Liquid crystal medium

Abstract

The present invention relates to a liquid crystal (LC) material with negative dielectric anisotropy as defined in claim 1 and its use for optical, electro-optical and electronic purposes, for example in LC displays, in particular energy-saving displays based on the ECB, IPS or FFS effect.

Description

[0001] The present invention relates to a liquid crystal (LC) medium having negative dielectric anisotropy and its use for optical, electro-optical and electronic purposes, in particular in LC displays.

[0002] One type of liquid crystal display (LCD) currently in use is the TN ("twisted nematic") mode. However, a disadvantage of TN LCDs is that the contrast has a strong dependence on the viewing angle.

[0003] In addition, so-called VA (vertical alignment) displays with a wider viewing angle are known. The LC cell of a VA display contains a layer of LC medium between two transparent electrodes, where the LC medium typically has negative dielectric anisotropy. In the non-powered state, the molecules of the LC layer are aligned perpendicular (homeotropically) to the electrode surfaces or have an inclined homeotropic alignment. When a voltage is applied to the two electrodes, reorientation of the LC molecules parallel to the electrode surfaces occurs.

[0004] Also known are so-called IPS ("in-plane switching") displays, which contain an LC layer between two substrates, where the two electrodes are arranged on only one of the two substrates and preferably have an intermeshing comb-like structure. When a voltage is applied to the electrodes, an electric field with a significant component parallel to the LC layer is generated therebetween. This causes reorientation of the LC molecules in the layer plane.

[0005] In addition, so-called FFS (fringe field switching) displays have been reported (see in particular S.H. Jung et al., Jpn. J. Appl. Phys., Vol. 43, No. 3, 2004, 1028), which contain two electrodes on the same substrate, one of which is structured in a comb-like manner and the other is unstructured. This results in a strong so-called "fringe field", i.e. a strong electric field close to the electrode edges, and such an electric field in the whole cell, which has both a strong vertical component and a strong horizontal component. FFS displays have a small contrast viewing angle dependence. FFS displays typically contain an LC medium with positive dielectric anisotropy and an alignment layer, usually an alignment layer of polyimide, which provides planar alignment of the molecules of the LC medium.

[0006] FFS displays can be operated as active matrix or passive matrix displays. In the case of an active matrix display, individual pixels are typically addressed by integrated non-linear active elements such as transistors (e.g. thin film transistors or "TFTs"), while in the case of a passive matrix display, individual pixels are typically addressed according to multiplexing methods known from the prior art.

[0007] In addition, FFS displays have been disclosed (see S.H. Lee et al., Appl. Phys. Lett. 73(20), 1998, 2882 - 2883 and S.H. Lee et al., Liquid Crystals 39(9), 2012, 1141 - 1148), which have an electrode design and layer thickness similar to those of FFS displays, but include a layer with an LC medium having negative dielectric anisotropy instead of a layer with an LC medium having positive dielectric anisotropy. The LC medium with negative dielectric anisotropy shows a more favorable director orientation compared to the LC medium with positive dielectric anisotropy, having an orientation with less tilt and more twist, as a result of which these displays have a higher transmittance. The display also includes an alignment layer, preferably polyimide provided on at least one substrate, which contacts the LC medium and induces planar alignment of the LC molecules of the LC medium. These displays are also referred to as "Ultra - Bright FFS (UB - FFS)" mode displays. These displays require an LC medium with high reliability.

[0008] In a newer type of VA display, the homogeneous alignment of LC molecules is limited to a plurality of relatively small domains within the LC cell. Disclinations, also called tilt domains, may exist between these domains. A VA display with tilt domains has a greater contrast and a viewing - angle independence of grey shade compared to a conventional VA display. Additionally, this type of display is easier to manufacture because no additional electrode surface treatment (such as by rubbing) is required to homogeneously align the molecules in the on - state. Instead, the preferential direction of the tilt angle or pre - tilt angle is controlled by a special design of the electrodes.

[0009] In so-called MVA (multi-domain vertical alignment) displays, this is typically achieved by electrodes with protrusions that cause local pre-tilting. Thereby, when a voltage is applied, the LC molecules are aligned parallel to the electrode surface in different, defined cell regions in different directions. Thereby, "controlled" switching is achieved and the formation of disturbing disclination lines is prevented. While this arrangement improves the viewing angle of the display, it results in a reduction of its light transmittance. A further improvement of MVA uses protrusions only on one electrode side, while the opposite electrode has slits, which improves the light transmittance. The slit electrode generates a non-uniform electric field in the LC cell when a voltage is applied, meaning that controlled switching is still achieved. To further improve the light transmittance, the spacing between the slit and the protrusion can be increased, but this in turn results in an increase in the response time. In so-called PVA ("patterned VA"), the protrusions are made completely redundant, since both electrodes are structured by slits on opposite sides, which results in increased contrast and improved light transmittance, but this is technically difficult and makes the display more sensitive to mechanical influences ("tapping", etc.). However, for many applications, such as monitors and especially TV screens, a shortening of the response time of the display as well as an improvement of the contrast and brightness (transmittance) of the display are required.

[0010] Another development is the so-called PS ("polymer sustained") or PSA ("polymer sustained alignment") display, for which the term "polymer stabilization" is also occasionally used. In these, a small amount (e.g., 0.3 wt%, typically <1 wt%) of one or more polymerizable compounds, preferably polymerizable monomer compounds, is added to the LC medium, and after the LC medium has been filled into the display, it is polymerized or crosslinked in-situ (usually by UV photopolymerization), while optionally applying a voltage to the electrodes of the display. The polymerization is carried out at the temperature at which the LC medium exhibits the liquid crystal phase, usually at room temperature. The addition of polymerizable mesogenic or liquid crystal compounds (also called reactive mesogens or "RMs") to the LC mixture has proven to be particularly suitable.

[0011] At the same time, the PS(A) principle is being used in various conventional LC display modes. Thus, for example, PS-VA, PS-OCB, PS-IPS, PS-FFS, PS-UB-FFS and PS-TN displays are known. The aggregation of the RM preferably occurs under the applied voltage in the case of PS-VA and PS-OCB displays and occurs with or without, preferably without, the applied voltage in the case of PS-IPS displays. As can be verified in a test cell, the PS(A) method results in a pretilt in the cell. In the case of PS-VA displays, this pretilt has a positive effect on the response time. For PS-VA displays, standard MVA or PVA pixel and electrode layouts can be used. However, additionally, for example, it is also possible to manage with only one structured electrode side without protrusions, which significantly simplifies production and at the same time results in very good contrast and very good transmittance.

[0012] PS-VA displays are described, for example, in EP1 170 626A2, US 6,861,107, US 7,169,449, US2004 / 0191428 A1, US2006 / 0066793 A1 and US 2006 / 0103804A1.

[0013] Especially for monitors and particularly for TV applications, there is a continuous requirement for the optimization of the response time as well as the contrast and brightness (and thus also the transmittance) of liquid crystal displays. The PSA method can offer crucial advantages here. Especially in the case of PS-VA, PS-IPS and PS-FFS displays, a shortening of the response time related to the pretilt measurable in a test cell can be achieved without a significant detrimental effect on other parameters.

[0014] Another problem observed in the prior art is that the use of conventional LC media in LC displays (including but not limited to PS-type displays) often results in non-uniformities in the display, especially when the LC medium is filled into a display cell manufactured using the one drop filling (ODF) method. This phenomenon is also referred to as "ODF non-uniformity". Therefore, there is a need to provide an LC medium that reduces ODF non-uniformity.

[0015] Another problem observed in the prior art is that LC media used in PSA displays, including but not limited to PSA type displays, often exhibit high viscosities and, as a result, high switching times. To reduce the viscosity and switching time of the LC media, the addition of LC compounds having alkenyl groups has been proposed in the prior art. However, it has been observed that LC media containing alkenyl compounds often show reduced reliability and stability, as well as a reduction in VHR, especially after exposure to UV radiation. In particular, for use in PSA displays, this is a significant drawback since the photopolymerization of the RM in PSA displays is typically carried out by exposure to UV radiation, which can result in a decrease in VHR in the LC media.

[0016] Furthermore, there is a great need for PSA displays and LC media and polymerizable compounds for such PSA displays that can achieve high specific resistance over a large operating temperature range, short response times even at low temperatures, low threshold voltages, low pretilt angles, a large number of gray levels, high contrast, and wide viewing angles, as well as high reliability and high values of VHR after UV exposure, and in the case of the polymerizable compounds, low melting points and high solubility in the LC host mixture. In PSA displays for mobile applications, in particular, there is a need for an available LC media that exhibits low threshold voltages and high birefringence.

[0017] One display trend is to achieve the fastest possible response times for optimal motion picture quality. In this regard, media having negative dielectric isotropy have an inherent disadvantage compared to LC media having positive dielectric anisotropy. On the other hand, mixtures having negative dielectric anisotropy can achieve higher transmittance in a standard FFS cell layout, and thus their use has a positive impact on power consumption and the environment. There is a need in the art to achieve both fast response times and higher transmittance. Especially for mobile devices, there is a great demand for displays having high transmittance, which enables the use of a lower intensity backlight, which in turn results in longer battery life and thus a more sustainable product. Alternatively, displays having higher brightness can be achieved, especially with improved contrast in ambient light. In addition, the popularity of 8K and gaming monitors has led to an increased demand for LC display panels having higher refresh rates, and thus an increased demand for LC media having faster response times.

[0018] Accordingly, there is still a great need for VA, FFS, or PSA displays and LC media optionally containing polymerizable compounds for VA, FFS, or PSA displays that do not exhibit the above-mentioned deficiencies, or exhibit them only to a lesser extent, and have improved properties.

[0019] The present invention is based on the following object: to provide novel suitable LC media which do not have the above-mentioned disadvantages or have them to a reduced extent.

[0020] Surprisingly, it has now been found that liquid crystal media having a suitably high negative Δε, a suitable phase range, and a high Δn and LTS can be achieved by using one or more compounds of formula I as defined below, which do not exhibit the disadvantages of the materials of the prior art or at least exhibit these disadvantages to a significantly smaller extent.

[0021] The present invention relates to a liquid crystal medium comprising

[0022] a) one or more compounds of formula I

[0023]

[0024] wherein

[0025] R 1 and R 2 , which are the same or different, represent H, halogen, a straight-chain alkyl or alkoxy group having 1 to 15 C atoms, a straight-chain alkenyl or alkenoxy group having 2 to 15 carbon atoms, or a branched-chain alkyl, alkoxy, alkenyl or alkenoxy group each having 3 to 15 C atoms, where one or more CH2 groups in these groups may each independently of one another be -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly connected to one another, and where one or more H atoms may be replaced by halogen,

[0026] L 11 and L 12 , each independently of one another, represent F, Cl, CF3 or CHF2,

[0027] L 13 and L 14 , each independently of one another, represent H, F, Cl, CF3 or CHF2,

[0028] Y 1 represents H, F, Cl, CF3, CHF2 or CH3, and

[0029] n is 0 or 1, preferably 1;

[0030] and

[0031] b) one or more compounds selected from the group of compounds of formulae IIA, IIB, IIC and IID

[0032]

[0033] wherein

[0034] R 2A ,R 2B ,R 2C and R 2D are the same or different and represent H, a straight-chain alkyl or alkoxy group having 1 to 15 C atoms, a straight-chain alkenyl or alkenyloxy group having 2 to 15 carbon atoms, or a branched-chain alkyl, alkoxy, alkenyl, alkenyloxy group each having 3 to 15 C atoms, where one or more CH2 groups in these groups may each independently of one another be replaced by -C≡C-, -CF2O-, -OCF2-,-CH=CH-, replaced by -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly connected to one another, and where one or more H atoms may be replaced by a halogen

[0035] L 1 ,L 2 ,L 3 and L 4 each independently of one another represent F, Cl, CF3 or CHF2

[0036] Y represents H, F, Cl, CF3, CHF2 or CH3

[0037] Z 2 ,Z 2B and Z 2D each independently of one another represent a single bond, -CH2CH2-,-CH=CH-,-CF2O-,-OCF2-,-CH2O-,-OCH2-,-COO-,-OCO-,-C2F4-,-CF=CF- or -CH=CHCH2O-

[0038] p represents 0, 1 or 2

[0039] q represents 0 or 1, and

[0040] v represents an integer from 1 to 6

[0041] The present invention also relates to a method for preparing an LC medium as described above and below, comprising the step of mixing one or more compounds of formula I with one or more compounds of formulae IIA, IIB, IIC and / or IID and optionally with one or more chiral dopants, and optionally with one or more polymerizable compounds and optionally with further LC compounds and / or additives

[0042] The invention also relates to the use of the LC medium according to the invention for electro-optical purposes, preferably for displays, very preferably for displays of the VA, IPS or FFS type, in particular for displays of the UB-FFS type.

[0043] The invention also relates to the use of the LC medium according to the invention in PSA displays, in particular in PSA displays containing the LC medium, for generating a tilt angle in the LC medium by in-situ polymerization of a polymerizable reactive mesogen (RM) in the PSA display (preferably in an electric or magnetic field).

[0044] The invention also relates to LC displays comprising the LC medium according to the invention, in particular VA, IPS, FFS or UB-FFS or PSA displays, particularly preferably FFS, UB-FFS, VA or PS-VA displays.

[0045] The invention also relates to the use of the LC medium according to the invention in polymer-stabilized SA-VA displays, and to polymer-stabilized SA-VA displays comprising the LC medium according to the invention.

[0046] According to another aspect of the invention, there is provided an energy-saving display for gaming, comprising a liquid crystal medium as defined in context. In a preferred embodiment, the medium of the energy-saving display for gaming has a birefringence in the range from 0.125 to 0.155.

[0047] The invention also relates to a method for manufacturing an LC display as described in context, comprising the steps of filling or otherwise providing an LC medium between the substrates of the display, said LC medium optionally comprising one or more polymerizable compounds as described in context, and optionally polymerizing said polymerizable compounds.

[0048] The LC medium according to the invention exhibits the following advantageous properties, particularly when used in FFS displays:

[0049] - Excellent low temperature stability (LTS)

[0050] - Improved contrast of the display,

[0051] - High transmittance of the display,

[0052] - High clearing temperature,

[0053] - High voltage holding ratio,

[0054] - Low rotational viscosity,

[0055] - Fast switching,

[0056] - Fast response time, enabling low-power LCDs to extend the battery life of mobile devices,

[0057] - Sufficient heat and / or UV stability, especially when used outdoors.

[0058] - A suitably high birefringence combined with a fast response time for gaming applications.

[0059] The compound of formula I is known from EP2239310A1.

[0060] An LC medium preferably containing the compound of formula I, wherein Y 1 represents H or methyl, preferably H, L 11 and L 12 represents F, L 13 and L 14 represents H, and R 1 and R 2 have the meanings defined above for formula I. Very preferably, n is 1.

