DE4100237A1 - 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 micro potty 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 hereinafter referred to 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) 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-modulated 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 n _o, 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-modulated 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 n _o 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, to the refractive index of the matrix n _x , which the liquid crystal has with a completely statistical orientation, to the refractive index of the matrix n _{M is} adjusted. 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 phase boundary network Liquid crystal 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 preferred on.

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 crystal mixtures are provided required by a high clearing point, high Δε, a wide nematic range and a high, UV and Temperature stability are marked.

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, watches,
• - 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 terphenylene 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 46 71 618 (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 than E8 , however at the same time the clearing point T _C = 60.5 ° C is considerably lower. The dielectric anisotropy of the mixture E7 is Δε 13.8 and is therefore somewhat smaller than that of E8 with Δε = 15.6. To achieve the lowest possible threshold voltages, significantly higher values for Δε are advantageous.

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 .

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 one uses liquid crystal mixtures for these systems used one or more connections of formula I contain

wherein

Q -A¹- (A²) _m -Z- or -A¹-Z-A²,
Z -CH₂CH₂- or a single bond,
one of the radicals A¹ and A² present in the molecule of the formula I.

where X is CH or N and the other radical A¹ or A², if present, 1,4-phenylene or trans-1,4-cyclohexylene,
m 0 or 1 and
R is alkyl with up to 12 carbon atoms, in which one or two non-adjacent CH₂ groups can also be replaced by -O-,

mean.  

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. with microdroplets Matrix systems can be 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 system according to the invention includes 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 only have layer thicknesses d that are significantly larger than a few mm 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 0.313.053. A significant difference between the electro-optic liquid crystal systems according to the invention and the hitherto usual ones is the liquid crystal used.

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

The compounds of the formula include dinuclear compounds of the formulas Ia-Id, which are preferred:

In the compounds of the formulas Ia-Id, R preferably denotes Alkyl or alkoxy with 1-10, but especially with 1-8 carbon atoms. Further preferred are n-alkoxyalkyl compounds and especially n-alkoxymethyl and n-alkoxyethyl compounds.

The compounds of Formulas Ia-Id, where R is methyl, ethyl, propyl, butyl, Pentyl, hexyl, heptyl, octyl, nonyl, decyl, methoxy, Ethoxy, butoxy, pentoxy, hexoxy, hetoxy or octoxy means. The compounds of formulas I and in particular the compounds of the formulas Ib and Id have high or relatively high values for the dielectric anisotropy Δε on. Which of the compounds Ia-Id the invention Preferably contain liquid crystal media, will largely depend on the intended application of the  electro-optical systems according to the invention determined. So z. B. the compounds of formulas Ia and Ib a relatively high clearing point and especially a relative one high optical anisotropy while the connections of the formulas Ic and Id z. B. by a comparative distinguish low flow viscosity.

The compounds of formula I further comprise trinuclear Compounds of the formulas IIa-IIh and IIIa-IIIq, where the compounds of the formulas IIIa-IIIq form a dimethylene bridge exhibit:

In the compounds of the formulas IIa-IIh and IIIa-IIIq R preferably denotes methyl, ethyl, propyl, butyl, Pentyl, hexyl, heptyl, octyl, nonyl, decyl, methoxy, Ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy,  Octoxy, nonoxy, decoxy, methoxymethyl, ethoxymethyl, Propoxymethyl, butoxymethyl, methoxyethyl, ethoxyethyl or propoxyethyl.

The compounds of formulas II and III, which are preferred have high or relatively high values for the dielectric anisotropy Δε; thereby stand out the compounds of the formulas IIf, IIh, IIIo and IIIq, which is the structural element

contained, from very particularly high values for Δε.

The compounds of the formulas are particularly preferred IIa, IIe, IIg, IIIn and IIIp, which are characterized by a high optical anisotropy with at the same time relatively high distinguish dielectric anisotropy.

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 one better solubility in the usual liquid crystalline Base materials may be important, but especially as chiral dopants if they are optically active. Electro-optical systems according to the preamble of claim 1, whose liquid crystal is one or more chiral Contains components are described in DE 39 11 255.1.

Branched groups of this type usually contain no more than a chain branch. Preferred branched Radicals R 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-methylpropyl, 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-methyloctyloxy, 2-methyl-3- oxapentyl, 2-methyl-3-oxahexyl.

