Devices for adjusting light transmission

Abstract

The present invention relates to devices for regulating light transmission, in particular to switchable windows. In particular, the invention relates to window elements comprising an electrically switchable optical cell having a switchable layer containing a liquid crystal medium having a clearing point within the operating temperature of the window element. The invention also relates to liquid crystal media for use in window elements.

Description

[0001] The present invention relates to devices for regulating light transmission, in particular to switchable windows. The invention particularly relates to window elements comprising an electrically switchable optical cell having a switchable layer comprising a liquid crystal medium having a clearing point within the operating temperature of the window element. The invention also relates to liquid crystal media for use in window elements.

[0002] Devices for controlling or modulating the transmission of light are commonly used in display applications, but they can also be used, for example, in so-called smart window applications. R. Baetens et al., “Properties, requirements and possibilities of smart windows for dynamic daylight and solar energy control in buildings: A state-of-the-art review,” Solar Energy Materials & Solar Cells, 94 (2010), pp. 87-105, review various dynamic smart windows. As described herein, smart windows can use several technologies to modulate the transmission of light, such as electrochromic devices, liquid crystal devices, and electrophoretic or suspended particle devices.

[0003] Light shutters and light intensity modulators, particularly those based on liquid crystals, can be used in switchable windows for architectural, automotive, railway, avionics, and marine applications.

[0004] Light modulation or conditioning devices can in principle rely on absorption of light or scattering of light or a combination of both.

[0005] In some devices, the transmission of light can be reversibly altered, wherein the intensity of incident light can be attenuated, dimmed, or colored. Such devices can thus operate in and switch between a bright state and a dark state, i.e., between a state of relatively high light transmission and a state of relatively low light transmission.

[0006] In principle, a variety of modes or configurations can be used to provide this reversible transmission change. For twisted nematic (TN), super twisted nematic (STN) and vertical alignment (VA) liquid crystal cells, polarizers are typically used to control light transmission. Guest-host liquid crystal cells based on a liquid crystal host doped with dichroic dye molecules can also be used. These guest-host systems can be used without any polarizer to change light transmission. However, in some embodiments and applications, guest-host liquid crystal cells are also used in combination with at least one polarizer.

[0007] In other cases, scattering devices can be used to change the transmittance of light by switching between a transparent non-scattering state (i.e., an optically clear or non-hazy state) and a light-scattering state (i.e., a translucent or hazy state), which can also be perceived or appear hazy, cloudy, diffuse, or opaque. Devices operating in a scattering mode can be particularly useful for privacy windows. In this case, a privacy mode can be provided when desired by switching the device, particularly a window element, from a clear state with possible viewing contact to a scattering state that provides a visual barrier.

[0008] In principle, based on the change of phase and optical state caused by changing the temperature above the phase transition temperature (in particular the clearing point, especially the nematic-isotropic phase transition temperature), the switching of liquid crystal-based devices between different optical states can be thermally controlled, as described, for example, in WO 2011 / 134582 A1.

[0009] In an alternative design, liquid crystal-based devices can adopt different optical states using electrical switching, where an applied voltage controls the switching. Such liquid crystal-based devices, in principle, employ changes in the orientation of liquid crystal (LC) molecules between two conductive electrodes by applying an electric field that results in a change in transmittance, as described, for example, in WO 2015 / 090506 A1.

[0010] In US 2019 / 0162989 A1, a multilayer filter assembly for smart windows is described, wherein in a dynamic filter, a nematic liquid crystal layer is thermally or electrically driven.

[0011] There remains a need in the art for devices for regulating the passage of light, and in particular switchable windows that provide effective and efficient switching performance.

[0012] It is therefore an object of the present invention to provide an improved device for regulating the passage of light, in particular a window element comprising an optical box, which provides reliable and uniform switching, especially at typical operating temperatures, while also offering benefits in terms of ease of construction and energy efficiency.

[0013] Another object is to provide liquid-crystalline media which can be advantageously used in these devices.Other objects of the present invention will be apparent to those skilled in the art from the detailed description which follows.

[0014] These 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.

[0015] The present invention particularly provides the following items, including main aspects, preferred embodiments and specific features, which individually and in combination contribute to solving the above-mentioned objects and ultimately provide additional advantages.

[0016] A first aspect of the present invention provides a window element comprising a switchable optical box, which can be electrically switched between at least two optical states, and the switchable optical box comprises a switchable layer inserted between two opposing transparent substrates, wherein each substrate is provided with an electrode structure, or one of the substrates is provided with two electrode structures and the other substrate is not provided with electrodes, and wherein the switchable layer comprises a liquid crystal medium with a clearing point within the operating temperature of the window element, wherein preferably, the clearing point is in the temperature range of 5°C to 65°C, more preferably in the temperature range of 15°C to 45°C.

[0017] Preferably and advantageously, the switchable optical cartridge is operable in and switchable between a light state and a dark state.

[0018] In the present invention, it has been recognized that it may be advantageous to provide a switchable window element based on a liquid crystal cell, wherein the switching can be controlled both thermally and by applying a voltage or an electric field. Thermal switching may advantageously contribute to energy efficiency, given that the switching is temperature-dependent, for example where the switching energy is supplied by the sun as an external source and no further energy input is required. Furthermore, for temperatures well below and above the clearing point, the respective given optical state may be maintained without applying an electric field. However, electrical switching may be useful when it is desired to switch to another optical state at a temperature below or even well below the clearing point of the provided switchable layer.

[0019] Additionally, it has been recognized that the efficiency and effectiveness of thermal switching at or near the clearing point can be enhanced or improved when supplemented by electrical switching capabilities.

[0020] In this respect, it has been found that the window element can have dimensions in which temperature gradients can act, wherein such temperature gradients can be caused, for example, by the window frame acting as a heat sink, uneven illumination from the light source, partial shading, etc. Consequently, under certain conditions, a non-uniform appearance can be obtained instead of the desired uniform optical state. In particular, considering that in the case of thermal switching control the clearing point is advantageously chosen to lie within the usual operating temperature range of the switchable window, temperature gradients may lead to uneven or non-uniform thermal switching over the window area, resulting in the presence of different optical states in different areas of the window element. Such coexistence of different optical states may detract from the intended visual appearance or aesthetics, for example giving a porthole or bull's-eye pattern instead of a uniform rectangular pattern, and it also leads to generally less effective changes in the optical state, for example less overall tinting or a dimming of the body light intensity.

[0021] It has now been discovered that, particularly in these situations where non-uniform appearance may potentially occur, it is beneficial to have the ability to at least temporarily use electrical switching to provide or accelerate switching to a specified state with a desired uniform appearance or a desired transmission level. Thus, such alternative or additional optical switching by applying or removing an electric field can advantageously contribute to the reliability and robustness of switching to a desired defect-free, uniform optical state.

