Liquid crystal-based light valve

Abstract

The present invention relates to an energy-efficient light valve comprising an LC material which is switchable between an optically transparent state and an opaque state and to the use of the light valve in spatial light modulators for handling occlusion in near-eye displays.

Description

[0001] Foreignfiling text P24-159

[0002] - 1 -

[0003] Liquid crystal-based light valve

[0004] The present invention relates to light valves comprising a liquid-crystalline medium which are operable in and switchable between an optically transparent state and an opaque state and to the use of the light valves in spatial light modulators for handling

[0005] 5 occlusion in near-eye displays.

[0006] Devices for controlling or modulating the transmission of light are commonly used in display applications and in window applications, and they may also be used in various mobile and portable devices such as eyewear, spectacles, goggles and visors and may be applied in the context of augmented and virtual reality environments. Optical intensity modulators such as light valves or light shutters can be based on liquid crystals (LCs). In principle, such light valves or light shutters may rely on the absorption of light and / or the scattering of light.

[0007] 15 In some devices the transmission of light can be reversibly changed, typically through electrical switching, wherein the intensity of incident light can be attenuated, dimmed or tinted, while however exhibiting little or no scattering or haze in the different states of operation. Such devices may thus be operated in and switched between a bright state and a dark state, i.e. a state of relatively higher light transmission and a state of

[0008] 20 relatively lower light transmission, wherein both states are substantially non-hazy.

[0009] Several modes or configurations may be employed to provide such reversible transmission change. For twisted nematic (TN), super-twisted nematic (STN) and vertical alignment (VA) liquid crystal cells polarizers are used to control the light transmission. It is also possible to use guest-host liquid crystal cells which are based on a liquid crystal host which is doped with dichroic dye molecules. These guest-host systems can be used without any polarizers to alter the light transmission. However, in some embodiments and applications guest-host liquid crystal cells are used in combination with at least one polarizer.

[0010] 30

[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 texture liquid crystal (PSCT) and dynamic scattering liquid crystal devices. These scattering-type devices can be switched between a Foreignfiling text P24-159

[0012] - 2 - transparent state, i.e. an optically clear or non-hazy state, and a light scattering state, i.e. a translucent or hazy state.

[0013] When such a scattering-type device is switched from a non-scattering state, i.e. an optically clear state, to a scattering state, the transmission of light is changed such that

[0014] 5 a translucent appearance is produced, which may also be perceived as cloudy, turbid, diffuse or hazy. A device based on the scattering mode can in particular be used to temporarily provide privacy or the cloaking of features or information when desired by switching, typically electrically switching, the device from the optically clear state into the scattering state.

[0015] It is also possible to combine in a device light modulation by absorption and by scattering. This way an opaque state may be obtained which in addition to giving haze also exhibits a reduced overall light intensity. In a particular implementation dichroic dyes may be used for the attenuation of light, and in some instances these dyes can

[0016] 15 furthermore provide colouring.

[0017] In WO 00 / 60407 A1 electro-optical glazing structures are described which have opaque and transparent modes of operation.

[0018] 20 US 2015 / 0323825 A1 describes non-polarizer based variable light attenuating devices which use a liquid crystal host and a guest dichroic dye.

[0019] B.-H. Yu et al. in “Light shutter using dye-doped cholesteric liquid crystals with polymer network structure”, Journal of Information Display, 18 (2017) on pages 13-17 propose a light shutter using dye-doped cholesteric liquid crystals with a polymer network structure for use in see-through displays.

[0020] Optical devices and systems may be implemented in near-eye devices or near-eye displays for augmented reality, virtual reality and / or mixed reality applications. In the

[0021] 30 case of augmented reality the devices are used to integrate additional virtual content into a real world environment, wherein virtual objects can be placed in the real environment to provide additional visual information or to change the nature of real objects in order to enhance or augment a user’s view of the real world.

[0022] US 11,428,977 B1 describes the use of an occluder or dimmer for a near-eye display to selectively attenuate or block ambient light of the environment at an area where a Foreignfiling text P24-159

[0023] - 3 - virtual object is to be displayed and to provide occlusion effects rendering added virtual objects opaque. This provision may in principle improve the contrast of the virtual object and / or make the virtual object appear to obscure the real world image, i.e. occlude the user’s view of the real environment. Such occlusion effect or occlusion handling may thus ensure that a virtual object closer to the viewer obscures the view of

[0024] 5 real objects further away along the line of sight.

[0025] There is a need in the art for further light modulators and switchable devices, in particular light valves such as light shutters, with improved optical and electro-optical performance.

[0026] An object of the present invention is therefore to provide light valves which are operable in and electrically switchable between an optically transparent state and an opaque state and which have an improved optical and electro-optical performance. In particular, it is an object of the present invention to provide light valves which have a

[0027] 15 favourable performance and which are particularly suitable for use in displays, windows, mobile and portable devices and especially in near-eye display devices and in augmented reality applications. Further objects of the present invention are immediately evident to the person skilled in the art from the following detailed description.

[0028] 20

[0029] The objects are 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.

[0030] The present invention in particular provides the following items including main aspects, preferred embodiments and particular features, which respectively alone and in combination contribute to solving the above objects and eventually provide additional advantages.

[0031] 30 A first aspect of the present invention provides a light valve which is operable in and electrically switchable between an optically transparent state and an opaque state and which comprises a switching layer containing a material, wherein the materials is

[0032] - a material which comprises a liquid-crystalline medium comprising one or more mesogenic compounds and a polymer component, wherein the polymer component is arranged as a polymer network and is obtained by or respectively obtainable from polymerisation of one or more polymerisable mesogenic Foreignfiling text P24-159

[0033] - 4 - compounds and wherein the polymer component is contained in the material in an amount, based on the overall contents of the material, of 20% by weight or less, and / or

[0034] - a material which comprises a liquid-crystalline medium comprising one or more

[0035] 5 mesogenic compounds and one or more dichroic dyes.

[0036] A light valve herein in particular means an element for the modulation of light which is configured as a cell formed of two walls, in particular two transparent substrates, which are spaced apart and which are provided with electrodes, and wherein the cell contains a light modulation material. The switching layer can thus be arranged or sandwiched between two substrates such as to give a switching element which is electrically switchable and operable in an optically transparent state and an opaque state.

[0037] It has surprisingly been found that an improved light valve can be obtained by providing

[0038] 15 a switching layer which contains the material as set forth above and below. The light valves are in particular useful as light variable devices to adjust light and in particular light intensity based on the scattering and / or dimming of light. The light valve according to the invention is useful in devices for regulating the passage of electromagnetic radiation, preferably light, and in particular sunlight but also light from artificial light

[0039] 20 sources.

[0040] The present invention advantageously provides light valves which can control light transparency or opacity with a desirably high contrast either by dimming through absorption or by providing haze through scattering, or a combination of both. In addition, the light valves can exhibit lightweight construction, fast switching speeds as well as low operating voltages and low power consumption. Furthermore, the devices can show stability at low temperatures and at high temperatures and with respect to sunlight illumination. The light valves may thus be particularly suitable for use as or respectively in shutters, displays, windows, mobile devices, portable devices, hand¬

[0041] 30 held devices or head-mounted devices.

[0042] The light valve can in particular give a reduced temperature dependence and reliable switching also at low temperatures, for example at 0°C and even below. The combined properties are especially useful in mobile or portable systems and applications. The light valve can temporarily, i.e. for given periods of time but not for others, contribute to achieving enhanced contrast or readability of information as desired in mobile, portable Foreignfiling text P24-159

[0043] - 5 - or wearable devices and applications, e.g. in transparent or normally see-through displays and under different lighting conditions, in particular different ambient light conditions.

[0044] The light valves can effectively control light transparency and / or opacity in real time. It

[0045] 5 was presently recognized that they can therefore particularly preferably and advantageously be used for efficient and high-performance local control of light intensity in augmented reality glasses. In particular, it was recognized that the valves can be used to handle occlusion and to seamlessly blend or merge real and virtual objects or elements in augmented reality applications. In this respect, the light valves can be useful to dynamically obscure real scene objects located behind added virtual objects by controlling the illumination of the real world objects such that virtual objects which are transparent can be integrated into real-world scenes.

[0046] The light valve can thus favourably be incorporated in near-eye display devices which

[0047] 15 comprise an optical see-through display. In this configuration the light valve, preferably arranged as a spatial light modulator, allows the device to adapt locally to the lighting conditions of the environments and in particular to provide optimal brightness and contrast in different lighting settings. In addition, the light valve can be useful to effectively blend virtual elements with the real world, e.g. by hiding a real-world scene

[0048] 20 behind a virtual object or by displaying shadows to add depth and enhance the perception of virtual objects within augmented reality environments. Such occlusion handling in a near-eye display, which in particular is configured to provide augmented reality contents to a wearer, can thus enable more realistic and seamless displays of the augmented reality contents and contribute to an immersive and more realistic experience of the wearer.

[0049] Therefore, in another aspect a near-eye display device is provided which comprises the light valve according to the invention.

[0050] 30 Such a wearable display can in particular be useful to observe the environment while additionally viewing generated content. In particular, the device can be favourably configured as an optical see-through near-eye display device, wherein the real world or environment can be seen directly through the display. The device contains the light valve according to the invention, which may particularly be embedded as a spatial light modulator in the optical see-through display, which can provide tunable dimming and / or scattering of the real-world illumination. Foreignfiling text P24-159

[0051] - 6 -

[0052] In this respect the display device can favourably include an occlusion capability, i.e. it may provide augmented images with occlusion handling. In particular, the included light valve, particularly provided as a spatial light modulator, can be used to attenuate or fully block ambient light rays coming from the real world at the position or location of

[0053] 5 the displayed virtual objects, where the light rays would otherwise impinge on the user’s eyes, and respectively to obtain fully opaque virtual objects to occlude the real world. This way undesired transparency effects for foreground virtual objects which should occlude the real objects are avoided such that visual interference is minimized.

[0054] In addition, the light modulator in the device can provide further benefits such as a favourably low switching voltage and low energy consumption, fast switching between the states as well as good reliability, durability and stability, e.g. with respect to electrical breakdown and light stability.

[0055] 15 Without limiting the present invention thereby, in the following the invention is illustrated by the detailed description of the aspects, embodiments and particular features, and particular embodiments are described in more detail.

[0056] The term light valve herein in particular refers to a device for controlling or varying the

[0057] 20 intensity of light, in particular such that light from a source can be regulated by the device to allow a specific amount of light to reach a target and to vary the amount of light as desired. The intensity of light may preferably be varied by blocking or attenuating light and / or diffusing or scattering of light, more preferably by dimming and scattering.

[0058] In a preferred embodiment the material as used in the switching layer comprises a liquid-crystalline medium comprising one or more mesogenic compounds and one or more dichroic dyes in combination with the polymer component as set forth herein. This provision can favourably contribute to obtaining an opaque state which exhibits both a

[0059] 30 favourably high haze and a favourably low overall light transmissivity.

[0060] Light may in principle include electromagnetic radiation in the IIV-A, VIS and NIR region, wherein the IIV-A region is taken to mean the wavelength range from 320 to 380 nm, the VIS region is taken to mean the wavelength range from 380 nm to 780 nm and the NIR region is taken to mean the wavelength range from 780 nm to 2000 nm. Preferably the term light is taken to mean visible electromagnetic radiation having Foreignfiling text P24-159

[0061] - 7 - wavelengths from 380 nm to 780 nm. Transmission and scattering of light thus preferably refers to the transmission and scattering of electromagnetic radiation in the spectral range from 380 nm to 780 nm.

[0062] The control and variation of light in the light valve may also or in addition be based on

[0063] 5 the variation or influencing of the phase and / or the polarization of the light.

[0064] The light valve may for example be configured as a shutter having a bright state of relatively higher light transmission and a dark state with minimal or low light transmission, or as intensity modulators to modulate the intensity of light beams having two or more switching states including the capability of setting gray scale values between extremal values.

[0065] In a preferred embodiment the light valve is arranged as a spatial light modulator. A spatial light modulator herein in particular refers to a device that can control the

[0066] 15 intensity, optionally including the phase and / or polarization, of light in a spatially varying manner.

[0067] It is particularly preferred that the light valve is arranged as a spatial light modulator for handling occlusion in a near-eye display.

[0068] 20

[0069] The near-eye display may comprise an image generator, an optical combiner and imaging optics and may be arranged as or respectively in a head-mounted device or particularly augmented reality eyewear, eyeglasses, spectacles, goggles or visors.

[0070] The light valve may thus for example be combined or integrated with projection elements and grating or waveguide elements.

[0071] The light valve according to the invention is electrically switchable between the optical states. The switching operation in electrical switching may take place by a

[0072] 30 (re)alignment of the molecules of the liquid-crystalline medium by the application of voltage. In particular, the liquid crystal-based device may employ a change in the orientation of liquid crystal molecules between two conductive electrodes by applying an electric field which results in a change of their transmittance. The light valve preferably comprises two or more electrodes which preferably consist of ITO (indium tin oxide) or a thin, preferably transparent metal and / or metal-oxide layer, for example Foreignfiling text P24-159

[0073] - 8 - silver or FTO (fluorine-doped tin oxide) or an alternative material known in the art for this use.

[0074] The device can thus be conveniently switched between the optical states by applying an electrical voltage.

[0075] 5

[0076] In case the device is provided as a spatial light modulator preferably segmentation of one or more electrodes is provided and smaller segments or pixels of the modulator may be addressed individually. The materials as used in the device favourably contribute to the possibility to use active matrix addressing in the switchable optical cell. Segmenting the light valve into a multitude of pixels may in particular enable the use in the context of augmented realities and the display and blending of real and virtual objects.

[0077] The light valve and in particular the spatial light modulator may favourably be included

[0078] 15 in a display device, in particular in an optical see-through display. The display device is preferably configured as a near-eye display.

[0079] It is particularly preferred that the near-eye display device is configured to provide augmented reality contents to a wearer. In this respect, the light valve and especially

[0080] 20 the spatial light modulator comprised in the display device can be used to provide occlusion effects with respect to added virtual objects.

[0081] In a particular embodiment the device comprises at least one curved substrate and / or at least one pixelated electrode. The light valve, the spatial light modulator and the display device may be provided with a curved arrangement, preferably having curvature in one or two dimensions.

[0082] The light valve is useful for regulating or modulating the passage of light, including light from artificial light sources like lamps, light-emitting diodes, in particular organic light¬

[0083] 30 emitting diodes, and light fixtures, and also sunlight. In particular, in the opaque state the light valve can produce a visual barrier or a blocking or attenuation of light.

[0084] In addition to near-eye display devices, the light valve can thus also favourably be used in other electro-optical displays, including curved displays, and in dimmable or switchable window. Foreignfiling text P24-159

[0085] - 9 -

[0086] The optically transparent state herein may refer to a low-haze state and / or a high- transmittance state, preferably to a low-haze high-transmittance state. In an embodiment the light valve in the optically transparent state has a haze, preferably determined according to ASTM D 1003, of less than 15%, preferably of less than 10%, more preferably of less than 5%, and in particular less than 2%. In another embodiment

[0087] 5 the light valve in the optically transparent state has a degree of light transmission, preferably determined in accordance with DIN EN410, of more than 40%, preferably of more than 50%, more preferably of more than 60%, and in particular of more than 70%. In a preferred embodiment the light valve in the optically transparent state has a haze, preferably determined according to ASTM D 1003, of less than 15%, preferably of less than 10%, more preferably of less than 5%, and in particular less than 2%, and a degree of light transmission, preferably determined in accordance with DIN EN410, of more than 40%, preferably of more than 50%, more preferably of more than 60%, and in particular of more than 70%.

[0088] 15 In a particular embodiment the light valve in the optically transparent state has a haze, preferably determined according to ASTM D 1003, of less than 10 %.

[0089] The opaque state herein may refer to a high-haze state and / or a low-transmittance state, preferably to a high-haze state low-transmittance state. In an embodiment the

[0090] 20 light valve in the opaque state has a haze, preferably determined according to ASTM D 1003, of more than 60%, preferably of more than 70%, more preferably of more than 80%, and in particular of more than 90%. In another embodiment the light valve in the opaque state has a degree of light transmission, preferably determined in accordance with DIN EN410, of less than 35%, preferably of less than 25%, more preferably of less than 10%, even more preferably of less than 5%, and in particular of less than 2%. In a preferred embodiment the light valve in the opaque state has a haze, preferably determined according to ASTM D 1003, of more than 60%, preferably of more than 70%, more preferably of more than 80%, and in particular of more than 90%, and degree of light transmission, preferably determined in accordance with DIN EN410, of

[0091] 30 less than 35%, preferably of less than 25%, more preferably of less than 10%, even more preferably of less than 5%, and in particular of less than 2%.

[0092] The light valve is provided as a device for light management, in particular by providing switchability between two different optical states, namely an optically transparent state and an opaque state, which can perform absorption of light or scattering of light, preferably both absorption and scattering of light when desired. In case where both Foreignfiling text P24-159

[0093] - 10 - absorption and scattering of light are provided, the device can transition between a low- haze high-transmittance state and a high-haze low-transmittance state.

[0094] For the measurement of haze hazemeters made by BYK-Gardner may be used. It is also possible to use spectrophotometers, in particular a spectrophotometer and an

[0095] 5 Ulbricht’s sphere.

[0096] In a preferred embodiment in the absence of an applied voltage the light valve is in the optically transparent state.

[0097] Preferably and favourably the light valve can give a large contrast between the switching states. It is particularly preferred that the device exhibits a high light transmission with minimal haze in the absence of an electric field and a high absorption and / or high haze in the presence of an electric field.

[0098] 15 The device thus can surprisingly give a favourable clear state, i.e. a favourably homogeneous low-haze and optically transparent state.

[0099] In the present invention it was recognized that favourable performance and appearance is desirable both in the optically transparent state and in the opaque state.

[0100] 20 In particular, in the optically transparent state unwanted haze should be avoided or minimized and the transmittance should be relatively high.

[0101] The light valve as provided according to the invention can favourably give such a low- haze transparent state, while furthermore giving adequately efficient and sufficiently uniform dimming and / or diffusing of light to adjust and in particular minimize the light transmission in the opaque state.

[0102] The light valve provided with the material as set forth herein can give an effective and efficient switching performance such that already the provision of only a single

[0103] 30 switching layer in the light valve can result is a suitable contrast or favourable setting of the light transmission. In addition, the thickness of the switching layer may be comparatively low, in particular substantially below 50 pm, which thus reduces the operating voltage and power consumption but also the use of material.

[0104] In a preferred embodiment the light valve thus comprises only one switching layer. Foreignfiling text P24-159

[0105] - 11 -

[0106] In an alternative embodiment the light valve comprises more than one switching layer, preferably two switching layers. The two switching layers may be arranged as a so- called double cell. In case two switching layers are provided, it is preferred that both switching layers have identical compositions. Alternatively, it is also possible that the two switching layers have different compositions and / or configurations, e.g. using one

[0107] 5 layer to provide light dimming by absorption and the other to provide light diffusing by scattering. In this case it is however also preferred that both switching layers comprise the materials as used according to the invention.

[0108] The term polymer network herein in particular refers to a polymer-based system having a two-dimensional or three-dimensional structure, preferably a three-dimensional structure, wherein the network structure or architecture is comprised of interconnected or conjoint macromolecules. Polymer networks thus give polymeric materials in which polymer chains are interconnected.

[0109] 15 In a particular embodiment the switching layer is arranged as a polymer-stabilized LC layer comprising LC molecules which are dispersed in or respectively aligned by a polymer network.

[0110] The liquid-crystalline media as used in the switching layer can have advantageous

[0111] 20 chemical, physical and electro-optical properties and can thus give particularly favourable modulation materials in the light valves. The media used as the modulation material can provide further benefits such as a broad liquid-crystalline phase, a suitably high optical anisotropy, a favourably high voltage holding ratio (VHR), good low- temperature stability and good light stability.

[0112] The term “liquid crystal” (LC) herein preferably relates to materials or media having liquid-crystalline mesophases in some temperature ranges (thermotropic LCs). They contain mesogenic compounds.

[0113] 30 The terms "mesogenic compound" and "liquid crystal compound" mean a compound comprising one or more calamitic (rod- or board / lath-shaped) or discotic (disc-shaped) mesogenic groups, i.e. groups with the ability to induce liquid-crystalline phase or mesophase behaviour.

[0114] The LC compounds or materials and the mesogenic compounds or materials comprising mesogenic groups do not necessarily have to exhibit a liquid-crystalline Foreignfiling text P24-159

[0115] - 12 - phase themselves. It is also possible that they show liquid-crystalline phase behaviour only in mixtures with other compounds. This includes low-molecular-weight non- reactive liquid-crystalline compounds, reactive or polymerisable liquid-crystalline compounds, and liquid-crystalline polymers.

