The present invention relates to novel compounds, in particular for use in liquid-crystal media, but also 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 ECB (electrically controlled birefrin gence) effect with dielectrically negative liquid crystals in a homeotropic initial alignment. The liquid-crystal media according to the invention are distinguished by a particularly short response time in the displays accordi- ng to the invention at the same time as a high voltage holding ratio (VHR or also just HR for short).

The principle of electrically controlled birefringence, the ECB effect or 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). Papers by J.F. Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869) followed.

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) have shown that liquid-crystalline phases must have high values for the ratio between the elastic constants K3/K1 , high values for the optical anisotropy Dh and values for the dielectric anisotropy De of < -0.5 in order to be suitable for use for high-information display elements based on the ECB effect. Electro-optical display ele- ments based on the ECB effect have a homeotropic edge alignment (VA technology = vertically aligned or also VAN = vertical aligned nematic). Di- electrically negative liquid-crystal media can also be used in displays which use the so-called IPS (in-glane switching) effect.

Industrial application of this effect in electro-optical display elements requires LC phases which have to meet a multiplicity of requirements. Par- ticularly important here are chemical resistance to moisture, air and physi- cal influences, such as heat, radiation in the infrared, visible and ultraviolet regions, and direct and alternating electric fields. Furthermore, LC phases which can be used industrially are required to have a liquid-crystalline mesophase in a suitable temperature range and low viscosity. None of the series of compounds having a liquid-crystalline mesophase that have been disclosed hitherto includes a single compound which meets all these requirements. Mixtures of two to 25, preferably three to 18, compounds are therefore generally prepared in order to obtain substances which can be used as LC phases.

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 in general use is made of thin-film transistors (TFTs), which are generally arranged on a glass plate as substrate.

A distinction is made between two technologies: TFTs comprising corn- pound semiconductors, such as, for example, CdSe, or TFTs based on polycrystalline and, inter alia, amorphous silicon. The latter technology currently has the greatest commercial importance worldwide.

The TFT matrix is applied to the inside of one glass plate of the display, while the other glass plate carries the transparent counterelectrode 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 located opposite each switchable pixel. The TFT displays most used hitherto usually operate with crossed polaris- ers in transmission and are backlit. For TV applications, IPS cells or ECB (or VAN) cells are used, whereas monitors usually use IPS cells or TN (twisted nematic) cells, and notebooks, laptops and mobile applications usually use TN cells. The term MLC displays here encompasses any matrix display having inte grated 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, monitors and notebooks or for displays with a high information density, for example in automobile manufacture or aircraft construction. Besides prob- lems regarding the angle dependence of the contrast and the response times, difficulties also arise in MLC displays due to insufficiently high spe- cific resistance of the liquid-crystal mixtures [TOGASHI, S., SEKIGUCHI, K„ TANABE, H„ YAMAMOTO, E„ SORIMACHI, K„ TAJIMA, E„ WATA- NABE, 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 contrast 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) resistance is very im- portant for displays that have to have acceptable resistance values over a long operating period.

Displays which use the ECB effect have become established as so-called VAN (vertically aligned nematic) displays, besides IPS displays (for exam- pie: 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 and 759) and the long-known TN displays, as one of the three more recent types of liquid-crystal display that are currently the most im- portant, in particular for television applications.

The most important designs which may be mentioned are: MVA (multi- domain vertical alignment, for example: Yoshide, H. et al., Paper 3.1 :

“MVA LCD for Notebook or Mobile PCs ...“, SID 2004 International Sympo- sium, 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 Symposium, 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) and ASV (advanced super view, for example: Shigeta, Mitzuhiro and Fukuoka, Hirofumi, Paper 15.2:“Development of High Qual- ity LCDTV“, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 754 to 757). In general form, the technologies are compared, 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“, Seminar Lecture Notes, M-7/1 to M-7/32. Although the response times of modern 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 International Symposium, Digest of Technical Papers, XXXV, Book I, pp. 106 to 109, the achieve- ment of video-compatible response times, in particular in the switching of grey shades, is still a problem which has not yet been solved to a satis- factory extent.

ECB displays, like ASV displays, use liquid-crystalline media having nega- tive dielectric anisotropy (De), whereas TN and to date all conventional IPS displays use liquid-crystalline media having positive dielectric anisotropy.

In liquid-crystal displays of this type, the liquid crystals are used as dielec- trics, whose optical properties change reversibly on application of an elec- trical voltage.

Since in displays in general, i.e. also in displays in accordance with these mentioned effects, the operating voltage should be as low as possible, use is made of liquid-crystal media which are generally predominantly corn- posed of liquid-crystal compounds, all of which have the same sign of the dielectric anisotropy and have the highest possible value of the dielectric anisotropy. In general, at most relatively small proportions of neutral com- pounds and if possible no compounds having a sign of the dielectric ani- sotropy which is opposite to that of the medium are employed. In the case of liquid-crystal media having negative dielectric anisotropy for ECB dis plays, predominantly compounds having negative dielectric anisotropy are thus employed. The liquid-crystal media employed generally consist pre- dominantly and usually even essentially of liquid-crystal compounds having negative dielectric anisotropy.

In the media used in accordance with the present application, at most sig- nificant amounts of dielectrically neutral liquid-crystal compounds and gen- erally only very small amounts of dielectrically positive compounds or even none at all are typically employed, since in general the liquid-crystal dis plays are intended to have the lowest possible addressing voltages.

For many practical applications in liquid-crystal displays, the known liquid- crystal media are not sufficiently stable. In particular, their stability to irra diation with UV, but also even with conventional backlighting, results in an impairment, in particular, of the electrical properties. Thus, for example, the conductivity increases significantly.

The use of so-called“hindered amine light stabilisers”, HALS for short, has already been proposed for the stabilisation of liquid-crystal mixtures.

Nematic liquid-crystal mixtures having negative dielectric anisotropy which comprise a small amount of TINUVIN ^® 770, a compound of the formula

as stabilisers, are proposed, for example, in WO 2009/129911 A1 and in WO 2012/076105 A1. However, the corresponding liquid-crystal mixtures do not have adequate properties for some practical applications. Inter alia, they are not sufficiently stable to irradiation using typical CCFL (cold cath- ode fluorescent lamp) and in particular the typical, modern LED (light- emitting diode) backlighting.

Similar liquid-crystal mixtures are also known, for example, from

EP 2 182 046 A1 , WO 2008/009417 A1 , WO 2009/021671 A1 and

WO 2009/115186 A1. However, the use of stabilisers is not indicated therein.

According to the disclosure therein, these liquid-crystal mixtures may optionally also comprise stabilisers of various types, such as, for example, phenols and sterically hindered amines (hindered amine light stabilisers, HALS for short). However, these liquid-crystal mixtures are characterised by relatively high threshold voltages and by at best moderate stabilities. In particular, their voltage holding ratio drops after exposure. In addition, a yellowish discoloration often arises.

The use of various stabilisers in liquid-crystalline media is described, for example, in JP (S)55-023169 (A), JP (H)05-117324 (A), WO 02/18515 A1 and JP (H) 09-291282 (A).

EP 2 993 216 A1 proposes, inter alia, the compound of the formula

for the stabilisation of dielectrically positive liquid-crystal media.

WO 2009/129911 A1 proposes the compounds

besides several others as second stabilisers besides nitrogen heterocycles for the stabilisation of dielectrically negative liquid-crystal media.

EP 2 514 800 A2 proposes the use of compounds of the formulae

in which R ¹¹ , besides other meanings, may also be O or OH, but not H, for stabilisation purposes in liquid-crystal media. However, the chemical stability of these compounds with respect to hydrolysis and particularly their solubility in liquid-crystal media are in most cases inadequate for practical use.

WO 2016/146245 A1 proposes the compound of the formula

for stabilisation purposes in liquid-crystal media. This compound, and the compound

are also proposed in DE 2016 005 083 A1 for stabilisation purposes in liquid-crystal media. However, the chemical stability, particularly with respect to hydrolysis, and especially the solubility in liquid-crystal media in the case of these compounds is in most cases inadequate for practical use.

The ether-linked compounds of the formulae

are proposed in the as yet unpublished application DE 10 2016 009485.0 for use as stabilisers for liquid-crystal mixtures.

The liquid-crystal media of the prior art having correspondingly low addressing voltages have relatively low electrical resistance values or a low VHR and often result in undesired flicker and/or inadequate transmission in the displays. In addition, they are not sufficiently stable to heating and/or UV exposure, at least if they have correspondingly high polarity, as is necessary for low addressing voltages.

On the other hand, the addressing voltage of the displays of the prior art which have a high VHR is often too high, in particular for displays which are not connected directly or not continuously to the power supply network, such as, for example, displays for mobile applications.

In addition, the phase range of the liquid-crystal mixture must be suffi- ciently broad for the intended application of the display. Thus, the low- temperature storage stability in the cell and preferably in bulk at -30°C should be 240 h or more.

The response times of the liquid-crystal media in the displays must be im- proved, i.e. reduced. This is particularly important for displays for television or multimedia applications. In order to improve the response times, it has repeatedly been proposed in the past to optimise the rota- tional viscosity of the liquid-crystal media (gi), i.e. to achieve media having the lowest possible rotational viscosity. However, the results achieved here are inadequate for many applications and therefore make it appear desirable to find further optimisation approaches.

Adequate stability of the media to extreme loads, in particular to UV expo- sure and heating, is very particularly important. This is particularly difficult with simultaneous optimisation of the rotational viscosity. In particular in the case of applications in displays in mobile equipment, such as, for example, mobile telephones, this may be crucial, since, in particular in the case of these devices, relatively low addressing frequencies are preferably used.

The disadvantage of the MLC displays disclosed hitherto is due to their comparatively low contrast, the relatively high viewing-angle dependence and the difficulty in producing grey shades in these displays, as well as their inadequate VHR and their inadequate lifetime.

There thus continues to be a great demand for MLC displays having very high specific 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 produced and which have, in particular, a good and stable VHR. The invention has the object of providing MLC displays, not only for moni- tor and TV applications, but also for mobile telephones and navigation systems, which are based on the ECB effect, the IPS effect or on the FFS (fringe field switching) effect, as described in Lee, S.H., Lee, S.L. and Kim, H.Y.“Electro-optical characteristics and switching principle of nematic liquid crystal cell controlled by fringe-field switching”, Appl. Phys. Letts., Vol. 73, No. 20, pp. 2881 - 2883 (1998), do not have the disadvantages indicated above, or only do so to a lesser extent, and at the same time have very high specific resistance values. In particular, it must be ensured for mobile telephones and navigation systems that they also work at extremely high and extremely low temperatures.

Surprisingly, it has been found that it is possible to achieve liquid-crystal displays which have, in particular in FFS displays, a low threshold voltage with short response times and at the same time a sufficiently broad nema- tic phase, favourable, relatively low birefringence (Dh), good stability to decomposition by heating and by exposure to UV, good solubility and a stable, high VHR if use is made in these display elements of nematic liquid-crystal mixtures which comprise at least one compound of the form- ula I and in each case at least one compound of the formula II, preferably of the sub-formula 11-1 , and/or at least one compound selected from the group of the compounds of the formulae 111-1 to III-4, preferably of the formula MI-2, and/or B. 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 displays and for FFS displays.

