Liquid crystal medium

Abstract

The present invention relates to a liquid crystal medium having a negative dielectric anisotropy and comprising an ionic dopant as specified herein; to guest-host liquid crystal media derived therefrom; and to the use of the medium in devices such as optical shutters, switchable windows and switchable mirrors.

Description

[0001] The present invention relates to a liquid crystal medium having a negative dielectric anisotropy and comprising an ionic dopant as specified herein, to a guest-host liquid crystal medium derived therefrom, and to the use of the medium in devices such as optical shutters, switchable windows and switchable mirrors.

[0002] Devices for controlling or regulating the transmission of light are commonly used in display applications and they can also be used in various mobile devices, such as eyewear, spectacles, goggles and visors and in the context of augmented and virtual reality environments. Light intensity modulators, such as light valves or shutters, can be based on liquid crystals (LC). In principle, such light valves or shutters can rely on light absorption or light scattering.

[0003] In some devices, light transmission can be reversibly altered, typically by electrical switching, wherein the intensity of the incident light can be attenuated, dimmed, or colored, while at the same time exhibiting little or no scattering or haze in different operating states. Thus, such devices can operate in and switch between a bright state and a dark state (i.e., a relatively high light transmission state and a relatively low light transmission state), wherein both states are substantially non-hazy.

[0004] Several modes or configurations may be employed to provide this reversible transmission change. For twisted nematic (TN), super twisted nematic (STN), and vertical alignment (VA) liquid crystal cells, polarizers are used to control light transmission. Guest-host liquid crystal cells may also be used, which are based on a liquid crystal host doped with dichroic dye molecules. These guest-host systems may be used without any polarizers to change light transmission. However, in some embodiments and applications, guest-host liquid crystal cells are used in combination with at least one polarizer.

[0005] Devices based on the guest-host effect were first described by GH Heilmeier and LAZanoni in Appl. Phys. Lett., 1968, 13, pp. 91-92, and have since been found to be widely used, mainly in LC display components. In a guest-host system, the liquid crystal medium contains one or more dichroic dyes in addition to the liquid crystal host material. When mixed together, the dichroic dyes generally have the ability to align themselves with nematic liquid crystal molecules. Due to the directional dependence of dye molecule absorption, when the dye changes its alignment together with the liquid crystal host molecules, the transparency of the liquid crystal (LC) to light can be modulated. This means that the maximum contrast between the bright state and the dark state of the guest-host LC box depends on the alignment of the dichroic dye. When an electric field is applied to this guest-host LC mixture, the nematic liquid crystal host molecules are reoriented and aligned with the electric field or perpendicular to the electric field to minimize the torque it suffers from the electric field. The dichroic dye (guest) molecules may not be directly affected by the external electric field, but can still be aligned with the liquid crystal host molecules. It is its interaction with the liquid crystal molecules that forces them to reorient themselves.

[0006] The initially bright state liquid crystal cell may be desirable due to its transparent bright state when no voltage is applied, due to switching from the bright state to the dark state and using a liquid crystal medium with negative dielectric anisotropy. This mode is particularly useful for devices that are normally transparent and dimmed on demand for relatively short periods of time, such as optical shutters and windows. This configuration is therefore more energy efficient than modes that consume energy when the transparent state must be actively switched on. It also provides a transparent fail-safe state by default in case of power outages.

[0007] The use of a liquid crystal medium having a negative dielectric anisotropy enables the provision of a liquid crystal cell in which (i) in the absence of an electric field across the cell substrates, the long axes of the liquid crystal and dye molecules are aligned relative to the substrates in such a way as to cause the dye molecules to absorb no or only minimally light directed through the guest-host liquid crystal mixture perpendicularly to the substrates, regardless of whether the light passing therethrough is polarized, whereby the liquid crystal cell remains in a relatively bright state in the absence of an electric field, and

[0008] (ii) In the presence of an electric field between the cell substrates, the long axes of the liquid crystal molecules and the dye molecules are arranged relative to the substrates in such a manner that the dye molecules absorb at least some of the light directed through the guest-host liquid crystal mixture perpendicular to the substrates, particularly light polarized along the long axis of the dye molecules, whereby the liquid crystal cell becomes darker in the presence of an electric field.

[0009] Guest-host vertically aligned LC displays are described, for example, in JP 2001100253.

[0010] In addition to the use in LC displays, devices of this type can also be provided as optical shutters or switching components for regulating the transfer of light or energy, as described, for example, in WO 2009 / 141295 and WO 2010 / 118422. Such switching components can be used as or applied in switchable windows that can be darkened as required by means of an electric field. Switchable mirrors (e.g., rearview mirrors for automotive applications) using guest-host liquid crystals are described in DE 3340670.

[0011] LC-based light modulators using light scattering include so-called polymer dispersed liquid crystal (PDLC) or encapsulated or nematic curvilinear aligned phase liquid crystal (NCAP), polymer network liquid crystal (PNLC), cholesteric liquid crystal (CLC), polymer stabilized cholesteric textured liquid crystal (PSCT), and dynamically scattering liquid crystal devices. These scattering devices can be switched between a transparent state (i.e., optically clear or non-hazy state) and a light scattering state (i.e., translucent or hazy state).

[0012] When such a scattering type device is switched from a non-scattering state (i.e., an optically clear state) to a scattering state, light transmission is altered so as to produce a translucent appearance, which may also be considered cloudy, turbid, diffuse, or hazy. Devices based on a scattering mode are particularly useful for temporarily providing privacy or masking of features or information when desired by switching (usually electrically) the device from an optically clear state to a scattering state.

[0013] GH Heilmeier et al. describe a dynamic scattering mode in Appl. Phys. Lett., 1968, 13, pp. 46-47, in which initially transparent nematic liquid crystals scatter light based on the disruptive effect of ion transport in the presence of an electric field.

[0014] It is also possible to combine light modulation in the device by absorption and by scattering. In this way, an opaque state can be obtained, which, in addition to obtaining haze, also exhibits a reduced total light intensity. In a particular embodiment, dichroic dyes can be used to attenuate light, and in some cases, these dyes can further provide coloration. In another embodiment, in the opaque state, this device can block background images and provide a black color. Such light shutters can therefore have potential applications in see-through displays and smart windows.

[0015] For example, US 2014 / 0226096 describes a combination of changing transmission, such as achieved by a guest-host cell having the ability to switch to an opaque state, in particular as obtained in a dynamic scattering mode. In particular, a device is described in which a liquid crystal mixture doped with a dichroic dye further containing a small amount of a salt such as hexadecyltrimethylammonium bromide, conductive salt 235 or dodecylethyldimethyl-ammonium-4-hexyloxybenzoate is used.

[0016] There is a need in the art for other light modulators, in particular light valves, such as light shutters, with improved optical and electro-optical properties. There is also a need in the art for suitable liquid crystal media that can be used in such switchable devices.

[0017] It is therefore an object of the present invention to provide switchable devices, in particular light valves and window assemblies, with advantageous reliability and stability, in particular with regard to electrochemical degradation and degradation by light (such as UV light), and improved and long-term optical and electro-optical properties, including switching states with efficient and sufficiently uniform haze and optional additional dimming and advantageously low energy consumption. A particular object of the present invention is to provide light valves with advantageous properties and particularly suitable for use in mobile and portable devices, and in the context of augmented reality or virtual reality. Another object is to provide an efficient and convenient method for preparing such devices.

[0018] Another object of the present invention is to provide an improved liquid crystal medium, which has favorable chemical, physical and electro-optical properties, and in particular exhibits good reliability and stability, in particular light stability, and in particular UV light stability and electrochemical stability; and a wide liquid crystal phase, which has a suitably high clearing point, and is particularly suitable for use in switching components and window components, in particular switchable components with a scattering mode that can optionally provide additional dimming. In addition, the liquid crystal medium needs to have a sufficiently high optical anisotropy and an advantageously high voltage holding ratio (VHR), good low temperature stability and suitable storage stability. From the following detailed description, other objects of the present invention are immediately apparent to those skilled in the art.

[0019] This object is solved by the subject matter defined in the independent claims, while preferred embodiments are set forth in the respective dependent claims and are further described below.

[0020] The present invention particularly provides the following items, including main aspects, preferred embodiments and specific features, which individually and in combination contribute to solving the above objects and ultimately provide additional advantages.

[0021] A first aspect of the present invention provides a liquid crystal medium having a negative dielectric anisotropy and a clearing point of 90° C. or greater, the liquid crystal medium comprising one or more ionic dopants of formula I

[0022] A + B - I

[0023] in

[0024] A + represents an organic cation, and

[0025] B -represents an anion selected from the group consisting of tetrafluoroborate, tetracyanoborate, hexafluorophosphate, hexafluoroantimonate, methanesulfonate, ethanesulfonate and trifluoromethanesulfonate.

[0026] According to the present invention, it is preferred that the liquid-crystalline medium further comprises one or more dichroic dyes, preferably two or more dichroic dyes and more preferably three or more dichroic dyes.

[0027] In the present invention it was recognised that there is a need to provide a liquid crystal medium which may be particularly suitable for use in electro-optical devices based on the dynamic scattering mode and which in this regard may offer particular benefits in terms of improved optical and electro-optical performance.

[0028] It has surprisingly been found that by providing a liquid crystal medium according to the invention, a significant improvement with respect to advantageous reliability and stability, in particular with respect to electrochemical degradation and degradation by light, such as UV light, and improved and long-term optical and electro-optical properties can be obtained. In particular, providing a specific ionic dopant as specified at present and a liquid crystal host medium with a negative dielectric anisotropy and a high definition bright spot as defined leads to advantageous and efficient switching media even at relatively low ionic dopant concentrations and relatively low values ​​of dielectric anisotropy.

[0029] Preferably, the liquid-crystalline medium has a relatively large optical anisotropy. Even under these conditions, the medium can exhibit reproducible and advantageous long-term properties.

[0030] It is further preferred that the medium contains one or more dichroic dyes. In addition to scattering, it is therefore possible to additionally provide a total intensity reduction or dimming based on the guest-host effect. In this regard, the liquid crystal medium can advantageously give sufficient solubility to the one or more dichroic dyes and to the one or more ionic dopants. In addition, the liquid crystal medium comprising the ionic dopant and optionally one or more dichroic dyes can advantageously exhibit electrochemical stability within the device under applied voltage, in particular under additional thermal or optical stress, in particular under UV load.

