Liquid-crystalline medium

Abstract

The application relates to a liquid-crystalline medium comprising at least one dichroic dye having a rylene structure which absorbs red light. The application furthermore relates to a device, preferably a device for the regulation of the passage of energy through a light-transmitting area, which contains the liquid-crystalline medium.

Claims

1. A liquid-crystalline medium comprising at least one dichroic dye F having a rylene structure whose longest-wave absorption maximum is at a wavelength of greater than 600 nm, and which is selected from the group consisting of compounds of formulae (F-I), (F-II), (F-III), (F-IV) and (F-V), ##STR00130## ##STR00131## wherein n is 1, 2, 3, 4, 5, 6, 7 or 8, Z.sup.F1 is, each independently, a single bond, C(O)O, OC(O), C(O)S, SC(O), CF.sub.2, CF.sub.2CF.sub.2, CF.sub.2O, OCF.sub.2 or O, R.sup.F1 is, each independently, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, R.sup.F2, R.sup.F3, R.sup.F4, R.sup.F5, R.sup.F6 are each independently, H, F, Cl, Br, OR.sup.FA, OCH.sub.2R.sup.FA, SR.sup.FA, SCH.sub.2R.sup.FA, C(O)OR.sup.FA, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aralkyl or heteroaralkyl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryloxy or heteroaryloxy group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, R.sup.FA is, each independently, F, Cl, Br, OCF.sub.2R.sup.FB, CF.sub.2OR.sup.FB, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, where the said groups are optionally substituted by one or more radicals R.sup.FB, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FB, and R.sup.FB is, each independently, F or an aliphatic, aromatic or heteroaromatic organic radical having 1 to 20 C atoms; and one or more compounds of formula (I) ##STR00132## wherein R.sup.11 is H, F, Cl, CN, NCS, R.sup.1OCO, R.sup.1COO, an alkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms, or an alkenyl, alkenyloxy or thioalkenyloxy group having 2 to 10 C atoms, in which one or more H atoms in the above-mentioned groups are optionally replaced by F, Cl or CN, and in which one or more CH.sub.2 groups in the above-mentioned groups are optionally replaced by O, S, OCO or COO, R.sup.1 is an alkyl group having 1 to 10 C atoms, in which one or more hydrogen atoms are optionally replaced by F or Cl, and in which one or more CH.sub.2 groups are optionally replaced by O or S, Z.sup.11 is COO, OCO, CF.sub.2CF.sub.2, CF.sub.2O, OCF.sub.2, CH.sub.2CH.sub.2, CHCH, CFCF, CFCH, CHCF, CC, OCH.sub.2, CH.sub.2Oor a single bond, A.sup.11 is ##STR00133## and X is, each independently, F, Cl, CN or an alkyl, alkoxy or alkylthio group having 1 to 10 C atoms, in which one or more hydrogen atoms in the above-mentioned groups are optionally replaced by F or Cl, and in which one or more CH.sub.2 groups in the above-mentioned groups are optionally replaced by O or S.

2. The liquid-crystalline medium according to claim 1, wherein the degree of anisotropy R of the dye F is greater than 0.4.

3. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F absorbs predominantly light in the wavelength range from 600 to 2000 nm.

4. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F is present in a concentration of 0.1% by weight to 10% by weight.

5. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F is a fluorescent dye.

6. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F contains a single rylene chromophore, which is the only rylene chromophore in the dichroic dye F.

7. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F contains a single chromophore, which is the only a chromophore in the dichroic dye F.

8. The liquid-crystalline medium according to claim 1, which, besides the dichroic dye F, comprises two or three further dichroic dyes, where at least one of the two or three further dichroic dyes absorbs green to yellow light and at least one other of the two or three further dichroic dyes absorbs blue light.

9. The liquid-crystalline medium according to claim 1, which, in addition to the dichroic dye F, comprises one or more further dichroic dyes which are selected from the group consisting of azo compounds, anthraquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, perylenes, terrylenes, quaterrylenes, higher rylenes and pyrromethenes.

10. The liquid-crystalline medium according to claim 1, which comprises exclusively dichroic dyes which are rylene dyes selected from the group consisting of compounds of formulae (F-I), (F-II), (F-III), (F-IV) and (F-V).

11. The liquid-crystalline medium according to claim 1, which has a dielectric anisotropy of greater than 3.

12. A process for preparing the liquid-crystalline medium according to claim 1, comprising first mixing the one or more compounds of formula (I) with one of more further compounds suitable for forming a liquid crystalline medium without the dichroic dye, and subsequently adding the dichroic dye to said liquid-crystalline medium and dissolving the dichroic dye therein.