[0116] 5 A calamitic mesogenic compound is usually comprising a mesogenic core consisting of one or more aromatic or non-aromatic cyclic groups connected to each other directly or via linkage groups, optionally comprising terminal groups attached to the ends of the mesogenic core, and optionally comprising one or more lateral groups attached to the long side of the mesogenic core, wherein these terminal and lateral groups are usually selected e.g. from carbyl or hydrocarbyl groups, polar groups like halogen, nitro, hydroxy, etc., or polymerisable groups.

[0117] For the sake of simplicity, the term “liquid crystal” or “liquid-crystalline” material or medium is used for both liquid crystal materials or media and mesogenic materials or

[0118] 15 media, and vice versa, and the term “mesogen” is used for the mesogenic groups of the material.

[0119] The term “non-mesogenic compound or material” means a compound or material that does not contain a mesogenic group as defined above.

[0120] 20

[0121] As used herein, the term "polymer" will be understood to mean a molecule that encompasses a backbone of one or more distinct types of repeating units (the smallest constitutional unit of the molecule) and is inclusive of the commonly known terms “oligomer”, “copolymer”, “homopolymer” and the like. Further, it will be understood that the term polymer is inclusive of, in addition to the polymer itself, residues from initiators, catalysts, and other elements attendant to the synthesis of such a polymer, where such residues are understood as not being covalently incorporated thereto. Further, such residues and other elements, while normally removed during postpolymerisation purification processes, are typically mixed or co-mingled with the

[0122] 30 polymer such that they generally remain with the polymer when it is transferred between vessels or between solvents or dispersion media.

[0123] The term “polymerisation” means the chemical process to form a polymer by bonding together multiple polymerisable groups or polymer precursors (polymerisable compounds) containing such polymerisable groups. Foreignfiling text P24-159

[0124] - 13 -

[0125] Polymerisable compounds with one polymerisable group are also referred to as "monoreactive" compounds, compounds with two polymerisable groups as "direactive" compounds, and compounds with more than two polymerisable groups as "multireactive" compounds. Compounds without a polymerisable group are also referred to as "non-reactive” or “non-polymerisable“ compounds.

[0126] 5

[0127] The terms "film" and "layer" include rigid or flexible, self-supporting or freestanding films or layers with more or less pronounced mechanical stability, as well as coatings or layers on a supporting substrate or between two substrates.

[0128] The term “chiral” in general is used to describe an object that is non-superimposable on its mirror image. By contrast, “achiral” (non-chiral) objects are objects that are identical to their mirror image. The medium as used in the switching layer in an embodiment exhibits chirality. This can be achieved by providing cholesteric liquid crystals, which are also known as chiral nematic liquid crystals. The terms chiral nematic and

[0129] 15 cholesteric are used synonymously herein, unless explicitly stated otherwise.

[0130] Herein

[0131] 20 denote trans-1 ,4-cyclohexylene.

[0132] Herein, unless explicitly stated otherwise, all concentrations are given in weight percent and relate to the respective complete mixture.

[0133] All temperatures are given in degrees centigrade (Celsius, °C) and all differences of temperatures in degrees centigrade. All physical properties and physicochemical or electro-optical parameters are determined and given for a temperature of 20 °C, unless explicitly stated otherwise.

[0134] 30

[0135] Switching preferably refers to the switching between binary states, wherein the optically transparent state preferably is non-scattering and appears substantially transparent or clear to the human eye, while the opaque state may e.g. be scattering or have diffusive transmission which appears translucent or opaque to the human eye and / or may give a black colour or alternatively another colour which does not cover the entire visible spectrum. Foreignfiling text P24-159

[0136] - 14 -

[0137] However, it is also possible for the switching layer according to the invention to have further switching states, in particular intermediate states.

[0138] Therefore, according to the invention preferably and favourably switching between a

[0139] 5 completely opaque state and a state with visibility through the device is obtainable.

[0140] The light valve according to the invention is electrically switchable. Electrical switching can typically be achieved by providing substrates, e.g. glass or plastic substrates, with electrodes. In an embodiment electrically conductive layers are provided on one or both substrates, wherein the conductive layers comprise or are formed of a transparent conductive material, e.g. a transparent conductive oxide, preferably indium tin oxide (ITO) or SnO2:F, in particular ITO, or a conductive polymer, or a thin transparent metal and / or metal oxide layer, for example silver. The electrically conductive layers are preferably provided with electrical connections. The voltage is preferably supplied by a

[0141] 15 battery, a rechargeable battery, a supercapacitor or an external current source, more preferably by an external current source.

[0142] It is preferred that alignment or orientation layers, e.g. made of polyimide (PI), are provided on the substrates. It is particularly preferred that electrically conductive layers

[0143] 20 and alignment layers are provided together on the substrates. In this case the orientation layer or alignment layer is provided on top of the conductive layer such that the alignment layer is contacting the LC medium. The alignment layers, preferably polyimide layers, may be arranged such that they provide, in particular at the interface, homogeneous or planar orientation or alternatively homeotropic orientation of the molecules of the liquid-crystalline medium.

[0144] Therefore, in a preferred embodiment the switching layer is in direct contact with at least one alignment layer.

[0145] 30 In an embodiment rubbed polyimide is used on both substrates having a difference in direction, in particular a difference in direction of 90° or approximately 90°, as used in the so-called twisted nematic (TN) geometry.

[0146] In some embodiments so-called pre-tilt angles can be set and obtained as desired. In the TN configuration, the twist angle is typically 90° or approximately 90°. Alternatively the configuration can be set in the super-twisted nematic (STN) configuration, where Foreignfiling text P24-159

[0147] - 15 - the twist angle exceeds 90° and is typically ranging from above 90° to 270°, preferably 180° or approximately 180°. However, it is also possible that the present STN configuration exhibits a twist angle which exceeds 270°.

[0148] Preferred configurations for the switchable layer(s) are the TN configuration, the STN

[0149] 5 configuration, the vertical alignment-twisted nematic (VA-TN) configuration and the vertical alignment-supertwisted nematic (VA-STN) configuration. In this respect, for TN and VA-TN the twist angle may range from greater 0° to including 90°, and for STN and VA-STN the twist angle exceeds 90°.

[0150] In a particular embodiment alignment layers with pre-tilt angles are used, e.g. having pre-tilt angles ranging from 0° to 20° for the TN geometry or from 80° to 90° for the vertically aligned (VA) geometry.

[0151] In another preferred embodiment the switching layer is in direct contact with at least

[0152] 15 one alignment layer, wherein the alignment layer is obtainable from a self-alignment additive, preferably obtainable from photoalignment. Preferred self-alignment additives for use in the LC media are shown in Table H below.

[0153] The use of self-alignment or respectively photoalignment is particularly preferred in

[0154] 20 cases where curved substrates and / or segmented electrodes are used.

[0155] Alternatively and according to another embodiment, substrates without orientation layers are used.

[0156] It is also possible to provide passivation or barrier layers on the substrates, alternatively but also in addition to orientation layers, e.g. passivation layers comprising silicon oxide or silicon nitride, preferably consisting of silicon oxide or silicon nitride. In case both a passivation layer and an orientation layer are provided on a substrate they are arranged such that the orientation layer is topmost, i.e. is contacting the LC

[0157] 30 medium.

[0158] In an embodiment the light valve is provided as a multilayer arrangement, comprising in this order

[0159] - a first transparent substrate,

[0160] - a first electrode layer,

[0161] - a first alignment layer, Foreignfiling text P24-159

[0162] - 16 -

[0163] - the switchable layer,

[0164] - a second alignment layer,

[0165] - a second electrode layer, and

[0166] - a second transparent substrate.

[0167] 5 Alternatively, it is also possible to provide the first and second electrodes on the same substrate, in particular for IPS and FFS configurations.

[0168] In a preferred embodiment the switching layer in the light valve contains a material which comprises a liquid-crystalline medium comprising one or more mesogenic compounds and a polymer component, wherein the polymer component is arranged as a polymer network and is obtained by or respectively obtainable from polymerisation of one or more polymerisable mesogenic compounds and wherein the polymer component is contained in the material in an amount, based on the overall contents of the material, of 20% by weight or less. Preferably, the polymer component is contained

[0169] 15 in the material in an amount of 15% by weight or less, and in particular of 10% by weight or less. In a preferred embodiment the polymer component is contained in the material in an amount, based on the overall contents of the material, in the range from 0.5% by weight to 20% by weight, preferably from 2.5% by weight to 15% by weight, and in particular from 5% by weight to 12.5% by weight. In a particularly preferred

[0170] 20 embodiment the polymer component is contained in the material in an amount, based on the overall contents of the material, in the range from 2% by weight to 8% by weight, preferably from 3% by weight to 6% by weight.

[0171] The polymer component comprises one or more polymeric structures, in particular network polymer structures, obtained by or respectively obtainable from polymerisation of one or more polymerisable mesogenic compounds. It is preferred that the polymer component is obtained from polymerising exclusively one or more polymerisable mesogenic compounds, i.e. that the polymer component consists of one or more polymeric structures which are only based on or respectively only derived from one or

[0172] 30 more polymerisable mesogenic compounds as the precursors.

[0173] In accordance with the present invention the polymer component is preferably prepared in situ, in particular in the switching layer, by polymerising one, two, three or more polymerisable mesogenic compounds, in particular one or two polymerisable mesogenic compounds. Foreignfiling text P24-159

[0174] - 17 -

[0175] Polymerisable mesogenic compounds according to the invention contain a mesogenic group and one or more polymerisable groups, i.e. functional groups which are suitable for polymerisation. These compounds are also known as reactive mesogens (RMs) or mesogenic monomers. The RMs can be monoreactive and / or di- or multireactive.

[0176] 5 It is preferred that the liquid-crystalline medium as used in the polymerisation comprises at least one di- or multireactive polymerisable mesogenic compound.

[0177] In a preferred embodiment the one or more polymerisable mesogenic compounds comprise one, two or more acrylate and / or methacrylate groups.

[0178] While it is preferred that the polymerisable compound(s) as used according to the invention include(s) only reactive mesogen(s), i.e. all the reactive monomers are mesogens, in an alternative embodiment it is also possible to use one or more RMs in combination with one or more non-mesogenic polymerisable compounds.

[0179] 15

[0180] The polymerisable compounds and the mesogenic compounds may be chosen in view of matching the refractive indices of the obtained polymer component and the LC medium in the modulation material, which in particular can favourably contribute to improving the optically transparent state.

[0181] 20

[0182] Preferably the liquid-crystalline medium as used in the light valve has a clearing point of 70°C or more, more preferably 80°C or more, even more preferably 90°C or more, yet even more preferably 100°C or more, still even more preferably 110°C or more, and in particular 115°C or more. It is preferred that the medium has a clearing point in the range from 70°C to 170°, more preferably from 90°C to 160°C and in particular from 100°C to 150°C.

[0183] All physical properties and physicochemical or electro-optical parameters are determined by generally known methods, in particular according to "Merck Liquid

[0184] 30 Crystals, Physical Properties of Liquid Crystals", Status Nov. 1997, Merck KGaA, Germany.

[0185] The clearing point, in particular the phase transition temperature between the (chiral) nematic phase and the isotropic phase, can be measured and determined by commonly known methods, e.g. using a Mettler oven, a hot-stage under a polarizing Foreignfiling text P24-159

[0186] - 18 - microscope, or differential scanning calorimetry (DSC) analysis. According to the invention the clearing point is preferably determined using a Mettler oven.

[0187] The high clearing point as defined can be beneficial in terms of the performance and the reliability of the devices which use the liquid crystalline medium. In particular, the

[0188] 5 medium can maintain its functional properties over a suitably broad temperature range and also at elevated temperatures. The high clearing point can also contribute to a favourably high degree of order of the liquid-crystalline host molecules, and hence the preferably added dichroic dye guest molecules at typical working temperatures, which can increase the obtainable contrast between the switching states.

[0189] In a particular embodiment the liquid-crystalline medium as used in the switching layer comprises one or more chiral compounds, preferably one or more chiral dopants.

[0190] The one or more chiral compounds may be useful to create a scattering or opaque

[0191] 15 state and they may also contribute to effective dimming in case one or more dichroic dyes are present in the liquid-crystalline medium.

[0192] In a particular embodiment the liquid-crystalline medium as used in the switching layer of the light valve exhibits a pitch of 0.55 pm or more in the opaque state.

[0193] 20

[0194] The chiral nematic medium as presently provided in an embodiment preferably has a relatively long pitch, and in particular a pitch which preferably gives Bragg-type reflection of greater than 780 nm. In this case also the planar texture may give favourable transmission over the visible light spectrum.

[0195] The pitch herein means the pitch p of the cholesteric helix, wherein the pitch p is the distance for the orientational axis (director) of the cholesteric LC to undergo a 2TT rotation. In a preferred embodiment the medium exhibits a pitch of 0.75 pm or more, even more preferably of 1.00 pm or more and in particular of 1.50 pm or more.

[0196] 30

[0197] Preferably the concentration of the one or more chiral dopants is set such that the resulting chiral pitch is in the range of 0.55 pm to 10 pm.

[0198] The pitch may be determined from NIR spectroscopic measurement, in particular at 20°C, of the wavelength of the selective reflection maximum Amax. The pitch p is Foreignfiling text P24-159

[0199] - 19 - determined from the measured value of Amax using the equation Amax = n(Amax) * p, wherein n(Amax) is the refractive index at Amax.

[0200] It is also possible to use the wedge cell method which is known in the art to measure, in particular at 20°C, the helical twisting power HTP and to confirm the determined the

[0201] 5 pitch.

[0202] The light valve according to the invention can be switched to and operated in an opaque state which gives efficient and sufficiently strong scattering and / or dimmining with a homogeneous appearance to the eye. This uniform appearance advantageously includes a colour-neutral appearance, which means that unwanted colour artefacts such as a rainbow-like appearance can be minimized or even avoided.

[0203] In addition, the light valve can advantageously have an optically clear state with little or no discernible residual haze and relatively large light transmittance.

[0204] 15

[0205] The light valve itself preferably does not comprise any light sources. The light valve may suitably be integrated into electro-optical devices such as displays, screens or spectacles, for example by lamination, gluing or mounting.

[0206] 20 Preferably the light valve contains no polarizer.

[0207] In an embodiment the light valve may be realized in a range of different sizes, e.g. from a small size of about 1 mm2up to a size of 1 m2and beyond, and it may have different shapes, e.g. square, rectangular, round, elliptic, triangular or polygonal.

[0208] According to the invention the state of the switching layer and the light valve is controlled using an electric field which is applied by means of electrodes. The electrodes are preferably transparent electrodes which are arranged on the substrates in the form of a coating. The coating is commonly applied to the substrate side or

[0209] 30 surface which is facing the switching layer.

[0210] In an embodiment the electrodes are not patterned and / or structured so that they are contiguous. Thus, the entire switchable area is addressed and switched at the same time by applying an electric field. In alternative embodiments the electrodes may be patterned to form individually addressable areas or pixels which may be switched independently from other areas by applying an electric field. In this case, commonly Foreignfiling text P24-159

[0211] - 20 - used TFT technology may be used to actively and independently address the segmented areas.

[0212] As described herein the liquid-crystalline medium is provided in the switching layers and light valves.

[0213] 5

[0214] In principle, a suitable LC medium, in particular LC host mixture, is any dielectrically negative or positive LC mixture, which e.g. is suitable for use in conventional VA, TN, STN, IPS or FFS displays.

[0215] Suitable LC mixtures are known in the art and are described in the literature. LC media for VA displays having negative dielectric anisotropy are described in for example EP 1 378 557 A1.

[0216] Suitable LC mixtures having positive dielectric anisotropy which are suitable for LCDs

[0217] 15 and especially for IPS displays are known, for example, from JP 07-181 439 (A), EP 0 667 555, EP 0 673 986, DE 195 09 410, DE 195 28 106, DE 195 28 107, WO 96 / 23 851 , WO 96 / 28 521 and WO2012 / 079676.

[0218] Preferred embodiments of the liquid-crystalline media having negative or positive

[0219] 20 dielectric anisotropy according to the invention are indicated below.

[0220] The LC host mixture preferably is a nematic LC mixture. In an embodiment the LC mixture does not have a chiral LC phase. In another embodiment the LC mixture exhibits a chiral LC phase.

[0221] In a particular embodiment the LC medium as used according to the invention has a positive dielectric anisotropy. In this case preference is given to liquid-crystalline mixtures having a dielectric anisotropy As in the range from 2.5 to 50.0, more preferably in the range from 5.0 to 25.0, and particularly preferably from 8.0 to 15.0.

[0222] 30

[0223] As denotes the dielectric anisotropy, wherein As = s - s±. The dielectric anisotropy As is determined at 20°C and 1 kHz.

[0224] In a preferred embodiment an LC medium having a negative dielectric anisotropy is provided. In this case preference is given to liquid-crystalline mixtures having a Foreignfiling text P24-159

[0225] - 21 - dielectric anisotropy As in the range from -2.0 to -8.0, more preferably in the range from -3.0 to -6.0, and particularly preferably from -3.5 to -5.0.

[0226] Favourably the medium according to the invention can have a suitably high optical anisotropy An, which is also known as the birefringence. The medium as described

[0227] 5 herein and as used in the switching layer and the light valve according to the invention preferably exhibits an optical anisotropy An, determined at 20°C and 589 nm, of 0.040 or more, more preferably of 0.075 or more, still more preferably of 0.010 or more, and in particular of 0.15 or more.

[0228] Above and below, An denotes the optical anisotropy, wherein An = ne- n0, and the optical anisotropy An is determined at 20°C and a wavelength of 589.3 nm.

[0229] It is preferred that the medium as used according to the invention comprises one or more mesogenic compounds selected from the compounds of formulae I and II

[0230] 15 wherein

[0231] R1and R2denote, independently of one another, a group selected from F, Cl, CF3, OCF3, and straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms or straight-chain or

[0232] 30 branched alkenyl having 2 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen and wherein one or more CH2 groups may be, in each case independently of one another, replaced by Foreignfiling text P24-159

[0233] - 22 - or -C=C- in such a manner that oxygen atoms are not linked directly to one another,

[0234] 5 A11denotes n denotes 0 or 1, and

[0235] A21, A31and A41denote, independently of one another,

[0236] 20 wherein L is on each occurrence, identically or differently, halogen selected from F, Cl and Br, and

[0237] R3and R4denote, independently of one another, a group Foreignfiling text P24-159

[0238] - 23 - selected from F, CF3, OCF3, CN, and straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms or straight-chain or branched alkenyl having 2 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen and wherein one or more CH2 groups

[0239] 5 may be, in each case independently of one another, replaced by such a manner that oxygen atoms are not linked directly to one another, and

[0240] L1, L2and L3denote, independently of one another, H or F.

[0241] It is particularly preferred that the medium as used according to the invention contains,

[0242] 15 based on the overall contents of the medium, at least 5% by weight, more preferably at least 10% by weight and even more preferably 15% by weight of the one or more mesogenic compounds selected from the compounds of formulae I and II.

[0243] In addition to a suitably high optical anisotropy, the medium according to the invention

[0244] 20 can advantageously exhibit a favourably high voltage holding ratio (VHR) in combination with good light stability and a suitably high clearing point.

[0245] Preferably the group A11as defined in formula I denotes

[0246] In an embodiment n as defined in formula I denotes 0.

[0247] 30

[0248] In a preferred embodiment the one or more compounds of formula I are selected from compounds of formulae la, lb and Ic, more preferably from compounds of formulae la and lb Foreignfiling text P24-159

[0249] 15 wherein

[0250] R1and R2denote, independently of one another, a group selected from F, Cl,

[0251] CF3, OCF3, and straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms or straight-chain or branched alkenyl having 2

[0252] 20 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen and wherein one or more CH2 groups may be, in each case independently of one another, replaced by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or - C=C- in such a manner that oxygen atoms are not linked directly to one another, preferably from F, CF3, OCF3, straight-chain alkyl or alkoxy having 1 to 9 carbon atoms or alkenyl having 2 to 9 carbon atoms, and

[0253] L is on each occurrence, identically or differently, H or halogen selected from F, Cl and Br, preferably from F and Cl, and more

[0254] 30 preferably is on each occurrence, identically or differently, H or F.

[0255] It is particularly preferred that in case the phenylene rings of the compounds of formula I are substituted that the substituent(s) is (are) F, and furthermore that the terminal groups R1and R2do not contain Cl. Foreignfiling text P24-159

[0256] - 25 -

[0257] In a particularly preferred embodiment the one or more compounds of formula I are selected from compounds which do not contain Cl.