The compounds of formula I are known per se Methods as described in the literature (e.g. in standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart Bd IX, P. 867 ff.) Are described, namely under reaction conditions, known for the above-mentioned implementations and are suitable. You can also use known, Variants not mentioned here do.

The compounds of formula I are preferably after in DE 36 00 052, DE 33 15 295, SU 10 63 100, SU 10 63 101, SU 10 69 413, SU 11 71 456, GB 21 18 934, Methods described in EP 00 97 033 and DE 34 11 571 shown.

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

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-,
Y is a single bond, -COO- or -OOC-, and

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 cyclohexylcyclohexane carboxylic acid, Cyclohexylphenyl ester of benzoic acid, cyclohexane carboxylic acid, or the cyclohexylcyclohexane carboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, Phenyl- or cyclohexyldioxane, phenyl- or cyclohexyl- 1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl- cyclohexyl) ethane, 1-cyclohexyl-2-biphenylethane, 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′-L-E-R ′ ′ (1)

R′-L-COO-E-R ′ ′ (2)

R′-L-OOC-E-R ′ ′ (3)

R′-L-CH₂CH₂-E-R ′ ′ (4)

R ′ ′ - L-C≡C-E-R ′ ′ (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- mean 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 alkanyloxy 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 according to the invention Systems used contain liquid crystals 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 according to the invention Systems used contain liquid crystals preferably 1-40%, especially 5-30% of compounds of formula I. The liquid crystals preferably contain 1-5, especially 1-3 compounds of formula I.  

The proportion of those consisting of compounds of formulas I-IV 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 1-6 described below, the mass fraction of mixtures 1-6 in the liquid crystal between 10% and 98% and especially between 15% and 95%. Mixtures 1-6 consist of 2 or more compounds that have 2, 3 or 4 formulas fall from the group of formulas I, II, III and IV to be chosen. Mixtures 1-6 preferably contain 2-40, but especially 2-38 and very special 2-35 connections. The mass fraction of these compounds on mixtures 1-6 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 is of course 100%.

Liquid crystal mixtures which are particularly preferred are in addition to compounds of the formula I, compounds of the formula V

included in what one of the rings

and the other

n and o 1 or 2 and
(n + o) 2, 3 or 4, but preferably 2 or 3

mean; R and Z have the meaning given above.

Liquid crystal mixtures are very particularly preferred, which in addition to compounds of formula I and V one or several compounds of the formulas II, III and / or IV contain.

The proportion of the compounds of formula V in the invention Liquid crystal mixtures is preferably 5-45%, but especially 8-35%.

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-optic liquid crystal Systems can be created by applying 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 <15.

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 Parameters of the media can be added. 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 proper 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 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 ver bonds to the mixture vary; for mixtures with very high Δn can e.g. B. in particular 4-alkyl or alkoxy-4 ′ or 4 ′ ′ - cyano-biphenyle or -erephenyle used 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 ins special ones additionally containing one or more Compounds of formulas II-IV, for use in inventions electro-optic liquid crystal systems according to the invention are particularly suitable. Are particularly suitable however, the liquid crystal mixtures 1-6, the additional to compounds of formula I one or more compounds Formula II-IV in defined mass percentage ranges contain. Liquid crystal mixtures are also particularly preferred, the at least one connection of the Formula I, one or more compounds of the formulas II, III and / or IV and additionally at least one compound of formula V.  

Liquid containing these compounds of formula I. crystal mixtures make 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 optical anisotropy Δn, high stability, low miscibility with the polymer used for the matrix, by a wide mesogenic range, a relatively high clearing point and in particular by advantageous values for the dielectric Anisotropy and a favorable temperature dependence of the electro-optical parameters. The liquid crystals correspond to the requirements described at the beginning, that when used in an electro-optical System according to the preamble of claim 1, to a particularly high degree and much better than Liquid crystals previously used in this system.

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 gives the conversion temperature in degrees Celsius.

The percentages given are percentages by mass.