[0031] In this regard, it should be appreciated that, in particular, the ionic dopant should have sufficient solubility in the liquid crystal host as well as high electrochemical stability. The ionic dopant should be soluble in an amount sufficient to exhibit the desired effect. However, in principle, this can cause problems, because salts generally have low solubility in highly lipophilic liquid crystal materials due to their highly polar nature, and because the addition of salts can cause reliability problems in liquid crystals (especially in dye-doped liquid crystals), because they may trigger decomposition processes, especially under thermal or optical stress. In addition, upon cooling, salt crystallization may occur.

[0032] It has been unexpectedly found that the ionic dopants as specified can exhibit the desired solubility, stability and performance in a liquid crystal host medium. In particular, the ionic dopants as specified can unexpectedly and advantageously contribute to the generation of sufficiently strong and uniform haze in the scattering state even at low concentrations and low operating voltages.

[0033] Therefore, a further aspect of the present invention relates to the use of one or more ionic dopants of the formula I as described herein in a liquid-crystalline medium.

[0034] Another aspect of the invention relates to a switching component which is operable in an optically clear state and a scattering state and which can be electrically switched between the optically clear state and the scattering state, the switching component comprising a switching layer containing a liquid crystal medium according to the invention, wherein the switching layer is inserted between two relatively transparent substrates, each of which is provided with an electrode.

[0035] A switching component and in particular a light valve in this context preferably means a component for modulating light, which component is configured as a box formed by two walls, in particular two transparent substrates, which are spaced apart and provided with electrodes, and wherein the box contains a light modulating material.

[0036] Preferably, the liquid crystal medium as described herein is configured and used in a switching layer. The switching layer thus comprises the medium, preferably consists of the medium. The switching layer is arranged between two substrates in order to obtain a switching component that is electrically switchable and operable in an optically transparent state and a scattering state. Preferably, the electrodes are configured as a conductive layer on or above the inner surface of each substrate.

[0037] According to the invention, an advantageous switching assembly is provided, which can be used in switchable windows for automotive applications, such as cars and commercial vehicles, and other transport applications, such as in trains, airplanes, ships and boats, and for architectural applications, such as in windows of facades, and also for use in room interiors, such as in partitions between rooms and in assemblies for separating individual compartments of rooms or spaces. The switching assembly is particularly suitable for use in mobile and portable devices and in the context of augmented reality or virtual reality, for example as a light shutter in a see-through display.

[0038] Based on the dynamic scattering pattern, the switching assembly according to the invention can switch from a clear to a scattering state, which can create a visual barrier between different spaces or different parts of a room. The switching assembly is therefore particularly suitable and efficient in providing a privacy mode when necessary, i.e. it provides switchability between a state with viewing contact and a privacy state creating a visual barrier. The device can conveniently switch between states by applying a voltage. Furthermore, the switching can be fast, in particular in the order of seconds and even down to one second or even less.

[0039] It has been found that based on the liquid crystal medium as provided according to the invention, switchable devices, in particular light valves and window components, can be provided which exhibit advantageous reliability and stability, in particular with regard to electrochemical degradation, degradation by light (such as UV light) and stability to high or low temperatures, and improved and long-term optical and electro-optical properties, including switching states with efficient and sufficiently uniform haze and advantageously low energy consumption. In a preferred embodiment, one or more dichroic dyes are included in the medium, in which case additional dimming based on the guest-host effect can be achieved.

[0040] The switching component according to the invention advantageously exhibits an advantageously low haze clear state and an advantageously turbid state with sufficiently strong and uniform scattering. In particular, the switching component exhibits advantageously reduced residual haze or even no discernible residual haze in the optically clear state, which is particularly desirable when the component forms part of a window.

[0041] The switching assembly and in particular the window assembly according to the invention is suitable for regulating or modulating the light transmission, in particular the transmission of sunlight, but also the light transmission from artificial light sources such as lamps and luminaires.

[0042] It has been surprisingly found that ionic dopants as provided according to the invention can be suitable and effective even in relatively small concentrations. Furthermore, even for liquid crystal media with relatively low values ​​of dielectric anisotropy, the inclusion of ionic dopants, in particular in relatively low amounts, can surprisingly produce strong scattering already at low operating voltages. These beneficial features in turn can result in reproducible and stable operation with little or even no hysteresis, increased reliability and reduced heating and increased lifetime and energy saving.

[0043] The advantageous chemical, physical and electro-optical properties of liquid-crystalline media as provided according to the present invention may therefore lead to significant benefits in terms of device performance and characteristics.

[0044] A further aspect of the invention therefore relates to the use of a liquid-crystal medium according to the invention or a switching component according to the invention in an electro-optical device, preferably in a light valve, a light shutter, a window, a car mirror, a sunroof, an augmented or virtual reality device, a mobile device or a portable device.

[0045] The present invention is illustrated below by describing in detail aspects, embodiments and specific features without limiting the invention thereby, and specific embodiments are described in more detail.

[0046] In this context, halogen means F, Cl, Br or I, preferably F or Cl, and more preferably F.

[0047] In the present context, alkyl and / or alkoxy are understood to mean straight-chain or branched alkyl radicals, which are preferably straight-chain, have 2, 3, 4, 5, 6 or 7 C atoms, and thus preferably represent ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy or heptyloxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, tridecyloxy or tetradecyloxy.

[0048] In the present context, oxaalkyl preferably denotes straight-chain 2-oxapropyl (=methoxymethyl); 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl); 2-, 3- or 4-oxapentyl; 2-, 3-, 4- or 5-oxahexyl; 2-, 3-, 4-, 5- or 6-oxaheptyl; 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl; 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanononyl; 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

[0049] In this context, an alkenyl group (i.e., one of the CH 2 The alkyl radical (which has been replaced by -CH=CH-) may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 C atoms. Thus, it particularly denotes vinyl; prop-1- or -2-enyl; but-1-, -2- or -3-enyl; pent-1-, -2-, -3- or -4-enyl; hex-1-, -2-, -3-, -4- or -5-enyl; hept-1-, -2-, -3-, -4-, -5- or -6-enyl; oct-1-, -2-, -3-, -4-, -5-, -6- or -7-enyl; non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl; dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

[0050] In this context, alkyl or alkenyl groups which are at least monosubstituted by halogen are preferably straight-chain, and halogen is preferably F or Cl. In the case of polysubstitution, halogen is preferably F. The resulting radicals also include perfluorinated radicals. In the case of monosubstitution, the fluorine or chlorine substituents may be in any desired position, but are preferably in the ω position.

[0051] In this context, monofluorinated or polyfluorinated alkyl or alkoxy radicals having 1, 2 or 3 C atoms or monofluorinated or polyfluorinated alkenyl radicals having 2 or 3 C atoms are particularly preferably F, Cl, CF 3 , CHF 2 、OCF 3 , OCHF 2 ,OCFHCF 3 、OCFHCHF2 、OCFHCHF 2 、OCF 2 CH 3 、OCF 2 CHF 2 、OCF 2 CHF 2 、OCF 2 CF 2 CHF 2 、OCF 2 CF 2 CHF 2 ,OCFHCF 2 CF 3 ,OCFHCF 2 CHF 2 、OCF 2 CF 2 CF 3 、OCF 2 CF 2 CClF 2 ,OCClFCF 2 CF 3 、OCH=CF 2 or CH=CF 2 , very particularly preferably F or OCF 3 , in addition to CF 3 、OCF=CF 2 , OCHF 2 Or OCH=CF 2 .

[0052] Herein, 1,4-cyclohexylene rings and 1,4-phenylene rings are depicted as follows:

[0053]

[0054] The cyclohexylene ring is a trans-1,4-cyclohexylene ring.

[0055] Liquid crystal media with negative dielectric anisotropy and in particular so-called liquid crystal hosts are widely used, for example, in displays with vertical alignment (VA) mode (Song, J. (2014). Vertical alignment Liquid Crystal mode. Handbook of Liquid Crystals (eds JW Goodby, C. Tschierske, P. Raynes, H. Gleeson, T. Kato and PJ Collings). doi: 10.1002 / 9783527671403.hlc126). Suitable media are well described in the literature, such as, for example, US 20030071244 A1 or US 20100134751 A1.

[0056] According to a preferred embodiment, the liquid-crystalline medium comprises one or more dichroic dyes, preferably two or more dichroic dyes and more preferably three or more dichroic dyes.

[0057] In this article, dichroic dyes are meant to be compounds with an elongated molecular structure, which are dissolved in a host liquid crystal for the purpose of absorbing light, wherein the dye molecules are aligned with the liquid crystal and can be oriented by the liquid crystal molecules when an electric field is applied. Preferably, the dichroic dyes used herein have an absorption maximum in the visible wavelength range. Dichroic dyes are well known to those skilled in the art and are fully described in the literature, for example in Liquid Crystals: Applications and Uses, Volumes 1 to 3, edited by Birenda Bahadur, World Scientific, 1992. Chapter 11: Dichroic Liquid Crystal Displays.

[0058] The absorption maximum of one or more dichroic dyes optionally used in the liquid crystal medium is not particularly limited, but preferably has an absorption maximum in the yellow region (Y), magenta region (M) or cyan region (C). The dichroic dye preferably used in the liquid crystal medium of the present invention may be a single compound or a combination of multiple dyes. When mixing several dyes, it is preferred to use a mixture of dichroic dyes having absorption maxima in the Y region, the M region and the C region, respectively. Dichroic dyes are known to those skilled in the art and are reviewed in, for example, Cowling, Stephen J., Liquid Crystal Dyes, in: Handbook of Liquid Crystals, Wiley-VCH Verlag GmbH & Co. KGaA (2014). The method of displaying full colors by mixing yellow dyes, magenta dyes and cyan dyes is specifically described in "Colour Chemistry" (Sumio Tokita, Maruzen Company, Limited, 1982). The yellow region is in the range of 430 to 490 nm, the magenta region is in the range of 500 to 580 nm, and the cyan region is in the range of 600 to 700 nm.

[0059] The chromophore used in the dichroic dye is not particularly limited, but preferably used are azo dyes, azulene dyes, anthraquinone dyes, benzoquinone dyes, naphthoquinone dyes, benzothiazole dyes, benzothiadiazole dyes, thiadiazoquinoxaline dyes, dithiobenzoquinones, perylene dyes, merocyanidin dyes, azomethine dyes, phthaloperylene dyes, indigo dyes, azulene dyes, dioxazine dyes, tetrazine dyes, polythiophene dyes, naphthylimidazolo-4,9-dione dyes, and phenoxazine dyes.

[0060] The liquid-crystalline medium preferably comprises one, two, three, four, five, six, seven, eight, nine or ten different dichroic dyes, particularly preferably two or three dichroic dyes.