[0258] In a particularly preferred embodiment the liquid-crystalline medium contains no Cl- containing compounds.

[0259] 5

[0260] It is furthermore particularly preferred that at least one of the rings A21, A31and A41according to formula I has at least one F substituent. It is furthermore particularly preferred that the rings A21, A31and A41according to formula I together have at least two F substituents.

[0261] In the medium according to the invention the use of compounds containing CN is preferably and favourably limited, preferably to 75% by weight or below, more preferably to 50% by weight or below, even more preferably to 25% by weight or below and in particular to 15% by weight or below. In a particularly preferred embodiment the

[0262] 15 use of compounds containing CN is completely avoided.

[0263] The liquid-crystalline medium preferably contains mesogenic compounds which are added in view of contributing to or maintaining the favourable properties of the medium, e.g. a good VHR and a favourable stability.

[0264] 20

[0265] In an embodiment the liquid-crystalline medium according to the invention comprises one or more compounds of formula II, preferably in an amount, based on the overall contents of the medium, in the range from 1% by weight to 45% by weight, more preferably from 5% by weight to 25% by weight. In some cases it can be beneficial and preferred that two, three or more compounds of formula I are contained in the medium.

[0266] In a further embodiment the liquid-crystalline medium according to the invention comprises one or more compounds of formula III

[0267] 30 Foreignfiling text P24-159

[0268] - 26 - wherein R5and R6are defined as R3and L4and L5are defined as L1for formula II.

[0269] Compounds of formula III preferably are used in the medium in a total concentration from 1% by weight to 45% by weight, more preferably from 5% by weight to 25% by weight.

[0270] 5

[0271] It is preferred that the medium contains one or more mesogenic compounds of formula I, optionally one or more photoinitiators, and one or more mesogenic compounds selected from the group of compounds of formulae II and III.

[0272] It is particularly preferred that the medium comprises one or more compounds of formula I, one or more compounds of formula II and one or more compounds of formula III as set forth above.

[0273] Preferably the liquid-crystalline medium according to the invention comprises,

[0274] 15 alternatively or preferably in addition, one or more compounds of formula IV wherein

[0275] R7denotes straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms, preferably 1 to 7 carbon atoms, or straight-chain or branched alkenyl having 2 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen and wherein one or more CH2 groups may be, in each case independently of one another, replaced by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C=C- in such a

[0276] 30 manner that oxygen atoms are not linked directly to one another, i is 0, 1 or 2,

[0277] L6and L7are, independently of one another, H or F, and

[0278] X1denotes F, CF3, OCF3 or CN. Foreignfiling text P24-159

[0279] - 27 -

[0280] Compounds of formula IV preferably are used in the medium in a total concentration from 1% by weight to 45% by weight, more preferably from 5% by weight to 25% by weight.

[0281] It is particularly preferred that the medium comprises one or more compounds of

[0282] 5 formula I as set forth above and below, one or more compounds of formula II, one or more compounds of formula III and one or more compounds of formula IV.

[0283] In a further embodiment the liquid-crystalline medium according to the invention comprises one or more compounds of formula V, preferably in an amount, based on the overall contents of the medium, in the range from 1% by weight to 15% by weight, more preferably from 5% by weight to 10% by weight,

[0284] 15 wherein

[0285] R8denotes straight-chain or branched alkyl or alkoxy having 1 to 15

[0286] 20 carbon atoms, preferably 1 to 7 carbon atoms, or straight-chain or branched alkenyl having 2 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen and wherein one or more CH2 groups may be, in each case independently of one another, replaced by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C=C- in such a manner that oxygen atoms are not linked directly to one another, and

[0287] X2denotes F, CF3, OCF3 or CN, preferably CF3.

[0288] 30 In a particularly preferred embodiment one or more of the one or more compounds of formula I are selected from compounds of formulae 1-1 and I-2 Foreignfiling text P24-159

[0289] - 28 - wherein

[0290] R1and R2are as defined for formula la above, and

[0291] L is on each occurrence, identically or differently, H or F.

[0292] 15 Optionally the medium further comprises one or more compounds selected from the compounds designated as CC-n-V and CC-n-Vm as shown and explained in Table D, wherein preferably n and m are independently of one another integers of 1 to 7, in particular in a concentration range from 1% by weight to 25% by weight.

[0293] 20 Optionally the media according to the present invention may comprise further liquid crystal compounds in order to adjust the physical properties. Such compounds are known in the field. The concentration of these optionally further included liquid crystal compounds in the media according to the present invention is preferably from 0% by weight to 30% by weight, more preferably from 0.1% by weight to 20% by weight and most preferably from 1% by weight to 15% by weight.

[0294] In an embodiment of the present invention the LC medium contains an LC host mixture with negative dielectric anisotropy. Accordingly, in preferred embodiments the mesogenic media according to the invention comprise components selected from the

[0295] 30 following items a) to x): a) Mesogenic medium which comprises one or more compounds selected from the group of compounds of the formulae CY, PY and AC: Foreignfiling textP24-159 wherein

[0296] 15 a denotes 0, 1 or 2, preferably 1 or 2, b denotes 0 or 1, c is 0, 1 or 2, d isOorl.

[0297] 30 Foreignfiling text P24-159

[0298] - 30 -

[0299] R1and R2

[0300] RAC1and RAC2each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH2 groups may

[0301] 30 be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms,

[0302] Zxand Zyeach, independently of one another, denote -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO- Foreignfiling text P24-159

[0303] - 31 -

[0304] O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, preferably a single bond,

[0305] L1'4each, independently of one another, denote F, Cl, CN, OCF3, CF3, CH3, CH2F, CHF2.

[0306] 5 in which the individual radicals have the following meanings: each, independently of one another, denote alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adjacent CH2 groups may be replaced by -O-, -CH=CH-, -CO-, -O-CO- or -CO-O- in such a way that O atoms are not linked directly to one another,

[0307] ZACdenotes -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO- O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond,

[0308] 15 preferably a single bond, and

[0309] Preferably, both L1and L2denote F or one of L1and L2denotes F and the other denotes Cl, or both L3and L4denote F or one of L3and L4denotes F and the other denotes Cl.

[0310] 20

[0311] The compounds of the formula CY are preferably selected from the group consisting of the following sub-formulae: Foreignfiling textP24-159

[0312] -32 - Foreignfiling textP24-159

[0313] -33- Foreignfiling textP24-159 Foreignfiling text P24-159 wherein a denotes 1 or 2, alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl denotes a straightchain alkenyl radical having 2-6 C atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes CH2=CH-, CH2=CHCH2CH2-, CH3-

[0314] 30 CH=CH-, CH3-CH2-CH=CH-, CH3-(CH2)2-CH=CH-, CH3-(CH2)3-CH=CH- or CH3- CH=CH-(CH2)2-.

[0315] The compounds of the formula PY are preferably selected from the group consisting of the following sub-formulae: Foreignfiling textP24-159 Foreignfiling textP24-159 Foreignfiling text P24-159

[0316] - 38 -

[0317] PY21

[0318] 20 wherein alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl denotes a straight-chain alkenyl radical having 2-6 C atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes 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-.

[0319] The compounds of the formula AC are preferably selected from the group of compounds of the following sub-formulae: Foreignfiling text P24-159

[0320] - 39 -

[0321] AC3

[0322] 5 b) Mesogenic medium which additionally comprises one or more compounds of the following formula:

[0323] ZK in which the individual radicals have the following meanings:

[0324] 15

[0325] 20

[0326] R3and R4each, independently of one another, denote alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adjacent CH2 groups may be replaced by -O-, -CH=CH-, -CO-, -O-CO- or -CO-O- in such a way that O atoms are not linked directly to one another, denotes -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-

[0327] 30 O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, preferably a single bond.

[0328] The compounds of the formula ZK are preferably selected from the group consisting of the following sub-formulae: Foreignfiling textP24-159

[0329] -40 - Foreignfiling text P24-159

[0330] - 41 - in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl denotes a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl preferably denotes CH2=CH-, CH2=CHCH2CH2-, CH3-CH=CH-, CH3-CH2-CH=CH-, CH3-(CH2)2-CH=CH-, CH3-

[0331] 5 (CH2)3-CH=CH- or CH3-CH=CH-(CH2)2-.

[0332] Especially preferred are compounds of formula ZK1 and ZK3.

[0333] Particularly preferred compounds of formula ZK are selected from the following sub Foreignfiling text P24-159

[0334] - 42 - wherein the propyl, butyl and pentyl groups are straight-chain groups.

[0335] Most preferred are compounds of formula ZK1a and ZK3a. c) Mesogenic medium which additionally comprises one or more compounds of the

[0336] 5 following formula: in which the individual radicals on each occurrence, identically or differently, have the following meanings:

[0337] R5and R6each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH2 groups

[0338] 15 may be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms, and e denotes 1 or 2.

[0339] 30

[0340] The compounds of the formula DK are preferably selected from the group consisting of the following sub-formulae:

[0341] DK1 Foreignfiling textP24-159

[0342] -43 - Foreignfiling text P24-159

[0343] - 44 - in which alkyl and alkyl* each, independently of one another, denote a straightchain alkyl radical having 1-6 C atoms, and alkenyl denotes a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl preferably denotes 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-.

[0344] Preference is given to compounds of the formulae DK1 , DK4, DK7, DK 9, DK10

[0345] 15 and DK11. d) Mesogenic medium which additionally comprises one or more compounds of the following formula:

[0346] 20 individual radicals have the following meanings:

[0347] 30 with at least one ring F being different from cyclohexylene, f denotes 1 or 2, Foreignfiling text P24-159

[0348] - 45 -

[0349] R1and R2each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH2 groups may be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

[0350] 5 denotes -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-

[0351] -CO-O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, preferably a single bond,

[0352] L1and L2each, independently of one another, denote F, Cl, OCF3, CF3, CH3, CH2F, CHF2.

[0353] Preferably, both radicals L1and L2denote F or one of the radicals L1and L2denotes F and the other denotes Cl.

[0354] 15 The compounds of the formula LY are preferably selected from the group consisting of the following sub-formulae: Foreignfiling textP24-159 Foreignfiling textP24-159

[0355] 20 Foreignfiling text P24-159

[0356] - 48 -

[0357] 15 in which R1has the meaning indicated above, alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, (O) denotes an oxygen atom or a single bond, and v denotes an integer from 1 to 6. R1preferably denotes straight-chain alkyl having

[0358] 20 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms, in particular CH3, C2H5, n-C3H7, n-C4H9, n-C5Hn, 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-. e) Mesogenic medium which additionally comprises one or more compounds selected from the group consisting of the following formulae:

[0359] 30 Foreignfiling text P24-159 in which alkyl denotes Ci-6-alkyl, Lxdenotes H or F, and X denotes F, Cl, OCF3, OCHF2 or OCH=CF2. Particular preference is given to compounds of the formula G1 in which X denotes F.

[0360] Mesogenic medium which additionally comprises one or more compounds selected from the group consisting of the following formulae: Foreignfiling textP24-159 Foreignfiling text P24-159 in which R5has one of the meanings indicated above for R1, alkyl denotes Ci-6-alkyl, d denotes 0 or 1 , and z and m each, independently of one another, denote an integer from 1 to 6. R5in these compounds is particularly preferably Ci-6-alkyl

[0361] 15 or -alkoxy or C2-6-alkenyl, d is preferably 1. The LC medium according to the invention preferably comprises one or more compounds of the above-mentioned formulae in amounts of > 5% by weight. g) Mesogenic medium which additionally comprises one or more biphenyl com¬

[0362] 20 pounds selected from the group consisting of the following formulae: in which alkyl, alkyl* and alkoxy each, independently of one another, denote a straight-chain alkyl or respectively alkoxy radical having 1-6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl Foreignfiling text P24-159

[0363] - 52 - radical having 2-6 C atoms. Alkenyl and alkenyl* preferably denote 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-.

[0364] The proportion of the biphenyls of the formulae B1 to B3 in the LC mixture is

[0365] 5 preferably at least 3% by weight, in particular > 5% by weight.

[0366] The compounds of the formula B2 are particularly preferred.

[0367] The compounds of the formulae B1 to B3 are preferably selected from the group consisting of the following sub-formulae: in which alkyl* denotes an alkyl radical having 1-6 C atoms. The medium according to the invention particularly preferably comprises one or more compounds of the formulae B1a and / or B2c. h) Mesogenic medium which additionally comprises one or more terphenyl com- pounds of the following formula:

[0368] 30 in which R5and R6each, independently of one another, have one of the meanings indicated above, and Foreignfiling text P24-159 each, independently of one another, denote

[0369] 5 in which L5denotes F or Cl, preferably F, and L6denotes F, Cl, OCF3, CF3, CH3, CH2F or CHF2, preferably F.

[0370] The compounds of the formula T are preferably selected from the group

[0371] 15 consisting of the following sub-formulae: Foreignfiling textP24-159

[0372] -54 Foreignfiling text P24-159 in which R denotes a straight-chain alkyl or alkoxy radical having 1-7 C atoms, R* denotes a straight-chain alkenyl radical having 2-7 C atoms, (O) denotes an Foreignfiling text P24-159

[0373] - 56 - oxygen atom or a single bond, and m denotes an integer from 1 to 6. R* preferably denotes 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-.

[0374] R preferably denotes methyl, ethyl, propyl, butyl, pentyl, hexyl, methoxy, ethoxy,

[0375] 5 propoxy, butoxy or pentoxy. i) Mesogenic medium which additionally comprises one or more compounds of the following formula O:

[0376] R°1, R°2each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH2 groups may

[0377] 30 be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

[0378] Z°1denotes -CH2CH2-, -CF2CF2-, -C=C- or a single bond,

[0379] Z°2denotes CH2O, -C(O)O-, -CH2CH2-, -CF2CF2-, or a single bond, Foreignfiling text P24-159

[0380] O is 1 or 2.

[0381] The compounds of the formula O are preferably selected from the group consisting of the following sub-formulae: Foreignfiling text P24-159

[0382] - 58 - in which R°1and R°2have the meanings indicated above and preferably each, independently of one another, denote straight-chain alkyl having 1 to 6 C atoms

[0383] 5 or straight-chain alkenyl having 2 to 6 C atoms.

[0384] Preferred media comprise one or more compounds selected from the formulae 03, 04 and 05. k) Mesogenic medium which additionally comprises one or more compounds of the following formula:

[0385] 30

[0386] R9denotes H, CH3, C2H5 or n-CsH?, (F) denotes an optional fluorine substituent, and q denotes 1 , 2 or 3, and R7has one of the meanings indicated for R1, preferably in amounts of > 3% by weight, in particular > 5% by weight and very particularly preferably 5-30% by weight. Foreignfiling text P24-159

[0387] - 59 -

[0388] Particularly preferred compounds of the formula Fl are selected from the group consisting of the following sub-formulae: Foreignfiling text P24-159

[0389] - 60 - in which R7preferably denotes straight-chain alkyl, and R9denotes CH3, C2H5 or n-CsH?. Particular preference is given to the compounds of the formulae Fl 1 , FI2 and FI3.

[0390] 15 I) Mesogenic medium which additionally comprises one or more compounds selected from the group consisting of the following formulae: in which R8has the meaning indicated for R1, and alkyl denotes a straight-chain alkyl radical having 1-6 C atoms. Foreignfiling text P24-159

[0391] - 61 - m) Mesogenic medium which additionally comprises one or more compounds which contain a tetrahydronaphthyl or naphthyl unit, such as, for example, the compounds selected from the group consisting of the following formulae: Foreignfiling text P24-159

[0392] 20 in which

[0393] R10and R11each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH2groups may be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms, and R10and R11preferably denote straight-chain alkyl or alkoxy having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms, and

[0394] 30

[0395] Z1and Z2each, independently of one another, denote -C2H4-, -CH=CH-, -(CH2)4-, -(CH2)3O-, -O(CH2)3-, -CH=CH- CH2CH2-, -CH2CH2CH=CH-, -CH2O-, -OCH2-, -CO-O-, -O-

[0396] CO-, -C2F4-, -CF=CF-, -CF=CH-, -CH=CF-, -CH2- or a single bond. Foreignfiling text P24-159

[0397] - 63 - n) Mesogenic medium which additionally comprises one or more difluorodibenzochromanes and / or chromanes of the following formulae: in which

[0398] R11and R12each, independently of one another, have one of the meanings

[0399] 20 indicated above for R11, ring M is trans- 1 ,4-cyclohexylene or 1 ,4-phenylene,

[0400] Zm-C2H4-, -CH2O-, -OCH2-, -CO-O- or -O-CO-, c is 0, 1 or 2, preferably in amounts of 3 to 20% by weight, in particular in amounts of 3 to 15% by weight.

[0401] Particularly preferred compounds of the formulae BC, CR and RC are selected from the group consisting of the following sub-formulae: Foreignfiling textP24-159

[0402] -64- Foreignfiling textP24-159

[0403] 20 Foreignfiling text P24-159

[0404] - 66 - in which alkyl and alkyl* each, independently of one another, denote a straight¬

[0405] 20 chain alkyl radical having 1-6 C atoms, (O) denotes an oxygen atom or a single bond, c is 1 or 2, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and alkenyl* preferably denote 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] Very particular preference is given to mixtures comprising one, two or three compounds of the formula BC-2. o) Mesogenic medium which additionally comprises one or more fluorinated

[0407] 30 phenanthrenes and / or dibenzofurans of the following formulae:

[0408] PH Foreignfiling text P24-159

[0409] - 67 - in which R11and R12each, independently of one another, have one of the meanings indicated above for R11, b denotes 0 or 1 , L denotes F, and r denotes 1 , 2 or 3.

[0410] Particularly preferred compounds of the formulae PH and BF are selected from the group consisting of the following sub-formulae:

[0411] 15 Foreignfiling text P24-159

[0412] - 68 -

[0413] BSF2

[0414] 5 in which R and R' each, independently of one another, denote a straight-chain alkyl or alkoxy radical having 1-7 C atoms.

[0415] In another embodiment the liquid-crystal medium comprises one or more compounds selected from the group of compounds of formulae B-1, B-2 and B-3 in which

[0416] R11and R12identically or differently, denote H or a straight-chain alkyl or alkoxy radical having 1 to 15 C atoms, in which one or more CH2 groups one

[0417] 30 or -O-CO- in such a way that O atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen, preferably a straight-chain alkoxy radical having 1 to 7 C atoms. Foreignfiling text P24-159

[0418] - 69 -

[0419] The compounds of formula B-1 are preferably selected from the group of compounds of the formulae B-1-a to B-1-e in which R11and R12, identically or differently, denote alkyl having 1 to 7 C atoms, preferably ethyl, n-propyl, n-butyl or n-pentyl.

[0420] The compounds of formula B-2 are preferably selected from the group of compounds of the formulae B-2-a to B-2-e Foreignfiling text P24-159

[0421] - 70 - in which R11and R12, identically or differently, denote alkyl having 1 to 12 C atoms,

[0422] 20 preferably alkyl having 1 to 7 C atoms.

[0423] The compounds of formula B-3 are preferably selected from the group of compounds of the formulae B-3-a to B-3-j Foreignfiling text P24-159 in which R12denotes alkyl having 1 to 7 C atoms, preferably ethyl, n-propyl or n-butyl.

[0424] 30

[0425] In a preferred embodiment the one or more compounds selected from the group of compounds of formulae B-1 , B-2 and B-3 are selected from the group of compounds B- A to B-J Foreignfiling textP24-159 Foreignfiling text P24-159

[0426] - 73 -

[0427] The one or more compounds selected from the group of compounds of formulae B-1, B-2 and B-3 are preferably comprised in the liquid-crystal medium in a total amount of from 0 to 15% by weight, more preferably 10% by weight or less and even more preferably 5% by weight or less.

[0428] 15 p) Mesogenic medium which additionally comprises one or more monocyclic compounds of the following formula

[0429] 20 wherein

[0430] R1and R2each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH2 groups may be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms,

[0431] 30

[0432] L1and L2each, independently of one another, denote F, Cl, OCF3, CF3, CH3, CH2F, CHF2.

[0433] Preferably, both L1and L2denote F or one of L1and L2denotes F and the other denotes Cl, Foreignfiling text P24-159

[0434] - 74 -

[0435] The compounds of the formula Y are preferably selected from the group consisting of the following sub-formulae: Foreignfiling text P24-159 in which, Alkyl and Alkyl* each, independently of one another, denote a straightchain alkyl radical having 1-6 C atoms, Alkoxy denotes a straight-chain alkoxy radical having 1-6 C atoms, Alkenyl and Alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 C atoms, and O denotes an oxygen atom or a single bond. Alkenyl and Alkenyl* preferably denote 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-.

