The present invention relates to an azo dye, to a liquid crystalline medium comprising the azo dye, the use of the medium for optical, electrooptical and electronic purposes, in particular in devices for regulating the passage of energy from an outside space into an inside space, for example in windows. The invention further relates to a device containing the liquid crystalline medium according to the invention.

Liquid crystals are used in particular as dielectrics in display devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are extremely well known to the person skilled in the art and can be based on various effects. Devices of this type are, for example, cells having dynamic scattering, DAP (deformation of aligned phases) cells, TN cells having a twisted nematic structure, STN ("supertwisted nematic") cells, SBE ("superbirefringence effect") cells, OMI ("optical mode interference") cells and guest-host cells.

The last-mentioned devices based on the guest-host effect were described for the first time by Heilmeier and Zanoni (G. H. Heilmeier et al., Appl.

Phys. Lett., 1968, 13, 91 f) and have since then found widespread use, principally in LC display elements. In a guest-host system, the LC medium comprises one or more dichroic dyes in addition to the liquid crystal. Owing to the directional dependence of the absorption by the dye molecules, the transparency of the liquid crystal to light can be modulated if the dyes change their alignment together with the liquid crystal.

Besides use in LC displays, devices of this type are known as switching elements for regulating the passage of light or energy, for example from WO 2009/141295 and WO 2010/118422; a device for regulating the passage of energy is in the present application taken to mean a device which regulates the passage of energy through an area which is arranged within a structure of relatively lower energy transmissivity. For example, the area of relatively high energy transmissivity can be a glass area or an open area, and the structure of lower energy transmissivity which contains the area of higher energy transmissivity can be a wall.

The device preferably regulates the passage of energy from insolation, either directly or indirectly.

The regulated passage of energy takes place from an outside space, pref- erably the environment exposed directly to insolation, into an inside space, for example a building or a vehicle, or another unit which is substantially sealed off from the environment. In the area of devices for regulating the passage of energy from an outside space into an inside space, a number of different technical solutions have been proposed in past years.

An advantageous solution is the use of switching layers comprising a liquid-crystalline medium in combination with one or more dichroic dyes. By application of a voltage, a change in the spatial alignment of the molecules of the dichroic compound can be achieved in these switching layers, caus- ing a change in the transmission of the switching layer owing to their direction-dependent absorption. A corresponding device is described, for example, in WO 2009/141295.

Alternatively, such a change in transmission can also be achieved without electrical voltage by a temperature-induced transition from an isotropic state of the liquid-crystalline medium to a liquid-crystalline state, as described, for example, in US 2010/0259698.

The prior art discloses liquid-crystal media for display elements of the guest-host type which comprise cyanobiphenyl derivatives and one or more dichroic dyes (WO 2009/141295 and WO 2010/118422). For the same application, US 6033598 and US 5762824 describe LC media which, besides one or more dichroic dyes, comprise one or more compounds each consisting of three ring elements which are substituted by one or more fluorine atoms.

Rylene dyes have been described for use in the above-mentioned devices, for example in WO 2009/141295, WO 2013/004677 and WO2014/090373. However, rylene dyes generally have some disadvantages, in particular they often have low solubility in LC media, result in low low-temperature stability of the liquid-crystal mixture and often exhibit low colour purity, which, in particular, makes use in windows more difficult, where, for archi- tectonic reasons, the aesthetic impression is important and the purest colours possible are desired. In WO2014/187529 A1 benzothiadiazole dyes are proposed for the above application. However, these compounds often show a high fluorescence giving rise to additional colour effects which may be aesthetically undesired, for example coloured emission in the inside space emanating from the fluorescent dyes in the switching layer. Such an emission has a negative influence in the colour purity. Poor colour purity is particularly undesired in window applications where, for architec- tonic reasons, the aesthetic impression is important and the purest colours possible are desired.

The invention is based on the object of providing novel dichroic dyes which do not exhibit the above-mentioned disadvantages, or only do so to a small extent, and in addition have at least one, preferably several of the following desired properties: good solubility of the dyes in the liquid-crystalline medium, good light and temperature stability and high anisotropy of the absorption, i.e. a high capacity of the dye to align with the liquid crystal, and very little, preferably no fluorescence in the VIS region of the

electromagnetic spectrum. In addition, the dyes should have strong light absorption in the VIS and/or NIR region of light. Furthermore, the invention was based on the object of providing compounds which not only have a favourable combination of the applicational parameters, but also, in addition, are distinguished by particularly high colour purity.

Surprisingly, it has been found that one or more of the requirements mentioned above are satisfied by compounds of the formula I as described below.

The invention relates to a compound of formula I

in which

W ¹¹ , W ¹² identically or differently, denote O, S or Se,

// on each occurrence, identically or differently, denotes

R ¹¹ , R ¹² , identically or differently, denote H, F, straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CFh groups may each be replaced, independently of one another, by -C(R ^Z )=C(R ^Z )-, -CºC-, -N(R ^Z )-, -O-, -S-, -CO-, -CO-O- , -O-CO- or -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more FI atoms may be replaced by F, Cl, Br, I or CN,

R ^z on each occurrence, identically or differently, denotes H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non- adjacent CFh groups may be replaced by -0-, -S-, -CO-, -C0-0-, -O-CO- or -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F or Cl,

A ¹¹ , A ¹² each, independently of one another, denote an aryl or heteroaryl group, which may be substituted by one or more radicals L,

A ²¹ , A ²² are each, independently of one another, defined like A ^{1 1} or denote a cyclic alkyl group having 3 to 10 C atoms, in which 1 to 4 Chte groups may be replaced by O in such a way that no two O atoms are adjacent,

L on each occurrence, identically or differently, denotes

OH, CH2OH, F, Cl, Br, I, -CN, -NO2, SF ₅ , -NCO, -NCS, -OCN, -SCN, -C(=0)N(R ^z ) ₂ , -C(=0)R ^z , -N(R ^z ) ₂ , optionally substituted silyl, optionally substituted aryl having 6 to 20 C atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which, in addition, one or more H atoms may be replaced by F or Cl, an aryl or heteroaryl group, which may be substituted by one or more radicals L, and alternatively two adjacent groups L together also denote a straight-chain or branched alkylene group having 2 to 10 C atoms, in which one, several or all H atoms may be replaced by F and in which one or more -CH2CH2- groups can be replaced by -CH=CH-,

Z ¹⁰ , Z ¹¹ , Z ¹² on each occurrence, identically or differently, denote a single bond, -N=N-, -CH=N-, -N=CH-, -N=N(0)-, -N(0)=N-, -CR ^x1 =CR ^x2 -, -(CR ^X1 =CR ^x2 ) ₂ -, -CºC-,

-C(=0)-, -CH=CH-C(=0)-, -C(=0)-CH=CH-, -CH=CH-

COO or -OCO-CH=CH-,

Z ²¹ , Z ²² on each occurrence, identically or differently, have one of the meanings of Z ¹⁰ or denote -O-, -S-, -CR ^y1 R ^y2 -,

-CF2O-, -OCF2-, -C(0)-0-, -O-C(O)-, -0-C(0)-0-, -OCH2-, -CH2O-, -SCH2-, -CH2S-, -CF2S-, -SCF2-, -(CH ₂ )m-, -CF2CH2-, -CH2CF2-, or -(CF ₂ )m-, R ^x1 , R ^x2 , independently of one another, denote H, F, Cl, CN or alkyl having 1 -12 C atoms,

R ^y1 , R ^y2 each, independently of one another, denote H or alkyl having 1 -12 C atoms, px1 1 px12

Rx ⁱ s, R ^x14 independently of one another, denote H, F, Cl, CN,

alkyl, alkenyl, alkoxy or alkenyloxy having 1 -12 C atoms, r and t independently of one another, denote 0, 1 or 2

preferably 0 or 1 , s 0 or 1 , preferably 0, and n1 denotes 1 , 2, 3 or 4, and wherein one or more of Z ¹⁰ , Z ^{1 1} , Z ¹² , Z ²¹ , Z ²² , preferably one, two or three, denote -N=N-.

The invention further relates to an LC medium comprising

a dye component A) comprising one or more compounds of the formula I and optionally further dichroic dyes,

a liquid-crystalline component B), also referred to below as "LC host mix- ture", comprising one or more, preferably two or more mesogenic corn- pounds.

Preference is given to LC media in which component B) is an LC corn- pound or an LC mixture which has a nematic liquid-crystal phase.

The invention further relates to the use of LC media comprising one or more dichroic dyes of the formula I as described above and below for optical, electro-optical and electronic purposes, in particular in devices for regulating the passage of energy from an outside space into an inside space.

The invention furthermore relates to devices for regulating the passage of energy from an outside space into an inside space comprising an LC medium as set forth above and below.

Advantageous embodiments of the invention are specified in the dependent claims and can be gathered from the description.

Herein, the following meanings apply: For the purposes of the present invention, the term energy is taken to mean, in particular, energy by electromagnetic radiation in the UV-A, VIS and NIR region. In particular, it is taken to mean energy by radiation which is not absorbed or is only absorbed to a negligible extent by the materials usually used in windows (for example glass). According to the definitions usually used, the UV-A region is taken to mean a wavelength of 320 to 380 nm, the VIS region is taken to mean a wavelength of 380 nm to 780 nm and the NIR region is taken to mean a wavelength of 780 nm to 2000 nm. Correspondingly, the term light is generally taken to mean electromagnetic radiation having wavelengths between 320 and 2000 nm.

For the purposes of the present invention, a dichroic dye is taken to mean a light-absorbing compound in which the absorption properties are depen- dent on the alignment of the compound with the direction of polarisation of the light. A dichroic dye compound in accordance with the present inven- tion typically has an elongate shape, i.e. the compound is significantly longer in one spatial direction (longitudinal axis) than in the other two spatial directions. The term "organic group" denotes a carbon or hydrocarbon group.

The term "carbon group" denotes a mono- or polyvalent organic group containing at least one carbon atom, where this either contains no further atoms (such as, for example, -CºC-) or optionally contains one or more further atoms, such as, for example, N, O, S, P, Si, Se, As, Te or Ge (for example carbonyl, etc.). The term "hydrocarbon group" denotes a carbon group which additionally contains one or more H atoms and optionally one or more heteroatoms, such as, for example, N, O, S, P, Si, Se, As, Te or Ge.