13. An electrically switchable LC device of the guest-host type, containing at least one liquid-crystalline medium according to claim 1 in a switching layer.

14. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F is a compound of formula (F-I) ##STR00134## wherein n is 1, 2, 3, 4, 5, 6, 7 or 8; Z.sup.F1 is, each independently, a single bond, C(O)O, OC(O), C(O)S, SC(O), CF.sub.2, CF.sub.2CF.sub.2, CF.sub.2O, OCF.sub.2 or O; R.sup.F1 is, each independently, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA; R.sup.F2, R.sup.F3 are each independently, H, F, Cl, Br, OR.sup.FA, OCH.sub.2R.sup.FA, SR.sup.FA, SCH.sub.2R.sup.FA, C(O)OR.sup.FA, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aralkyl or heteroaralkyl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryloxy or heteroaryloxy group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA is, each independently, F, Cl, Br, OCF.sub.2R.sup.FB, CF.sub.2OR.sup.FB, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, where the said groups are optionally substituted by one or more radicals R.sup.FB, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FB; and R.sup.FB is, each independently, F or an aliphatic, aromatic or heteroaromatic organic radical having 1 to 20 C atoms.

15. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F is a compound of formula (F-II) ##STR00135## wherein n is 1, 2, 3, 4, 5, 6, 7 or 8; R.sup.F2, R.sup.F3, R.sup.F4 are each independently, H, F, Cl, Br, OR.sup.FA, OCH.sub.2R.sup.FA, SR.sup.FA, SCH.sub.2R.sup.FA, C(O)OR.sup.FA, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aralkyl or heteroaralkyl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryloxy or heteroaryloxy group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA; R.sup.FA is, each independently, F, Cl, Br, OCF.sub.2R.sup.FB, CF.sub.2OR.sup.FB, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, where the said groups are optionally substituted by one or more radicals R.sup.FB, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FB; and R.sup.FB is, each independently, F or an aliphatic, aromatic or heteroaromatic organic radical having 1 to 20 C atoms.

16. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F is a compound of formula (F-III) ##STR00136## wherein n is 1, 2, 3, 4, 5, 6, 7 or 8; R.sup.F2, R.sup.F3, R.sup.F5 are each independently, H, F, Cl, Br, OR.sup.FA, OCH.sub.2R.sup.FA, SR.sup.FA, SCH.sub.2R.sup.FA, C(O)OR.sup.FA, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aralkyl or heteroaralkyl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryloxy or heteroaryloxy group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA; R.sup.FA is, each independently, F, Cl, Br, OCF.sub.2R.sup.FB, CF.sub.2OR.sup.FB, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, where the said groups are optionally substituted by one or more radicals R.sup.FB, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FB; and R.sup.FB is, each independently, F or an aliphatic, aromatic or heteroaromatic organic radical having 1 to 20 C atoms.

17. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F is a compound of formula (F-IV) ##STR00137## wherein n is 1, 2, 3, 4, 5, 6, 7 or 8; R.sup.F2, R.sup.F3, R.sup.F6 are each independently, H, F, Cl, Br, OR.sup.FA, OCH.sub.2R.sup.FA, SR.sup.FA, SCH.sub.2R.sup.FA, C(O)OR.sup.FA, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aralkyl or heteroaralkyl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryloxy or heteroaryloxy group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA; R.sup.FA is, each independently, F, Cl, Br, OCF.sub.2R.sup.FB, CF.sub.2OR.sup.FB, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, where the said groups are optionally substituted by one or more radicals R.sup.FB, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FB; and R.sup.FB is, each independently, F or an aliphatic, aromatic or heteroaromatic organic radical having 1 to 20 C atoms.

18. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F is a compound of formula (F-V) ##STR00138## wherein n is 1, 2, 3, 4, 5, 6, 7 or 8; R.sup.F2, R.sup.F3, R.sup.F6 are each independently, H, F, Cl, Br, OR.sup.FA, OCH.sub.2R.sup.FA, SR.sup.FA, SCH.sub.2R.sup.FA, C(O)OR.sup.FA, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aralkyl or heteroaralkyl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA, or an aryloxy or heteroaryloxy group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FA; R.sup.FA is, each independently, F, Cl, Br, OCF.sub.2R.sup.FB, CF.sub.2OR.sup.FB, an alkyl or alkoxy group having 1 to 10 C atoms, or an alkenyl or alkynyl group having 2 to 10 C atoms, or a cycloalkyl group having 3 to 10 C atoms, where the said groups are optionally substituted by one or more radicals R.sup.FB, or an aryl or heteroaryl group having 6 to 30 aromatic ring atoms, which are optionally substituted by one or more radicals R.sup.FB; and R.sup.FB is, each independently, F or an aliphatic, aromatic or heteroaromatic organic radical having 1 to 20 C atoms.

19. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F has its longest-wave absorption maximum at a wavelength of greater than 600 nm and up to 655 nm.

20. The liquid-crystalline medium according to claim 1, wherein the dichroic dye F has a color blue.

21. A liquid-crystalline medium comprising at least one dichroic dye F having a rylene structure whose longest-wave absorption maximum is at a wavelength of greater than 600 nm, and which is selected from the group consisting of the following compounds ##STR00139## and one or more compounds of formula (I) ##STR00140## wherein R.sup.11 is H, F, Cl, CN, NCS, R.sup.1OCO, R.sup.1COO, an alkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms, or an alkenyl, alkenyloxy or thioalkenyloxy group having 2 to 10 C atoms, in which one or more H atoms in the above-mentioned groups are optionally replaced by F, Cl or CN, and in which one or more CH.sub.2 groups in the above-mentioned groups are optionally replaced by O, S, OCO or COO, R.sup.1 is an alkyl group having 1 to 10 C atoms, in which one or more hydrogen atoms are optionally replaced by F or Cl, and in which one or more CH.sub.2 groups are optionally replaced by O or S, Z.sup.11 is COO, OCO, CF.sub.2CF.sub.2, CF.sub.2O, OCF.sub.2, CH.sub.2CH.sub.2, CHCH, CFCF, CFCH, CHCF, CC, OCH.sub.2, CH.sub.2Oor a single bond, A.sup.11 is ##STR00141## and X is, each independently, F, Cl, CN or an alkyl, alkoxy or alkylthio group having 1 to 10 C atoms, in which one or more hydrogen atoms in the above-mentioned groups are optionally replaced by F or Cl, and in which one or more CH.sub.2 groups in the above-mentioned groups are optionally replaced by O or S.

Description

WORKING EXAMPLES

(1) The following examples illustrate the present invention and are not to be interpreted as restrictive.

(2) In the present application, structures of liquid-crystalline compounds are reproduced by abbreviations (acronyms). These abbreviations are explicitly presented and explained in WO 2012/052100 (pp. 63-89), so that reference is made to the said published application for an explanation of the abbreviations in the present application.

(3) The following liquid-crystalline media (M-1 to M-13) are prepared by mixing the components indicated. The parameters clearing point, delta-n, n.sub.e, n.sub.o, the solubility of various dyes, the stability of the solutions and the degree of anisotropy of the dye in the liquid-crystalline medium in question are determined for the mixtures and indicated below.

(4) All physical properties are determined in accordance with Merck Liquid Crystals, Physical Properties of Liquid Crystals, Status November 1997, Merck KGaA, Germany, and apply for a temperature of 20 C. The value of n is determined at 589 nm, and the value of is determined at 1 kHz, unless explicitly stated otherwise in each case. n.sub.e and n.sub.o are in each case the refractive indices of the extraordinary and ordinary light beam under the conditions indicated above.

(5) 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 and/or reflections, each measurement is carried out against an identical mixture comprising no dye, and the value obtained is subtracted.

(6) 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 directions. The measurement of E(p) and E(s) is thus carried out via the rotation of the vibration direction of the incident polarised light.

(7) 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)+.sub.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-crystalline media comprising a dichroic dye is also given in B. Bahadur, Liquid CrystalsApplications and Uses, Vol. 3, 1992, World Scientific Publishing, Section 11.4.2.
A) Mixtures Used

(8) The liquid-crystalline media M-1 to M-13 shown below are mixed with the rylene dyes according to the invention. Good solubility and high stability of the mixtures are apparent here.