[0436] 15

[0437] Particularly preferred compounds of the formula Y are selected from the group consisting of the following sub-formulae:

[0438] 20

[0439] Alkoxy Alkoxy wherein Alkoxy preferably denotes straight-chain alkoxy with 3, 4, or 5 C atoms.

[0440] 30 q) Mesogenic medium which comprises 1 to 15, preferably 3 to 12, compounds of the formulae CY1 , CY2, PY1, PY2, AC1, AC2 and / or AC3. The proportion of these compounds in the mixture as a whole is preferably 20 to 99%, more preferably 30 to 95%, particularly preferably 40 to 90%. The content of these individual compounds is preferably in each case 2 to 20%. Foreignfiling text P24-159

[0441] - 76 - r) Mesogenic medium which comprises 1 to 10, preferably 1 to 8, compounds of the formula ZK, in particular compounds of the formulae ZK1 , ZK2 and / or ZK6. The proportion of these compounds in the mixture as a whole is preferably 3 to 25%, particularly preferably 5 to 45%. The content of these individual compounds is preferably in each case 2 to 20%.

[0442] 5 s) Mesogenic medium in which the proportion of compounds of the formulae CY, PY and ZK in the mixture as a whole is greater than 70%, preferably greater than 80%. t) Mesogenic medium which contains one or more, preferably 1 to 5, compounds selected of formula PY1-PY8, very preferably of formula PY2. The proportion of these compounds in the mixture as a whole is preferably 1 to 30%, particularly preferably 2 to 20%. The content of these individual compounds is preferably in each case 1 to 20%.

[0443] 15 u) Mesogenic medium which contains one or more, preferably 1 , 2 or 3, compounds of formula T2. The content of these compounds in the mixture as a whole is preferably 1 to 20%.

[0444] 20 The LC medium according to the invention preferably comprises the terphenyls of the formula T and the preferred sub-formulae thereof in an amount of 0.5-30% by weight, in particular 1-20% by weight.

[0445] Particular preference is given to compounds of the formulae T1 , T2, T3 and T21. In these compounds, R preferably denotes alkyl, furthermore alkoxy, each having 1-5 C atoms.

[0446] The terphenyls are preferably employed in mixtures according to the invention if the An value of the mixture is to be > 0.1. Preferred mixtures comprise 2-20% by weight of one or more terphenyl compounds of the formula T, preferably selected from

[0447] 30 the group of compounds T1 to T22. v) Mesogenic medium which contains one or more, preferably 1 , 2 or 3, compounds of formula BF1 and / or BSF1. The total content of these compounds in the mixture as a whole is preferably 1 to 15%, preferably 2 to 10% particularly preferably 4 to 8%. Foreignfiling text P24-159

[0448] - 77 - w) Preferred media comprise one or more compounds of formula O, preferably selected from the formulae 03, 04 and 05 in a total concentration of 2 to 25%, preferably 3 to 20%, particularly preferably 5 to 15%. x) Preferred media comprise one or more compounds of formula DK, preferably

[0449] 5 selected from the formulae DK1 , DK4, DK7, DK 9, DK10 and DK11. The total concentration of compounds of formulae DK9, DK10 and DK11 is preferably 2 to 25%, more preferably 3 to 20%, particularly preferably 5 to 15%.

[0450] In another embodiment of the present invention the LC medium contains an LC host mixture with positive dielectric anisotropy. Accordingly, in further preferred embodiments the mesogenic media according to the invention comprise components selected from the following items aa) to zz): aa) Mesogenic medium which comprises one or more compounds selected from the

[0451] 15 group of compounds of the formulae I l-A to Vlll-A as set forth below, in particular of the formulae I l-A and 11 l-A wherein

[0452] 30

[0453] R20each, identically or differently, denote a halogenated or unsubstituted alkyl or alkoxy radical having 1 to 15 C atoms, where, in addition, one or more CH2 groups in these radicals may each be replaced, independently of one another, by -C=C-, -CF2O-, -CH=CH-, Foreignfiling text P24-159

[0454] - 78 -

[0455] , -CO-O- or -O-CO- in such a way that O atoms are not linked directly to one another,

[0456] X20each, identically or differently, denote F, Cl, CN, SFs, SCN, NCS, a halogenated alkyl radical, a halogenated alkenyl radical, a halogenated

[0457] 5 alkoxy radical or a halogenated alkenyloxy radical, each having up to 6 C atoms, and y20-24 each, identically or differently, denote H or F; y of one another, denote

[0458] The compounds of the formula I l-A are preferably selected from the following formulae:

[0459] 20 Foreignfiling text P24-159 wherein R20and X20have the meanings indicated above.

[0460] 15

[0461] R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F. Particular preference is given to compounds of the formulae Ila and lib, in particular compounds of the formulae Ila and lib wherein X denotes F.

[0462] 20 In an embodiment the liquid-crystal medium comprises one or more compounds selected from the group of compounds of formulae 11-1 and 11-2 in which

[0463] R2denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C atoms, Foreignfiling text P24-159

[0464] - 80 - in which optionally one or more CH2 groups, independently of one another, may be replaced by dependently of each other

[0465] L21, L22,

[0466] L23and L24independently of each other, denote H or F,

[0467] L25denotes H or CH3, and

[0468] X2denotes halogen, halogenated alkyl or alkoxy with 1 to 3 C atoms or halogenated alkenyl or alkenyloxy with 2 or 3 C atoms.

[0469] 30 In a further embodiment the liquid-crystal medium comprises one or more compounds selected from the group of compounds of formulae ll-1-a to ll-1-h a Foreignfiling text P24-159

[0470] - 81 - , wherein R2has the meaning as given in formula 11-1.

[0471] In a further embodiment the liquid-crystal medium comprises one or more compounds selected from the compounds of formulae ll-2-a to II-2-I Foreignfiling textP24-159 Foreignfiling text P24-159 wherein R2has the meaning given for formula 11-2 above.

[0472] 20 The compounds of the formula lll-A are preferably selected from the following formulae: Foreignfiling text P24-159

[0473] 15 wherein R20and X20have the meanings indicated above.

[0474] R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F. Particular preference is given to compounds of the formulae Illa and Hie, in particular compounds of the formula Illa.

[0475] 20 bb) The mesogenic medium may alternatively or additionally comprise one or more compounds selected from the following formulae: Foreignfiling text P24-159

[0476] 15 wherein

[0477] R20, X20and Y20'23have the meanings indicated above, and

[0478] Z20denotes -C2H4-, -(CH2)4-, -CH=CH-, -CF=CF-

[0479] 20 , -C2F4-, -CH2CF2-, -CF2CH2-, -CH2O-, -OCH2-, -COO- or -OCF2-, in formulae V and VI also a single bond, in formulae V and VIII also -CF2O-, r denotes 0 or 1 , and s denotes 0 or 1 ;

[0480] The compounds of the formula IV-A are preferably selected from the following formulae: Foreignfiling text P24-159

[0481] - 86 - wherein R20and X20have the meanings indicated above.

[0482] R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F, CN

[0483] 15 or OCF3, furthermore OCF=CF2 or Cl;

[0484] The compounds of the formula V-A are preferably selected from the following formulae: Foreignfiling text P24-159

[0485] 20 wherein R20and X20have the meanings indicated above.

[0486] R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F and OCF3, furthermore OCHF2, CF3, OCF=CF2 and OCH=CF2;

[0487] The compounds of the formula Vl-A are preferably selected from the following formulae:

[0488] 30

[0489] Via Foreignfiling text P24-159

[0490] 15 wherein R20and X20have the meanings indicated above.

[0491] R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F, furthermore OCF3, CF3, CF=CF2, OCHF2 and OCH=CF2;

[0492] 20 The compounds of the formula Vll-A are preferably selected from the following formulae: wherein R20and X20have the meanings indicated above.

[0493] R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F, furthermore OCF3, OCHF2 and OCH=CF2. Foreignfiling text P24-159

[0494] - 89 - cc) The mesogenic medium may additionally comprise one or more compounds selected from the formulae ZK1 to ZK10 given above. Especially preferred are compounds of formula ZK1 and ZK3. Particularly preferred compounds of formula ZK are selected from the sub-formulae ZK1a, ZK1 b, ZK1c, ZK3a, ZK3b,

[0495] 5 ZK3c and ZK3d. dd) In an embodiment the mesogenic medium additionally comprises one or more compounds selected from the formulae DK1 to DK12 given above. Especially preferred compounds are DK1 , DK4, DK7, DK 9, DK10 and DK11. ee) In an embodiment the mesogenic medium additionally comprises one or more compounds of the following formula:

[0496] 15 wherein X20has the meanings indicated above,

[0497] 20 denotes H or F, and

[0498] "alkenyl" denotes C2-6-alkenyl. ff) The compounds of the formulae DK3 and IX are preferably selected from the wherein "alkyl" denotes Ci-6-alkyl, preferably n-CsH?, n-C^g or n-CsHn, in particular n-C3H7. Foreignfiling text P24-159

[0499] - 90 - gg) In an embodiment the medium additionally comprises one or more compounds selected from the formulae B1 , B2 and B3 given above, preferably from the formula B2. The compounds of the formulae B1 to B3 are particularly preferably selected from the formulae B1a, B2a, B2b and B2c.

[0500] 5 hh) In an embodiment the medium additionally comprises one or more compounds of the following formula: wherein L20, L21denote H or F, and R21and R22each, identically or differently,

[0501] 15 denote n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 6 C atoms, and preferably each, identically or differently, denote alkyl having 1 to 6 C atoms. ii) In an embodiment the medium comprises one or more compounds of the

[0502] 20 following formulae: wherein R20, X20and Y20-23have the meanings indicated in formula III, and Foreignfiling text P24-159

[0503] - 91 - each, independently of one another, denote

[0504] 15

[0505] The compounds of the formulae XI and XII are preferably selected from the following formulae: Foreignfiling textP24-159 Foreignfiling text P24-159

[0506] 15 wherein R20and X20have the meaning indicated above and preferably R20denotes alkyl having 1 to 6 C atoms and X20denotes F.

[0507] The mixture according to the invention particularly preferably comprises at least one compound of the formula XI la and / or Xlle.

[0508] 20 jj) In an embodiment the medium comprises one or more compounds of formula T given above, preferably selected from the group of compounds of the formulae T21 toT23 and T25 to T27.

[0509] Particular preference is given to compounds of the formulae T21 to T23. Very particular preference is given to the compounds of the formulae

[0510] 30 Foreignfiling text P24-159

[0511] 15

[0512] 20 kk) In an embodiment the medium comprises one or more compounds selected from the group of formulae DK9, DK10 and DK11 given above.

[0513] II) In an embodiment the medium additionally comprises one or more compounds selected from the following formulae:

[0514] XIII Foreignfiling text P24-159

[0515] - 95 -

[0516] 30 wherein R20and X20each, independently of one another, have one of the meanings indicated above, and Y20'23each, independently of one another, denote H or F. X20is preferably F, Cl, CF3, OCF3 or OCHF2. R20preferably denotes alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 6 C atoms.

[0517] The mixture according to the invention particularly preferably comprises one or more compounds of the formula XVIII-a, Foreignfiling text P24-159

[0518] - 96 -

[0519] XVIII-a

[0520] 5 wherein R20has the meanings indicated above. R20preferably denotes straightchain alkyl, in particular ethyl, n-propyl, n-butyl and n-pentyl and very particularly preferably n-propyl. The compound(s) of the formula XVIII, in particular of the formula XVIII-a, is (are) preferably employed in the mixtures according to the invention in amounts of 0.5-20% by weight, particularly preferably 1-15% by weight. mm) In an embodiment the medium additionally comprises one or more compounds of the formula XIX,

[0521] 15

[0522] 20 wherein R20, X20and Y20-25have the meanings indicated in formula III, s denotes 0 or 1 , and

[0523] In the formula XIX, X20may also denote an alkyl radical having 1-6 C atoms or an alkoxy radical having 1-6 C atoms. The alkyl or alkoxy radical is preferably straight-chain.

[0524] 30

[0525] R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F;

[0526] The compounds of the formula XIX are preferably selected from the following formulae: Foreignfiling textP24-159 Foreignfiling text P24-159

[0527] XlXh

[0528] 5 wherein R20, X20and Y20have the meanings indicated above. R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F, and Y20is preferably F;

[0529] R20is straight-chain alkyl or alkenyl having 2 to 6 C atoms. nn) In an embodiment the medium comprises one or more compounds of the formulae G1 to G4 given above, preferably selected from G1 and G2 wherein alkyl denotes Ci-6-alkyl, Lxdenotes H and X denotes F or Cl. In G2, X particularly

[0530] 30 preferably denotes Cl. oo) In an embodiment the medium comprises one or more compounds of the following formulae: Foreignfiling text P24-159

[0531] 15 wherein R20and X20have the meanings indicated above. R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F. The medium according to the invention particularly preferably comprises one or more compounds of the formula XXII wherein X20preferably denotes F. The compound(s) of the formulae

[0532] 20 XX - XXII is (are) preferably employed in the mixtures according to the invention in amounts of 1-20% by weight, particularly preferably 1-15% by weight. Particularly preferred mixtures comprise at least one compound of the formula XXII. pp) In an embodiment the medium comprises one or more compounds of the following pyrimidine or pyridine compounds of the formulae

[0533] M-1

[0534] 30 Foreignfiling text P24-159 wherein R20and X20have the meanings indicated above. R20preferably denotes alkyl having 1 to 6 C atoms. X20preferably denotes F. The medium according to the invention particularly preferably comprises one or more compounds of the formula M-1 , wherein X20preferably denotes F. The compound(s) of the formulae

[0535] 15 M-1 - M-3 is (are) preferably employed in the mixtures according to the invention in amounts of 1-20% by weight, particularly preferably 1-15% by weight. qq) In an embodiment the medium comprises two or more compounds of the formula XII, in particular of the formula XI la and / or Xlle.

[0536] 20 rr) In an embodiment the medium comprises 2-30% by weight, preferably 3-20% by weight, particularly preferably 3-15% by weight, of compounds of the formula XII. ss) In an embodiment, besides the compounds of the formulae XII, the medium may comprise further compounds selected from the group of the compounds of the formulae I l-A to XVIII shown above. tt) In an embodiment the proportion of compounds of the formulae I l-A to XVIII in the mixture as a whole is 40 to 95%, preferably 50 to 90%, particularly preferably 55

[0537] 30 to 88% by weight. uu) The medium preferably comprises 10-40%, more preferably 12-30%, particularly preferably 15 to 25% by weight of compounds of the formulae I l-A and / or 11 l-A. vv) In an embodiment the medium comprises 1-10% by weight, particularly preferably 2-7% by weight, of compounds of the formula XV and / or XVI. Foreignfiling text P24-159

[0538] - 101 - ww) In an embodiment the medium comprises at least one compound of the formula XI la and / or at least one compound of the formula XI I e and at least one compound of the formula Illa and / or Ila.

[0539] 5 xx) Preferred media comprise one or more compounds of formula O, preferably selected from the formulae 03, 04 and 05 in a total concentration of 2 to 25%, preferably 3 to 20%, particularly preferably 5 to 15%. yy) Preferred media comprise one or more compounds of formula DK, preferably selected from the formulae DK1, DK4, DK7, DK 9, DK10 and DK11. The total concentration of compounds of formulae DK9, DK10 and DK11 is preferably 2 to 25%, more preferably 3 to 20%, particularly preferably 5 to 15%. zz) Preferred media comprise one or more compounds of formulae IV-A to Vl-a,

[0540] 15 preferably selected from the group of compounds of formulae IVa, IVb, IVc, IVd, Va, Vc and Vlb in a concentration of 10 to 80%, preferably 12 to 75%, particularly preferably 15 to 70% by weight.

[0541] In an embodiment the liquid-crystalline medium is a cholesteric or chiral nematic

[0542] 20 medium.

[0543] In a particular embodiment cholesteric liquid crystals (CLCs) are provided which contain a medium which has, for example, in the initial state a planar structure which reflects light having a certain wavelength, and which can be switched into a focal conic, light-scattering structure by application of an electrical alternating-voltage pulse, or vice versa. On application of a stronger voltage, in particular a stronger voltage pulse, the CLC medium can be switched into a homeotropic, transparent state, from which it relaxes into the planar state after rapid switching-off of the voltage or into the focal conic state after slow switching-off.

[0544] 30

[0545] In the planar texture Bragg reflection occurs, where the reflected light has the same handedness as the cholesteric helix.

[0546] In the focal conic state, the helical axes are randomly arranged and the texture shows light scattering because of the discontinuous spatial variations of the refractive indices at the domain boundaries. Foreignfiling text P24-159

[0547] - 102 -

[0548] Both planar and focal conic configurations are typically stable in the absence of an external electric field. The effect of electric-field-driven textural transitions between planar and focal conic states forms the basis of operation of CLC displays, wherein when the texture of the CLC is switched from the planar to the focal conic texture, the

[0549] 5 Bragg reflection disappears and the CLC scatters the incident light due to the helical axes being randomly distributed.

[0550] However, the switching between the states is typically achieved only through the homeotropic state, where the cholesteric helix is completely unwound by a dielectric coupling between LC molecules with positive dielectric anisotropy (As > 0) and a vertical electric field.

[0551] In an embodiment a hazy opaque state of the switching layer can be the focal conic state described above.

[0552] 15

[0553] Alternatively, and according to a preferred embodiment, in the present invention a high haze state is formed by a polydomain structure. Preferably this polydomain structure can produce sufficiently strong scattering, while at the same time Bragg-type reflection behaviour still remains observable, at least to some extent. In this phase which

[0554] 20 comprises, preferably consists of, polydomains the orientation of the helical axis typically varies from domain to domain, and domain boundaries typically occur. Macroscopically however the phase can appear homogeneous, in particular homogeneously opaque or hazy to the human eye, and be free from visible defects over the entire layer area.

[0555] The polydomain structure is obtainable, for example, using conventional orientation layers oriented in a planar or homeotropic manner and advantageously switching to the polydomain state may be achievable at a comparatively low voltage. The polydomain structure is however also obtainable when orientation layers are not present.

[0556] 30

[0557] In addition, the presence of the polymer component in the modulation material and the switching layer can favourably influence and stabilize the scattering performance.

[0558] In a preferred embodiment a non-scattering or clear state can be formed by the homeotropic state described above. In this respect the advantageously high VHR that is presently obtainable can be useful in stabilizing the element in this state against self- Foreignfiling text P24-159

[0559] - 103 - discharging behaviour and thus allowing to sustain the state even with significantly lower refresh rates and / or lower power consumption.

[0560] Alternatively, a non-scattering or clear state can be formed by the planar texture described above.

[0561] 5

[0562] Using a chiral nematic or cholesteric medium can be beneficial in that relatively stable states, and even bistability, can be provided such that devices comprising the medium may consume less energy. In particular, a respective state may be retained, at least for a considerable time, after the electric field has been switched off, and less frequent addressing or refreshing of voltage may be possible.

[0563] Preferably the light valve according to the invention does not use dual frequency addressing, which can simplify the required electronics.

[0564] 15 As described above, in case a cholesteric medium is provided, the medium preferably exhibits a selective reflection with a wavelength of greater than 780 nm. Accordingly the medium preferably reflects in the near infrared (NIR) spectral region.

[0565] Chiral dopants and their concentrations can be provided such that the cholesteric pitch

[0566] 20 of the medium is suitably set or adjusted. A CLC medium can be prepared, for example, by doping a nematic LC medium with a chiral dopant having a high twisting power. The pitch p of the induced cholesteric helix is then given by the concentration c and the helical twisting power HTP of the chiral dopant in accordance with equation (1): p = (HTP c)'1(1)

[0567] It is also possible to use two or more dopants, for example in order to compensate for the temperature dependence of the HTP of the individual dopants and thus to achieve small temperature dependence of the helix pitch and the reflection wavelength of the

[0568] 30 CLC medium. For the total HTP (HTPtotai) then approximately equation (2) holds:

[0569] HTPtotai = Zi Q HTPi (2) wherein Cj is the concentration of each individual dopant and HTPi is the helical twisting power of each individual dopant. Foreignfiling text P24-159

[0570] - 104 -

[0571] In an embodiment the liquid-crystalline medium contains one or more chiral compounds, in particular one or more chiral dopants. The chiral dopants preferably have a high absolute value of the HTP and can generally be added in relatively low concentrations to mesogenic base mixtures and have good solubility in the achiral component. If two or more chiral compounds are employed, they may have the same

[0572] 5 or opposite direction of rotation and the same or opposite temperature dependence of the twist.