[0061] More preferably, the compound of formula I is selected from the compounds of formula Ia, Ib, Ic, Id, and Ie, and very preferably the compound of formula Ib:

[0062]

[0063]

[0064] wherein, R 1 and R 2 independently represent a straight-chain alkyl group having 1 to 15 carbon atoms, a straight-chain alkenyl group having 2 to 15 carbon atoms, or a branched-chain alkyl or alkenyl group having 3 to 15 carbon atoms, wherein one or more CH2 groups in these groups may each be independently replaced by and one or more H atoms may be replaced by fluorine;

[0065] Preferably, R 11 and R 12 both represent a straight-chain alkyl group having 1 to 6 carbon atoms.

[0066] The preferred compound of formula Ia is selected from the compounds of formula Ia-1 to Ia-36.

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] Wherein v is an integer from 1 to 6.

[0073] The preferred compounds of formula Ib are selected from the compounds of formulae Ib-1 to Ib-36.

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] Wherein v is an integer from 1 to 6.

[0080] The preferred compounds of formula Ic are selected from the compounds of formulae Ic-1 to Ic-36.

[0081]

[0082]

[0083]

[0084]

[0085]

[0086] Wherein v is an integer from 1 to 6.

[0087] The preferred compounds of formula Id are selected from the compounds of formulae Id-1 to Id-36.

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094] Wherein v is an integer from 1 to 6.

[0095] Preferred compounds of formula Ie are selected from the compounds of formulae Ie-1 to Ie-36.

[0096]

[0097]

[0098]

[0099]

[0100]

[0101] wherein v is an integer from 1 to 6.

[0102] Preferred compounds of formulae IIA, IIB, IIC and IID are as follows:

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] Wherein the parameter a represents 1 or 2, alkyl and alkyl* each independently of one another represent straight-chain alkyls having 1-6 C atoms, and alkenyl represents a straight-chain alkenyl having 2-6 C atoms, and (O) represents an oxygen atom or a single bond. Alkenyl preferably represents CH2=CH-, CH2=CHCH2CH2-, CH3-CH=CH-, CH3-CH2-CH=CH-, CH3-(CH2)2-CH=CH-, CH3-(CH2)3-CH=CH- or CH3-CH=CH-(CH2)2-.

[0119] Very preferably, the compounds of formula IID are selected from the following sub-formulas:

[0120]

[0121]

[0122]

[0123]

[0124]

[0125] In a preferred embodiment, the medium comprises one or more compounds of formula IID-10a

[0126]

[0127] wherein the groups and parameters occurring have the meanings given above under formula IID, and

[0128] R 2 represents where r is 0, 1, 2, 3, 4, 5 or 6 and s is 1, 2 or 3.

[0129] Preferred compounds of formula IID-10a are compounds IID-10a-1 to IID-10a-14.

[0130]

[0131]

[0132]

[0133] Particularly preferred mixtures according to the invention comprise one or more compounds of formula IIA-2, IIA-8, IIA-10, IIA-16, IIA-18, IIA-40, IIA-41, IIA-42, IIA-43, IIB-2, IIB-10, IIB-16, IIC-1, IID-4 and IID-10.

[0134] Preferred media according to the invention comprise at least one compound of formula IIC-1,

[0135]

[0136] wherein alkyl and alkyl* have the meanings given above.

[0137] In particular, the medium comprises one or more compounds of formula IIA-2 selected from the following sub-formulas:

[0138]

[0139] Alternatively, preferably in addition to the compounds of formulas IIA-2-1 to IIA-2-5, the medium further comprises one or more compounds of formulas IIA-2a-1 to IIA-2a-5:

[0140]

[0141]

[0142] In particular, the medium comprises one or more compounds of formula IIA-10 selected from the following sub-formulas:

[0143]

[0144]

[0145] Alternatively, preferably, in addition to the compounds of formulas IIA-10-1 to IIA-10-5, the medium further comprises one or more compounds of formulas IIA-10a-1 to IIA-10a-5:

[0146]

[0147] In particular, the medium comprises one or more compounds of formula IIB-10 selected from the following sub-formulas:

[0148]

[0149]

[0150] Alternatively, preferably in addition to the compounds of formulas IIB-10-1 to IIB-10-5, the medium further comprises one or more compounds of formulas IIB-10a-1 to IIB-10a-5:

[0151]

[0152] The media according to the invention preferably comprise one or more compounds of formula III

[0153]

[0154] wherein

[0155] R 31 and R 32 each independently of one another represent H, an alkyl or alkoxy group having 1 to 15 C atoms, where one or more CH2 groups in these groups are each independently of one another replaced by -C≡C-, -CF2O-, -OCF2-, -CH=CH-, replaced by -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly connected to one another, and where one or more H atoms may be replaced by halogen,

[0156] A 31 each independently of one another, when occurring each time, represent

[0157] a) 1,4-cyclohexenylene or 1,4-cyclohexylene, where one or two non-adjacent CH2 groups may be replaced by -O- or -S-,

[0158] b) 1,4-phenylene, where one or two CH groups may be replaced by N, or

[0159] c) a group selected from: spiro[3.3]heptane-2,6-diyl, 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl,

[0160] where the groups a), b) and c) may be mono- or polysubstituted by halogen atoms,

[0161] n represents 0, 1 or 2, preferably 0 or 1,

[0162] Z 31 each independently of one another, when occurring each time, represent -CO-O-, -O-CO-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CH2-, -CH2CH2-, -(CH2)4-, -CH=CH-CH2O-, -C2F4-, -CH2CF2-, -CF2CH2-, -CF=CF-, -CH=CF-, -CF=CH-, -CH=CH-, -C≡C- or a single bond, and

[0163] L 31 and L 32 each independently of one another represent F, Cl, CF3 or CHF2, preferably H or F, most preferably F, and

[0164] W represents O or S.

[0165] The compound of formula III is preferably selected from the compounds of formula III-1 and / or III-2

[0166]

[0167]

[0168] wherein the groups present have the same meanings as those given for formula III above, and preferably

[0169] R 31 and R 32 each independently of one another is alkyl, alkenyl or alkoxy having at most 15 C atoms, more preferably one or both of them represent alkoxy, and

[0170] L 31 and L 32 each preferably represents F.

[0171] Preferably, the compound of formula III-1 is selected from the compounds of formula III-1-1 to III-1-11, preferably formula III-1-6

[0172]

[0173]

[0174] wherein

[0175] alkyl and alkyl* each independently of one another represent a straight-chain alkyl having 1-6 C atoms, alkenyl and alkenyl* each independently of one another represent a straight-chain alkenyl having 2-6 C atoms, alkoxy and alkoxy* each independently of one another represent a straight-chain alkoxy having 1-6 C atoms, and L 31 and L 32 each independently of one another represent F or Cl, preferably both are F.

[0176] The compound of formula III-2 is preferably selected from the compounds of formula III-2-1 to III-2-10, preferably formula III-2-6,

[0177]

[0178]

[0179] wherein

[0180] alkyl and alkyl* each independently of one another represent straight-chain alkyl groups having 1 to 6 C atoms, alkenyl and alkenyl* each independently of one another represent straight-chain alkenyl groups having 2 to 6 C atoms, alkoxy and alkoxy* each independently of one another represent straight-chain alkoxy groups having 1 to 6 C atoms, and L 31 and L 32 each independently of one another represent F or Cl, preferably both are F.

[0181] Optionally, the medium comprises one or more compounds of formula IIIA-1 and / or IIIA-2

[0182]

[0183] wherein L 31 and L 32 have the same meaning as given under formula III, (O) represents O or a single bond,

[0184] R IIIA represents an alkyl or alkenyl group having at most 7 C atoms or the group Cy-C m H 2m+1 -,

[0185] m and n are the same or different and are 0, 1, 2, 3, 4, 5 or 6, preferably 1, 2 or 3, very preferably 1,

[0186] Cy represents an alicyclic group having 3, 4 or 5 ring atoms, which is optionally substituted by: alkyl or alkenyl groups each having at most 3 C atoms, or halogen or CN, and preferably represents cyclopropyl, cyclobutyl, cyclopentyl, cyclopent-1-enyl, cyclopent-2-enyl and cyclopent-3-enyl.

[0187] The compounds of formula IIIA-1 and / or IIIA-2 may alternatively or in addition to the compounds of formula III preferably additionally be comprised in the medium.

[0188] Very preferred compounds of formula IIIA-1 and IIIA-2 are as follows:

[0189]

[0190]

[0191] wherein alkoxy represents a straight-chain alkoxy group having 1 to 6 C atoms or alternatively is -(CH2) n F, where n is 2, 3, 4, or 5, preferably C2H4F.

[0192] In a preferred embodiment of the invention, the medium comprises one or more compounds of formula III-3

[0193]

[0194] wherein

[0195] R 31 ,R 32 independently of one another, identically or differently, represents H, an alkyl or alkoxy group having 1 to 15 C atoms, where one or more CH2 groups in these groups are optionally replaced, independently of one another, by -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly linked to one another, and where, in addition, one or more H atoms may be replaced by halogen.

[0196] The compounds of formula III-3 are preferably selected from the compounds of formulae III-3-1 to III-3-10:

[0197]

[0198]

[0199] where R 32 represents an alkyl group having 1 to 7 C atoms, preferably ethyl, n-propyl or n-butyl, or alternatively cyclopropylmethyl, cyclobutylmethyl or cyclopentylmethyl, or alternatively -(CH2) n F, where n is 2, 3, 4 or 5, preferably C2H4F.

[0200] In a preferred embodiment of the invention, the medium comprises one or more compounds of formulae III-4 to III-6, preferably of formula III-5,

[0201]

[0202]

[0203] where the parameters have the meanings given above, R 31 preferably represents a straight-chain alkyl group and R 32 preferably represents an alkoxy group, each having 1 to 7 C atoms.

[0204] In a preferred embodiment, the medium comprises one or more compounds of formula III which are selected from the compounds of formulae III-7 to III-9, preferably of formula III-8,

[0205]

[0206] where the parameters have the meanings given above, R 31Preferably represents a straight-chain alkyl group and R 32 Preferably represents an alkoxy group, each having 1 to 7 C atoms.

[0207] In a preferred embodiment, the medium comprises one or more compounds of formula IV,

[0208]

[0209] wherein

[0210] R 41 represents an unsubstituted alkyl group having 1 to 7 C atoms or an unsubstituted alkenyl group having 2 to 7 C atoms, preferably a normal alkyl group, particularly preferably having 2, 3, 4 or 5 C atoms, and

[0211] R 42 represents an unsubstituted alkyl group having 1 to 7 C atoms or an unsubstituted alkoxy group having 1 to 6 C atoms (both preferably having 2 to 5 C atoms), an unsubstituted alkenyl group having 2 to 7 C atoms, preferably having 2, 3 or 4 C atoms, more preferably vinyl or 1-propenyl, especially vinyl.

[0212] The compounds of formula IV are preferably selected from the compounds of formula IV-1 to IV-4,

[0213]

[0214] wherein

[0215] alkyl and alkyl’, independently of one another, represent an alkyl group having 1 to 7 C atoms, preferably having 2 to 5 C atoms,

[0216] alkenyl represents an alkenyl group having 2 to 5 C atoms, preferably having 2 to 4 C atoms, particularly preferably 2 C atoms,

[0217] alkenyl’ represents an alkenyl group having 2 to 5 C atoms, preferably having 2 to 4 C atoms, particularly preferably having 2 to 3 C atoms, and

[0218] alkoxy represents an alkoxy group having 1 to 5 C atoms, preferably having 2 to 4 C atoms.

[0219] The compounds of formula IV-1 are preferably selected from the compounds of formula IV-1-1 to IV-1-5:

[0220]

[0221]

[0222] The compounds of formula IV-2 are preferably selected from the compounds of formula IV-2-1 and IV-2-2

[0223]

[0224] The compound of formula IV-3 is preferably selected from the compounds of formula IV-3-1 and IV-3-2

[0225]

[0226] wherein alkyl has the meaning defined above.

[0227] The compounds of formula IV-3-1 and IV-3-2 are preferably selected from the following compounds:

[0228]

[0229]

[0230] Very preferably, the medium according to the invention comprises a compound of formula IV-4, in particular selected from the compounds of formula IV-4-1 to IV-4-3

[0231]

[0232] In one embodiment, the medium according to the invention comprises a combination of a compound of formula I selected from one or more compounds of formula I-1 to I-4 and a compound selected from one or more compounds of formula IA-1 to IA-9:

[0233]

[0234]

[0235] wherein alkyl represents methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or n-pentyl.

[0236] The liquid crystal medium preferably further comprises one or more compounds of formula IVa,

[0237]

[0238] wherein

[0239] R 41 and R 42 each independently of one another represent a straight-chain alkyl, alkoxy, alkenyl, alkoxyalkyl or alkoxy having at most 12 C atoms, and represents

[0240] Z 4represents a single bond, -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -COO-, -OCO-, -C2F4-, -C4H8-, -CF=CF-.

[0241] Preferred compounds of formula IVa are as follows:

[0242]

[0243]

[0244] wherein

[0245] alkyl and alkyl* each independently of one another represent straight-chain alkyls having 1 to 6 C atoms.

[0246] The medium according to the invention preferably comprises at least one compound of formula IVa-1 and / or IVa-2.

[0247] The proportion of the compound of formula IVa in the overall mixture is preferably less than 5% by weight, very preferably less than 2% by weight.

[0248] Preferably, the medium comprises one or more compounds of formulae IVb-1 to IVb-3

[0249]

[0250] wherein

[0251] alkyl and alkyl* each independently of one another represent straight-chain alkyls having 1 to 6 C atoms, and

[0252] alkenyl and alkenyl* each independently of one another represent straight-chain alkenyls having 2 to 6 C atoms.

[0253] Among the compounds of formulae IVb-1 to IVb-3, the compound of formula IVb-2 is particularly preferred.

[0254] Particularly preferred biphenyls are

[0255]

[0256] where alkyl* represents an alkyl having 1 to 6 C atoms and preferably represents n-propyl. The medium according to the invention particularly preferably comprises one or more compounds of formula IVb-1-1 and / or IVb-2-3.

[0257] In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula V

[0258]

[0259] wherein

[0260] R 51 ,R 52 represents an alkyl group having 1 to 7 carbon atoms, an alkoxy group having 1 to 7 carbon atoms, or an alkoxyalkyl, alkenyl or alkenyloxy group having 2 to 7 carbon atoms, identically or differently, represents

[0261] Z 51 ,Z 52 each independently of one another represents -CH2-CH2-, -CH2-O-, -CH=CH-, -C≡C-, -COO- or a single bond, and

[0262] n is 1 or 2,

[0263] wherein compounds of formula CL are excluded.

[0264] Compounds of formula V are preferably selected from compounds of formulae V-1 to V-16:

[0265]

[0266] wherein R 51 and R 52 have the meanings as shown in formula V above.

[0267] R 51 and R 52 are preferably each independently of one another a straight-chain alkyl group having 1 to 7 carbon atoms or an alkenyl group having 2 to 7 carbon atoms.

[0268] Preferred media comprise one or more compounds of formulae V-1, V-5, V-6, V-8, V-9, V-10, V-11, V-12, V-14, V-15, and / or V-16, very preferably V-5 or V-6.

