LIQUID-CRYSTAL MATERIAL

Abstract

The present application relates to a liquid-crystalline material comprising a sterically hindered N-oxide and a dye. The invention furthermore relates to the use of the liquid-crystalline material in an optical switching device for regulation of the passage of sunlight.

Claims

1. Liquid-crystalline material, characterised in that it comprises a dye and a compound (I) containing a sterically hindered group of the formula (1) ##STR00098## where the bonds marked by * are the bonds by means of which the group of the formula (1) is connected to the remainder of the compound.

2. Liquid-crystalline material according to claim 1, characterised in that a quaternary carbon atom is bonded to both bonds of the nitrogen atom of the NO unit in formula (I).

3. Liquid-crystalline material according to claim 1, characterised in that the compound (I) contains a group of the formula (1-1) or (1-2) ##STR00099## where the bond marked by * is the bond by means of which the group is connected to the remainder of the compound, and where R.sup.1 is selected on each occurrence, identically or differently, from Si(R.sup.3).sub.3 and alkyl groups having 1 to 12 C atoms, which may be substituted by one or more radicals selected from F, Cl and CN; and where R.sup.2 is selected on each occurrence, identically or differently, from H, F, C(O)R.sup.3, CN, Si(R.sup.3).sub.3, N(R.sup.3).sub.2, P(O)(R.sup.3).sub.2, OR.sup.3, S(O)R.sup.3, S(O).sub.2R.sup.3, straight-chain alkyl or alkoxy groups having 1 to 20 C atoms, branched or cyclic alkyl or alkoxy groups having 3 to 20 C atoms, alkenyl or alkynyl groups having 2 to 20 C atoms, aryl groups having 6 to 40 aromatic ring atoms and heteroaryl groups having 5 to 40 aromatic ring atoms; where the said alkyl, alkoxy, alkenyl and alkynyl groups and the said aryl groups and heteroaryl groups may in each case be substituted by one or more radicals R.sup.3; and where one or more CH.sub.2 groups in the said alkyl, alkoxy, alkenyl and alkynyl groups may be replaced by R.sup.3CCR.sup.3, CC, Si(R.sup.3).sub.2, CO, CNR.sup.3, C(O)O, C(O)NR.sup.3, NR.sup.3, P(O)(R.sup.3), O, S, SO or SO.sub.2; and where R.sup.3 is selected on each occurrence, identically or differently, from H, D, F, CN, alkyl or alkoxy groups having 1 to 20 C atoms, alkenyl or alkynyl groups having 2 to 20 C atoms, aryl groups having 6 to 40 aromatic ring atoms and heteroaryl groups having 5 to 40 aromatic ring atoms; where two or more radicals R.sup.3 may be linked to one another and may form a ring; and where the said alkyl, alkoxy, alkenyl and alkynyl groups, aryl groups and heteroaryl groups may be substituted by F or CN.

4. Liquid-crystalline material according to claim 1, characterised in that the compound (I) conforms to a formula (I) ##STR00100## where the following applies to the variables occurring: U is selected on each occurrence, identically or differently, from CH.sub.2, O, S and NH; Sp is selected from alkylene groups having 2 to 10 C atoms, which may in each case be substituted by one or more radicals R.sup.4, alkenylene groups having 2 to 10 C atoms, which may in each case be substituted by one or more radicals R.sup.4, alkynylene groups having 2 to 10 C atoms, which may in each case be substituted by one or more radicals R.sup.4, aryl groups having 6 to 40 aromatic ring atoms, which may in each case be substituted by one or more radicals R.sup.4, and heteroaryl groups having 5 to 40 aromatic ring atoms, which may in each case be substituted by one or more radicals R.sup.4; R.sup.1 is selected on each occurrence, identically or differently, from Si(R.sup.3).sub.3 and alkyl groups having 1 to 12 C atoms, which may be substituted by one or more radicals selected from F, Cl and CN; R.sup.4 is selected on each occurrence, identically or differently, from H, D, F, CN, alkyl or alkoxy groups having 1 to 20 C atoms, alkenyl or alkynyl groups having 2 to 20 C atoms, aryl groups having 6 to 40 aromatic ring atoms and heteroaryl groups having 5 to 40 aromatic ring atoms; where two or more radicals R.sup.3 may be linked to one another and may form a ring; and where the said alkyl, alkoxy, alkenyl and alkynyl groups, aryl groups and heteroaryl groups may be substituted by F or CN; i is on each occurrence, identically or differently, 0 or 1; p is equal to 2, 3 or 4.

