LIQUID-CRYSTALLINE MEDIUM

Abstract

The invention relates to a liquid-crystalline medium having negative dielectric anisotropy comprising one or more compounds of formula I

##STR00001##

and
one or more compounds selected from the group of the compounds of the formulae IIA, IIB and IIC,

##STR00002##

wherein the groups and parameters have the meanings indicated in claim 1, to a guest-host liquid crystal medium derived therefrom comprising one or more dichroic dyes and the use of said medium in devices such as light shutters, switchable windows, switchable mirrors and guest-host displays. The invention further relates to devices containing the liquid crystalline medium according to the invention.

Claims

1. Liquid-crystalline medium, characterised in that it comprises one or more compounds of the formula I, ##STR00289## wherein R.sup.1 denotes alkyl or alkenyl having up to 12 C atoms, wherein one or more non adjacent CH.sub.2 groups may be replaced by O and/or a cycloalkyl ring having 3 to 5 C atoms, and wherein one or more H atoms may be replaced by F, A.sup.1 on each occurrence, identically or differently, denotes (a) a trans-1,4-cyclohexylene radical, in which one or more non-adjacent CH.sub.2 groups may be replaced by O and/or S, (b) a 1,4-phenylene radical, in which one or two CH groups may be replaced by N, (c) trans-1,4-cyclohexenylene, (d) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals (a) to (d) may be substituted by one or two fluorine atoms, Z.sup.1 on each occurrence, independently of one another, COO, OCO, CH.sub.2O, OCH.sub.2, CH.sub.2CH.sub.2, CHCH, CC, (CH.sub.2).sub.4, OCF.sub.2, CF.sub.2O, CF.sub.2CF.sub.2, or a single bond, L.sup.11, L.sup.12, L.sup.13 and L.sup.14 each, independently of one another, denote H, Cl, or F, n is 1, 2 or 3; and one or more compounds selected from the group of the compounds of the formulae IIA, IIB and IIC, ##STR00290## in which R.sup.2A, R.sup.2B and R.sup.2C each, independently of one another, denote H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF.sub.3 or at least monosubstituted by halogen, where, in addition, one or more CH.sub.2 groups in these radicals may be replaced by O, S, CC, CF.sub.2O, OCF.sub.2, OCO or OCO in such a way that O atoms are not linked directly to one another, or a cycloalkyl ring having 3 to 6 C atoms, L.sup.1-4 each, independently of one another, denote F, Cl, CF.sub.3 or CHF.sub.2, Z.sup.2 and Z.sup.2 each, independently of one another, denote a single bond, CH.sub.2CH.sub.2, CHCH, CF.sub.2O, OCF.sub.2, CH.sub.2O, OCH.sub.2, C(O)O, OC(O), C.sub.2F.sub.4, CFCF, CHCHCH.sub.2O, p denotes 1 or 2, q denotes 0 or 1, and v denotes 1 to 6.

2. Liquid-crystalline medium according to claim 1, wherein the one or more compounds of formula I are selected from the group of compounds of the sub-formulae I-1 and I-2 ##STR00291## wherein R.sup.1 denotes alkyl or alkenyl having up to 7 C atoms, A.sup.11 and A.sup.12 identically or differently, denote ##STR00292## L.sup.11 and L.sup.12 independently of one another, denote H or F, and Z.sup.1 COO, OCO, CH.sub.2O, OCH.sub.2, CH.sub.2CH.sub.2, OCF.sub.2, CF.sub.2O, or a single bond.

3. Liquid-crystalline medium according to claim 1, wherein the compounds of formulae IIA, IIB and IIC are selected from the group of compounds of the following formulae: ##STR00293## wherein alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, alkenyl denotes a straight chain alkenyl radical having 2 to 6 C atoms, and (O) denotes O or a single bond.

4. Liquid-crystalline medium according to claim 1, characterised in that it comprises one or more dichroic dyes.

5. Liquid-crystalline medium according to claim 4, wherein the one or more dichroic dyes are selected from the group of compounds of the formulae ##STR00294##

6. Liquid-crystalline medium according to claim 4, wherein the concentration of the dichroic dye or dyes is 1% by weight or more.

7. Liquid-crystalline medium according to claim 1, characterised in that the medium additionally comprises one or more terphenyls of the formulae T-1 to T-21, ##STR00295## ##STR00296## in which R denotes a straight-chain alkyl or alkoxy radical having 1-7 C atoms or straight-chain alkenyl radical having 2-7 C atoms, and m denotes 1-6.