The invention thus relates to a liquid-crystalline medium based on a mix- ture of polar compounds which comprises at least one compound of the formula I and at least one compound which contains one or more corn- pounds of the formula II and preferably in addition one or or more corn- pounds selected from the group of the compounds of the formulae MI-1 to MI-4, and/or of the formula B. The mixtures according to the invention exhibit very broad nematic phase ranges with clearing points > 70°C, very favourable values for the capaci- tive threshold, relatively high values for the holding ratio and at the same time good low-temperature stabilities at -20°C and -30°C, as well as very low rotational viscosities. The mixtures according to the invention are fur- thermore distinguished by a good ratio of clearing point and rotational vis- cosity and by a high negative dielectric anisotropy.

Surprisingly, it has now been found that it is possible to achieve liquid- crystalline media having a suitably high De, a suitable phase range and Dh which do not have the disadvantages of the prior-art materials, or at least only do so to a considerably reduced extent.

Surprisingly, it has been found here that the compounds of the formula I, even when used alone without additional heat stabilisers, result in consid- erable, in many cases adequate, stabilisation of liquid-crystal mixtures both to UV exposure and also to heating. This is the case, in particular, in most cases in which the parameter p in the compounds of the formula I used denotes 2 and n * p denotes 4 or 6. In an embodiment of the present invention, the compounds of the formula I in which p denotes 2 and n denotes 3 or 4 are therefore particularly preferred, and the use of precisely these compounds in the liquid-crystal mixtures according to the invention is particularly preferred. Preference is likewise given to the compounds of the formula I in which the group -Z ¹¹ -S ¹¹ -Z ¹² - denotes w-bisoxyalkylene, i.e. -0-S ¹¹ -0-.

However, adequate stabilisation of liquid-crystal mixtures both against UV exposure and against heating can also be achieved, in particular, if one or more further compounds, preferably phenolic stabilisers, are present in the liquid-crystal mixture in addition to the compound of the formula I, or the compounds of the formula I. These further compounds are suitable as heat stabilisers.

The invention thus relates to compounds of the formula I, and to a liquid- crystalline medium having a nematic phase and negative dielectric anisot- ropy which comprises a) one or more compounds of the formula I, preferably in a concentra- tion in the range from 1 ppm to 2.500 ppm, preferably to 2.000 ppm, preferably to 1 .500 ppm, particularly preferably to 1 .000 ppm, preferably in the range from 1 ppm to 500 ppm, particularly preferably in the range from 1 ppm to 250 ppm,

in which

R ¹¹ on each occurrence, independently of one another, denotes H, F, a straight-chain or branched alkyl chain having 1 -20 C atoms, in which one -CH ₂ - group or, if present, a plurality of -CH ₂ - groups may be replaced by -O- or -C(=0)-, but two adjacent -CH ₂ - groups cannot be replaced by -O-, and one or, if present, a plurality of -CH ₂ - groups may be replaced by-CH=CH- or -CºC-, and in which one H atom or a plurality of H atoms may be replaced by F, OR ¹³ , N(R ¹³ )(R ¹⁴ ) or R ¹⁵ ,

R ¹¹ preferably denotes FI or alkyl, particularly preferably alkyl, especially preferably n-alkyl and very particularly preferably n-butyl,

R ¹² on each occurrence, independently of one another, denotes a straight-chain or branched alkyl chain having 1 -20 C atoms, in which one -CFI ₂ - group or a plurality of -CFI ₂ - groups may be replaced by -O- or -C(=0)-, but two adjacent -CFI ₂ - groups cannot be replaced by -O-, a hydrocarbon radical which contains a cycloalkyl or alkylcycloalkyl unit and in which one -CFI ₂ - group or a plurality of -CFI ₂ - groups may be replaced by -O- or -C(=0)-, but two adjacent -CH ₂ - groups cannot be replaced by -0-, and in which one H atom or a plurality of H atoms may be replaced by F, OR ¹³ , N(R ¹³ )(R ¹⁴ ) or R ¹⁵ , or an aromatic or heteroaromatic hydrocarbon radical, in which one H atom or a plurality of H atoms may be replaced by F, OR ¹³ , N(R ¹³ )(R ¹⁴ ) or R ¹⁵ ,

R ¹² preferably denotes H, unbranched alkyl or branched alkyl, particularly preferably FI or unbranched alkyl,

R ¹³ on each occurrence, independently of one another, denotes a straight-chain or branched alkyl or acyl group having 1 to 10 C atoms, preferably n-alkyl, or an aro- matic hydrocarbon or carboxylic acid radical having 6- 12 C atoms,

R ¹⁴ on each occurrence, independently of one another, denotes a straight-chain or branched alkyl or acyl group having 1 to 10 C atoms, preferably n-alkyl, or an aro- matic hydrocarbon or carboxylic acid radical having 6-

12 C atoms,

R ¹⁵ on each occurrence, independently of one another, denotes a straight-chain or branched alkyl group having 1 to 10 C atoms, in which one -CFI ₂ - group or a plurality of -CFI ₂ - groups may be replaced by -O- or -C(=0)-, but two adjacent -CFI ₂ - groups cannot be replaced by -O-,

S ¹¹ and S ¹² on each occurrence, independently of one another, denote an alkylene group having 1 to 20 C atoms, which is branched or, preferably, straight-chain, preferably -(CFi ₂ -) _n having 1 -20 C atoms, preferably 1 - 10 C atoms, particularly preferably having 1 to 8 C atoms, in which one -CFI ₂ - group or, if present, a plurality of -CFI ₂ - groups may be replaced by -O- or -

C(=0)-, but two adjacent -CFI ₂ - groups cannot be replaced by -0-, and one or, if present, a plurality of - CH ₂ - groups may be replaced by -CH=CH- or -CºC- and in which one H atom or a plurality of H atoms may be replaced by F, OR ¹³ , N(R ¹³ )(R ¹⁴ ) or R ¹⁵ , or denote a single bond,

X ¹¹ denotes C,

Y ¹¹ to Y ¹⁴ each, independently of one another, denote methyl or ethyl, particularly preferably all denote either methyl or ethyl and very particularly preferably methyl,

Z ¹¹ to Z ¹⁴ on each occurrence, independently of one another, denote -0-, -(C=0)-, -0-(C=0)-, -(C=0)-0-, -0-(C=0)- 0-, -(N-R ¹³ )-, -N-R ¹³ -(C=0)- or a single bond if S ¹¹ is a single bond, but both Z ¹¹ and Z ¹² do not simultaneously denote -0-, and, however, if S ¹² is a single bond, both Z ¹³ and Z ¹⁴ do not simultaneously denote -0-, and, however, if -X ¹¹ [-R ¹¹ ] ₀ - is a single bond, both Z ¹² and Z ¹³ are not simultaneously -0-,

Z ¹¹ preferably denotes -0-,

Z ¹³ preferably denotes a single bond, n ^* p denotes an integer from 3 to 10, preferably to 8, P denotes 1 or 2, denotes (3-p), in the case where p = 1 n denotes 3, 4, 5, 6 or 8, particularly preferably 4, 6 or 8 very particularly preferably 4 or 6, and m denotes (10-n), and

in the case where p = 2, n denotes an integer from 2 to 4, preferably 2 or 3, partic- ularly preferably 3, and m denotes (4-n) denotes an organic radical having (m+n) bonding sites, preferably having up to 4 bonding sites, preferably an alkanediyl, alkanetriyl or alkanetetrayl unit having 1 to 30 C atoms, in which, in addition to the m groups R ¹² present in the molecule, but independently thereof, a further H atom may be replaced by R ¹² or a plurality of further H atoms may be replaced by R ¹² , preferably an alkanetetrayl unit having one or two valences on each of the terminal C atoms, in which one -CH ₂ - group or a plurality of -CH ₂ - groups may be replaced by -O- or -(C=0)- in such a way that two O atoms are not bonded directly to one another, or a substituted or unsubsti- tuted aromatic or heteroaromatic hydrocarbon radical having up to 10 valences, in which, in addition to the m groups R ¹² present in the molecule, but independently thereof, a further H atom may be replaced by R ¹² or a plurality of further H atoms may be replaced by R ¹² , and, in the case where p = 1 , -X ¹¹ [-R ¹¹ ] ₀ - may alternatively also denote a single bond,

and b) one or more compounds selected from the group of compounds of formulae II and III, preferably being dielectrically positive, preferably having a dielectric anisotropy of 3 or more each: in which R ² denotes H, unfluorinated or fluorinated alkyl or

unfluorinated or fluorinated alkoxy having 1 to 17 C atoms, or unfluorinated or fluorinated alkenyl, unfluori- nated or fluorinated alkenyloxy or unfluorinated or fluorinated alkoxyalkyl having 2 to 15 C atoms, in which

preferably alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms and preferably alkyl or alkenyl,

on each appearance, independently of one another, denote

in which R ^L , on each occurrence identically or differently, denotes H or alkyl having 1 to 6 C atoms, or

more preferably

L ²¹ and L ²² denote independently of each other H or F, preferably

L ²¹ denotes F,

X ² denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy hav- ing 2 or 3 C atoms, preferably F, Cl, -OCF ₃ ,

-O-CH2CF3, -0-CH=CH ₂ , -0-CH=CF ₂ or -CF ₃ , very preferably F, Cl, -0-CFI=CF ₂ or -OCF ₃ , m denotes 0, 1 , 2 or 3, preferably 1 or 2 and particularly preferably 1 , R ³ has the meaning(s) given for R ² , i.e. denotes H, unfluorinated or fluorinated alkyl or unfluorinated or fluorinated alkoxy having 1 to 17 C atoms, or

unfluorinated or fluorinated alkenyl, unfluorinated or fluorinated alkenyloxy or unfluorinated or fluorinated alkoxyalkyl having 2 to 15 C atoms, in which one or

preferably alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms and preferably alkyl or alkenyl,

on each appearance, independently of one another, have one of the meanings given for

L ³¹ and L ³² independently of one another, denote FI or F, preferably

L ³¹ denotes F,

X ³ denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy hav- ing 2 or 3 C atoms, preferably F, Cl, -OCF ₃ , -OCFIF ₂ , -0-CH ₂ CF ₃ , -0-CH=CF ₂ , -0-CH=CH ₂ or -CF ₃ , very preferably F, Cl, -0-CFI=CF ₂ , -OCFIF ₂ or -OCF ₃ ,

Z ³ denotes -CH ₂ CH ₂ -, -CF ₂ CF ₂ -, -COO-, trans- CFI=CFI-, trans- CF=CF-, -CFI ₂ 0- or a single bond, preferably -CFI ₂ CFI ₂ -, -COO-, trans- CFI=CFI- or a single bond and very preferably -COO-, trans- CFI=CFI- or a single bond, and n denotes 0, 1 , 2 or 3, preferably 1 , 2 or 3 and particularly preferably 1 , and c) optionally one or more compounds selected from the group of

compounds of formulae IV and V, preferably being dielectrically neutral : in which