[0573] Preferably, the one or more chiral compounds according to the invention have an absolute value of the helical twisting power of 5 pm-1or more, more preferably of 10 pm-1or more and even more preferably of 15 pm-1or more, preferably in the commercial liquid-crystal mixture MLC-6828 from Merck KGaA. Particular preference is given to chiral compounds having an absolute value of the helical twisting power (HTP) of 20 pm-1or more, more preferably of 40 pm-1or more, even more preferably of 60 pm-1or more, and most preferably in the range of 80 pm-1or more to 260 pm-1or

[0574] 15 less, preferably in the commercial liquid-crystal mixture MLC-6828 from Merck KGaA.

[0575] Preferably the one or more chiral compounds are contained in the liquid-crystalline medium in an amount, based on the overall contents of the medium, of 2% by weight or less, more preferably 1% by weight or less and even more preferably 0.5% by weight or

[0576] 20 less.

[0577] In a preferred embodiment of the present invention, the chiral component consists of two or more chiral compounds which all have the same sign of the HTP. The temperature dependence of the HTP of the individual compounds may be high or low. The temperature dependence of the pitch of the medium can be compensated by mixing compounds having different temperature dependence of the HTP in corresponding ratios.

[0578] Suitable chiral dopants are known in the art, some of which are commercially available,

[0579] 30 such as, for example, cholesteryl nonanoate, R / S-811, R / S-1011, R / S-2011 , R / S-3011, R / S-4011 , R / S-5011, in particular R-5011, B(OC)2C*H-C-3 or CB15 (all Merck KGaA, Darmstadt, Germany).

[0580] Particularly suitable chiral dopants are compounds which contain one or more chiral radicals and one or more mesogenic groups, or one or more aromatic or alicyclic groups which form a mesogenic group with the chiral radical. Foreignfiling text P24-159

[0581] - 105 -

[0582] Suitable chiral radicals are, for example, chiral branched hydrocarbon radicals, chiral ethanediols, binaphthols or dioxolanes, furthermore mono- or polyvalent chiral radicals selected from the group consisting of sugar derivatives, sugar alcohols, sugar acids, lactic acids, chiral substituted glycols, steroid derivatives, terpene derivatives, amino

[0583] 5 acids or sequences of a few, preferably 1-5, amino acids.

[0584] Preferred chiral radicals are sugar derivatives, such as glucose, mannose, galactose, fructose, arabinose and dextrose; sugar alcohols, such as, for example, sorbitol, mannitol, iditol, galactitol or anhydro derivatives thereof, in particular dianhydrohexitols, such as dianhydrosorbide (1,4:3,6-dianhydro-D-sorbide, isosorbide), dianhydromannitol (isosorbitol) or dianhydroiditol (isoiditol); sugar acids, such as, for example, gluconic acid, gulonic acid and ketogulonic acid; chiral substituted glycol radicals, such as, for example, mono- or oligoethylene or propylene glycols, wherein one or more CH2 groups are substituted by alkyl or alkoxy; amino acids, such as, for example, alanine,

[0585] 15 valine, phenylglycine or phenylalanine, or sequences of from 2 to 5 of these amino acids; steroid derivatives, such as, for example, cholesteryl or cholic acid radicals; terpene derivatives, such as, for example, menthyl, neomenthyl, campheyl, pineyl, terpineyl, isolongifolyl, fenchyl, carreyl, myrthenyl, nopyl, geraniyl, linaloyl, neryl, citronellyl or dihydrocitronellyl.

[0586] 20

[0587] Suitable chiral radicals and mesogenic chiral compounds are described, for example, in DE 34 25 503, DE 35 34777, DE 35 34 778, DE 35 34 779 and DE 35 34 780, DE 43 42 280, EP 01 038 941 and DE 19541 820.

[0588] Preferable chiral compounds used according to the present invention are selected from the following groups of compounds.

[0589] In an embodiment preference is given to dopants selected from the group consisting of compounds of the following formulae A-l to A-lll:

[0590] 30 Foreignfiling text P24-159

[0591] - 106 - in which

[0592] Ra11and Ra12, independently of one another, are alkyl, oxaalkyl or alkenyl having from 2 to 9, preferably up to 7, carbon atoms, and Ra11is alternatively methyl or alkoxy having from 1 to 9 carbon atoms, preferably both are alkyl,

[0593] 15 preferably n-alkyl,

[0594] Ra21and Ra22, independently of one another, are alkyl or alkoxy having from 1 to 9, preferably up to 7, carbon atoms, oxaalkyl, alkenyl or alkenyloxy having from 2 to 9, preferably up to 7, carbon atoms, preferably both are alkyl,

[0595] 20 preferably n-alkyl,

[0596] Ra31and Ra32, independently of one another, are alkyl, oxaalkyl or alkenyl having from 2 to 9, preferably up to 7, carbon atoms, and Ra11is alternatively methyl or alkoxy having from 1 to 9 carbon atoms, preferably both are alkyl, preferably n-alkyl.

[0597] Particular preference is given to chiral dopants selected from the group consisting of the compounds of the following formulae:

[0598] 30 Foreignfiling text P24-159

[0599] Further preferred dopants are derivatives of isosorbide, isomannitol or isoiditol of the following formula A-IV Foreignfiling text P24-159

[0600] - 108 - preferably dianhydrosorbitol, and chiral ethanediols, such as, for example, diphenylethanediol (hydrobenzoin), in particular mesogenic hydrobenzoin derivatives of the following formula A-V

[0601] 5 including the (R,S), (S,R), (R,R) and (S,S) enantiomers, which are not shown, in which

[0602] 15 are each, independently of one another, 1,4-phenylene, which may also be mono-, di- or trisubstituted by L, or 1 ,4-cyclo- hexylene, H, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkoxycarbonyloxy having 1-7 carbon atoms, c is O or 1,

[0603] Z° is -COO-, -OCO-, -CH2CH2- or a single bond, and

[0604] 30

[0605] R° is alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy having 1-12 carbon atoms.

[0606] Compounds of formula A-IV are described in WO 98 / 00428. Compounds of the formula A-V are described in GB-A-2,328,207. Foreignfiling text P24-159

[0607] - 109 -

[0608] In another embodiment particularly preferred chiral 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 bridging group and a terminal or

[0609] 5 central chiral group, as described in WO 02 / 06196 and WO 02 / 06195.

[0610] Particular preference is given to chiral compounds of formula A-VI

[0611] 15 in which

[0612] X1, X2, Y1and Y2are each, independently of one another, F, Cl, Br, I, CN, SCN, SFs, straight-chain or branched alkyl having from 1 to 25 carbon atoms, which

[0613] 20 may be monosubstituted or polysubstituted by F, Cl, Br, I or CN and in which, in addition, one or more non-adjacent CH2 groups may each, independently of one another, be replaced by -O-, -S-, -NH-,

[0614] NR0-, -CO-, -COO-, -OCO-, -OCOO-, -S-CO-, -CO-S-, -CH=CH- or -C^C- in such a way that O and / or S atoms are not bonded directly to one another, a polymerisable group or cycloalkyl or aryl having up to 20 carbon atoms, which may optionally be monosubstituted or polysubstituted by halogen, preferably F, or by a polymerisable group, x1and x2are each, independently of one another, 0, 1 or 2,

[0615] 30 y1and y2are each, independently of one another, 0, 1 , 2, 3 or 4,

[0616] B1and B2are each, independently of one another, an aromatic or partially or fully saturated aliphatic six-membered ring in which one or more CH groups may Foreignfiling text P24-159

[0617] - 1 10 - be replaced by N atoms and one or more non-adjacent CH2 groups may be replaced by O and / or S,

[0618] W1and W2are each, independently of one another, -Z1-A1-(Z2-A2)m-R, and one of the two is alternatively R1or A3, but both are not simultaneously H, or

[0619] 5

[0620] II1and II2are each, independently of one another, CH2, O, S, CO or CS,

[0621] V1and V2are each, independently of one another, (CH2)n, in which from one to four

[0622] 15 non-adjacent CH2 groups may be replaced by O and / or S, and one of V1and V2and, in the case where H-, - CH=CF-, -CF=CF-, -C=C-, a combination of two of these groups, where no two O and / or S and / or N atoms are bonded directly to one another, preferably -CH=CH-COO-, or -COO-CH=CH-, or a single bond,

[0623] A1, A2and A3are each, independently of one another, 1 ,4-phenylene, in which one or

[0624] 30 two non-adjacent CH groups may be replaced by N, 1 ,4-cyclohexylene, in which one or two non-adjacent CH2 groups may be replaced by O and / or S, 1 ,3-dioxolane-4,5-diyl, 1 ,4-cyclohexenylene, 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, where each of these groups may be monosubstituted or polysubstituted by L, and in addition A1is a single bond, Foreignfiling text P24-159

[0625] - 1 1 1 -

[0626] L is a halogen atom, preferably F, CN, NO2, alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkoxycarbonyloxy having 1-7 carbon atoms, in which one or more H atoms may be replaced by F or Cl,

[0627] 5 m is in each case, independently, 0, 1 , 2 or 3, and

[0628] R and R1are each, independently of one another, H, F, Cl, Br, I, CN, SCN, SF5, straight-chain or branched alkyl having from 1 or 3 to 25 carbon atoms respectively, which may optionally be monosubstituted or polysubstituted by F, Cl, Br, I or CN, and in which one or more non-adjacent CH2 groups may be replaced by -O-, -S-, -NH-, -NR0-, -CO-, -COO-, -OCO-, -O- COO-, -S-CO-, -CO-S-, -CH=CH- or -C=C-, where no two O and / or S atoms are bonded directly to one another, or a polymerisable group.

[0629] 15 Particular preference is given to chiral binaphthyl derivatives of the formula A-VI-1 in particular those selected from the following formulae A-VI-1a to A-VI-1c: Foreignfiling text P24-159

[0630] - 112 -

[0631] 5 in which B and Z° are as defined for formula A-IV, and Z° more preferably is -OCO- or a single bond,

[0632] R° is as defined for formula A-IV or H or alkyl having from 1 to 4 carbon atoms, and b is 0, 1 or 2.

[0633] 15 Particular preference is furthermore given to chiral binaphthyl derivatives of the formula

[0634] A-VI-2 in particular to those selected from the following formulae A-VI-2a to A-VI-2f: Foreignfiling text P24-159

[0635] - 113 -

[0636] 30 in which R° is as defined for formula A-VI, and X is H, F, Cl, CN or R°, preferably F.

[0637] In a particularly preferred embodiment, the chiral medium according to the invention comprises one or more compounds of formulae R-811 , S-811 , R-5011 and S-5011 which are shown in Table F below. In a preferred embodiment the medium contains S- 811. In an alternative embodiment the medium contains R-811. In an embodiment the medium contains R-5011. In yet another embodiment the medium contains S-5011. Foreignfiling text P24-159

[0638] - 114 -

[0639] The LC medium according to the present invention preferably and favourably exhibits a high reliability and a high electric resistivity. The LC medium according to the present invention also preferably and favourably exhibits a high voltage holding ratio (VHR), see S. Matsumoto et al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID

[0640] 5 Conference, San Francisco, June 1984, p. 304 (1984); T. Jacob and U. Finkenzeller in "Merck Liquid Crystals - Physical Properties of Liquid Crystals", 1997. The VHR of an LC medium according to the invention is preferably > 75 %, more preferably > 85 %, even more preferably > 95 % and particularly preferably > 98 %. Unless described otherwise, the measurement of the VHR is carried out as described in T. Jacob, U. Finkenzeller in "Merck Liquid Crystals - Physical Properties of Liquid Crystals", 1997.

[0641] In a preferred embodiment of the invention the material of or respectively in the switching layer is prepared by providing a liquid-crystalline medium which comprises one or more polymerisable mesogenic compounds in an amount, based on the overall

[0642] 15 contents of the medium, of 20% by weight or less, and by subsequently polymerising the one or more polymerisable mesogenic compounds, preferably in situ in the switching layer.

[0643] Preferably, the one or more polymerisable mesogenic compounds are contained in the

[0644] 20 medium in an amount, based on the overall contents of the medium, in an amount of 15% by weight or less, even more preferably in an amount of 10% by weight or less and particularly preferably in an amount of 5% by weight or less.

[0645] Preferably, the one or more polymerisable mesogenic compounds comprise one, two or more acrylate and / or methacrylate groups.

[0646] In the medium preferably one or more polymerisable, curable or hardenable compounds are provided, preferably one or more photocurable monomers, which can favourably serve as the precursors for the polymer component, in particular the polymer

[0647] 30 network, in the modulation material and the switching layer.

[0648] The reactive mesogens (RMs) or mesogenic monomers used contain a mesogenic group and one or more polymerisable groups, i.e. functional groups which are suitable for polymerisation. Foreignfiling text P24-159

[0649] - 115 -

[0650] In a particularly preferred embodiment the polymerisable compound(s) used include(s) only reactive mesogen(s), i.e. all the reactive monomers are mesogens.Alternatively, RMs can be provided in combination with one or more non-mesogenic polymerisable compounds.

[0651] 5 The RMs can be monoreactive and / or di- or multireactive. Preferably, the RMs used are di- or multireactive, in particular direactive. In an embodiment one or more direactive RMs are used in combination with at least one monoreactive RM.

[0652] In a preferred embodiment of the invention the one or more polymerisable mesogenic compounds are selected from the compounds of the formula M

[0653] RMa-AM1-(ZM1-AM2)m1-RMb M in which the individual radicals are defined as follows:

[0654] 15

[0655] RMaand RMbare each independently P, P-Sp-, H, F, Cl, Br, I, -CN,

[0656] -NO2, -NCO, -NCS, -OCN, -SCN, SF5 or straight-chain or branched alkyl having 1 to 25 carbon atoms, in which one or more non-adjacent CH2 groups may each independently also be replaced by -C(R°)=C(R00)-, -

[0657] 20 C=C-, -N(R00)-, -O-, -S-,

[0658] -CO-, -CO-O-, -O-CO-, -O-CO-O-, in such a way that no oxygen and / or sulphur atoms are joined directly to one another, and in which one or more hydrogen atoms may also be replaced by F, Cl, Br, I, CN, P or P- Sp-, where preferably at least one of the RMaand RMbradicals is or contains a P or P-Sp- group, preferably

[0659] RMaand RMbare each independently P, P-Sp-, H, halogen, SF5, NO2, an alkyl, alkenyl or alkynyl group, where preferably at least one of the RMaand RMbradicals is or contains a P or P-Sp- group,

[0660] 30

[0661] P is a polymerisable group,

[0662] Sp is a spacer group or a single bond,

[0663] AM1andAM2are each independently an aromatic, heteroaromatic, alicyclic or heterocyclic group, preferably having 4 to 25 ring atoms, preferably Foreignfiling text P24-159

[0664] - 116 - carbon atoms, which also comprises or may contain fused rings, and which may optionally be mono- or polysubstituted by L,

[0665] L is P, P-Sp-, OH, CH2OH, F, Cl, Br, I, -CN, -NO2, -NCO, -NCS,

[0666] -OCN, -SCN, -C(=O)N(RX)2, -C(=O)Y1, -C(=O)RX, -N(RX)2, optionally

[0667] 5 substituted silyl, optionally substituted aryl having 6 to 20 carbon atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 carbon atoms or alkenyl or alkynyl having 2 to 25 carbon atoms, in which one or more hydrogen atoms may also be replaced by F, Cl, P or P-Sp-, preferably P, P-Sp-, H, OH, CH2OH, halogen, SF5, NO2, an alkyl, alkenyl or alkynyl group,

[0668] Y1is halogen, preferably F,

[0669] 15 ZM1is -O-, -S-, -CO-, -CO-O-, -OCO-, -O-CO-O-, -OCH2-, -CH2O-,

[0670] -SCH2-, -CH2S-, -CF2O-, -OCF2-, -CF2S-, -SCF2-, -(CH2)ni-, -CF2CH2-, -CH2CF2-, -(CF2)ni-, -CH=CH-, -CF=CF-, -C=C-, -CH=CH-, -COO-, -OCO-CH=CH-, CR°R00or a single bond,

[0671] 20 R° and R00are each independently H or alkyl having 1 to 12 carbon atoms,

[0672] Rxis P, P-Sp-, H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 carbon atoms, in which one or more non-adjacent CH2 groups may also be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, in such a way that no oxygen and / or sulphur atoms are joined directly to one another, and in which one or more hydrogen atoms may also be replaced by F, Cl, P or P-Sp-, an optionally substituted aryl or aryloxy group having 6 to 40 carbon atoms, or an optionally substituted heteroaryl or heteroaryloxy group having 2 to

[0673] 30 40 carbon atoms, ml is 0, 1 , 2, 3 or 4, and n1 is 1 , 2, 3 or 4, Foreignfiling text P24-159

[0674] - 1 17 - where at least one substituent, preferably one, two or three substituents and more preferably one or two substituents from the group of RMa, RMband the substituent L present is a P or P-Sp- group or contains at least one P or P-Sp- group.

[0675] Particular preference is given to compounds of the formula M in which one of Rmaand

[0676] 5 Rmbor both are P or P-Sp-.

[0677] Suitable and preferred RMs for use in the liquid-crystalline media as used according to the invention are, for example, selected from the following formulae: Foreignfiling textP24-159

[0678] -118- Forei^lingJe)<tP24-1sg

[0679] -119- Foreignfiling textP24-159

[0680] -120- Foreignfiling text P24-159 in which the individual radicals are defined as follows:

[0681] P1to P3are each independently a polymerisable group, preferably having one of

[0682] 30 the definitions specified above and below for P, more preferably an acrylate, methacrylate, fluoroacrylate, oxetane, vinyloxy or epoxy group,

[0683] Sp1to Sp3are each independently a single bond or a spacer group, preferably having one of the definitions of Sp given above and below, and more preferably -(CH2)PI-, -(CH2)PI-O-, -(CH2)PI-CO-O- or -(CH2)PI-O-CO-O-, in Foreignfiling text P24-159

[0684] - 122 - which p1 is an integer from 1 to 12, and where the bond to the adjacent ring in the latter groups is via the oxygen atom, where one of the P1-Sp1- , P2-Sp2- and P3-Sp3- radicals may also be Raa,

[0685] Raais H, F, Cl, CN or straight-chain or branched alkyl having 1 to 25 carbon

[0686] 5 atoms, in which one or more non-adjacent CH2 groups may each independently also be replaced by C(R°)=C(R00)-, -C=C-, -N(R°)-, -O-, - S-, -CO-, -CO-O-,

[0687] -O-CO-, -O-CO-O-, in such a way that no oxygen and / or sulphur atoms are joined directly to one another, and in which one or more hydrogen atoms may also be replaced by F, Cl, CN or P1-Sp1-, more preferably straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, or alkylcarbonyloxy having 1 to 12 carbon atoms (where the alkenyl and alkynyl radicals have at least two and the branched radicals at least

[0688] 15 three carbon atoms),

[0689] R° and R°° are the same or different at each instance and are each independently H or alkyl having 1 to 12 carbon atoms,

[0690] 20 Ryand Rzare each independently H, F, CH3 or CF3,

[0691] Z1is -O-, -CO-, -C(RyRz)- or -CF2CF2-,

[0692] Z2and Z3are each independently -CO-O-, -O-CO-, -CH2O-,

[0693] -OCH2-, -CF2O-, -OCF2- or -(CH2)n-, where n is 2, 3 or 4,

[0694] L is the same or different at each instance and has the meaning given under formula M above, preferably is F, Cl, CN, or straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl,

[0695] 30 alkynyl, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy having 1 to 12 carbon atoms, preferably F,

[0696] L' and L" are each independently H, F or Cl,

[0697] X1to X3are independently of one another -CO-O-, -O-CO- or a single bond, Foreignfiling text P24-159

[0698] - 123 - r is 0, 1 , 2, 3 or 4, s is 0, 1 , 2 or 3, t is 0, 1 or 2, and

[0699] 5 x is O or l .

[0700] Suitable polymerisable compounds are listed, for example, in Table G and are shown in the respective Examples.

[0701] The polymerisable compounds have at least one polymerisable group. The polymerisable group is preferably selected from CH2=CW1-COO-,

[0702] O

[0703] 150

[0704] W2HC - CH - , W2^^ (C H2)kr° CH2=CW2-(O)ki-, CH3-CH=CH-O-, (COO)ki-Phe-(O)k2-, Phe-CH=CH-, HOOC-, OCN-, with W1being H, Cl, CN, phenyl or

[0705] 20 alkyl with 1 to 5 C atoms, in particular H, Cl or CH3, W2and W3being independently of each other H or alkyl with 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, Phe being 1 ,4-phenylene and ki and k2being independently of each other 0 or 1. The polymerisable or reactive group is preferably selected from a vinyl group, an acrylate group, a methacrylate group, a fluoroacrylate group, an oxetane group or an epoxy group, especially preferably an acrylate group or a methacrylate group.