[0022] Unlike switching due to thermal switching alone, assisting or supplementing thermal switching with electrical switching can accelerate the transition from one transmission state to another. This arrangement can also be beneficial because the clearing point of the liquid crystal material can be less tightly controlled and the transition temperature range can be slightly wider than with thermal switching alone.

[0023] In addition to providing beneficial switching properties at different temperatures, particularly at the most typical operating temperatures, the construction of the window element according to the present invention enables both thermal and electrical switching control while advantageously utilizing only a single switching layer. This can provide further benefits in terms of economical use of materials and components, as well as ease of assembly of the device.

[0024] The configuration of the present invention also advantageously offers the possibility of using dichroic dyes to impart improved properties to the guest-host system.

[0025] Furthermore, suitably efficient and advantageous optical properties can be achieved, in particular with respect to maintaining a suitable transmittance in the bright state as well as in the dark state, thereby offering the possibility of providing a sufficiently high contrast between the switching states.

[0026] Based on the advantageous optical, electro-optical and thermal properties of the switchable optical cartridge, the device of the present invention can be advantageously used in several different window and shutter applications.

[0027] In another aspect, the window element according to the invention is used for a window of a building or a vehicle. Vehicles may include, for example, road vehicles such as cars, buses and trucks, as well as trains, ships, boats and airplanes.

[0028] In a further aspect of the present invention, a liquid-crystalline medium is provided which can advantageously be used in window elements, in particular a liquid-crystalline medium having a clearing point in the temperature range from 5° C. to 65° C. and comprising one or more compounds selected from the group of compounds of the formulae CY, PY and AC,

[0029]

[0030] in

[0031] a means 1 or 2,

[0032] b represents 0 or 1,

[0033] c represents 0, 1 or 2,

[0034] d represents 0 or 1,

[0035] express and express

[0036]

[0037] express

[0038]

[0039] R 1 、R 2 、R AC1 and R AC2 each independently of one another represents an alkyl radical having 1 to 12 C atoms, wherein additionally one or two non-adjacent CH2 groups may be -O-, -CH=CH-, -CO-, -OCO- or -COO- are replaced in such a way that the O atoms are not directly linked to one another, preferably by alkyl or alkoxy groups having 1 to 6 C atoms,

[0040] Z x ,Z y and Z AC each independently represents -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, preferably a single bond, and

[0041] L 1-4 Each independently of one another represents F, Cl, CN, OCF3, CF3, CH3, CH2F or CHF2, preferably F.

[0042] In the following, without limiting the invention thereby, the invention is illustrated by a detailed description of the aspects, embodiments and specific features, and specific embodiments are described in more detail.

[0043] The operating temperature, in particular the operating temperature of a window element, is herein the ambient or environmental temperature at which the window element operates and by which the window element is influenced and actuated. The operating temperature is therefore in the range of typical ambient or environmental temperatures of the natural environment (including solar radiation), for example between -25°C and 80°C, more typically between -15°C and 70°C, in particular between -5°C and 55°C.

[0044] The clearing point of the liquid-crystalline medium is particularly preferably within the temperature range generally prevailing in interior spaces such as buildings and homes. Preferably, the clearing point of the liquid-crystalline medium used according to the invention is within a temperature range of 5° C. to 65° C., more preferably 15° C. to 45° C., in particular 30° C. to 40° C.

[0045] The clearing point of a liquid-crystalline medium marks the temperature at which the phase transition from the nematic or chiral nematic liquid-crystalline state to the isotropic state occurs.

[0046] In this respect, for typical liquid crystal mixtures comprising several different compounds, a clearing temperature range, for example a range of several degrees Celsius, can be observed in which nematic and isotropic phases or domains coexist. In this case, the clearing point of the liquid crystal medium is the temperature at which a completely homogeneous nematic or chiral nematic phase initially transforms into a mixed phase system comprising one or more isotropic domains.

[0047] The clearing point, in particular the phase transition temperature between the nematic phase or chiral nematic phase and the isotropic phase, can be measured and determined by generally known methods, for example using a Mettler oven or a hot stage under a polarizing microscope, and is preferably determined using a Mettler oven herein.

[0048] It has now been recognized that for liquid-crystalline media, in particular for multicomponent systems, and in particular for multicomponent systems with broad liquid-crystalline phases down to, for example, -20° C. or even -40° C. or lower, a clearing temperature range of up to several degrees Celsius can be observed instead of a sharp phase transition. In particular, in this clearing temperature range, mixed-phase systems with different domains can occur, which can lead to an undesirably inhomogeneous appearance of the window element in this temperature range.

[0049] It has been further recognized that in some cases, the temperature change may be gradual or slow, wherein a change of a few degrees Celsius may occur over the course of only a few minutes or even up to a few hours. In such cases, the thermally controlled transition from the nematic state to the isotropic state or vice versa may take a relatively long time, so that the visually non-uniform appearance of the window element will potentially persist for an extended period of time, which will degrade device performance.

[0050] According to the present invention, the optical cell of the window element can be electrically switched in addition to or as an alternative to temperature. Thus, electrical switching can be advantageously used, in particular at temperatures at or near the clearing point of the liquid crystal medium, in order to accelerate the phase transition to a uniformly transmissive state and more quickly achieve a uniform device appearance across the entire element area.

[0051] Furthermore, the ability to electrically switch the optical cell is advantageous since it provides switchability of the window element and hence also control of the optical state in a fully homogeneous nematic phase (in particular well below the clearing point).

[0052] Such an additional optional switch may be useful, for example, in situations where the light transmission should be adjusted quickly or only briefly, for example to reduce temporary glare.

[0053] Furthermore, where multiple window elements are employed, for example in a facade of a building, electrical switching may also be suitably used to specifically address only a single window element or a subassembly of elements, for example when attenuation or attenuation of light is desired only in parts of the building.

[0054] According to the invention, a switchable layer is provided between two substrates in order to give an optical cartridge which is operable in different optical states and which can be switched or actuated both electrically and thermally.

[0055] The first and second substrates can comprise glass or polymer, preferably consist of glass or polymer, in particular glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide (PI), COP (cycloolefin polymer) or TAC (triacetyl cellulose). In a particularly preferred embodiment, a glass substrate is used.

[0056] The electrical switchability according to the invention is achieved by providing each substrate with an electrode structure or by providing one substrate with two electrode structures and the other substrate with no electrodes.Preferably, each substrate is provided with an electrode structure.

[0057] Therefore, in a preferred embodiment, a substrate (e.g., a glass substrate or a plastic substrate) is provided with a first electrode and a second electrode. Preferably, a conductive layer is provided on the substrate, wherein the conductive layer comprises or is formed from a transparent conductive material, such as a transparent conductive oxide, preferably indium tin oxide (ITO), SnO2:F, or doped zinc oxide, in particular ITO, or a conductive polymer, such as poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), or poly(4,4-dioctylcyclopentadithiophene), or a thin transparent metal and / or metal oxide layer, such as silver. Preferably, the transparent conductive material is a transparent conductive oxide, more preferably indium tin oxide. The transparent electrode is preferably applied to the substrate by a coating process. For example, ITO can be sputtered to typically achieve a layer thickness in the range of 5 nm to 250 nm or a sheet resistance in the range of 5 Ω / □ to 500 Ω / □.