R ⁴¹ and R ⁴² , independently of one another, have the meaning indicated above for R ² under formula II, preferably R ⁴¹ denotes alkyl and R ⁴² denotes alkyl or alkoxy or R ⁴¹ denotes alkenyl and R ⁴² denotes alkyl,

also these independently of one another, have one of the meanings given for

preferably one or more of

Z ⁴¹ and Z ⁴² independently of one another and, if Z ⁴¹ occurs twice, also these independently of one another, denote -CH ₂ CH ₂ -, -COO-, frans-CH=CH-, trans-CF=CF-, -CFI ₂ 0-, -CF ₂ 0-, -CºC- or a single bond, preferably one or more thereof denotes/denote a single bond, and

P denotes 0, 1 or 2, preferably 0 or 1

R ⁵¹ and R ⁵² , independently of one another, have one of the meanings given for R ⁴¹ and R ⁴² 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, have one of the meanings given for

preferably

denotes and, if present,

preferably denotes

Z ⁵¹ to Z ⁵³ 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, 1 or 2, more preferably 0 or 1 and, most preferably, 1 , d) again optionally, either alternatively or additionally, one or more compounds selected from the group of compounds of formulae VI to IX, preferably being dielectrically negative:

in which

R ⁶¹ , R ⁶² , R ⁷¹ , R ⁷² , R ⁸¹ and R ⁸² ,

independently of one another, have one of the meanings given for R ⁴¹ and R ⁴² above, preferably

R ⁶¹ denotes an unsubstituted alkyl radical having 1 to 7 C atoms, preferably a straight-chain alkyl radical, more preferably an n-alkyl radical, most preferably propyl or pentyl, an unsubstituted alkenyl radical having 2 to 7 C atoms, preferably a straight-chain alkenyl radical, particu- larly preferably having 2 to 5 C atoms, an unsubstituted alkoxy radical having 1 to 6 C atoms or an unsubstituted alkenyloxy radical having 2 to 6 C atoms,

R ⁶² denotes an unsubstituted alkyl radical having 1 to 7 C atoms, an unsubstituted alkoxy radical having 1 to 6 C atoms or an unsubstituted alkenyloxy radical having 2 to 6 C atoms, and denotes 0 or 1 ,

R ⁷¹ denotes an unsubstituted alkyl radical having 1 to 7 C atoms, preferably a straight-chain alkyl radical, more preferably an n-alkyl radical, most preferably propyl or pentyl, or an unsubstituted alkenyl radical having 2 to 7 C atoms, preferably a straight-chain alkenyl radical, particu- larly preferably having 2 to 5 C atoms,

R ⁷² denotes an unsubstituted alkyl radical having 1 to 7 C atoms, preferably having 2 to 5 C atoms, an unsubstituted alkoxy radical having 1 to 6 C atoms, preferably having 1 , 2, 3 or 4 C atoms, or an unsubstituted alkenyloxy radical having 2 to 6 C atoms, preferably having 2, 3 or 4 C atoms, R ⁸¹ denotes an unsubstituted alkyl radical having 1 to 7 C atoms, preferably a straight-chain alkyl radical, more preferably an n-alkyl radical, most preferably propyl or pentyl, or an unsubstituted alkenyl radical having 2 to 7 C atoms, preferably a straight-chain alkenyl radical, particu- larly preferably having 2 to 5 C atoms,

R ⁸² denotes an unsubstituted alkyl radical having 1 to 7 C atoms, preferably having 2 to 5 C atoms, an unsubstituted alkoxy radical having 1 to 6 C atoms, preferably having 1 , 2, 3 or 4 C atoms, or an unsubstituted alkenyloxy radical having 2 to 6 C atoms, preferably having 2, 3 or 4 C atoms, and

preferably

or

more preferably Z ⁸ denotes -(C=0)-0-, -CH2-O-, -CF2-O- or -CH2-CH2-,

preferably

-(C=0)-0- or -CH2-O-, and o denotes 0 or 1 ,

R ⁹¹ and R ⁹² independently of one another have the meaning given for R ⁷² above,

R ⁹¹ preferably denotes an alkyl radical having 2 to 5 C atoms, preferably having 3 to 5 C atoms,

R ⁹² preferably denotes an alkyl or alkoxy radical having 2 to 5 C atoms, more preferably an alkoxy radical having 2 to 4 C atoms, or an alkenyloxy radical having 2 to 4 C atoms.

p and q independently of each other denote 0 or 1 , and

(p + q) preferably denotes 0 or 1 , and in case

alternatively, preferably p = q = 1 e) again optionally, one or more compounds of formula IN, having both a high dielectric constant perpendicular to the director and parallel to the director, preferably in a concentration in the range from 1 % to 60 %, more preferably in the range from 5 % to 40 %, particularly preferably in the range from 8 % to 35 %,

R ¹¹ and R ¹² independently of each other denote alkyl, alkoxy,

fluorinated alkyl or fluorinated alkoxy, preferably having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms and preferably alkyl, alkoxy, alkenyl or alkenyloxy, most preferably alkyl, alkoxy or alkenyloxy, and R ¹¹ alternatively denotes R ¹ and R ¹² alternatively denotes X ¹ , R ¹ denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy, preferably having 1 to 7 C atoms, in which one - CH ₂ - group may be replaced by cyclo-propylene, 1 ,3- cyclobutylene, 1 ,3-cyclopentylene, 1 ,3-cyclo- pentenylene, preferably by cyclopropylene or 1 ,3- cyclopentylene, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms in which one - CH ₂ - group may be replaced by cyclo-propylene, 1 ,3- cyclobutylene, 1 ,3-cyclo-pentylene, 1 ,3-cyclo- pentenylene, preferably by cyclo-propylene or 1 ,3- cyclopentylene, and preferably alkyl or alkenyl,

1 ,3-Cyclopentenylene is a moiety selected from the group of the formulae

preferably most preferably

X ¹ denotes F, Cl, fluorinated alkyl, fluorinated alkenyl, fluorinated alkoxy or fluorinated alkenyoxy, the latter four groups preferably having 1 to 4 C atoms, preferably F, Cl, CF ₃ or OCF ₃ , in particular for formulae 1-1 and I-2 preferably F and for formula I-4 preferably OCF ₃ and f) again optionally, one or more compounds of formula B, having both a high dielectric constant perpendicular to the director and parallel to the director, preferably in a concentration in the range from 1 % to 60 %, more preferably in the range from 5 % to 40 %, particularly preferably in the range from 8 % to 35 %,

R ^B1 and R ^B2 independently of each other denote alkyl, alkoxy,

fluorinated alkyl or fluorinated alkoxy, preferably having 1 to 7 C atoms, in which one -CH ₂ - group may be replaced by cyclopropylene, 1 ,3-cyclobutylene, 1 ,3- cyclopentylene, 1 ,3-cyclo-pentenylene, preferably by cyclopropylene or 1 ,3-cyclopentylene, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, in which one -CH ₂ - group may be replaced by cyclopropylene, 1 ,3-cyclobutylene, 1 ,3- cyclopentylene, 1 ,3-cyclo-pentenylene, preferably by cyclopropylene or 1 ,3-cyclopentylene, and preferably alkyl, alkoxy, alkenyl or alkenyloxy, most preferably alkyl, alkoxy or alkenyloxy, and n denotes 0 or 1 , preferably 0. g) again optionally, one or more compounds of formula S, having both a high dielectric constant perpendicular to the director and parallel to the director, preferably in a concentration in the range from 1 % to 60 %, more preferably in the range from 5 % to 40 %, particularly preferably in the range from 8 % to 35 %,

R ^S1 and R ^S2 independently of each other denote alkyl, alkoxy,

fluorinated alkyl or fluorinated alkoxy, preferably having 1 to 7 C atoms, in which one -CH ₂ - group may be replaced by cyclopropylene, 1 ,3-cyclobutylene, 1 ,3- cyclopentylene, 1 ,3-cyclo-pentenylene, preferably by cyclopropylene or 1 ,3-cyclopentylene, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms, in which one -CH ₂ - group may be replaced by cyclopropylene, 1 ,3-cyclobutylene, 1 ,3- cyclopentylene, 1 ,3-cyclo-pentenylene, preferably by cyclopropylene or 1 ,3-cyclopentylene, and preferably alkyl, alkoxy, alkenyl or alkenyloxy, most preferably alkyl, alkoxy or alkenyloxy, and n denotes 0 or 1 , preferably 1.

The liquid-crystalline media in accordance with the present application preferably have a nematic phase.

In the compounds of the formula I, the groups N(R ¹³ )(R ¹⁴ ) may preferably also be amines.

Preference is given to the following embodiments:

P is 2, is an organic radical having 4 bonding sites, preferably an alkanetetrayl unit having 1 to 30 C atoms, in which, in addition to the m groups R ¹² present in the molecule, but independently thereof, a further H atom may be replaced by R ¹² or a plurality of further H atoms may be replaced by R ¹² , preferably an alkanetetrayl unit having one or two valences on each of the two terminal C atoms, in which one -CH ₂ - group or a plurality of -CH ₂ - groups may be replaced by -O- or -(C=0)- in such a way that two O atoms are not bonded directly to one another, or a substituted or unsubstituted aromatic or heteroaromatic hydrocarbon radical having up to 8 valences, in which, in addition to the m groups R ¹² present in the molecule, but independently thereof, a further H atom may be replaced by R ¹² or a plurality of further H atoms may be replaced by R ¹² ,

, \3,3 -tetray ) (benzene- , , ,5-tetray )

>CH-[CH ₂ ] _r CH< (where r e {0, 1 , 2, 3, 4, 5 to 18}, -CH ₂ -(CH-)-[CH ₂ ] _q -(CH-)-CH ₂ -< (where q e {0, 1 , 2, 3 4, 5 to 16},

, pentane-1 ,5-diyl, butane-1 ,4-diyl, propane-1 ,3-diyl, ethane-1 ,2-diyl, or

cyclohexylene).

In an alternative preferred embodiment,

p denotes 1.

In the present application, the elements all include their respective iso- topes. In particular, one or more H in the compounds may be replaced by D, and this is also particularly preferred in some embodiments. A corre- spondingly high degree of deuteration of the corresponding compounds enables, for example, detection and recognition of the compounds. This is very helpful in some cases, in particular in the case of the compounds of the formula I.

In the present application, alkyl particularly preferably denotes straight-chain alkyl, in par- ticular CH ₃ -, C ₂ H ₅ -, n- C ₃ H ₇ -, n-C ₄ H ₉ - or n-CsHu-, and alkenyl particularly preferably denotes CH ₂ =CH-, E-CH ₃ -CH=CH-,

CH ₂ =CH-CH ₂ -CH ₂ -, E-CH ₃ -CH=CH-CH ₂ -CH ₂ - or

E-(n-C ₃ H ₇ )-CH=CH-.

The liquid-crystalline media in accordance with the present application preferably comprise in total 1 ppm to 2500 ppm, preferably 1 ppm to 1500 ppm, preferably 1 to 600 ppm, even more preferably 1 to 250 ppm, preferably to 200 ppm, and very particularly preferably 1 ppm to 100 ppm, of compounds of the formula I.

