DE4001843A1 - Electro-optical LC system - Google Patents

Abstract

(+1.11.89(2), 9.12.89, 10.1.90(2), 12.1.90, 16.1.90, 19.1.90(3), 22.1.90, 23.1.90, 25.1.90-DE-936307/8, 940788, 000470/1, 000723, 001023, 001539, 001540/1, 001683, 001843, 002146) Electro-optical LC system comprises a dielectrically positive LC mixt. (LCM) and another optically transparent medium (M2) between 2 electrodes which may be mounted on substrate plates; the LC mols. have an irregular orientation in the "off" state one of the refractive indices of LCM matches that of the matrix (nM) and/or the ratio of the masses (LCM):(M2) is 1.5 or above, and the system shows reduced transmission in one of the switching states w.r.t. the other state, irrespective of the polarisation of the incident light; the novelty is that LCM contains cpd(s). of formula (I). In (I), Q1 = A1-Z1-(Z2-Z2)m- (with A1, A2 = trans-1,4-cyclohexylene (Cyc), 1,4-phenylene (Phe), 2-fluoro-Phe or 3-fluoro-Phe; one of the gps. A1 and (if present) A2 can also = pyridine-, pyrimidine-, 1,3-dioxan- or tetrahydropyran-2,5-diyl, or naphthalene-2,6-diyl; Z1, Z2 = single bond, CH2CH2, COO, OCO, -CC-, and/or CH2O; m = 0, 1 or 2); Y, X = H or F; one gp. X or Y can also = Cl; W = CN, Cl, F, CF3, OCF3, OCHF2, NCS or R2 (with R2 = as for R1 below); R1 = 1-12C alkyl, opt. with 1 or 2 non-adjacent CH2 gps. replaced by O or CH=CH.

Description

The invention relates to electro-optical liquid crystal systems according to the preamble of claim 1.

The optically transparent medium can be distinguished from one another Contain liquid crystal microdroplets or form a spongy, 3-dimensional network, in whose pores, to a greater or lesser extent merge into each other, the liquid crystal is. By the expression liquid crystal microdroplets small, separate liquid crystal compartments marked, which is by no means a spherical Must have shape, but irregular can be shaped and / or deformed.

Contains the optically transparent medium liquid crystal microdroplets, it is referred to below as the matrix; on the other hand there is a spongy, 3-dimensional networked structure before, the medium is through the expression Network characterized.

NCAP and PDLC films (NCAP = nematic curvilinearly aligned phases, PDLC = polymer dispersed liquid crystal) Examples of electro-optic liquid crystal systems, where the liquid crystal is in the form of microdroplets is embedded in the matrix. NCAP films become common obtained by encapsulating the polymer  Material such as B. polyvinyl alcohol, the liquid crystal mixture and a carrier material such as e.g. B. water, in be mixed intimately in a colloid mill. Subsequently the carrier material z. B. removed by drying. A corresponding method is described in US 44 35 047. In contrast, the z. B. in EP 02 72 582 and US 46 88 900 described production of PDLC films the liquid crystal mixture first with monomers or Oligomers of the matrix-forming material mixed homogeneously. The mixture is then polymerized and induced phase separation, with between TIPS (temperature-induced phase separation), SIPS (solvent-induced phase separation) and PIPS (polymerization-induced phase separation) is distinguished (Mol. Cryst. Liq. Cryst. Inc. Nonlin. Opt. 157 (1988) 427).

The PN system described in EP 03 13 053 (PN = polymer Network) has a spongy network structure optically transparent medium. The proportion of liquid crystal is at the mass of the light-modulating layer generally greater than 60% and in particular lies between 70-90%. To manufacture the PN systems usually a mixture of the liquid crystal, Monomers or oligomers of the 3-dimensional network forming material and a polymerization initiator, especially a photoinitiator, between 2 with electrodes provided substrate plates and then z. B. polymerized by exposure to light.

The liquid crystal generally has a positive dielectric anisotropy Δε and a relatively high optical anisotropy. In microdroplet matrix systems, one of the refractive indices of the liquid crystal, usually the ordinary refractive index n₀, is chosen so that it more or less coincides with the refractive index n _{M of} the polymeric matrix. In network systems, it is not absolutely necessary to adjust the refractive indices because of the usually much higher proportion of liquid crystal in the light-modulating layer, but it can be done to increase the light throughput and the contrast.

One observes on these electro-optic liquid crystal systems an electrically switchable light scattering effect. There is no voltage on the electrodes between which the matrix or the network usually sandwiches is arranged, created, becomes striking Light on the statistically aligned liquid crystal molecules heavily scattered, the system is opaque. When a voltage is applied, the liquid crystal molecules parallel to the field and perpendicular to the E-vector of the light passing through.

In microdroplet matrix systems, vertically incident light sees an optically isotropic medium due to the adaptation of n₀ and n _M and the system appears transparent. Adjustment is required to avoid light scattering at the matrix / liquid crystal droplet phase boundary. Another embodiment is described in EP 02 72 585, in which the refractive index n _x , which the liquid crystal has with a completely statistical orientation, is matched to the refractive index of the matrix n _M. In this case, the system is transparent in the field-free state, and it is converted to the opaque state by applying a voltage.

In the case of network systems, the refractive indices have to be adjusted not absolutely necessary because of the high Liquid crystal portion of the mass of the light modulating Layer the scatter at the network liquid crystal phase boundary is obviously less strong. The System appears without when switched on Transparent refractive index adjustment. With network systems  is to achieve the lowest possible Transmission in the non-switched state use of liquid crystals with high optical anisotropy prefers.

Electro-optical liquid crystal systems according to the generic term of claim 1 are mainly for large areas Display systems, for architectural applications (windows, Room dividers, sun roofs etc.) and for motor vehicles (Windows, sun roofs, etc.) have been proposed, whereby these systems are also used for temperature regulation controlled shielding of solar radiation are suitable. they can by applying a DC or AC voltage be switched.