[0061] Preferred dyes according to the present invention are azo dyes, perylene dyes, anthraquinone dyes, benzothiazole dyes and benzothiadiazole dyes, with azo dyes being particularly preferred.

[0062] The azo dye may contain any number of azo groups, such as monoazo dye, disazo dye, triazo dye, tetrakisazo dye and pentazo dye, and is preferably monoazo dye, disazo dye and trisazo dye.

[0063] The cyclic structure contained in the azo dye is preferably an aryl group and / or a heteroaryl group.

[0064] Preferred aryl groups are derived from, for example, parent structures benzene, biphenyl, terphenyl, naphthalene, anthracene, phenanthrene, pyrene, dihydropyrene, Perylene, fluorene, indene, etc.

[0065] Preferred heteroaryl groups are, for example, 5-membered rings such as pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, furan, thiophene, 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, benzimidazole, benzotriazole, purine azine, naphthimidazole, phenanthimidazole, pyridimidazole, pyrazimidazole, quinoxalineimidazole, benzoxazole, naphthimidazole, anthraxidazole, phenanthimidazole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, benzo-5,6-quinoline, benzo-6,7-quinoline, benzo-7,8-quinoline, benzisoquinoline, acridine, phenanthroline Thiazine, phenoxazine, benzopyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarboline, phenanthridine, phenanthroline, thieno[2,3b]thiophene, thieno[3,2b]thiophene, dithienothiophene, dihydrothieno[3,4-b]-1,4-dioxazine, isobenzothiophene, dibenzothiophene, benzothiadiazolothiophene or a combination of these groups.

[0066] The aryl and heteroaryl groups may also be substituted with alkyl, cycloalkyl, alkoxy, sulfanyl, alkylamino, dialkylamino, fluorine, fluoroalkyl or other aryl or heteroaryl groups.

[0067] In a particularly preferred embodiment, the liquid-crystalline medium comprises one or more dichroic dyes selected from the group of compounds of the formulae Dye-1, Dye-2 and Dye-3:

[0068]

[0069] Additionally or alternatively, it may also be preferred to use other types of dyes known to have the same effects as the above-mentioned dyes.

[0070] Each of the one or more dichroic dyes is preferably present in the liquid crystal medium in a proportion of 0.005% to 12.5% ​​by weight, more preferably 0.01% to 10% by weight, even more preferably 0.025% to 7.5% by weight, yet even more preferably 0.05% to 5% by weight, yet even more preferably 0.1% to 2.5% by weight, and particularly preferably 0.25% to 1% by weight, based on the total weight of the entire medium.

[0071] Preferably, the one or more dichroic dyes are present in the total liquid-crystalline medium in a total concentration in the range of 0.01% to 30% by weight, more preferably 0.025% to 25% by weight, even more preferably 0.05% to 15% by weight, yet even more preferably 0.1% to 10% by weight, and especially preferably 0.5% to 5% by weight.

[0072] The concentration of the dye is preferably chosen such that suitable properties of the resulting modulated material are ensured, in particular with regard to the desired color and / or shading effect.

[0073] In one embodiment, the absorption spectra of the dichroic dyes optionally contained in the medium or the switchable layer are preferably complementary to one another in such a way that the eye produces the impression of black. Preferably two or more, more preferably three or more, dichroic dyes are used in the liquid-crystalline medium to preferably cover a large part of the visible spectrum. The precise manner in which dye mixtures which appear black or grey to the eye can be prepared is known to the person skilled in the art and is described, for example, in M. Richter, Einführung in die Farbmetrik [Introduction to Colorimetry], 2nd edition, 1981, ISBN 3 11-008209-8, Walter de Gruyter & Co.

[0074] In another embodiment, different color settings are implemented, such as red, green or blue.

[0075] The setting of the color position of the dye mixture is described in the colorimetric area. For this purpose, the spectra of the individual dyes are calculated taking into account the Lambert-Beer law to obtain the total spectrum and converted into corresponding color positions and brightness values ​​according to the colorimetric rules under the relevant illumination (e.g. daylight source D65). The position of the white point is fixed by the individual light sources (e.g. D65) and is quoted in the table, e.g., above in the references. Different color positions can be set by changing the ratio of the various dyes.

[0076] According to the present invention, the liquid crystal medium comprises one or more ionic dopants of formula I as defined herein. The ionic dopants are provided as additives to induce or produce the desired dynamic scattering effect. In particular, the ionic dopants are ionic compounds or conductive salts that are sufficiently soluble in the medium and dissolve and dissociate into cation and anion components and have sufficient ion mobility or ion conductivity.

[0077] It has been unexpectedly found that, in addition to favorable solubility, ionic dopants as used according to the present invention also exhibit high electrochemical stability. Furthermore, ionic dopants may be particularly effective in achieving dynamic scattering in the presence of an applied electric field, even at relatively low concentrations and at relatively low operating voltages. Ionic dopants may produce sufficient ion mobility and fast switching response times, wherein the medium may advantageously have little or no electrochemical degradation and / or undesirable heating.

[0078] In a preferred embodiment, the liquid-crystalline medium contains no further salts than the ionic dopants of the present formula I. This means that preferably, apart from potential traces of unintentional ionic impurities, only ionic compounds of the formula I are present in the medium and no further ionic compounds are added.

[0079] In a preferred embodiment, one or more ionic dopants of the formula I each have a melting point above 100° C., preferably above 125° C. and in particular above 150° C.

[0080] The ionic dopant of formula I is advantageously effective already at low concentrations. The ionic dopant is advantageously used in an amount that induces dynamic scattering (preferably, significant dynamic scattering) in the medium while still allowing the liquid crystal to maintain the desired orientation in the absence of an electric field. This can produce the desired haze in the presence of an electric field, and only minimal or even indiscernible haze in the absence of an electric field.

[0081] In the optically clear state according to the invention, the switching component preferably has a haze measured according to ASTM D 1003 of less than 15%, more preferably less than 10%, even more preferably less than 5%, still more preferably less than 3.5% and in particular less than 2.5%.

[0082] In the diffuse state according to the present invention, the switching component preferably has a haze of more than 50%, more preferably more than 75%, even more preferably more than 85%, measured according to ASTM D 1003. It is particularly preferred that in the diffuse state, the switching component according to the present invention has a haze of 95% or more, measured according to ASTM D 1003.

[0083] To measure the haze, a turbidity meter manufactured by BYK-Gardner can be used. It is also possible to use a spectrophotometer, in particular a spectrophotometer with an Ulbricht's sphere.

[0084] Preferably, the total concentration of one or more ionic dopants of formula I, in particular the preferred ionic dopants as specified herein, in the liquid-crystalline medium is 0.10% by weight or less, more preferably 0.05% by weight or less, even more preferably 0.02% by weight or less, and in particular 0.01% by weight or less. In a preferred embodiment, the total concentration of one or more ionic dopants of formula I in the liquid-crystalline medium is in the range of 0.001% by weight to 0.10% by weight, preferably 0.005% by weight to 0.05% by weight, and particularly preferably 0.007% by weight to 0.025% by weight.

[0085] Preferably, the liquid-crystalline medium comprises exactly one ionic dopant of the formula I. In this case, the same preferred concentrations of the ionic dopant apply.

[0086] The ionic dopant used in the present invention is an organic cation A + and anion B - A salt thereof selected from the group consisting of tetrafluoroborate, tetracyanoborate, hexafluorophosphate, hexafluoroantimonate, methanesulfonate, ethanesulfonate and trifluoromethanesulfonate.

[0087] Preferably, in formula I, anion B - It is tetrafluoroborate or hexafluorophosphate, more preferably tetrafluoroborate.

[0088] Organic cations herein preferably denote molecular cations containing at least one carbon-hydrogen bond.

[0089] Preferably, the one or more ionic dopants of formula I comprise a cation A selected from the group consisting of + : ammonium, in particular organic ammonium, pyrrolidinium, imidazolium, pyridinium and guanidinium. Particularly preferably, the cation A + It is ammonium, especially organic ammonium.

[0090] In a preferred embodiment, the cation A + It is a quaternary ammonium.

[0091] In this context, quaternary ammonium means in particular an ammonium cation which has four organic radicals attached to a nitrogen atom and contains no hydrogen atoms bonded to the nitrogen atom.

[0092] Preferably, A + NR 4 +, in which R identically or differently represent optionally substituted aryl or heteroaryl, or optionally substituted alkyl or alkenyl, in particular optionally substituted aryl having 6 to 20 carbon atoms, or straight-chain or branched alkyl having 1 to 20 carbon atoms, or alkenyl having 2 to 20 carbon atoms, in which one or more hydrogen atoms may also be replaced by halogen.

[0093] Even more preferably, the cation A + It is a tetraalkylammonium.

[0094] In one embodiment, in the tetraalkylammonium cation, the alkyl radicals may be identical or different and are linear or branched, preferably having 1 to 15 C atoms, more preferably 2 to 10 C atoms, wherein preferably the alkyl radical is unsubstituted, but optionally and alternatively may also be mono- or polysubstituted, in particular by halogen, wherein halogen preferably denotes F or Cl, more preferably F. More preferably, the alkyl radical is linear and has 1, 2, 3, 4, 5, 6 or 7 C atoms.

[0095] Particularly preferably, the cation A + It is tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, tetrapentylammonium, tetrahexylammonium or tetraheptylammonium, even more preferably tetrapropylammonium, tetrabutylammonium or tetrapentylammonium, and in particular tetrabutylammonium.

[0096] Preferably, the one or more ionic dopants of formula I are ammonium tetrafluoroborate salts, preferably tetraalkylammonium tetrafluoroborate.

[0097] It is particularly preferred that the liquid-crystalline medium according to the invention comprises tetrabutylammonium tetrafluoroborate Bu represented by the structure 4 NBF 4 :

[0098]

[0099] Preferably, tetrabutylammonium tetrafluoroborate is contained in the liquid crystal medium in an amount ranging from 0.001% to 0.100% by weight, preferably from 0.005% to 0.050% by weight.

[0100] With particular preference, the liquid-crystalline medium comprises tetrabutylammonium tetrafluoroborate as the sole ionic dopant.

[0101] However, in an alternative embodiment, it is also possible to include tetrabutylammonium tetrafluoroborate as well as other salts.