In a preferred embodiment of the present invention, in the compounds of the formula I,

(benzene- , , - r y ) 2-) _3> -(CH ₂ -) _4> -(CH ₂ -) _5> -(CH ₂ -

ethane-1 ,2-diyl, propane-1 ,3-diyl, butane-1 ,4-diyl, pentane-1 ,5-diyl, hexane-1 ,6-diyl, heptane-1 ,7-diyl, octane-1 ,8-diyl, 1 ,4-phenylene), -phenylene), phenylene) or trans- 1 ,4-cyclohexylene) and/or

Z -S -Z - on each occurrence, independently of one another, denotes -0-, S ¹¹ -0-, -0-S ¹¹ -0-, -(C=0)-0-S ¹¹ -0-, -0-(C=0)-S ¹¹ -0-, -0-(C=0)-S ¹¹ -(C=0)-0-,

-0-S ¹¹ -(C=0)-0-, -(C=0)-0-S ¹¹ -C,

-(C=0)-0-S ¹¹ -0-(C=0)- or -(N-R ¹³ )-S ¹¹ -0-,

-(N-R ¹³ -C(=0)-S ¹¹ -(C=0)-0 or a single bond, preferably -0-, -S ¹¹ -0-, -0-S ¹¹ -0-, -(C=0)-0-S ¹¹ -0-,

-0-(C=0)-S ¹¹ -0- or -0-S ¹¹ -(C=0)-0-, and/or

S ¹¹ preferably denotes an alkylene group having 1 to 20 C atoms, and/or

R ¹¹ , if present, denotes alkyl, alkoxy or H, preferably H or alkyl, and/or

R ¹² denotes H, methyl, ethyl, propyl, isopropyl or 3-heptyl, or cyclohexyl.

In a preferred embodiment of the present application, in the compounds of the formula I, denotes a group selected from the group of the formulae

or

In a preferred embodiment of the present application, in the corn- pounds of the formula I, denotes a group selected from the group of the formulae

in a preferred embodiment of the present application, in the corn- pounds of the formula I in which p preferably denotes 1 ,

d eno es pre era y - - ¹ -0-, -S ¹¹ -0- or -O-S ¹¹ -, particularly preferably -0-S ¹¹ -0- or -S ¹¹ -0-.

In a further preferred embodiment of the present application, in the compounds of the formula I, the group

preferably denotes a group selected from the group of the formulae

In a further preferred embodiment of the present application in which p is 2, which may may be identical to or different from those described above, in the compounds of the formula I,

preferably denotes a group selected from the group of the formulae In a further preferred embodiment of the present invention, which may be identical to or different from those described above, in the compounds of the formula I, the group

on each occurrence, independently of one another, denotes

In a particularly preferred embodiment of the present invention, in the compounds of the formula I, all groups

present have the same meaning. These compounds are highly suitable as stabilisers in liquid-crystal mix- tures. In particular, they stabilise the VHR of the mixtures against UV exposure. In a preferred embodiment of the present invention, the media according to the invention comprise in each case one or more compounds of the formula I selected from the following group of the compounds of the for- mulae 1-1 to 1-11 , preferably selected from the group of the compounds of the formulae 1-1 to 1-10, particularly preferably selected from the group of the compounds of the formulae I-2 to 1-10 and very particularly preferably of the formula I-2 and/or I-3 and/or I-4,



 -46

and

In an even more preferred embodiment of the present invention, the media according to the invention comprise in each case one or more compounds of the formula I selected from the group of the following compounds of the formulae 1-1 and/or I-3 to I -7 and/or I-8 and/or I-9 and/or 1-10.

In an even more preferred embodiment of the present invention, the media according to the invention comprise in each case one or more compounds of the formula I selected from the group of the following compounds of the formulae I-2 and/or I -7 and/or I-9 and/or 1-10.

In addition to the compounds of the formula I or the preferred sub-formulae thereof, the media in accordance with the present invention preferably comprise one or more compounds of formula II in a total concentration in the range from 1 % or more to 90 % or less, preferably from 10 % or more to 80 % or less, particularly preferably from 20 % or more to 70 % or less. In a preferred embodiment of the present invention, the liquid-crystal medium comprises one or more, preferably dielectrically positive, compounds preferably having a dielectric anisotropy of 3 or more, selected from the group of the compounds of the formulae 11-1 and II-2:

in which the parameters have the respective meanings indicated above under formula II, and L ²³ and L ²⁴ , independently of one another, denote FI or F, preferably L ²³ denotes F, and has one of the meanings given for

and, in the case of formulae 11-1 and II-2, X ² preferably denotes F or OCF ₃ , particularly preferably F, and, in the case of formula II-2,

and , independently of one another, preferably denote

In addition to the compounds of the formula I or the preferred sub-formulae thereof, the media in accordance with the present invention preferably comprise one or more compounds of formula III in a total concentration in the range from

1 % or more to 40 % or less, preferably from 3 % or more to 20 % or less, particularly preferably from 4 % or more to 10 % or less. The compounds of ormula III are preferably selected from the group of the compounds of the formulae 111-1 and III-2:

in which the parameters have the meanings given under formula III 5 and the media in accordance with the present invention may comprise, alternatively or in addition to the compounds of the formulae 111-1 and/or III-2, one or more compounds of the formula MI-3

in which the parameters have the respective meanings indicated above, and the parameters L ³¹ and L ³² , independently of one another and of the other parameters, denote H or F.

The liquid-crystal medium preferably comprises compounds selected from the group of the compounds of the formulae 11-1 and II-2 in which L ²¹ and L ²² and/or L ²³ and L ²⁴ both denote F.

In a preferred embodiment, the liquid-crystal medium comprises corn- pounds selected from the group of the compounds of the formulae 11-1 and II-2 in which L ²¹ , L ²² , L ²³ and L ²⁴ all denote F. The liquid-crystal medium preferably comprises one or more compounds of the formula 11-1 . The compounds of the formula 11-1 are preferably selected from the group of the compounds of the formulae 11-1 a to 11-1 e, preferably one or more compounds of formulaell-1 a and/or 11-1 b and/or II- 1 d, preferably of formula 11-1 a and/or 11-1 d or 11-1 b and/or 11-1 d, most preferably of formula 11-1 d:

in which the parameters have the respective meanings indicated above, and L ²⁵ and L ²⁶ , independently of one another and of the other parameters, denote H or F, and preferably

in the formulae 11-1 a and 11-1 b,

L ²¹ and L ²² both denote F,

in the formulae 11-1 c and 11-1 d,

L ²¹ and L ²² both denote F and/or L ²³ and L ²⁴ both denote F, and

in formula 11-1 e,

L ²¹ , L ²² and L ²³ denote F.

The liquid-crystal medium preferably comprises one or more compounds of the formula II-2, which are preferably selected from the group of the compounds of the formulae ll-2a to ll-2k, preferably one or more

compounds each of formulae ll-2a and/or ll-2h and/or ll-2j:

in which the parameters have the respective meanings indicated above, and L ²⁵ to L ²⁸ , independently of one another, denote FI or F, preferably L ²⁷ and L ²⁸ both denote FI, particularly preferably L ²⁶ denotes FI.

The liquid-crystal medium preferably comprises compounds selected from the group of the compounds of the formulae 11-1 a to 11-1 e in which L ²¹ and L ²² both denote F and/or L ²³ and L ²⁴ both denote F.

In a preferred embodiment, the liquid-crystal medium comprises corn- pounds selected from the group of the compounds of the formulae ll-2a to ll-2k in which L ²¹ , L ²² , L ²³ and L ²⁴ all denote F. Especially preferred compounds of the formula 11-2 are the compounds of the following formulae, particularly preferred of formulae ll-2a-1 and/or II- 2h-1 and/or ll-2k-2:

in which R ² and X ² have the meanings indicated above, and X ² preferably denotes F.

The liquid-crystal medium preferably comprises one or more compounds of the formula 111-1 . The compounds of the formula 111-1 are preferably selected from the group of the compounds of the formulae lll-1 a to MI-1 j, preferably from formulae MI-1 c, MI-1 f, MI-1 g and MI-1 j:

3 5 in which the parameters have the meanings given above and preferably in which the parameters have the respective meanings indicated above, the parameters L ³⁵ and L ³⁶ , independently of one another and of the other parameters, denote H or F, and the parameters L ³⁵ and L ³⁶ , independently of one another and of the other parameters, denote H or F. The liquid-crystal medium preferably comprises one or more compounds of the formula MI-1 c, which are preferably selected from the group of the compounds of the formulae MI-1 c-1 to MI-1 c-5, preferably of formulae MI-1 c- 1 and/or MI-1 c-2, most preferably of formula 111-1 c-1 :

in which R ³ has the meaning indicated above.

The liquid-crystal medium preferably comprises one or more compounds of the formula MI-1 f, which are preferably selected from the group of the compounds of the formulae MI-1 f-1 to MI-1 f-6, preferably of formulae MI-1 f-1 and/or 111-1 f-2 and/or MI-1 f-3 and /or 111-1 f-6, more preferably of formula MI-1 f-3 and/or MI-1 f-6, more preferably of formula MI-1 f-6:

in which R ³ has the meaning indicated above.

The liquid-crystal medium preferably comprises one or more compounds of the formula MI-1 g, which are preferably selected from the group of the compounds of the formulae MI-1 g-1 to MI-1 g-5, preferably of formula MI-1 g- 3:

in which R ³ has the meaning indicated above.

The liquid-crystal medium preferably comprises one or more compounds of the formula MI-1 h, which are preferably selected from the group of the compounds of the formulae 111-1 h-1 to 111-1 h-3, preferably of the formula 111-1 h-3:

in which the parameters have the meanings given above, and X ³ prefera- bly denotes F.

The liquid-crystal medium preferably comprises one or more compounds of the formula 111-1 i, which are preferably selected from the group of the compounds of the formulae 111-1 i-1 and MI-1 i-2, preferably of the formula MI-1 i-2:

in which the parameters have the meanings given above, and X ³ prefera- bly denotes F.

The liquid-crystal medium preferably comprises one or more compounds of the formula MI-1 j, which are preferably selected from the group of the compounds of the formulae lll-1j-1 and MI-1 j-2, preferably of the formula III- 1 j-1 :

in which the parameters have the meanings given above.

The liquid-crystal medium preferably comprises one or more compounds of the formula ill-2. The compounds of the formula ill-2 are preferably selected from the group of the compounds of the formulae lll-2a and lll-2b, preferably of formula lll-2b:

in which the parameters have the respective meanings indicated above, and the parameters L ³³ and L ³⁴ , independently of one another and of the other parameters, denote H or F.

The liquid-crystal medium preferably comprises one or more compounds of the formula lll-2a, which are preferably selected from the group of the compounds of the formulae lll-2a-1 to lll-2a-6:

lll-2a-1 -2a-2

in which R ³ has the meaning indicated above. The liquid-crystal medium preferably comprises one or more compounds of the formula lll-2b, which are preferably selected from the group of the compounds of the formulae lll-2b-1 to lll-2b-4, preferably lll-2b-4:

in which R ³ has the meaning indicated above.

Alternatively or in addition to the compounds of the formulae 111-1 and/or III-2, the media in accordance with the present invention may comprise one or more compounds of the formula MI-3

in which the parameters have the respective meanings indicated above under formula III. These compounds are preferably selected from the group of the formulae lll-3a and lll-3b:

in which R ³ has the meaning indicated above.