Because these systems are particularly suitable for "outdoor" applications liquid crystals are required, which has a wide nematic due to a high clearing point Range and high UV and temperature stability are. Next is a high value for the dielectric Anisotropy Δε preferred to be low To obtain threshold voltage.

Other applications include:

• - GH display systems, the spectrum being simple Segment displays up to displays on which with any electrode pattern using conventional printing techniques can be applied. Applications: Motor vehicle, large advertisements, advertising space, clocks
• - Matrix displays with high information content
• - projection systems
• - Counter.

Here too, liquid crystal mixtures are used in particular high Δε and high electrical resistance required.

Up to now, micro-droplet matrix systems have been common LC mixtures used, which consist of alkyl or alkoxycyanobiphenyls and -therphenylene exist. So z. B. in US 46 88 900 and in EP 02 72 585 the use of the liquid crystal mixture E8 (manufactured by BDH, Poole, Great Britain). This liquid crystal mixture draws by a high value for the optical anisotropy Δn of 0.247 and a relatively high value for the flow viscosity η (20 ° C) from 54 mm² / s, but at the same time a relatively low clearing point of only 72 ° C. Polynuclear polyphenyl compounds are added to the mixture to increase the clearing point results in a higher one Value for the flow viscosity η and an unchanged high or higher value for the optical anisotropy Δn. Height On the one hand, Δn values ensure strong light scattering in the opaque state, but on the other hand they can Turbidity of the system in the switched state ("haze") and thus a significant deterioration in the electro-optical Effect properties. In systems developed by a relatively low frequency AC voltage a high flow viscosity η is desired to achieve a get flicker-free display; on the other hand, however in matrix displays with high information content for Realization of fast switching times of liquid crystal mixtures with a relatively low viscosity.

The liquid crystal mixture E7 used in US Pat. No. 4,671,618 (manufactured by BDH, Poole, Great Britain), which also consists of alkyl and alkoxycyanobiphenylene and terphenylene, has a lower flow viscosity with η = 39 mm² / s and with Δn = 0.225 one somewhat smaller optical anisotropy Δn than E8, but at the same time the clearing point T _C = 60.5 ° C is considerably lower.

EP 03 13 053 proposes liquid crystal mixtures based on 2- (4-cyanophenyl) pyridines for network systems. Such liquid crystals do have relatively high values for the dielectric anisotropy Δε and thus relatively low threshold voltages and high to very high values for the optical anisotropy Δn. At the same time, however, these liquid crystals are characterized by a relatively high viscosity η and a relatively low clearing point T _c . Furthermore, cyanophenylpyridine compounds generally have a lower temperature and UV stability than cyanooligophenyls.

The liquid crystals used so far meet the Demands for a wide nematic area, one high clearing point, very high stability, one Absence of smectic phases down to low temperatures, one that can be optimized with regard to the respective application optical anisotropy Δn and flow viscosity η and a high Δε is insufficient.

In addition, the previous liquid crystals often have one insufficient miscibility with the monomers and / or oligomers used to form the matrix or network Polymers on what the manufacture of PN systems significantly impaired and with microdroplet matrix systems especially the application of PIPS technology significantly restricted. In addition, the liquid crystals often due to excessive solubility in the matrix or network-forming polymer. Another There is often a disadvantage of the previous liquid crystals in that the liquid crystal for each application unfavorable values of the electro-optical parameters such. B. the steepness of the electro-optical characteristic and / or the Temperature dependence of the electro-optical parameters such as e.g. B. shows the threshold voltage.

There is therefore still a great need for electro-optical Liquid crystal systems that match the corresponding Better meet requirements and the described Do not have disadvantages or only to a lesser extent.

The invention was based on the object of electro-optical To provide liquid crystal systems that the listed Disadvantages of conventional systems not or only to a small extent.

Surprisingly, it has now been found that this task can be solved if you have liquid crystals for these systems used one or more connections of formula I contain

R-Q¹-Q²-W-F (I)

wherein

W -CF₂-; -OCF₂-, -OCHF- or a single bond,
Q² 1,4-phenylene, 2-fluoro-1,4-phenylene or 3-fluoro-1,4-phenylene
Q¹ A¹- (A²) _m -Z- or -A¹-Z-A²-,
Z äCH₂CH₂-, a single bond, -CO-O-, or -O-CO-,
A¹ and A² are each independently 1,4-phenylene, trans-1,4-cyclohexylene, pyrimidine-2,5-diyl or pyridine-2,5-diyl
m 0 or 1, and
R alkyl having up to 12 carbon atoms, in which one or two non-adjacent CH₂ groups can also be replaced by -O-,

mean.

For the sake of simplicity, Phe in the following means 1,4-phenylene, Phe.2F 2-fluoro-1,4-phenylene, Phe.3F 3-fluoro-1,4-phenylene, Cyc trans-1,4-cyclohexylene, pyr pyrimidine-2,5-diyl and Pyd Pyridine-2,5-diyl, whereby the two abbreviations Pyr and Pyd each comprises the two possible positional isomers are. Phe. (F) is also intended to be a 1,4-phenylene group are referred to as unsubstituted or in the 2- or 3-position can be monofluorinated.

The invention thus relates to an electro-optical Liquid crystal system,

• - Which between 2 electrodes, if necessary are applied to substrate plates, one dielectric positive liquid crystal and a contains another optically transparent medium,
• - Its liquid crystal molecules when switched off Irregular orientation,
• in which one of the refractive indices of the liquid crystal essentially corresponds to the refractive index of the matrix n _M and / or in which the quotient of the mass of the liquid crystal and the mass of the optically transparent medium is 1.5 or more,
• - Which is independent in one of the two switching states of the polarization of the incident light reduced transmission compared to the other state has, wherein the liquid crystal one or more Contains compounds of formula I.

The structure of the electro-optical liquid crystal systems according to the invention corresponds to that for such systems usual design. The term common design is here broad and embraces all variations and modifications.