"Halogen" denotes F, Cl, Br or I.

A carbon or hydrocarbon group can be a saturated or unsaturated group. Unsaturated groups are, for example, aryl, alkenyl or alkynyl groups. A carbon or hydrocarbon radical having 3 or more atoms can be straight- chain, branched and/or cyclic and may also contain spiro links or con- densed rings.

The terms "alkyl", "aryl", "heteroaryl", etc., also encompass polyvalent groups, for example alkylene, arylene, heteroarylene, etc.

The term "aryl" denotes an aromatic carbon group or a group derived therefrom. The term "heteroaryl" denotes "aryl" as defined above, contain- ing one or more heteroatoms.

Preferred carbon and hydrocarbon groups are optionally substituted alkyl, alkenyl, alkynyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy having 1 to 40, preferably 1 to 25, particularly pref- erably 1 to 18, C atoms, optionally substituted aryl or aryloxy having 6 to 40, preferably 6 to 25, C atoms, or optionally substituted alkylaryl, arylalkyl, alkylaryloxy, arylalkyloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxy having 6 to 40, preferably 6 to 25, C atoms. Further preferred carbon and hydrocarbon groups are Ci-C ₄ o alkyl, C2-C ₄ o alkenyl, C2-C ₄ o alkynyl, C3-C ₄ o allyl, C ₄ -C ₄ o alkyldienyl, C ₄ -C ₄ o polyenyl, Ce- C ₄ o aryl, C6-C ₄ o alkylaryl, C6-C ₄ o arylalkyl, C6-C ₄ o alkylaryloxy, C6-C ₄ o aryl- alkyloxy, C2-C ₄ o heteroaryl, C ₄ -C ₄ o cycloalkyl, C ₄ -C ₄ o cycloalkenyl, etc. Particular preference is given to C1-C22 alkyl, C2-C22 alkenyl, C2-C22 alkynyl, C3-C22 allyl, C ₄ -C22 alkyldienyl, C6-C12 aryl, C6-C20 arylalkyl and C2-C20 heteroaryl.

Further preferred carbon and hydrocarbon groups are straight-chain, branched or cyclic alkyl radicals having 1 to 40, preferably 1 to 25, C atoms, which are unsubstituted or mono- or polysubstituted by F, Cl, Br, I or CN and in which one more non-adjacent CFI2 groups may each be replaced, independently of one another, by -C(R ^Z )=C(R ^Z )-, -CºC-, -N(R ^Z )-, -0-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another.

R ^z preferably denotes H, halogen, a straight-chain, branched or cyclic alkyl chain having 1 to 25 C atoms, in which, in addition, one or more non- adjacent C atoms may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO- or -O-CO-O- and in which one or more FI atoms may be replaced by fluorine, an optionally substituted aryl or aryloxy group having 6 to 40 C atoms, or an optionally substituted heteroaryl or heteroaryloxy group having 2 to 40 C atoms.

Preferred alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methylbutyl, n-pentyl, s-pentyl, cyclo- pentyl, n-hexyl, cyclohexyl, 2-ethyl hexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, trifluoromethyl, perfluoro-n-butyl, 2,2,2-trifluoroethyl, peril uorooctyl and perfluorohexyl. Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl and cyclooctenyl.

Preferred alkynyl groups are, for example, ethynyl, propynyl, butynyl, pentynyl, hexynyl and octynyl.

Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxy- ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2-methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n-decoxy, n-undecoxy and n-dodecoxy.

Preferred amino groups are, for example, dimethylamino, methylamino, methylphenylamino and phenylamino.

Aryl and heteroaryl groups can be monocyclic or polycyclic, i.e. they can contain one ring (such as, for example, phenyl) or two or more rings, which may also be fused (such as, for example, naphthyl) or covalently bonded (such as, for example, biphenyl), or contain a combination of fused and linked rings. Heteroaryl groups contain one or more heteroatoms, pref- erably selected from O, N, S and Se. A ring system of this type may also contain individual non-conjugated units, as is the case, for example, in the fluorene basic structure.

Particular preference is given to mono-, bi- or tricyclic aryl groups having 6 to 25 C atoms and mono-, bi- or tricyclic heteroaryl groups having 2 to 25 C atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6- or 7-membered aryl and hetero- aryl groups, in which, in addition, one or more CH groups may be replaced by N, S or O in such a way that O atoms and/or S atoms are not linked directly to one another. Preferred aryl groups are derived, for example, from the parent structures benzene, biphenyl, terphenyl, [1 ,1 ':3 ^, ,1 "]terphenyl, naphthalene, anthra- cene, binaphthyl, phenanthrene, pyrene, dihydropyrene, chrysene, peryl- ene, tetracene, pentacene, benzopyrene, fluorene, indene, indenofluorene, spirobifluorene, etc.

Preferred heteroaryl groups are, for example, 5-membered rings, such as pyrrole, pyrazole, imidazole, 1 ,2,3-triazole, 1 ,2,4-triazole, tetrazole, furan, thiophene, selenophene, oxazole, isoxazole, 1 ,2-thiazole, 1 ,3-thiazole,

1.2.3-oxadiazole, 1 ,2,4-oxadiazole, 1 ,2,5-oxadiazole, 1 ,3,4-oxadiazole,

1.2.3-thiadiazole, 1 ,2,4-thiadiazole, 1 ,2,5-thiadiazole, 1 ,3,4-thiadiazole, 6-membered rings, such as pyridine, pyridazine, pyrimidine, pyrazine,

1 ,3,5-triazine, 1 ,2,4-triazine, 1 ,2,3-triazine, 1 ,2,4,5-tetrazine, 1 ,2,3,4-tetra- zine, 1 ,2,3,5-tetrazine, or condensed groups, such as indole, isoindole, indolizine, indazole, benzimidazole, benzotriazole, purine, naphthimid- azole, phenanthrimidazole, pyridimidazole, pyrazinimidazole, quinoxalin- imidazole, benzoxazole, naphthoxazole, anthroxazole, phenanthroxazole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quino- line, isoquinoline, pteridine, benzo-5, 6-quinoline, benzo-6, 7-quinoline, benzo-7, 8-quinoline, benzoisoquinoline, acridine, phenothiazine, phenoxa- zine, benzopyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyri- dine, azacarbazole, benzocarboline, phenanthridine, phenanthroline, thieno[2,3b]thiophene, thieno[3,2b]thiophene, dithienothiophene, dihydro- thieno [3, 4-b]-1 ,4-dioxin, isobenzothiophene, dibenzothiophene, benzothia- diazothiophene, or combinations of these groups. The heteroaryl groups may also be substituted by alkyl, alkoxy, thioalkyl, fluorine, fluoroalkyl or further aryl or heteroaryl groups.

The (non-aromatic) alicyclic and heterocyclic groups encompass both saturated rings, i.e. those containing exclusively single bonds, and also partially unsaturated rings, i.e. those which may also contain multiple bonds. Heterocyclic rings contain one or more heteroatoms, preferably selected from Si, O, N, S and Se.

The (non-aromatic) alicyclic and heterocyclic groups can be monocyclic, i.e. contain only one ring (such as, for example, cyclohexane), or poly- cyclic, i.e. contain a plurality of rings (such as, for example, decahydro- naphthalene or bicyclooctane). Particular preference is given to saturated groups. Preference is furthermore given to mono-, bi- or tricyclic groups having 3 to 25 C atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6-, 7- or 8-membered carbocyclic groups, in which, in addition, one or more C atoms may be replaced by Si and/or one or more CH groups may be replaced by N and/or one or more non-adjacent Chte groups may be replaced by -O- and/or -S-.

Preferred alicyclic and heterocyclic groups are, for example, 5-membered groups, such as cyclopentane, tetrahydrofuran, tetrahydrothiofuran, pyrroli dine, 6-membered groups, such as cyclohexane, silinane, cyclohexene, tetrahydropyran, tetrahydrothiopyran, 1 ,3-dioxane, 1 ,3-dithiane, piperidine, 7-membered groups, such as cycloheptane, and fused groups, such as tetrahydronaphthalene, decahydronaphthalene, indane, bicyclo[1 .1 .1 ]- pentane-1 ,3-diyl, bicyclo[2.2.2]octane-1 ,4-diyl, spiro[3.3]heptane-2,6-diyl, octahydro-4,7-methanoindane-2,5-diyl.

The aryl, heteroaryl, carbon and hydrocarbon radicals optionally have one or more substituents, which are preferably selected from the group com- prising silyl, sulfo, sulfonyl, formyl, amine, imine, nitrile, mercapto, nitro, halogen, CM2 alkyl, Ce-12 aryl, CM2 alkoxy, hydroxyl, or combinations of these groups. Preferred substituents are, for example, solubility-promoting groups, such as alkyl or alkoxy, and electron-withdrawing groups, such as fluorine, nitro or nitrile.

Preferred substituents, also referred to as "L" above and below, are F, Cl, Br, I, -CN, -NO2 , -NCO, -NCS, -OCN, -SCN, -C(=0)N(R ^z ) ₂ , -C(=0)Y ¹ , - C(=0)R ^z , -N(R ^z ) ₂ , in which R ^z has the meaning indicated above, and Y ¹ denotes halogen, optionally substituted silyl or aryl having 6 to 40, preferably 6 to 20, C atoms, and straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, preferably 2 to 12, in which one or more H atoms may optionally be replaced by F or Cl.

"Substituted silyl or aryl" preferably means substituted by halogen, -CN,

R ^y \ -OR ^y \ -CO-R ^y \ -CO-0-R ^y \ -O-CO-R ^y1 or -0-C0-0-R ^y \ in which R ^y1 has the meaning indicated above.

Particularly preferred substituents L are, for example, F, Cl, CN, CFb, C ₂ Fl ₅ , -CFI(CFl3) ₂ , OCFI3, OC ₂ Fl5, CF3, OCF3, OCFIF ₂ , OC ₂ FS, furthermore phenyl.

In a preferred embodiment, W in formula I denotes -S-.