The liquid-crystalline media in accordance with the present invention pref- erably comprise one or more dielectrically neutral compounds, preferably having a dielectric anisotropy in the range from -1 .5 to 3, preferably selected from the group of the compounds of the formulae VI, VII, VIII and IX.

In the present application, the elements all include their respective iso- topes. In particular, one or more H in the compounds may be replaced by D, and this is also particularly preferred in some embodiments. A corre- spondingly high degree of deuteration of the corresponding compounds enables, for example, detection and recognition of the compounds. This is very helpful in some cases, in particular in the case of the compounds of formula I.

In the present application, alkyl particularly preferably denotes straight-chain alkyl, in par- ticular CH ₃ -, C ₂ H ₅ -, n- C ₃ H ₇ -, n-C ₄ H ₉ - or n-CsHu-, and alkenyl particularly preferably denotes CH ₂ =CH-, E-CH ₃ -CH=CH-,

CH ₂ =CH-CH ₂ -CH ₂ -, E-CH ₃ -CH=CH-CH ₂ -CH ₂ - or

E-(n-C ₃ H ₇ )-CH=CH-.

In a preferred embodiment of the present invention, the media according to the invention comprise one or more compounds of the formula B, preferably of formula B-1 , preferably in a concentration of %1 to 20 %, particularly preferably 2 % to 15 % and very particularly preferably 3 % to 9 %,

in which the parameters have the respective meanings given under formula B above and preferably

R ^B1 and R ^B2 in each case, independently of one another, denote an un- substituted alkyl radical, alkoxy radical, oxaalkyl radical or alkoxyalkyl radical having 1 to 7 C atoms, or an alkenyl radical or alkenyloxy radical having 2 to 7 C atoms, prefer- ably both denote an alkoxy radical, and L ^B1 and L ^B2 in each case, independently of one another, denote F or

Cl, preferably F.

In a particularly preferred embodiment, the media according to the inven- tion comprise one or more compounds selected from the group of the com- pounds of the formulae OH-1 to OH-6,

These compounds are highly suitable for the stabilisation of the media against thermal loads.

In another preferred embodiment of the present invention, in which the media according to the invention comprise, in particular, one or more com- pounds of the formula I in which p denotes 2 and n denotes 2, 3 or 4, preferably 2 or 3, particularly preferably 3, these media have excellent stability.

In a further preferred embodiment of the present invention, the media according to the invention comprise at least in each case one or more compounds of the formula I in which p denotes 1 and n denotes 3, 4, 5 or 6, preferably 4, and the groups -Z ¹¹ -S ¹¹ -Z ¹² - denote w-bisoxyalkylene, i.e. -0-S ¹¹ -0-, these media have excellent stability. 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 IPS, FFS, VA or ECB effect preferably on the IPS or FFS effect, and in particular those which are addressed by means of an active-matrix addressing device.

Accordingly, the present invention likewise 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 I are mixed with one or more compounds of the formula II, preferably with one or more compounds of the sub-formula 11-1 , and with one or more further compounds, preferably selected from the group of the compounds of the formulae III and IV and/or V and or VI to IX and or IN and/or B and/or S.

In addition, the present invention relates to a process for the stabilisation of a liquid-crystalline medium which comprises one or more compounds of the formula II and one or more compounds selected from the group of the compounds of the formulae III to IX, B, S and IN, characterised in that one or more compounds of the formula I are added to the medium.

In a particularly preferred embodiment, the medium comprises one or more compounds of formula IV selected from the group of the compounds of the formulae IV-1 to IV-4, preferably of formula IV-1 and or IV-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 and alkenyl’ independently of one another, denote an alkenyl radical having 2 to 5 C atoms, preferably having 2 to 4 C atoms, particularly preferably 2 C atoms, alkenyl’ denotes an alkenyl radical having 2 to 5 C atoms, prefera- bly 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 formula IV-1 and/or one or more compounds of formula IV-2.

Especially preferred compounds of formula IV-1 are selected from the group of the compounds of the following formulae

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. Especially preferred compounds of formula IV- are selected from the group of the compounds of the following formulae

In a further preferred embodiment, the medium comprises one or more compounds of the formula V selected from the group of the compounds of the formulae V-1 to V-11 , preferably selected from the group of the corn- pounds of the formulae V-1 to V-5,

in which the parameters have the meanings given above under formula V

35 and Y ⁵ denotes H or F, and preferably

R ⁵¹ denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to

7 C atoms, and

R ⁵² 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 V-1 selected from the group of the compounds of the formulae V-1 a and V-1 b, preferably of the formula V-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 V-3 selected from the group of the compounds of the formulae V-3a and V-3b, V-3a 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 V-4 selected from the group of the compounds of the formulae V-4a and V-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 a further preferred embodiment, the medium comprises one or more compounds of the formula V-5 selected from the group of the compounds of the formulae V-5a to V5d, preferably of formula V-5a and/or V-5b,

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 and alkenyl’ independently of one another, denote an alkenyl radical having 2 to 5 C atoms, preferably having 2 to 4 C atoms, particularly preferably 4 C atoms.

The liquid-crystal media in accordance with the present invention may comprise one or more chiral compounds.

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 Table D. i. The liquid-crystalline medium has a birefringence of 0.060 or more, particularly preferably 0.070 or more. ii. The liquid-crystalline medium has a birefringence of 0.130 or less, particularly preferably 0.120 or less. iii. The liquid-crystalline medium has a birefringence in the range from 0.090 or more to 0.120 or less.

IV. The liquid-crystalline medium has a negative dielectric anisotropy having a value of 2.0 or more, particularly preferably 3.0 or more v. The liquid-crystalline medium has a negative dielectric anisotropy having a value of 5.5 or less, particularly preferably 5.0 or less. vi. The liquid-crystalline medium has a negative dielectric anisotropy having a value in the range from 3.6 or more to 5.2 or less. vii. The total concentration of the compounds of the formula II in the mix- ture as a whole is 25 % or more, preferably 30 % or more, and is preferably in the range from 25 % or more to 49 % or less, particularly preferably in the range from 29 % or more to 47 % or less, and very particularly preferably in the range from 37 % or more to 44 % or less. viii. The liquid-crystalline medium comprises one or more compounds of the formula IV 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 up to 50 % or less, particu- larly preferably up to 42 % or less, and optionally additionally

CC-3-V1 , preferably in a concentration of up to 15 % or less, and/or CC-4-V, preferably in a concentration of up to 20 % or less, particu- larly preferably up to 10% or less. ix. The total concentration of the compounds of the formula CC-3-V in the mixture as a whole is 20 % or more, preferably 25 % or more. x. The proportion of compounds of the formulae II and III in the mixture as a whole is 10 % or more and preferably 75 % or less. xi. The liquid-crystalline medium essentially consists of compounds of the formulae I, II, III, IV, V and B and/or S, preferably of compounds of the formulae I, II, III, IV, V and S. The invention furthermore relates to an electro-optical display having active-matrix addressing based on the VA or ECB effect, characterised in that it contains, as dielectric, a liquid-crystalline medium in accordance with the present invention.

The liquid-crystal mixture preferably has a nematic phase range having a width of at least 80 degrees and a flow viscosity v ₂ o of at most 30 mm ² · 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 150 mPa s or less, in particular 120 mPa s or less and very particularly preferably 120 mPa s or less.

The mixtures according to the invention are suitable for all IPS and FFS- TFT applications. They are furthermore suitable for all VA applications, such as, for example, VAN, MVA, (S)-PVA and ASV applications, and PALC applications 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.

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 and 111-1 to III-4, and/or IV and/or V.

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 to V, 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, whose total concentration is preferably 10 % or less, based on the entire medium.

In a preferred embodiment, the liquid-crystal media according to the inven- tion comprise in total, based on the mixture as a whole,

100 ppm or more to 2500 ppm or less, preferably 300 ppm or more to 2000 ppm or less, particularly preferably 500 ppm or more to 1500 ppm or less and very particularly preferably 700 ppm or more to 1200 ppm or less, of the compound of the formula I,

20 % or more to 60 % or less, preferably 25 % or more to 50 % or less, particularly preferably 30 % or more to 45 % or less, of compounds of the formula II, and

50 % or more to 70 % or less of compounds of the formulae I to IX and/or IN and/or B and or S.

In a preferred embodiment, the liquid-crystal media according to the inven- tion comprise one or more compounds selected from the group of the compounds of the formulae II, III, IV, V, VI, VII, VIII and IX, preferably selected from the group of the compounds of the formulae II and/or III and/or IV and/or V, which comprise one or more rings independently of each other selected from the following group of substituted 1 ,4-phenylenes

In a particularly preferred embodiment of the preferred empbodiment above, the liquid-crystal media according to the invention comprise one or more compounds selected from the following group of compounds

In a preferred embodiment, the liquid-crystal media according to the inven- tion comprise one or more compounds selected from the group of compounds of formulae II, III, IV, V, VI, VII, VIII and IX, preferably selected from the group of the compounds of the formulae II and/or III and/or IV and/or V, which comprise one end group or, if present, two endgroups, preferably one end group, selected from the following group of endgroups

3-fluoro-propyl, cyclopropyl, cyclopropylmethyl, 2-cyclopropylethyl, cyclobutyl, cyclobutylmethyl, cyclopentyl and cyclopentylmethyl, preferably selected from 3-fluoro-propyl, cyclopropyl, cyclopropylmethyl, 2- cyclopropylethyl, cyclobutylmethyl and cyclopentylmethyl. In a particularly preferred embodiment of the preferred empbodiment above, the liquid-crystal media according to the invention comprise one or more compounds selected from the following group of compounds

 PCT/EP2019/063561

35

35

In a preferred embodiment, the liquid-crystal media according to the inven- tion comprise compounds selected from the group of the compounds of the formulae I, II, III, IV, V, In, B and S, preferably selected from the group of the compounds of the formulae I, II and/or III and/or B and/or S, they pref- erably consist predominantly, particularly preferably essentially and very particularly preferably virtually completely of the compounds of the said formulae.

The liquid-crystal media according to the invention preferably 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 are observed at low temperatures at the corresponding temperature and on the other hand that no clearing occurs on heating out 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. In addition, the shelf life at low temperatures in bulk (1 ml_ of sample) is determined in glass vials at temperatures of -20°C or -30°C. At these temperatures, preferably at -30°C, the stable shelf lives are preferably 120 h or more, particularly preferably 240 h more.

In a preferred embodiment, the liquid-crystal media according to the inven- tion are characterised by optical anisotropy values in the moderate to low range. The birefringence values are preferably in the range from 0.065 or more to 0.130 or less, particularly preferably in the range from 0.080 or more to 0.120 or less and very particularly preferably in the range from 0.085 or more to 0.110 or less.

In this embodiment, the liquid-crystal media according to the invention have negative dielectric anisotropy and relatively high absolute values of the dielectric anisotropy (I DeI ) which are preferably in the range from 2.7 or more to 5.3 or less, preferably to 4.5 or less, preferably from 2.9 or more to 4.5 or less, particularly preferably from 3.0 or more to 4.0 or less and very particularly preferably from 3.5 or more to 3.9 or less.