So z. B. in PDLC or NCAP films from the transparent Medium formed matrix in which the liquid crystal mixture microdispersed or microencapsulated is sandwiched between conductive electrodes.

The electrodes are i. a. on substrate plates from z. B. Glass, plastic or similar applied; if necessary, the matrix but can also be provided directly with electrodes, so that the use of substrates can be dispensed with can.

The liquid crystal is in network systems in the pores of the spongy, 3-dimensional network. The network is usually between electrodes provided substrates arranged to escape the To prevent liquid crystal.

Both PN systems and microdroplet matrix systems can be operated reflectively or transmissively, so that at least one electrode and, if available, the associated substrate are transparent. Both systems usually do not contain polarizers, which means a significantly higher light throughput results. Farther  no orientation layers are required, which is a considerable technological simplification in production of these systems compared to conventional liquid crystal systems such as B. TN or STN cells.

The matrix or the 3-dimensional network are based in particular on isotropic thermoplastics, thermosets and Elastomers. The systems obtained can be used as intended Use flexible, elastic or rigid.

A system based on a thermoplastic polymer can at temperatures greater than the glass temperature the matrix, easily by the action of a mechanical Tension can be deformed. This can e.g. B. in microdroplet matrix systems used to create a deliberately deformed shape of the droplets by cooling the matrix to temperatures below the glass temperature freeze.

While flexible and / or elastic systems are preferred based on thermoplastics and / or elastomers preferably thermosetting for the production of rigid systems Polymers used. This can occur during curing be mechanically deformed, being in the cured Matrix z. B. the shape and arrangement of the microdroplets is fixed.

Especially for the production of the matrix or the network preferred polymers are e.g. B. in US 39 35 337, US 46 88 900, US 46 71 618, US 46 73 255, US 44 35 047, EP 03 13 053 and EP 02 72 585 discloses.

In addition, other transparent materials can also be used such as B. inorganic oxide glass monoliths (US 48 14 211), other inorganic materials (see. e.g. B. Japanese Patent Application 3 03 325/1988) or other materials can also be used.  

Preferred embodiment of the electro-optical according to the invention Liquid crystal systems are NCAP films, PDLC films and produced by modified processes Micro droplet matrix systems. Manufacturing process these films are e.g. B. in US 39 35 337, US 46 88 900, US 46 73 255, US 46 71 618, US 44 35 047 and EP 02 72 595 described.

Another preferred embodiment of the invention electro-optical systems are the network systems their manufacture z. B. is described in EP 03 13 053.

However, such embodiments of FIG Invention comprises, in which the transparent medium Structure that is between the network structure one side and the microdroplet matrix configuration is on the other side.

The electro-optical systems according to the invention include also "inverse microdroplet matrix configurations", where the transparent medium in the form of individual e.g. B. spherical particles dispersed in the liquid crystal is. Such an arrangement is e.g. B. in GB 14 42 360 described.

There are also others that are not explicitly mentioned here Embodiments of the invention include.

The thickness d of the electro-optical systems d is usually chosen to be small in order to achieve the lowest possible threshold voltage V _th . So z. B. reported in US 44 35 047 layer thicknesses of 0.8 and 1.6 mm, while for the layer thickness in US 46 88 900 values between 10 microns and 300 microns and in EP 03 13 053 between 5 microns and 30 microns are given. The electro-optical systems according to the invention have a layer thickness d that is significantly greater than a few mm only in exceptional cases; layer thicknesses d ≦ 2 mm are preferred.

The threshold voltage is also influenced by the size of the microdroplets or the mesh size of the network. In general, smaller microdroplets result in a higher threshold voltage V _th , but shorter switching times t _on and t _off (US Pat. No. 4,673,255). Experimental methods for influencing the mean droplet size are e.g. B. in US 46 73 255 and in JL West, Mol. Cryst. Liq. Cryst. Inc. Nonlin. Opt., 157 (1988) 427. In US 46 73 255 mean drop diameters between 0.1 microns and 8 microns are given, while z. B. a matrix based on a glass monolith has pores with a diameter between 15 and 2000 Å. A preferred range between 0.5 and 2 μm is specified for the mesh size of the network of PN systems in EP 03 13 053.

A major difference between the electro-optical according to the invention Liquid crystal systems to the usual ones however, consists in the liquid crystal used.

The liquid crystals according to the invention contain at least a compound of formula I.

The compounds of the formula I comprise dinuclear compounds of the formulas Ia1 to Ia4, which are preferred:

R-A¹-Z-Phe. (F) -F (Ia1)
R-A¹-Z-Phe. (F) -CF₃ (Ia2)
R-A¹-Z-Phe. (F) -OCF₃ (Ia3)
R-A¹-Z-Phe. (F) -OCHF₂ (Ia4)

In the compounds of the formulas Ia1-Ia4, R preferably denotes Alkyl or alkoxy with 1-10, in particular however with 1-8 C atoms, the straight-chain residues are preferred. Further preferred are n-alkoxyalkyl compounds and especially n-alkoxymethyl and n-alkoxyethyl compounds. Z is preferably -CH₂CH₂-, -COO- or a single bond, especially a single bond or -CH₂CH₂- and especially one Single bond.

The compounds of formula I further include trinuclear Compounds of the formulas Ib1-Ib8

R-A¹-A²-Z-Phe. (F) -F (Ib1)
R-A¹-A²-Z-Phe. (F) -CF₃ (Ib2)
R-A¹-A²-Z-Phe. (F) -OCF₃ (Ib3)
R-A¹-A²-Z-Phe. (F) -OCHF₂ (Ib4)
R-A¹-Z-A²-Phe. (F) -F (Ib5)
R-A¹-Z-A²-Phe. (F) -CF₃ (Ib6)
R-A¹-Z-A²-Phe. (F) -OCF₃ (Ib7)
R-A¹-Z-A²-Phe. (F) -OCHF₂ (Ib8)

In the compounds of the formulas Ib1-1b8, R preferably denotes n-alkyl or n-alkoxy with 1-10 C atoms, next to it also n-alkoxymethyl or n-alkoxyethyl with 1-8 C atoms.  