[0269] Preferably, the media according to the invention comprise one or more compounds of formula CL

[0270]

[0271] wherein

[0272] R L represents H, a straight-chain or branched-chain alkyl or alkoxy group having 1 to 15 carbon atoms, or a straight-chain or branched-chain alkenyl group having 2 to 15 carbon atoms, where one or more CH2 groups in these groups may each independently of one another be -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O- or -O-CO- are replaced in such a way that the O atoms are not directly linked to one another, and in which, furthermore, one or more H atoms may be replaced by halogen,

[0273] X L represents F, Cl, CN, CHF2, CF3, OCF3, or, identically or differently, has one of the meanings of R L as defined herein,

[0274] Y L represents H, F, Cl or CH3.

[0275] Compounds of formula CL are preferably selected from the group of compounds of formulae CL-1, CL-2 and CL-3

[0276]

[0277] wherein

[0278] R L1 and R L2 , identically or differently, have the meanings given above for formula I, and preferably represent an alkyl or alkenyl group having 1-7 C atoms or 2-7 C atoms respectively, where CH2 groups may be replaced by cyclopropane-1,2-diyl, and R L2 optionally represents an alkoxy group having 1 to 5 carbon atoms.

[0279] Very preferred compounds of formula I are selected from the compounds of formulae CL-3-1 to CL-3-12:

[0280]

[0281]

[0282] In a preferred embodiment, the medium according to the invention comprises the compound CL-3-1.

[0283] In a preferred embodiment of the invention, the medium further comprises one or more compounds of formulae VI-1 to VI-21, preferably formula VI-4:

[0284]

[0285]

[0286]

[0287] wherein R 6represents a straight-chain alkyl or alkoxy group having 1 to 6 carbon atoms, (O) represents -O- or a single bond, and m is 0, 1, 2, 3, 4, 5 or 6 and n is 0, 1, 2, 3 or 4.

[0288] R preferably represents methyl, ethyl, propyl, butyl, pentyl, hexyl, methoxy, ethoxy, propoxy, butoxy, pentyloxy.

[0289] In the compound of formula VI-4, (O) preferably represents -O-.

[0290] In a preferred embodiment of the present invention, the medium further comprises one or more compounds of formula VII-1 to VII-9

[0291]

[0292]

[0293] wherein

[0294] R 7 represents a straight-chain alkyl or alkoxy group having 1 to 6 carbon atoms, or a straight-chain alkenyl group having 2 - 6 carbon atoms, and

[0295] w is an integer from 1 to 6.

[0296] Preferably, the medium according to the present invention comprises one or more compounds of formula VIII:

[0297]

[0298] wherein

[0299] R 81 and R 82 , which are the same or different, represent H, halogen, CN, SCN, a straight-chain alkyl or alkoxy group having 1 to 15 carbon atoms, a straight-chain alkenyl or alkenyloxy group having 2 to 15 carbon atoms, or a branched-chain alkyl, alkoxy, alkenyl or alkenyloxy group having 3 to 15 carbon atoms, wherein one or more CH2 groups in these groups may each be independently replaced by the following groups in such a way that O atoms are not directly connected to each other: -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O- or -O-CO-, and wherein one or more H atoms may be replaced by halogen,

[0300] R 83 represents H, a straight-chain alkyl or alkoxy group having 1 to 10 carbon atoms, a straight-chain alkenyl or alkenyloxy group having 2 to 10 carbon atoms, or cyclopropyl, preferably H, methyl or ethyl, very preferably H or methyl, especially H;

[0301] A 0 、A 81 and A 82 each independently represents a phenylene-1,4-diyl group, where one or two CH groups may be replaced by N, and one or more H atoms may be replaced by a halogen, CN, CH3, CHF2, CH2F, CF3, OCH3, OCHF2 or OCF3; a cyclohexane-1,4-diyl group, where one or two non-adjacent CH2 groups may be independently replaced by O and / or S, and one or more H atoms may be replaced by F; a cyclohexene-1,4-diyl group; a bicyclo[1.1.1]pentane-1,3-diyl group; a bicyclo[2.2.2]octane-1,4-diyl group; a spiro[3.3]heptane-2,6-diyl group; a tetrahydropyran-2,5-diyl group or a 1,3-dioxane-2,5-diyl group;

[0302] Z 81 and Z 82 each independently represents -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C2H4-, -C2F4, -CF2CH2-, -CH2CF2-, -CFHCFH-, -CFHCH2-, -CH2CFH-, -CF2CFH-, -CFHCF2-, -CH=CH-, -CF=CH-, -CH=CF-, -CF=CF-, -C≡C- or a single bond;

[0303] n represents 0, 1, 2 or 3, preferably 0, 1 or 2, very preferably 0 or 1, particularly preferably 0; and

[0304] m represents 0, 1, 2 or 3, preferably 0, 1 or 2, very preferably 1 or 2, especially 1;

[0305] wherein the compound of formula I is not included in formula VIII.

[0306] A in formula I 81 and A 82 preferably represents a phenylene-1,4-diyl group, which may also be mono- or polysubstituted by F, and may also represent a cyclohexane-1,4-diyl group, a cyclohexenyl-1,4-diyl group, a tetrahydropyran-2,5-diyl group or a 1,3-dioxane-2,5-diyl group, very preferably a phenylene-1,4-diyl group (which may also be mono- or polysubstituted by F), or a cyclohexane-1,4-diyl group.

[0307] Z in formula I 81 and Z 82 preferably represents -CF2O-, -OCF2- or a single bond, very preferably a single bond.

[0308] A in formula I81 and A 82 Particularly preferably represents

[0309] wherein L represents halogen, CF3 or CN, preferably F.

[0310] Furthermore, preferred are compounds of formula VIII, wherein R 81 and R 82 each independently of one another represent H, F, or an alkyl, alkoxy, alkenyl or alkynyl group having 1 to 8, preferably 1 to 5 carbon atoms, each carbon atom optionally being substituted by halogen, especially by F.

[0311] R 81 and R 82 preferably represent H, an optionally fluorinated alkyl or alkoxy group having 1 to 7 carbon atoms, an optionally fluorinated alkenyl or alkynyl group having 2 to 7 carbon atoms, an optionally fluorinated cycloalkyl group having 3 to 12 carbon atoms.

[0312] Preferably, at least one of R 81 and R 82 is not H, particularly preferably neither R 81 and R 82 is H. R 81 Very particularly preferably an alkyl group. Furthermore, R 82 is preferably H, alkyl or fluorine. Very particularly preferably R 81 is an alkyl group, and R 82 is H or an alkyl group. R 81 and R 82 each independently of one another very particularly preferably represent an unbranched alkyl group having 1 to 5 carbon atoms. If R 81 and R 82 represent a substituted alkyl, alkoxy, alkenyl or alkynyl group, then the total number of carbon atoms in the R 81 and R 82 two groups is preferably less than 10.

[0313] Preferred compounds of formula VIII are selected from the following sub-formulas, more preferably from compounds of formula VIII-3:

[0314]

[0315]

[0316] wherein R 81 、R 82 and R 83 have the meanings as described above, and r, s and t are independently 0, 1, 2, 3 or 4. r is preferably 1 or 2, very preferably 2, and s and t are independently preferably 0 or 1, very preferably 0. R81 and R 82 independently represents in particular a normal alkyl group having 1 to 5 carbon atoms.

[0317] In a first very preferred embodiment, the compounds of formula VIII-1 to VIII-6 are selected from the compounds of formula VIII-1a to VIII-6a, in particular the compound of formula VIII-3a:

[0318]

[0319]

[0320] wherein R 81 、R 82 、R 83 、r and s have the above definitions.

[0321] In a second very preferred embodiment, the compounds of formula VIII-1 to VIII-6 are selected from the compounds of formula VIII-1b to VIII-5b, in particular the compound of formula VIII-2b:

[0322]

[0323]

[0324] wherein R 81 、R 82 、R 83 、r and s have the above definitions.

[0325] In a third very preferred embodiment, the compounds of formula VIII-1 to VIII-6 are selected from the compounds of formula VIII-1c to VIII-6c, in particular the compound of formula I3-c:

[0326]

[0327] wherein R 81 、R 82 、R 83 、r and s have the above definitions.

[0328] In a fourth very preferred embodiment, the compounds of formula VIII-1 to VIII-6 are selected from the compounds of formula VIII-1d to VIII-6d, especially the compound of formula VIII-3d:

[0329]

[0330]

[0331] wherein R 81, R 82 , R 83 , r and s have the definitions given above.

[0332] In a particularly preferred embodiment, the medium according to the invention comprises one or more compounds selected from compounds of formulae VIII-1a to VIII-6a and one or more compounds selected from compounds of formulae VIII-1b to VIII-6b.

[0333] Very particularly preferably, the medium comprises one or more compounds selected from the group consisting of compounds of formulae VIII-3a, VIII-2b, VIII-3c and VIII-3d:

[0334]

[0335]

[0336] wherein R 81 , R 82 , R 83 , r and s have the definitions given above. And preferably r is 0. Most preferred compounds of formula I specifically include one or more of the following:

[0337]

[0338]

[0339]

[0340] Alternatively or additionally, the following compounds of formula I can be used:

[0341]

[0342]

[0343]

[0344]

[0345]

[0346] In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula IX

[0347]

[0348] wherein

[0349] R 91 and R 92, identically or differently, represent H, halogen, a straight-chain alkyl or alkoxy group having 1 to 15 C atoms, a straight-chain alkenyl or alkenyloxy group having 2 to 15 carbon atoms, or a branched alkyl, alkoxy or alkenyl or alkenyloxy group each having 3 to 15 C atoms, where one or more CH2 groups in these groups may each independently of one another be replaced by -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly linked to one another, and where one or more H atoms may be replaced by halogen,

[0350] L 91 and L 92 , each independently of one another, represent F, Cl, CF3 or CHF2,

[0351] L 93 and L 94 , each independently of one another, represent H, F, Cl, CF3 or CHF2,

[0352] Y 1 represents H, F, Cl, CF3, CHF2 or CH3, preferably H or CH3, very preferably H, and

[0353] n is 0 or 1, preferably 0.

[0354] Very preferably, the compounds of formula IX are selected from the compounds of formulae IX-1 to IX-35

[0355]

[0356]

[0357]

[0358]

[0359]

[0360]

[0361]

[0362] Further preferred embodiments are listed below.

[0363] a) a liquid crystal medium which comprises at least one compound of formulae Z-1 to Z-7,

[0364]

[0365] wherein R and alkyl have the meanings indicated above for formula III.

[0366] b) A preferred liquid crystal medium according to the invention comprises one or more substances containing a tetrahydronaphthyl or naphthyl unit, for example, compounds of formulas N-1 to N-5,

[0367]

[0368] wherein R 1N and R 2N each independently of one another have the meanings indicated for R 2A and preferably represent a straight-chain alkyl, straight-chain alkoxy or straight-chain alkenyl, and

[0369] Z 1 and Z 2 each independently of one another represent -C2H4-, -CH=CH-, -(CH2)4-, -(CH2)3O-, -O(CH2)3-, -CH=CHCH2CH2-, -CH2CH2CH=CH-, -CH2O-, -OCH2-, -COO-, -OCO-, -C2F4-, -CF=CF-, -CF=CH-, -CH=CF-, -CF2O-, -OCF2-, -CH2- or a single bond.

[0370] c) Preferred mixtures comprise one or more compounds selected from difluorodibenzochroman compounds of formula BC, chromans of formula CR, and fluorophenanthrenes of formulas PH-1 and PH-2,

[0371]

[0372]

[0373] wherein R B1 , R B2 , R CR1 , R CR2 , R 1 , R 2 each independently of one another have the meaning of R 2A . c is 0, 1 or 2. R 1 and R 2 preferably, independently of one another, represent an alkyl or alkoxy having 1-6 C atoms.

[0374] Particularly preferred compounds of formulas BC and CR are compounds BC-1 to BC-7 and CR-1 to CR-5,

[0375]

[0376]

[0377]

[0378] wherein

[0379] alkyl and alkyl* each independently of the other represent a straight-chain alkyl group having 1 to 6 C atoms, and

[0380] alkenyl and alkenyl* each independently of the other represent a straight-chain alkenyl group having 2 to 6 C atoms.

[0381] Very particularly preferred are mixtures comprising one, two or three compounds of formula BC-2 and / or BC-3.

[0382] d) Preferred mixtures comprise one or more compounds of formula In indane,

[0383]

[0384] wherein

[0385] R 11 , R 12 , and R 13 each independently of the other represent a straight-chain alkyl, alkoxy, alkoxyalkyl or alkenyl group having 1-6 C atoms,

[0386] R 12 and R 13 alternatively represent halogen, preferably F,

[0387] represents

[0388]

[0389] i represents 0, 1 or 2.

[0390] Preferred compounds of formula In are the compounds of formulae In-1 to In-16 described below:

[0391]

[0392]

[0393] Particularly preferred are the compounds of formulae In-1, In-2, In-3 and In-4.

[0394] e) Preferred mixtures additionally comprise one or more compounds of formulae L-1 to L-5,

[0395]

[0396] wherein

[0397] R, R 1 and R 2 each independently of one another have the meanings given above for R in formula IIA 2A and alkyl represents an alkyl group having 1 - 6 C atoms. The parameter s represents 1 or 2.

[0398] The compounds of formulae L - 1 to L - 9 are preferably used at a concentration of 5 - 15 wt%, in particular 5 - 12 wt% and very particularly preferably 8 - 10 wt%.

[0399] f) The preferred mixture additionally contains one or more compounds of formula IIA - Y

[0400]

[0401] wherein R 11 and R 12 have one of the meanings given above for R in formula IIA 2A and L 1 and L 2 identically or differently represent F or Cl,

[0402] The preferred compounds of formula IIA - Y are selected from the following sub - formulae

[0403]

[0404]

[0405] wherein, Alkyl and Alkyl* each independently of one another represent a straight - chain alkyl group having 1 - 6 C atoms, Alkoxy represents a straight - chain alkoxy group having 1 - 6 C atoms, Alkenyl and Alkenyl* each independently of one another represent a straight - chain alkenyl group having 2 - 6 carbon atoms, and O represents an oxygen atom or a single bond. Alkenyl and Alkenyl* preferably represent CH2 = CH -, CH2 = CHCH2CH2 -, CH3 - CH = CH -, CH3 - CH2 - CH = CH -, CH3-(CH2)2 - CH = CH -, CH3-(CH2)3 - CH = CH - or CH3 - CH = CH-(CH2)2-.

[0406] The particularly preferred compounds of formula IIA - Y are selected from the following sub - formulae:

[0407]

[0408] wherein Alkoxy and Alkoxy* have the meanings defined above and preferably represent methoxy, ethoxy, n - propyloxy, n - butyloxy or n - pentyloxy.