Z ¹¹ and Z ¹² preferably, independently of one another, denote a single bond, -N=N-, -CFI=CFI-, -CF=CF- or -CºC-, particularly preferably -N=N- or a single bond.

Z ²¹ and Z ²² preferably denote, independently of one another, a single bond, -N=N-, -CH ₂ CH ₂ -, -CF ₂ CF ₂ -, -CH=CH-, -CF=CF-, -CºC-, -OCH ₂ -, -CH ₂ O-, -OCF ₂ - or -CF ₂ 0-, particularly preferably -N=N-, -OCF ₂ -, -CF ₂ 0- or a single bond, and very particularly preferably -N=N- or a single bond. A ¹¹ , A ¹² , A ²¹ , A ²² preferably on each occurrence, identically or differently, represent an aryl group having 6 to 15 C atoms or a heteroaryl group hav- ing 2 to 15 C atoms, which may be substituted by one or more radicals L.

A ¹¹ , A ¹² , A ²¹ , A ²² are preferably selected on each occurrence, identically or differently, from groups, optionally substituted by radicals L, derived from the parent substances benzene, fluorene, naphthalene, pyridine, pyrimidine, thiophene, thiadiazole, dihydrothienodioxin, benzothiophene, dibenzothiophene, benzodithiophene, cyclopentadithiophene,

thienothiophene, indenothiophene, furan, benzofuran, dibenzofuran and quinoline, very particularly preferably benzene, naphthalene, thiadiazole, thienothiophene and thiophene.

Particularly preferred substituents L are, for example, F, Cl, CN, CFb, C2H ₅ , OCH3, CF3, OCF3, OCFIF2, OC2F5, furthermore phenyl.

In another preferred embodiment, one substituent L is OFI.

The groups R ¹¹ and R ¹² are preferably, independently of one another, a branched alkyl group having 3 to 25 C atoms, in which one or more FI atoms can be replaced by F, one or more CFI2 groups can be replaced by O and/or NH and one or more CFI groups can be replaced by N.

The groups R ¹¹ and R ¹² particularly preferably, independently of one another, denote a branched alkyl group, preferably with a methyl, ethyl, n- propyl, n-butyl, or n-pentyl group bonded to an ethyl, n-propyl, n-hexyl, n- heptyl, n-octyl, n-nonyl or n-decyl group, for example 2-ethylhexyl,

2-ethylheptyl, 2-ethyloctyl, 2-ethylnonyl, 2-ethyldecyl, 3-ethylhexyl, 3- ethylheptyl, 3-ethyloctyl, 3-ethylnonyl, 3-ethyldecyl, and the like. In another preferred embodiment, the groups R ¹¹ and R ¹² , independently of one another, denote a straight chain or branched alkyl or dialkylamino group having 1 to 25 C atoms per alkyl group.

The groups R ^x1 and R ^x2 are preferably on each occurrence, identically or differently, H, F or an alkyl group having 1 to 6 C atoms. R ^x1 and R ^x2 are particularly preferably on each occurrence, identically or differently, H or F, very particularly preferably H.

Preferably, the compounds of formula I are selected from the group of compounds of the formulae 1-1 , I-2, I-3 and I-4:

in which the occurring groups have the meanings given above for formula I, and preferably, taken alone or in combination with one another,

Z ¹¹ , Z ¹² , Z ²² on each occurrence, identically or differently, denote a single bond, -CR ^x1 =CR ^x2 - or -CºC-, particularly preferably a single bond,

R ¹¹ and R ¹² independently from one another denote a straight-chain alkyl or alkoxy group having 1 to 15 C atoms or a branched alkyl or alkoxy group having 3 to 25 C atoms, particularly preferably n-pentyl, n-hexyl, n-heptyl, or 2-ethylhexyl, 2-ethylheptyl, 2- ethyloctyl, 2-ethylnonyl, 2-ethyldecyl, 3-ethylhexyl, 3-ethylheptyl, 3-ethyloctyl, 3-ethylnonyl, 3-ethyldecy, 2-octyldodecyl,

A ¹¹ , A ¹² denote 1 ,4-phenylene, 1 ,4-naphthylene, 2,6-naphthylene,

thiazole-2,5-diyl, thiophene-2, 5-diyl, or thienothiophene-2,5-diyl. The groups may be substituted by one or more radicals L defined above, in particular F, Cl, branchend or unbranched alkyl, alkenyl or alkoxy each having 1 to 5 C atoms, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or OH, denotes

particularly preferably in which

px1 1 px12

px13 px14 independently of one another, denote H, F, Cl, CN, alkyl, alkenyl, alkoxy or alkenyloxy each having 1 -12 C atoms, preferably H or alkyl having 1 to 6 C atoms.

Particularly preferred compounds of the formula I are selected from the group of compounds of formulae 1-1 -1 to I-4-7, very particularly of sub- formulae 1-1-1 to 1-1 -8

in which

R ¹¹ and R ¹² independently from one another denote a straight-chain alkyl or alkoxy group having 1 to 15 C atoms or a branched alkyl or alkoxy group having 3 to 25 C atoms, particularly preferably n-pentyl, n-hexyl, n-heptyl, or 2-ethylhexyl, 2-ethylheptyl, 2-ethyloctyl, 2-ethylnonyl, 2-ethyldecyl, 3-ethylhexyl, 3-ethylheptyl, 3-ethyloctyl, 3-ethylnonyl, 3-ethyldecy, or 2- octyldodecyl.

The compounds of the formula I can be prepared analogously to processes known to the person skilled in the art and described in standard works of organic chemistry, such as, for example, Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Thieme Verlag, Stuttgart. Particularly suitable processes in general form are indicated below. For specific processes for the preparation of compounds of the formula I, refer- ence is furthermore made to the known literature and to the working examples.

Preferred processes for the preparation of compounds of the formula I are depicted in Schemes 1 and 2.

coupling

1

Scheme 1

In Schemes 1 to 3, R’ denotes H, alkyl or alkylene, =X-X= is defined above for formula I, Lg is a leaving group, preferably selected from Cl, Br, I, Tosylate, Mesylate and Triflate, Ar, Ar’ are aromatic rings having one of the meanings of A ¹¹ defined above for formula I. Hal denotes, identically or differently, Cl, Br, I.

Suitable building blocks are commercially available, known in the literature, or can be prepared accordingly. Suitable benzothiadiazole derivatives are described in WO 2014/187529 A1 , WO 2016/177449 A1 ,

WO 2017/174619 A1 , WO 2018/015320 A1 and WO 2018/001919 A1.

Azoarenes for the coupling reaction in Scheme 1 are preferably prepared from nitrosoarenes and aminoarenes as described in for example Drillaud,

N. et al Journal of Organic Chemistry, 77(21 ), 9553-9561 ; 2012.

The compounds of formulae I-3 and I-4 are preferably prepared starting from the building block 2 according to schemes 2 to 4. The compounds 2 are either known to the literature or can be prepared analogously. The synthesis is exemplified by the preparation of the compound 1-3-1 (scheme 2)

1-3-1

Scheme 2

The compounds of formula I-4 are accessible via the diarylhydrazine 3, a group that can be oxidised to an azo group (scheme 3).

Scheme 3 From the intermediate 5, the compounds of formula 1-4 according to the invention are then prepared using transformations commonly known, as exemplified by the Stille coupling to give compound 1-4-4, shown in scheme 4.

Scheme 4

The compound of the formula I is preferably a positively dichroic dye, i.e. a dye which has a positive degree of anisotropy R.

The degree of anisotropy R is determined from the value for the extinction coefficient of the LC mixture comprising the dye in the case of alignment of the molecules parallel to the direction of polarisation of the light and the value for the extinction coefficient in the case of perpendicular alignment of the molecules to the direction of polarisation of the light.

The degree of anisotropy R is particularly preferably greater than 0.4, very particularly preferably greater than 0.6 and most preferably greater than 0.7. The absorption preferably reaches a maximum when the polarisation direc- tion of the light is parallel to the direction of the longest elongation of the molecule of the formula I, and it reaches a minimum when the polarisation direction of the light is perpendicular to the direction of the longest elonga- tion of the molecule of the formula I. In principle, a suitable host mixture is any dielectrically negative or positive LC mixture which is suitable for use in conventional VA, TN, IPS or FFS displays.

Suitable LC mixtures are known to the person skilled 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.

Suitable LC mixtures having positive dielectric anisotropy which are suitable for LCDs 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.

Preferred embodiments of the liquid-crystalline medium having negative or positive dielectric anisotropy according to the invention are indicated below.

The LC host mixture is preferably a nematic LC mixture, and preferably does not have a chiral LC phase.

In a preferred embodiment of the present invention the LC medium contains an LC host mixture with negative dielectric anisotropy. Preferred

embodiments of such an LC medium, and the corresponding LC host mixture, are those of sections a)-w) below: a) LC medium which comprises one or more compounds selected from the group of compounds of the formulae CY, PY and AC:

wherein

a is 1 or 2,

b is 0 or 1,

c is 0, 1 or 2,

d is 0 or 1,

and

denotes

R ¹ , R ² ,

R ^AC1 and R ^AC2 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non- adjacent CFh groups may be replaced

by -0-, -CFI=CFI-, -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,

Z ^x , Z ^y , Z ^AC each, independently of one another,

denote -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OC H2-, -CO-O-, -O-CO-, -C ₂ F ₄ -, -CF=CF-, -CH=CH-CH ₂ 0- or a single bond, preferably a single bond, and

|_1-4 each, independently of one another, denote F, Cl, CN

OCFs, CFs, CHs, CH ₂ F, CHF ₂ .

Preferably, both L ¹ and L ² denote F or one of L ¹ and L ² denotes F and the other denotes Cl, or both L ³ and L ⁴ denote F or one of L ³ and L ⁴ denotes F and the other denotes Cl. The compounds of the formula CY are preferably selected from the group consisting of the following sub-formulae: 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 straight-chain alkenyl radical having 2-6 C atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes CH ₂ =CH-, CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-, CH ₃ -CH ₂ - CH=CH-, CH ₃ -(CH ₂ ) ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH- (CH ₂ ) ₂ -.

The compounds of the formula PY are preferably selected from the group consisting of the following sub-formulae:

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-, CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-, CH ₃ -CH ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₂ - CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH-(CH ₂ ) ₂ -.