The liquid-crystal media according to the invention have relatively low val- ues for the threshold voltage (V ₀ ) in the range from 1.7 V or more to 2.5 V or less, preferably from 1.8 V or more to 2.4 V or less, particularly prefera- bly from 1.9 V or more to 2.3 V or less and very particularly preferably from 1.95 V or more to 2.1 V or less.

In a further preferred embodiment, the liquid-crystal media according to the invention preferably have relatively low values of the average dielectric anisotropy ( _av. º (e + 2e _± )/3) which are preferably in the range from 5.0 or more to 7.0 or less, preferably from 5.5 or more to 6.5 or less, still more preferably from 5.7 or more to 6.4 or less, particularly preferably from 5.8 or more to 6.2 or less and very particularly preferably from 5.9 or more to 6.1 or less. 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 preferably 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 90 %, preferably greater than or equal to 93 %, particularly preferably greater than or equal to 96 % and very particularly preferably greater than or equal to 98 %. 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 of formula I and one or more compounds of the formula IV, 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. In a preferred embodiment, the liquid-crystalline media according to the invention comprise: one or more compounds of formula I and/or one or more compounds of formula II, preferably of the formulae PUQU-n-F, CDUQU-n-F, APUQU-n-F, DPUQU-n-F and PGUQU-n-F, and/or one or more compounds of formula III, preferably of the formulae

CCG-n-FCCP-n-OT, CLP-n-T, CGG-n-F, CGG-n-OD and PPGU-n-F and/or one or more compounds of formula IV, preferably of the formulae

CC-n-V, CC-n-Vm, CC-n-m, CC-V-V, CCVC-n-V and/or one or more compounds of formula V, preferably of the formulae

CP-n-Om CCP-n-m, CCP-V-n, CCP-V2-n, CLP-V-n, CCVC-n-V, CGP-n-m, PGP-n-m, PGP-n-mV and CPGP-n-m and/or optionally, preferably obligatorily, one or more compounds of formula VI, preferably of the formulae Y-n-Om, Y-nO-Om and/or CY-n-Om, selected from the group of the compounds of the formulae Y-3-01 , Y-40-04, CY-3-02, CY-3-04, CY-5-02 and CY-5-04, and/or

optionally, preferably obligatorily, one or more compounds of formula VII- 1 , preferably selected from the group of the compounds of the formulae

CCY-n-m and CCY-n-Om, preferably of 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, and/or optionally, preferably obligatorily, one or more compounds of formula VII- 2, preferably of formula CLY-n-Om, preferably selected from the group of the compounds of the formulae CLY-2-04, CLY-3-02,

CLY-3-03, and/or one or more compounds of formula VIII, preferably of the formulae

CZY-n-On and CCOY-n-m and/or one or more compounds of formula IX, preferably selected from the group of the compounds of the formulae PYP-n-m and PGIY.n-Om and/or one or more compounds of formula B and/or one or more compounds of formula S and/or optionally, preferably obligatorily, one or more compounds of formula IV, preferably selected from the group of the compounds of the formulae CC-n-V, CC-n-Vm and CC-nV-Vm, preferably CC-3-V, CC-3-V1 , CC-4-V, CC-5-V and CC-V-V, particularly preferably selected from the group of the compounds CC-3-V, CC-3-V1 , CC-4-V and CC-V-V, very particularly preferably the compound CC-3-V, and optionally additionally the

compound(s) CC-4-V and/or CC-3-V1 and/or CC-V-V.

In a specific preferred embodiment of the present invention, the media according to the invention comprise one or more compounds of formula PPGU-n-F. The compounds of formula PPGU-n-F are also highly suitable as stabilisers in liquid-crystal mixtures.

In a specific preferred embodiment of the present invention, the media according to the invention comprise one or more compounds of formula IX.

The compounds of formula IX, are also highly suitable as stabilisers in liquid-crystal mixtures, especially in case p = q = 1 and ring A ⁹ = 1 ,4- phenylene. In particular, they stabilise the VFIR of the mixtures against UV exposure.

In a preferred embodiment the media according to the invention comprise one or more compounds of formula IX selected from one or more formulae of the group of the compounds of the formulae IX-1 to IX-4, very

particularly preferably of the formulae IX-1 to IX-3,

in which the parameters have the meanings given under formula IX and F/H means F or H.

In a further preferred embodiment, the medium comprises one or more compounds of formula IX-3, preferably of formula IX-3-a,

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 case the compounds of formula IX are used in the liquid crystalline media according to the present application, they are preferably present in a concentration of 20 % or less, more preferably of 10 % or less and, most preferably, of 5 % or less and for the individual i.e. (homologous) compounds preferably in a concentration of 10 % or less and, more preferably, of 5 % or less. For the present invention, the following definitions apply in connection with the specification of the constituents of the compositions, unless indicated otherwise in individual cases: - "comprise": the concentration of the constituents in question in the composition is preferably 5 % or more, particularly preferably 10 % or more, very particularly preferably 20 % or more,

- "predominantly consist of: the concentration of the constituents in question in the composition is preferably 50 % or more, particularly preferably 55 % or more and very particularly preferably 60 % or more,

- "essentially consist of: the concentration of the constituents in

question in the composition is preferably 80 % or more, particularly preferably 90 % or more and very particularly preferably 95 % or more, and

- "virtually completely consist of: the concentration of the constituents in question in the composition is preferably 98 % or more, particularly preferably 99 % or more and very particularly preferably 100.0 %.

This applies both to the media as compositions with their constituents, which can be components and compounds, and also to the components with their constituents, the compounds. Only in relation to the concentra- tion of an individual compound relative to the medium as a whole does the term comprise mean: the concentration of the compound in question is preferably 1 % or more, particularly preferably 2 % or more, very particularly preferably 4 % or more. For the present invention, "<" means less than or equal to, preferably less than, and ">" means greater than or equal to, preferably greater than.

For the present invention, denote trans- 1 ,4-cyclohexylene denotes 1 ,4-cyclohexylene, preferably trans- 1 ,4-cyclohexylene, and denote 1 ,4-phenylene.

For the present invention, the expression "dielectrically positive corn- pounds" means compounds having a De of > 1.5, the expression "dielectri- cally neutral compounds" generally means those where -1.5 < De < 1.5 and the expression "dielectrically negative compounds” means those where De < -1.5. The dielectric anisotropy of the compounds is determined here by dissolving 10 % of the compounds in a liquid-crystalline host and deter- mining 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 homo- geneous surface alignment at a temperature of 20°C and at a frequency of 1 kHz. The measurement voltage is typically 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 pur- pose, the concentration is halved in steps until the investigation can be carried out at the desired temperature. The compounds of the formula I according to the invention, or the corn- pounds of the formula I to be employed in accordance with the invention, can advantageously be prepared in accordance with the following reaction schemes.

Synthesis Scheme 1

ring structure g rng srucure reaction on Rg

ring structure

in which n preferably denotes 2, 3 or 4, particularly preferably 3 or 4. Synthesis Scheme 2

in which n preferably denotes 2, 3 or 4, particularly preferably 3 or 4.

Synthesis Scheme 3

reduction

ction

in which m denotes an integer from 3 to 6, particularly preferably 4 or 6.

In the reaction schemes above, Pg denotes a protecting group and Rg denotes a leaving group and the parameter n has the meaning given in the case of formula I, furthermore R ¹ has the meanings given for for R ¹¹ in the case of formula I, the ring structure has the meanings given for ZG in the case of formula I, Sp ¹ and Sp ² have the meanings given for S ¹ and S ² respectively in the case of formula I, and preferably n denotes 3 or 4, the ring structure denotes an aromatic or aliphatic radical, Sp ¹ and Sp ² denote a single bond or an alkylene radical having 1 to 8 C atoms and R ¹ denotes an alkyl radical having 1 to 8 C atoms. For the present invention, the following definitions apply in connection with the specification of the constituents of the compositions, unless indicated otherwise in individual cases: - "comprise": the concentration of the constituents in question in the composition is preferably 5 % or more, particularly preferably 10 % or more, very particularly preferably 20 % or more,

- "predominantly consist of: the concentration of the constituents in question in the composition is preferably 50 % or more, particularly preferably 55 % or more and very particularly preferably 60 % or more,

- "essentially consist of: the concentration of the constituents in

question in the composition is preferably 80 % or more, particularly preferably 90 % or more and very particularly preferably 95 % or more, and

- "virtually completely consist of: the concentration of the constituents in question in the composition is preferably 98 % or more, particularly preferably 99 % or more and very particularly preferably 100.0 %.

This applies both to the media as compositions with their constituents, which can be components and compounds, and also to the components with their constituents, the compounds. Only in relation to the concentra- tion of an individual compound relative to the medium as a whole does the term comprise mean: the concentration of the compound in question is preferably 1 % or more, particularly preferably 2 % or more, very particularly preferably 4 % or more. For the present invention, "<" means less than or equal to, preferably less than, and ">" means greater than or equal to, preferably greater than.

For the present invention, denote trans-1 ,4-cyclohexylene, and denote 1 ,4-phenylene.

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 dissolving 10 % of the compounds in a liquid-crystalline host and deter- mining 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 homo- geneous 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 pur- pose, 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 employed is preferably 0.1 % or more to 3 % or less. The concentration of these and similar additives is generally not taken into account when specifying 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 specify- ing the concentrations and concentration ranges of the liquid-crystal corn- 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 clearing 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 according 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 corresponds to the usual geometry, as described, for example, in

EP-A 0 240 379. 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, GFI 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 (V ₀ ), 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 kHz, unless explicitly indicated otherwise in each case.

The electro-optical properties, for example the threshold voltage (V ₀ ) (capacitive measurement), are, as is the switching behaviour, determined in test cells produced at Merck Japan. The measurement cells have soda- lime glass substrates and are constructed in an ECB or VA configuration with polyimide alignment layers (SE-1211 with diluent **26 (mixing ratio 1 :1 ), both from Nissan Chemicals, Japan), which have been rubbed per- pendicularly to one another and effect homeotropic alignment of the liquid crystals. The surface area of the transparent, virtually square ITO elec- trodes is 1 cm ² .

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 meas- urement cells have soda-lime glass substrates and are constructed with polyimide alignment layers (for example AL-3046 from Japan Synthetic Rubber, Japan, unless indicated otherwise) with a layer thickness of 50 nm or with the alignment layers described in the examples, which have been rubbed perpendicularly to one another. The layer thickness is a uniform 6.0 pm. The surface area of the transparent ITO electrodes is 1 cm ² .

The VHR is determined at 20°C (VHR ₂ o) and after 5 minutes in an oven at 100°C (VHR-ioo) in a commercially available instrument from Autronic Melchers, Germany. The voltage used has a frequency of 60 Hz, or the conditions indicated in the examples.

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 2.0 hours without additional heating. The irradiation power in the wavelength range from 300 nm to 800 nm is 765 W/m ² V, or the conditions indicated in the examples. 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 deter- mined in accordance with the following equation (1 ): AVHR(t ) = VHR(t ) - VHR(t = 0) (1) .

The relative stability (S _rei ) of an LC mixture to a load for a time t is deter- mined in accordance with the following equeation, Equation (2): _{s (f)} _ VHRrefjt = 0) - VHRrefjt)

(2) ,

r ^e ‘ ^{1 }} VHR(t = 0) - VHR(t) where“ref stands for the corresponding unstabilised mixture.