8. Liquid-crystalline medium according to claim 1, characterised in that the medium additionally comprises one or more compounds of the formulae O-1 to O-16, ##STR00297## in which R.sup.1 and R.sup.2 each, independently of one another, denote H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted monosubstituted by CN or CF.sub.3 or at least monosubstituted by halogen, where, in addition one or more CH.sub.2 groups in these radicals may be replaced by O, S, CC, CF.sub.2O, OCF.sub.2, OC or OCO in such a way that O atoms are not linked directly to one another, or a cycloalkyl ring having 3 to 6 C atoms.

9. Liquid-crystalline medium according to claim 1, characterised in that the proportion of compounds of the formula I in the mixture as a whole is 20% by weight or less.

10. Process for the preparation of a liquid-crystalline medium according to claim 1, characterised in that at least the compound of the formula I is mixed with at least one further liquid-crystalline compound, and optionally one or more additives and optionally at least one polymerisable compound are added.

11. A method which comprises including the liquid-crystalline medium according to claim 1 in a light shutter, switchable window, guest-host display or automotive mirror.

12. Electro-optical device, characterised in that it contains, as dielectric, a liquid-crystalline medium according to claim 1.

13. Device according to claim 12, wherein the device is a light shutter, a switchable window, a guest-host display or a switchable mirror.

Description

WORKING EXAMPLES

[0200] The following examples are intended to explain the invention without limiting it. In the examples, m.p. denotes the melting point and C denotes the clearing point of a liquid-crystalline substance in degrees Celsius; boiling temperatures are denoted by b.p. Furthermore:

[0201] C denotes crystalline solid state, S denotes smectic phase (the index denotes the phase type), N denotes nematic state, Ch denotes cholesteric phase, I denotes isotropic phase, T.sub.g denotes glass-transition temperature. The number between two symbols indicates the conversion temperature in degrees Celsius.

[0202] The host mixture used for determination of the optical anisotropy n of the compounds of the formula I is the commercial mixture ZLI-4792 (Merck KGaA). The dielectric anisotropy is determined using commercial mixture ZLI-2857. The physical data of the compound to be investigated are obtained from the change in the dielectric constants of the host mixture after addition of the compound to be investigated and extrapolation to 100% of the compound employed. In general, 10% of the compound to be investigated are dissolved in the host mixture, depending on the solubility.

[0203] Unless indicated otherwise, parts or percent data denote parts by weight or percent by weight.

[0204] Above and below, the symbols and abbreviations have the following meanings: [0205] V.sub.o threshold voltage, capacitive [V] at 20 C. [0206] n the optical anisotropy measured at 20 C. and 589 nm [0207] the dielectric anisotropy at 20 C. and 1 kHz [0208] cl.p. clearing point [ C.] [0209] K.sub.1 elastic constant, splay deformation at 20 C. [pN] [0210] K.sub.3 elastic constant, bend deformation at 20 C. [pN] [0211] .sub.1 rotational viscosity measured at 20 C. [mPa.Math.s], determined by the rotation method in a magnetic field [0212] LTS low-temperature stability (nematic phase), determined in test cells.

[0213] The display used for measurement of the threshold voltage has two plane-parallel outer plates at a separation of 20 m and electrode layers with alignment layers comprising SE-1211 (Nissan Chemicals) on top on the insides of the outer plates, which effect a homeotropic alignment of the liquid crystals.

[0214] All concentrations in this application, unless explicitly indicated otherwise, relate to the corresponding mixture or mixture component. All physical properties are determined in accordance with Merck Liquid Crystals, Physical Properties of Liquid Crystals, status November 1997, Merck KGaA, Germany, and apply to a temperature of 20 C., unless explicitly indicated otherwise.