[0409] Preferably, the medium according to the invention comprises a compound selected from the compounds of formulae ST-1 to ST-18, very preferably formula ST-3:

[0410]

[0411]

[0412]

[0413]

[0414] wherein

[0415] R ST represents H, an alkyl or alkoxy group having 1 to 15 C atoms, wherein, in addition, one or more CH2 groups in these groups may each independently of one another be replaced by -C≡C-, -CF2O-, -OCF2-, -CH=CH-,

[0416] -O-, -CO-O-,-O-CO- in such a way that the O atoms are not directly connected to one another, and wherein, in addition, one or more H atoms may be replaced by halogen,

[0417] in each occurrence, the same or different, represents

[0418] Z ST each independently of one another represents -CO-O-, -O-CO-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CH2-, -CH2CH2-, -(CH2)4-, -CH=CH-, -CH2O-, -C2F4-, -CH2CF2-, -CF2CH2-, -CF=CF-, -CH=CF-, -CF=CH-, -CH=CH-, -C≡C- or a single bond,

[0419] L 1 and L 2 each independently of one another represents F, Cl, CH3, CF3 or CHF2,

[0420] p represents 0, 1 or 2,

[0421] q represents 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0422] Among the compounds of formula ST, the compounds of formula ST-3 are particularly preferred, especially:

[0423]

[0424] where n = 1, 2, 3, 4, 5, 6 or 7, preferably n

[0425] = 3

[0426]

[0427] where n = 1, 2, 3, 4, 5, 6 or 7, preferably n = 3

[0428]

[0429] where n = 1, 2, 3, 4, 5, 6 or 7, preferably n = 1 or 7

[0430]

[0431]

[0432] In the compounds of formulas ST-3a and ST-3b, n preferably represents 3. In the compounds of formula ST-2a, n preferably represents 7.

[0433] Very particularly preferred mixtures according to the invention comprise one or more stabilizers selected from the compounds of formulas ST-2a-1, ST-3a-1, ST-3b-1, ST-8-1, ST-9-1 and ST-12:

[0434]

[0435]

[0436] Preferably, the medium comprises one or more compounds of formula S

[0437]

[0438] where

[0439] Ar represents a methylene group or an aromatic hydrocarbon group having 6 to 40 C atoms or a heteroaromatic hydrocarbon group having 4 to 40 C atoms; preferably an aromatic hydrocarbon group having 6 to 40 C atoms;

[0440] Sp represents a spacer group;

[0441] R S represents H, an alkyl group having 1 to 12 C atoms or an alkenyl group having 2 to 12 C atoms;

[0442] Z S represents -O-, -C(O)O-, -(CH2) z -, or -(CH2) z O-, or a single bond;

[0443] HA represents

[0444] R H represents H, O · , CH3, OH or OR S ;

[0445] R S1 , R S2 , R S3 and R S4 , which are the same or different and represent an alkyl group having 1 to 6 C atoms, preferably having 1 to 3 C atoms, very preferably CH3;

[0446] G represents H or R S or group Z S -HA;

[0447] z is an integer from 1 to 6, and

[0448] q is 2, 3 or 4, preferably 3 or 4.

[0449] In formula S, aryl represents an aromatic or heteroaromatic hydrocarbon group having 4 to 40 C atoms, including one, two, three or four aromatic rings including fused rings, which may be directly linked or linked via an alkylene linking group having 1 to 12 carbon atoms, where one or more H atoms are optionally replaced by an alkyl or alkoxy group having 1 to 6 C atoms or an alkenyl group having 2 to 6 C atoms, or optionally replaced by CN, CF3 or a halogen, and where one or more CH2 groups may each independently of one another be replaced by -O-, -S-, -NH-, -N(C1-C4-alkyl)-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH=CH- or -C≡C- in such a way that O or S atoms are not directly linked to one another.

[0450] Preferred aryl groups are benzene, naphthalene, anthracene, biphenyl, m-terphenyl, p-terphenyl and (phenylalkyl)benzene, where the alkyl group is a straight-chain alkyl group having 1-12 C atoms.

[0451] In a preferred embodiment, the medium according to the invention comprises a compound of formula S, where the parameter q is 3 and G represents group Z S -HA.

[0452] In another preferred embodiment, the medium according to the invention comprises a compound of formula S, where the parameter q is 4 and G represents H or R S .

[0453] The compounds of formula S are preferably selected from the compounds of formula S-1, S-2 and S-3:

[0454]

[0455]

[0456] wherein R H has the meaning and preferred representation H or O as given above . ,

[0457] Sp represents, identically or differently each time it appears, a spacer group, and

[0458] W represents a straight-chain or branched-chain, optionally unsaturated, alkylene group having 1 - 12 C atoms, wherein one or more non-adjacent -CH2- groups may be replaced by -O-.

[0459] Preferred compounds of formula S-1 are selected from the compounds of formula S-1-1:

[0460]

[0461] wherein R H has the meaning and preferred representation H or O as given above . , and n is an integer from 0 to 12, preferably 5, 6, 7, 8 or 9, very preferably 7.

[0462] Preferred compounds of formula S-2 are selected from the compounds of formula S-2-1:

[0463]

[0464] wherein R H has the meaning and preferred representation H or O as given above . , and n2, identically or differently each time it appears, preferably identically, is an integer from 1 to 12, preferably 2, 3, 4, 5, or 6, very preferably 3, and R S , identically or differently each time it appears, preferably identically represents an alkyl group having 1 to 6 C atoms, preferably n-butyl.

[0465] Preferred compounds of formula S-3 are selected from the compounds of formula S-3-1:

[0466]

[0467] wherein R H has the meaning and preferred representation H or O as given above . , and n is an integer from 0 to 12, preferably 5, 6, 7, 8 or 9, very preferably 7.

[0468] Based on the mixture, the compounds of formula S and ST-1 to ST-18 are preferably each present in the liquid crystal mixture according to the invention in an amount of 0.005 - 0.5%.

[0469] If the mixture according to the invention comprises two or more compounds of the formulae S and ST-1 to ST-18, then, based on the mixture, in the case of two compounds, the concentration is increased accordingly to 0.01 - 1%.

[0470] However, based on the mixture according to the invention, the total proportion of the compounds of the formulae S and ST-1 to ST-18 should not exceed 2%.

[0471] The liquid crystal medium according to the invention (also referred to herein as a liquid crystal host mixture) is suitable for use in polymer-stabilized displays. For this purpose, the medium according to the invention optionally comprises one or more polymerizable compounds of the formula P:

[0472] P-Sp-A 1 -(Z 1 -A 2 ) z -R P

[0473] wherein, independently of one another and each time the same or different

[0474] P represents a polymerizable group,

[0475] Sp represents a spacer group or a single bond,

[0476] A 1 、A 2 represents an aromatic, heteroaromatic, cycloaliphatic or heterocyclic group, preferably having 4 to 25 ring atoms, which may also contain fused rings and which is unsubstituted or mono- or polysubstituted by L,

[0477] Z 1 represents -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -OCH2-, -CH2O-, -SCH2-, -CH2S-,-CF2O-, -OCF2-, -CF2S-, -SCF2-, -(CH2) n1 -, -CF2CH2-, -CH2CF2-, -(CF2) n1 -, -CH=CH-, -CF=CF-, -CH=CF-, -CF=CH-, -C≡C-, -CH=CH-CO-O-, -O-CO-CH=CH-, -CH2-CH2-CO-O-, -O-CO-CH2-CH2-, -CR 0 R 00 -, or a single bond,

[0478] R 0 ,R 00 represents H or an alkyl group having 1 to 12 C atoms,

[0479] R represents H, L, or P-Sp-

[0480] L represents F, Cl, -CN, P-Sp- or a straight-chain, branched-chain or cycloalkyl group having 1 to 25 C atoms, where one or more non-adjacent CH₂ groups are optionally replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and / or S atoms are not directly linked to each other, and where one or more H atoms are each optionally replaced by P-Sp-, F or Cl

[0481] z is 0, 1, 2 or 3, and

[0482] n1 is 1, 2, 3 or 4.

[0483] As used herein, the term "reliability" means the quality of the performance of a display over time and under different stress loads, such as light load, temperature, humidity, voltage, and includes display effects such as image sticking (surface and line image sticking), non-uniformity (mura), smudging (yogore), etc., which are known to those skilled in the art of LC displays. As a standard parameter for classifying reliability, the voltage holding ratio (VHR) value is usually used, which is a measure of the ability to maintain a constant voltage in a test display. Among other factors, a high VHR is a prerequisite for high reliability of the LC medium.

[0484] Unless otherwise stated, the term "PSA" is used hereinafter when generally referring to displays in which the polymer maintains the alignment type, and the term "PS" is used when referring to specific display modes (such as PS-VA, PS-TN, etc.).

[0485] As used herein, the terms "active layer" and "switchable layer" denote, in an electro-optical display, for example in an LC display, a layer containing one or more molecules having structural and optical anisotropy (such as LC molecules), which change their orientation when subjected to an external stimulus such as an electric or magnetic field, which results in a change in the transmittance of the layer for polarized or non-polarized light.

[0486] As used herein, the terms "tilt" and "tilt angle" should be understood to denote the tilted alignment of the LC molecules of the LC medium with respect to the cell surface in an LC display (preferably a PSA display here). The tilt angle here represents the average angle (<90°) between the longitudinal molecular axis (LC director) of the LC molecules and the outer plate parallel to the plane forming the LC cell. Here, a low value of the tilt angle (i.e., a large deviation from the 90° angle) corresponds to a large tilt. A suitable method for measuring the tilt angle is given in the examples. Unless otherwise stated, the tilt angle values disclosed in the context are related to this measurement method.

[0487] As used herein, the terms "reactive mesogen" and "RM" are understood to denote a compound comprising a mesogenic or liquid crystalline backbone, and one or more functional groups attached thereto that are suitable for use in polymerization, and said functional groups are also referred to as "polymerizable groups" or "P".

[0488] Unless otherwise specified, the term "polymerizable compound" as used herein is understood to be a polymerizable monomeric compound.

[0489] As used herein, the term "low molecular weight compound" is understood to denote monomeric and / or compounds that are not prepared by a polymerization reaction, as opposed to "polymeric compounds" or "polymers".

[0490] As used herein, the term "non-polymerizable compound" is understood to denote a compound that does not contain functional groups suitable for use in polymerization under the conditions normally applied to the polymerization of RM.

[0491] As used herein, the term "mesogenic group" is known to those skilled in the art and has been described in the literature, and it denotes a group that substantially contributes to the formation of a liquid crystal (LC) phase in a low molecular weight or polymeric material due to the anisotropy of its attractive and repulsive interactions. Compounds containing a mesogenic group (mesogenic compounds) do not necessarily have an LC phase themselves. Mesogenic compounds can also exhibit LC phase behavior only after mixing with other compounds and / or after polymerization. Typical mesogenic groups are, for example, rigid rod-like or disc-like units. Terms and definitions related to mesogenic or LC compounds are given in Pure Appl. Chem. 2001, 73(5), 888 and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340 - 6368.

[0492] As used herein, the terms "optically active" and "chiral" are synonyms for a material that can induce a helical pitch in a nematic host material, also referred to as a "chiral dopant".

[0493] As used herein, the term "spacer group" (also referred to as "Sp" in the context) is known to those skilled in the art in the prior art and has been described in the literature, see for example Pure Appl. Chem. 2001, 73(5), 888 and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340 - 6368. As used herein, the term "spacer group" or "spacer" denotes a flexible group, for example an alkylene group, that connects the mesogenic group and the polymerizable group(s) in a polymerizable mesogenic compound.

[0494] Similarly, in the compounds of formula I, the spacer group connects the central hydrocarbon group to the photoactive, stable sterically hindered amine functional group.

[0495] In the context, represents a trans-1,4-cyclohexylene ring.

[0496] In the group the single bond shown between two ring atoms can be connected to any free position of the benzene ring.

[0497] "Organic group" in the context means a carbon or hydrocarbon group.

[0498] "Carbon group" means a mono- or polyvalent organic group containing at least one carbon atom, where the group contains no other atoms (e.g., -C≡C-) or optionally contains one or more other atoms such as N, O, S, B, P, Si, Se, As, Te or Ge (e.g., carbonyl, etc.). The term "hydrocarbon group" means a carbon group which additionally contains one or more H atoms and optionally one or more heteroatoms such as N, O, S, B, P, Si, Se, As, Te or Ge.

[0499] "Halogen" means F, Cl, Br or I, preferably F or Cl.

[0500] -CO-, -C(=O)- and -C(O)- represent a carbonyl group, i.e.,

[0501] The carbon or hydrocarbon group can be a saturated or unsaturated group. Unsaturated groups are, for example, aryl, alkenyl or alkynyl groups. The carbon or hydrocarbon group having more than 3 C atoms can be straight-chain, branched and / or cyclic and can also contain spiro linkages or fused rings.

[0502] The terms "alkyl", "aryl", "heteroaryl", etc. also include polyvalent groups such as alkylene, arylene, heteroarylene, etc.

[0503] The term "aryl" means an aromatic carbon group or a group derived therefrom. The term "heteroaryl" means an "aryl" as defined above which contains one or more heteroatoms (preferably selected from N, O, S, Se, Te, Si and Ge).

[0504] Preferred carbon and hydrocarbyl groups are optionally substituted, straight-chain, branched or cyclic alkyl, alkenyl, alkynyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy having 1 to 40, preferably 1 to 20, very preferably 1 to 12 C atoms, optionally substituted aryl or aryloxy having 5 to 30, preferably 6 to 25 C atoms, or optionally substituted alkylaryl, aralkyl, alkylaryloxy, arylalkyloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxy having 5 to 30, preferably 6 to 25 C atoms, where one or more C atoms may also be replaced by heteroatoms (preferably selected from N, O, S, Se, Te, Si and Ge).

[0505] Further preferred carbon and hydrocarbyl groups are C1-C 20 alkyl, C2-C 20 alkenyl, C2-C 20 alkynyl, C3-C 20 allyl, C4-C 20 alkyl diene, C4-C 20 polyene, C6-C 20 cycloalkyl, C4-C 15 cycloalkenyl, C6-C 30 aryl, C6-C 30 alkylaryl, C6-C 30 aralkyl, C6-C 30 alkylaryloxy, C6-C 30 arylalkyloxy, C2-C 30 heteroaryl, C2-C 30 heteroaryloxy.

[0506] Particularly preferred are C1-C 12 alkyl, C2-C 12 alkenyl, C2-C 12 alkynyl, C6-C 25 aryl and C2-C 25 heteroaryl.

[0507] Further preferred carbon-based and hydrocarbyl groups are straight-chain, branched or cyclic alkyls having 1-20, preferably 1-12 C atoms, which are unsubstituted or mono- or poly-substituted by F, Cl, Br, I or CN, and where one or more non-adjacent CH2 groups may each independently of one another be replaced by -C(R x )=C(R x )-, -C≡-, -N(R x )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and / or S atoms are not directly linked to one another.

