(Remark: * All VHR values measured at 1 V, 1 Hz and at 60°C.)