5. Liquid-crystalline material according to claim 1, characterised in that the compound (I) is present in the liquid-crystalline material in a proportion of 0.01% by weight to 1% by weight.

6. Liquid-crystalline material according to claim 1, characterised in that the liquid-crystalline material comprises at least one compound which contains at least one group selected from the following: ##STR00101## where the bond marked by * is the bond by means of which the group is connected to the remainder of the compound.

7. Liquid-crystalline material according to claim 1, characterised in that the liquid-crystalline material additionally comprises a compound (II) which contains a sterically hindered hydroxyphenyl group.

8. Liquid-crystalline material according to claim 1, characterised in that the compound (II) contains a group of the formula (2) ##STR00102## where the bond marked by * is the bond by means of which the group is connected to the remainder of the compound, and where R.sup.21 is selected on each occurrence, identically or differently, from H; silyl groups which carry radicals selected from alkyl groups having 1 to 12 C atoms and aryl groups having 6 to 40 aromatic ring atoms; and alkyl groups having 1 to 12 C atoms, which may be substituted by one or more radicals selected from F, Cl and CN, where at least one R.sup.21 is selected from silyl groups which carry radicals selected from alkyl groups having 1 to 12 C atoms and aryl groups having 6 to 40 aromatic ring atoms; and alkyl groups having 1 to 12 C atoms, which may be substituted by one or more radicals selected from F, Cl and CN; and where R.sup.22 is selected on each occurrence, identically or differently, from H and alkyl groups having 1 to 12 C atoms, which may be substituted by one or more radicals selected from F, Cl and CN.

9. Liquid-crystalline material according to claim 1, characterised in that the compound (II) is present in the liquid-crystalline material in a proportion of 0.01% by weight to 1% by weight.

10. Liquid-crystalline material according to claim 1, characterised in that the dye is a dichroic dye.

11. Liquid-crystalline material according to claim 1, characterised in that the liquid-crystalline material comprises at least three different dyes.

12. Liquid-crystalline material according to claim 1, characterised in that the dye is selected from azo compounds, anthraquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, rylenes, benzothiadiazoles, pyrromethenes and diketopyrrolopyrroles.

13. A method which comprises the step of including the liquid-crystalline material according to claim 1 in a layer of a switchable window.

14. Optical switching device for regulation of the passage of sunlight, containing a layer comprising a liquid-crystalline material according to claim 1.

15. Optical switching device according to claim 14, characterised in that it comprises the following layer sequence: polarisation layer substrate layer electrically conductive transparent layer alignment layer switching layer comprising the liquid-crystalline material alignment layer electrically conductive transparent layer substrate layer, where the polarisation layer faces the sun.

Description

WORKING EXAMPLES

[0160] 1) Preparation of the Liquid-Crystalline Mixtures

[0161] The base mixture uses the following mixture M1:

TABLE-US-00004 Composition of host mixture M1 Clearing point 114.5 C. Delta-n 0.1342 n.sub.e 1.6293 n.sub.o 1.4951 Composition Compound % by weight CPG-3-F 5 CPG-5-F 5 CPU-3-F 15 CPU-5-F 15 CP-3-N 16 CP-5-N 16 CCGU-3-F 7 CGPC-3-3 4 CGPC-5-3 4 CGPC-5-5 4 CCZPC-3-3 3 CCZPC-3-4 3 CCZPC-3-5 3

[0162] Mixture M1-F is obtained by adding dyes F1, F2 and F3 to mixture M1 in the proportions by weight indicated:

TABLE-US-00005 Proportion by weight Dye (% by weight) F1 0.385 F2 0.73 F3 0.84

[0163] Structures of the Dyes:

##STR00096##

[0164] The following liquid-crystalline mixtures are prepared from mixture M1-F by addition of additives A1 and/or A2:

TABLE-US-00006 Proportion of compound A1 Proportion of compound A2 (% by weight) (% by weight) LC1 0.03 0 LC2 0.06 0 LC3 0.1 0 LC4 0.25 0 LC5 0.5 0 LC6 0.1 0.1 LC7 0.1 0.03 LC8 0.15 0.05 LC9 0.05 0.15 LC10 0.15 0.15

[0165] Furthermore, the following liquid-crystalline mixtures are prepared as reference:

TABLE-US-00007 Proportion of Proportion of Proportion of compound A2 compound A3 compound A4 (% by weight) (% by weight) (% by weight) V-LC1 0.03 0 0 V-LC2 0.1 0 0 V-LC3 0 0.1 0 V-LC4 0 0 0.1

[0166] Additives A1, A2, A3 and A4 have the following structures:

##STR00097##

[0167] The mixtures are introduced into LC cells with polyimide alignment layers (rubbed antiparallel, polyimide AL-1054 for planar alignment). The layer thickness of the layer comprising the mixtures is 25 m. The cells are sealed using UV adhesive (Norland).

[0168] The light exposure test is carried out on the cells as follows:

[0169] The cells are measured spectroscopically (initial value). They are then exposed to light for 16 weeks in a Suntest CPS+ from MTS Atlas with the setting Black Standard Temperature 70 C. (=surface temperature of the samples) and using a Schott GG400 UV edge filter, which screens the sample hermetically against relatively short-wave UV light.

[0170] The heat exposure test is carried out on the cells as follows:

[0171] The samples are measured spectroscopically (initial value) and then stored in an oven at 100 C. for 7 days. The spectrum is subsequently remeasured at room temperature.

[0172] Determination of the colour values and the colour separation E*:

[0173] The x, y, and z values are determined from the transmission curves of the respective spectra by the method described by M. Richter, Einfhrung in die Farbmetrik [Introduction into Colorimetry] (Sammlung Gschen, Volume 2608). The x, y and z values are used to determine L*,a*,b* and from these the corresponding differences L*, a* and b*, by the method described by M. Richter, Einfhrung in die Farbmetrik [Introduction into Colorimetry]. The spectrometer used is a Perkin Elmer Lambda 1050.

[0174] Finally, the colour separation (colour difference) E* calculated in the Lab colour space is calculated as follows:

E*=[(L*).sup.2+(a*).sup.2+(b*).sup.2].sup.0.5

[0175] The following results are obtained for the cells produced:

TABLE-US-00008 E* after light E* after heat Device containing exposure test exposure test LC1 6 5.3 LC2 5.5 5.4 LC3 3.1 5.5 LC4 1.8 5.4 LC5 4.1 5.3 LC6 3.1 0.3 LC7 2.9 1.1 LC8 2.8 0.6 LC9 4.9 0.5 LC10 2.9 0.5

[0176] The following results are obtained for devices containing the reference mixtures:

TABLE-US-00009 E* after light E* after heat Device containing exposure test exposure test V-LC1 17.6 0.3 V-LC2 15.1 0.15 V-LC3 18.8 n.d. V-LC4 15.9 n.d. M1-F 23.0 n.d. (without additives)

[0177] The results obtained show that good values for the colour difference E* are obtained in the light exposure test for the devices which contain mixtures comprising additive A1 (LC1 to LC5).

[0178] Relatively good values for the colour difference E* are also obtained in the heat stability test with additive A1.

[0179] By contrast, very poor, unacceptable values for the colour difference E* are obtained in the light exposure test for the reference devices which contain mixtures comprising additives A2, A3 or A4 (V-LC1 to V-LC4). The same applies to mixture M1-F without stabilising additives.

[0180] Very good values for the colour difference E*, both in the light stability test and also in the heat stability test, are obtained with devices which contain both additives A1 and A2 (LC6 to LC10). These again exceed the good values obtained with additive A1 alone.