[0058] The conductive layer is preferably provided with an electrical connection, in particular a busbar (busbars). The voltage is preferably provided by a battery, a rechargeable battery, a supercapacitor or an external current source, more preferably provided by an external current source. In this regard, the connection of the terminal to the busbar can be achieved by soldering, welding or using a conductive adhesive or a conductive film. In particular, an anisotropic conductive film connection can be used to join a flat cable to the corresponding busbar as a terminal wire. The terminal can be used to provide a connection to a controller or a driver, which generates a drive signal for controlling the state of the switchable medium located inside the electro-optical element. The terminal can, for example, be configured as a terminal wire or a connector for attaching a wire.

[0059] The switchable optical box has at least two optical states. For example, the optical states may include a light state and a dark state, or a clear or transparent state and a hazy state, or a mixture of these states.

[0060] The window element preferably comprises an optical box that can be switched between a light state and a dark state. In this respect, the light state has a greater degree of light transmission than the dark state.

[0061] In one embodiment, it is particularly preferred that the light state exists at a relatively low temperature and the dark state exists at a relatively high temperature.

[0062] In the bright state, the window element according to the invention preferably has a visible light transmission measured according to DIN EN 410 of more than 40%, more preferably more than 50% and even more preferably more than 65%.

[0063] In the dark state, the window element according to the invention preferably has a visible light transmission of less than 35%, more preferably less than 30%, and even more preferably less than 20%, measured in accordance with DIN EN 410. In a preferred embodiment, in the dark state, the window element has a visible light transmission in the range of 1 to 35%, more preferably in the range of 2 to 30%, in particular in the range of 5 to 20%, measured in accordance with DIN EN 410.

[0064] The visible spectrum is defined herein as light with wavelengths between 380 nm and 780 nm.

[0065] The liquid-crystalline media used in accordance with the invention can have positive or negative dielectric anisotropy.

[0066] In order to achieve efficient electrical switching, the absolute value or magnitude of the dielectric anisotropy of the liquid-crystalline medium is preferably 2.5 or greater, more preferably 3.0 or greater, in particular 4.0 or greater.

[0067] In this context, Δε represents dielectric anisotropy, where Δε = ε|| - ε ⊥ The dielectric anisotropy Δε is preferably measured at 20° C. and 1 kHz.

[0068] In a preferred embodiment, the liquid-crystalline medium comprises one or more dichroic dyes.

[0069] As used herein, a dichroic dye refers to a light-absorbing compound whose absorption properties depend on the compound's orientation relative to the direction of light polarization. Dichroic dye compounds according to the present invention typically have an elongated shape, meaning the compound is significantly longer in one spatial direction (i.e., along the longitudinal axis) than in the other two spatial directions. Dichroic dyes absorb, or preferentially absorb, light in one orientation, making it possible to modulate light transmission by varying the dichroic dye's orientation.

[0070] Thus, guest-host liquid crystal cells based on a liquid crystal host doped with dichroic dye molecules can be used, wherein these guest-host systems can be used without any polarizers to vary the light transmission.

[0071] The one or more dichroic dyes are each preferably present in the liquid-crystalline medium in a proportion of 0.005 to 12.5% ​​by weight, more preferably 0.01 to 10% by weight, even more preferably 0.025 to 7.5% by weight, yet even more preferably 0.05 to 5% by weight, yet even more preferably 0.1 to 2.5% by weight and particularly preferably 0.25 to 1% by weight, based on the total weight of the entire medium.

[0072] Preferably, the one or more dichroic dyes are present in the liquid-crystalline medium as a whole in a total concentration of 0.01% to 30% by weight, more preferably 0.025% to 25% by weight, even more preferably 0.05% to 15% by weight, still even more preferably 0.1% to 10% by weight and particularly preferably 0.5% to 5% by weight.

[0073] The concentration of the dye is preferably chosen so as to ensure suitable properties of the resulting modulated material, in particular with respect to the desired colour and / or dampening effect.

[0074] The dichroic dyes can preferably be selected, for example, from azo dyes, anthraquinones, thienothraquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, pyrromethene dyes, malononitrile dyes, nickel dithioles, (metal)phthalocyanines, (metal)naphthalocyanines and (metal)porphyrins, rylenes, in particular perylenes and terylenes, thiadiazole dyes, thienothiadiazole dyes, benzothiadiazoles, thiadiazoquinoxals and diketopyrrolopyrroles. Particularly preferred are azo compounds, anthraquinones, thienoanthraquinones, benzothiadiazoles, in particular as described in WO 2014 / 187529, diketopyrrolopyrroles, in particular as described in WO 2015 / 090497, thiadiazoloquinoxalines, in particular as described in WO 2016 / 177449, and rylenes, in particular as described in WO 2014 / 090373.

[0075] The liquid-crystalline medium preferably comprises one, two, three, four, five, six, seven, eight, nine or ten different dichroic dyes, particularly preferably two or three dichroic dyes.

[0076] In one embodiment, the absorption spectra of the dichroic dyes optionally contained in the medium or the switchable layer are preferably complementary to one another in such a way that a black impression is produced to the eye. Preferably, two or more, more preferably three or more, dichroic dyes are used in the liquid-crystalline medium, preferably to cover a large part of the visible spectrum. The precise manner in which dye mixtures that appear black or grey to the eye can be prepared is known in the art and is described, for example, in M. Richter, Ein-führungin die Farbmetrik [Introduction to Colorimetry], 2nd edition, 1981, ISBN 3-11-008209-8, Walter de Gruyter & Co.

[0077] In another embodiment, settings of different colors are implemented, such as red, green or blue.

[0078] The field of colorimetry describes the setting of color positions for dye mixtures. To this end, the spectra of the individual dyes are calculated using the Lambert-Beer law to give a total spectrum, which is then converted into the corresponding color position and brightness values ​​under the relevant illumination (e.g., illuminant D65 for daylight) according to the rules of colorimetry. The position of the white point is fixed by the corresponding illuminant (e.g., D65) and is cited in tables, such as those in the aforementioned references. Different color positions can be set by varying the ratios of the individual dyes.

[0079] In a preferred embodiment, three or more different dichroic dyes are contained in the liquid-crystalline medium.

[0080] According to a preferred embodiment, the medium and the switchable layer comprise one or more dichroic dyes which absorb light in the red and NIR region, ie light with a wavelength of 600 nm to 2000 nm, preferably 600 nm to 1800 nm, particularly preferably 650 nm to 1300 nm.