A further characteristic quantity which, besides the VHR, can characterise the conductivity of the liquid-crystal mixtures is the ion density. High values of the ion density often result in the occurrence of display faults, such as image sticking and flickering. The ion density is preferably determined in test cells produced at Merck Japan Ltd. The test cells have substrates made from soda-lime glass and are designed with polyimide alignment layers (for example AL-3046 from Japan Synthetic Rubber, Japan, unless indicated otherwise) having a polyimide layer thickness of 40 nm. The layer thickness of the liquid-crystal mixture is a uniform 6.0 pm. The area of the circular, transparent ITO electrodes, which are additionally fitted with a guard ring, is 1 cm ² . The accuracy of the measurement method is about ± 15 %. The cells are dried overnight in an oven at 120°C before filling with the relevant liquid-crystal mixture.

The ion density is measured using a commercially available instrument from TOYO, Japan. The measurement method is essentially a measure- ment method which is analogous to cyclic voltammetry, as described in M. Inoue, "Recent Measurement of Liquid Crystal Material Characteristics", Proceedings IDW 2006, LCT-7-1 ,647. In this method, an applied direct voltage is varied between a positive and negative maximum value in accordance with a pre-specified triangular profile. A complete run through the profile thus forms one measurement cycle. If the applied voltage is sufficiently large that the ions in the field are able to move to the respective electrode, an ion current forms due to discharge of the ions. The amount of charge transferred here is typically in the range from a few pC to a few nC. This makes highly sensitive detection necessary, which is ensured by the above-mentioned instrument. The results are depicted in a current/voltage curve. The ion current here is evident from the occurrence of a peak at voltages which are smaller than the threshold voltage of the liquid-crystal mixture. Integration of the peak area gives the value for the ion density of the mixture investigated. Four test cells are measured per mixture. The repetition frequency of the triangular voltage is 0.033 Hz, the measurement temperature is 60°C, the maximum voltage is ± 3 V to ± 10 V, depending on the magnitude of the dielectric anisotropy of the relevant mixture.

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 mm ² -s ¹ , 14 mm ² -s ¹ and 27 mm ² -s ¹ respectively.

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, n ₀ ordinary refractive index measured at 20°C and 589 nm,

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

i dielectric susceptibility perpendicular to the director at 20°C and 1 kHz,

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 [mm ² -s ¹ ],

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

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

K ₂ elastic constant, "twist" deformation at 20°C [pN],

K ₃ 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 _n H _2n+i , C _m H _2m+1 and C ₁ H ₂₁₊₁ or C _n H _2n , C _m H _2m and CiH _2i 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 corn- posed of the codes for the ring elements with optional linking groups, fol lowed 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 illustrative structures of compounds together with their respective abbreviations.

Table A: Ring elements



Table C: End groups

On the left individually or in combiOn the right individually or in com- nation bination

-n- CnH2n ₊₁ ^_ -n -CnH2n ₊₁

-nO- C _n H _2n+1 -0- -nO -O- CnH2n ₊₁

-V- CH ₂ =CH- -V -CH=CH ₂

-nV- C _n H _2n+i -CH=CH- -nV -C _n H ₂ n-CH=CH ₂

-Vn- CH ₂ =CH- C _n H _2n - -Vn -CH=CH-C _n H ₂ n ₊ i -nVm- CnH _2n+1 -CH-CH-CmH _2m -nVm - CnH _2n -CH-CH-CmH _2m+1

-N- NºC- -N -CºN

-S- S=C=N- -S -N=C=S

-F- F- -F -F

-CL- Cl- -CL -Cl

-M- CFH ₂ - -M -CFH ₂

-D- CF ₂ H- -D -CF ₂ H

-T- CF ₃ - -T -CF ₃

-MO- CFH ₂ O - -OM -OCFH ₂

-DO- CF ₂ HO - -OD -OCF ₂ H

-TO- CFsO - -OT -OCF ₃

-A- H-CºC- -A -CºC-H

-nA- C _n H _2n+1 -C=C- -An -C=C-C _n H _2n+1

-NA- NºC-CºC- -AN -CºC-CºN

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

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

Besides the compounds of the formula I, the mixtures according to the invention preferably comprise one or more compounds of the compounds mentioned below.

The following abbreviations are used:

(n, m and z are, independently of one another, each an integer, preferably 1 to 6).

Table D

CP-n-F

CCG-n-F

CPG-n-F

GGP-n-F

CC-V-mV

CCP-V-m

PGP-n-mVI

CZY-n-Om

CPY-n-Om

B-n-m

B(S)-nO-Om Table E shows chiral dopants which are preferably employed in the mix- tures according to the invention.

Table E

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 E.

Table F shows stabilisers which can preferably be employed in the mix- tures according to the invention in addition to the compounds of the for- mula I. The parameter n here denotes an integer in the range from 1 to 12. In particular, the phenol derivatives shown can be employed as additional stabilisers since they act as antioxidants.

Table F

35

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, in particular one or more compounds selected from the group of the compounds of the two formulae

Examples

The following examples explain the present invention without restricting it

Ί Q in any way. However, 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.

15

Substance Examples

The following substances are preferred substances of the formula I in

accordance with the present application or substances of the formula I

20 preferably to be employed in accordance with the present application.

1

35

2 3



and 

1

The following examples explain the present invention without limiting it in

any way. However, the physical properties make it clear to the person

skilled in the art which properties are to be achieved and in what ranges

they can be modified. In particular, the combination of the various proper- ties which can preferably be achieved is thus well defined for the person

skilled in the art.

Synthesis Example 1 : Synthesis of bis(1 -oxyl-2,2,6,6-tetramethylpiperidin- 4-yl) 2-{3-[2,5-bis({4-butyl-5-[(1 -oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]- 4-{[(1 -oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]carbonyl}-5-oxop entyl})- phenyl]propyl}-2-butylpropanedioate 1

(Substance Example 1 )

1 Step 1.1 : Synthesis of 3-[3,4-bis(3-hydroxypropyl)phenyl]propan-1 -ol A

A

51.34 g (484.0 mmol) of anhydrous sodium carbonate are dissolved in 171.7 ml of water. A solution of 25.0 g (79.0 mmol) of 1 ,2,4-tribromo- benzene and 67.7 g (476 mmol) of 2-butoxy-1 ,2-oxaborolane in 965.2 ml of tetrahydrofuran (THF) is added, 1.65 ml (11.9 mmol) of triethylamine are added, and the mixture is stirred and degassed for 30 min. using a stream of argon. 1.40 g (7.49 mmol) of palladium(ll) chloride (59 % of palladium, anhydrous) and 1.85 g (3.97 mmol) of 2-dicyclohexylphoshino-2 ^' ,6 ^' -di- isopropoxy-1 ,1 ^' -biphenyl are added, and the reaction mixture is stirred under reflux for 18 hours. The reaction mixture is allowed to cool to room temperature (RT), water and methyl tertiary-butyl ether (MTBE) are added, and the phases are separated. The water phase is extracted with MTBE, and the combined organic phases are washed with saturated NaCI solu- tion, dried over sodium sulfate, filtered and evaporated in vacuo. The product is obtained as a yellowish oil and is filtered through silica gel with a mixture of ethyl acetate (EA) and methanol (9:1 ). The product fractions are combined and evaporated in vacuo, giving the reaction product as a pale-yellow oil. The product is characterised by means of NMR

spectroscopy.

¹ H NMR (500 MHz, DMSO-d6)

8— 1.66 (me, 6H, CH2), 2.42— 2.69 (m(superimposed with DMSO), 6H, CH2,), 3.36— 3.49 (m, 6H, CH ₂ ), 4.44 (t, J = 5.15 Hz, 1 H), 4.48 (m _c , 2H), 6.92 (dd, J =

1.7, 7.72 Hz, 1 H), 6.95 (d, J = 1.53 Hz, 1 H), 7.03 (d, J = 7.7 Hz, 1 H).

Step 1.2: Synthesis of 1 ,2,4-tris(3-iodopropyl)benzene B

30.2 ml (138 mmol) of triphenylphosphine are dissolved in 513 ml of aceto- nitrile, and a solution of 34.92 g (138.0 mmol) of iodine in 513 ml of aceto- nitrile is added dropwise with gentle cooling. An orange suspension forms during this addition. When the addition is complete, the mixture is stirred for a further 10 min. 13.3 g (197 mmol) of imidazole are added, and a solu- tion of 10.0 g (39.3 mmol) of triol A in 100 ml of acetonitrile is subse- quently added dropwise (a clear, yellow solution forms during this addi- tion). The reaction solution is stirred at RT for 3 hours (h) and carefully poured into a cold sodium thiosulfate solution (decolouration occurs), and heptane is added. After washing by stirring, the phases are separated, the water phase is extracted with heptane, and the combined organic phases are washed with water, dried over sodium sulfate, filtered and evaporated in vacuo. The crude product is filtered through silica gel with heptane (H) and ethyl acetate (8:2), and evaporation of the product fractions gives the product as a colourless oil. The product is characterised by means of mass spectrometry

MS (El) = 582.0

Step 1.3: Synthesis of 2-butylpropanedioyl dichloride C

C 76.00 g (474.5 mmol) of 2-butylmalonic acid are initially introduced in the reaction apparatus and warmed to 40°C. 90.00 ml (1.240 mol) of thionyl chloride are then added dropwise over the course of about 30 min. (care, evolution of gas), and the mixture is stirred at room temperature (RT) for a further 5 hours (h). The evolution of gas decreases significantly within this time span. The reaction solution is then stirred at 50°C for 18 h and subse- quently at 70°C for 5 h. On each increase in temperature, slight evolution of gas re-occurs. The reaction mixture is then cooled to room temperature and taken up in 300 ml of dry toluene, and excess thionyl chloride is sepa- rated off by distillation together with the toluene (8 mbar and RT to max. bath temperature of 80°C), giving the crude product as a brownish liquid, which can be employed directly in the next synthesis step.

Step 1.4: Synthesis of bis(1 -oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2- butyl- propanedioate D

45.3 g (262.9 mmol) of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1 -oxyl (free radical) and 40.1 ml (289.15 mmol) of triethylamine are dissolved in 419 ml of dichloromethane (DCM) and cooled to -11 °C. A solution of 25.9 g (131.4 mmol) of the acid chloride C in 252 ml of DCM is then added dropwise at -11 °C to -6°C over the course of 1.5 hours (h). The reaction mixture is stirred at max. 0°C for about 3 h, slowly thawed and stirred at room tem- perature (RT) for 18 h. Saturated NaHC0 ₃ solution is added at 3-6°C with cooling, the mixture is stirred briefly, and the phases are separated. The water phase is extracted with DCM, and the organic phases are combined, washed with saturated NaCI solution, dried over sodium sulfate, filtered and evaporated in vacuo. The crude product obtained (orange solid) is filtered through silica gel with DCM / MTBE (9:1 ), and the product fractions are evaporated in vacuo, giving the product as orange crystals.