[0102] In a preferred embodiment, the liquid crystal medium, in particular the nematic host, comprises one or more compounds selected from the group consisting of compounds of the formulae IIA, IIB and IIC

[0103]

[0104] in

[0105] R 2A , R 2B and R 2C each independently of one another represents H; an alkyl or alkenyl group having up to 15 C atoms, which is unsubstituted, substituted with CN or CF 3 monosubstituted or at least monosubstituted by halogen, wherein in addition, one or more CH 2 The groups may be connected in such a way that the O atoms are not directly connected to each other. -O-, -S-, -C≡C-, -CF 2 O-、-OCF 2 -, -OC-O- or -O-CO-; or a cycloalkyl ring having 3 to 6 C atoms,

[0106] L 1-4 Each independently represents F, Cl, CF 3 or CHF 2 ,

[0107] Z 2 and Z 2’ Each independently represents a single bond, -CH 2 CH 2 -、-CH=CH-、-C≡C-、-CF 2 O-、-OCF 2 -、-CH 2 O-、-OCH 2 -、-C(O)O-、-OC(O)-、-C 2 F 4 -, -CF=CF- or -CH=CHCH 2 O-,

[0108] p means 1 or 2,

[0109] q represents 0 or 1, and

[0110] v represents 1 to 6.

[0111] In the compounds of formula IIA and IIB, Z 2 can have the same or different meanings. In the compounds of formula IIB, Z 2 and Z 2’ can have the same or different meanings.

[0112] In the compounds of formula IIA, IIB and IIC, R 2A , R 2B and R 2C each preferably represents an alkyl radical having 1 to 6 C atoms, in particular CH3 , C 2 H 5 , positive C 3 H 7 , positive C 4 H 9 , positive C 5 H 11 .

[0113] In the compounds of Formula IIA and IIB, L 1 , L 2 , L 3 and L 4 Preferably, L 1 =L 2 =F and L 3 =L 4 =F, and L 1 =F and L 2 =Cl, L 1 =Cl and L 2 =F, L 3 =F and L 4 =Cl, L 3 =Cl and L 4 =F. Z in Formula IIA and IIB 2 and Z 2’ Preferably each independently of one another represents a single bond, furthermore -C 2 H 4 -or-CH 2 O-bridge.

[0114] If in Formula IIB, Z 2 Indicates -C 2 H 4 -or-CH 2 O-, then Z 2’ Preferably a single bond, or if Z 2’ Indicates -C 2 H 4 -or-CH 2 O-, then Z 2 In the compounds of formula IIA and IIB, (O)C v H 2v+1 Preferably means OC v H 2v+1 , in addition, C v H 2v+1 In the compound of formula IIC, (O)C v H 2v+1 Preferably, C v H 2v+1 In the compound of formula IIC, L 3 and L 4 Preferably each represents F.

[0115] Preferred compounds of formula IIA, IIB and IIC are indicated below:

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

[0123] wherein alkyl and alkyl* each independently represent a straight-chain alkyl radical having 1 to 7 C atoms,

[0124] Alkenyl represents a straight-chain alkenyl group having 2 to 7 C atoms, and (O) represents -O- or a single bond.

[0125] Particularly preferred mixtures according to the invention comprise one or more compounds of the formulae IIA-2, IIA-8, IIA-14, IIA-26, IIA-28, IIA-33, IIA-39, IIA-45, IIA-46, IIA-47, IIB-2, IIB-11, IIB-16, IIB-17, IIB-18 and IIC-1.

[0126] The proportion of the compounds of the formula IIA and / or formula IIB in the mixture as a whole is preferably at least 20% by weight.

[0127] Particularly preferred media according to the invention comprise at least one compound of the formula IIC-1,

[0128]

[0129] wherein alkyl and alkyl* have the meanings indicated above, preferably in an amount >3% by weight, in particular >5% by weight, preferably in the range of 10% to 40% by weight, particularly preferably 20% to 30% by weight.

[0130] Preferably, the liquid-crystalline media according to the invention comprise one or more compounds of the formula N,

[0131]

[0132] in

[0133] R N represents an alkyl or alkenyl group having up to 12 C atoms, in which one or more non-adjacent CH 2 The group may be replaced by -O- and / or a cycloalkyl ring having 3 to 5 C atoms, in which one or more H atoms may be replaced by F,

[0134] A N In each occurrence, the same or different

[0135] (a) trans-1,4-cyclohexylene, in which one or more non-adjacent CH 2 The group may be substituted by -O- and / or -S-,

[0136] (b) 1,4-phenylene, one or two CH groups of which may be replaced by N,

[0137] (c) trans-1,4-cyclohexenylene,

[0138] (d) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,

[0139] wherein the groups (a) to (d) may be substituted by one or two fluorine atoms,

[0140] Z N Each occurrence represents independently of each other -CO-O-, -O-CO-, -CH 2 O-、-OCH 2 -、-CH 2 CH 2 -, -CH=CH-, -C≡C-, -(CH 2 ) 4 -、-OCF 2 -、-CF 2 O-、-CF 2 CF 2 - or single key,

[0141] L N1 , L N2 , L N3 and L N4 each independently represents H, Cl or F,

[0142] n is 1, 2 or 3.

[0143] Preferred compounds of formula N are selected from the group consisting of compounds of formula N-1 and N-2:

[0144]

[0145] in

[0146] R N denotes an alkyl or alkenyl group having up to 7 C atoms,

[0147] A N1 and A N2 Same or different

[0148]

[0149] Best

[0150] L N1 and L N2 independently represent H or F, and

[0151] Z N Represents -CO-O-, -O-CO-, -CH 2 O-、-OCH 2 -、-CH 2 CH 2 -、-OCF 2 -、-CF 2 O- or a single bond, preferably a single bond.

[0152] Particularly preferred compounds of the formula N are selected from the group consisting of compounds of the formulae N-1 to N-8, very particularly preferred are compounds of the formula N-1:

[0153]

[0154]

[0155] In a preferred embodiment, the liquid-crystalline medium comprises one or more further additives, preferably stabilizers and / or chiral dopants.

[0156] In a particularly preferred embodiment of the present invention, the liquid-crystalline medium comprises one or more stabilizers, preferably selected from the group consisting of compounds of the formulae ST-1 to ST-18.

[0157]

[0158]

[0159]

[0160]

[0161] in

[0162] R STrepresents H, alkyl or alkoxy having 1 to 15 C atoms, wherein in addition, one or more of these radicals CH 2 The groups can be independently connected to each other via -C≡C-, -CF 2 O-、-OCF 2 -、-CH=CH-、 -O-, -CO-O- or -O-CO-, and wherein in addition one or more H atoms may each be replaced by a halogen,

[0163] express

[0164]

[0165]

[0166] Z ST Each independently represents -CO-O-, -O-CO-, -CF 2 O-、-OCF 2 -、-CH 2 O-、-OCH 2 -、-CH 2 -、-CH 2 CH 2 -、-(CH 2 ) 4 -、-CH=CH-CH 2 O-、-C 2 F 4 -、-CH 2 CF 2 -、-CF 2 CH 2 -, -CF=CF-, -CH=CF-, -CF=CH-, -CH=CH-, -C≡C- or a single bond,

[0167] L 1 and L 2 Each independently represents F, Cl, CF 3 or CHF 2 ,

[0168] p means 1 or 2,

[0169] q represents 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0170] Among the compounds of formulae ST-1 to ST-18, particularly preferred are compounds of the following formula

[0171]

[0172] wherein n=1, 2, 3, 4, 5, 6 or 7, preferably, n=1 or 7

[0173]

[0174] wherein n=1, 2, 3, 4, 5, 6 or 7, preferably n=3

[0175]

[0176] wherein n=1, 2, 3, 4, 5, 6 or 7, preferably n=3

[0177]

[0178]

[0179] In the compounds of formulae ST-3a and ST-3b, n preferably represents 3. In the compounds of formula ST-2a, n preferably represents 7.

[0180] Very particularly preferred liquid-crystal mixtures according to the invention comprise one or more stabilizers from the group of compounds of the formulae ST-2a-1, ST-3a-1, ST-3b-1, ST-8-1, ST-9-1 and ST-12:

[0181]

[0182]

[0183]

[0184] One or more compounds selected from the compounds of the formulae ST-1 to ST-18 are preferably each present in the liquid-crystal mixture according to the invention in an amount of 0.005% to 0.5% by weight, based on the mixture.

[0185] If the mixture according to the invention contains two or more compounds from the group of compounds of the formulae ST-1 to ST-18, the total concentration of these compounds, based on the mixture, is preferably in the range from 0.01% to 2.5% by weight, more preferably in the range from 0.05% to 1.0% by weight.

[0186] However, the total proportion of compounds of the formulae ST-1 to ST-18, based on the mixture according to the invention, should preferably not exceed 3% by weight.

[0187] In a preferred embodiment, the media according to the invention comprise one or more chiral dopants and therefore exhibit a cholesteric phase.

[0188] Preferably, these chiral dopants have a -1 Up to 150μm -1 In the range of 10 μm, preferably -1 Up to 100 μm -1 In the case where the medium contains two or more chiral dopants, these may have opposite signs to their HTP values. This condition is preferred for some specific embodiments, since it allows to compensate the chirality of the individual compounds to a certain extent and can therefore be used to compensate for various temperature-dependent properties of the resulting medium in the device. However, in general, it is preferred that most, preferably all, of the chiral compounds optionally in the medium according to the invention have the same sign as their HTP values.

[0189] Preferably, the chiral dopant present in the medium according to the invention is a mesogenic compound and most preferably it exhibits a mesophase alone.

[0190] The temperature dependence of the HTP of each compound may be high or low. The temperature dependence of the pitch of the medium may be compensated by mixing compounds with different HTP temperature dependencies in corresponding ratios.

[0191] For the optically active component, a variety of chiral dopants known in the art can be used, such as, for example, cholesteryl nonanoate, R- and S-811, R- and S-1011, R- and S-2011, R- and S-3011, R- and S-4011, R- and S-5011, B(OC)2C*HC-3 or CB15 (all from Merck KGaA, Darmstadt).

[0192] Particularly suitable dopants are compounds which contain one or more chiral groups and one or more mesogenic groups, or one or more aromatic or alicyclic groups which form mesogenic groups with chiral groups.

[0193] Suitable chiral groups are, for example, chiral branched hydrocarbon groups, chiral ethylene glycol, binaphthol or dioxolane, furthermore mono- or polyvalent chiral groups selected from the group consisting of sugar derivatives, sugar alcohols, sugar acids, lactic acid, chiral substituted diols, steroid derivatives, terpenoid derivatives, amino acids or sequences of several (preferably 1 to 5) amino acids.