Compounds of the formulas are very particularly preferred Ib1-Ib8, where R is methyl, ethyl, propyl, butyl, pentyl, Hexyl, heptyl, octyl, nonyl, decyl, methoxy, ethoxy, Propoxy, butoxy, pentoxy, hexoxy, heptoxy, octoxy, Methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, Methoxyethyl, ethoxyethyl or propoxyethyl means. Z means in the compounds of the formulas Ib1-Ib8 preferably -CH₂CH₂-, -COO- or a single bond and in particular -CH₂CH₂- or a single bond.

Liquid crystals that contain one or more compounds of the formulas Ia1-Ia4 and Ib1-Ib8 with Phe. (F) = Phe.3F contain, have advantageous values for the dielectric Anisotropy Δε. Particularly advantageous Such compounds of the formulas have values for Δε Ia1-Ia4 and Ib1-Ib8, for which Phe. (F) = Phe.3F and A¹ or A², if any,

Binuclear compounds of the are particularly preferred Formulas Ia1-Ia4, where Phe. (F) means Phe or Phe.3F. Dinuclear compounds of the formulas Ia1-Ia4, where Phe. (F) means Phe.2F, are characterized by good miscibility with other liquid crystals and are also particularly preferred.

The following smaller group is more preferably trinuclear Links:

R-Phe-Phe-Z-Phe. (F) -F (Ib11)
R-Phe-Phe-Z-Phe. (F) -CF₃ (Ib21)
R-Phe-Phe-Z-Phe. (F) -OCF₃ (Ib31)
R-Phe-Phe-Z-Phe. (F) -OCHF₂ (Ib41)

R-Cyc-Phe-Z-Phe. (F) -F (Ib12)
R-Cyc-Phe-Z-Phe. (F) -CF₃ (Ib22)
R-Cyc-Phe-Z-Phe. (F) -OCF₃ (Ib32)
R-Cyc-Phe-Z-Phe. (F) -OCHF₂ (Ib42)

R-Phe-Z-Phe-Phe. (F) -F (Ib51)
R-Phe-Z-Phe-Phe. (F) -CF₃ (Ib61)
R-Phe-Z-Phe-Phe. (F) -OCF₃ (Ib71)
R-Phe-Z-Phe-Phe. (F) -OCHF₂ (Ib81)

R-Cyc-Z-Phe-Phe. (F) -F (Ib52)
R-Cyc-Z-Phe-Phe. (F) -CF₃ (Ib62)
R-Cyc-Z-Phe-Phe. (F) -OCF₃ (Ib72)
R-Cyc-Z-Phe-Phe. (F) -OCHF₂ (Ib82)

In these compounds, Phe. (F) means in particular Phe or Phe.3F; however, very particularly preferably means Phe. (F) = Phe and Z is a single bond or CH₂CH₂.

The radical R in the compounds of the formula I can be straight-chain or be branched. R is preferably straight-chain, however, compounds of formula I with branched alkyl or alkoxy radicals occasionally because of a better solubility in the usual liquid crystalline Base materials may be important, especially but as chiral dopants if they are optically active. Electro-optical systems according to the The preamble of claim 1, the liquid crystal of which or contains several chiral components are in DE 39 11 255.1.

Branched groups of this type usually contain no more than a chain branch. Preferred branched Residues are isopropyl, 2-butyl (= 1-methylpropyl), Isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl,  2-ethylhexyl, 2-propylpentyl, 2-octyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl, 2-nonyl, 6-methyloctoxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl.

The compounds of formula I are either known and / or are displayed according to known methods, as described in the literature (e.g. in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart vol. IX, pp. 867 ff.) are, and under reaction conditions that for the mentioned implementations are known and suitable. Here you can also from well-known, not closer here make use of the variants mentioned.

The compounds of formula I are preferably after in DE 31 02 017, JP 5 71 40 747, DE 32 33 641, DE 29 37 911, EP 00 97 033, DE 35 09 260, DE 37 32 284, DE 39 28 783, EP 01 94 153, JP 5 81 26 839, JP 5 82 10 045, WO 85/04 874, DE 33 15 295, EP 01 93 191, JP 6 32 80 063 and DE 38 25 428 described processes.

The liquid crystal mixtures according to the invention are based in addition to compounds of formula I preferably on compounds of formulas II-V

wherein
R¹ are each independently an alkyl group with 1-15 C atoms, in which one or two non-adjacent CH₂ groups can also be replaced by -O-, -CO- and / or -CH = CH,

mean.

The liquid crystals according to the invention can be further Contain ingredients, preferably selected are made from nematic or nematogenic (monotropic or isotropic) substances, especially substances from the Classes of azoxybenzenes, benzylidene anilines, biphenyls, Terphenyls, phenyl or cyclohexyl benzoates, cyclohexane carboxylic acid phenyl or cyclohexyl ester, phenyl or Cyclohexyl ester of cyclohexylbenzoic acid, phenyl or Cyclohexyl ester of cyclohexylcyclohexane carboxylic acid, Cyclohexylphenyl ester of benzoic acid, cyclohexane carboxylic acid, or the cyclohexylcyclohexane carboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, Phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane,  1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenylcyclohexyl) ethane, 1-cyclohexyl-2-biphenylylethane, 1-phenyl-2-cyclohexylphenylethane, optionally halogenated Stilbene, benzylphenyl ether, tolanes and substituted Cinnamic acids. The 1,4-phenylene groups in these Compounds can also be fluorinated.