The compounds of the formula AC are preferably selected from the group of compounds of the following sub-formulae:

b) LC medium which additionally comprises one or more compounds of the following formula: in which the individual radicals have the following meanings:

R ³ and R ⁴ each, independently of one another, denote alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adja- cent CFI2 groups may be replaced

by -0-, -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-, -C0-0-, -0-C0-, -C ₂ F ₄ -, -CF=CF-, -CH=CH- CFI2O- or a single bond, preferably a single bond.

The compounds of the formula ZK are preferably selected from the group consisting of the following sub-formulae:

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 CH ₂ =CH-, CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-, CH ₃ -CH ₂ - CH=CH-, CH ₃ -(CH ₂ ) ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH- (CH ₂ ) ₂ -. Especially preferred are compounds of formula ZK1 and ZK3.

Particularly preferred compounds of formula ZK are selected from the

following sub-formulae:

wherein the propyl, butyl and pentyl groups are straight-chain groups. Most preferred are compounds of formula ZK1 a and ZK3a. c) LC medium which additionally comprises one or more compounds of the following formula:

DK

in which the individual radicals on each occurrence, identically or differently, have the following meanings:

R ⁵ and R ⁶ each, independently of one another, denote alkyl having

1 to 12 C atoms, where, in addition, one or two non- adjacent CFte groups may be replaced by -0-, -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,

e denotes 1 or 2.

The compounds of the formula DK are preferably selected from the group consisting of the following sub-formulae: 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 CH ₂ =CH-, CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-, CH ₃ -CH ₂ - CH=CH-, CH ₃ -(CH ₂ ) ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH- (CH ₂ ) ₂ -.

Preference is give to compounds of the formulae DK1 , DK4, DK7, DK 9, DK10 and DK1 1 . d) LC medium which additionally comprises one or more compounds of the following formula:

in which the individual radicals have the following meanings: with at least one ring F being different from cyclohexylene, f denotes 1 or 2,

R ¹ and R ² each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CFI ₂ groups may be replaced

by -0-, -CFI=CFI-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

Z*denotes -CH ₂ CH ₂ -, -CH=CH-, -CF ₂ 0-, -OCF ₂ -, -CH ₂ 0-, -OCH ₂ -, -CO- 0-, -0-C0-, -C ₂ F ₄ -, -CF=CF-, -CH=CH-CH ₂ 0- or a single bond, preferably a single bond,

L ¹ and L ² each, independently of one another, denote F, Cl, OCF3,

CFs, CHs, CH ₂ F, CHF ₂ .

Preferably, both radicals L ¹ and L ² denote F or one of the radicals L ¹ and L ² denotes F and the other denotes Cl.

The compounds of the formula LY are preferably selected from the group consisting of the following sub-formulae: in which R ¹ has the meaning indicated above, alkyl denotes a straight-chain alkyl radical having 1 -6 C atoms, (O) denotes an oxy- gen atom or a single bond, and v denotes an integer from 1 to 6. R ¹ preferably denotes straight-chain alkyl having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms, in particular CH3, C2H5, n-CsH 7, n-C ₄ H ₉ , n-C ₅ Hn, CH ₂ =CH-, CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-,

CH ₃ -CH ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH-(CH ₂ ) ₂ -. e) LC medium which additionally comprises one or more compounds selected from the group consisting of the following formulae:

in which alkyl denotes Ci- ₆ -alkyl, L ^x denotes FI or F, and X denotes F, Cl, OCF3, OCFIF ₂ or OCFI=CF ₂ . Particular preference is given to corn- pounds of the formula G1 in which X denotes F. f) LC medium which additionally comprises one or more compounds selected from the group consisting of the following formulae:

in which R ⁵ has one of the meanings indicated above for R ¹ , 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. R ⁵ in these compounds is particularly preferably Ci- ₆ -alkyl 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) LC medium which additionally comprises one or more biphenyl corn- pounds selected from the group consisting of the following formulae:

in which alkyl and alkyl ^* each, independently of one another, denote a straight-chain alkyl radical having 1 -6 C atoms, 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 CH ₂ =CH-, CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-, CH ₃ -CH ₂ -

CH=CH-, CH ₃ -(CH ₂ ) ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH- (CH ₂ ) ₂ -. The proportion of the biphenyls of the formulae B1 to B3 in the LC mixture is preferably at least 3% by weight, in particular > 5% by weight.

The compounds of the formula B2 are particularly preferred.

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 B1 a and/or B2c. h) LC medium which additionally comprises one or more terphenyl corn- pounds of the following formula: in which R ⁵ and R ⁶ each, independently of one another, have one of the meanings indicated above, and

each, independently of one another, denote

in which L ⁵ denotes F or Cl, preferably F, and L ⁶ denotes F, Cl, OCF3, CF3, CFI3, CFI2F or CFIF2, preferably F.

The compounds of the formula T are preferably selected from the group consisting of the following sub-formulae:

F F F F

M° MM ⁰ MM ⁰ ° ^c _mHm T17

F F F F

M° MM ⁰ MM ⁰ o)c _mHm T18

F F F F

M° MM ⁰ MM ⁰ o)c _mHm T19

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 oxygen atom or a single bond, and m denotes an integer from 1 to 6. R* preferably denotes CH2=CH-,

CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-, CH ₃ -CH ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₂ - CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH-(CH ₂ ) ₂ -. R preferably denotes methyl, ethyl, propyl, butyl, pentyl, hexyl, meth- oxy, ethoxy, propoxy, butoxy or pentoxy. i) LC medium which additionally comprises one or more compounds of the following formula O:

R ⁰¹ , R ⁰² each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent Chte groups may be replaced

by -0-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

Z ⁰¹ denotes -CH2CH2-, -CF2CF2-, -C=C- or a single bond, Z ⁰² denotes CH2O, -C(0)0-, -CH2CH2-, -CF2CF2-, or a single bond, o is 1 or 2.

The compounds of the formula O are preferably selected from the group consisting of the following sub-formulae:

in which R ⁰¹ and R ⁰² have the meanings indicated above and prefer- ably each, independently of one another, denote straight-chain alkyl having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms.

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

in which

R ⁹ denotes H, CH3, C2H5 or n-CsFF, (F) denotes an optional fluorine substituent, and q denotes 1 , 2 or 3, and R ⁷ has one of the meanings indicated for R ¹ , preferably in amounts of > 3% by weight, in particular > 5% by weight and very particularly preferably 5-30% by weight.

Particularly preferred compounds of the formula FI are selected from the group consisting of the following sub-formulae:

 in which R ⁷ preferably denotes straight-chain alkyl, and R ⁹ denotes CH3, C2H ₅ or n-C3H ₇ . Particular preference is given to the compounds of the formulae FI1 , FI2 and FI3.

I) LC medium which additionally comprises one or more compounds selected from the group consisting of the following formulae:

in which R ⁸ has the meaning indicated for R ¹ , and alkyl denotes a straight-chain alkyl radical having 1 -6 C atoms. m) LC 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:

35

in which

R ¹⁰ and R ¹¹ each, independently of one another, denote alkyl having

1 to 12 C atoms, where, in addition, one or two non- adjacent Chte groups may be replaced

by -0-, -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 R ¹⁰ and R ¹¹ preferably denote straight-chain alkyl or alkoxy having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms and Z ¹ and Z ² each, independently of one another, denote -C ₂ H ₄ -, -CH=CH-, -(CH ₂ ) ₄ -, -(CH ₂ ) ₃ 0-, -0(CH ₂ ) ₃ -, -C=C-CH ₂ CH ₂ -, -CH ₂ CH ₂ CH=CH-, -CH ₂ O-, -OCH ₂ -, -CO-0-,

-O-CO-, -C ₂ F ₄ -, -CF=CF-, -CF=CH-, -CH=CF-, -CH ₂ - or a single bond. n) LC medium which additionally comprises one or more difluoro- dibenzochromans and/or chromans of the following formulae:

in which

R ^{1 1} and R ¹ each, independently of one another, have one of the meanings indicated above for R ^{1 1} ,

ring M is trans-1 ,4-cyclohexylene or 1 ,4-phenylene,

Z ^m -C ₂ H ₄ -, -CH ₂ 0-, -OCH ₂ -, -CO-0- 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.

Particularly preferred compounds of the formulae BC, CR and RC are selected from the group consisting of the following sub-formulae:

in which alkyl and alkyl* each, independently of one another, denote a straight-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

CH ₂ =CH-, CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-, CH ₃ -CH ₂ -CH=CH-, CH ₃ -

(CH ₂ ) ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH-(CH ₂ ) ₂ -. Very particular preference is given to mixtures comprising one, two or three compounds of the formula BC-2. o) LC medium which additionally comprises one or more fluorinated phenanthrenes and/or dibenzofurans of the following formulae:

in which R ¹¹ and R ¹² each, independently of one another, have one of the meanings indicated above for R ¹¹ , b denotes 0 or 1 , L denotes F, and r denotes 1 , 2 or 3.

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

in which R and R' each, independently of one another, denote a straight-chain alkyl or alkoxy radical having 1 -7 C atoms. p) LC medium which additionally comprises one or more monocyclic compounds of the following formula

in which

R ¹ and R ² each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent Chte groups may be replaced

by -0-, -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,

L ¹ and L ² each, independently of one another, denote F, Cl, OCF3

CFs, CHs, CH ₂ F, CHF ₂ .

Preferably, both L ¹ and L ² denote F or one of L ¹ and L ² denotes F and the other denotes Cl.

The compounds of the formula Y are preferably selected from the group consisting of the following sub-formulae:

Y1

Alkoxy Alkoxy

0

in which, Alkyl and Alkyl* each, independently of one another, denote a straight-chain 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-,

CH ₂ =CHCH ₂ CH ₂ -, CH ₃ -CH=CH-, CH ₃ -CH ₂ -CH=CH-, CH ₃ -(CH ₂ ) ₂ - CH=CH-, CH ₃ -(CH ₂ ) ₃ -CH=CH- or CH ₃ -CH=CH-(CH ₂ ) ₂ -.