[0194] Preferred chiral groups are sugar derivatives, such as glucose, mannose, galactose, fructose, arabinose and dextrose; sugar alcohols, such as sorbitol, mannitol, iditol, galactitol or their dehydrated derivatives, in particular dianhydrohexitols, such as dianhydrosorbitol (1,4:3,6-dianhydro-D-sorbitol, isosorbide), dianhydromannitol (isosorbide) or dianhydroiditol (isoiditol); sugar acids, such as gluconic acid, gulonic acid and ketogulonic acid; chiral substituted diol groups, such as mono- or oligoethylene glycol or propylene glycol, in which one or more CH 2 The group is substituted by an alkyl or alkoxy group; an amino acid, for example, alanine, valine, phenylglycine or phenylalanine or a sequence of 1 to 5 of these amino acids; a steroid derivative, for example, a cholesteryl or cholic acid group; a terpene derivative, for example, menthyl, neomenthyl, campheyl, pineyl, terpineyl, isolongifolyl, fenchyl, carreyl, myrthenyl, nopyl, geraniyl, linaloyl, neryl, citronellyl or dihydrocitronellyl.

[0195] Suitable chiral groups and mesogenic chiral compounds are described, for example, in DE 34 25 503, DE 35 34 777, DE 35 34 778, DE 35 34 779 and DE 35 34 780, DE 43 42 280, EP 01 038 941 and DE 195 41 820. Examples are also the compounds listed in Table B below.

[0196] Particularly preferred are chiral dopants selected from the group consisting of compounds of the following formulae AI to A-III and A-Ch:

[0197]

[0198] in

[0199] R a11 , R a12 and R b12 independently of one another represent an alkyl radical having 1 to 15 C atoms, wherein in addition, one or more non-adjacent CH 2 The group may be independently connected to each other through -C(R) in such a way that the O and / or S atoms are not directly connected to each other. z )=C(R z)-, -C≡C-, -O-, -S-, -CO-, -CO-O-, -O-CO- or -O-CO-O-, and wherein in addition, one or more H atoms may be replaced by F, Cl, Br, I or CN,

[0200] It is preferably an alkyl group, more preferably a normal alkyl group, with the restriction that R a12 With R b12 different,

[0201] R a21 and R a22 independently of one another represent an alkyl radical having 1 to 15 C atoms, wherein in addition, one or more non-adjacent CH 2 The group may be independently connected to each other through -C(R) in such a way that the O and / or S atoms are not directly connected to each other. z )=C(R z )-, -C≡C-, -O-, -S-, -CO-, -CO-O-, -O-CO- or -O-CO-O-, and wherein in addition, one or more H atoms may be replaced by F, Cl, Br, I or CN, preferably all of which are alkyl, more preferably n-alkyl,

[0202] R a31 , R a32 and R b32 independently of one another represent straight-chain or branched alkyl radicals having 1 to 15 C atoms, wherein in addition, one or more non-adjacent CH 2 The group may be independently connected to each other through -C(R) in such a way that the O and / or S atoms are not directly connected to each other. z )=C(R z )-, -C≡C-, -O-, -S-, -CO-, -CO-O-, -O-CO- or -O-CO-O-, and in addition, one or more H atoms may be replaced by F, Cl, Br, I or CN, preferably alkyl, more preferably n-alkyl, with the restriction that R a32 With R b32 different;

[0203] R z Indicates H, CH 3 , F, Cl or CN, preferably H or F,

[0204] R 8 With the R given above a11 one of the meanings of , preferably an alkyl group, more preferably a n-alkyl group having 1 to 15 C atoms,

[0205] Z 8 Indicates -C(O)O-, CH 2 O.CF 2O or a single bond, preferably -C(O)O-,

[0206] A 11 As shown in the following A 12 defined, or alternatively

[0207]

[0208] A 12 express

[0209]

[0210] Preferably

[0211]

[0212] in

[0213] r is 0, 1, 2, 3, or 4,

[0214] L and L 11 represents, independently of one another, on each occurrence alkyl, alkenyl or alkoxy having up to 12 C atoms, wherein one or more H atoms are optionally replaced by halogen; halogen; SF 5 ; or CN,

[0215] Preferably, it is Me (methyl), Et (ethyl), Cl or F, and particularly preferably F,

[0216] A 21 express

[0217]

[0218] A 22 With A 12 The meaning given

[0219] A 31 With A 11 The meaning given, or

[0220] Alternatively,

[0221] A 32 With A 12 The meaning given,

[0222] n2 is 0, 1 or 2, either identically or differently at each occurrence, and

[0223] n3 is 1, 2 or 3.

[0224] Particularly preferred are chiral dopants selected from the group consisting of compounds of the following formulae:

[0225]

[0226]

[0227] in

[0228] m is, at each occurrence, identical or different, an integer from 1 to 9, and

[0229] n is an integer from 2 to 9, identically or differently on each occurrence.

[0230] Particularly preferred compounds of formula A are compounds of formula A-III.

[0231] Other preferred dopants are derivatives of isosorbide, isomannide or isoidide of the following formula A-IV:

[0232]

[0233] Among them for

[0234]

[0235] Sorbitan is preferred.

[0236] Other preferred dopants are chiral glycols such as, for example, diphenyl glycol (hydrobenzoin), in particular the mesogenic hydrobenzoin derivatives of the following formula AV:

[0237]

[0238] including (R,S), (S,R), (R,R) and (S,S) enantiomers not shown,

[0239] in

[0240]

[0241] and

[0242] are each independently 1,4-phenylene, which may also be mono-, di- or tri-substituted by L; or 1,4-cyclohexylene,

[0243] L is H, F, Cl, CN or an optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkoxycarbonyloxy group having 1 to 7 carbon atoms,

[0244] c is 0 or 1,

[0245] X is CH 2 or -C(O)-,

[0246] Z 0 -COO-, -OCO-, -CH 2 CH 2 - or a single key, and

[0247] R 0 It is an alkyl group, an alkoxy group, an alkylcarbonyl group, an alkoxycarbonyl group or an alkylcarbonyloxy group having 1 to 12 carbon atoms.

[0248] Preferably the chiral compound used according to the present invention is selected from the group consisting of the formulae shown below.

[0249] Examples of compounds of formula A-IV are:

[0250]

[0251]

[0252] Compounds of formula AV are described in GB-A-2,328,207.

[0253] Very particularly preferred dopants are chiral binaphthyl derivatives, as described in WO 02 / 94805; chiral binaphthol acetal derivatives, as described in WO 02 / 34739; chiral TADDOL derivatives, as described in WO 02 / 06265; and chiral dopants having at least one fluorinated bridge group and a terminal or central chiral group, as described in WO 02 / 06196 and WO 02 / 06195.

[0254] Particularly preferred are chiral compounds of formula A-VI

[0255]

[0256] in

[0257] X 1 , X 2 , Y 1 and Y 2 Each independently is F, Cl, Br, I, CN, SCN, SF 5 ; a straight-chain or branched alkyl radical having 1 to 25 carbon atoms, which is unsubstituted or mono- or polysubstituted by F, Cl, Br, I or CN, and in which in addition, one or more non-adjacent CH 2 The groups may be independently connected to each other via -O-, -S-, -NH-, NR- 0-, -CO-, -COO-, -OCO-, -OCOO-, -S-CO-, -CO-S-, -CH=CH- or -C≡C-; a ​​polymerizable group or a cycloalkyl or aryl group having up to 20 carbon atoms, which may optionally be mono- or polysubstituted by halogen, preferably F, or by a polymerizable group,

[0258] R 0 is H or an alkyl radical having 1 to 12 C atoms,

[0259] x 1 and x 2 are each independently 0, 1 or 2,

[0260] y 1 and 2 are each independently 0, 1, 2, 3 or 4,

[0261] B 1 and B 2 Each independently of one another is an aromatic or partially or fully saturated aliphatic six-membered ring, in which one or more CH groups may each be replaced by N, and one or more non-adjacent CH 2 The groups may be substituted by O or S,

[0262] W 1 and W 2 Each independently of the other is -Z 1 -A 1 -(Z 2 -A 2 ) m -R, and either one may alternatively be R 1 or A 3 , but they are not both H at the same time, or

[0263] for

[0264] U 1 and U 2 Each independently is CH 2 , O, S, CO or CS,

[0265] V 1 and V 2 Each independently of each other is (CH 2 ) n , where one to four non-adjacent CH 2 The groups may be substituted by O or S, and V 1 and V 2 One of them

[0266] for In all cases, single key

[0267] n is 1, 2, or 3,

[0268] Z 1 and Z 2 Each is independently -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -CO-NR 0 -、-NR 0 -CO-, -O-CH 2 -、-CH 2 -O-、-S-CH 2 -、-CH 2 -S-, -CF 2 -O-, -O-CF 2 -、-CF 2 -S-, -S-CF 2 -、-CH 2 -CH 2 -、-CF 2 -CH 2 -、-CH 2 -CF 2 -、-CF 2 -CF 2 -, -CH=N-, -N=CH-, -N=N-, -CH=CH-, -CF=CH-, -CH=CF-, -CF=CF-, -C≡C-, a combination of two of these groups, wherein no two O and / or S and / or N atoms are directly bonded to each other (preferably -CH=CH-COO- or -COO-CH=CH-); or a single bond,

[0269] A 1 , A 2 and A 3 are each independently 1,4-phenylene, in which one or two non-adjacent CH groups may each be replaced by N; 1,4-cyclohexylene, in which one or two non-adjacent CH 2 The groups may each be replaced by O or S; 1,3-dioxolane-4,5-diyl; 1,4-cyclohexenyl; 1,4-bicyclo[2.2.2]octylene; piperidine-1,4-diyl; naphthalene-2,6-diyl; decahydronaphthalene-2,6-diyl; or 1,2,3,4-tetrahydronaphthalene-2,6-diyl, wherein each of these groups may be mono- or polysubstituted by L, and in addition, A 1 Can be a single key,

[0270] L is a halogen atom, preferably F, CN, NO 2, an alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkoxycarbonyloxy radical having 1 to 7 carbon atoms, wherein one or more H atoms may each be replaced by F or Cl,

[0271] m is independently at each occurrence 0, 1, 2 or 3, and

[0272] R and R 1 Each independently is H, F, Cl, Br, I, CN, SCN, SF 5 ; a straight-chain or branched alkyl radical having 1 or 3 to 25 carbon atoms, which may be optionally mono- or poly-substituted by F, Cl, Br, I or CN, and wherein one or more non-adjacent CH 2 The groups may be each substituted by -O-, -S-, -NH-, -NR 0 -, -CO-, -COO-, -OCO-, -O-COO-, -S-CO-, -CO-S-, -CH=CH- or -C≡C-, wherein no two O and / or S atoms are directly bonded to each other; or a polymerizable group.