(9) TABLE-US-00004 M-1 M-2 Clearing point 114.5 C. 113 C. Delta-n 0.1342 0.1393 n.sub.e 1.6293 1.6345 n.sub.o 1.4951 1.4952 Composition Compound % Compound % CPG-3-F 5 CPG-3-F 5 CPG-5-F 5 CPG-5-F 5 CPU-3-F 15 CPU-3-F 12 CPU-S-F 15 CPU-S-F 12 CP-3-N 16 CP-3-N 16 CP-5-N 16 CP-5-N 16 CCGU-3-F 7 CCGU-3-F 7 CGPC-3-3 4 CPGU-3--OT 4 CGPC-5-3 4 CCZPC-3-3 4 CGPC-5-5 4 CCZPC-3-4 4 CCZPC-3-3 3 CCZPC-3-5 3 CCZPC-3-4 3 CPZG-3-N 4 CCZPC-3-5 3 CPZG-4-N 4 CPZG-5-N 4 M-3 M-4 Clearing point 110 C. 115.5 C. Delta-n 0.1234 not measured n.sub.e 1.6150 not measured n.sub.o 1.4916 not measured Composition Compound % Compound % CP-3-N 18 CPG-2-F 3 CP-4-N 12 CPG-3-F 4 CP-5-N 21 CPG-5-F 4 CP-3-O1 13 CPU-3-F 4 CPPC-3-3 3 CPU-5-F 4 CPPC-5-3 3 CCU-2-F 4 CPPC-5-5 3 CCU-3-F 4 CGPC-3-3 3 CCU-S-F 4 CGPC-5-3 3 CCGU-3-F 5 CGPC-5-5 3 CP-3-O1 12 CCZGI-3-3 4 CP-3-O2 18 CCZGI-3-5 5 CGPC-3-3 3 CCZPC-3-3 3 CGPC-5-3 3 CCZPC-3-4 3 CGPC-5-5 3 CCZPC-3-5 3 CCZPC-3-3 3 CCZPC-3-4 3 CCZPC-3-5 3 CCP-2-OT 4 CCP-3-OT 4 CCP-4-OT 4 CCP-5-OT 4 M-5 M-6 Clearing point 110.5 C. 110.0 C. Low-temperature stability 37 45 (in days) Composition Compound % Compound % CPU-3-F 20 CPU-3-F 20 CPU-5-F 20 CPU-5-F 20 CP-3-N 16 CCU-3-F 5 CP-5-N 16 CP-3-N 16 CCGU-3-F 7 CP-5-N 15 CGPC-3-3 4 CGPC-3-3 4 CGPC-5-3 4 CGPC-5-3 4 CGPC-5-5 4 CGPC-5-5 4 CCZPC-3-3 3 CCZPC-3-3 4 CCZPC-3-4 3 CCZPC-3-4 3 CCZPC-3-5 3 CCZPC-3-5 3 CPPC-3-3 2 M-7 M-8 Clearing point 109.0 C. 112.0 C. Low-temperature stability 40 39 (in days) Composition Compound % Compound % CPU-3-F 8 CPU-2-F 6 CPU-5-F 20 CPU-3-F 8 CCU-3-F 8 CPU-5-F 15 CCG-V-F 11 CPU-7-F 17 CP-3-N 16 CP-3-N 14 CP-5-N 15 CP-5-N 15 CGPC-3-3 4 CGPC-3-3 4 CGPC-5-3 4 CGPC-5-3 4 CGPC-5-5 4 CGPC-5-5 4 CCZPC-3-3 4 CCZPC-3-3 4 CCZPC-3-4 3 CCZPC-3-4 4 CCZPC-3-5 3 CCZPC-3-5 4 CPPC-3-3 1 M-9 M-10 Clearing point 116.0 C. 112.0 C. Low-temperature stability 55 36 (in days) Composition Compound % Compound % CPU-5-F 15 CPU-3-F 15 CPU-7-F 17 CPU-5-F 15 CP-3-N 18 CP-3-N 13 CP-5-N 15 CP-5-N 12 CP-1V-N 7 CP-1V-N 5 CGPC-3-3 4 CG-3-N 5 CGPC-5-3 4 CU-3-N 5 CGPC-5-5 4 CGPC-3-3 4 CCZPC-3-3 3 CGPC-5-3 4 CCZPC-3-4 3 CGPC-5-5 4 CCZPC-3-5 2 CCZPC-3-3 3 CPPC-3-3 2 CCZPC-3-4 3 CPGP-4-3 3 CCZPC-3-5 2 CPGP-5-2 3 CPPC-3-3 4 CPGP-4-3 3 CPGP-5-2 3 M-11 M-12 Clearing point 111.0 C. 110.0 C. Low-temperature stability 45 57 (in days) Composition Compound % Compound % CPU-3-F 10 CPU-3-F 10 CPU-5-F 13 CPU-5-F 13 CPG-3-F 5 CPG-3-F 5 CPG-5-F 7 CPG-5-F 7 CP-3-N 13 CP-3-N 15 CP-5-N 12 CP-1V-N 9 CP-1V-N 9 CP-V2-N 10 CG-3-N 5 CG-1V-N 5 CGPC-3-3 4 CGPC-3-3 4 CGPC-5-3 4 CGPC-5-3 4 CGPC-5-5 4 CGPC-5-5 4 CCZPC-3-3 4 CCZPC-3-3 4 CPPC-3-3 4 CPPC-3-3 4 CPPC-3-3 4 CPPC-3-3 4 CPGP-4-3 3 CPGP-4-3 3 CPGP-5-2 3 CPGP-5-2 3 M-13 Clearing point 113.0 C. Low-temperature stability 67 (in days) Composition Compound % CPU-3-F 12 CPU-5-F 15 CPG-3-F 3 CPG-5-F 5 CP-3-N 15 CP-5-N 10 CP-1V-N 6 CGPC-3-3 4 CGPC-5-3 3 CGPC-5-5 3 CPPC-3-3 4 CPZIC-3-4 8 CCZP-3-3 5 CPZP-3-3 5 CCZGI-3-3 2
B) Dichroic Dyes Used