[0081] In one embodiment, the dichroic dyes that may be provided in the medium and the switchable layer are preferably selected from the classes of dyes shown in B. Bahadur, Liquid Crystals—Applications and Uses, Vol. 3, 1992, World Scientific Publishing, Section 11.2.1, and are particularly preferably selected from the explicit compounds given in the table present therein.

[0082] The dyes mentioned belong to the class of dichroic dyes which are known from the prior art and 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, 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 are described in EP 43904, DE 43905, DE 43906, DE 43907, DE 43908, DE 43909, DE 439103, DE 439114 3123519, WO82 / 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: Mol. Cryst. Liq. 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 are described, for example, in EP 2166040, US 2011 / 0042651, EP 68427, EP 47027, EP 60895, DE 3110960 and EP698649.

[0083] In some embodiments, it is preferred that in one optical state, in particular in the presence of an electric field, the switchable layer has a twisted or super-twisted configuration.

[0084] Thus, the liquid-crystalline medium may optionally further comprise one or more chiral compounds, in particular one or more chiral dopants.

[0085] Chiral compounds, in particular chiral dopants, and their concentrations can be provided such that the cholesteric pitch of the liquid crystal medium can be appropriately set or adjusted. Pitch in this context refers to the pitch p of the cholesteric helix, wherein the pitch p is the distance over which the orientation axis (director) of the cholesteric liquid crystal undergoes a 2π rotation. In a preferred embodiment, the cholesteric medium is prepared by doping a nematic liquid crystal medium with a chiral dopant having a high helical twisting power (HTP). Two or more chiral dopants can also be used, for example to compensate for the temperature dependence of the HTP of the individual dopants, thereby achieving a very low temperature dependence of the helical pitch.

[0086] Therefore, the liquid crystal medium in the switching layer preferably contains one or more chiral compounds, in particular chiral dopants. Chiral dopants preferably have a high absolute HTP value, can generally be added to the mesogenic base mixture at relatively low concentrations, and have good solubility in the achiral component. If two or more chiral compounds are used, they can have the same or opposite directions of rotation and the same or opposite torsional temperature dependence.

[0087] Preferably, the one or more chiral compounds optionally contained in the liquid-crystalline medium have a -1 or larger, more preferably 10 μm -1 or greater and even more preferably 15 μm -1 or greater absolute value of the helical twisting force, preferably in the commercial liquid crystal mixture MLC6828 from Merck KGaA. Particularly preferred are those having 20 μm -1 or larger, more preferably 40 μm -1 or greater, even more preferably 60 μm -1 or larger, and most preferably at 80 μm -1 or larger up to 260μm -1 Chiral compounds having an absolute value of the helical twisting force in the range of 1 Å to 1 Å or less, preferably in the commercial liquid crystal mixture MLC 6828 from Merck KGaA.

[0088] Preferably, the chiral compound or compounds are contained in the liquid-crystalline medium in an amount of 2% by weight or less, more preferably 1% by weight or less, based on the total content of the medium.

[0089] Suitable chiral dopants are known in the art and some of them are commercially available, such as cholesteryl nonanoate, R / S-811, R / S-1011, R / S-2011, R / S-3011, R / S-4011, R / S-5011, B(OC)2C*HC-3 or CB15 (all from Merck KGaA, Darmstadt, Germany).

[0090] Particularly suitable chiral dopants are compounds which contain one or more chiral groups and one or more mesogenic groups, or one or more aromatic or alicyclic groups which form mesogenic groups with chiral groups.

[0091] In some embodiments, the layer thickness d of the switchable layer is purposefully set relative to the pitch p of the medium, wherein the ratio d / p is preferably in the range of 0 to 1 and particularly preferably 0.25 or approximately 0.25.

[0092] In another embodiment, the ratio d / p is set within the range of 1 to 50.

[0093] In a preferred embodiment, the optical state in the presence of an electric field has a twisted nematic (TN) geometry with a twist of 90°. In another preferred embodiment, a super twisted (STN) configuration with a twist of, for example, 240° can be provided.

[0094] In a preferred embodiment, a liquid-crystalline medium having a negative dielectric anisotropy is provided and used in the switchable layer. Preference is given to liquid-crystalline mixtures having a dielectric anisotropy Δε in the range from -7 to -2.5, more preferably from -6 to -3.

[0095] To align or align the liquid crystal molecules on the cell walls or substrate surface, an alignment layer, also called an orientation layer, may be used to provide an interface that specifically induces or pre-determined or desired molecular orientation. In many cases, the liquid crystal molecules at or near the interface are tilted on average, even and especially in the absence of an applied voltage. In this regard, the average tilt angle of the liquid crystal molecules, measured from the cell wall plane or the interface plane, is referred to as the pretilt angle.

[0096] In a preferred embodiment, the switchable optical box in the window element has a layer structure, which comprises in sequence:

[0097] - first substrate,

[0098] - first electrode layer,

[0099] - first alignment layer,

[0100] - switchable layers,

[0101] - second alignment layer,

[0102] - a second electrode layer, and

[0103] - a second substrate.

[0104] It is particularly preferred that the first alignment layer and / or the second alignment layer is a homeotropic alignment layer.

[0105] Thus, it is preferred that, in one optical state, the liquid-crystalline medium in the switchable layer is homeotropically aligned, in particular in the absence of an electric field.

[0106] It is particularly preferred that the switchable optical cell is switchable between a bright state and a dark state, wherein below a clearing point and in the absence of an electric field the switchable layer is homeotropically aligned.

[0107] Preferably, the two substrates of the switchable optical cartridge are arranged such that each substrate has at least one region that does not overlap with the other substrate. These non-overlapping regions can thus provide access to the corresponding transparent electrodes, and the busbars can be conveniently placed in these non-overlapping regions. The non-overlapping regions are preferably offset between the first and second substrates, with the offset being in the range of 1 mm to 20 mm, preferably in the range of 2 mm to 10 mm, and for example, approximately 4 mm.

[0108] The liquid crystal medium can be included in the electro-optical cell in a suitable manner, for example using vacuum fill or drop fill. Typically, an edge sealant is provided to enclose the cell or to accommodate the medium separately. Examples of suitable materials for sealing the cell include epoxy sealants, polyurethanes, hot melt sealants, and acrylates.

[0109] In a window element, in particular in a switchable optical cell, the thickness of the switchable layer is preferably at least 5 μm, more preferably at least 7 μm, even more preferably at least 10 μm, still more preferably at least 15 μm, particularly preferably at least 20 μm. In one embodiment, the thickness of the switchable layer comprising the liquid-crystalline medium is from 5 μm to 100 μm, more preferably from 10 μm to 50 μm, in particular from 15 μm to 25 μm.