Example 1

• a) An electro-optical liquid crystal system containing a liquid crystal mixture which consists of the following compounds 14.4% p-trans-4-propylcyclohexyl-benzonitrile
  11.2% p-trans-4-butylcyclohexyl-benzontril
  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% of 2- (4-cyanophenyl) -5-propylpyridine and the following physical parameters: clearing point T _c = 80 ° C
  Viscosity η = 33 mm² s ^-1 (20 ° C)
  optical anisotropy Δn = 0.16 (20 ° C, 589 nm)
  dielectric anisotropy Δε = 15.5 (20 ° C, 1 kHz)
• b) The electro-optic liquid crystal system is manufactured according to different methods 1.1-1.3 and 2.
  • 1. microdroplet matrix systems,
  • 1.1 The liquid crystal mixture from a) is stirred with the UV-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 is cured at room temperature after about 1/2 hour. 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 at 85 ° C. for 1 hour 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 mixed with tri methylolpropane 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, with the addition of spacers with a thickness of 20 μm, placed between 2 glass plates provided with electrode layers. To harden the polymer, the system obtained was driven 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 a broad Working temperature range, favorable values for the electro-optical Parameters and their temperature dependence and especially characterized by a low threshold voltage.

Example 2

• a) An electro-optic liquid crystal system containing a liquid crystal mixture consisting of the following compounds 14.5% 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
  6.4% 4-trans-4-propylcyclohexyl) phenyl trans-4-butylcyclohexyl carboxylate
  5.6% 4- (trans-4-pentylcyclohexyl) -4'-cyanobiphenyl
  4.8% 4-pentyl-4 ′ ′ - cyanoterphenyl
  20% of 2- (4-cyanophenyl) -5-pentylpyrimidine and the following physical parameters: clearing point T _c = 82 ° C
  Viscosity η = 34 mm² s ^-1 (20 ° C)
  optical anisotropy Δn = 0.16 (20 ° C, 589 nm)
  dielectric anisotropy Δε = 16.1 (20 ° C, 1 kHz)
• b) The electro-optic liquid crystal system is after the method described in Example 1, b).

Example 3

• a) An electro-optical liquid crystal system containing a liquid crystal mixture consisting of the following compounds: 28% 1- (4-cyanophenyl) -5-ethylpyridine
  28% 2- (4-cyanophenyl) -5-propylpyridine
  28% 2- (4-cyanophenyl) -5-butylpyridine
  16% 4-pentyl-3 ′ ′, 5 ′ ′ - difluoro-4 ′ ′ - cyanoterphenyl
• b) The electro-optic liquid crystal system is after the method described in Example 1, b).

Example 4

• a) An electro-optic liquid crystal system containing a liquid crystal mixture which consists of the following compounds: 20% 2- (4-cyanophenyl) -5-propylpyridine
  20% 2- (4-cyanophenyl) -5-butylpyridine
  20% 2- (4-cyanophenyl) -5-pentylpyridine
  25% 4-pentyl-4'-cyanobiphenyl
  15% 4-pentyl-4 ′ ′ - cyanoterphenyl
• b) The electro-optic liquid crystal system is after the method described in Example 1, b) poses.

Example 5

• a) An electro-optic liquid crystal system containing a liquid crystal mixture which consists of the following compounds: 20% 2- (4-cyanophenyl) -5-propylpyridine
  20% 2- (4-cyanophenyl) -5-butylpyridine
  20% 2- (4-cyanophenyl) -5-pentylpyridine
  20% 4-pentyl-2-fluoro-4'-cyanobiphenyl
  10% 1- (4- (4-pentylphenyl) phenyl) -2- (3-fluoro-4-cyanophenyl) ethane
  10% 4-pentyl-4'-cyanoterphenyl
• b) The electro-optic liquid crystal system is after the method described in Example 1, b) poses.

Example 6

• a) An electro-optic liquid crystal system containing a liquid crystal mixture which consists of the following compounds: 30% 2- (4-cyanophenyl) -5-propylpyridine
  30% 2- (4-cyanophenyl) -5-butylpyridine
  20% 2- (4-cyanophenyl) -5-pentylpyridine
  10% 2- (4-cyanophenyl) -5- (4-pentylphenyl) pyridine
  10% 1- (4- (5-Pentylpyridin-2-yl) phenyl) -2- (3-fluoro-4-cyanophenyl) ethane
• b) The electro-optic liquid crystal system is after the method described in Example 1, b) poses.