(10) The following dyes are prepared by known processes or purchased commercially:

(11) For the dyes, the absorption maximum, the degree of anisotropy R and the solubility in liquid-crystalline medium M-1 are determined.

(12) TABLE-US-00005 Absorption Degree of Solubility in % Name maximum/nm Colour anisotropy R by weight in M-1 D-1 472 Yellow 0.50 0.25 D-2 477 Yellow 0.77 0.50 D-3 472 Yellow 0.62 0.40 D-4 580 Red 0.08 0.15 D-5 529 Red 0.60 0.15 D-7 522 Red 0.54 0.25 D-8 524 Red 0.75 0.25 D-9 523 Red 0.69 0.25 D-10 523 Red 0.76 0.15 D-11 590 Red-violet 0.68 0.50 D-12 655 Blue 0.76 0.70 D-13 610 Blue 0.76 0.50 D-14 624 Blue 0.81 0.30 D-15 745 NIR absorb. 0.80 0.20 D-16 835 NIR absorb. 0.83 0.20 D-17 925 NIR absorb. 0.81 0.20 D-18 1015 NIR absorb. 0.83 0.20 D-19 1105 NIR absorb. 0.82 0.20 D-21 570 Red-violet 0.59 0.13
Structures of the Dyes:

(13) ##STR00126## ##STR00127## ##STR00128## ##STR00129##
C) Preparation of Mixtures Comprising a Plurality of Dichroic Dyes and Use in LC Devices of the Guest-Host Type

(14) For the preparation of the mixtures according to the invention, in all cases the mixture of two, three or four different dichroic dyes indicated in the respective cases is added to liquid-crystalline medium M-1 (cf. table above).

(15) The liquid-crystal mixture is introduced into a display. The liquid-crystal layer in this arrangement has a planar alignment with an antiparallel pretilt angle. This alignment is achieved by two polyimide layers rubbed antiparallel to one another which, considered in the lying display, are located above and below the liquid-crystal layer. The polyimide alignment layer is followed, in the viewing direction, on the outside by an electrically conductive transparent layer of indium tin oxide (ITO). The thickness of the liquid-crystal layer is controlled by spacers. The displays used have a layer thickness, depending on the choice of spacer, in the region of 20, 25 or 50 microns. Other layer thicknesses are possible through the choice of corresponding spacers.

(16) The measurement is carried out with the guest-host cell in the measurement beam and a cell of identical design containing the host in the reference beam. This eliminates reflection and absorption losses of the cell.

(17) Values for the degree of light transmission .sub.v and the direct degree of radiation transmission .sub.e are determined for both the dark and bright switching state of the device and are shown below. Furthermore, the colour location of the device in the dark and bright state is determined, and the values are indicated in CIE coordinates.

(18) The values .sub.e and .sub.v and the CIE coordinates are defined as follows:

(19) .sub.v=degree of light transmission in accordance with DIN EN410

(20) .sub.e=direct degree of radiation transmission in accordance with DIN EN410 (solar direct transmittance)

(21) The colour location (for white, grey black) of standard illuminant D65 forming the basis here is at x=0.3127 and y=0.3290 (Manfred Richter, Einfhrung in die Farbmetrik [Introduction to Colorimetry], second edition 1991, ISBN 3-11-008209-8). The colour locations indicated (x,y) all relate to standard illuminant D65 and a 2 standard observer in accordance with CIE 1931.