[0706] In an embodiment, non-mesogenic monomers are included in the medium in addition to the one or more RMs. Preferably, one or more polymerisable compounds, either the non-mesogenic monomers or the RMs or both, are selected from acrylates,

[0707] 30 methacrylates, fluoroacrylates and vinyl acetate, wherein the composition more preferably further comprises one or more direactive and / or trireactive polymerisable compounds, preferably selected from diacrylates, dimethacrylates, triacrylates and trimethacrylates.

[0708] In a preferred embodiment the medium as used according to the invention comprises one or more non-mesogenic monoacrylates, particularly preferably one or more Foreignfiling text P24-159

[0709] - 124 - compounds selected from methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, nonyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxy-butyl acrylate and isobornyl acrylate.

[0710] 5 Additionally or alternatively the medium as used according to the invention preferably comprises one or more non-mesogenic monomethacrylates, particularly preferably one or more compounds selected from methyl methacrylate, ethyl methacrylate, propyl methacrylate, ispropyl methacrylate, butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, nonyl methacrylate, dodecyl methacrylate, 2-ethyl- hexyl methacrylate, 2-hydroxy-ethyl methacrylate, 2-hydroxy-butyl methacrylate, isobornyl methacrylate and 1-adamantyl methacrylate.

[0711] It is particularly preferred that at least one crosslinking agent is added to the medium, i.e. a polymerisable compound containing two or more polymerisable groups, wherein

[0712] 15 preferably di- or multireactive RMs are used.

[0713] In this respect, direactive and / or multireactive compounds can serve to form polymer networks of their own and / or to crosslink polymer chains formed substantially from polymerising monoreactive compounds.

[0714] 20

[0715] Alternatively or additionally, conventional crosslinkers known in the art can be used. It is particularly preferred to additionally provide direactive or multireactive acrylates and / or methacrylates. Particularly preferred compounds are selected from ethylene diacrylate, propylene diacrylate, butylene diacrylate, pentylene diacrylate, hexylene diacrylate, glycol diacrylate, glycerol diacrylate, pentaerythritol tetraacrylate, ethylene dimethacrylate, also known as ethyleneglycol dimethacrylate, propylene diamethcrylate, butylene dimethacrylate, pentylene dimethacrylate, hexylene dimethacrylate, tripropylene glycol diacrylate, glycol dimethacrylate, glycerol dimethacrylate, trimethylpropane trimethacrylate and pentaerythritol triacrylate.

[0716] 30

[0717] The ratio of monoreactive monomers and di- or multireactive monomers can be favourably set and adjusted to influence the properties of the polymeric component to be formed.

[0718] Suitable and conventionally used initiators, in particular photoinitiators, can be added to the medium to facilitate the reaction, for example azo compounds or organic peroxides Foreignfiling text P24-159

[0719] - 125 - such as Luperox type initiators. Moreover, suitable conditions for the polymerisation and suitable types and amounts of initiators are known in the art and are described in the literature. In case a polymerisation initiator is included in the medium, the use of a photoinitiator is preferred.

[0720] 5 For example, when polymerising by means of UV light, a photoinitiator can be used that decomposes under UV irradiation to produce free radicals or ions that start the polymerisation reaction. For polymerising acrylate or methacrylate groups preferably a radical photoinitiator is used. For polymerising vinyl, epoxide or oxetane groups preferably a cationic photoinitiator is used. It is also possible to use a thermal polymerisation initiator that decomposes when heated to produce free radicals or ions that start the polymerisation. Typical radical photoinitiators are for example the commercially available Irgacure®, e.g. Irgacure 651 (available from BASF, containing 2,2-dimethoxy-1 ,2-diphenyl ethan-1-one), or Darocure® (Ciba Geigy AG, Basel, Switzerland). A typical cationic photoinitiator is for example UVI 6974 (Union Carbide).

[0721] 15 Further useful photoiniators include a-aminoketones, e.g. Irgacure 907, coumarins, phosphine oxides, e.g. Irgacure 2100, acyl phosphines, e.g. Irgacure 819.

[0722] In a particular embodiment the added polymerisation initiator, preferably photoinitiator, comprises, preferably consists of, one or more mesogenic polymerisation initiators,

[0723] 20 preferably one or more mesogenic photoinitiators, i.e. one or more reactive compounds which can initiate polymerisation and which themselves have anisotropic and mesogenic properties.

[0724] However, according to a particularly preferred embodiment no polymerisation initiator, in particular no photoinitiator, is used. In certain cases this may improve the VHR and reduce the tendency to produce ions in the switching layer. This can contribute to obtaining and maintaining a modulation material and a light valve having good reliability and stability. Therefore, according to a preferred embodiment in the liquid-crystalline medium for use in the method according to the invention no polymerisation initiator is

[0725] 30 added.

[0726] In order to maintain and achieve a good VHR, preferably impurities in the reaction products of the polymerisation are kept at a minimum or are substantially avoided. In particular, residual reactive species and charged contaminants are suitably and preferably kept at a minimum. For example, in case UV polymerisation is carried out, in a preferred embodiment light with a comparatively long wavelength which is Foreignfiling text P24-159

[0727] - 126 - approaching the visible spectrum is used, preferably UV light in the range from 340 nm to 380 nm, and even more preferably from 360 nm to 380 nm is advantageously used. This way unwanted photodegradation or decomposition of components of the LC medium, and especially of the preferably added one or more dichroic dyes, may be avoided or at least minimized. In case a photoinitiator is used, the irradiation

[0728] 5 wavelength and the photoinitiator can be suitably matched or adjusted.

[0729] In the preferred case where no photoinitiator is used, the wavelength range of the light may be set such that at least some of the polymerisable compounds can undergo a photoreaction and initiate the polymerisation reaction by themselves, while furthermore degradation or decomposition of non-reactive components of the LC medium and in particular of the optionally added one or more dichroic dyes may be avoided or at least minimized. Obtaining and setting of the desired wavelength range can be achieved by conventional methods known in the art, e.g. by using optical filters, in particular edge filters or bandpass filters.

[0730] 15

[0731] It has surprisingly been found that the medium as used according to the invention can be favourably used to produce polymeric structures in situ by providing the one or more polymerisable mesogenic compounds as set forth above and below in the medium. In addition, by preferably and suitably choosing the one or more polymerisable mesogenic

[0732] 20 compounds together with one or more dichroic dyes and by setting and adjusting the wavelength of the light used in the photopolymerisation with respect to the absorption characteristics of the dichroic dyes, an efficient and robust method can be provided which gives the desired polymerisation and polymeric products in the material while furthermore preserving the dichroic dyes and their performance. In an embodiment the wavelength or respectively the wavelength spectrum of the irradiation light is chosen such that an overlap with the absorption bands of the dichroic dyes is minimized.

[0733] The polymerisable compounds in the medium may be chosen such that after the polymerisation a stable system is obtained, which e.g. can be stable in further

[0734] 30 processing steps such as thermal heating steps, wherein a good VHR may be maintained.

[0735] In a preferred aspect of the invention the medium is used to prepare a modulation material which comprises a polymeric component, in particular a polymeric network, wherein the polymeric component is obtained by or respectively obtainable from polymerising the polymerisable compound(s) as set forth above and below. Foreignfiling text P24-159

[0736] - 127 -

[0737] The provision of the polymer component as defined herein may be useful in stabilizing one or more states or phases of the LC medium. Alternatively or additionally, the provision of the polymer component as defined herein may be useful for producing scattering or light diffusion in one of the optical states of the switchable light valve.

[0738] 5

[0739] Preferably, the polymer component is contained in the medium or respectively the material as defined herein in an amount, based on the overall contents of the medium, in the range from 3% by weight to 20% by weight, more preferably in the range from 6% by weight to 12% by weight.

[0740] The polymer component can contribute to the advantageous properties of the obtainable material. For example, the polymer component may contribute to a significantly more effective hazy or opaque state. It may also contribute to achieving the fast switching times.

[0741] 15

[0742] Furthermore, the polymeric component as provided in the material can favourably influence the scattering efficiency and appearance, e.g. in terms of uniformity and viewing angle dependence. Thereby colour artefacts which may arise under oblique viewing angles can be significantly reduced.

[0743] 20

[0744] In a preferred embodiment the modulation material comprises the liquid-crystalline medium and the polymer component, where the polymer component comprises a polymer network which is obtained by polymerisation of reactive mesogens, where the reactive mesogens preferably contain at least one group selected from acrylate groups, particularly preferably from monoacrylate groups, diacrylate groups or triacrylate groups, vinyl ether groups and epoxide groups. Compounds containing acrylate group(s) as used herein comprise acrylic monomers, methacrylic monomers, and mixtures of such monomers.

[0745] 30 Polymerisation can be carried out using conventional methods. The polymerisation can be carried out in one or more steps. Preferably polymerisation of the polymerisable compound(s) is achieved by exposure to actinic radiation, wherein exposure to actinic radiation means irradiation with light, like UV light, visible light or IR light, irradiation with X-rays or gamma rays, or irradiation with high-energy particles, such as ions or electrons. In a preferred embodiment free radical polymerisation is carried out. Foreignfiling text P24-159

[0746] - 128 -

[0747] For the photopolymerisation the use of UV light is preferred. It is also possible to use visible light in addition to or instead of UV light, in particular violet or blue light. For example, light in the spectral range from 340 nm to 420 nm, preferably from 360 nm to 405 nm may be used. It is also possible to only use visible light, in particular in the range from 380 nm to 415 nm, for example using visible light from a laser source or an

[0748] 5 LED source.

[0749] Polymerisation can be carried out at a suitable temperature. In an embodiment polymerisation is performed at a temperature below the clearing point of the mesogenic mixture. In an alternative embodiment it is however also possible to carry out the polymerisation at or above the clearing point.

[0750] Preferably polymerisation is carried out by photoirradiation, i.e. with light, preferably UV light. As a source for actinic radiation, for example a single UV lamp or a set of UV lamps can be used. When using a high lamp power the curing time can be reduced.

[0751] 15 Another possible source for photoradiation is a laser, like e.g. a UV laser, a visible laser or an I R laser.

[0752] In an embodiment, polymerisation is carried out by adding to the liquid crystalline host mixture, preferably the dye-doped and / or chiral liquid-crystalline host mixture, one or

[0753] 20 more polymerisable compounds, preferably comprising a di-reactive compound and optionally a suitable photoinitiator, and polymerising the polymerisable compounds by exposure to UV irradiation.

[0754] Preferably the polymerisation is carried out in electro-optical cells maintained in a predetermined state of the liquid-crystalline host mixture. In an embodiment polymerisation, preferably polymerisation using UV light, is carried out when the medium is in the homeotropic state, wherein optionally an electric field is applied.

[0755] For the photopolymerisation of the material in the layer preferably an exposure time

[0756] 30 from 30 s to 300 min, more preferably from 1 min to 240 min is used, preferably using irradiation intensities in the range from 0.01 mW / cm2to 100 mW / cm2, more preferably from 0.1 mW / cm2to 100 mW / cm2, and even more preferably from 0.5 mW / cm2to 75 mW / cm2. In a particular embodiment preferred time periods for photopolymerisation and in particular preferred UV exposure times are in the range from 1 minute to 120 minutes, more preferably from 5 minutes to 60 minutes and in particular from 10 Foreignfiling text P24-159

[0757] - 129 - minutes to 30 minutes, wherein the UV light intensities are preferably in the range from 1 mW / cm2to 50 mW / cm2.

[0758] Photopolymerisation may be carried out at room temperature, but in an alternative embodiment it is preferred to perform photopolymerisation at elevated temperatures.

[0759] 5

[0760] Therefore, in an embodiment a thermal pre-heating step is carried out before the photopolymerisation to raise the temperature above ambient room temperature. In this case it is preferred to set and maintain a temperature below the clearing point. This way polymerisation can be performed at a higher temperature with the medium however having a nematic or respectively chiral nematic phase.

[0761] In a preferred embodiment one or more dichroic dyes are provided in the material and in particular in the liquid-crystalline medium of the switching layer, preferably in solution. This provision can favourably contribute to adjusting and minimizing the light

[0762] 15 transmittance especially in the opaque state as desired, while optionally also giving the possibility to provide a coloured opaque state.

[0763] Preferably the liquid-crystalline medium contains one or more pleochroic dyes, in particular one or more dichroic dyes, preferably in an amount from 0.05% by weight to

[0764] 20 10% by weight, more preferably from 0.1% by weight to 5% by weight, and in particular from 0.2% by weight to 3% by weight.

[0765] The one or more dichroic dyes preferably have suitable solubility, stability and reliability in liquid-crystalline media. In addition, the dyes preferably exhibit a favourably large extinction coefficient, preferably within the visible light spectrum and / or within the NIR spectrum, in particular within the visible light spectrum.

[0766] The concentration of the dye(s) is preferably chosen such that optionally photopolymerisation of added RMs and / or other reactive monomers can be carried out

[0767] 30 effectively and efficiently, while furthermore ensuring the proper performance of the obtained modulation material, in particular in terms of the desired colour and dimming effects.

[0768] The dyes preferably exhibit an absorption maximum at a wavelength in the visible or NIR spectrum, more preferably at a wavelength in the visible light spectrum. Foreignfiling text P24-159

[0769] - 130 -

[0770] The dichroic dyes can favourably be used as guest compounds in liquid-crystalline host mixtures. Therefore, in a preferred embodiment the dyes are dissolved in the LC medium.

[0771] In such a guest-host system, the LC medium comprises one or more dichroic dyes in

[0772] 5 addition to the liquid crystal host. Owing to the directional dependence of the absorption by the dye molecules, the transmissivity of the dye-doped liquid crystal to light can be modulated when the dyes change their alignment together with the liquid crystal host.

[0773] In an embodiment the one or more dichroic dyes are positive dichroic dyes, i.e. dyes which have a positive degree of anisotropy R.

[0774] The degree of anisotropy R is determined for the LC mixture comprising the dye from the values of the extinction coefficients for parallel and perpendicular alignment of the

[0775] 15 molecules relative to the direction of the polarisation of the light.

[0776] According to the invention the degree of anisotropy R preferably is greater than 0.5, more preferably greater than 0.6, even more preferably greater than 0.7, and in particular greater than 0.8.

[0777] 20

[0778] The absorption preferably reaches a maximum when the polarisation direction of the light is parallel to the direction of the longest molecular elongation of the dichroic dye compounds, and it preferably reaches a minimum when the polarisation direction of the light is perpendicular to the direction of the longest molecular elongation of the dichroic dye compounds.

[0779] In a preferred embodiment the liquid-crystalline medium comprises at least one dichroic dye. The liquid-crystalline medium preferably comprises one, two, three, four, five, six, seven, eight, nine or ten dichroic dyes. In a particularly preferred embodiment

[0780] 30 the liquid-crystalline medium comprises at least three different dichroic dyes.

[0781] The absorption spectra of the dichroic dyes preferably complement one another in such a way that the impression of a black colour, or respectively grey colour or colourneutral appearance, arises for the eye. The preferably two or more, more preferably three or more dichroic dyes of the liquid-crystalline medium according to the invention preferably cover a large part of the visible spectrum, more preferably cover the whole Foreignfiling text P24-159

[0782] - 131 - visible spectrum. The precise way in which a mixture of dyes which appears black or grey to the eye can be prepared is known in the art and is described, for example, in M. Richter, Einfuhrung in die Farbmetrik [Introduction to Colorimetry], 2nd Edition, 1981 , ISBN 3-11-008209-8, Walter de Gruyter & Co.

[0783] 5 In another embodiment the setting of a different colour is performed, e.g. red, green or blue.

[0784] The setting of the colour location of a mixture of dyes is described in the area of colorimetry. To this end, the spectra of the individual dyes are calculated taking into account the Lambert-Beer law to give an overall spectrum and converted into the corresponding colour locations and luminance values under the associated illumination, for example illuminant D65 for daylight, in accordance with the rules of colorimetry. The position of the white point is fixed by the respective illuminant, for example D65, and is quoted in tables, for example in the reference above. Different colour locations can be

[0785] 15 set by changing the proportions of the various dyes.

[0786] According to a preferred embodiment, the medium comprises one or more dichroic dyes which absorb light in the red and NIR region, i.e. at a wavelength of 600 nm to 2000 nm, preferably in the range from 600 nm to 1800 nm, particularly preferably in the

[0787] 20 range from 650 nm to 1300 nm.

[0788] Preferably the one or more dichroic dyes are selected from azo dyes, anthraquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, perylenes, terrylenes, quaterrylenes, higher rylenes, pyrromethenes, thiadiazoles, benzothiadiazoles, nickel dithiolenes, (metal) phthalocyanines, (metal) naphthalocyanines and (metal) porphyrins. Of these, particular preference is given to azo dyes, thiadiazoles and benzothiadiazoles.

[0789] In an embodiment the dichroic dyes are preferably selected from the dye classes indi¬

[0790] 30 cated in B. Bahadur, Liquid Crystals - Applications and Uses, Vol. 3, 1992, World Scientific Publishing, Section 11.2.1 , and particularly preferably from the explicit compounds given in the table present therein.

[0791] Said dyes belong to the classes of dichroic dyes which are known in the art and have been described in the literature. Thus, for example, anthraquinone dyes are described in EP 34832, EP 44893, EP 48583, EP 54217, EP 56492, EP 59036, GB 2065158, Foreignfiling text P24-159

[0792] - 132 -

[0793] GB 2065695, GB 2081736, GB 2082196, GB 2094822, GB 2094825, JP-A 55-123673, DE 3017877, DE 3040102, DE 3115147, DE 3115762, DE 3150803 and DE 3201120, naphthoquinone dyes are described in DE 3126108 and DE 3202761, azo dyes in EP 43904, DE 3123519, WO 82 / 2054, GB 2079770, JP-A 56-57850, JP-A 56-104984, US 4308161, US 4308162, US 4340973, T. Uchida, C. Shishido, H. Seki and M. Wada:

[0794] 5 Mol. Cryst. Lig. Cryst. 39, 39-52 (1977), and H. Seki, C. Shishido, S. Yasui and T. Uchida: Jpn. J. Appl. Phys. 21, 191-192 (1982), and perylenes are described in EP 60895, EP 68427 and WO 82 / 1191. Rylene dyes as described, for example, in EP 2166040, US 2011 / 0042651, EP 68427, EP 47027, EP 60895, DE 3110960 and EP 698649.

[0795] In a preferred embodiment benzothiadiazoles, in particular as described in WO 2014 / 187529 and in WO 2020 / 104563, and / or thiadiazoloquinoxalines, in particular as described in WO 2016 / 177449 and in WO 2020 / 104563, are used as the dichroic dyes.

[0796] 15 Preferably the medium comprises one or more benzothiadiazole derivatives in combination with one or more thiadiazoloquinoxaline derivatives. Even more preferably the medium comprises two or more benzothiadiazole derivatives in combination with two or more thiadiazoloquinoxaline derivatives.

[0797] 20 In a particularly preferred embodiment the liquid-crystalline medium comprises at least one compound, preferably at least two compounds, selected from the group of compounds of the following formulae D-1 to D-10 Foreignfiling textP24-159

[0798] 30 Foreignfiling_text P24-159 Foreignfiling text P24-159

[0799] It is preferred that the medium comprises one or more compounds selected from the group of compounds of formulae D-1 , D-2, D-3, D-4 and D-5, more preferably two or more compounds selected from the group of compounds of formulae D-1, D-2, D-3,

[0800] 15 D-4 and D-5.

[0801] In an embodiment it is preferred that the medium comprises one or more compounds selected from the group of compounds of formulae D-6, D-7, D-8, D-9 and D-10, more preferably two or more compounds selected from the group of compounds of formulae

[0802] 20 D-6, D-7, D-8, D-9 and D-10.

[0803] It is particularly preferred that the medium comprises one or more compounds selected from the group of compounds of formulae D-1 , D-2, D-3, D-4 and D-5 together with one or more compounds selected from the group of compounds of formulae D-6, D-7, D-8, D-9 and D-10, more preferably two or more compounds selected from the group of compounds of formulae D-1, D-2, D-3, D-4 and D-5 together with two or more compounds selected from the group of compounds of formulae D-6, D-7, D-8, D-9 and D-10

[0804] 30 In another embodiment one or more dichroic dyes which may be present in the medium and the switching layer of the light valve are preferably selected from the following compounds Foreignfiling textP24-159 Foreignfiling textP24-159

[0805] - 137 - Foreignfiling textP24-159

[0806] -138-

[0807] -6CL-

[0808] 6SkV2d)X3) BuiiyuBisjod Foreignfiling_text P24-159 Foreignfiling text P24-159

[0809] - 141 -

[0810] 15

[0811] The dyes in switching layer can provide variability of the overall transmission and can give a coloured or respectively black appearance in the opaque state.