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

Alkoxy Alkoxy Y6A

Alkoxy Alkoxy Y6B

wherein Alkoxy preferably denotes straight-chain alkoxy with 3, 4, or 5 C atoms. q) LC 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%. r) LC 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%. s) LC 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) LC 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%. u) LC 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%.

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.

Particular preference is given to compounds of the formulae T1 , T2, T3 and T21. In these compounds, R preferably denotes alkyl, further- more alkoxy, each having 1-5 C atoms. The terphenyls are preferably employed in mixtures according to the invention if the Dh value of the mixture is to be > 0.1. Preferred mix- tures comprise 2-20% by weight of one or more terphenyl compounds of the formula T, preferably selected from the group of compounds T 1 _c to T22.

5 v) LC 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%,

¹ 0 preferably 2 to 10% particularly preferbly 4 to 8%. v) Preferred media comprise one or more compounds of formula O, preferably selected from the formulae 03, 04 and 05 in a total 15 concentration of 2 to 25%, preferably 3 to 20%, particularly

prerferably 5 to 15%. w) 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 prerferably 5 to 15%.

In another preferred embodiment of the present invention the LC medium contains an LC host mixture with positive dielectric anisotropy. Preferred embodiments of such an LC medium, and the corresponding LC host mixture, are those of sections aa) - zz) below:

30

aa) LC-medium, characterised in that it comprises one or more

compounds selected from the group of compounds of the formulae II and III

35 wherein

R ²⁰ each, identically or differently, denote a halogenated or un- substituted alkyl or alkoxy radical having 1 to 15 C atoms, where, in addition, one or more CFh groups in these radicals may each be replaced, independently of one another,

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

X ²⁰ each, identically or differently, denote F, Cl, CN, SFs, SCN,

NCS, a halogenated alkyl radical, a halogenated alkenyl radical, a halogenated alkoxy radical or a halogenated alkenyloxy radical, each having up to 6 C atoms, and g20-24 each, identically or differently, denote FI or F;

each, independently of one another, denote

The compounds of the formula II are preferably selected from the following formulae:

wherein R ²⁰ and X ²⁰ have the meanings indicated above.

R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F. Particular preference is given to compounds of the forrnu- lae lla and Mb, in particular compounds of the formulae lla and Mb wherein X denotes F.

The compounds of the formula III are preferably selected from the following formulae:

wherein R ²⁰ and X ²⁰ have the meanings indicated above.

R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F. Particular preference is given to compounds of the formu- iae Ilia and llle, in particular compounds of the formula Ilia; bb) LC-medium additionally comprising one or more compounds selected from the following formulae:

wherein

R ²⁰ , X ²⁰ and Y ²⁰ - ²³ have the meanings indicated above, and

Z ²⁰ denotes -C ₂ H ₄ -, -(CH ₂ ) ₄ -, -CH=CH-, -CF=CF-

, -C ₂ F ₄ -, -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 ;

The compounds of the formula IV are preferably selected from the fol lowing formulae:

wherein R ²⁰ and X ²⁰ have the meanings indicated above.

R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F, CN or OCF3, furthermore OCF=CF ₂ or Cl; - The compounds of the formula V are preferably selected from the fol lowing formulae:

35 wherein R ²⁰ and X ²⁰ have the meanings indicated above.

R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F and OCF3, furthermore OCFIF2, CF3, OCF=CF2 and OCH=CF ₂ ;

The compounds of the formula VI are preferably selected from the fol lowing formulae:

wherein R ²⁰ and X ²⁰ have the meanings indicated above. R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F, furthermore OCF3, CF3, CF=CF2, OCFIF2 and OCFI=CF2;

The compounds of the formula VII are preferably selected from the following formulae:

wherein R ²⁰ and X ²⁰ have the meanings indicated above. R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F, furthermore OCF3, OCFIF2 and OCFI=CF2. cc) The medium additionally comprises 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 ZK1 a, ZK1 b, ZK1 c, ZK3a, ZK3b, ZK3c and ZK3d. dd) The 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 DK1 1 . ee) The medium additionally comprises one or more compounds selected from the following formulae:

IX wherein X ²⁰ has the meanings indicated above, and

^ L denotes H or F,

"alkenyl" denotes C2-6-alkenyl.

15 ff) The compounds of the formulae DK-3a and IX are preferably

selected from the following formulae: 3a

wherein "alkyl" denotes Ci-6-alkyl, preferably n-Cshl·, n-C ₄ Hg or n-CsHn, in particular n-CsHl·. gg) 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 B1 a, B2a, B2b and B2c.

35 hh) The medium additionally comprises one or more compounds selected from the following formula:

wherein L ²⁰ , L ²¹ denote FI or F, and R ²¹ and R ²² each, identically or differently, 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) The medium comprises one or more compounds of the following

formulae:

wherein R ²⁰ , X ²⁰ and Y ²⁰ - ²³ have the meanings indicated in formula III, and

The compounds of the formulae XI and XII are preferably selected from the following formulae:

wherein R ²⁰ and X ²⁰ have the meaning indicated above and

preferably R ²⁰ denotes alkyl having 1 to 6 C atoms and X ²⁰ denotes F. The mixture according to the invention particularly preferably comprises at least one compound of the formula XI la and/or Xlle. jj) The medium comprises one or more compounds of formula T given above, preferably selected from the group of compounds of the for- mulae T21 toT23 and T25 to T27.

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

kk) The medium comprises one or more compounds selected from the group of formulae DK9, DK10 and DK11 given above.

The medium additionally comprises one or more compounds selected from the following formulae:

wherein R ²⁰ and X ²⁰ each, independently of one another, have one of the meanings indicated above, and Y ²⁰ - ²³ each, independently of one another, denote H or F. X ²⁰ is preferably F, Cl, CF3, OCF3 or OCFIF ₂ . R ²⁰ preferably denotes alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 6 C atoms.

The mixture according to the invention particularly preferably comprises one or more compounds of the formula XVIII-a,

wherein R ²⁰ has the meanings indicated above. R ²⁰ preferably denotes straight-chain 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) The medium additionally comprises one or more compounds of the for- mula XIX,

wherein R ²⁰ , X ²⁰ and Y ²⁰ - ²⁵ have the meanings indicated in formula I, s denotes 0 or 1 , and

In the formula XIX, X ²⁰ may 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.

R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F;

The compounds of the formula XIX are preferably selected from the following formulae: wherein R ²⁰ , X ²⁰ and Y ²⁰ have the meanings indicated above. R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F, and Y ²⁰ is preferably F;

R ²⁰ is straight-chain alkyl or alkenyl having 2 to 6 C atoms; nn) 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, L ^x denotes H and X denotes F or Cl. In G2, X particularly preferably denotes Cl. oo) The medium comprises one or more compounds of the following

formulae:

wherein R ²⁰ and X ²⁰ have the meanings indicated above. R ²⁰ preferably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F. The medium according to the invention particularly preferably comprises one or more compounds of the formula XXII wherein X ²⁰ preferably denotes F. The compound(s) of the formulae 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) The medium comprises one or more compounds of the following

pyrimidine or pyridine compounds of the formulae

wherein R ²⁰ and X ²⁰ have the meanings indicated above. R ²⁰ prefer- ably denotes alkyl having 1 to 6 C atoms. X ²⁰ preferably denotes F.

The medium according to the invention particularly preferably comprises one or more compounds of the formula M-1 , wherein X ²⁰ preferably denotes F. The compound(s) of the formulae 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.

Further preferred embodiments are indicated below: qq) The medium comprises two or more compounds of the formula XII, in particular of the formula XI la and/or Xlle; rr) 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) Besides the compounds of the formulae XII, the medium comprises further compounds selected from the group of the compounds of the formulae ll-XVIII; tt) The proportion of compounds of the formulae ll-XVIII in the mixture as a whole is 40 to 95%, preferably 50 to 90%, particularly preferably 55 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 II and/or III; vv) The medium comprises 1 -10% by weight, particularly preferably 2-7% by weight, of compounds of the formula XV and/or XVI; ww) The medium comprises at least one compound of the formula Xlla and/or at least one compound of the formula Xlle and at least one compound of the formula Ilia and/or lla. 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 to VI, 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.

In case the medium has negative dielectric anisotropy (De), the value for De is preferably 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.

In case the medium has positive dielectric anisotropy, the value for De is preferably in the range from 3.0 to 60.0, more preferably in the range from 5.0 to 30.0, and particularly preferably from 8.0 to 15.0.

The liquid-crystal media in accordance with the present invention prefera- bly have a clearing point of 80°C or more, more preferably 90°C or more, even more preferably 105°C or more, and particularly preferably 110°C or more.

The nematic phase of the media according to the invention preferably extends at least from -10°C or less to 80°C or more, preferably up to 90°C or more, more preferably at least from -20°C or less to 100°C or more and particularly preferably from -30°C or less to 110°C or more.

In a preferred embodiment of the present invention the birefringence (Dh) of the liquid crystal media is in the range of 0.040 or more to 0.080 or less, more preferably in the range of 0.045 or more to 0.070 or less and most preferably in the range of 0.050 or more to 0.060 or less. In this embodiment, the dielectric anisotropy is positive or negative, preferably negative.

In another preferred embodiment of the present invention the Dh of the liquid crystal media is n the range of 0.075 or more to 0.130 or less, more preferably in the range of 0.090 or more to 0.125 or less and most preferably in the range of 0.095 or more to 0.120 or less.

In yet another preferred embodiment of the present invention the Dh of the liquid crystal media is n the range of 0.100 or more to 0.200 or less, more preferably in the range of 0.110 or more to 0.180 or less and most preferably in the range of 0.120 or more to 0.160 or less.

The dichroic compound of the formula I is preferably present in the switch- ing layer in a proportion of 0.01 to 10% by weight, particularly preferably 0.05 to 7% by weight and very particularly preferably 0.1 to 7% by weight. The media preferably comprise one, two, three, four or five compounds of the formula I according to the invention.

The LC medium according to the invention is preferably a nematic liquid crystal.