[0110] In order to maintain an appropriate thickness for the switching layer, spacers may be included within the cell gap of the switching layer. Typically, the spacers have a spherical shape with a diameter within the cell gap. For example, a non-conductive spacer made of a polymer or glass with a spherical shape having a predetermined diameter may be used. In some embodiments, it may be useful to provide a sticky spacer, i.e. a spacer having some inherent adhesive properties to better adhere to the surface. For example, in order to avoid or minimize unwanted light leakage, black spacers may also be usefully used. It may be particularly beneficial to use spacers that are black and sticky. Alternatively, the cell thickness may be set or maintained by other suitable means, such as by using columnar spacers. Columnar spacers may also be formed to provide compartments, thereby optionally allowing for a freely cuttable structure.

[0111] In this context, the terms film and layer encompass 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.

[0112] A passivation layer or barrier layer may also be provided on the substrate, for example comprising, preferably consisting of, silicon oxide or silicon nitride. In this case, the passivation layer is arranged on the substrate such that the alignment layer is on top, ie in contact with the LC medium.

[0113] Preferably, the transparent conductive electrode layer is respectively embedded between two transparent dielectric layers. Thus, according to a particularly preferred embodiment, in the optical device, a liquid crystal medium is provided in the switchable layer, wherein the switchable layer is sandwiched between and in direct contact with a first alignment layer and a second alignment layer, and wherein the electrodes are respectively arranged on the passivation layer, in particular embedded between two transparent dielectric layers.

[0114] In a preferred embodiment, the window element comprises only a single switchable optical cartridge. It is also preferred that the switchable optical cartridge comprises only a single switchable layer. It is therefore particularly preferred that the window element comprises only a single switchable optical cartridge, which single switchable optical cartridge comprises only a single switchable layer.

[0115] It has surprisingly been found that providing only a single switchable layer in a window element according to the invention can be sufficient to provide effective thermal and electrical switchability, i.e. providing both electrically and thermally controlled or driven switching. This can provide benefits in terms of improved and simplified device construction and assembly.

[0116] However, in alternative embodiments, two or more switchable layers may also be provided, for example in a so-called double-box configuration, wherein for example two switchable layers or two switchable optical boxes according to the present invention are comprised in the window element.

[0117] The window element may comprise further functional layers, such as UV blocking layers, low-E layers and / or color filters.

[0118] The optical cell and the window element are preferably characterized in that they do not contain a polymer-based polarizer, particularly preferably do not contain a polarizer in a solid material phase, and very particularly preferably do not contain a polarizer at all. Therefore, in a particularly preferred embodiment, the device, in particular the window element, does not contain a polarizer.

[0119] However, according to an alternative embodiment, the device may also include one or more polarizers. Thus, in one embodiment, at least one polarizing layer and optionally at least one retardation layer are provided in the optical device. In this case, the polarizer is preferably a linear polarizer. Absorbing polarizers and reflective polarizers may optionally be used. Preferably, the polarizer is in the form of an optical film.

[0120] Thus, in addition to or as an alternative to providing one or more dichroic dyes in the liquid crystal medium, a window element may be provided, wherein the switchable optical cell further comprises one or more polarizer layers and optionally one or more optical retardation layers.

[0121] In a particular alternative, it is preferred that the device comprises only one polarizer. If exactly one polarizer is present, a Heilmeier-type guest-host arrangement is preferably used. In another alternative, a liquid crystal cell having two polarizers, preferably in the absence of any dichroic dye in the liquid crystal medium, is used to control light transmission.

[0122] In one embodiment, the window element is configured as an insulating glazing unit or is comprised in an insulating glazing unit, preferably as a double-glazed window or a triple-glazed window.

[0123] Preferably, the switchable optical box is arranged in a laminate, wherein preferably a UV blocking laminate layer is provided, and wherein preferably the laminate faces the light source.

[0124] This arrangement may help to protect or stabilize the active material in the switchable layer from degradation by light, particularly UV light.

[0125] Preferably, the optical box is provided with sufficient thermal contact with the outermost pane or glazing in the window element, wherein the outermost layer is the energy incident surface of the element. This is useful to ensure that the external or external light source and / or heat source can more effectively influence and affect the thermal switching behavior of the device.

[0126] Preferably, the optical cell comprises a first and a second alignment layer.In principle, the first alignment layer and the second alignment layer can be formed based on conventional materials and methods.

[0127] Preferably, the first alignment layer and the second alignment layer comprise an organic material, more preferably consist of an organic material, wherein in particular the organic material is rubbed, in particular mechanically rubbed, or phototreated, in particular photoaligned. For example, organic materials such as lecithin, in particular polyimide, can be used.

[0128] Preferably, the first and second alignment layers are polyimide-based layers. Thus, in a preferred embodiment, the alignment layers comprise, and more preferably consist of, polyimide. Chemically modified or reinforced polyimides, such as azobenzene-containing polyimides, may also be used or included. The alignment layers, preferably comprising polyimide, may also be rubbed or prepared by photoalignment methods.

[0129] The alignment layers, preferably polyimide layers, are preferably arranged such that they provide a homeotropic orientation of the liquid-crystalline medium molecules, in particular at the interface. In a particularly preferred embodiment, rubbed polyimide layers are used on both substrates.

[0130] It is also possible to use polyimide layers produced by photoalignment using light-induced orientational ordering of the alignment surface. This can be achieved by photolysis, photodimerization or photoisomerization with the aid of polarized light.

[0131] In a preferred embodiment, the switchable layer is a homeotropic or vertically aligned liquid crystal layer. Therefore, the liquid crystal medium preferably has a negative dielectric anisotropy Δε, i.e., perpendicular to the electric field. Thus, by applying an electric field perpendicular to the plane, the medium can be switched to an orientation parallel to the plane of the layer structure.

[0132] Examples of liquid-crystalline media having negative dielectric anisotropy are given in EP 1 378 558 A1.

[0133] The liquid-crystalline medium may comprise additives. In particular, the liquid-crystalline medium preferably comprises an antioxidant or stabilizer in a concentration of at least 5 ppm.

[0134] In a preferred embodiment, the liquid-crystalline medium comprises from 0 to 10% by weight, more preferably from 5 ppm to 5% by weight, particularly preferably from 10 ppm to 1% by weight, of stabilizer.

[0135] In this context, Δn represents the optical anisotropy, where Δn=n e -n o , and wherein the optical anisotropy Δn is preferably measured at 20° C. and a wavelength of 589.3 nm. The liquid-crystalline medium preferably has an optical anisotropy Δn of 0.03 to 0.30, more preferably 0.04 to 0.27, even more preferably 0.06 to 0.21, in particular 0.09 to 0.16.

[0136] All physical properties and physicochemical or electro-optical parameters were determined by generally known methods, in particular according to “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and are given at a temperature of 20° C., unless expressly stated otherwise.

[0137] In this document, unless expressly stated otherwise, all concentrations are given as percentages by weight and relate to the corresponding complete mixture.

[0138] The transmission and scattering of light preferably refers to the transmission and scattering of electromagnetic radiation in the spectral range from 380 nm to 780 nm.