[0273] Particularly preferred are chiral binaphthyl derivatives of formula A-VI-1

[0274]

[0275] Among them, ring B, R 0 and Z 0 As defined for formulae A-IV and AV, and b is 0, 1 or 2, in particular those selected from the following formulae A-VI-1a to A-VI-1c:

[0276]

[0277]

[0278] Among them, ring B, R 0 and Z 0 As defined for Formula A-VI-1, and

[0279] R 0 As defined for formula A-IV or H or an alkyl radical having 1 to 4 carbon atoms, and b is 0, 1 or 2,

[0280] And Z 0 Especially -OCO- or a single bond.

[0281] Furthermore, particularly preferred are chiral binaphthyl derivatives of formula A-VI-2

[0282]

[0283] In particular those selected from the following formulae A-VI-2a to A-VI-2f:

[0284]

[0285]

[0286] Where R 0 As defined for Formula A-VI, and X is H, F, Cl, CN or R 0 , preferably F.

[0287] The concentration of one or more chiral dopants optionally contained in the liquid crystal medium is preferably in the range of 0.001% to 20% by weight, more preferably 0.05% to 5% by weight, even more preferably 0.1% to 2% by weight, and in particular 0.5% to 1.5% by weight. These preferred concentration ranges apply in particular to the chiral dopants S-4011 or R-4011 and S-5011 or R-5011 (all from Merck KGaA) and to chiral dopants having the same or similar HTP.

[0288] Preferably, the liquid-crystalline medium additionally comprises one or more compounds of the formula III,

[0289]

[0290] in

[0291] R 31 and R 32 each independently of one another represents a straight-chain alkyl, alkenyl, alkoxyalkyl or alkoxy radical having up to 12 C atoms, and express

[0292] Z 3 Represents a single bond, -CH 2 CH 2 -、-CH=CH-、-CF 2 O-、-OCF 2 -、-CH 2 O-、-OCH 2 -、-COO-、-OCO-、-C 2 F 4 -、-C 4 H 8 -or-CF=CF-.

[0293] Preferred compounds of formula III are selected from the group of compounds of the following sub-formulae:

[0294]

[0295]

[0296] wherein alkyl and alkyl* each independently represent a straight-chain alkyl radical having 1 to 6 C atoms, and alkenyl represents a straight-chain alkenyl radical having 2 to 6 C atoms. 2 =CH-, CH 2 =CHCH 2 CH 2 -、CH 3 -CH=CH-, CH 3 -CH 2 -CH=CH-, CH 3 -(CH 2 ) 2 -CH=CH-, CH 3 -(CH 2 ) 3 -CH=CH- or CH 3 -CH=CH-(CH 2 ) 2 -.

[0297] Particularly preferred are compounds of formulae III-1 and III-3.

[0298] The proportion of the compound of the formula III in the mixture as a whole is preferably at least 5% by weight.

[0299] Particularly preferred compounds of formula III-1 are the following:

[0300]

[0301] Particularly preferred compounds of formula III-3 are the following:

[0302]

[0303]

[0304] Preferably, the liquid-crystalline medium comprises one or more tetracyclic compounds of the formula

[0305]

[0306] in

[0307] R 7-10 Each independently has R for Formula IIA 2A w and x each independently represent 1 to 6.

[0308] Especially preferred are mixtures comprising at least one compound of the formula V-9.

[0309] Preferably, the liquid crystal medium comprises one or more compounds of the formulae Y-1 to Y-6

[0310]

[0311] Where R 14 To R 19 Each independently represents an alkyl group or an alkoxy group having 1 to 6 C atoms; z and m each independently represent 1 to 6; and x represents 0, 1, 2 or 3.

[0312] The medium according to the invention particularly preferably comprises one or more compounds of the formulae Y-1 to Y-6 in an amount of 5% by weight or more.

[0313] Preferably, the liquid crystal medium comprises one or more fluorinated terphenyls of the formulae T-1 to T-21

[0314]

[0315]

[0316]

[0317] in

[0318] R represents a straight-chain alkyl or alkoxy group having 1 to 7 C atoms, or an alkenyl group having 2 to 7 C atoms, preferably a methyl, ethyl, propyl, butyl, pentyl, hexyl, methoxy, ethoxy, propoxy, butoxy, pentyloxy group, and m=0, 1, 2, 3, 4, 5 or 6, and n represents 0, 1, 2, 3 or 4.

[0319] The medium according to the invention preferably comprises the terphenyls of the formulae T-1 to T-21 in an amount of 2% to 30% by weight, in particular 5% to 20% by weight.

[0320] Particularly preferred are compounds of the formulae T-1, T-2, T-20 and T-21, very especially compounds of the formula T-1. In these compounds, R preferably represents an alkyl group each having 1 to 5 C atoms, furthermore an alkoxy group. In compounds of the formula T-20, R preferably represents an alkyl group or an alkenyl group, in particular an alkyl group. In compounds of the formula T-21, R preferably represents an alkyl group.

[0321] Terphenyl is preferably used in the mixture according to the invention if the Δn value of the mixture is ≥ 0.1. Preferred mixtures comprise 2% to 20% by weight of one or more terphenyl compounds selected from the group of compounds T-1 to T-21.

[0322] In a particularly preferred embodiment, the liquid-crystalline media according to the invention comprise one or more compounds of the formula T-1, preferably in a total concentration in the range from 3% to 15% by weight, more preferably from 5% to 10% by weight.

[0323] Preferably, the liquid-crystalline medium additionally comprises one or more biphenyls of the formulae B-1 to B-6

[0324]

[0325] in

[0326] Alkyl and alkyl* each independently represent a straight-chain alkyl radical having 1 to 6 C atoms,

[0327] alkenyl and alkenyl* each independently represent a straight-chain alkenyl radical having 2 to 6 C atoms, and

[0328] Alkoxy represents straight-chain alkoxy having 1 to 6 C atoms.

[0329] The proportion of biphenyls of the formulae B-1 to B-6, preferably of the formula B-5, in the mixture as a whole is preferably at least 3% by weight, in particular 5% by weight or more, preferably in the range from 7% by weight to 15% by weight.

[0330] Among the compounds of formulae B-1 to B-4, the compound of formula B-2 is particularly preferred.

[0331] Very particularly preferred biphenyls are

[0332]

[0333] Therein alkyl* denotes an alkyl radical having 1 to 6 C atoms. The medium according to the invention particularly preferably comprises one or more compounds of the formula B-1a and / or B-2c.

[0334] Preferably, the liquid-crystalline medium comprises at least one compound of the formulae Z-1 to Z-7

[0335]

[0336]

[0337] in

[0338] R represents a straight-chain alkyl or alkoxy group having 1 to 7 C atoms, or an alkenyl group having 2 to 7 C atoms,

[0339] Alkyl represents an alkyl group having 1 to 6 C atoms, and

[0340] (O)alkyl represents an alkyl group or an Oalkyl group (alkoxy group).

[0341] Preferably, the liquid-crystalline medium comprises at least one compound of the formulae O-1 to O-16

[0342]

[0343]

[0344] Where R 1 and R 2 With R 2A The meaning indicated. 1 and R 2 Preferably each independently represents a straight-chain alkyl group having 1 to 6 C atoms, or R 1 represents a straight-chain alkyl group having 1 to 6 C atoms, and R 2 represents an alkenyl group having 2 to 6 C atoms.

[0345] Preferred media comprise one or more compounds of formula O-1, O-3, O-4, O-5, O-9, O-12, O-14, O-15 and / or O-16.

[0346] The mixtures according to the invention very particularly preferably comprise the compounds of the formulae O-9, O-12 and / or O-16, in particular in amounts of 5% to 30% by weight.

[0347] Preferred compounds of formula O-9 are indicated below:

[0348]

[0349]

[0350] Preferably, the liquid-crystalline medium comprises one or more compounds of the formula BA

[0351]

[0352] in

[0353] alkenyl and alkenyl* each independently represent straight-chain alkenyl having 2 to 12 C atoms,

[0354] express

[0355] Z 3 Represents a single bond, -CH 2 CH 2 -、-CH=CH-、-CF 2 O-、-OCF 2 -、-CH 2 O-、-OCH2 -、-COO-、-OCO-、-C 2 F 4 -、-C 4 H 8 -, -CF=CF-.

[0356] Preferred compounds of formula BA are indicated below:

[0357]

[0358] Preferred mixtures contain one or more indane compounds of the formula In,

[0359]

[0360] in

[0361] R 11 , R 12 , R 13 each independently of one another represents a straight-chain alkyl, alkoxy, alkoxyalkyl or alkenyl radical having 1 to 6 C atoms or 2 to 6 C atoms,

[0362] R 12 and R 13 In addition, it represents halogen, preferably F,

[0363] express

[0364]

[0365] i represents 0, 1 or 2.

[0366] Preferred compounds of formula In are compounds of formula In-1 to In-16 indicated below:

[0367]

[0368]

[0369]

[0370] Particularly preferred are compounds of formulae In-1, In-2, In-3 and In-4.

[0371] The compounds of the formula In and subformulae In-1 to In-16 are preferably used in the mixture according to the invention in a concentration of ≥5% by weight, in particular 5% to 30% by weight and very particularly preferably 5% to 25% by weight.

[0372] Preferably, the medium additionally comprises one or more compounds selected from the following formulae:

[0373]

[0374]

[0375] In the compounds of formulae Q-1 to Q-9, R Q and X Q Each independently has R as defined for Formula IIA 2A Meaning of R Q and X Q Preferably it denotes straight-chain alkyl having 1 to 6 C atoms, in particular having 2 to 5 C atoms.

[0376] Particularly preferred mixture concepts are indicated below, wherein the acronyms used are explained below in Tables 1 to 3 and Table A. Here, n and m are each independently of one another an integer from 1 to 9, preferably from 1 to 6.