Step 1.5: Synthesis of bis(1 -oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-{3- [2,5-bis({4-butyl-5-[(1 -oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]-4-{[(1 - oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]carbonyl}-5- oxopentyl})phenyl]propyl}-2-butylpropanedioate 1

0.31 g (7.80 mmol) of sodium hydride (60 % suspension in paraffin oil) is suspended in 9.7 ml of N,N-dimethylformamide (DMF). 3.75 g (7.87 mmol) of a solution of the bisradical D dissolved in 29.0 ml DMF are added drop- wise with gentle cooling (evolution of gas), and the mixture is stirred at RT for 1 hour. 1.40 g (2.39 mmol) of trisiodide B are added dropwise to the reaction solution (5°C evolution of heat over 5 minutes), and the mixture is stirred at RT for 3 h. The reaction mixture is carefully added to ammonium chloride solution and extracted with MTBE. The phases are separated, the water phase is extracted with MTBE, washed with saturated NaCI solution, dried over sodium sulfate, filtered and evaporated in vacuo. The orange crude product obtained is filtered through silica gel with ethyl acetate / heptane (1 :1 ), and the product fractions are evaporated in vacuo, giving the product as an orange solid which foams up in a glass-like manner. The product has the following properties. Phases: glass transition temperature (TG) = 23.5°C, decomposition from 150°C

MS (APCI) = 1605.1 [M + H ⁺ ]

Synthesis Example 2: Synthesis of bis(1 -oxyl-2,2,6,6-tetramethylpiperidin- 4-yl) 2-(3-{3,5-bis[({4-butyl-5-[(1 -oxyl-2,2,6,6-tetramethylpiperidin-4- yl)oxy]-4-{[(1 -oxy-2,2,6,6-tetramethylpiperidin-4-yl)oxy]carbonyl}-5- oxopentyl}oxy)carbonyl]benzoyloxy}propyl)-2-butylpropanedioa te 2

(Substance example 2)

2

Step 2.1 : Synthesis of bis(1 -oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-butyl- 2-[3-(oxan-2-yloxy)propyl]propanedioate E

3.20 g (80.4 mmol) of sodium hydride (60 % suspension in paraffin oil) are suspended in 30 ml of DMF. A solution of 32.40 g (69.14 mmol) of bisradi- cal D (from the synthesis of compound 1) in 300 ml of DMF is added drop- wise to the reaction solution with gentle cooling (evolution of gas), and the mixture is stirred at RT for 1 h. A solution of 19.0 g (85.16 mmol) of 2-(3- bromopropoxy)tetrahydropyran in 200 ml of DMF is then added dropwise at RT (0.5°C evolution of heat). For degassing of the reaction mixture before an increase in temperature, a gentle stream of argon is passed through the reaction mixture by means of an immersed Pasteur pipette for 30 minutes, and the mixture is subsequently stirred at 35°C for 18 h. The reaction solution is allowed to cool to RT, added to saturated NaCI solution and extracted with MTBE, and the phases are separated. The aqueous phase is extracted with MTBE, and the organic phases are combined, washed with saturated NaCI solution, dried over sodium sulfate, filtered and evaporated in vacuo, giving the crude product as a red oil, which, for purification, is filtered through silica gel with DCM / MTBE (9:1 ), giving the product as a red oil.

Step 2.2: Synthesis of bis(1 -hydroxy-2, 2, 6, 6-tetramethylpiperidin-4-yl) 2- butyl-2-(3-hydroxypropyl)propanedioate F

36.5 g (56.1 mmol) of bisradical E and 9.50 g (55.2 mmol) of toluene-4- sulfonic acid monohydrate are dissolved in a mixture of 500 ml of methanol and 50 ml of water, and the mixture is stirred at 40°C for 5 h. The reaction solution is cooled to RT and adjusted to pH = 9 using NaFICOs solution with cooling and evaporated in vacuo. The aqueous residue is extracted with MTBE, and the combined organic phases are washed with saturated NaCI solution, dried over sodium sulfate, filtered and evaporated in vacuo, giving a red oil, which is dissolved in 250 ml of DCM, 6.00 g (55.6 mmol) of Mn0 ₂ are added, and the mixture is stirred at RT for 1 h. (In the case of removal of the THP protecting group, the free radical is in some cases also converted into the OH compound, which is reversed using Mn0 ₂ ). The reaction mixture is filtered through silica gel with DCM and evaporated in vacuo. The crude product obtained is filtered through silica gel with DCM / MTBE (7:3), and the product fractions are evaporated in vacuo to give a red oil.

Step 2.3: Synthesis of bis(1 -oxyl-2,2,6,6-tetramethylpiperidin-4-yl) 2-(3- {3,5-bis[({4-butyl-5-[(1 -oxyl-2,2,6,6-tetramethylpiperidin-4-yl)oxy]-4-{[(1 - oxy-2,2,6,6-tetramethylpiperidin-4-yl)oxy]carbonyl}-5- oxopentyl}oxy)carbonyl]-benzoyloxy}propyl)-2-butylpropanedio ate 2

2

6.70 g (11.7 mmol of F and 50.0 mg (0.41 mmol) of 4-(dimethylamino)- pyridine are dissolved in 100 ml of dichloromethane at RT, and the mixture is cooled to 4°C. 5.00 ml (36.1 mmol) of triethylamine are then added, and a solution of 1.00 g (3.77 mmol) of 1 ,3,5-benzenetricarbonyl chloride in 10 ml of DCM is subsequently added dropwise at 3-4°C. When the evolu- tion of heat is complete, the mixture is allowed to warm to RT and is sub- sequently stirred at RT for 18 h. Ammonium chloride solution is then added with cooling, the mixture is stirred briefly, the phases are separated, and the aqueous phase is extracted with DCM. The combined organic phases are washed with dilute NaCI solution (better phase separation), dried over sodium sulfate, filtered and evaporated in vacuo, giving the reaction product as a red, solidifying foam. For further purification, the product is filtered through silica gel with DCM / MTBE (9:1 to 85:15), and the product fractions are evaporated in vacuo. The reaction product obtained is a red, solidifying foam. It has the following properties.

Phases: T _g (glass transition temperature) 52°C, C (melting point) 57°C I, decomposition > 175°C.

MS (APCI) = 1734.

The following compounds are prepared analogously to the synthesis sequence(s) described.

Substance/Svnthesis Example 3:

Phases: T _g (glass transition temperature) -3°C I (isotropic), decomposition > 100°C. Substance/Svnthesis Example 4:

4

Phases: T _g (glass transition temperature) 5°C I (isotropic), decomposition > 180°C.

Substance/Svnthesis Example 5:

Phases: T _g (glass transition temperature) 5°C I (isotropic), decomposition > 170°C. Substance/Svnthesis Example 6:

Phases: T _g (glass transition temperature) 27°C I (isotropic). Substance/Svnthesis Example 7:

Substance/Svnthesis Example 8:

Phases: T _g (glass transition temperature) -3°C I (isotropic).

Substance/Svnthesis Example 9:

Phases: T _g 22 K 1 12 I. Substanc/Svnthesis Example 10:

Phases: T _g -2 I. Substance/Svnthesis Example 1 1 :

Mixture examples

Example 1 and corresponding comparative examples

Liquid-crystal mixtures having the compositions and properties as indi cated in the following tables are prepared and investigated. The improved stability of the mixtures comprising compounds of the formula I is shown by comparison with unstabilised base mixtures as reference (Ref.). Mixture (M-1 ) below is prepared and investigated.

Firstly, the stability of the voltage holding ratio of mixture (M-1 ) itself is determined. The stability of mixture M-1 to irradiation with a backlight is investigated in a test cell having an alignment material for planar align- ment, with a layer thickness of 6.0 pm and flat ITO electrodes. To this end, the mixture is, or the mixtures are, subjected to a test for exposure to a backlight. To this end, the stability of the corresponding test cells to illumi nation with an LED (light-emitting diode) backlight for LCDs is investigated. To this end, corresponding test cells are filled and sealed. These cells are then exposed to illumination with a commercial LCD backlight for various times. There is no additional heating applied besides the heat generated by the backlight. The“voltage holding ratio” is then in each case determined after 5 minutes at a temperature of 100°C. The results are compiled in the following table, Table 1 a.

Here, as below, six test cells are filled and investigated for each individual mixture. The values indicated are the average of the six individual values.

The relative deviations of the“voltage holding ratio” values in various measurement series are typically in the range from about 3 % to 4 %.

100 ppm, 500 ppm, respectively 1.000 ppm of the reference compound R-1

are added to one each of three further parts of mixture M-1 , and 100 ppm, 500 ppm, respectively 1.000 ppm of of the compound R2

are added to each of three further parts of mixture M-1 , and the stability of the resultant mixtures (C-1.1 , C-1.2 and C-1.3, as well as M-1.1 , M-1.2 and M-1.3) is investigated as described above. The results are shown in the tables below, Tables 1 a to 1 c.

Besides compounds of formuoa I alsi efernce compound R-1 and additionally refervcne compound R-3 have been used here.

Table 6a

Example 2 and corresponding comparative examples Mixture (M-2) below is prepared and investigated.

Firstly, the stability of the voltage holding ratio of mixture (M-2) itself is determined. The stability of mixture M-2 to irradiation with a backlight is investigated in a test cell having an alignment material for planar align- ment, with a layer thickness of 6.0 pm and flat ITO electrodes. To this end, the mixture is, or the mixtures are, subjected to a test for exposure to a backlight. To this end, the stability of the corresponding test cells to illumi nation with an LED (light-emitting diode) backlight for LCDs is

investigated. To this end, corresponding test cells are filled and sealed. These cells are then exposed to illumination with a commercial LCD backlight for various times. There is no additional heating applied besides the heat generated by the backlight. The“voltage holding ratio” is then in each case determined after 5 minutes at a temperature of 100°C.

Example 3 and corresponding comparative examples

The following mixture (M-3) is prepared and investigated. This mixture, mixture M-3, is investigated below with respect to the stability of its voltage holding ratio to irradiation with UV radiation. To this end, this mixture is also divided into several parts. Firstly, the stability of mixture (M-3) itself is determined. To this end, the stability of mixture M-3 to UV exposure is investigated in a test cell having an appropriate polyimide as alignment material for planar alignment, with a layer thickness of 6.0 pm and flat ITO electrodes. To this end, correspond- ing test cells are irradiated in the Suntest for 30 min. The voltage holding ratio is then in each case determined after 5 minutes at a temperature of 100°C. The addressing frequency (or measurement frequency) here is 60 Hz, unless indicated otherwise in detail.

Example 4

The following mixture (M-4) is prepared and investigated.

As described in Examples 1 to 3, mixture M-4 is also divided into several parts and its stability to exposure to an LCD backlight and to a UV source is investigated as such and with various added compounds in a test cell with an alignment material for planar alignment and flat ITO electrodes. Example 5

The following mixture (M-5) is prepared and investigated.

As described in Examples 1 to 4, mixture M-5 is also divided into several parts and its stability to exposure to an LCD backlight and to a UV source is investigated as such and with various added compounds in a test cell with an alignment material for planar alignment and flat ITO electrodes. Example 6

The following mixture (M-6) is prepared and investigated.

As described in Examples 1 to 6, mixture M-6 is also divided into several parts and its stability to exposure to an LCD backlight and to a UV source is investigated as such and with various added compounds in a test cell with an alignment material for planar alignment and flat ITO electrodes.