[0139] Furthermore, the liquid-crystalline media preferably exhibit advantageous low-temperature stability without visible crystallization or decomposition, in particular a long shelf life of more than 200 hours measured in bulk at −40° C.

[0140] Preferably, the liquid-crystalline media used according to the invention comprise one or more compounds selected from the group consisting of compounds of the formulae CY, PY and AC:

[0141]

[0142] in

[0143] a means 1 or 2,

[0144] b represents 0 or 1,

[0145] c represents 0, 1 or 2,

[0146] d represents 0 or 1,

[0147] express

[0148] and

[0149] express

[0150]

[0151] express

[0152]

[0153] R 1 、R 2 、R AC1 and R AC2 each independently of one another represents an alkyl radical having 1 to 12 C atoms, wherein additionally one or two non-adjacent CH2 groups may be -O-, -CH=CH-, -CO-, -OCO- or -COO- are replaced in such a way that the O atoms are not directly linked to one another, preferably by alkyl or alkoxy groups having 1 to 6 C atoms,

[0154] Z x ,Z y and Z AC each independently represents -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, preferably a single bond, and

[0155] L 1-4 Each independently of one another represents F, Cl, CN, OCF3, CF3, CH3, CH2F or CHF2, preferably F.

[0156] Preferably, L 1 and L 2 Both mean F or L 1 and L 2 One of them represents F and the other represents Cl, and L 3 and L 4 Both represent F, or L 3 and L 4 One of represents F and the other represents Cl.

[0157] Here

[0158]

[0159] represents trans-1,4-cyclohexylene.

[0160] Particularly preferably, the liquid-crystalline media used according to the invention contain one or more compounds selected from the compounds of the formulae CY, PY and AC in an amount of at least 20% by weight, more preferably at least 25% by weight, even more preferably at least 30% by weight, still more preferably at least 35% by weight, yet more preferably at least 40% by weight and particularly preferably at least 50% by weight, based on the total content of the medium.

[0161] The compound of formula CY is preferably selected from the compounds of the following formulae:

[0162]

[0163]

[0164]

[0165]

[0166]

[0167] wherein a represents 1 or 2, alkyl and alkyl* each independently represent a straight-chain alkyl group having 1 to 6 carbon atoms, and alkenyl represents a straight-chain alkenyl group having 2 to 6 carbon atoms, and (O) represents an oxygen atom or a single bond. Alkenyl preferably represents CH2=CH-, CH2=CHCH2CH2-, CH3-CH=CH-, CH3-CH2-CH=CH-, CH3-(CH2)2-CH=CH-, CH3-(CH2)3-CH=CH- or CH3-CH=CH-(CH2)2-.

[0168] The compound of formula PY is preferably selected from the compounds of the following formulae:

[0169]

[0170]

[0171]

[0172]

[0173] wherein alkyl and alkyl* each independently represent a straight-chain alkyl group having 1 to 6 carbon atoms, and alkenyl represents a straight-chain alkenyl group having 2 to 6 carbon atoms, and (O) represents an oxygen atom or a single bond. Alkenyl preferably represents CH2=CH-, CH2=CHCH2CH2-, CH3-CH=CH-, CH3-CH2-CH=CH-, CH3-(CH2)2-CH=CH-, CH3-(CH2)3-CH=CH- or CH3-CH=CH-(CH2)2-.

[0174] The compound of formula AC is preferably selected from the compounds of the following formulae:

[0175]

[0176] where R 3 and R 4 With R as mentioned above AC1 and R AC2 meaning.

[0177] Particularly preferably, the liquid-crystalline medium comprises one or more compounds selected from the group consisting of compounds of the following formulae CY-a and AC-a:

[0178]

[0179] where R 3 、R 4 、R 5 and R 6 each independently of one another represents an alkyl radical having 1 to 12 C atoms, wherein additionally one or two non-adjacent CH2 groups may be

[0180] -O-, -CH=CH-, -CO-, -OCO- or -COO- are replaced in such a way that the O atoms are not directly connected to each other, and preferably R 3 、R 5 and R 6 each independently of one another represents an alkyl group having 1 to 6 C atoms and preferably R 4 represents an alkoxy group having 1 to 6 C atoms.

[0181] In one embodiment, the group R in formula Ac-a 5 and R6 One or both of are cycloalkyl, in particular selected from cyclopropyl, cyclobutyl and cyclopentyl.

[0182] Preferably, the liquid-crystalline media used according to the invention further comprise one or more compounds of the formula I

[0183]

[0184] in

[0185] R 41 and R 42 each independently of one another represents an alkyl radical having 1 to 12 C atoms, wherein additionally one or two non-adjacent CH2 groups may be -O-, -CH=CH-, -CO-, -OCO- or -COO- is substituted in such a way that the O atoms are not directly bonded to each other.

[0186] The compound of formula I is preferably selected from the compounds of the following formulae:

[0187]

[0188]

[0189] wherein alkyl and alkyl* each independently represent a straight-chain alkyl group having 1 to 6 C atoms, and (O) represents an oxygen atom or a single bond.

[0190] The mesogenic compounds described above and below are known or can be prepared by methods known per se, as described in the literature (e.g. in standard works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), specifically under reaction conditions known and suitable for the described reaction. Variants known per se can also be used here, but are not mentioned in greater detail here. The media according to the invention are prepared in a conventional manner per se. Generally, the components are preferably soluble in one another at elevated temperatures. Suitable additives or substances can be added to alter the dielectric anisotropy, viscosity and / or orientation of the liquid-crystalline phase.

[0191] The term "alkyl" according to the present invention preferably includes straight-chain and branched alkyl groups, preferably having 1 to 7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2 to 5 carbon atoms are generally preferred.

[0192] Alkoxy may be linear or branched and is preferably linear and has 1, 2, 3, 4, 5, 6 or 7 carbon atoms and is therefore preferably methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy or heptyloxy.

[0193] Term " alkenyl " according to the present invention preferably comprises straight and branched alkenyl, preferably has 2-7 carbon atoms, particularly straight chain group.Particularly preferred alkenyl is C2-C7-1E alkenyl, C4-C7-3E alkenyl, C5-C7-4E alkenyl, C6-C7-5E alkenyl and C7-6E alkenyl, particularly C2-C7-1E alkenyl, C4-C7-3E alkenyl and C5-C7-4E alkenyl.The example of preferred alkenyl is vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-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.

[0194] The fluorinated alkyl or alkoxy group preferably comprises CF3, OCF3, CFH2, OCFH2, CF2H, 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. In a preferred embodiment, the fluoroalkyl group comprises a linear group having a terminal fluorine, i.e., a fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl group. However, other positions of fluorine are not excluded.

[0195] The oxaalkyl group preferably comprises a group of formula C n H 2n+1 -O-(CH2) m wherein n and m are each independently 1 to 6. Preferably, n=1 and m is 1 to 6.

[0196] Oxaalkyl is preferably a straight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxopentyl, 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.