The most important as further components of the in the electro-optical systems according to the invention used Leave liquid crystals in question are characterized by the formulas 1, 2, 3, 4 and 5:

R′-LER ′ ′ (1)
R′-L-COO-ER ′ ′ (2)
R′-L-OOC-ER ′ ′ (3)
R′-L-CH₂CH₂-ER ′ ′ (4)
R′-LC≡CER ′ ′ (5)

In formulas 1, 2, 3, 4 and 5, L and E denote that can be the same or different, each independently one bivalent residue from the other from -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images formed Group, where Phe is unsubstituted or substituted by fluorine 1,4-phenylene, cyc trans-1,4-cyclohexylene or 1,4-cyclohexenylene, pyr pyrimidine-2,5-diyl or Pyridine-2,5-diyl, dio 1,3-dioxane-2,5-diyl and G 2- (trans-1,4-cyclohexyl) ethyl, Pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

Preferably one of the residues L and E is Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. Preferably contain the liquid crystals according to the invention one or more components selected from the compounds of formulas 1, 2, 3, 4 and 5, wherein L and E are selected from the group Cyc, Phe and Pyr and  one or more components selected at the same time from the compounds of the formulas 1, 2, 3, 4 and 5, in which one of the residues L and E is selected from the group Cyc, Phe and Pyr and the other residue is selected from the group -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein the residues L and E are selected from the Group -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc.

R 'and R' 'in the compounds of the sub-formulas 1a, 2a, 3a, 4a and 5a each independently Alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy with up to 8 carbon atoms. Most of these connections R 'and R' 'are different from each other, whereby one of these residues is mostly alkyl or alkenyl. In the Connections of sub-formulas 1b, 2b, 3b, 4b and 5b means R '' -CN, -CF₃, F, Cl or -NCS; R has the specified for the compounds of the sub-formulas 1a to 5a Meaning and is preferably alkyl or alkenyl. But other variants of the proposed substituents in the compounds of formulas 1, 2, 3, 4 and 5 in use. Many such substances or mixtures of which are commercially available. All of these substances are by methods known from the literature or by analogy available for this.

The in the electro-optical liquid crystal systems according to the invention used liquid crystals contain preferably in addition to components from the group of compounds 1a, 2a, 3a, 4a and 5a (group 1) also components from the group of compounds 1b, 2b, 3b, 4b, and 5b (Group 2), the proportions of which are preferably as follows are:

Group 1: 0 to 60%, in particular 5 to 50%,
Group 2: 0 to 60%, especially 5 to 40%.

The in the electro-optical liquid crystal systems according to the invention used liquid crystals contain preferably 1-40%, especially 5-30% of compounds of formula I. The liquid crystals preferably contain 1-5, but especially 1-3 compounds of formula I.

The proportion of those consisting of compounds of the formulas I-V Base mixture on the in the electro-optical according to the invention Liquid crystal systems used liquid crystals is preferably 15% -100%, especially however 25% -100%. The basic mix is based on compounds of formula I particularly preferred on the following smaller group of compounds, wherein R¹ is the has the meaning given above.

Liquid crystals based on based on the mixtures 1-12 described below, the mass fraction of mixtures 1-12 in the liquid crystal between 10% and 98% and especially between 15% and 95%. Mixtures 1-12 consist of 2 or more compounds listed under 2, 3, 4 or 5 formulas fall from the group of formulas I, II, III, IV and V can be selected. Mixtures 1-12 preferably contain 2-40, but especially 2-38 and very special 2-35 connections. The mass fraction of these compounds on mixtures 1-12 can be within the specified Limits for optimal adaptation to the respective Display type can be varied, the sum of these mass fractions of the mixtures 1-12 of course 100% is.

The electro-optical liquid crystal systems according to the invention are preferably characterized in that none or only one during the manufacture of the system little interaction of the components of the liquid crystal mixture with the polymeric carrier material polar groups comes about.

The electro-optical liquid crystal systems according to the invention can apply a DC or AC voltage be switched. However, one is preferred AC voltage is used, which has an effective AC voltage amplitude between 1 and 240 volts and one Has alternating voltage frequency between 10 and 10 kHz. Amplitudes between 2 and 220 volts and frequencies between 20 and 120 Hz. Quite the amplitude of the alternating voltage is particularly preferred between 2 and 130 V.

The dielectric anisotropy of the liquid crystal mixture used is positive Δε <0 and preferably Δε <3. For smaller values of the dielectric anisotropy Δε very high threshold voltages are observed. Values Δε <5 are particularly preferred, in particular Δε <10 and very particularly Δε <10.  

The preparation of the liquid crystal mixtures which can be used according to the invention takes place in a conventional manner. As a rule, the desired amount is less Amount of components used in the main ingredient constituent components solved, useful at elevated temperature. It is also possible to find solutions to the Components in an organic solvent, e.g. B. in Mix acetone, chloroform or methanol and that Remove solvent after thorough mixing, for example by distillation.

The liquid crystal mixtures described can be added by suitable additives be modified so that they are in all electro-optical systems according to the generic term of claim 1 can be used.

Such additives are known to the expert and in the Literature described in detail. So z. B. pleochroic Dyes for the production of colored electro-optical Systems or substances to change the dielectric anisotropy, optical anisotropy, the viscosity and / or the temperature dependence of electro-optical Liquid crystal parameters added will. Such substances are e.g. B. in H. Kelker, R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980 and in DE-OS 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430, 28 53 728 and 29 02 177.

Electro-optical liquid crystal systems in which the Liquid crystal pleochroic dyes in one Weight percentage range from 0-25%, especially 0-20% and especially 0-15% are preferred.  

The professional can be more nematic from the large pool or nematogenic substances additives to those described Select liquid crystal mixtures so that the birefringence Δn and / or the ordinary refractive index n₀ and / or other refractive indices and / or the viscosity and / or dielectric anisotropy and / or others Liquid crystal parameters with regard to the respective application can be optimized.

To increase the clearing point, the person skilled in the art Systems used according to the invention liquid crystal mixtures e.g. B. add clarifying substances such. B.

where R² and R³ are each independently alkyl, Methoxy, alkoxycarbonyl or alkanoyloxy with 1-15 C atoms mean. The person skilled in the art becomes more concentrated in this way Choose additives preferably so that in particular Δn and / or n₀ and / or another, at the respective Design of the electro-optical according to the invention Refractive index and / or Δε to be adjusted only in an acceptable and / or small and / or in particular negligible extent is affected.