MIXTURE EXAMPLES

Comparative Example C1

[0215]

TABLE-US-00009 CBC-33 3.0% Clearing point [ C.]: 112.5 CBC-33F 3.0% n [589 nm, 20 C.]: 0.1995 CCY-3-O1 3.0% [1 kHz, 20 C.]: 4.9 CCY-3-O2 11.0% .sub. [1 kHz, 20 C.]: 4.1 CPY-2-O2 12.0% K.sub.1 [pN, 20 C.]: 18.0 CPY-3-O2 12.0% K.sub.3 [pN, 20 C.]: 22.8 PGIGI-3-F 8.0% PY-3-O2 20.0% PYP-2-3 14.0% PYP-2-4 14.0%

Example M1

[0216]

TABLE-US-00010 PCH-3 10.0% Clearing point [ C.]: 100.5 CBC-33 3.0% n [589 nm, 20 C.]: 0.1865 CBC-33F 2.0% [1 kHz, 20 C.]: 1.4 CCY-3-O1 3.0% .sub. [1 kHz, 20 C.]: 7.4 CCY-3-O2 10.0% K.sub.1 [pN, 20 C.]: 13.5 CPY-2-O2 11.0% K.sub.3 [pN, 20 C.]: 18.8 CPY-3-O2 11.0% .sub.1 [mPa .Math. s, 20 C.]: 65 PGIGI-3-F 7.0% PY-3-O2 18.0% PYP-2-3 13.0% PYP-2-4 12.0%

Example M2

[0217]

TABLE-US-00011 PCH-3 6.0% Clearing point [ C.]: 102 CCY-3-O1 8.0% n [589 nm, 20 C.]: 0.1880 CCY-3-O2 11.0% [1 kHz, 20 C.]: 3.1 CPY-2-O2 12.0% .sub. [1 kHz, 20 C.]: 6.2 CPY-3-O2 12.0% K.sub.1 [pN, 20 C.]: 13.9 PGIGI-3-F 8.0% K.sub.3 [pN, 20 C.]: 19.3 PY-3-O2 15.0% V.sub.0 [20 C., V]: 2.65 PYP-2-3 14.0% PYP-2-4 14.0%

Example M3

[0218]

TABLE-US-00012 PCH-3 6.0% Clearing point [ C.]: 111 CCY-3-O1 8.0% n [589 nm, 20 C.]: 0.1912 CCY-3-O2 11.0% [1 kHz, 20 C.]: 2.9 CPY-2-O2 12.0% .sub. [1 kHz, 20 C.]: 6.1 CPY-3-O2 15.0% PGIGI-3-F 8.0% PY-3-O2 10.0% PYP-2-3 15.0% PYP-2-4 15.0%

[0219] From the Mixtures C1, M1, M2 and M3, guest-host liquid crystal mixtures GHC1, GH1, GH2, GH3 and GH4 are prepared having the compositions given in the tables below, using a dye mixture consisting of the following components Dye-1, Dye-2 and Dye-3, whose different absorption characteristics together result in a black colour, and in the case of GH3, the additives Add-1 and Add-2.

##STR00288##

Comparative Example GHC1

[0220]

TABLE-US-00013 weight component proportion C1 100.0 Dye-1 0.338 Dye-2 0.511 Dye-3 0.950

Example GH1

[0221]

TABLE-US-00014 weight component proportion M1 100.0 Dye-1 0.338 Dye-2 0.511 Dye-3 0.950

Example GH2

[0222]

TABLE-US-00015 weight component proportion M2 100.0 Dye 1 0.338 Dye 2 0.338 Dye 3 0.338

Example GH3

[0223]

TABLE-US-00016 weight component proportion M2 100.0 Dye 1 0.338 Dye 2 0.511 Dye 3 0.950 Add-1 0.100 Add-2 0.100

Example GH4

[0224]

TABLE-US-00017 weight component proportion M3 100.0 Dye 1 0.338 Dye 2 0.511 Dye 3 0.950

[0225] Surprisingly, in the mixtures M1, M2 and M3 comprising the compound PCH-3 of formula I, the dye mixture consisting of Dye-1, Dye-2 and Dye-3 shows significantly better solubility than in the mixture of comparative example C1. In the case of Comparative Example GHC1, the concentration of dyes is very close to the saturation limit which bears the risk of crystallisation of dyes in display panels upon storage. In case of the Examples GH1 to GH4 the saturation limit is not reached.

[0226] The guest-host mixtures GH1, GH2, GH3 and GH4 have very good properties for applications in devices as for example light shutters, switchable windows and guest host displays because of their high clearing temperature and broad nematic phase ranges, low threshold voltage and very good low temperature stability. Due to the excellent solubility of the dyes Dye-1, Dye-2 and Dye-3 in the mixtures M1, M2 and M3, a high contrast can be achieved having a very good black (dark) state after application of a voltage.