[0197] Halogen is preferably F or Cl, in particular F.

[0198] If one of the abovementioned radicals is an alkyl radical in which one CH2 group has been replaced by -CH=CH-, it may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Thus, it is especially 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-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or dec-9-enyl.

[0199] If one of the above groups is an alkyl radical in which one CH2 group is replaced by -O- and one CH2 group by -CO-, they are preferably adjacent. Thus, they contain acyloxy -CO-O- or oxycarbonyl -O-CO-. These are preferably straight-chain and have 2 to 6 carbon atoms. They are therefore especially acetoxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl, 3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

[0200] If one of the above radicals is an alkyl radical in which one CH2 group has been replaced by an unsubstituted or substituted -CH=CH- radical and the adjacent CH2 group has been replaced by CO, CO-O or O-CO, it may be straight-chain or branched. It is preferably straight-chain and has 4 to 13 carbon atoms. Thus, it is particularly an acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl radical.

[0201] If one of the above radicals is an alkyl or alkenyl radical which is monosubstituted by CN or CF3, this radical is preferably straight-chain. The CN or CF3 substitution is at any position.

[0202] If one of the above groups is an alkyl or alkenyl group which is at least monosubstituted by halogen, this group is preferably straight-chain, the halogen being preferably F or Cl, more preferably F. In the case of polysubstitution, the halogen is preferably F. The resulting groups also include perfluorinated groups. In the case of monosubstitution, the fluorine or chlorine substituent can be in any desired position, but is preferably in the ω-position.

[0203] Compounds containing branching groups can sometimes be important due to improved solubility in some conventional liquid-crystalline base materials. However, if they are optically active, they are particularly suitable as chiral dopants.

[0204] Branched groups of this type usually contain no more than one branch. Preferred branched groups are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexyloxy, 1-methylhexyloxy or 1-methylheptyloxy.

[0205] If one of the above groups is an alkyl radical in which two or more CH2 groups are replaced by -O- and / or -CO-O, it may be straight-chain or branched. It is preferably branched and has 3 to 12 carbon atoms. Thus, in particular, it is a dicarboxymethyl, 2,2-dicarboxyethyl, 3,3-dicarboxypropyl, 4,4-dicarboxybutyl, 5,5-dicarboxypentyl, 6,6-dicarboxyhexyl, 7,7-dicarboxyheptyl, 8,8-dicarboxyoctyl, 9,9-dicarboxynonyl, 10,10-dicarboxydecyl, bis(methoxycarbonyl)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(ethoxycarbonyl)methyl, 2,2-bis(ethoxycarbonyl)ethyl, 3,3-bis(ethoxycarbonyl)propyl, 4,4-bis(ethoxycarbonyl)butyl or 5,5-bis(ethoxycarbonyl)pentyl.

[0206] In addition to a suitably high optical anisotropy, the liquid-crystalline medium comprised in the switchable layer may advantageously exhibit an advantageously high voltage holding ratio (VHR) and a good photostability.

[0207] In a particular embodiment, the switchable layer is polymer-stabilized.It has surprisingly been found that polymer stabilization can advantageously help to obtain and maintain over time an optical state having a desired alignment and configuration.

[0208] In this respect, one or more polymerizable, curable or hardenable compounds, preferably one or more photocurable monomers, are preferably provided in the liquid-crystalline medium as precursors of the polymer component for polymer stabilization, and these reactive compounds are subsequently polymerized in situ.

[0209] Thus, in one embodiment, one or more polymerizable compounds are included in the liquid-crystalline medium as precursors of polymers for polymer stabilization.In one embodiment, polymerizable mesogens or liquid-crystalline compounds, also called reactive mesogens (RMs) or mesogenic monomers, are used.

[0210] The optical box and the window element can have various shapes, such as square, rectangular, triangular, or polygonal. The window element can, for example, be included or arranged in a double-glazed window unit or a triple-glazed window unit, in particular an insulating glazing unit. The window element can be suitably and advantageously used in buildings or vehicles.

[0211] Preferred switchable optical boxes contain only a single switching layer.In one embodiment of the invention, the window element comprises exactly one switchable optical box.

[0212] In another case, however, the window element comprises an additional switchable optical box. In the latter case, the two switching layers are provided separately or individually in the optical box and then combined and constructed as a so-called double box, in particular by using a connection such as lamination or adhesive.

[0213] The area of ​​the window element is preferably at least 100 cm 2 , more preferably at least 1600 cm 2 , even more preferably at least 10,000 cm 2 Furthermore, it is preferred that the switchable layer is unsegmented, or in the alternative case that the switchable layer is segmented into compartments, said compartments each have an area of ​​at least 1 cm 2 , more preferably at least 10 cm 2 , even more preferably at least 50 cm 2 In contrast to conventional liquid crystal displays, which exhibit a large number of tiny pixels, the window element typically comprises an extended, continuous area of ​​liquid crystal material and an equally extended, uniform electrode area.

[0214] The following examples are merely illustrative of the present invention and should not be considered to limit the scope of the present invention in any way. In view of this disclosure, the examples and their modifications or other equivalents will be obvious to those skilled in the art.

[0215] However, the physical properties and compositions shown below illustrate which properties can be achieved and within which ranges they can be varied. In particular, the combinations of properties that can preferably be achieved are therefore well defined. Example

[0216] The following liquid crystal mixtures were prepared and studied.

[0217] Example 1

[0218] A mixture M-1 having the following composition was prepared.

[0219]

[0220] Mixture M-1 had a clearing point of 36.0°C.

[0221] Example 2

[0222] Mixture M-2 was prepared by mixing 99.70% of mixture M-1 with 0.30% of the compound of the formula

[0223]

[0224] Example 3

[0225] By mixing 96.914% of the mixture M-1, 0.544% of the compound of the formula

[0226]

[0227] 1.152% of the compound of the formula

[0228]

[0229] 1.390% of the compound of the formula

[0230]

[0231] Mixture M-3 was prepared.

[0232] The clearing point of mixture M-3 was 41.6°C.

[0233] The mixture M-3 was filled into an electro-optical cell having a glass substrate with an ITO electrode and a polyimide alignment layer giving homeotropic alignment, wherein the cell gap was 25 μm.

[0234] Thermal and electrical switching properties were investigated using a hot plate and spectrometer, as well as a microscope hot stage system.

[0235] In the absence of an electric field, the liquid crystal medium in the electro-optical cell exhibits a nematic phase at room temperature, giving the device a uniform, bright appearance. A clearing point was observed at 41.6°C. At this temperature, the nematic phase begins to transform into a multiphase system, with dark droplets of isotropic medium embedded within bright nematic domains. This clearing temperature range, where nematic and isotropic domains coexist, lies between 41.6°C and 44°C, where a non-uniform visual appearance of the device is observed.