If the system according to the invention with an AC voltage controlled, is the use of a highly viscous liquid crystal mixture required, otherwise otherwise in particular low to medium frequencies a flickering display results. A person skilled in the art can increase the viscosity  the liquid crystal mixture highly viscous liquid crystal compounds or in particular one or more Side chain polymers, as described in DE 39 19 942 is to clog. Will the electro-optical system oppose it e.g. B. used as a matrix display with high information content, are especially low-viscosity liquid crystal mixtures preferred to achieve short switching times. The professional can be nematic or out of the large pool nematogenic compounds of low viscosity select how B.

where R² and R³ have the meaning given above. The person skilled in the art will choose the substances used for modifying the viscosity and their concentration so that other decisive parameters of the liquid crystal mixture, such as, for. B. Δn, Δε and when using viscosity depressants in particular T _{c is} only influenced to an acceptable and / or small and / or insignificant extent.

If necessary, highly nematogenic substances such. B.

can be added, the expert taking into account that through such additions other parameters and in particular the solubility of the liquid crystal mixture in the for the polymer used did not change too much will.  

The person skilled in the art can modify the birefringence e.g. B. in liquid crystal mixtures, the compounds of Formulas II-IV contain the relative proportion of these compounds vary on the mix; for mixtures with very high Δn can e.g. B. in particular 4-alkyl or alkoxy-4 'or 4' '- cyano-biphenyls or -terphenyls used will.

To achieve low threshold voltages i. a. Liquid crystal mixtures with very high dielectric Anisotropy Δε required. The expert can increase of Δε compounds such. B.

clog. These connections are extremely strong dielectric positive; the propyl homologue (alkyl = C₃H₇) z. B. a value Δε = 50. The expert will Select the concentration of such additives so that the Liquid crystal mixture on the respective design the electro-optical system is optimally matched; in particular, he will take care that Δn and / or n₀ and / or one or more further refractive indices of the Liquid crystal only in an acceptable and / or small and / or negligible dimensions will.

Due to the additives described, the liquid crystal modified with regard to the respective application and be optimized. It is crucial, however, that liquid crystals, containing compounds of formula I and in particular those additionally containing one or more  Compounds of formulas II-V, for use in the invention electro-optic liquid crystal systems are particularly suitable. Are particularly suitable however, the liquid crystal mixtures 1-12, the additional to compounds of formula I one or more compounds Formula II-V in defined mass percentage ranges contain.

Liquid crystal mixtures containing these compounds of the formula I. places for use in electro-optical Systems also particularly suitable "stable Framework mixtures ", which are generally described by the Additives optimized with regard to special requirements can be without other parameters of the mixture at the same time too drastic and usability the mixture in the electro-optical systems considerably experienced adverse change.

Draw the liquid crystals that can be used according to the invention advantageous values for the dielectric Anisotropy Δε, high stability, easy to manufacture, low miscibility with that for the matrix polymer used and in particular by a wide mesogenic area, a relatively high clearing point and advantageous values for birefringence and flow viscosity out. The liquid crystals correspond to the requirements described at the outset, which at a Use in an electro-optical system according to the Preamble of claim 1 are made in particular to a great extent and much better than before in these Systems used liquid crystals.

The following examples are intended to illustrate the invention, without limiting it.

It means:

K: crystalline solid state,
S: smectic phase (the index indicates the phase type),
N: nematic phase,
Ch: cholesteric phase,
I: Isotropic phase.

The number between two symbols indicates the transition temperature in degrees Celsius.

The percentages given are percentages by mass.  

example 1

a) Containing an electro-optic liquid crystal system a liquid crystal mixture resulting from the following Connections exist

14.4% p-trans-4-propylcyclohexyl benzonitrile
11.2% p-trans-4-butylcyclohexyl benzonitrile
20% p-trans-4-pentylcyclohexyl benzonitrile
12% p-trans-4-heptylcyclohexyl benzonitrile
5.6% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
4.8% 4-pentyl-4 ′ ′ - cyanoterphenyl
6.4% 4- (trans-4-propylcycohexyl) phenyl-trans-4-butylcyclohexyl-carboxyla-t
5.6% 4- (trans-4-pentylcyclohexyl) -4'-cyanobiphenyl
10% 4- (trans-4-propylcyclohexyl) -4'-difluoromethoxybiphenyl
10% 4- (trans-4-pentylcyclohexyl) -4'-difluoromethoxybiphenyl

and has the following physical parameters:

Clear point T _C = 102 ° C
Viscosity η = 31 mm² s ^-1 (20 ° C)
optical anisotropy Δn = 0.15 (20 ° C, 589 nm)
dielectric anisotropy Δε = 11.4 (20 ° C, 1 kHz)

b) The electro-optic liquid crystal system is after different procedures 1.1-1.3 and 2 are produced.

• 1. microdroplet matrix systems
  • 1.1 The liquid crystal mixture from a) is stirred with the US radiation-curable adhesive NOA 65 (Norland Products) in a ratio of 1.6: 1 at room temperature until a clear solution is obtained which, together with spacers (20 µm), between 2 transparent , glass substrates provided with electrode layers is brought. The glass substrates are pressed together, whereby a uniform film with a thickness of 20 μm is obtained, which is cured by UV radiation for 1 minute.
  • 1.2 The liquid crystal mixture from a) is stirred with Epikote 828 and Capcure 3-800 (Miller Stephenson Company) in a ratio of 1: 1: 1 at room temperature until a clear solution is obtained; the stirring time is kept as short as possible, since the solution has already hardened after about ½ h at room temperature. The solution is placed together with spacers (20 µm) between two transparent glass substrates with electrode layers, which are pressed together, whereby a uniform film with a thickness of 20 µm is obtained. To accelerate the curing process, the films can be heated to temperatures up to 100 ° C.
  • 1.3 5 g of the liquid crystal mixture from a) are stirred with 15 g of 20% aqueous PVA solution at room temperature for 2 minutes at 2000 rpm. The solution obtained is degassed for 24 hours and applied together with spacers (20 μm) in a thin layer to a glass substrate provided with an electrode layer. The arrangement is dried for 1 h to 85 ° C. before a second glass substrate provided with an electrode layer is pressed on, whereby a uniform film with a thickness of 20 μm is obtained. The system obtained in this way is dried at 85 ° C. for a further 24 h.
• 2. Network system
  • The liquid crystal mixture from a) is made with trimethylpropane triacrylate as the polymerizable compound and 2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocure 1173, commercial product from E. Merck, Darmstadt) as a photoinitiator in a ratio of 80: 19.8 : 0.2 stirred and placed with the addition of spacers with a thickness of 20 microns between 2 glass plates provided with electrode layers. To harden the polymer, the system obtained was moved through the radiation field of a halogen lamp (70 W / cm) at a defined speed (3 m / min).