The media according to the invention are prepared in a manner conven- tional per se. In general, the components are dissolved in one another, preferably at elevated temperature. The mixing is preferably carried out under inert gas, for example under nitrogen or argon. One or more dyes of the formula I and optionally further dichroic dyes are subsequently added, preferably at elevated temperature, particularly preferably at above 40°C and very particularly preferably at above 50°C. In general, the desired amount of the components used in smaller amount is dissolved in the components making up the principal constituent. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, toluene, chloroform or methanol, and to remove the solvent again, for example by distillation, after mixing. The invention furthermore relates to the process for the preparation of the LC media according to the invention.

The invention furthermore relates to the use of an LC medium comprising at least one compound of the formula I in a liquid-crystal display of the guest-host type. The invention furthermore relates to a liquid-crystal display of the guest- host type containing an LC medium which comprises at least one corn- pound of the formula I. The invention furthermore relates to the use of a mixture comprising a liquid-crystalline medium and at least one compound of a formula I in a device for regulating the passage of energy from an outside space into an inside space.

The device according to the invention, in addition to one or more corn- pounds of the formula I, and preferably a liquid-crystalline medium, pref- erably also comprises further dichroic dyes having a different structure to formula I in the switching layer. It particularly preferably comprises one, two, three or four further dyes, very particularly preferably two or three further dyes and most preferably three further dyes having a different structure to formula I.

With respect to the property of dichroism, the preferred properties described for the compound of the formula I are also preferred for the optional further dichroic dyes.

The absorption spectra of the dichroic dyes of the switching layer prefera- bly complement one another in such a way that the impression of a black colour arises for the eye. The two or more dichroic dyes of the liquid- crystalline medium according to the invention preferably cover a large part of the visible spectrum. The precise way in which a mixture of dyes which appears black or grey to the eye can be prepared is known to the person skilled in the art and is described, for example, in Manfred Richter, Ein- fiihrung in die Farbmetrik [Introduction to Colorimetry], 2nd Edition, 1981 , ISBN 3-11 -008209-8, Verlag Walter de Gruyter & Co.

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 cal- culated taking into account the Lambert-Beer law to give an overall spec- trum 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 reference above). Different colour locations can be set by changing the proportions of the various dyes.

According to a preferred embodiment, the switching layer comprises one or more dichroic dyes which absorb light in the red and NIR region, i.e. at a wavelength of 600 to 2000 nm, preferably in the range from 650 to

1800 nm, particularly preferably in the range from 650 to 1300 nm. In a preferred embodiment, these dichroic dyes are selected from azo corn- pounds, anthraquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, perylenes, ter- rylenes, quaterrylenes, higher rylenes, pyrromethenes, azo dyes, nickel dithiolenes, (metal) phthalocyanines, (metal) naphthalocyanines and (metal) porphyrins. Of these, particular preference is given to perylenes and terrylenes.

The further dichroic dyes of the switching layer having a different structure to the formula I are preferably selected from the dye classes indicated 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.

The said dyes belong to the classes of dichroic dyes which are known to the person skilled in the art and have been described many times 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 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: Mol. Cryst. Lig. Cryst. 39, 39-52 (1977), and H. Seki, C. Shi shido, 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.

According to a preferred embodiment, the switching layer of the device according to the invention comprises, besides compounds of the formula I, exclusively dichroic dyes selected from rylene dyes.

Examples of preferred further dichroic dyes which may be present in the switching layer of the device are shown in Table 1 below:

Table 1

In a preferred embodiment, the switching layer of the device according to the invention comprises one or more quencher compounds. This is particu- larly preferred if the device according to the invention comprises one or more fluorescent dyes in its switching layer.

Quencher compounds are compounds which quench the fluorescence. The quencher compounds can take on the electronic excitation energy of adja- cent molecules, such as, for example, fluorescent dyes, in the switching layer and undergo a transition into an electronically excited state in the pro- cess. The quenched fluorescent dye is thus converted into the electronic ground state and is thus prevented from emitting fluorescence or under- going a subsequent reaction. The quencher compound itself returns to the ground state through radiation-free deactivation or by emission of light and is again available for further quenching.

The quencher compound may have various functions in the switching layer of the device according to the invention. Firstly, the quencher compound may contribute to extending the lifetime of a dye system, by deactivation of electronic excitation energy. Secondly, the quencher compound eliminates additional colour effects which may be aesthetically undesired, for example coloured emission in the inside space emanating from the fluorescent dyes in the switching layer.

In order to achieve effective quenching, the quencher compound should be adapted to the respective dye system, in particular the dye absorbing at the longest wavelength in a dye combination. The way to do this is known to the person skilled in the art.

Preferred quencher compounds are described, for example, in Table 8.1 on page 279 in Joseph R. Lakowicz, Principles of Fluorescence Spectros- copy, 3 ^rd Edition, 2010, ISBN 10: 0-387-31278-1 , Verlag Springer Science+ Business Media LLC. Further classes of molecule are familiar to the person skilled in the art, for example under the key words dark quencher or black hole quencher. Examples are azo dyes and aminoanthraquinones. The quencher compounds used in the switching layer of the device according to the invention may also be non-fluorescent dyes or dyes which only fluo- resce in the NIR.

In a preferred embodiment of the switching layer according to the inven- tion, any quencher compounds present are selected so that fluorescence in the visible part of the spectrum is suppressed.

Preferably, only compounds according to the present invention which show no fluorescence in the visible range of the electromagnetic spectrum are used in the liquid crystal medium, and no additional quencher compound is used.

In an alternative embodiment, dyes having a free phenolic OH group can be used in addition to or instead of the compounds of formula I in order to quench fluorescence. However, it is advantageous not to use compounds having a free phenolic group in liquid crystal mixtures because such compounds may cause low voltage holding ratio or can initiate

decomposition of dyes or host molecules, especially under UV load, due to their acidic character.

The device according to the invention is preferably suitable for regulating the passage of energy in the form of sunlight from the environment into an inside space. The passage of energy to be regulated here takes place from the environment (the outside space) into an inside space.

The inside space here can be any desired space that is substantially sealed off from the environment, for example a building, a vehicle or a con tainer.

The invention therefore furthermore relates to the use of the device for reg- ulating the passage of energy from an outside space into an inside space.

However, the device can also be employed for aesthetic room design, for example for light and colour effects. For example, door and wall elements containing the device according to the invention in grey or in colour can be switched to transparent. Furthermore, the device may also comprise white or coloured flat backlighting which is modulated in brightness or yellow flat backlighting which is modulated in colour by means of a blue guest-host display. One or both glass sides of the device according to the invention may be provided with roughened or structured glass for the coupling-out of light and/or for the generation of light effects. In a further alternative use, the device is employed for regulating the inci dence of light on the eyes, for example in protective goggles, visors or sun- glasses, where the device keeps the incidence of light on the eyes low in one switching state and reduces the incidence of light less in another switching state.

The device according to the invention is preferably arranged in an opening in a relatively large two-dimensional structure, where the two-dimensional structure itself only allows slight passage of energy, or none at all, and where the opening has relatively high energy transmissivity. The two- dimensional structure is preferably a wall or another boundary of an inside space to the outside. Furthermore, the two-dimensional structure prefera- bly covers an area of at least equal size, particularly preferably an area at least twice as large as the opening in it in which the device according to the invention is disposed.

The device is preferably characterised in that it has an area of at least 0.05 m ² , preferably at least 0.1 m ² , particularly preferably at least 0.5 m ² and very particularly preferably at least 0.8 m ² .

The device is preferably accommodated in an opening having relatively high energy transmissivity, as described above, in a building, a container, a vehicle or another substantially closed space. The device can generally be used for any desired inside spaces, particularly if they have only limited exchange of air with the environment and have light-transmitting boundary surfaces through which input of energy from the outside in the form of light energy can take place. The use of the device for inside spaces which are subjected to strong insolation through light-transmitting areas, for example through window areas, is particularly relevant. The device according to the invention is switchable. Switching here is taken to mean a change in the passage of energy through the device. The device according to the invention is preferably electrically switchable, as described, for example, in WO 2009/141295 and in WO 2014/090373.

However, it may also be thermally switchable, as described, for example, in WO 2010/118422. In this case, the switching preferably takes place through a transition from a nematic state to an isotropic state through a change in the temperature of the switching layer comprising the compound of the formula I and a liquid-crystalline medium. In the nematic state, the molecules of the liquid-crystalline medium are in ordered form and thus so is the compound of the formula I, for example aligned parallel to the sur- face of the device through the action of an alignment layer. In the isotropic state, the molecules are in unordered form, and thus so is the compound of the formula I. The difference between ordered and unordered presence of the dichroic compound of the formula I causes a difference in the light transmissivity of the switching layer of the device according to the inven- tion, in accordance with the principle that dichroic compounds have a higher or lower absorption coefficient depending on the alignment in rela- tion to the plane of vibration of the light.

If the device is electrically switchable, it preferably comprises two or more electrodes, which are installed on both sides of the switching layer. The electrodes preferably consist of ITO or a thin, preferably transparent metal and/or metal-oxide layer, for example silver or FTO (fluorine-doped tin oxide) or an alternative material known to the person skilled in the art for this use. The electrodes are preferably provided with electrical connec- tions. The voltage is preferably provided by a battery, a rechargeable bat- tery or an external power supply. The switching operation in the case of electrical switching takes place through an alignment of the molecules of the liquid-crystalline medium by the application of voltage.

In a preferred embodiment, the device is converted from a state having high absorption, i.e. low light transmissivity, which is present without volt- age, into a state having lower absorption, i.e. higher light transmissivity.

The liquid-crystalline medium of the switching layer is preferably nematic in both states. The voltage-free state is preferably characterised in that the molecules of the liquid-crystalline medium, and thus the molecules of the compound of the formula I, are aligned parallel to the plane of the switching layer. This is preferably achieved by a correspondingly selected alignment layer. The state under voltage is preferably characterised in that the mole- cules of the liquid-crystalline medium, and thus the molecules of the corn- pound of the formula I, are perpendicular to the plane of the switching layer.