Example 7

• a) An electro-optic liquid crystal system containing a liquid crystal mixture which consists of the following compounds: 30% 2- (4-cyanophenyl) -5-propylpyridine
  30% 2- (4-cyanophenyl) -5-butylpyridine
  20% 2- (4-cyanophenyl) -5-pentylpyridine
  10% 1- (4- (4-pentylphenyl) phenyl) -2- (3-fluoro-4-cyanophenyl) ethane
  10% 1- (4-pentylphenyl) -2- (4- (4-cyanophenyl) phenyl) ethane
• b) The electro-optic liquid crystal system is after the method described in Example 1, b) poses.

Example 8

• a) An electro-optical liquid crystal system containing a liquid crystal mixture which consists of the following compounds: 20% 2- (4-cyanophenyl) -5-ethylpyrimidine
  20% 2- (4-cyanophenyl) -5-propylpyrimidine
  20% 2- (4-cyanophenyl) -5-pentylpyrimidine
  20% 4-pentyl-3 ′ ′, 5 ′ ′ - difluoro-4 ′ ′ - cyano-terphenyl
  20% 2-fluoro-4-pentyl-4'-cyanobiphenyl
• b) The electro-optic liquid crystal system is after the method described in Example 1, b) poses.

Example 9

• a) An electro-optic liquid crystal system containing a liquid crystal mixture consisting of the following compounds: 20% 4-pentyl-4'-cyanobiphenyl
  23% 2- (4-cyanophenyl) -5-pentylpyridine
  17% 4-propoxy-4'-cyanobiphenyl
  13% 4-pentoxy-4'-cyanobiphenyl
  17% 4-octoxy-4'-cyanobiphenyl
  10% 4-pentyl-4 ′ ′ - cyanoterphenyl and has the following physical parameters: clearing point T _c = 70.4 ° C
  Viscosity η = 61 mm² / s (20 ° C)
• b) The electro-optic liquid crystal system is after the method described in Example 1, b) poses.

Example 10

• a) An electro-optic liquid crystal system containing a liquid crystal mixture which consists of the following compounds: 12% 2- (4-cyanophenyl) -5-propylpyridine
  15% 2- (4-cyanophenyl) -5-pentylpyridine
  18% 4-pentyl-4'-cyanobiphenyl
  9% 4-propoxy-4'-cyanobiphenyl
  9% 4-pentyl-4 ′ ′ - cyanoterphenyl
  22% 4-propyl-2'-fluoro-4 '' - cyanoterphenyl
  15% 4-trans-4-pentylcyclohexyl) -4′-cyanobiphenyl and has the following physical parameters: clearing point T _c = 114 ° C
  Viscosity η = 86.6 mm² / s (20 ° C)
• b) The electro-optic liquid crystal system is after the method described in Example 1, b) poses.

Example 11

• a) An electro-optic liquid crystal system containing a liquid crystal mixture which consists of the following compounds: 12% 2- (4-cyanophenyl) -5-propylpyridine
  15% 2- (4-cyanophenyl) -5-pentylpyridine
  5% 4-cyanobiphenyl
  8.5% 4-ethyl-4'-cyanobiphenyl
  8.5% 4-propyl-4'-cyanobiphenyl
  20% 4-pentyl-4'-cyanobiphenyl
  17% 4-propyl-2'-fluoro-4 '' - cyanoterphenyl
  9% 4-pentyl-4 ′ ′ - cyanoterphenyl and has the following physical parameters: clearing point T _c = 69.6 ° C
  Viscosity η = 51 mm² / s
• b) The electro-optic liquid crystal system is after the method described in Example 1, b) poses.

Example 120

• a) An electro-optic liquid crystal system containing a liquid crystal mixture which consists of the following compounds: 25% 2- (4-cyanophenyl) -5-propylpyridine
  25% 2- (4-cyanophenyl) -5-butylpyridine
  25% 2- (4-cyanophenyl) -5-pentylpyridine
  25% 2- (4-cyanophenyl) -5- (4-pentylphenyl) pyridine and has the following physical properties: clearing point T _c = 85 ° C
  Viscosity η = 70 mm² / s
  optical anisotropy Δn = 0.269 (20 ° C, 589 nm)
  dielectric anisotropy Δε = 24.1 (20 ° C, 1 kHz)
  ordinary refractive index n₀ = 1.529 (20 ° C, 589 nm)
• b) The electro-optical system is produced according to the methods described in Example 1 b), 1.1, 1.2, 1.3 and 2, but in the method analogous to 1.1, a ratio of liquid crystal to NOA 65 of 1: 1 is chosen and spacers of 10 µm were used.
  In Fig. 1 is the relative transmission for the electro-optical system produced according to the method described in Example 1 b), 1.1 as a function of the applied voltage (sinusoidal AC voltage (effective values), frequency 100 Hz). This system is characterized in particular by good contact and a low threshold voltage.