[0508] Rx Preferably represents H, F, Cl, CN, a straight-chain, branched-chain or cyclic alkyl chain having 1 to 25 C atoms, wherein, additionally, one or more non-adjacent C atoms may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, and wherein one or more H atoms may be replaced by F or Cl, or represents an optionally substituted aryl or aryloxy group having 6 to 30 C atoms, or an optionally substituted heteroaryl or heteroaryloxy group having 2 to 30 C atoms.

[0509] Preferred alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, 2-methylbutyl, n-pentyl, sec-pentyl, cyclopentyl, n-hexyl, cyclohexyl, 2-ethylhexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, dodecyl, trifluoromethyl, perfluorobutyl, 2,2,2-trifluoroethyl, perfluorooctyl, perfluorohexyl, etc.

[0510] Preferred alkenyl groups are, for example, vinyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl, cyclooctenyl, etc.

[0511] Preferred alkynyl groups are, for example, ethynyl, propynyl, butynyl, pentynyl, hexynyl, octynyl, etc.

[0512] Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxyethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, 2-methylbutoxy, n-pentyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy, n-nonyloxy, n-decyloxy, n-undecyloxy, n-dodecyloxy, etc.

[0513] Preferred amino groups are, for example, dimethylamino, methylamino, methylphenylamino, phenylamino, etc.

[0514] Aryl and heteroaryl groups can be monocyclic or polycyclic, i.e., they can contain one ring (e.g., phenyl) or two or more rings, which can also be fused (e.g., naphthyl) or covalently bonded (e.g., biphenyl), or contain a combination of fused and linked rings. Heteroaryl contains one or more heteroatoms, preferably selected from O, N, S, and Se.

[0515] Particularly preferred are mono-, bi- or tricyclic aryl groups having 6-25 C atoms and mono-, bi- or tricyclic heteroaryl groups having 5-25 ring atoms, which optionally contain fused rings and are optionally substituted. Further preferred are 5-, 6- or 7-membered aryl and heteroaryl groups, wherein additionally, one or more CH groups may be replaced by N, S or O in such a way that O atoms and / or S atoms are not directly linked to each other.

[0516] Preferred aryl groups are, for example, phenyl, biphenyl, terphenyl, [1,1':3',1”]-terphenyl-2'-yl, naphthyl, anthracenyl, binaphthyl, phenanthryl, 9,10-dihydro-phenanthryl, pyrene, dihydropyrene, perylene, tetracene, pentacene, benzopyrene, fluorene, indene, indenofluorene, spirobifluorene and the like.

[0517] Preferred heteroaryl groups are, for example, 5-membered rings such as pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, tetrazole, furan, thiophene, selenophene, oxazole, isoxazole, 1,2-thiazole, 1,3-thiazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, 1,3,4-thiadiazole, 6-membered rings such as pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, 1,2,4-triazine, 1,2,3-triazine, 1,2,4,5-tetrazine, 1,2,3,4-tetrazine, 1,2,3,5-tetrazine or fused groups such as indole, isoindole, indolizine, indazole, benzimidazole, benzotriazole, purine, naphthimidazole, phenanthrimidazole, pyridinimidazole, pyrazinimidazole, quinoxalinimidazole, benzoxazole, naphthoxazole, anthroxazole, phenanthroxazole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5,6-quinoline, benzo-6,7-quinoline, benzo-7,8-quinoline, benzoisoquinoline, acridine, phenothiazine, phenoxazine, benzopyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarbazole, phenanthridine, phenanthroline, thiophene[2,3b]thiophene, thiophene[3,2b]thiophene, dithienothiophene, isobenzothiophene, dibenzothiophene, benzothiophene, benzothiadiazolethiophene, or combinations of these groups.

[0518] The aryl and heteroaryl groups mentioned in the context may also be substituted by alkyl, alkoxy, thioalkyl, fluorine, fluoroalkyl or other aryl or heteroaryl groups.

[0519] (Non-aromatic) alicyclic groups and heterocyclic groups include both saturated rings, i.e., rings containing only single bonds, and partially unsaturated rings, i.e., those that can also contain multiple bonds. Heterocycles contain one or more heteroatoms, preferably selected from Si, O, N, S, and Se.

[0520] (Non-aromatic) alicyclic groups and heterocyclic groups can be monocyclic, i.e., containing only one ring (e.g., cyclohexane), or polycyclic, i.e., containing multiple rings (e.g., decalin or bicyclooctane). Saturated groups are particularly preferred. Additionally preferred are mono-, bi-, or tricyclic groups having 5 - 25 ring atoms, which optionally contain fused rings and are optionally substituted. Further preferred are 5-, 6-, 7-, or 8-membered carbocyclic groups, where additionally, one or more C atoms can be replaced by Si and / or one or more CH groups can be replaced by N and / or one or more non-adjacent CH2 groups can be replaced by -O- and / or -S-.

[0521] Preferred alicyclic groups and heterocyclic groups are, for example, 5-membered groups such as cyclopentane, tetrahydrofuran, tetrahydrothiophene, pyrrolidine; 6-membered groups such as cyclohexane, silinane, cyclohexene, tetrahydropyran, tetrahydrothiopyran, 1,3-dioxane, 1,3-dithiane, piperidine; 7-membered groups such as cycloheptane; and fused groups such as tetralin, decalin, indane, bicyclo[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, octahydro-4,7-methanoindane-2,5-diyl.

[0522] Preferred substituents are, for example, solubility-promoting groups such as alkyl or alkoxy; electron-withdrawing groups such as fluorine, nitro, or nitrile; or substituents for increasing the glass transition temperature (Tg) of the polymer, especially bulky groups such as tert-butyl or optionally substituted aryl.

[0523] Preferred substituents, also referred to hereinafter as "L" S ", are, for example, F, Cl, Br, I, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, -C(=O)N(R x )2, -C(=O)Y 1 , -C(=O)R x , -N(R x )2, straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy, or alkoxycarbonyloxy having 1 - 25 C atoms, where one or more H atoms can optionally be replaced by F or Cl, optionally substituted silyl having 1 to 20 Si atoms, or optionally substituted aryl having 6 to 25, preferably 6 to 15 C atoms.

[0524] wherein R x represents H, F, Cl, CN, or a straight-chain, branched-chain or cyclic alkyl group having 1 to 25 C atoms, wherein one or more non-adjacent CH2-groups are optionally replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O- and / or S-atoms are not directly linked to one another, and wherein one or more H atoms are each optionally replaced by F, Cl, P- or P-Sp-, and

[0525] Y 1 represents a halogen.

[0526] "substituted silyl or aryl" preferably means that it is substituted by a halogen, -CN, R 0 , -OR 0 , -CO-R 0 , -CO-O-R 0 , -O-CO-R 0 or -O-CO-O-R 0 , where R 0 represents H or an alkyl group having 1 to 20 C atoms.

[0527] Particularly preferred substituents L are, for example, F, Cl, CN, NO2, CH3, C2H5, OCH3, OC2H5, COCH3, COC2H5, COOCH3, COOC2H5, CF3, OCF3, OCHF2, OC2F5, and also phenyl.

[0528] A 1 and A 2 very preferably mean wherein L has one of the above meanings and r represents 0, 1, 2, 3 or 4, in particular

[0529] means

[0530]

[0531] The polymerizable group P is a group suitable for polymerization reactions (e.g. free-radical or ionic chain polymerization, addition polymerization or condensation polymerization), or for polymer-analogous reactions (e.g. addition or condensation on the polymer backbone). Particular preference is given to groups for chain polymerization, in particular those containing a C═C double bond or a -C≡C- triple bond, and groups suitable for ring-opening polymerization, such as oxetanyl or epoxy groups.

[0532] Preferred groups P are selected from the group consisting of: CH2═CW 1 -CO-O-, CH2═CW1 -CO-、

[0533] CH2=CW 2 -(O) k3 -、CW 1 =CH-CO-(O) k3 -、CW 1 =CH-CO-NH-、CH2=CW 1 -CO-NH-、

[0534] CH3-CH=CH-O-、(CH2=CH)2CH-OCO-、(CH2=CH-CH2)2CH-OCO-、

[0535] (CH2=CH)2CH-O-、(CH2=CH-CH2)2N-、(CH2=CH-CH2)2N-CO-、HO-CW 2 W 3 -、HS-CW 2 W 3 -、HW 2 N-、HO-CW 2 W 3 -NH-、CH2=CW 1 -CO-NH-、CH2=CH-(COO) k1 -Phe-(O) k2 -、CH2=CH-(CO) k1 -Phe-(O) k2 -、Phe-CH=CH-、HOOC-、OCN- and W 4 W 5 W 6 Si-, where W 1 represents H, F, Cl, CN, CF3, phenyl or an alkyl group having 1 to 5 C atoms, especially H, F, Cl or CH3, W 2 and W 3 each independently of one another represent H or an alkyl group having 1 to 5 C atoms, especially H, methyl, ethyl or n-propyl, W 4 、W 5 and W 6 each independently of one another represent Cl, an oxaalkyl group or an oxacarbonylalkyl group having 1 to 5 C atoms, W 7 and W 8Each independently represents H, Cl or an alkyl group having 1 to 5 C atoms, Phe represents 1,4-phenylene, which is optionally substituted by one or more groups L different from P-SP- as defined above, k1, k2 and k3 each independently represent 0 or 1, k3 preferably represents 1, and k4 represents an integer from 1 to 10.

[0536] Very preferred groups P are selected from the group consisting of: CH2=CW 1 -CO-O-, CH2=CW 1 -CO-, CH2=CW 2 -O-, CH2=CW 2 -, CW 1 =CH-CO-(O) k3 -, CW 1 =CH-CO-NH-, CH2=CW 1 -CO-NH-, (CH2=CH)2CH-OCO-, (CH2=CH-CH2)2CH-OCO-, (CH2=CH)2CH-O-, (CH2=CH-CH2)2N-, (CH2=CH-CH2)2N-CO-, CH2=CW 1 -CO-NH-, CH2=CH-(COO) k1 -Phe-(O) k2 -, CH2=CH-(CO) k1 -Phe-(O) k2 -, Phe-CH=CH- and W 4 W 5 W 6 Si-, where W 1 represents H, F, Cl, CN, CF3, phenyl or an alkyl group having 1 to 5 C atoms, especially H, F, Cl or CH3, W 2 and W 3 each independently represent H or an alkyl group having 1 to 5 C atoms, especially H, methyl, ethyl or n-propyl, W 4 、W 5 and W 6 each independently represent Cl, an oxaalkyl group or an oxacarbonylalkyl group having 1 to 5 C atoms, W 7 and W 8 Each independently represents H, Cl or an alkyl group having 1 to 5 C atoms, Phe represents 1,4-phenylene, k1, k2 and k3 each independently represent 0 or 1, k3 preferably represents 1, and k4 represents an integer from 1 to 10.

[0537] A very preferred group P is selected from the group consisting of: CH2=CW 1 -CO-O-, especially CH2=CH-CO-O-, CH2=C(CH3)-CO-O- and CH2=CF-CO-O-, and also CH2=CH-O-, (CH2=CH)2CH-O-CO-, (CH2=CH)2CH-O-,

[0538] Other particularly preferred polymerizable groups P are selected from vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetanyl and epoxy groups, and most preferably from acrylate and methacrylate groups.

[0539] If the spacer group Sp is different from a single bond, it is preferably of the formula Sp"-X" such that each group P-Sp- corresponds to the formula R-Sp"-X"-, where

[0540] Sp" represents a straight-chain or branched alkylene having 1 to 20, preferably 1 to 12 C atoms, which is optionally mono- or polysubstituted by F, Cl, Br, I or CN, and wherein additionally, one or more non-adjacent CH2 groups are each independently replaced by -O-, -S-, -NH-, -N(R 0 )-, -Si(R 0 R 00 )-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -S-CO-, -CO-S-, -N(R 00 )-CO-O-, -O-CO-N(R 0 )-, -N(R 0 )-CO-N(R 00 )-, -CH=CH- or -C≡C- in such a way that O and / or S atoms are not directly connected to each other,

[0541] X" represents -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CO-N(R 0 )-, -N(R 0 )-CO-, -N(R 0 )-CO-N(R 00 )-, -OCH2-, -CH2O-, -SCH2-, -CH2S-, -CF2O-, -OCF2-, -CF2S-, -SCF2-, -CF2CH2-, -CH2CF2-, -CF2CF2-, -CH=N-, -N=CH-, -N=N-, -CH=CR 0 -, -CY 2 =CY 3-, -C≡C-, -CH=CH-CO-O-, -O-CO-CH=CH- or a single bond,

[0542] R 0 and R 00 each independently of one another represent H or an alkyl group having 1 to 20 C atoms, and

[0543] Y 2 and Y 3 each independently of one another represent H, F, Cl or CN.

[0544] X" is preferably -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -CO-NR 0 -, -NR 0 -, -NR 0 -, -CO-NR 00 - or a single bond.

[0545] Typical spacer groups Sp and -Sp"-X"- are for example -(CH2) p1 -, -(CH2) p1 -O-, -(CH2) p1 -O-CO-, -(CH2) p1 -CO-O-, -(CH2) p1 -O-CO-O-, -(CH2CH2O) q1 -CH2CH2-, -CH2CH2-S-CH2CH2-, -CH2CH2-NH-CH2CH2- or -(SiR 0 R 00 -O) p1 -, where p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R 0 and R 00 have the meanings indicated above.

[0546] Particularly preferred groups Sp and -Sp"-X"- are -(CH2) p1 -, -(CH2) p1 -O-, -(CH2) p1 -O-CO-, -(CH2) p1 -CO-O-, -(CH2) p1 -O-CO-O-, where p1 and q1 have the meanings indicated above.

[0547] Particularly preferred groups Sp" are, in each case, straight-chain ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethyl-N-methylimino-ethylene, 1-methylalkylene, vinylidene, propenylene and butenylene.

[0548] In a preferred embodiment of the present invention, the compounds of formula P and its sub-formulae contain a spacer group Sp substituted by one or more polymerizable groups P such that the group Sp-P corresponds to Sp(P) s , where s is ≥ 2 (branched polymerizable groups).

[0549] Preferred compounds of formula P according to this preferred embodiment are those in which s is 2, i.e., compounds containing the group Sp(P)2. Very preferred compounds of formula P according to this preferred embodiment contain a group selected from the following formulae:

[0550] -X-alkyl-CHPP S1

[0551] -X-alkyl-CH((CH2) aa P)((CH2) bb P) S2

[0552] -X-N((CH2) aa P)((CH2) bb P) S3

[0553] -X-alkyl-CHP-CH2-CH2P S4

[0554] -X-alkyl-C(CH2P)(CH2P)-C aa H 2aa+1 S5

[0555] -X-alkyl-CHP-CH2P S6

[0556] -X-alkyl-CPP-C aa H 2aa+1 S7

[0557] -X-alkyl-CHPCHP-C aa H 2aa+1 S8

[0558] where P is as defined in formula P,

[0559] "alkyl" represents a single bond or a straight-chain or branched alkylene group having 1 to 12 C atoms, which is unsubstituted or mono- or poly-substituted by F, Cl or CN, and one or more non-adjacent CH2 groups may each independently be replaced by -C(R 0 )=C(R 0 )-, -C≡C-, -N(R 0 )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, where R 0 has the meaning indicated above,

[0560] aa and bb each independently represent 0, 1, 2, 3, 4, 5 or 6,

[0561] X has one of the meanings indicated for X", and is preferably O, CO, SO2, O-CO-, CO-O or a single bond.