In an alternative embodiment to the embodiment mentioned above, the device is converted from a state having low absorption, i.e. high light transmissivity, which is present without voltage, into a state having higher absorption, i.e. lower light transmissivity. The liquid-crystalline medium of the switching layer is preferably nematic in both states. The voltage-free state is preferably characterised in that the molecules of the liquid-crystal- line medium of the switching layer, and thus the molecules of the corn- pound of the formula I, are aligned perpendicular to the plane of the switch- ing layer. This is preferably achieved by a correspondingly selected align ment layer. The state under voltage is preferably characterised in that the molecules of the liquid-crystalline medium of the switching layer, and thus the molecules of the compound of the formula I, are parallel to the plane of the switching layer. According to a preferred embodiment of the invention, the device can be operated without an external power supply by providing the energy required by means of a solar cell or another device for conversion of light and/or heat energy into electrical energy which is connected to the device. The provision of the energy by means of the solar cell can take place directly or indirectly, i.e. via a battery or rechargeable battery or other unit for the storage of energy connected in-between. The solar cell is preferably mounted on the outside of the device or is an internal component of the device, as disclosed, for example, in WO 2009/141295. Particular prefer- ence is given here to solar cells which are particularly efficient in the case of diffuse light, and transparent solar cells.

The device according to the invention preferably has the following layer sequence, where further layers may additionally be present. The layers indicated below are preferably directly adjacent to one another in the device:

- substrate layer, preferably comprising glass or polymer

- electrically conductive transparent layer, preferably comprising ITO

- alignment layer

- switching layer comprising one or more compounds of the formula I

- alignment layer

- electrically conductive transparent layer, preferably comprising ITO

- substrate layer, preferably comprising glass or polymer

The preferred embodiments of the individual layers are described below.

The device according to the invention preferably comprises one or more, particularly preferably two, alignment layers. The alignment layers are pref- erably directly adjacent to the two sides of the switching layer comprising the compound of the formula I. The alignment layers used in the device according to the invention can be any desired layers known to the person skilled in the art for this purpose. Preference is given to polyimide layers, particularly preferably layers com- prising rubbed polyimide. Polyimide rubbed in a certain manner known to the person skilled in the art results in alignment of the molecules of the liquid-crystalline medium in the rubbing direction if the molecules are par- allel to the alignment layer (planar alignment). It is preferred here for the molecules of the liquid-crystalline medium not to be completely planar on the alignment layer, but instead to have a slight pretilt angle. In order to achieve vertical alignment of the compounds of the liquid-crystalline medium to the surface of the alignment layer (homeotropic alignment), polyimide treated in a certain manner is preferably employed as material for the alignment layer (polyimide for very high pretilt angles). Furthermore, polymers obtained by an exposure process to polarised light can be used as alignment layer in order to achieve alignment of the compounds of the liquid-crystalline medium in accordance with an alignment axis (photo- alignment).

The switching layer in the device according to the invention is furthermore preferably arranged between two substrate layers or enclosed thereby. The substrate layers can consist, for example, of glass or a polymer, preferably a light-transmitting polymer.

The device is preferably characterised in that it does not comprise a poly- mer-based polariser, particularly preferably does not comprise a polariser in the solid material phase and very particularly preferably comprises no polariser at all.

However, in accordance with an alternative embodiment, the device may also comprise one or more polarisers. The polarisers in this case are pref- erably linear polarisers. If precisely one polariser is present, its absorption direction is preferably perpendicular to the orientation axis of the compounds of the liquid-crystal- line medium of the device according to the invention on the side of the switching layer on which the polariser is located.

In the device according to the invention , both absorptive and also reflec- tive polarisers can be employed. Preference is given to the use of polari- sers which are in the form of thin optical films. Examples of reflective polarisers which can be used in the device according to the invention are DRPF (diffusive reflective polariser film, 3M), DBEF (dual brightness enhanced film, 3M), DBR (layered-polymer distributed Bragg reflectors, as described in US 7,038,745 and US 6,099,758) and APF films (advanced polariser film, 3M, cf. Technical Digest SID 2006, 45.1 , US 2011/0043732 and US 7,023,602). It is furthermore possible to employ polarisers based on wire grids (WGPs, wire-grid polarisers) which reflect infrared light.

Examples of absorptive polarisers which can be employed in the devices according to the invention are the Itos XP38 polariser film and the Nitto Denko GU-1220DUN polariser film. An example of a circular polariser which can be used in accordance with the invention is the APNCP37-035- STD polariser (American Polarizers). A further example is the CP42 polar- iser (ITOS).

The device according to the invention furthermore preferably comprises an optical waveguide system which transports the light to a solar cell or another device for the conversion of light and/or heat energy into electrical energy, preferably as described in WO 2009/141295. The optical wave- guide system collects and concentrates light hitting the device. It preferably collects and concentrates light emitted by fluorescent dichroic dyes in the switching layer. The optical waveguide system is in contact with a device for the conversion of light energy into electrical energy, preferably a solar cell, so that the collected light hits the latter in concentrated form. In a pre- ferred embodiment of the invention, the device for the conversion of light energy into electrical energy is mounted at the edge of the device accord- ing to the invention, integrated into the latter and electrically connected to means for the electrical switching of the device.

In a preferred embodiment, the device according to the invention is a con- stituent of a window, particularly preferably a window comprising at least one glass surface, very particularly preferably a window which comprises multipane insulating glass.

Window here is taken to mean, in particular, a structure in a building which comprises a frame and at least one glass pane surrounded by this frame. It preferably comprises a heat-insulating frame and two or more glass panes (multipane insulating glass).

According to a preferred embodiment, the device according to the invention is applied directly to a glass surface of a window, particularly preferably in the interspace between two glass panes of multipane insulating glass.

The invention furthermore relates to a window comprising a device accord- ing to the invention, preferably having the preferred features indicated above.

Owing to the electronic properties of the compounds according to the invention, they are also suitable, besides the use as dye, as organic semi- conductors.

The invention therefore furthermore relates to the use of compounds of the formula I in organic electronic components, such as, for example, organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), printed circuits, radio frequency identification elements (RFIDs), lighting elements, photovoltaic devices and optical sensors. Owing to their coloured nature and good solubility in organic materials, the compounds according to the invention are eminently suitable as dyes.

The invention therefore likewise relates to the use of dyes of the formula I for colouring a polymer.

In the present invention and especially in the following examples, the struc- tures of the mesogenic compounds are indicated by means of abbrevia- tions, also called acronyms. In these acronyms, the chemical formulae are abbreviated as follows using Tables A to C below. All groups C _n H _2n+i , C _m H _2m+i and C1H21 ₊₁ or C _n H _2n-1 , C _m H _2m-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, 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.

Table A: Ring elements

Table B: Linkinq groups

E -CH2CH2- Z -co-o-

V -CH=CH- Zl -o-co-

X -CF=CH- O -CH ₂ -0-

XI -CH=CF- Ol -0-CH2- B -CF=CF- Q -CF ₂ -0-

T -CºC- Ql -0-CF2- w -CF2CF2- T -cºc-

Table C: End groups

Left-hand side Right-hand side

Use alone

-n- CnFten _+l - -n — CnFten _+l

-nO- C _n H _2n+1 -0- -nO -O-CnFten _+i

-V- CH ₂ =CH- -V -CH=CH ₂ -nV- CnH _2n+ i-CH=CH- -nV -C _n H2n-CH=CH ₂

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

-nVm- CnH ₂ n+1-CH=CH-C _m H ₂ m- -nVm -CnH ₂ n-CH = CH-CmH _2m+ 1

-N- NºC- -N -CºN

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

-F- F- -F -F

-CL- Cl- -CL -Cl

-M- CFH ₂ - -M -CFH ₂

-D- CF ₂ H- -D -CF ₂ H

-T- CFs- -T -CFs

-MO- CFH ₂ 0 - -OM -OCFH ₂

-DO- CF ₂ HO - -OD -OCF ₂ H

-TO- CFsO - -OT -OCFs

-FXO- CF ₂ =CH-0- -OXF -0-CH=CF ₂

-A- H-CºC- -A -CºC-H

-nA- C _n H _2n+i -CºC- -An -CºC-C _n H _2n+i

-NA- NºC-CºC- -AN -CºC-CºN

Use together with one another and with others

-...A...- -CºC- -...A... -CºC-

-...V...- CH=CH- -...V... -CH=CH- -co-o-

-...Zl...- -o-co- -...Zl... -o-co-

-...K...- -co- -...K... -co-

-...W...- -CF=CF- -...W... -CF=CF- in which n and m each denote integers, and the three dots“...” are place- holders for other abbreviations from this table.

The following table shows illustrative structures together with their respec- tive abbreviations. These are shown in order to illustrate the meaning of the rules for the abbreviations. They furthermore represent compounds which are preferably used.

cc-v-v 0

CC-V-mV 5

CP-Vn-m

PP-nO-m

CCP-n-V

CPP-n-m

CPP-nVm-l

CCZC-n-Om

CCZPC-n-m

CP-n-N

CCG-n-F

CGU-n-F

CCGU-n-F

CCQG-n-F

PUQU-n-F

PGPQG-n-F

CVC-n-m CVY-V-m

CQY-n-(0)m CQIY-n-(0)m

BCH-nm BCH-nmF

PPC(CN)-n-m CPP(F,CN)-n-Om in which n, m and I preferably, independently of one another, denote 1 to 7.

Table E

Table E shows possible stabilisers which can be added to the LC media according to the invention.

(n here denotes an integer from 1 to 12, preferably 1 , 2, 3, 4, 5, 6, 7 or 8, terminal methyl groups are not shown).

35



The LC media preferably comprise 0 to 10% by weight, in particular 1 ppm to 5% by weight, particularly preferably 1 ppm to 1 % by weight, of stabilis- ers.

Table F below shows illustrative compounds which can preferably be used as chiral dopants in the mesogenic media according to the present inven- tion.

Table F

R/S-1011

R/S-5011

In a preferred embodiment of the present invention, the mesogenic media comprise one or more compounds selected from the group of the com- pounds from Table F.

The mesogenic media according to the present application preferably corn- prise two or more, preferably four or more, compounds selected from the group consisting of the compounds from the above tables.

The liquid-crystal media according to the present invention preferably corn- prise seven or more, preferably eight or more, individual compounds, preferably of three or more, particularly preferably of four or more, different formulae, selected from the group of the compounds from Table D. The proportions of these compounds and other components present in minor amounts are neglected when indicating the proportions of the liquid- crystalline compounds and the dichroic dyes.