[0812] In a preferred embodiment, the switching layer of the device according to the invention comprises one or more quencher compounds. This is particularly preferred if the device

[0813] 30 according to the invention comprises one or more fluorescent dyes in the switching layer.

[0814] Preferably, the medium as used according to the invention contains, based on the overall contents of the medium, at least 5% by weight, more preferably at least 10% by weight and even more preferably 15% by weight of the one or more mesogenic compounds selected from the compounds of formulae I and II. In an embodiment the Foreignfiling text P24-159

[0815] - 142 - medium contains one or more compounds of formula I, preferably in an amount, based on the overall contents of the medium, in the range from 5% by weight to 30% by weight. In some cases it can be beneficial and preferred that two, three or more compounds of formula I are contained in the medium.

[0816] 5 Preferably the medium as used according to the present invention comprises a compound of formula R-5011 or S-811 as shown in Table F below.

[0817] The liquid-crystalline media according to the present invention may contain further additives in usual concentrations. The total concentration of these further constituents is in the range of 0 % to 5 %, preferably 0.1 % to 4 %, based on the total mixture. The concentrations of the individual compounds used each are preferably in the range of 0.01 % to 3 %. The concentration of these and of similar additives is herein not taken into consideration for the values and ranges of the concentrations of the liquid crystal components and compounds of the liquid crystal media. In particular, the medium may

[0818] 15 further comprise customary and suitable additives such as stabilizers, antioxidants, free radical scavengers, chain transfer agents, e.g. thioethers, and / or plasticizers, preferably in an amount from 0.01% by weight to 5% by weight. Stabilizers may be useful to further stabilize the medium and the modulation material against degradation or oxidation, e.g. due to thermal stress or light stress.

[0819] 20

[0820] Herein, unless explicitly stated otherwise, all concentrations are given in weight percent.

[0821] The liquid-crystalline media according to the present invention consist of several compounds, preferably of 3 to 30, more preferably of 4 to 20, and most preferably of 4 to 16 compounds. These compounds are mixed in a conventional way. As a rule, the required amount of the compound used in the smaller amount is dissolved in the compound used in the greater amount. In case the temperature is above the clearing point of the compound used in the higher concentration, it is particularly easy to

[0822] 30 observe completion of the process of dissolution. It is, however, also possible to prepare the media by other conventional ways, e.g. using so called pre-mixtures, which can be e.g. homologous or eutectic mixtures of compounds or using so called multibottle systems, the constituents of which are ready to use mixtures themselves.

[0823] Many of the mesogenic compounds or mixtures thereof described above and below are commercially available. These compounds are either known or can be prepared by Foreignfiling text P24-159

[0824] - 143 - methods which are known perse, as described in the literature (for example in the standard works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for said reactions. Use may also be made here of variants which are known perse, but are not mentioned here in greater detail.

[0825] 5 The media according to the invention are prepared in a manner conventional perse. In general, the components are dissolved in one another, preferably at elevated temperature. Suitable additives or substances can be added to modify the dielectric anisotropy, the viscosity and / or the alignment of the liquid-crystalline phases.

[0826] The term “alkyl” according to the present invention preferably encompasses straightchain and branched alkyl groups having 1 to 7 carbon atoms, particularly the straightchain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2 to 5 carbon atoms are generally preferred.

[0827] 15 An alkoxy can be straight-chain or branched, and it preferably is straight-chain and has 1 , 2, 3, 4, 5, 6 or 7 carbon atoms, and accordingly is preferably methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy.

[0828] The term “alkenyl” according to the present invention preferably encompasses straight¬

[0829] 20 chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straightchain groups. Particularly preferred alkenyl groups are C2-C?-1 E-alkenyl, C4-C?-3E-alkenyl, C5-C?-4E-alkenyl, Ce-CySE-alkenyl and C?-6E-alkenyl, in particular C2-C7-1 E-alkenyl, C4-C7-3E-alkenyl and Cs-C7-4E-alkenyl. Examples of preferred alkenyl groups are vinyl, 1 E-propenyl, 1 E-butenyl, 1 E-pentenyl, 1 E-hexenyl, 1 E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl and 6-heptenyl. Groups having up to 5 carbon atoms are generally preferred.

[0830] Fluorinated alkyl or alkoxy preferably comprises CF3, OCF3, CFH2, OCFH2, CF2H,

[0831] 30 OCF2H, C2F5, OC2F5, CFHCF3, CFHCF2H, CFHCFH2, CH2CF3, CH2CF2H, CH2CFH2, CF2CF2H, CF2CFH2, OCFHCF3, OCFHCF2H, OCFHCFH2, OCH2CF3, OCH2CF2H, OCH2CFH2, OCF2CF2H, OCF2CFH2, C3F7 or OC3F7, in particular CF3, OCF3, CF2H, OCF2H, C2F5, OC2F5, CFHCF3, CFHCF2H, CFHCFH2, CF2CF2H, CF2CFH2, OCFHCF3, OCFHCF2H, OCFHCFH2, OCF2CF2H, OCF2CFH2, C3F7 or OC3F7, particularly preferably OCF3 or OCF2H. Fluoroalkyl in a preferred embodiment encompasses straight-chain groups with terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, Foreignfiling text P24-159

[0832] - 144 -

[0833] 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions of fluorine are not precluded, however.

[0834] Oxaalkyl preferably encompasses straight-chain groups of the formula CnH2n+i-O-(CH2)m, where n and m are each, independently of one another, from 1 to 6.

[0835] 5 Preferably, n = 1 and m is 1 to 6.

[0836] Oxaalkyl is preferably straight-chain 2-oxapropyl (= methoxy methyl), 2-(= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

[0837] Halogen is preferably F or Cl, in particular F.

[0838] If one of the above-mentioned groups is an alkyl group in which one CH2 group has

[0839] 15 been replaced by -CH=CH-, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it is in particular vinyl, prop-1- or prop-2-enyl, but-1-, -2- or but-3-enyl, pent-1-, -2-, -3- or pent-4-enyl, hex-1-, -2-, -3-, -4- or hex- 5-enyl, hept-1-, -2-, -3-, -4-, -5- or hept-6-enyl, oct-1-, -2-, -3-, -4-, -5-, -6- or oct-7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or non-8-enyl, dec-1-,

[0840] 20 -2-, -3-, -4-, -5-, -6-, -7-, -8- or dec-9-enyl.

[0841] If one of the above-mentioned groups is an alkyl group in which one CH2 group has been replaced by -O- and one has been replaced by -CO-, these are preferably adjacent. These thus contain an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. These are preferably straight-chain and have 2 to 6 carbon atoms.

[0842] They are accordingly in particular acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pen- tanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxy-

[0843] 30 propyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(meth- oxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxy- carbonyl) propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl. Foreignfiling text P24-159

[0844] - 145 -

[0845] If one of the above-mentioned groups is an alkyl group in which one CH2 group has been replaced by unsubstituted or substituted -CH=CH- and an adjacent CH2 group has been replaced by CO, CO-O or O-CO, this can be straight-chain or branched. It is preferably straight-chain and has 4 to 13 carbon atoms. Accordingly, it is in particular acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl,

[0846] 5 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl,

[0847] 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl.

[0848] If one of the above-mentioned groups is an alkyl or alkenyl group which is monosubstituted by CN or CF3, this group is preferably straight-chain. The substitution by CN or CF3 is in any position.

[0849] 15 If one of the above-mentioned groups is an alkyl or alkenyl group which is at least monosubstituted by halogen, this group is preferably straight-chain and halogen is preferably F or Cl, more preferably F. In the case of polysubstitution, halogen is preferably F. The resulting groups also include perfluorinated groups. In the case of monosubstitution, the fluoro or chloro substituent can be in any desired position, but is

[0850] 20 preferably in the ra-position.

[0851] Compounds containing branched groups may occasionally be of importance owing to better solubility in some conventional liquid-crystalline base materials. However, they are particularly suitable as chiral dopants if they are optically active.

[0852] Branched groups of this type generally contain not more than one chain branch. Preferred branched groups are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl,

[0853] 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy,

[0854] 30 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1 -methylhexoxy or 1 -methylheptoxy.

[0855] If one of the above-mentioned groups is an alkyl group in which two or more CH2 groups have been replaced by -O- and / or -CO-O-, this can be straight-chain or branched. It is preferably branched and has 3 to 12 carbon atoms. Accordingly, it is in particular biscarboxymethyl, 2,2-biscarboxyethyl, 3,3-biscarboxypropyl, 4,4-biscarboxy- Foreignfiling text P24-159

[0856] - 146 - butyl, 5,5-biscarboxypentyl, 6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxyoctyl, 9,9-biscarboxynonyl, 10,10-biscarboxydecyl, bis(methoxycar- bonyl)methyl, 2,2-bis(methoxycarbonyl)ethyl, 3,3-bis(methoxycarbonyl)propyl, 4,4-bis- (methoxycarbonyl)butyl, 5,5-bis(methoxycarbonyl)pentyl, 6,6-bis(methoxycarbonyl)- hexyl, 7,7-bis(methoxycarbonyl)heptyl, 8,8-bis(methoxycarbonyl)octyl, bis(ethoxy-

[0857] 5 carbonyl)methyl, 2,2-bis(ethoxycarbonyl)ethyl, 3,3-bis(ethoxycarbonyl)propyl, 4,4-bis(ethoxycarbonyl)butyl or 5,5-bis(ethoxycarbonyl)pentyl.

[0858] In another aspect of the invention a switching layer is provided which comprises the medium or the modulation material according to the invention.

[0859] The switching layer as used in the light valve preferably has a thickness in the range from 1 pm to 100 pm, more preferably from 2 pm to 50 pm, even more preferably from 4 pm to 40 pm and in particular from 8 pm to 25 pm.

[0860] 15 In the light valve the switching layer is arranged between two substrates, in particular two transparent substrates.

[0861] The substrates may comprise, preferably consist of, glass or a polymer, in particular glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN),

[0862] 20 polyvinylbutyral (PVB), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide (PI), COP (cyclic olefin polymers) or TAC (triacetylcellulose).

[0863] In a particularly preferred embodiment glass substrates are used.

[0864] The finally assembled light valve can further comprise one or more layers which block UV light.

[0865] Advantageously the light valve can be produced by the facile and efficient process described herein.

[0866] 30

[0867] In a preferred preparation method the liquid-crystalline medium which optionally comprises the one or more polymerisable mesogenic compounds is provided as a layer between two opposing transparent substrates which are each provided with an electrode. Preferably the electrodes are arranged as conductive layers above the inner surface of each substrate, wherein more preferably the conductive layers are respectively arranged on a passivation layer, even more preferably arranged between Foreignfiling text P24-159

[0868] - 147 - passivation layers, and wherein optionally alignment layers are further provided which are in direct contact with the liquid-crystalline medium.

[0869] In case one or more polymerisable mesogenic compounds are included in the medium, subsequently the one or more polymerisable mesogenic compounds are polymerised,

[0870] 5 in particular using photopolymerisation. Preferably, the photopolymerisation of the one or more polymerisable mesogenic compounds is carried out in the presence of an electric field in the layer, preferably an alternating current electric field, wherein preferably the layer has a thickness in the range from 2 pm to 50 pm, more preferably from 5 pm to 25 pm. In a particular embodiment the applied electric field induces a homeotropic alignment in the layer comprising the liquid-crystalline medium.

[0871] In the method described herein polymerising is preferably carried out by photopolymerisation, preferably using UV light. In a particularly preferred embodiment during the polymerisation, at least temporarily, an electric field is applied to induce an

[0872] 15 alignment of the medium, preferably a homeotropic alignment. The application of a voltage to set a predetermined orientation during polymerisation can favourably influence the product properties of the switching layer and the light valve. For example, inducing a homeotropic alignment during polymerisation can contribute to achieving a homogeneous low-haze clear state, while furthermore a homogeneous and suitably

[0873] 20 strong haze can be obtained in the opaque state.

[0874] It is possible to control the temperature during photopolymerisation, for example in a range from 20°C to 100°C, preferably below the clearing point.

[0875] In a preferred embodiment the reactive mesogens are self-starting, while in another embodiment a photoinitiator is used to trigger the polymerisation.

[0876] For the photopolymerisation of the material in the switching layer preferably an exposure time from 30 s to 240 min, more preferably from 1 min to 120 min is used,

[0877] 30 preferably using irradiation intensities in the range from 0.01 mW / cm2to 100 mW / cm2, more preferably from 0.1 mW / cm2to 50 mW / cm2, even more preferably from 1 mW / cm2to 50 mW / cm2and in particular from 2 mW / cm2to 40 mW / cm2.

[0878] For the polymerisation several parameters may be suitably set or varied, e.g. the irradiation dose, the magnitude or respectively the frequency of the optionally applied Foreignfiling text P24-159

[0879] - 148 - voltage or respectively the electric field strength, and the amount of chiral dopant and dichroic dye in the medium.

[0880] Following the photopolymerisation, further treatments may be carried out. Preferably, a thermal treatment is carried out after the polymerisation step. The thermal treatment,

[0881] 5 i.e. an exposure to an increased temperature relative to the previous polymerisation step, may lead to further curing or further conversion rate or completion of the polymerisation. This can be beneficial in terms of the product performance and stability, in particular in that in the product the amount of residual unreacted monomer is minimized.

[0882] The optional thermal treatment step following polymerisation is preferably performed for a period of time in the range from 5 minutes to 240 minutes, more preferably from 10 minutes to 120 minutes and in particular from 20 minutes to 60 minutes. The thermal treatment preferably uses a temperature in the range from 85°C to 200°C, more

[0883] 15 preferably from 110°C to 190°C and in particular from 140°C to 180°C.

[0884] It is also possible to perform pre-treatment steps on the substrates used, for example surface treatment methods such as a UV-ozone treatment or a plasma treatment, which can improve alignment and wetting behaviour over larger areas and contribute to

[0885] 20 an improved homogeneity as well as a favourable reduction of unwanted haze in the clear state.

[0886] The method described herein is advantageously useful to produce a light valve with favourable durability, a low-haze clear state, and a state giving favourable opacity, in particular based on strong scattering and / or dimming, even in the case where only a single switching layer is used in the device.

[0887] In the present invention and especially in the following Examples, the structures of the mesogenic compounds are indicated by means of abbreviations, also called acronyms.

[0888] 30 In these acronyms, the chemical formulae are abbreviated as follows using Tables A to C below. All groups CnH2n+1. CmH2m+1 and C1H21+1 or CnH2n-1. CmH2m-1 and C1H21-1 denote straight-chain alkyl or alkenyl, preferably 1-E-alkenyl, each having n, m and I C atoms respectively. Table A lists the codes used for the ring elements of the core structures of the compounds, while Table B shows the linking groups. Table C gives the meanings of the codes for the left-hand or right-hand end groups. The acronyms are composed of the codes for the ring elements with optional linking groups, Foreignfiling text P24-159

[0889] - 149 - followed by a first hyphen and the codes for the left-hand end group, and a second hyphen and the codes for the right-hand end group. Table D shows illustrative structures of compounds together with their respective abbreviations.

[0890] Table A: Ring elements

[0891] 5 Foreignfiling textP24-159

[0892] Table B: Foreignfiling_text P24-159

[0893] - 151 -

[0894] E -CH2CH2- z -co-o-

[0895] V -CH=CH- Zl -O-CO-

[0896] X -CF=CH- O -CH2-O-

[0897] XI -CH=CF- Ol -O-CH2-

[0898] B -CF=CF- Q -CF2-O-

[0899] -C=C- QI -O-CF2-

[0900] -CF2CF2-

[0901] Table C: End groups

[0902] Left-hand side Right-hand side

[0903] Used alone

[0904] -n- CnH2n+i- -n -CnH2n+1

[0905] -nO- CnH2n+i-O- -On -O-CnH2n+1

[0906] 15 -V- CH2=CH- -V -CH=CH2

[0907] -nV- CnH2n+i-CH=CH- -nV -CnH2n-CH=CH2

[0908] -Vn- CH2=CH- CnH2n+i- -Vn -CH=CH-CnH2n+1

[0909] -nVm- CnH2n+i-CH=CH-CmH2m- -nVm -CnH2n-CH=CH-CmH2m+1

[0910] -N- NEC- -N -CEN

[0911] 20 -S- S=C=N- -S -N=C=S

[0912] -F- F- -F -F

[0913] -M- CFH2- -M -CFH2

[0914] -D- CF2H- -D -CF2H

[0915] 25 -T- CF3- -T -CF3

[0916] -MO- CFH2O - -OM -OCFH2

[0917] -DO- CF2HO - -OD -OCF2H

[0918] -TO- CF3O - -OT -OCF3

[0919] -FXO- CF2=CH-O- -OXF -O-CH=CF2 Foreignfiling text P24-159

[0920] - 152 -

[0921] -...V...- CH=CH- -...V... -CH=CH-

[0922] -...Z...- -CO-O- -...Z... -CO-O-

[0923] -...Zl...- -O-CO- -...Zl... -O-CO-

[0924] -...K...- -CO- -...K... -CO-

[0925] -...W...- -CF=CF- -...W... -CF=CF-

[0926] 5 wherein n and m each denote integers, and the three dots “...” are placeholders for other abbreviations from this table.

[0927] The following table shows illustrative structures together with their respective abbreviations. These are shown in order to illustrate the meaning of the rules for the abbreviations. They furthermore represent compounds which may be preferably used.

[0928] Table D: Illustrative structures

[0929] CC-n-mVI Foreignfiling textP24-159

[0930] -153- Foreignfiling textP24-159

[0931] -154-

[0932] CCP-n-m

[0933] CPP-n-Om Foreignfiling textP24-159

[0934] -155- Foreignfiling textP24-159

[0935] -156-

[0936] PGIGP-n-m Foreignfiling textP24-159

[0937] - 157 -

[0938] CCG-V-F Foreignfiling textP24-159

[0939] -158-

[0940] PGIGI-n-F Foreignfiling textP24-159

[0941] -159- Foreignfiling textP24-159

[0942] -160- Foreignfiling textP24-159 Foreignfiling_text P24-159

[0943] - 162 - Foreignfiling textP24-159

[0944] -163-

[0945] CCP-V-m Foreignfiling textP24-159

[0946] -164-

[0947] CPQY-n-(O)m Foreignfiling textP24-159

[0948] -165-

[0949] CPYC-n-m

[0950] DFDBC-n(O)-(O)m Foreignfiling textP24-159

[0951] BCH-7F.F.F Foreignfiling text P24-159

[0952] PPC(CN)-n-m CPP(F,CN)-n-Om wherein n, m and I preferably, independently of one another, denote 1 to 10, more preferably 1 to 7.

[0953] 15

[0954] In an embodiment the LC media according to the present invention preferably comprise three or more, more preferably five or more compounds shown in Table D.

[0955] Table E

[0956] 20

[0957] Table E shows illustrative stabilizers which can be added to the LC media according to the invention, wherein n denotes an integer from 1 to 12, preferably 1, 2, 3, 4, 5, 6, 7 or 8, terminal methyl groups are not shown. Foreignfiling textP24-159 Foreignfiling textP24-159

[0958] -169- Foreignfilingjext P24-159 Foreignfiling_text P24-159 Foreignfiling_text P24-159 Foreignfiling text P24-159

[0959] - 173 -

[0960] 15

[0961] The LC media preferably comprise 0 to 10% by weight, in particular 1 ppm to 5% by weight, and particularly preferably 1 ppm to 1% by weight of stabilizers.

[0962] Table F

[0963] 20

[0964] Table F shows illustrative compounds which can preferably be used as chiral dopants in the mesogenic media according to the present invention.

[0965] CM 21 R / S-811 Foreignfiling text P24-159

[0966] - 174 -

[0967] The LC media preferably comprise 0 to 10% by weight, in particular 0.01 to 5% by weight, and particularly preferably 0.1 to 3% by weight of chiral dopants. The LC media preferably comprise one or more dopants selected from the group consisting of the compounds from Table F.

[0968] 30

[0969] The mesogenic media according to the present invention preferably comprise two or more, preferably four or more, compounds selected from the compounds shown in the above tables D to F.