[0236] The cell was electrically switched (30 V) in the temperature region of 41.6°C to 44°C, and the nematic domains quickly switched to the dark state, giving the device as a whole a uniformly dark appearance.

[0237] In order to give particularly improved switching properties and an aesthetically advantageous appearance, the electrical switching is carried out at a temperature just below the clearing point, in particular between 40.5° C. and 41.5° C.

[0238] Furthermore, electrical switching at room temperature gives fast transitions between bright and dark states with excellent contrast and uniformity.

[0239] The electro-optical box filled with the mixture M-3 was incorporated into the window member by lamination.

[0240] Example 4

[0241] Dye-doped mixture M-4 was prepared analogously to Example 3, mixture M-2 being used instead of mixture M-1.

[0242] Example 5

[0243] A mixture M-5 having the following composition was prepared.

[0244]

[0245] Mixture M-5-1 was prepared by mixing 99.70% of mixture M-5 with 0.03% of the compound of the formula

[0246]

[0247] Mixture M-5-2 was prepared by mixing 99.51% of mixture M-5 and 0.49% of chiral dopant S-811 available from Merck KGaA, Darmstadt, Germany.

[0248] Example 6

[0249] By mixing 96.914% of the mixture M-5, 0.544% of the compound of the formula

[0250]

[0251] 1.152% of the compound of the formula

[0252] and

[0253] 1.390% of the compound of the formula

[0254]

[0255] Mixing was performed to prepare mixture M-6.

[0256] The clearing point of mixture M-6 was 50.5°C.

[0257] The mixture M-6 was filled into an electro-optical cell having a glass substrate with an ITO electrode and a polyimide alignment layer giving homeotropic alignment, wherein the cell gap was 25 μm.

[0258] Thermal and electrical switching properties were investigated using a hot plate and spectrometer, as well as a microscope hot stage system.

[0259] In the absence of an electric field, the liquid crystal medium in the electro-optical cell exhibits a nematic phase at room temperature, giving the device a uniform, bright appearance. A clearing point was observed at 50.5°C. At this temperature, the nematic phase begins to transform into a multiphase system, with dark droplets of isotropic medium embedded within bright nematic domains. The clearing temperature range, where nematic and isotropic domains coexist, lies between 50.5°C and 53°C, where a non-uniform visual appearance of the device is observed.

[0260] The cell was electrically switched (30 V) in the temperature region of 50.5°C to 53°C, and the nematic domains quickly switched to the dark state, giving the device as a whole a uniformly dark appearance.

[0261] In order to give particularly improved switching properties and an aesthetically advantageous appearance, the electrical switching is carried out at a temperature just below the clearing point, in particular between 49.4° C. and 50.4° C.

[0262] Furthermore, electrical switching at room temperature gives fast transitions between bright and dark states with excellent contrast and uniformity.

[0263] The electro-optical box filled with the mixture M-6 was incorporated into the window member by lamination.

[0264] Examples 7 and 8

[0265] Dye-doped mixtures M-7 and M-8 were prepared analogously to Example 6, using mixtures M-5-1 and M-5-2, respectively, instead of mixture M-5.

Claims

1. A window element comprising a switchable optical cell which is electrically switchable between at least two optical states and which comprises a switchable layer interposed between two opposing transparent substrates, wherein each substrate is provided with an electrode structure, or one of the substrates is provided with two electrode structures and the other substrate is provided with no electrodes, and wherein the switchable layer comprises a liquid crystal medium having a clearing point within an operating temperature of the window element; and The operating temperature of the window element is between -5°C and 55°C. 2 . The window element according to claim 1 , wherein the absolute value of the dielectric anisotropy of the liquid crystal medium is 2.5 or greater. 3 . The window element according to claim 1 , wherein the liquid crystal medium comprises one or more dichroic dyes. 4 . The window element according to claim 1 , wherein the liquid-crystalline medium comprises a chiral dopant. 5 . The window element according to claim 1 , wherein the liquid-crystalline medium has a negative dielectric anisotropy.

6. The window element according to any one of claims 1 to 3, wherein the switchable optical box has a layer structure, the layer structure comprising in sequence: - first substrate, - first electrode layer, - first alignment layer, - switchable layers, - second alignment layer, - a second electrode layer, and - a second substrate. 7 . The window element according to claim 6 , wherein the first alignment layer and / or the second alignment layer is a homeotropic alignment layer.

8. The window element according to any one of claims 1 to 3, wherein the switchable optical cell is switchable between a light state and a dark state, and wherein below a clearing point and in the absence of an electric field the switchable layer is homeotropically aligned.

9. The window element according to any one of claims 1 to 3, wherein the element is configured as an insulating glazing unit.

10. The window element according to claim 9, wherein the element is configured as a double-glazed window or a triple-glazed window.

11. The window element according to any one of claims 1 to 3, wherein the switchable optical box is arranged in a laminate.

12. Window element according to claim 11, wherein a UV-blocking lamination layer is provided.

13. The window element of claim 11, wherein the laminate faces a light source.

14. The window element according to any one of claims 1 to 3, wherein the liquid-crystalline medium comprises one or more compounds selected from the group consisting of compounds of the formulae CY, PY and AC: in a means 1 or 2, b represents 0 or 1, c represents 0, 1 or 2, d represents 0 or 1, express and express express R 1 、R 2 、R AC1 and R AC2 each independently of one another represents an alkyl radical having 1 to 12 C atoms, wherein additionally one or two non-adjacent CH2 groups may be -O-, -CH=CH-, -CO-, -OCO- or -COO- are replaced in such a way that the O atoms are not directly linked to each other, Z x ,Z y and Z AC each independently represents -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, and L 1-4 Each independently of one another represents F, Cl, CN, OCF3, CF3, CH3, CH2F or CHF2.

15. The window element according to claim 14, wherein R 1 、R 2 、R AC1 and R AC2 Each independently of one another represents an alkyl or alkoxy radical having 1 to 6 C atoms.

16. The window element according to claim 14, wherein Z x ,Z y and Z AC Each independently of one another represents a single bond.

17. The window element according to claim 14, wherein L 1-4 Each represents F independently of the others.

18. The window element according to any one of claims 1 to 3, wherein the liquid-crystalline medium comprises one or more compounds selected from the group consisting of compounds of the formulae CY-a and AC-a where R 3 ,R 4 ,R 5 and R 6 each independently of one another represents an alkyl radical having 1 to 12 C atoms, wherein additionally one or two non-adjacent CH2 groups may be -O-, -CH=CH-, -CO-, -OCO- or -COO- is substituted in such a way that the O atoms are not directly bonded to each other.

19. The window element according to claim 18, wherein R 3 、R 5 and R 6 Each independently of one another represents an alkyl group having 1 to 6 carbon atoms.

20. The window element according to claim 18, wherein R 4 represents an alkoxy group having 1 to 6 C atoms.

21. Use of a window element according to any one of claims 1 to 20 in a window of a building or a vehicle.

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