[0562] The preferred spacer group Sp(P)2 is selected from formulae S1, S2 and S3.

[0563] The very preferred spacer group Sp(P)2 is selected from the following sub-formulae:

[0564] -CHPP S1a

[0565] -O-CHPP S1b

[0566] -CH2-CHPP S1c

[0567] -OCH2-CHPP S1d

[0568] -CH(CH2-P)(CH2-P) S2a

[0569] -OCH(CH2-P)(CH2-P) S2b

[0570] -CH2-CH(CH2-P)(CH2-P) S2c

[0571] -OCH2-CH(CH2-P)(CH2-P) S2d

[0572] -CO-NH((CH2)2P)((CH2)2P) S3a

[0573] In the compounds of formula P and its sub-formulae as described above and below, P is preferably selected from the group consisting of: vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and epoxide, most preferably selected from acrylate and methacrylate.

[0574] More preferably, it is a compound of formula P and its sub-formulas as described above and below, wherein all polymerizable groups P present in the compound have the same meaning, and very preferably represent acrylate or methacrylate, and most preferably methacrylate.

[0575] In the compounds of formula P and its sub-formulas as described above and below, R preferably represents P-Sp-.

[0576] More preferably, it is a compound of formula P and its sub-formulas as described above and below, wherein Sp represents a single bond or -(CH2) p1 -, -O-(CH2) p1 -, -O-CO-(CH2) p1 or -CO-O-(CH2) p1 , where p1 is 2, 3, 4, 5 or 6, and if Sp is -O-(CH2) p1 -, -O-CO-(CH2) p1 or -CO-O-(CH2) p1 , then the O-atom or the CO-group is respectively connected to the benzene ring.

[0577] More preferably, it is a compound of formula P and its sub-formulas as described above and below, wherein at least one group Sp is a single bond.

[0578] More preferably, it is a compound of formula P and its sub-formulas as described above and below, wherein at least one group Sp is different from a single bond, and is preferably selected from -(CH2) p1 -, -O-(CH2) p1 -, -O-CO-(CH2) p1 or -CO-O-(CH2) p1 , where p1 is 2, 3, 4, 5 or 6, and if Sp is -O-(CH2) p1 -, -O-CO-(CH2) p1 or -CO-O-(CH2) p1 , then the O-atom or the CO-group is respectively connected to the benzene ring.

[0579] The very preferred group -A 1 -(Z-A 2 ) z - is selected from the following formulas

[0580]

[0581]

[0582] wherein at least one benzene ring is substituted by at least one group L and the benzene ring is optionally further substituted by one or more groups L or P-Sp-.

[0583] Preferred compounds of formula P and its sub-formulas are selected from the following preferred embodiments, including any combination thereof:

[0584] - All groups P in the compound have the same meaning,

[0585] --A 1 -(Z - A 2 ) z - Selected from formulae A1, A2 and A5,

[0586] - The compound contains exactly two polymerizable groups (represented by the group P),

[0587] - The compound contains exactly three polymerizable groups (represented by the group P),

[0588] - P is selected from the group consisting of acrylate, methacrylate and oxetane, very preferably acrylate or methacrylate,

[0589] - P is methacrylate,

[0590] - All groups Sp are single bonds,

[0591] - At least one of the groups Sp is a single bond and at least one of the groups Sp is different from a single bond,

[0592] - When Sp is different from a single bond, it is -(CH2) p2 -、-(CH2) p2 -O -、-(CH2) p2 -CO - O -、-(CH2) p2 -O - CO -, where p2 is 2, 3, 4, 5 or 6, and the O atom or the CO - group is respectively connected to the benzene ring,

[0593] - Sp is a single bond or represents -(CH2) p2 -、-(CH2) p2 -O -、-(CH2) p2 -CO - O -、-(CH2) p2 -O - CO -, where p2 is 2, 3, 4, 5 or 6, and the O atom or the CO - group is respectively connected to the benzene ring,

[0594] - R represents P - Sp -,

[0595] - R does not represent or contain a polymerizable group,

[0596] -R does not represent or contain a polymerizable group and represents a straight-chain, branched-chain or cyclic alkyl group having 1 to 25 C atoms, where one or more non-adjacent CH2 groups are optionally replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and / or S atoms are not directly connected to each other, and where one or more H atoms are each optionally replaced by F, Cl or L a is replaced by

[0597] -L or L’ represents F, Cl or CN,

[0598] -L is F.

[0599] Suitable and preferred compounds of formula P are selected from the following formulas:

[0600]

[0601]

[0602]

[0603]

[0604] wherein each group has the following meanings:

[0605] P 1 、P 2 and P 3 each independently of one another represent an acrylate group or a methacrylate group,

[0606] Sp 1 、Sp 2 and Sp 3 each independently of one another represent a single bond or a spacer group (having one of the meanings as defined for Sp in the context), and particularly preferably represent -(CH2) p1 -, -(CH2) p1 -O-, -(CH2) p1 -CO-O-, -(CH2) p1 -O-CO- or -(CH2) p1 -O-CO-O-, where p1 is an integer from 1 to 12, and furthermore where the group P 1 -Sp 1 -, P 2 -Sp 2 - and P 3 -Sp 3 - one or more of which may represent R aa , provided that the groups P 1 -Sp 1 -, P 2 -Sp2 - and P 3 -Sp 3 - at least one of which is different from R aa ,

[0607] R aa represents H, F, Cl, CN or a straight-chain or branched alkyl group having 1 to 25 C atoms, where one or more additional non-adjacent CH2 groups may also be independently replaced by -C(R 0 )=C(R 00 )-, -C≡C-, -N(R 0 )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and / or S atoms are not directly connected to each other, and where one or more additional H atoms may be replaced by F, Cl, CN or P 1 -Sp 1 -, particularly preferably a straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy group having 1 to 12 C atoms (where the alkenyl and alkynyl groups have at least two C atoms and the branched groups have at least three C atoms),

[0608] R 0 , R 00 each independently of one another and each time they occur the same or different, represent H or an alkyl group having 1 to 12 C atoms,

[0609] R y and R z each independently of one another represent H, F, CH3 or CF3,

[0610] X 1 、X 2 and X 3 each independently of one another represent -CO-O-, -O-CO- or a single bond,

[0611] Z 1 represents -O-, -CO-, -C(R y R z )- or CF2CF2-,

[0612] Z 2 and Z 3 each independently of one another represent -CO-O-, -O-CO-, -CH2O-, -OCH2-, -CF2O-, -OCF2- or -(CH2) n -, where n is 2, 3 or 4,

[0613] L, each occurrence being the same or different, represents F, Cl, CN or a straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy group having 1 to 12 carbon atoms, preferably F,

[0614] L' and L” each independently of one another represent H, F or Cl,

[0615] k represents 0 or 1,

[0616] r represents 0, 1, 2, 3 or 4,

[0617] s represents 0, 1, 2 or 3,

[0618] t represents 0, 1 or 2,

[0619] x represents 0 or 1.

[0620] Particularly preferred are the compounds of the formulas P2, P13, P17, P22, P23, P24, P30, P31 and P32.

[0621] Further preferred are the tri-reactive compounds P15 to P30, in particular P17, P18, P19, P22, P23, P24, P25, P26, P30, P31 and P32.

[0622] In the compounds of the formulas P1 to P32, the group

[0623] preferably

[0624]

[0625] wherein L, each occurrence being the same or different, has one of the meanings given above or below, and is preferably F, Cl, CN, NO2, CH3, C2H5, C(CH3)3, CH(CH3)2, CH2CH(CH3)C2H5, OCH3, OC2H5, COCH3, COC2H5, COOCH3, COOC2H5, CF3, OCF3, OCHF2, OC2F5 or P-Sp-, very preferably F, Cl, CN, CH3, C2H5, OCH3, COCH3, OCF3 or P-Sp-, more preferably F, Cl, CH3, OCH3, COCH3 or OCF3, especially F or CH3.

[0626] Highly particularly preferred compounds of formula P are selected from Table E below, especially from formulae RM-1, RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM-40, RM-41, RM-48, RM-52, RM-54, RM-57, RM-58, RM-64, RM-74, RM-76, RM-88, RM-91, RM-102, RM-103, RM-109, RM-116, RM-117, RM-120, RM-121, RM-122, RM-139, RM-140, RM-142, RM-143, RM-145, RM-146, RM-147, RM-149, RM-156 to RM-163, RM-169, RM-170 and RM-171 to RM-183.

[0627] For the production of PSA displays, the polymerizable compounds comprised in the LC medium are polymerized or crosslinked (if a compound comprises two or more polymerizable groups) by in-situ polymerization in the LC medium (between the substrates of the LC display), optionally while applying a voltage to the electrodes simultaneously.

[0628] The structure of the PSA displays according to the invention corresponds to the usual geometry of PSA displays as described in the prior art cited at the beginning. A geometry without protrusions is preferred, wherein, additionally, especially those in which the electrodes on the color filter side are unstructured and only the electrodes on the TFT side have slots. A particularly suitable and preferred electrode structure for PS-VA displays is described, for example, in US2006 / 0066793A1.

[0629] Preferred PSA type LC displays according to the invention comprise:

[0630] - A first substrate which comprises pixel electrodes defining pixel regions (the pixel electrodes being connected to switching elements arranged in each pixel region and optionally comprising a micro-slit pattern), and optionally a first alignment layer arranged on the pixel electrodes,

[0631] - A second substrate which comprises a common electrode layer (which may be arranged over the entire part of the second substrate facing the first substrate), and optionally a second alignment layer,

[0632] - An LC layer which is arranged between the first substrate and the second substrate and which comprises an LC medium which comprises a polymerizable component and a liquid crystal host, the polymerizable component comprising one or more compounds of formula R, the liquid crystal host comprising as described above and below, wherein the polymerizable component may also be polymerized.

[0633] The first and / or second alignment layer controls the alignment direction of the LC molecules in the LC layer. For example, in a PS-VA display, an alignment layer is selected to impart a homeotropic (or vertical) alignment (i.e., perpendicular to the surface) or an inclined alignment to the LC molecules. Such an alignment layer may comprise, for example, polyimide, which may also be rubbed or may be prepared by a photo-alignment method.

[0634] The LC layer having the LC medium can be deposited between the substrates of the display by methods conventionally used by display manufacturers (such as the so-called one-drop filling (ODF) method). The polymerizable components of the LC medium are then polymerized, for example, by UV photopolymerization. This polymerization can be carried out in one step or in two or more steps.

[0635] The PSA display may include other elements, such as color filters, black matrices, passivation layers, optical retardation layers, transistor elements for individual pixel addressing, etc., all of which are well known to those skilled in the art and can be used without creative skills.

[0636] Those skilled in the art can design the electrode structure depending on the individual display type. For example, in a PS-VA display, a multi-domain alignment of the LC molecules can be induced by providing an electrode having slits and / or bumps or protrusions in order to generate two, four or more different inclined alignment directions.

[0637] After polymerization, the polymerizable compound forms a crosslinked polymer, which results in a certain pretilt of the LC molecules in the LC medium. Without wishing to be bound by a particular theory, it is believed that at least a portion of the crosslinked polymer formed by the polymerizable compound phase separates or precipitates from the LC medium and forms a polymer layer on the substrate or electrode, or on the alignment layer provided thereon. Microscopic measurement data (such as SEM and AFM) have confirmed that at least a portion of the polymer formed accumulates at the LC / substrate interface.

[0638] The polymerization can be carried out in one step. It is also possible to first carry out the polymerization in a first step (optionally while applying a voltage) in order to generate a pretilt angle, and then polymerize or crosslink the compounds that did not react in the first step in a second polymerization step without applying a voltage ("final curing").

[0639] Suitable and preferred polymerization methods are, for example, thermal or photopolymerization, preferably photopolymerization, especially UV-induced photopolymerization, which can be achieved by exposing the polymerizable compound to UV radiation.

[0640] Optionally, one or more polymerization initiators are added to the LC medium. Suitable conditions for polymerization, as well as suitable types and amounts of initiators, are known to those skilled in the art and are described in the literature. Suitable for free-radical polymerization are, for example, commercially available photoinitiators or (Ciba AG). If a polymerization initiator is used, its proportion is preferably from 0.001 to 5% by weight, particularly preferably from 0.001 to 1% by weight.

[0641] The polymerizable compounds according to the invention are also suitable for polymerization without initiators, which is accompanied by a number of advantages, such as low material costs and, in particular, less contamination of the LC medium by possible residual amounts of initiators or their degradation products. Polymerization can thus also be carried out without the addition of initiators. In a preferred embodiment, the LC medium thus does not contain a polymerization initiator.

[0642] The LC medium can also contain one or more stabilizers in order to prevent the spontaneous polymerization of undesired RMs, for example during storage or transport. Suitable types and amounts of stabilizers are known to those skilled in the art and are described in the literature. Particularly suitable are, for example, stabilizers commercially available from series (Ciba AG), such as 1076. If stabilizers are used, their proportion is preferably from 10 - 500,000 ppm, particularly preferably from 50 - 50,000 ppm, based on the total amount of RM or polymerizable components (component P).

[0643] The polymerizable compounds of formula P do in fact particularly exhibit good UV absorption and are thus particularly suitable for production methods of PSA displays comprising one or more of the following features:

[0644] - The polymerizable medium in the display is exposed to UV light in a two-step process, which includes a first UV exposure step ("UV-1 step") to generate an inclination angle, and a second UV exposure step ("UV-2 step") to complete the polymerization,

[0645] - The polymerizable medium in the display is exposed to UV light generated by energy-saving UV lamps (also referred to as "green UV lamps"). These lamps are characterized by a relatively low intensity in their absorption spectrum of 300 - 380 nm (1 / 100 - 1 / 10 of a conventional UV1 lamp), and are preferably used in the UV2 step, but can also optionally be used in the UV1 step when it is necessary to avoid high intensities for the process.

[0646] - The polymerizable medium in the display is exposed to UV light generated by a UV lamp, which has a radiation spectrum that moves to longer wavelengths (preferably 340 nm or longer) to avoid short UV light exposure in the PS-VA process.

[0647] Both low-intensity and longer-wavelength-shifted UV are used to protect the organic layer from damage that may be caused by UV light.

[0648] Preferred embodiments of the present invention relate to methods for preparing PSA displays as described in the context, which include one or more of the following features:

[0649] - The polymerizable LC medium is exposed to UV light in a two-step process that includes a first UV exposure step ("UV-1 step") to generate an inclination angle and a second UV exposure step ("UV-2 step") to complete polymerization.

[0650] - The polymerizable LC medium is exposed to UV light generated by a UV lamp having an intensity of 0.5 mW / cm 2 to 10 mW / cm 2 in the wavelength range of 300 - 380 nm, preferably for the UV2 step and optionally also for the UV1 step.