[0970] Table G Foreignfiling text P24-159

[0971] - 175 -

[0972] Table G shows illustrative reactive mesogenic compounds, also referred to as polymerisable mesogenic compounds, which can be used in the LC media and materials in accordance with the present invention. Foreignfiling textP24-159

[0973] -176-

[0974] RM-11 RM-12

[0975] RM-25 RM-26 Foreignfiling textP24-159

[0976] - 177 -

[0977] RM-37 RM-38 Foreignfiling textP24-159

[0978] -178-

[0979] RM-49 Foreignfiling textP24-159 Foreignfiling textP24-159

[0980] -180-

[0981] RM-60 RM-61

[0982] RM-74 Foreignfiling textP24-159

[0983] - 181 -

[0984] RM-86 RM-87 Foreignfiling textP24-159

[0985] - 182 - Foreignfiling textP24-159

[0986] -183-

[0987] RM-98 RM-99 Foreignfiling textP24-159

[0988] -184-

[0989] RM-104 Foreignfiling textP24-159

[0990] -185-

[0991] 30 Foreignfiling textP24-159 Foreignfiling_text P24-159 Foreignfiling textP24-159

[0992] RM-139 RM-140 Foreignfiling textP24-159

[0993] -189-

[0994] RM-151 RM-152 Foreignfiling textP24-159

[0995] -190-

[0996] RM-157 RM-158 Foreignfiling_text P24-159 Foreignfiling text P24-159

[0997] In a preferred embodiment, the materials and media according to the invention comprise one or more polymerisable compounds, preferably selected from the polymerisable compounds of the formulae RM-1 to RM-185. Of these, compounds

[0998] 20 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.

[0999] In particular embodiments an initiator or a mixture of two or more initiators is added for the polymerisation. The initiator or initiator mixture is preferably added in amounts of 0.001% to 2% by weight, based on the mixture. A suitable initiator is, for example, lrgacure®651 (from BASF).

[1000] 30 In particular embodiments it may be desirable to diminish the amount of perfluorocarbons and to preferably use polymerisable compounds which further contribute to environmental sustainability.

[1001] In a preferred embodiment of the present invention, the mesogenic media comprise one or more compounds selected from the group of the compounds from Table G. Foreignfiling text P24-159

[1002] - 193 -

[1003] Table H

[1004] Table H shows self-alignment additives which can preferably be used in the LC media, in particular for SA-VA and SA-FFS devices according to the present invention, in particular together with the polymerisable compounds:

[1005] 5 Foreignfiling_text P24-159

[1006] -194- Foreignfiling_text P24-159

[1007] -195- Foreignfiling_text P24-159

[1008] -196- Foreignfiling textP24-159 Foreignfiling_text P24-159

[1009] -198- Foreignfiling_text P24-159

[1010] -199- Foreignfiling_text P24-159

[1011] -200- Foreignfiling textP24-159

[1012] -201 - Foreignfiling_text P24-159 Foreignfiling text P24-159

[1013] - 203 -

[1014] In a preferred embodiment, the LC media and materials and the devices according to the present invention comprise one or more SA additives selected from formulae SA-1 to SA-48, preferably from formulae SA-14 to SA-48, very preferably from formulae SA- 20 to SA-34 and SA-44, in particular in combination with one or more RMs.

[1015] The liquid-crystalline media as used according to the present invention comprise preferably four or more, more preferably six or more, even more preferably seven or more, and particularly preferably eight or more compounds selected from the group of

[1016] 15 compounds of Table D, preferably compounds of three or more different formulae selected from the group of formulae of Table D. It is particularly preferred that the medium additionally contains one, two or more compounds selected from the group of formulae of Table E. Even more preferably the medium further contains one, two or more compounds selected from the group of formulae of Table G.

[1017] 20

[1018] The following examples are merely illustrative of the present invention and they should not be considered as limiting the scope of the invention in any way. The examples and modifications or other equivalents thereof will become apparent to those skilled in the art in the light of the present disclosure.

[1019] However, the physical properties and compositions shown in the following illustrate which properties can be achieved and in which ranges they can be modified. Especially the combination of the various properties, which can be preferably achieved, is thus well defined.

[1020] 30

[1021] Examples

[1022] In the Examples,

[1023] Vo denotes threshold voltage, capacitive [V] at 20°C, nedenotes extraordinary refractive index at 20°C and 589 nm, n0denotes ordinary refractive index at 20°C and 589 nm, Foreignfiling text P24-159

[1024] - 204 -

[1025] An denotes optical anisotropy at 20°C and 589 nm, s denotes dielectric permittivity parallel to the director at 20°C and 1 kHz, si denotes dielectric permittivity perpendicular to the director at 20°C and 1 kHz,

[1026] As denotes dielectric anisotropy at 20°C and 1 kHz,

[1027] 5 cl.p. , T(N, I) denotes clearing point [°C], yi denotes rotational viscosity measured at 20°C [mPa-s], determined by the rotation method in a magnetic field,

[1028] Ki denotes elastic constant, "splay" deformation at 20°C [pN],

[1029] K2 denotes elastic constant, "twist" deformation at 20°C [pN],

[1030] K3 denotes elastic constant, "bend" deformation at 20°C [pN] .

[1031] The term "threshold voltage" for the present invention relates to the capacitive threshold (Vo), unless explicitly indicated otherwise. In the Examples, as is generally usual, the optical threshold can also be indicated for 10% relative contrast (V ).

[1032] 15

[1033] Liquid crystal mixtures and composite systems are realized with the compositions and properties as given in the following. Their properties and optical performance are investigated.

[1034] 20 Reference Example 1

[1035] A liquid-crystal base mixture B-1 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

[1036] CC(CN)-4-7 14.00% clearing point [°C]: 114.6

[1037] CC(CN)-5-5 14.00% An [589 nm, 20°CJ: 0.046

[1038] CC(CN)-3-3 6.00% ne[589 nm, 20°CJ: 1.52

[1039] CCZC-3-3 3.00% As [1 kHz, 20°CJ: -5.2

[1040] 30

[1041] CCZC-3-5 3.00% si [1 kHz, 20°CJ: 8.5

[1042] CCZC-4-3 3.00%

[1043] CCZC-4-5 3.00%

[1044] CC-3-O1 11.00%

[1045] CC-5-O1 4.00%

[1046] CC-5-02 4.00% Foreignfiling text P24-159

[1047] - 205 -

[1048] CC(CN)C-3-5 10.00%

[1049] CC(CN)C-5-5 12.00%

[1050] CC(CN)C-5-3 10.00%

[1051] CCZPC-3-3 3.00%

[1052] E 100.00%

[1053] 5

[1054] Reference Example 2

[1055] A liquid-crystal base mixture B-2 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

[1056] CPP-3-2 16.00% clearing point [°C]: 103.8

[1057] CC-3-O1 8.00% An [589 nm, 20°C]:0.130

[1058] CCY-3-01 5.00% ne[589 nm, 20°C]: 62

[1059] 15 CCY-3-02 8.00% As [1 kHz, 20°C]: .42

[1060] CCY-3-03 8.00% si [1 kHz, 20°C]: 7.9

[1061] CCY-4-02 8.00%

[1062] CCY-5-02 8.00%

[1063] CY-3-04 13.00%

[1064] 20 CY-5-02 10.00%

[1065] PYP-2-3 16.00%

[1066] E 100.00%

[1067] Reference Example 3

[1068] A liquid-crystal base mixture B-3 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

[1069] 30 CPG-3-F 8.00% clearing point [°C]: 114

[1070] CPG-5-F 8.00% An [589 nm, 20°C]: 0.130

[1071] CPU-5-F 14.00% ne[589 nm, 20°C]: 1.62

[1072] CPU-7-F 11.00% As [1 kHz, 20°C]: 10.0

[1073] CP-5-N 18.00% si [1 kHz, 20°C]: 4.0

[1074] CP-7-N 13.00% Foreignfiling text P24-159

[1075] - 206 -

[1076] CCGU-3-F 7.00%

[1077] CC-3-03 2.00%

[1078] CBC-33F 4.00%

[1079] CBC-53F 4.00%

[1080] CBC-55F 3.00%

[1081] 5 CCZPC-3-3 3.00%

[1082] CCZPC-3-4 3.00%

[1083] CCZPC-3-5 2.00%

[1084] E 100.00%

[1085] Example 1

[1086] A mixture H-1 is prepared by mixing 99.97% of mixture B-1 as described in Reference

[1087] Example 1 above with 0.03% of the compound of formula , which in the following will be referred to as

[1088] 20 ST-1. A mixture M-1 is prepared by mixing 93.09% of mixture H-1 with 0.81% of compound of formula DD-1 DD-1 ,

[1089] 30 0.91% of compound of formula DD-2 Foreignfiling text P24-159

[1090] - 207 -

[1091] 0.51% of compound of formula DD-3

[1092] 0.60% of compound of formula DD-5 Foreignfiling text P24-159

[1093] - 208 -

[1094] 1.26% of compound of formula DD-6

[1095] DD-6 and 1.48% of compound of formula DD-7

[1096] A mixture M-1.1 is prepared by mixing 98.98% of mixture M-1 with 1.02% of the chiral dopant S-811 as described in Table F above.

[1097] The mixture M-1.1 is filled into an electro-optical cell, wherein the cell has a thickness of 8 pm and a vertical alignment in the absence of an electric field and wherein in the presence of an electric field a supertwisted nematic configuration is obtained.

[1098] In the absence of an electric field the cell has a transmission of visible light of 62% and

[1099] 30 in the presence of an electric field (at 60V) has a transmission of visible light of 16%. The device exhibits a favourable contrast between the bright state and the dark state.

[1100] The mixture M-1.1 is well suited for the use in light valves and in particular in spatial light modulators for occlusion handling. In particular, the optical shutter can give an optically transparent state with high transmissivity without an applied voltage which Foreignfiling text P24-159

[1101] - 209 - gives both power efficiency and optimized visibility in the transparent state. This is particularly beneficial for wearable AR applications.

[1102] Example 2

[1103] 5 A mixture M-2 is prepared by mixing 98.609% of mixture B-2 as described in Reference Example 2 above with 0.204% of the compound of formula DD-1, 0.677% of the compound of formula DD-2, 0.296% of the compound of formula DD-4 and 0.214% of the compound of formula DD-6.

[1104] The mixture M-2 is filled into an electro-optical cell, wherein the cell has a thickness of 25 pm and a vertical alignment in the absence of an electric field.

[1105] In the absence of an electric field the cell has a transmission of visible light of 69% and in the presence of an electric field (at 60V) has a transmission of visible light of 39%.

[1106] 15 The device exhibits a suitable contrast between the bright state and the dark state.

[1107] The mixture M-2 is well suited for the use in light valves and in particular in spatial light modulators for occlusion handling.

[1108] 20 Example 3

[1109] A mixture M-3 is prepared by mixing 94.00% of mixture B-2 as described in Reference

[1110] Example 2 above with 6.00% of the compound of formula , which in the following will be referred to as RM-1. A mixture M-3.1 is prepared by mixing 99.00% of mixture M-3 with 1.00% of the photoinitiator Irgacure® 651 Foreignfiling text P24-159

[1111] - 210 -

[1112] , available from Ciba, Switzerland, and which in the

[1113] 5 following will be referred to as IRG-651.

[1114] The mixture M-3.1 is filled into an electro-optical cell, wherein the cell has a thickness of 25 pm and a vertical alignment in the absence of an electric field.

[1115] The cell is preheated to 40°C. Subsequently polymerisation is carried out at 40°C by irradiating the cell with UV light (Hdnle UV Cube with intensity cut-off below 340 nm, 30 mW / cm2light intensity) for 60 minutes to obtain a polymer network in situ.

[1116] In the absence of an electric field the obtained cell has an optically transparent state

[1117] 15 with a transmission of visible light of 86% and a haze of 10%. In the presence of an electric field (at 60V) the obtained cell has an opaque state with a transmission of visible light of 78% and a haze of 95%.

[1118] The cell in the opaque state can effectively obscure information such as printed text

[1119] 20 placed behind the cell.

[1120] The mixture M-3.1 is well suited for the use in light valves and in particular in spatial light modulators for occlusion handling.

[1121] Example 4

[1122] A mixture M-4 is prepared by mixing 95.609% of mixture B-2 as described in Reference Example 2 above with 0.204% of the compound of formula DD-1, 0.677% of the compound of formula DD-2, 0.296% of the compound of formula DD-4, 0.214% of the

[1123] 30 compound of formula DD-6 and 3.000% of the compound RM-1.

[1124] The mixture M-4 is filled into an electro-optical cell, wherein the cell has a thickness of 25 pm and a vertical alignment in the absence of an electric field. Foreignfiling text P24-159

[1125] - 211 -

[1126] The cell is preheated to 40°C. Subsequently polymerisation is carried out at 40°C by irradiating the cell with UV light (Hdnle UV Cube with intensity cut-off below 340 nm, 30 mW / cm2light intensity) for 60 minutes to obtain a polymer network in situ.

[1127] In the absence of an electric field the obtained cell has an optically transparent state,

[1128] 5 and in the presence of an electric field (at 60V) the obtained cell has an opaque state with effective scattering and dimming.

[1129] In the opaque state at 60 V the obtained cell at 20°C has a Tonof 4 ms and a of 48 ms.

[1130] The cell in the opaque state can effectively obscure information such as printed text placed behind the cell.

[1131] The mixture M-4 is well suited for the use in light valves and in particular in spatial light

[1132] 15 modulators for occlusion handling.

[1133] Example 5

[1134] An electro-optical cell prepared according to Example 1 and an electro-optical cell

[1135] 20 prepared according to Example 3 are combined in a stack as a double cell.

[1136] The double cell has a very effective opaque state giving both scattering and dimming, in both cases where light enters either side of the stack.

[1137] Example 6

[1138] A mixture M-6 is prepared by mixing 95.0% of mixture B-2 as described in Reference Example 2 above with 5.0% of the compound RM-1.

[1139] 30 The mixture M-6 is filled into an electro-optical cell, wherein the cell has a thickness of 15 pm.

[1140] The cell is preheated to 40°C. Subsequently polymerisation is carried out at 40°C by irradiating the cell with UV light (Hdnle UV Cube with intensity cut-off below 340 nm, 30 mW / cm2light intensity) for 60 minutes to obtain a polymer network in situ. Foreignfiling text P24-159

[1141] - 212 -

[1142] The obtained cell has an opaque state with maximum haze at 40 V.

[1143] Example 7

[1144] A mixture M-7 is prepared by mixing 95.9% of mixture B-2 as described in Reference

[1145] 5 Example 2 above with 3.0% of the compound RM-1 , 0.5% of the compound IRG-651 and 0.6% of the self-alignment additive SA-32 shown in Table H above.

[1146] The mixture M-7 is filled into an electro-optical cell, wherein the cell has a thickness of 10 pm and is provided without polyimide alignment layers.

[1147] The cell is preheated to 40°C. Subsequently the cell is irradiated with UV light (Hdnle UV Cube with intensity cut-off below 340 nm, 20 mW / cm2light intensity) at 40°C for 10 minutes.

[1148] 15 In the absence of an electric field the obtained cell has an optically transparent state with a transmission of visible light of 88% and a haze of 4%. In the presence of an electric field (at 60V) the obtained cell has an opaque state with a transmission of visible light of 78% and a haze of 89%.

[1149] 20 The cell in the opaque state can effectively obscure information such as printed text placed behind the cell.

[1150] The mixture M-7 is well suited for the use in light valves, in particular light valves using curved substrates, and in particular in spatial light modulators for occlusion handling.

[1151] Example 8

[1152] A mixture M-8 is prepared by mixing 98.609% of mixture B-3 as described in Reference Example 3 above with 0.204% of the compound of formula DD-1, 0.677% of the

[1153] 30 compound of formula DD-2, 0.296% of the compound of formula DD-4 and 0.214% of the compound of formula DD-6.

[1154] The mixture M-8 is filled into an electro-optical cell having glass substrates (0.7 mm alkali-free glass) with ITO electrodes as well as polyimide alignment layers (AL- 1054 from Japan Synthetic Rubber, planar, TN-rubbed), wherein the cell gap is 25 pm. Foreignfiling text P24-159

[1155] - 213 -

[1156] The obtained cell exhibits a favourable electro-optical performance in the opaque state and in the optically transparent state.

[1157] Example 9

[1158] 5 A mixture M-9 is prepared by mixing 87.0% of mixture B-2 as described in Reference Example 2 above with 12.5% of the compound RM-1 and 0.5% of the compound IRG- 651.

[1159] The mixture M-9 is treated analogous to the mixture M-3.1 as described in Example 3 above.

[1160] The mixture M-9 is well suited for the use in light valves and for obscuring information or objects.

[1161] 15

[1162] 20

[1163] 30

Claims

Foreignfiling text P24-159- 214 -Claims1 . A light valve which is operable in and electrically switchable between an optically transparent state and an opaque state and which comprises a switching layer containing a material, wherein the material is5 - a material which comprises a liquid-crystalline medium comprising one or more mesogenic compounds and a polymer component, wherein the polymer component is arranged as a polymer network and is obtained by or respectively obtainable from polymerisation of one or more polymerisable mesogenic compounds and wherein the polymer component is contained in the material in an amount, based on the overall contents of the material, of 20% by weight or less, and / or- a material which comprises a liquid-crystalline medium comprising one or more mesogenic compounds and one or more dichroic dyes.

152. The light valve according to claim 1 , wherein the light valve is arranged as a spatial light modulator for handling occlusion in a near-eye display.

3. The light valve according to claim 1 or 2, wherein the material comprises a liquid¬20 crystalline medium comprising one or more mesogenic compounds and one or more dichroic dyes and the polymer component as set forth in claim 1 .

4. The light valve according to one or more of claims 1 to 3, wherein the liquidcrystalline medium comprises one or more chiral compounds.

5. The light valve according to one or more of claims 1 to 4, wherein the light valve comprises two switching layers, wherein preferably both switching layers conform to the switching layer according to one or more of claims 1 to 4.30 6. The light valve according to one or more of claims 1 to 5, wherein the polymer component is obtained by photopolymerisation, preferably without the use of photoinitiators.

7. The light valve according to one or more of claims 1 to 6, wherein the light valve in the optically transparent state has a haze, preferably determined according to ASTM D 1003, of less than 10 %.Foreignfiling text P24-159- 215 -8. The light valve according to one or more of claims 1 to 7, wherein in the absence of an applied voltage the light valve is in the optically transparent state.

9. The light valve according to one or more of claims 1 to 8, wherein the liquid¬5 crystalline medium has a clearing point of 70°C or more and / or wherein the liquid-crystalline medium has a negative dielectric anisotropy.

10. The light valve according to one or more of claims 1 to 9, wherein the liquidcrystalline medium comprises one or more mesogenic compounds selected from the compounds of formulae I and II1520 whereinR1and R2denote, independently of one another, a group selected from F, Cl, CF3, OCF3, and straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms or straight-chain or branched alkenyl having 2 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen and wherein one or more CH2 groups may be, in each case independently of one another, replaced by30or -C=C- in such a manner that oxygen atoms are not linked directly to one another,Foreignfiling text P24-159n denotes 0 or 1, andA21, A31and A41denote, independently of one another,15wherein L is on each occurrence, identically or differently, halogen selected from F, Cl and Br, and30R3and R4denote, independently of one another, a group selected from F, CF3, OCF3, CN, and straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms or straight-chain or branched alkenyl having 2 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or mono- orForeignfiling text P24-159- 217 - polysubstituted by halogen and wherein one or more CH2 groups may be, in each case independently of one another, replaced by5-C=C- in such a manner that oxygen atoms are not linked directly to one another, andL1, L2and L3denote, independently of one another, H or F.

11. The light valve according to one or more of claims 1 to 10, wherein the liquidcrystalline medium comprises at least three different dichroic dyes.

12. The light valve according to one or more of claims 1 to 11 , wherein the one or more polymerisable mesogenic compounds comprise one, two or more acrylate15 and / or methacrylate groups, and wherein preferably the liquid-crystalline medium comprises at least one di- or multireactive polymerisable mesogenic compound.

13. The light valve according to one or more of claims 1 to 12, wherein the switching20 layer is in direct contact with at least one alignment layer, wherein the alignment layer is preferably obtainable from a self-alignment additive, more preferably is obtainable from photoalignment.

14. A near-eye display device comprising the light valve according to one or more of claims 1 to 13.

15. The device according to claim 14, wherein the device comprises an optical see- through display.30 16. The device according to claim 14 or 15, wherein the device is configured to provide augmented reality contents to a wearer.

17. The device according to one or more of claims 14 to 16, wherein the device comprises at least one curved substrate and / or at least one pixelated electrode.

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