[0377] The liquid-crystal mixture according to the invention preferably comprises

[0378] - a compound of formula N and one or more compounds of formula IIB, preferably CPY-n-Om, in particular CPY-2-O2, CPY-3-O2 and / or CPY-5-O2, preferably in a concentration >5%, more preferably in the range of 20% to 60%, very particularly in the range of 30% to 50%,

[0379] and / or

[0380] -CY-n-Om, preferably CY-3-O2, CY-3-O4, CY-5-O2 and / or CY-5-O4, preferably in a concentration >5%, more preferably in the range of 5% to 25%, in particular 10% to 15%,

[0381] and / or

[0382] -CCY-n-Om, preferably CCY-4-O2, CCY-3-O2, CCY-3-O3, CCY-3-O1 and / or CCY-5-O2, preferably in a concentration >5%, more preferably in the range of 10% to 30%,

[0383] and / or

[0384] - CPY-n-Om and optionally PTY-n-Om, preferably in a total concentration ranging from 5% to 50%, more preferably from 10% to 40%, particularly preferably from 20% to 30%,

[0385] and / or

[0386] - CPY-n-Om and PY-n-Om, preferably CPY-2-O2 and / or CPY-3-O2 and PY-3-O2, preferably in a concentration of 10% to 40%,

[0387] and / or

[0388] - CBC-nm and / or CBC-nmF, preferably in a total concentration of 2% to 10%,

[0389] and / or

[0390] -PGIY-n-Om, preferably with a total concentration ranging from 3% to 15%,

[0391] and / or

[0392] -PGIGI-nF, preferably in a total concentration ranging from 3% to 15%,

[0393] and / or

[0394] -PTP-n-Om, preferably with a total concentration ranging from 5% to 15%.

[0395] Besides one or more compounds of the formula I, the medium preferably comprises 4 to 15, in particular 5 to 12 and particularly preferably <10 compounds of the formulae IIA, IIB and / or IIC.

[0396] In addition to the compound of formula I and the compound of formula IIA, IIB and / or IIC, further ingredients may be present, for example, in an amount of up to 45%, but preferably up to 35%, in particular up to 10%, of the mixture as a whole.

[0397] Furthermore, these liquid-crystalline phases may also comprise more than 18 components, preferably from 18 to 25 components.

[0398] Polymerizable compounds (non-mesogenic or mesogenic, the latter being referred to as reactive mesogens (RM)) can additionally be added to the mixture according to the invention, preferably in a concentration of 0.1% to 40% by weight.

[0399] The mixtures according to the invention may additionally comprise customary additives such as, for example, stabilizers, antioxidants, UV absorbers, nanoparticles, microparticles and the like.

[0400] In a particularly preferred embodiment, the liquid-crystalline medium does not contain tolan.Tolan in the present context refers to a compound comprising a moiety in which an unsubstituted or substituted phenylene group is attached to both ends of a carbon-carbon triple bond.

[0401] In a further preferred embodiment, the liquid-crystalline medium contains no compounds having -C≡C- bonds.

[0402] The liquid-crystalline media according to the invention have a clearing point of 90° C. or higher.

[0403] The clearing point marks the temperature at which the phase transition from the nematic liquid crystal state to the isotropic state occurs. The clearing point, in particular the phase transition temperature between the nematic phase and the isotropic phase, can be measured and determined by commonly known methods, such as using a Mettler oven or a hot stage under a polarizing microscope, and is preferably determined using a Mettler oven herein.

[0404] The liquid-crystalline medium preferably has a clearing point, preferably the phase transition from the nematic liquid-crystalline state to the isotropic state, above 95° C., more preferably above 100° C., particularly preferably above 105° C., very particularly preferably above 110° C., and most preferably above 115° C. In one embodiment, the liquid-crystalline medium as used in the present invention preferably has a clearing point in the temperature range of 90° C. to 170° C., more preferably 100° C. to 160° C., even more preferably 105° C. to 150° C., and in particular 110° C. to 140° C.

[0405] The liquid crystal medium or nematic host according to the invention preferably exhibits a very broad nematic phase range. In particular, the liquid crystal medium as used in the switching component preferably has a nematic phase at the operating temperature of the switching component. Particularly preferably, nematic liquid crystals are present in the range of + / -20° C., very particularly preferably in the range of + / -30° C., above and below the operating temperature of the switching component. Preferably, the liquid crystal medium has a favorable capacitance threshold, a relatively high voltage holding ratio value and at the same time very good low temperature stability at -20° C. and -30° C., as well as a low rotational viscosity and a short response time, and further preferably in the range of a rotational viscosity γ 1 Improvements have been shown.

[0406] Unless expressly stated otherwise, all physical properties and physicochemical or electro-optical parameters were determined by generally known methods, in particular according to “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and are given for a temperature of 20° C.

[0407] In this text, unless expressly stated otherwise, all concentrations are given as percentages by weight, ie the percentage data indicate percentages by weight and relate to the respective complete mixture, and all temperature values ​​indicated are in ° C.

[0408] The transmission and scattering of light preferably refers to the transmission and scattering of electromagnetic radiation in the spectrum ranging from 380 nm to 780 nm.

[0409] The liquid-crystalline media according to the invention have a negative dielectric anisotropy Δε, ie perpendicular to the electric field.

[0410] In the above and below, Δε denotes dielectric anisotropy, where Δε=ε || -ε ⊥ The dielectric anisotropy Δε is preferably measured at 20° C. and 1 kHz. The liquid-crystalline medium preferably has a dielectric anisotropy Δε in the range from −0.5 to −20, preferably from −1.0 to −10.

[0411] Particularly preferably, the liquid crystal medium exhibits a dielectric anisotropy Δε in the range of -5.0 to -1.0. It has surprisingly been found that even at relatively small values ​​of the dielectric anisotropy, an efficient modulation medium can be obtained, which in addition to the desired efficient dynamic scattering can also provide other benefits, for example in terms of operational reliability and stability.

[0412] In the above and below, Δn represents the optical anisotropy, where Δn=n e -n o , and wherein the optical anisotropy Δn is preferably measured at 20° C. and a wavelength of 589.3 nm. The liquid-crystalline medium preferably has an optical anisotropy Δn of at least 0.15, more preferably in the range of 0.15 to 0.30, even more preferably 0.18 to 0.27 and in particular 0.20 to 0.25.

[0413] Providing a relatively large optical anisotropy of the liquid crystal medium may advantageously facilitate obtaining an efficient and effective modulation material.

[0414] For the present invention, unless otherwise expressly indicated, the term "threshold voltage" refers to the capacitance threshold (V 0 ), also known as the Freedericks threshold.

[0415] Furthermore, the liquid-crystalline media according to the invention have high voltage holding ratio values ​​in liquid-crystal cells.

[0416] In the switching assembly according to the invention, the switching layer comprising the liquid crystal medium preferably has a thickness in the range of 1 μm to 100 μm, more preferably 2 μm to 50 μm, even more preferably 4 μm to 40 μm and in particular 10 μm to 25 μm.

[0417] To maintain the appropriate thickness of the switching layer, spacers may be included within the cell gap of the switching layer. Typically, the spacer has a spherical shape with a diameter within the range of the cell gap. For example, a non-conductive spacer of a spherical shape having a predetermined diameter made of a polymer or glass may be used. In some embodiments, it may be applicable to provide a sticky spacer (i.e., a spacer having some inherent adhesion characteristics to better adhere to the surface). It may also be applicable to use a black spacer, for example, to avoid or minimize unwanted light leakage. The use of a black and sticky spacer may be particularly beneficial. Alternatively, the cell thickness may be set or maintained by other suitable components, such as by using a columnar spacer. Columnar spacers may also be formed to obtain compartments, thereby optionally allowing a freely cuttable structure.

[0418] The substrate of the switching element may comprise, preferably consist of, glass or a polymer, in particular glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide (PI), COP (cyclic olefin polymer) or TAC (triacetyl cellulose). In a particularly preferred embodiment, a glass substrate is used.

[0419] The electrical switching according to the invention is achieved by providing a substrate, such as a glass substrate or a plastic substrate, with electrodes. Preferably, a conductive layer is arranged on the substrate, wherein the conductive layer comprises or is formed by a transparent conductive material, such as a transparent conductive oxide, preferably indium tin oxide (ITO), SnO2:F or doped zinc oxide, in particular ITO; or a conductive polymer, such as poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) or poly(4,4-dioctylcyclopentadithiophene), or a thin transparent metal and / or metal oxide layer, such as silver. Preferably, the transparent conductive material is a transparent conductive oxide, more preferably indium tin oxide. The transparent electrode is preferably applied to the substrate by a coating method. For example, ITO can be sputtered to typically obtain a layer thickness in the range of 5 nm to 250 nm or a sheet resistance in the range of 5Ω / □ to 500Ω / □.

[0420] In a preferred embodiment, the switching component can switch from a first transparent state having low haze to a second transparent state having low haze and a transmittance lower than the first transparent state at a first voltage, and in addition, the switching component can switch to an opaque state having high haze at a second voltage higher than the first voltage.

[0421] Described below are figures which further illustrate the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0422] Picture display:

[0423] Figure 1 The total transmittance of a test cell containing a comparative liquid crystal medium is shown as a function of the applied voltage.

[0424] Figure 2 The haze of a test cell comprising a comparative liquid crystal medium is shown as a function of applied voltage.

[0425] Figure 3 The variation of the total transmission of a test cell comprising a liquid-crystalline medium according to the invention as a function of the applied voltage is shown.

[0426] Figure 4 The variation of the haze of a test cell comprising a liquid-crystalline medium according to the invention as a function of the applied voltage is shown.

[0427] In the text and in the working examples, the structures of the liquid crystal compounds are indicated with the aid of acronyms. Unless otherwise indicated, the conversion into chemical formulae is carried out according to Tables 1 to 3. All radicals C n H 2n+1 , C m H 2m+1 and C m’ H 2m’+1 or C n H 2n and C m H 2m Each is a straight-chain alkyl or alkylene radical having in each case n, m, m' or z C atoms. n, m, m' and z each independently represent 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, preferably 1, 2, 3, 4, 5 or 6. In Table 1, the ring elements of the individual compounds are coded, in Table 2, the bridging members are listed, and in Table 3, the meaning of the symbols indicating the left or right side chains of the compounds.

[0428] Table 1: Ring elements

[0429]

[0430]

[0431]

[0432] Table 2: Bridge members

[0433]

[0434] Table 3: Sidechains

[0435]

[0436] Among and / or in addition to the compounds of the formula IIA and / or IIB and / or IIC and one or more compounds of the formula I, the mixtures according to the invention preferably comprise one or more compounds from Table A indicated below.

[0437] Table A

[0438] The following abbreviations are used:

[0439] n, m, m', z each independently represent 1, 2, 3, 4, 5, 6, 7, 8 or 9, preferably 1, 2, 3, 4, 5 or 6;

[0440] (O)C m H 2m+1 Meaning OC m H 2m+1 or C m H 2m+1

[0441]

[0442]

[0443]

[0444]

[0445]

[0446]

[0447]

[0448]

[0449]

[0450]

[0451]

[0452]

[0453]

[0454]

[0455]

[0456]

[0457]

[0458]

[0459]

[0460]

[0461]

[0462]

[0463]

[0464] The liquid-crystal mixtures which can be used according to the invention are prepared in a manner conventional per se. In general, the desired amount of the component used in smaller amounts is advantageously dissolved at elevated temperature in the component constituting the main constituent. It is also possible to mix solutions of the components in an organic solvent (for example in acetone, chloroform or methanol) and to remove the solvent again after thorough mixing, for example by distillation.