The manufactured according to the method b) 1.1-1.3 and 2 electro-optical systems are characterized by good Manufacturability a wide working temperature range, favorable values for the electro-optical parameters and their temperature dependence, a low threshold voltage and a good contrast.

Example 2

a) Containing an electro-optic liquid crystal system a liquid crystal mixture resulting from the following Connections exist

16.2% p-trans-4-propylcyclohexyl benzonitrile
12.6% p-trans-4-butylcyclohexyl benzonitrile
22.5% p-trans-4-pentylcyclohexyl benzonitrile
5.4% 4-pentyl-4 ′ ′ - cyanoterphenyl
7.2% 4- (trans-4-propylcyclohexyl) phenyl-trans-4-butylcyclohexyl-carboxylate
6.3% 4- (trans-4-pentylcyclohexyl) -4'-cyanobiphenyl
10% 4-pentyl-4 ′ ′ - difluoromethoxy-terphenyl
13.5% p-trans-4-heptylcyclohexyl benzonitrile
6.3% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl

b) The electro-optic liquid crystal system is after that described in Example 1b), 1.1-1.3 and 2 Process manufactured.

The manufactured according to the method b) 1.1-1.3 and 2 electro-optical systems are characterized by good Manufacturability a wide working temperature range, favorable values for the electro-optical parameters and their temperature dependence, a low threshold voltage and a good contrast.

Example 3

a) Containing an electro-optic liquid crystal system a liquid crystal mixture resulting from the following Connections exist

14.4% p-trans-4-propylcyclohexyl benzonitrile
11.2% p-trans-4-butylcyclohexyl benzonitrile
20% p-trans-4-pentylcyclohexyl benzonitrile
12% p-trans-4-heptylcyclohexyl benzonitrile
5.6% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
4.8% 4-pentyl-4 ′ ′ - cyanoterphenyl
6.4% 4- (trans-4-propylcyclohexyl) phenyl trans-4-butylcyclohexyl carboxylate
5.6% 4- (trans-4-pentylcyclohexyl) -4'-cyano-biphenyl
20% 1- (trans-4-pentylcyclohexyl) -4-fluorobenzene

and has the following physical parameters:

Viscosity η = 20 mm² s ^-1 (20 ° C)
optical anisotropy Δn = 0.12 (20 ° C, 589 nm)
dielectric anisotropy Δε = 10.2 (20 ° C, 1 kHz)

b) The electro-optic liquid crystal system is after that described in Example 1b), 1.1-1.3 and 2 Process manufactured.

The manufactured according to the method b) 1.1-1.3 and 2 electro-optical systems are characterized by good Manufacturability a wide working temperature range, favorable values for the electro-optical parameters and their temperature dependence, a low threshold voltage and a good contrast.

Example 4

a) Containing an electro-optic liquid crystal system a liquid crystal mixture resulting from the following Connections exist

14.4% p-trans-4-propylcyclohexyl benzonitrile
11.2% p-trans-4-butylcyclohexyl benzonitrile
20% p-trans-4-pentylcyclohexyl benzonitrile
12% p-trans-4-heptylcyclohexyl benzonitrile
5.6% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
4.8% 4-pentyl-4 ′ ′ - cyanoterphenyl
6.4% 4- (trans-4-propylcyclohexyl) phenyl trans-4-butylcyclohexyl carboxylate
5.6% 4- (trans-4-pentylcyclohexyl) -4'-cyano-biphenyl
20% 2- (4- (3,4-difluorophenyl) phenyl) -5-heptylpyrimidine

and has the following physical parameters:

Clear point T _C = 97 ° C
Viscosity η = 48 mm² s ^-1 (20 ° C)
optical anisotropy Δn = 0.16 (20 ° C, 589 nm)
dielectric anisotropy Δε = 12.9 (20 ° C, 1 kHz)

b) The electro-optic liquid crystal system is after that described in Example 1b), 1.1-1.3 and 2 Process manufactured.

The manufactured according to the method b) 1.1-1.3 and 2 electro-optical systems are characterized by good Manufacturability a wide working temperature range, favorable values for the electro-optical parameters and their temperature dependence, a low threshold voltage and a good contrast.  

Example 5

a) Containing an electro-optic liquid crystal system a liquid crystal mixture consisting of the following compounds consists

17% 1-difluoromethoxy-2-fluoro-4- [trans-4- (trans-4-ethylcyclohexyl) cyclohexyl] benzene
17% 1-difluoromethoxy-2-fluoro-4- [trans-4- (trans-4-butylcyclohexyl) cyclohexyl] benzene
17% 1-difluoromethoxy-2-fluoro-4- [trans-4- (trans-4-pentylcyclohexyl) cyclohexyl] benzene
11% 1-difluoromethoxy-4- [trans-4- (trans-4-pentylcyclohexyl) cyclohexyl] benzene
6% 1- (trans-4-propylcyclohexyl) -2- (4-difluoromethoxyphenyl) ethane
6% 1- (trans-4-pentylcyclohexyl) -2- (4-difluoromethoxyphenyl) ethane
6% 1-difluoromethoxy-4- (trans-4-pentylcyclohexyl) benzene
8% 4-propyl-4'-difluoromethoxy-biphenyl
12% 4- (trans-4-propylcyclohexyl) -4'-difluoromethoxy-biphenyl

and has the following physical parameters:

Clear point T _c = 87 ° C
Viscosity η = 19 mm² s ^-1 (20 ° C)
optical anisotropy Δn = 0.0985 (20 ° C, 589 nm)
dielectric anisotropy Δε = 6.3 (20 ° C, 1 kHz)

b) The electro-optical liquid crystal system is after procedures described in Example 1b), 1.1-1.3 and 2 produced.