(22) All examples show good stability of the liquid-crystalline media according to the invention and adequate solubility of the dyes in the liquid-crystalline media. The devices according to the invention can be switched from a dark state having significantly reduced light transmission to a bright state having significantly increased light transmission.

1) Example Device B-1

(23) Dyes: 0.26% of D-2, 0.43% of D-3, 0.63% of D-11

(24) Dark switching state: colour grey. Layer thickness 25 microns

(25) Colour location x=0.308, y=0.327;

(26) .sub.v=34%, .sub.e=70%

(27) Bright switching state: colour grey. Layer thickness 25 microns

(28) Colour location x=0.316, y=0.336;

(29) .sub.v=60%, .sub.e=80%

2) Example Device B-2

(30) Dyes: 0.44% of D-2, 0.33% of D-3, 0.22% of D-11, 0.17% of D-20

(31) Dark switching state: colour grey. Layer thickness 25 microns

(32) Colour location x=0.311, y=0.325;

(33) .sub.v=34%, .sub.e=69%

(34) Bright switching state: colour grey. Layer thickness 25 microns

(35) Colour location x=0.317, y=0.335;

(36) .sub.v=63%, .sub.e=82%

3) Example Device B-3

(37) Dyes: 0.34% of D-13, 0.43% of D-3, 0.44% of D-11

(38) Dark switching state: colour grey. Layer thickness 25 microns

(39) Colour location x=0.313, y=0.328;

(40) .sub.v=35%, .sub.e=71%

(41) Bright switching state: colour grey. Layer thickness 25 microns

(42) Colour location x=0.316, y=0.340;

(43) .sub.v=61%, .sub.e=81%

4) Example Device B-4

(44) Dyes: 0.34% of D-13, 0.43% of D-3, 0.44% of D-11

(45) Dark switching state: colour grey. Layer thickness 25 microns

(46) Colour location x=0.313, y=0.328;

(47) .sub.v=35%, .sub.e=71%

(48) Bright switching state: colour grey. Layer thickness 25 microns

(49) Colour location x=0.316, y=0.340;

(50) .sub.v=61%, .sub.e=81%

5) Example Device B-5

(51) Dyes: 0.40% of D-14, 0.42% of D-3, 0.60% of D-11

(52) Dark switching state: colour grey. Layer thickness 25 microns

(53) Colour location x=0.31, y=0.329;

(54) .sub.v=34%, .sub.e=68%

(55) Bright switching state: colour grey. Layer thickness 25 microns

(56) Colour location x=0.318, y=0.341;

(57) .sub.v=61%, .sub.e=79%

6) Example Device B-6

(58) Dyes: 0.40% of D-14, 0.42% of D-3, 0.60% of D-11

(59) Dark switching state: colour grey. Layer thickness 25 microns

(60) Colour location x=0.313, y=0.326;

(61) .sub.v=35%, .sub.e=67%

(62) Bright switching state: colour grey. Layer thickness 25 microns

(63) Colour location x=0.320, y=0.336;

(64) .sub.v=63%, .sub.e=78%

7) Example Device B-7

(65) Dyes: 0.40% of D-2, 0.15% of D-11

(66) Dark switching state: colour blue. Layer thickness 50 microns

(67) Colour location x=0.247, y=0.246;

(68) .sub.v=38%, .sub.e=74%

(69) Bright switching state: colour blue. Layer thickness 50 microns

(70) Colour location x=0.286, y=0.305;

(71) .sub.v=64%, .sub.e=84%

(72) In this example (B-7), only two different dichroic dyes are present in the mixture. The mixture is therefore not grey or black, but instead blue. Although the CIE coordinates change significantly on switching, the colour type, however, remains constant at colour type 17.

8) Example Device B-8

(73) Dyes: 0.45% of D-3, 0.5% of D-11, 0.25% of D-2, 0.08% of D-15, 0.20% of D-16, 0.20% of D-17

(74) Dark switching state: colour grey. Layer thickness 20 microns, antiparallel or TN arrangement

(75) Colour location x=0.304, y=0.327;

(76) .sub.v=33%, .sub.e=54%

(77) Bright switching state: colour grey. Layer thickness 20 microns, antiparallel or TN arrangement

(78) Colour location x=0.312, y=0.329;

(79) .sub.v=53%, .sub.e=69%

(80) This example (B-8) shows that use of higher rylenes, such as quaterrylenes, pentarylenes and hexarylenes, can significantly reduce the direct degree of radiation transmissionin the present example to .sub.e=54%.