[0651] - The polymerizable LC medium is exposed to UV light having a wavelength of 340 nm or longer, and preferably 400 nm or shorter.

[0652] Such a preferred method is carried out, for example, by using a desired UV lamp or by using a bandpass filter and / or a cut-off filter that is substantially transmissive to UV light having respective desired wavelengths and substantially blocks UV light having respective undesired wavelengths. For example, when radiation of UV light having a wavelength λ in the range of 300 - 400 nm is desired, the UV exposure can be carried out using a broadband pass filter that is substantially transmissive for wavelengths of 300 nm < λ < 400 nm. When radiation of UV light having a wavelength λ greater than 340 nm is desired, the UV exposure can be carried out using a cut-off filter that is substantially transmissive for wavelengths of λ > 340 nm.

[0653] "Substantially transmissive" means that the filter transmits most, preferably at least 50%, of the intensity of the incident light of the desired wavelength. "Substantially blocks" means that the filter does not transmit most, preferably at least 50%, of the intensity of the incident light of the undesired wavelength. "Desired (undesired) wavelength" means, for example, in the case of a bandpass filter, a wavelength within (outside) a given λ range, and in the case of a cut-off filter, a wavelength higher (lower) than a given λ value.

[0654] This preferred method makes it possible to manufacture displays using longer UV wavelengths, thereby reducing or even avoiding the harmful and damaging effects of the short UV light component.

[0655] The UV radiation energy is generally from 6 to 100 J, depending on the production method conditions.

[0656] Preferably, the LC medium according to the invention essentially consists of a polymerizable component P) comprising one or more polymerizable compounds of formula P as described above and below, and an LC host mixture, and an optically active component comprising one or more chiral dopants. However, the LC medium may additionally contain one or more other components or additives, preferably selected from the list including but not limited to the following: comonomers, polymerization initiators, inhibitors, stabilizers, surfactants, wetting agents, lubricants, dispersants, water repellents, binders, flow improvers, defoamers, degassing agents, diluents, reactive diluents, auxiliaries, colorants, dyes, pigments, and nanoparticles.

[0657] Particularly preferred is an LC medium containing one, two or three polymerizable compounds of formula P.

[0658] The proportion of the preferred compound of formula P in the LC medium is >0 to <5%, very preferably >0 to <1%, and most preferably 0.01 to 0.5%.

[0659] In a preferred embodiment, the medium according to the invention preferably contains one or more compounds of formula S, the total concentration range of which is from 10 ppm to 2000 ppm, more preferably from 100 ppm to 1000 ppm, still more preferably from 150 ppm to 500 ppm, very preferably from 200 ppm to 400 ppm, and especially from 250 to 300 ppm.

[0660] In another preferred embodiment, the medium according to the invention preferably contains one or more compounds of formula S, the total concentration range of which is from 1000 ppm to 5000 ppm, more preferably more than 1000 ppm to 5000 ppm, still more preferably from 1200 ppm to 4500 ppm, very preferably from 2000 ppm to 4000 ppm, and especially from 2500 to 3500 ppm.

[0661] The medium according to the invention preferably has negative dielectric anisotropy.

[0662] The medium according to the invention contains one or more compounds of formula I, preferably in a total concentration range of >0% to 20%, preferably 1% to 15%, more preferably 2% to 13%, very preferably 3% to 12%.

[0663] The medium according to the invention preferably contains

[0664] - One or more compounds selected from the group of compounds of formulae IIA, IIB, IIC and IID or the group of compounds of formulae IIB, IIC and IID, in a total concentration range of 9% to 70%, more preferably 10% to 65% and very preferably 1% to 64%, in particular 34% to 42%;

[0665] and / or

[0666] - One or more compounds selected from the group of compounds of formulae IIB, IIC and IID and in addition one or more compounds of formula III and in addition one or more compounds of formula VI-4, in a total concentration range of 32% to 70%, more preferably 38% to 65% and very preferably 48% to 60%;

[0667] and / or

[0668] - One or more compounds of formula IIA in a total amount of less than 3%, more preferably less than 2% and very preferably less than 1%;

[0669] or

[0670] - One or more compounds of formula IIA in a total amount of 0% to 1%, very preferably 0%;

[0671] and / or

[0672] - One or more compounds of formula IIB, preferably formula IIB-2 and / or IIB-10, more preferably IIB-2 and IIB-10, in a total concentration range of 10% to 50%, more preferably 15% to 45%, still more preferably 20% to 40%, in particular 25% to 35%;

[0673] and / or

[0674] - One or more compounds of formula IIC, preferably in a total concentration range of 0% to 10%, more preferably 0.5% to 8% and very preferably 1% to 6%, in particular 1% to 4%;

[0675] and / or

[0676] - One or more compounds of formula IID and preferably formula IID-4, preferably in a total concentration range of 1% to 15%, more preferably 2% to 12% and very preferably 3% to 10%;

[0677] and / or

[0678] - One or more compounds of formulae IIB and IID, in a total concentration range of 20% to 50%, more preferably 28% to 45% and very preferably 33% to 40%;

[0679] and / or

[0680] - One or more compounds of formulae IIB and IIC, with a total concentration ranging from 20% to 50%, more preferably from 25% to 42% and very preferably from 30% to 38%;

[0681] and / or

[0682] - One or more compounds of formula III, preferably formula III-2, more preferably formula III-2-6, with a total concentration preferably ranging from 3% to 20%, more preferably from 5% to 17% and very preferably from 6% to 15%;

[0683] and / or

[0684] - One or more compounds of formula III-2, more preferably formula III-2-6, and one or more compounds of formula III-3, with a total concentration ranging from 10% to 30%, more preferably from 15% to 27% and very preferably from 18% to 24%;

[0685] and / or

[0686] - One or more compounds of formulae IIB, IID and III, preferably with a total concentration ranging from 30% to 60%, more preferably from 40% to 53%, very preferably from 43% to 50%;

[0687] and / or

[0688] - One or more compounds of formula VI-4, preferably with a total concentration ranging from 1% to 15%, more preferably from 2% to 12%, and very preferably from 3% to 10%;

[0689] and / or

[0690] - One or more compounds of formulae IIC and VI-4, preferably with a total concentration ranging from 1% to 18%, more preferably from 3% to 15%, and very preferably from 4% to 12%;

[0691] and / or

[0692] - One or more compounds of formulae IIA, IIB, IIC and IID and one or more compounds of formula VI-4, preferably with a total concentration ranging from 26% to 60%, more preferably from 32% to 56%, very preferably from 38% to 50%;

[0693] and / or

[0694] - One or more compounds of formulae IIA, IIB, IIC and IID and one or more compounds of formula III and one or more compounds of formula VI-4, preferably with a total concentration ranging from 35% to 71%, more preferably from 42% to 65%, and very preferably from 48% to 60%;

[0695] and / or

[0696] - one or more compounds of formula IIB and IID and one or more compounds of formula IIC and / or VI-4, and one or more compounds of formula III, preferably in a total concentration range of 35% to 71%, more preferably 42% to 65%, and very preferably 48% to 60%;

[0697] and / or

[0698] - one or more compounds of formula IV, more preferably formula IV-3, in a total concentration range of 20% to 65%, more preferably 25% to 58%, still more preferably 28% to 55% and very preferably 30% to 50%, especially 33% to 45%;

[0699] and / or

[0700] - one or more compounds of formula IV-1, preferably in a total concentration range of 1% to 15%, more preferably 2% to 12%, still more preferably 3% to 10% and very preferably 3% to 8%;

[0701] and / or

[0702] - one or more compounds of formula IV-2, preferably in a total concentration range of 0.2% to 5%, more preferably 0.5% to 3%, still more preferably 1% to 2%;

[0703] and / or

[0704] - one or more compounds of formula V, more preferably formula V-6, in a total concentration range of 0.1% to 15%, more preferably 0.2% to 10%, still more preferably 0.5% to 5% and very preferably 1% to 2%;

[0705] and / or

[0706] one or more compounds of formula IIA-Y, preferably formula IIA-Y6, in a total concentration range of 0.5% to 10%, more preferably 1% to 8%, and very preferably 2% to 5%;

[0707] and / or

[0708] one or more compounds of formula CL-3, preferably selected from the compounds CLP-V-m, CLP-V-Om, CLP-n-m and CLP-n-Om, where n and m are independently 1, 2, 3, 4 or 5, preferably in a total concentration range of 1% to 12%, more preferably 2% to 10%, and very preferably 3% to 7%.

[0709] For the liquid crystal medium according to the invention, it is preferably advantageous to have a nematic phase of ≤ -20 °C to ≥ 70 °C, particularly preferably ≤ -30 °C to ≥ 72 °C, and very particularly preferably ≤ -40 °C to ≥ 74 °C.

[0710] In a first preferred embodiment, the medium according to the invention has a clearing temperature of 70 °C or higher, preferably 72 °C or higher, more preferably 73 °C or higher and especially 74 °C or higher.

[0711] The expression "having a nematic phase" here means on the one hand that no smectic phase and no crystallization are observed at the corresponding temperature at low temperatures and on the other hand that it does not become clear (phase transition to the isotropic phase) when heated from the nematic phase. The low-temperature studies are carried out in a flow viscosimeter at the corresponding temperature and are checked by storing in a test cell having a layer thickness corresponding to electro-optical use for at least 100 hours. If the storage stability in the corresponding test cell at a temperature of -20 °C is 1000 hours or more, the medium is said to be stable at this temperature. At temperatures of -30 °C and -40 °C, the response times are 500 hours and 250 hours respectively. At high temperatures, the clearing point is measured in a capillary by conventional methods.

[0712] The liquid-crystal mixture preferably has a flow viscosity ν of at most 30 mm 2 ·s -1 at 20 °C. 20 .

[0713] The liquid-crystal mixture according to the invention is nematic, preferably at a temperature of -20 °C or lower, preferably at -30 °C or lower, very preferably at -40 °C or lower.

[0714] In a preferred embodiment of the invention, the birefringence of the medium ranges from 0.100 to 0.155, preferably from 0.120 to 0.150, very preferably from 0.125 to 0.145 and especially from 0.128 to 0.138.

[0715] In a preferred embodiment, the dielectric anisotropy Δε of the liquid-crystal mixture according to the invention is from -2.5 to -6.0, preferably from -3.5 to -5.0, especially from -3.8 to -4.5.

[0716] The rotational viscosity γ1 at 20 °C preferably ranges from 60 to 120 mPas, more preferably from 80 to 110 mPa s.

[0717] The elastic constant K1 preferably ranges from 12.0 to 17.0., more preferably from 13.0 to 16.0, especially from 14.0 to 15.5.

[0718] The elastic constant K3 preferably ranges from 12.0 to 16.0, more preferably from 13.0 to 15.0, especially from 13.5 to 14.5.

[0719] Furthermore, the liquid-crystal medium according to the invention has a high voltage holding ratio value in the liquid-crystal cell.

[0720] Generally, liquid crystal dielectrics with low addressing voltage or threshold voltage exhibit lower voltage holding ratios than those with higher addressing voltage or threshold voltage, and vice versa.

[0721] For the present invention, the term "dielectrically positive compound" denotes compounds having Δε > 1.5, the term "dielectrically neutral compounds" denotes those having -1.5 ≤ Δε ≤ 1.5 and the term "dielectrically negative compounds" denotes those having Δε < -1.5. Here, the dielectric anisotropy of the compound is determined by dissolving 10% of the compound in a liquid crystal host in at least one test cell and measuring the capacitance of the resulting mixture, the test cell having a layer thickness of 20 μm and homeotropic and planar surface alignment at 1 kHz in each case. The measurement voltage is generally 0.5 V - 1.0 V, but always below the capacitance threshold of the respective liquid crystal mixtures under investigation.

[0722] All temperature values stated in the present invention are given in °C.

[0723] The mixtures according to the invention are suitable for all VA-TFT applications, such as, for example, VAN, MVA, (S)-PVA, ASV, PSA (polymer sustained VA,) and PS-VA (polymer stabilized VA). They are furthermore suitable for IPS (in-plane switching) and FFS (fringe field switching) applications with negative Δε, in particular UB-FFS.

[0724] It goes without saying for the person skilled in the art that the VA, IPS or FFS mixtures according to the invention can also contain compounds in which, for example, H, N, O, Cl and F are replaced by the corresponding isotopes.

[0725] The compounds according to the invention can be synthesized by or analogously to known methods described in the literature (for example in standard works, such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), under reaction conditions known and suitable for the said reaction. Variants known per se can also be used here, but are not mentioned further here. In particular, they can be prepared as described in the following reaction schemes or analogously to the following reaction schemes. Other methods for preparing the compounds of the invention can be obtained from the examples.

[0726] Other mesogenic compounds not explicitly mentioned above can also optionally and advantageously be used in the dielectrics according to the invention. Such compounds are known to the person skilled in the art.

[0727] For the present invention and in the following examples, the structures of the liquid crystal compounds are represented by abbreviations and converted into chemical formulae according to Tables A to C below. All groups Cm H 2m+1 , C n H 2n+1 , and C l H 2l+1 or C m H 2m-1 , C n H 2n-1 and C l H 2l-1 is a straight-chain alkyl group or an alkylene group, each having n, m and 1 C atoms. Preferably, n, m and 1 are independently 1, 2, 3, 4, 5, 6 or 7. Table A shows the codes for the ring elements of the compound core, Table B lists the bridging units, and Table C lists the symbolic meanings of the left-hand and right-hand end groups of the molecule. The abbreviations consist of the code for the ring element with the optional linking group, followed by the first hyphen and the left-hand end group code, and the second hyphen and the right-hand end group code. Table D shows the exemplary structures of the compounds and their respective abbreviations.

[0728] Table A: Ring elements

[0729]

[0730]

[0731]

[0732] Table B: Bridging units

[0733]

[0734]

[0735] Table C: End groups

[0736]

[0737]

[0738] where n and m are each integers, and the three dots "..." are placeholders for other abbreviations from the table.

[0739] Besides the compounds of the formulae I, IIA, IIB, IIC and / or IID, IVa, IVb and V, the mixtures according to the invention optionally comprise one or more compounds of the following compounds.

[0740] The following abbreviations are used:

[0741] (n, m, k, and l are each independently integers, preferably from 1 to 9, more preferably from 1 to 7, k and l may also be 0 and are preferably from 0 to 4, more preferably 0 or 2 and most preferably 2, n is preferably 1, 2, 3, 4, or 5, and in the combination "-nO-", it is preferably 1, 2, 3, or 4, more preferably 2 or 4, m is preferably 1, 2, 3, 4, or 5, and in the combination "-Om", it is preferably 1, 2, 3, or 4, more preferably 2 or 4. The combination "-lVm" is preferably "2V1".)