It goes without saying to the person skilled in the art that the LC media according to the invention may also comprise compounds in which, for example, H, N, O, Cl or F have been replaced by the corresponding isotopes.

All per cent data and amount ratios are per cent by weight.

Examples

The present invention is described in detail by the following, non-restrictive examples.

All physical properties are determined in accordance with "Merck Liquid Crystals, Physical Properties of Liquid Crystals", Status Nov. 1997, Merck KGaA, Germany, and apply for a temperature of 20°C. The value of Dh is determined at 589 nm, and the value of De is determined at 1 kHz, unless explicitly indicated otherwise in each case. n _e and n ₀ are in each case the refractive indices of the extraordinary and ordinary light beam under the conditions indicated above.

The degree of anisotropy R is determined from the value for the extinction coefficient E(p) (extinction coefficient of the mixture in the case of parallel alignment of the molecules to the polarisation direction of the light) and the value for the extinction coefficient of the mixture E(s) (extinction coefficient of the mixture in the case of perpendicular alignment of the molecules to the polarisation direction of the light), in each case at the wavelength of the maximum of the absorption band of the dye in question. If the dye has a plurality of absorption bands, the strongest absorption band is selected. The alignment of the molecules of the mixture is achieved by an alignment layer, as known to the person skilled in the art in the area of LC display technology. In order to eliminate influences by liquid-crystalline medium, other absorptions or reflections, each measurement is carried out against an identical mixture comprising no dye, and the value obtained is sub- tracted.

The measurement is carried out using linear-polarised light whose vibration direction is either parallel to the alignment direction (determination of E(p)) or perpendicular to the alignment direction (determination of E(s)). This can be achieved by a linear polariser, where the polariser is rotated with respect to the device in order to achieve the two different vibration direc- tions. The measurement of E(p) and E(s) is thus carried out via the rotation of the vibration direction of the incident polarised light.

The degree of anisotropy R is calculated from the resultant values for E(s) and E(p) in accordance with the formula

R=[E(p)-E(s)] / [E(p) + 2 ^* E(s)],

as indicated, inter alia, in "Polarized Light in Optics and Spectroscopy",

D. S. Kliger et al ., Academic Press, 1990. A detailed description of the method for the determination of the degree of anisotropy of liquid-crystal- line media comprising a dichroic dye is also given in B. Bahadur, Liquid Crystals - Applications and Uses, Vol. 3, 1992, World Scientific Publishing, Section 11.4.2.

Synthesis Examples

Example 1 [Azo-1]:

Azo-1 4,7-Bis-(4,4,5,5-tetramethyl-[1 ,3,2]dioxaborolan-2-yl)- benzo[1 ,2,5]thiadiazole (50.0 mg) and (4-bromo-phenyl)-(4-propyl-phenyl)- diazene (76.9 mg) water (3.20 ml; 0.178 mol), sodium (20.22 mg; 0.241 mmol) and THF (6ml) are placed in a round bottom flask under argon and bis(tri-tert.-butylphosphin)palladium(0) (0.12 mg; 0.241 pmol) are added. The reaction is heated under reflux and stirred overnight at room temp. Aqeous work up and filtration of the crude product with toluene through silica yields (4-Propylphenyl)-[4-[4-[4-[(4-propylphenyl)azo]phenyl]-2,1 ,3- benzothiadiazol-7-yl]phenyl]diazene.

Phase sequence K 183 N 290 I (decomp.)

Example 2 [Azo-2]:

In analogy to Example 1 , from 4,7-bis-(4,4,5,5-tetramethyl- [1 ,3,2]dioxaborolan-2-yl)-benzo[1 ,2,5]thiadiazole and (4-bromo-phenyl)-(2- fluoro-4-(3-ethylheptyl)-phenyl)-diazene, [4-(3-ethylheptyl)-2-fluoro-phenyl]- [4-[4-[4-[[4-(3-ethylheptyl)-2-fluoro-phenyl]azo]phenyl]-2,1 ,3- benzothiadiazol-7-yl]phenyl]diazene is obtained.

Phase sequence: K 102 SmA 164 N 208 I

Example 3 [Azo-3]

In analogy to Example 1 , from 4,7-bis-(4,4,5,5-tetramethyl- [1 ,3,2]dioxaborolan-2-yl)-benzo[1 ,2,5]thiadiazole and (4-bromophenyl)-[4- (2-ethylhexoxy)-1 -naphthyl]diazene, [4-(2-ethylhexoxy)-1 -naphthyl]-[4-[4-[4- [[4-(2-ethylhexoxy)-1 -naphthyl]azo]phenyl]-2,1 ,3-benzothiadiazol-7- yl]phenyl]diazene is obtained. Phase sequence: K 188 N (168) I

Example 4 [Azo-4]

In analogy to Example 1 , from 4,7-bis-(4,4,5,5-tetramethyl- [1 ,3,2]dioxaborolan-2-yl)-benzo[1 ,2,5]thiadiazole and (4-bromophenyl)-[4- (2-ethylhexoxy)-1 -phenyl]diazene, [4-(2-ethylhexoxy)-1 -naphthyl]-[4-[4-[4- [[4-(2-ethylhexoxy)-1 -phenyl]azo]phenyl]-2,1 ,3-benzothiadiazol-7- yl]phenyl]diazene is obtained.

Phase sequence: K 129 SmX 203 N 246 I

Example 5 [Azo-5]

In analogy to Example 1 , from 4,7-bis-(4,4,5,5-tetramethyl- [1 ,3,2]dioxaborolan-2-yl)-benzo[1 ,2,5]thiadiazole and 0.5 equivalents each of (4-bromophenyl)-[4-(2-ethylhexoxy)-1 -naphthyl]diazene and 2-bromo-5- [4-(3-ethylheptyl)-2-fluoro-phenyl]thiophene, [4-[4-[5-[4-(3-ethylheptyl)-2- fluoro-phenyl]-2-thienyl]-2,1 ,3-benzothiadiazol-7-yl]phenyl]-[4-(2- ethylhexoxy)-1 -naphthyl]diazene is obtained.

Phase sequence: Tg -5 K 92 N (85.2) I

Example 6 [Azo-6]

In analogy to Example 1 , from 4,7-bis-(4,4,5,5-tetramethyl- [1 ,3,2]dioxaborolan-2-yl)-benzo[1 ,2,5]thiadiazole and 0.5 equivalents each of (4-bromophenyl)-[4-(2-ethylhexoxy)-1 -phenyl]diazene and 2-bromo-5- [4-(3-ethylheptyl)-2-fluoro-phenyl]thiophene, [4-[4-[5-[4-(3-ethylheptyl)-2- fluoro-phenyl]-2-thienyl]-2,1 ,3-benzothiadiazol-7-yl]phenyl]-[4-(2- ethylhexoxy)-1 -phenyl]diazene is obtained.

Phase sequence: K 124 SmX (121 ) 1

In analogy to the above described procedures, the following examples are obtained:

Azo-10

Use Examples

The dyes prepared are investigated with respect to their physical properties in order to establish their suitability for use in devices for regulating energy transmission. For comparison, the corresponding properties for compounds BTD-1 to BTD-3 and AD-1 to AD-3 known from the state of the are given. BTD-1

AD-3

Optionally, a stabiliser ST-1 or ST-2 is added to the medium

Preparation of liquid-crystalline dye mixtures

Nematic LC host mixtures N-1 to N-20 are prepared as follows:

Mixture N-20

CPG-3-F 11.4 % T(N,i). [°C]:

CPG-5-F 9.5 % Dh (589.3 nm, 20°C)

CCEP-3-0T 4.75 % n _e (589.3 nm, 20°C)

CCEP-5-0T 4.75 % n ₀ (589.3 nm, 20°C)

CGPC-3-3 1.9 % De (1 kHz, 20°C): CGPC-5-3 1.9 % e (1 kHz, 20°C):

CGPC-5-5 1.9 % si (1 kHz, 20°C): CP-6-F 7.6 % gi [mPa s], (20°C): CP-7-F 5.7 % Ki [pN], (20°C): CCP-2-0T 7.6 % K ₃ [pN], (20°C):

CCP-3-0T 11.4 % Vo [V], (20°C):

CCP-4-0T 6.65 %

CCP-5-0T 10.45 %

CP-7-F 9.5 % PM-5-N 5.0 %

å 100.0 %

To the host mixtures given above, the dyes according to the invention are added in the concentration given in table 1 below.

Table 1.

For the mixtures M-25 to M-29 comprising the dyes Azo-1 to Azo-5, respectively, the maximum absorption wavelength ( _ma x), the extinction coefficient at the absorption maximum (e (l _3c ) ) and the degree of anisotropy (R) are determined as follows (table 2):

Table 2.

For comparison, the following comparative Mixtures C-1 to C-4 are prepared (table 3).

Table 3.

ln Table 3, the given concentration of the one or more dyes and optionally stabiliser and of the host mixture add up to a total concentration of 100%.

It can be seen, that the compounds Azo-1 to Azo-5 have similar absorption characteristics and R values as the compounds BTD-1 to BTD-3 and are equally well suitable for the applications according to the invention, especially in devices for regulating the passage of energy from an outside space into an inside space, preferably in windows.

The compounds according to the invention are distinguished by a surprisingly high solubility in liquid crystalline media and a high degree of anisotropy (R).

Fluorescence spectra are measured using an Ocean Optics USB-400 fluorescence spectrometer with a Monoscan 2000 monochromator and a UVA/is/NIR DH-2000-BAL light source in a THF solution at a concentration of 10 mg/I .

Surprisingly, the dyes of formula I according to the invention show acceptably low fluorescence in the visible region of the electromagnetic spectrum compared to compounds of the state of the art. As the emission of light by fluorescence of the dyes is unwanted in applications for example in windows because of the resulting coloration, the dyes according to the invention are particularly suitable for window applications.

The following fluorescence values are observed (table 4): Table 4.

The dyes BTD-1 , BTD-2 and BTD-3 show strong emissions in the visible range with a peak emission at the respective wavelength given in table 4. Under the same conditions, for the compounds Azo-1 to Azo-6 no fluorescence is detectable.