The manufactured according to the method b) 1.1-1.3 and 2 electro-optical systems are characterized by good Manufacturability a wide working temperature range, favorable values for the electro-optical parameters and their temperature dependence, a low one Threshold voltage and a good contrast.

Claims (20)

1. electro-optic liquid crystal system,

• which contains a dielectric positive liquid crystal and another optically transparent medium between two electrodes, which are optionally applied to substrate plates,
• whose liquid crystal molecules have an irregular orientation when switched off,
• in which one of the refractive indices of the liquid crystal essentially corresponds to the refractive index of the matrix n _M and / or in which the quotient of the mass of the liquid crystal and the mass of the optically transparent medium is 1.5 or more,
• which in one of the two switching states has a transmission which is reduced compared to the other state, regardless of the polarization of the incident light,

characterized in that the liquid crystal contains one or more compounds of the formula I R-Q¹-Q²-WF (I) whereinW -CF₂-; -OCF₂-, -OCHF- or a single bond,
Q² 1,4-phenylene, 2-fluoro-1,4-phenylene or 3-fluoro-1,4-phenylene
Q¹ -A¹- (A²) _m -Z- or -A¹-Z-A²-,
Z -CH₂CH₂-, a single bond, -CO-O-, or -O-CO-,
A¹ and A² are each independently 1,4-phenylene, trans-1,4-cyclohexylene, pyrimidine-2,5-diyl or pyridine-2,5-diyl,
m 0 or 1, and
R alkyl with up to 12 carbon atoms, in which one or two non-adjacent CH₂ groups can be replaced by -O-. 2. System according to claim 1, characterized in that the liquid crystal one or more compounds of the formula contains. 3. System according to claim 2, characterized in that means. 4. System according to claim 3, characterized in that Z means -CH₂-CH₂- or a single bond. 5. System according to claim 2, characterized in that means. 6. System according to claim 5, characterized in that Z means -CH₂CH₂- or a single bond. 7. System according to at least one of claims 1-6, characterized in that the liquid crystal contains one or more compounds selected from the compounds of the formulas II-V, in which R.sup.1 each independently represents an alkyl group with 1-15 C atoms, in which one or two non-adjacent CH.sub.2 groups can also be replaced by -O-, -CO- and / or -CH = CH, mean. 8. System according to claim 7, characterized in that the proportion of those consisting of compounds I-V Base mixture on the liquid crystal 15-100% is. 9. System according to at least one of claims 1-8, characterized in that the liquid crystal contains further connections from the classes of azoxybenzenes, benzylidene anilines, biphenyls, Terphenyls, phenyl or cyclohexyl benzoates, cyclohexane carboxylic acid phenyl or cyclohexyl esters, Phenyl or cyclohexyl ester of cyclohexylbenzoic acid, Phenyl or cyclohexyl ester of cyclohexylcyclohexane carboxylic acid, Cyclohexylphenyl ester of  Benzoic acid, the cyclohexane carboxylic acid, or the Cyclohexylcyclohexane carboxylic acid, phenylcyclohexane, Cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, Phenyl or cyclohexyl dioxanes, phenyl or Cyclohexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenylcyclohexyl) ethane, 1-cyclohexyl-2-biphenylylethane, 1-phenyl-2-cyclohexylphenylethane, halogenated stilbene, benzylphenyl ether, Tolanes and substituted cinnamic acids selected be, the 1,4-phenylene groups in these compounds can also be fluorinated. 10. System according to at least one of claims 1-9, characterized in that the liquid crystal contains further compounds of the formulas 1-5 R'-LER '' (1)
R′-L-COO-ER ′ ′ (2)
R′-L-OOC-ER ′ ′ (3)
R′-L-CH₂CH₂-ER ′ ′ (4)
R'-LC≡CER '' (5) L and E each independently of one another a bivalent radical from -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, - Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images formed group, where Phe unsubstituted or substituted by fluorine-1,4-phenylene, Cyc trans-1,4-cyclohexylene or 1,4- Cyclohexenylene, pyr pyrimidine-2,5-diyl or pyridine-2,5-diyl, dio 1,3-dioxane-2,5-diyl and G 2- (trans-1,4-cyclohexyl) ethyl, pyrimidine-2 , 5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl, and
R 'and R''each independently of one another alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy each with 1-8 C atoms or CN, CF₃, F, Cl or NCS
mean. 11. System according to at least one of claims 1-10, characterized in that the liquid crystal is based on one of the mixtures 1-12, the mass fraction of the mixtures 1-12 in the Liquid crystal is between 10% and 98%. 12. System according to at least one of claims 1-11, characterized in that the liquid crystal has a dielectric anisotropy Δε <3. 13. System according to at least one of claims 1-12, characterized in that the liquid crystal at least contains a pleochroic dye. 14. System according to at least one of claims 1-13, characterized in that the liquid crystal in Form of microdroplets in the optically transparent Medium is embedded.   15. System according to at least one of claims 1-14, characterized in that the optically transparent Medium forms a 3-dimensional network in which The liquid crystal is located in the pores. 16. Liquid crystal, characterized in that it with the liquid crystal in an electro-optical system identical to at least one of claims 7-13 is. 17. Use of a liquid crystal containing at least a compound of formula I, in one system according to claim 14 or 15. 18. Use of a liquid crystal according to claim 11 in a system according to claim 14 or 15.