[0742] Table D

[0743]

[0744]

[0745]

[0746]

[0747]

[0748]

[0749]

[0750]

[0751]

[0752]

[0753]

[0754]

[0755]

[0756]

[0757]

[0758]

[0759]

[0760]

[0761]

[0762] Table E

[0763] Table E shows illustrative reactive mesogenic compounds that can be used in the LC medium according to the present invention

[0764]

[0765]

[0766]

[0767]

[0768]

[0769]

[0770]

[0771]

[0772]

[0773]

[0774]

[0775]

[0776]

[0777]

[0778]

[0779]

[0780]

[0781]

[0782]

[0783]

[0784] In a preferred embodiment, the mixture according to the invention comprises one or more polymerizable compounds, preferably selected from the polymerizable compounds of formulae RM-1 to RM-182. Among these, the compounds RM-1, RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM-40, RM-41, RM-48, RM-52, RM-54, RM-57, RM-58, RM-64, RM-74, RM-76, RM-88, RM-91, RM-102, RM-103, RM-109, RM-116, RM-117, RM-120, RM-121, RM-122, RM-139, RM-140, RM-142, RM-143, RM-145, RM-146, RM-147, RM-149, RM-156 to RM-163, RM-169, RM-170 and RM-171 to RM-183 are particularly preferred. Examples

[0785] The present invention will be described in detail by the following non-limiting working examples.

[0786] The following abbreviations and symbols are used:

[0787] V o represents the threshold voltage at 20 °C, capacitive [V],

[0788] n e represents the extraordinary refractive index at 20 °C and 589 nm,

[0789] n o represents the ordinary refractive index at 20 °C and 589 nm,

[0790] Δn represents the optical anisotropy at 20 °C and 589 nm,

[0791] ε ⊥ represents the dielectric constant perpendicular to the director at 20 °C and 1 kHz,

[0792] ε || represents the dielectric constant parallel to the director at 20 °C and 1 kHz,

[0793] Δε represents the dielectric anisotropy at 20 °C and 1 kHz,

[0794] cl.p., T(N,I) represents the clearing point [°C],

[0795] γ1 represents the rotational viscosity at 20 °C [mPa·s],

[0796] K1 represents the elastic constant, the "splay" deformation at 20 °C [pN],

[0797] K2 represents the elastic constant, the "twist" deformation at 20 °C [pN],

[0798] K3 represents the elastic constant, the "bend" deformation at 20 °C [pN],

[0799] Unless otherwise expressly stated, all concentrations in this application are expressed as weight percentages and relate to the corresponding mixture as a whole, which includes all solid or liquid crystal components and excludes solvents.

[0800] Unless otherwise stated, all temperature values indicated in this application, such as the melting point T(C,N), the transition from the smectic phase (S) to the nematic phase (N) T(S,N), and the clearing point T(N,I), are cited in degrees Celsius (°C). M.p. represents the melting point, cl.p. = the clearing point. In addition, C = crystalline state, N = nematic phase, S = smectic phase, and I = isotropic phase. The data between these symbols represent the transition temperatures.

[0801] Unless otherwise stated, in each case, 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 applied at a temperature of 20 °C, with Δn measured at 589 nm and Δε measured at 1 kHz.

[0802] The term "threshold voltage" used in the present invention relates to the capacitive threshold (V0), which is also referred to as the Freedericks threshold, unless otherwise stated. In the examples, as usual, the optical threshold can also be that for a 10% relative contrast (V 10 ) cited.

[0803] Unless otherwise stated, the method for polymerizing the polymerizable compound in the PSA display as described above and below is carried out at a temperature at which the LC medium exhibits a liquid crystal phase, preferably a nematic phase, and most preferably at room temperature.

[0804] Unless otherwise specified, the method for preparing the test cell and measuring its electro-optical and other properties should be carried out using the method described below or a method similar thereto.

[0805] The display for measuring the capacitive threshold voltage consists of two planar parallel glass outer plates spaced 25 μm apart, each outer plate having an electrode layer on the inner side and an unrubbed polyimide alignment layer on the top, which results in a vertical alignment of the liquid crystal molecules.

[0806] A display or test cell for measuring tilt angle consists of two parallel glass outer plates spaced 4 μm apart. Each of the outer plates has an electrode layer on the inner side and a polyimide alignment layer on top, where the two polyimide layers are rubbed antiparallel to each other and cause a vertical edge alignment of liquid crystal molecules.

[0807] The polymerizable compound is polymerized in the display or test cell by irradiating with UV light of a defined intensity for a predetermined time while applying a voltage (usually 10V - 30V AC, 1kHz) to the display. In the examples, unless otherwise stated, a fluorescent lamp and an intensity of 0 to 20 mW / cm 2 are used for polymerization. The intensity is measured using a standard meter (Ushio Accumulate UV meter with a center wavelength of 313 nm).

[0808] Transmittance measurements are carried out in a test cell with a fishbone electrode layout (from Merck Ltd., Japan; 1 pixel fishbone electrode (ITO, 10x10 mm, fishbone angle 47.7°, 3μm line / 3μm space), 3.2μm cell gap, AF - glass, tilt angle 1°).

[0809] At a given temperature T, the storage stability (LTS 本体 ) in the bulk of the medium according to the present invention is determined by visual inspection. 2 g of the medium of interest is filled into a glass container (bottle) of a suitable size placed in a refrigerator at a predetermined temperature. The bottles are checked at defined time intervals for the occurrence of smectic phase or crystallization. For each material and each temperature, two bottles are stored. If crystallization or the appearance of the smectic phase is observed in at least one of the two corresponding bottles, the test is terminated, and the time of the last check before the appearance of the higher ordered phase is recorded as the corresponding storage stability.

[0810] Mixture example

[0811] Mixture Examples M1 to M25 and P1 to P9 have the compositions and physical properties shown in the following table:

[0812] Comparative example C1

[0813]

[0814] Mixture example M1

[0815]

[0816] In the following table, the key parameters of mixtures C1 to M1 are summarized.

[0817] Δε Δn <![CDATA[K avg [pN]]]> <![CDATA[γ1[mPas]]]> <![CDATA[γ1 / K 11 [mPas / pN]]]> C1 -4.0 0.132 12.0 99 6.9 M1 -4.0 0.131 12.2 97 6.5

[0818] The difference between Mixture Example M1 and Comparative Example C1 lies in the presence of the compound SPY-4-O2. By using the compound of Formula I, it was surprisingly found that a favorable low rotational viscosity (γ1) could be achieved while having a very low ratio of γ1 / K1, which improves the response time of the display.

[0819] Mixture example M2

[0820]

[0821] Mixture example M3

[0822]

[0823]

[0824] Mixture example M4

[0825]

[0826] Mixture example M5

[0827]

[0828]

[0829] Mixture example M6

[0830]

[0831] Mixture example M7

[0832]

[0833]

[0834] Mixture example M8

[0835]

[0836] Mixture example M9

[0837]

[0838] Mixture example M10

[0839]

[0840]

[0841] Mixture example M11

[0842]

[0843] Mixture example M12

[0844]

[0845]

[0846] Mixture example M13

[0847]

[0848] Mixture example M14

[0849]

[0850]

[0851] Mixture example M15

[0852]

[0853] Mixture example M16

[0854]

[0855] Mixture example M17

[0856]

[0857]

[0858] Mixture example M18

[0859] Example M18 of the mixture consists of 99.98% of Example M1 of the mixture and 0.02% of the compound of formula ST-12b-1

[0860]

[0861] Mixture example M19

[0862] Example M19 of the mixture consists of 99.985% of Example M1 of the mixture and 0.015% of the compound of formula S1-1a

[0863]

[0864] Mixture example M20

[0865] Mixture Example M20 consists of 99.98% of Mixture Example M2 and 0.02% of the compound of formula S2-1a

[0866]

[0867] Mixture example M21

[0868]

[0869] Mixture example M22

[0870]

[0871]

[0872] Mixture example M23

[0873]

[0874]

[0875] Mixture example M24

[0876] Mixture Example M24 consists of 99.975% of the medium of Mixture Example M1 and 0.025% of the compound ST-3a-2:

[0877]

[0878] Mixture example M25

[0879] Mixture Example M25 consists of 99.980% of the medium of Mixture Example M2 and 0.020% of the compound ST-3b-2:

[0880]

[0881] Polymerizable mixture

[0882] The polymerizable mixtures P1 to P9 are prepared from the nematic mixtures given in Table 1 by adding a reactive mesogen (RM) selected from the group of compounds of formulae RM-1, RM-17, RM-35, RM-64 and RM-171 in the amounts (%RM) given in Table 1.

[0883]

[0884]

[0885] Table 1: Polymerizable Mixture

[0886]

[0887]

[0888] Mixture example P10

[0889] The polymerizable mixture P10 consists of 99.434% of the mixture of Example M1, 0.300% of RM-1, 0.200% of RM-145, 0.050% of RM-163, 0.001% of 1076 and 0.015% of the compound ST-3a-1.

[0890]

Claims

1. A liquid crystal medium comprising a) one or more compounds of formula I wherein R 1 and R 2 , which are the same or different and represent H, halogen, a straight-chain alkyl or alkoxy group having 1 to 15 C atoms, a straight-chain alkenyl or alkenyloxy group having 2 to 15 carbon atoms, or a branched-chain alkyl, alkoxy, alkenyl or alkenyloxy group having 3 to 15 C atoms, where one or more CH2 groups in these groups may each independently of one another be replaced by -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly linked to one another, and where one or more H atoms may be replaced by halogen, L 11 and L 12 each, independently of one another, represents F, Cl, CF3 or CHF2; L 13 and L 14 each, independently of one another, represents H, F, Cl, CF3 or CHF2; Y 1 represents H, F, Cl, CF3, CHF2 or CH3; and n is 0 or 1; and b) one or more compounds selected from the group of compounds of formulae IIA, IIB, IIC and IID wherein R 2A ,R 2B ,R 2C and R 2D identically or differently denote H, a straight-chain alkyl or alkoxy group having 1 to 15 C atoms, a straight-chain alkenyl or alkenyloxy group having 2 to 15 carbon atoms, or a branched alkyl, alkoxy, alkenyl, alkenyloxy group each having 3 to 15 C atoms, where one or more CH2 groups in these groups may each independently of one another be replaced by -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly linked to one another, and where one or more H atoms may be replaced by halogen, L 1 and L 2 each independently represents F, Cl, CF3 or CHF2, Y represents H, F, Cl, CF3, CHF2 or CH3, Z 2 , Z 2B and Z 2D each independently of one another represents a single bond, -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -COO-, -OCO-, -C2F4-, -CF=CF- or -CH=CHCH2O- p represents 0, 1 or 2, q represents 0 or 1, and v represents an integer from 1 to 6.

2. The liquid crystal medium according to claim 1, wherein n is 0 or 1, Y 1 represents H or CH3, L 11 and L 12 represents F, and L 13 and L 14 represents H.

3. The liquid crystal medium according to claim 1 or 2, wherein the medium comprises a compound selected from the group of compounds of formulae VI-1 to VI-21: wherein R 6 represents a straight-chain alkyl or alkoxy group having 1 to 6 C atoms, (O) represents -O- or a single bond, and m is 0, 1, 2, 3, 4, 5 or 6, and n is 0, 1, 2, 3 or 4.

4. The liquid crystal medium according to one or more of claims 1 to 3, wherein the medium comprises one or more compounds of formula III wherein R 31 and R 32 each independently represent H, an alkyl or alkoxy group having 1 to 15 C atoms, where one or more CH2 groups in these groups may each independently be -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O- or -O-CO- are substituted in such a way that O atoms are not directly connected to each other, and one or more H atoms may be substituted by halogen, A 31 each independently represents, at each occurrence a) 1,4 - cyclohexenylene or 1,4 - cyclohexylene, wherein one or two non - adjacent CH2 groups may be substituted by -O- or -S-, b) 1,4 - phenylene, wherein one or two CH groups may be substituted by N, or c) a group selected from: spiro[3.3]heptane - 2,6 - diyl, 1,4 - bicyclo[2.2.2]octylene, naphthalene - 2,6 - diyl, decahydronaphthalene - 2,6 - diyl, 1,2,3,4 - tetrahydronaphthalene - 2,6 - diyl, phenanthrene - 2,7 - diyl and fluorene - 2,7 - diyl, wherein the groups a), b) and c) may be mono - substituted or poly - substituted by halogen atoms, n represents 0, 1 or 2, Z 31 Each occurrence independently represents, at each occurrence, -CO-O-, -O-CO-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CH2-, -CH2CH2-, -(CH2)4-, -CH=CH-CH2O-, -C2F4-, -CH2CF2-, -CF2CH2-, -CF=CF-, -CH=CF-, -CF=CH-, -CH=CH-, -C≡C- or a single bond, L 31 and L 32 each independently represents F, Cl, CF3 or CHF2, and W represents O or S.

5. The liquid crystal medium according to claim 4, wherein W in formula III represents S.

6. The liquid crystal medium according to one or more of claims 1 to 5, wherein the medium comprises one or more compounds of formula IV wherein R 41 represents an unsubstituted alkyl group having 1 to 7 C atoms, or an unsubstituted alkenyl group having 2 to 7 C atoms, R 42 represents an unsubstituted alkyl group having 1 to 7 C atoms, or an unsubstituted alkoxy group having 1 to 6 C atoms, or an unsubstituted alkenyl group having 2 to 7 C atoms.

7. The liquid crystal medium according to one or more of claims 1 to 6, wherein the medium comprises a compound selected from the group of compounds of formulae IV - 3 - 1 and IV - 3 - 2: wherein alkyl represents a straight - chain alkyl having 1 to 7 C atoms.

8. The liquid crystal medium according to one or more of claims 1 to 7, wherein the medium comprises one or more compounds of formula V wherein R 51 ,R 52 represents an alkyl group having 1 to 7 C atoms, an alkoxy group having 1 to 7 C atoms, or an alkoxyalkyl, alkenyl or alkenyloxy group having 2 to 7 C atoms, which are the same or different and represent Z 51 and Z 52 which, the same or different, represents -CH2-CH2-, -CH2-O-, -CH=CH-, -C≡C-, -COO- or a single bond, and n is 1 or 2.

9. The liquid crystal medium according to one or more of claims 1 to 8, wherein the medium has a birefringence of 0.12 or greater at a temperature of 20 °C and a wavelength of 589 nm.

10. The liquid crystal medium according to one or more of claims 1 to 9, wherein the medium comprises a polymerizable compound.

11. A liquid crystal display comprising the liquid crystal medium according to any one of claims 1 to 10.

12. The liquid crystal display according to claim 11, wherein the display is a VA, IPS, FFS, PS - VA, PS - IPS or PS - FFS type display.

13. Use of the liquid crystal medium according to one or more of claims 1 to 10 in a VA, IPS, FFS, PS - VA, PS - IPS or PS - FFS display.

14. An energy-saving display for a game, comprising a liquid crystal medium according to one or more of claims 1 to 10.

15. A method for preparing a liquid crystal medium according to any one of claims 1 to 10, comprising the step of mixing one or more compounds of formula I with one or more compounds selected from the group consisting of formulas IIA, IIB, IIC and IID and optionally with a polymerizable compound or other liquid crystal compounds or additives.

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