[0465] The mixture may also contain other additives known to those skilled in the art and described in the literature, such as, for example, UV absorbers, antioxidants, nanoparticles and free radical scavengers. For example, stabilizers or chiral dopants may be added. Suitable stabilizers for the mixture according to the invention are in particular those listed in Table C.

[0466] Table B

[0467] Table B shows possible chiral dopants which can be optionally added to the mixture according to the invention. The mixture preferably comprises 0 to 10% by weight, in particular 0.01 to 5% by weight, and particularly preferably 0.01 to 3% by weight of chiral dopants. If the mixture comprises only one chiral dopant, the chiral dopant is used in an amount of 0.01 to 4% by weight, preferably 0.1 to 1.0% by weight.

[0468]

[0469]

[0470] Table C

[0471] Stabilizers which can preferably be added to the mixture according to the invention in an amount of 0% to 10% by weight, preferably 0.01% to 3% by weight, are shown below.

[0472]

[0473]

[0474]

[0475]

[0476]

[0477] The media according to the invention particularly preferably comprise the following: 770 (bis(2,2,6,6-tetramethyl-4-piperidinyl sebacate)).

[0478] Examples of preferred further dichroic dyes which can be used in the liquid-crystalline media according to the invention are listed in Table D.

[0479] Table D

[0480]

[0481]

[0482]

[0483]

[0484]

[0485]

[0486] The following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the present invention in any way. In view of this disclosure, the embodiments and their modifications or other equivalents will become apparent to those skilled in the art.

[0487] However, the physical properties and compositions presented below illustrate which properties can be achieved and within what range they can be modified. Therefore, in particular the combination of various properties that can be preferably achieved is fully defined.

[0488] Working Example

[0489] Unless otherwise indicated, parts or percentages refer to parts or percentages by weight, based on the mixture as a whole.

[0490] The symbols and abbreviations have the following meanings:

[0491] V o Threshold voltage at 20℃, capacitance [V]

[0492] Δn Optical anisotropy measured at 20°C and 589nm

[0493] Dielectric anisotropy of Δε at 20℃ and 1kHz

[0494] cl.p. clearing point [℃]

[0495] K 1 Elastic constant, "bending" deformation at 20°C [pN]

[0496] K 3 Elastic constant, "bending" deformation at 20°C [pN]

[0497] γ 1 Rotational viscosity [mPa·s] measured at 20°C, determined by the rotation method in a magnetic field

[0498] LTS Low temperature stability (nematic phase), which is determined in a test cell.

[0499] Unless otherwise explicitly indicated, the term "threshold voltage" in the present invention refers to the capacitance threshold (V 0 In an embodiment, as is common, for example, a 10% relative contrast ratio (V 10 )'s optical threshold.

[0500] Reference mixture example

[0501] Nematic host mixtures H1 to H5 were prepared as follows:

[0502] Reference mixture H1

[0503]

[0504]

[0505] Reference mixture H2

[0506]

[0507] Reference mixture H3

[0508]

[0509]

[0510] Reference mixture H4

[0511]

[0512] Reference mixture H5

[0513]

[0514]

[0515] Comparative Mixture Example 1

[0516] Dye-doped mixture D1 was prepared by mixing 98.60% of reference mixture H1 with:

[0517] 0.26% Dye-1

[0518]

[0519] 0.40% Dye-2

[0520]

[0521] and 0.74% dye-3

[0522]

[0523] The absorption characteristics of the dyes work together to produce the color black.

[0524] Comparative mixture CM1 was prepared by mixing 99.90% of mixture D1 with 0.10% of 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate.

[0525] Mixture Example 1

[0526] Mixture M1 was prepared by mixing 99.99% of mixture D1 as described above in comparative mixture example 1 with 0.01% of tetrabutylammonium tetrafluoroborate.

[0527] Mixture Examples 2 to 5

[0528] Dye-doped mixtures D2, D3, D4 and D5 were prepared as described above for mixture D1 in Comparative Mixture Example 1, wherein reference mixtures H2, H3, H4 and H5, respectively, were used in place of reference mixture H1.

[0529] Mixtures M2, M3, M4 and M5 were prepared by mixing 99.99% of mixtures D2, D3, D4 and D5 respectively with 0.01% of tetrabutylammonium tetrafluoroborate.

[0530] Use Example

[0531] Comparative Use Example 1

[0532] A test cell was prepared having a cell size of 35 mm×35 mm using an ITO-coated glass substrate and a cell gap of 10 μm using a spacer, wherein an alignment layer for homeotropic alignment (JALS 2096-R1 from JSR (Japan Synthetic Rubber), Japan) was applied. The test cell was filled with comparative mixture CM1.

[0533] The transmittance and haze were measured using a commercially available turbidity meter (Model NDH7000SP II, Nippon Denshoku Industries Co., Ltd., Tokyo, Japan) depending on the applied voltage (square wave, 60 Hz, rms).

[0534] The results are shown in Figure 1 and Figure 2 middle.

[0535] It was observed that an operating voltage of 60 V was required to achieve a haze of 95%.

[0536] Use Example 1

[0537] The test cell was prepared as described above in Comparative Use Example 1. The test cell was filled with mixture M1.

[0538] The transmittance and haze were measured using a commercially available turbidity meter (Model NDH7000SP II, Nippon Denshoku Industries Co., Ltd., Tokyo, Japan) depending on the applied voltage (square wave, 60 Hz, rms).

[0539] The results are shown in Figure 3 and Figure 4 middle.

[0540] Despite the use of relatively small amounts of ionic dopants, in particular 0.01% tetrabutylammonium tetrafluoroborate, haze of 95% has been observed at an operating voltage of 40 V. In addition, the onset of transmittance reduction occurs at advantageously lower voltages.

[0541] The devices exhibit benefits in terms of electro-optical performance, particularly in terms of efficiency and energy saving, reliability, stability and reproducibility.

Claims

1. A liquid crystal medium having a negative dielectric anisotropy and a clearing point of 90° C. or higher, the liquid crystal medium comprising one or more ionic dopants of formula I A + B - I in A + is a quaternary ammonium, and B - is tetrafluoroborate, wherein the medium further comprises three or more dichroic dyes, wherein the medium comprises one or more compounds selected from the group of compounds of formula IIA, IIB and IIC, R 2A , R 2B and R 2C each independently of one another represents H; alkyl or alkenyl having up to 15 C atoms, which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, wherein in addition one or more CH2 groups in these groups may be connected in such a way that the O atoms are not directly connected to one another via , , -O-, -S-, -C≡C-, -CF2O-, -OCF2-, -OC-O- or -O-CO-; or a cycloalkyl ring having 3 to 6 C atoms, L 1-4 each independently represents F, Cl, CF3 or CHF2, Z 2 and Z 2’ each independently represents a single bond, -CH2CH2-, -CH=CH-, -C≡C-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -C(O)O-, -OC(O)-, -C2F4-, -CF=CF- or -CH=CHCH2O-, p means 1 or 2, q represents 0 or 1, and v represents 1 to 6. 2 . The liquid-crystalline medium according to claim 1 , wherein the liquid-crystalline medium exhibits a dielectric anisotropy Δε in the range from −5.0 to −1.0 and an optical anisotropy Δn of at least 0.

15. 3 . The liquid-crystalline medium according to claim 1 , wherein the total concentration of the one or more ionic dopants of the formula I in the medium is 0.10% by weight or less. 4 . The liquid-crystalline medium according to claim 3 , wherein the total concentration of the one or more ionic dopants of the formula I in the medium is 0.05% by weight or less.

5. A liquid crystal medium according to claim 1, wherein the cation A + It is a tetraalkylammonium.

6. A liquid-crystalline medium according to claim 5, wherein the cation A + It is tetrabutylammonium.

7. A liquid-crystalline medium according to claim 1, wherein the medium comprises one or more compounds of the formula N and T-1, R N and R each independently of one another denote an alkyl or alkenyl group having up to 12 C atoms, wherein one or more non-adjacent CH2 groups may be replaced by -O- and / or a cycloalkyl ring having 3 to 5 C atoms, and wherein one or more H atoms may be replaced by F, A N In each occurrence, the same or different (a) trans-1,4-cyclohexylene, in which one or more non-adjacent CH2 groups may be replaced by -O- and / or -S-, (b) 1,4-phenylene, one or both CH groups of which may be replaced by N, (c) trans-1,4-cyclohexenylene, or (d) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl, wherein the groups (a) to (d) may be substituted by one or two fluorine atoms, Z N represents, independently of one another, at each occurrence -CO-O-, -O-CO-, -CH2O-, -OCH2-, -CH2CH2-, -CH=CH-, -C≡C-, -(CH2)4-, -OCF2-, -CF2O-, -CF2CF2- or a single bond, L N1 , L N2 , L N3 and L N4 each independently represents H, Cl or F, and n is 1, 2, or 3.

8. A liquid-crystalline medium according to claim 1, wherein the medium comprises three dichroic dyes selected from the group of compounds of the following formulae 9. Liquid-crystalline medium according to claim 1, wherein the medium comprises one or more further additives.

10. Liquid-crystalline medium according to claim 9, wherein the medium comprises stabilizers and / or chiral dopants.

11. A liquid-crystalline medium according to claim 1, wherein the medium is free of tolan.

12. A switching component which can be operated in an optically clear state and a scattering state and can be electrically switched between the optically clear state and the scattering state, the switching component comprising a switching layer containing a liquid crystal medium according to any one of claims 1 to 11, wherein the switching layer is inserted between two relatively transparent substrates, each of which is provided with an electrode.

13. A switching component according to claim 12, wherein the switching component can be switched from a first transparent state having low haze to a second transparent state having low haze and a transmittance lower than the first transparent state at a first voltage, and wherein the switching component can be switched to an opaque state having high haze at a second voltage higher than the first voltage.

14. Use of a liquid-crystalline medium according to any of claims 1 to 11 or a switching component according to claim 12 or 13 in an electro-optical device.

15. Use of a liquid-crystalline medium according to any one of claims 1 to 11 or a switching component according to claim 12 or 13 in a light valve, a light shutter, a window, a car mirror, a sunroof, an augmented or virtual reality device, a mobile device or a portable device.

16. Use of one or more ionic dopants of formula I contained in a liquid crystal medium as set out in any one of claims 1 and 5 to 6, in a liquid crystal medium according to any one of claims 1 to 11.

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