Example 13

• a) An electro-optical liquid crystal system containing a liquid crystal mixture consisting of the following compounds: 15% p-trans-4-propylcyclohexyl-benzonitrile
  15% p-trans-4-butylcyclohexyl benzonitrile
  20% p-trans-4-pentylcyclohexyl benzonitrile
  10% 2- (4-cyanophenyl) -5-pentylpyridine
  15% 2- (4-cyanophenyl) -5- (4-pentylphenyl) pyridine
  7.5% 4-ethoxy-4'-fluorotolane
  7.5% 4-butoxy-4'-fluorotolane
• b) The electro-optical system, which according to the example 1 b) described method is produced through a wide working temperature range, a good manufacturability, favorable values for the electro-optical Parameters, a low threshold voltage and especially high stability.

Example 14

• a) An electro-optic liquid crystal system containing a liquid crystal mixture consisting of the following compounds: 17.5% 4-propyl-4'-cyanobiphenyl
  17.5% 4-butyl-4'cyanobiphenyl
  17.5% 4-pentyl-4'-cyanobiphenyl
  17.5% 2- (4-cyanophenyl) -5- (4-pentylphenyl) pyridine

Example 15

• a) An electro-optic liquid crystal system containing a liquid crystal mixture consisting of the following compounds: 17.5% 2- (4-cyanophenyl) -5-propylpyridine
  17.5% 2- (4-cyanophenyl) -5-butylpyridine
  17.5% 2- (4-cyanophenyl) -5-pentylpyridine
  17.5% 2- (4-cyanophenyl) -5- (4-pentylphenyl) pyridine
  15.0% 1- [4- (4-propylphenyl) phenyl] -2- (4-cyanophenyl) ethane
  15.0% of 1- [4- (4-pentylphenyl) phenyl -] - 2- (4-cyanophenyl) ethane and has the following physical properties: clearing point T _c = 04 ° C
  optical anisotropy Δn = 0.2722 (20 ° C, 589 nm)
  dielectric anisotropy Δε = 25.6 (20 ° C, 1 kHz)
• b) The electro-optical system, which according to the example 1 b) described method is produced through a wide working temperature range, a good manufacturability, favorable values for the electro-optical parameters and in particular by a low threshold voltage.

Example 16

• a) An electro-optic liquid crystal system containing a liquid crystal mixture consisting of the following compounds: 20.0% 2- (4-cyanophenyl) -5-propylpyridine
  20.0% 2- (4-cyanophenyl) -5-butylpyridine
  20.0% 2- (4-cyanophenyl) -5-pentylpyridine
  20.0% 2- (4-cyanophenyl) -5- (4-pentylphenyl) pyridine
  10.0% 4- (trans-4-propylcyclohexyl) -3 ′, 4′-difluorobiphenyl
  10.0% 4- (trans-4-pentylcyclohexyl) -3 ′, 4′-difluorobiphenyl and has the following physical properties: clearing point T _c = 86 ° C
  optical anisotropy Δn = 0.2436 (20 ° C, 589 nm)
  ordinary refractive index n₀ = 1.5259 (20 ° C, 589 nm)
  dielectric anisotropy Δε = 21.8 (1 kHz, 20 ° C)
• b) The electro-optical system is produced according to the methods described in Example 1 b), 1.1, 1.2, 1.3 and 2, but in the method analogous to 1.1, a ratio of liquid crystal to NOA 65 of 1: 1 is chosen and spacers of 10 µm were used.
  In FIG. 2, the relative transmission for the b to in Example 1), 100 Hz) represented procedure produced electro-optical system described 1.1 as a function of applied voltage (sinusoidal alternating voltage (effective value), frequency.
  This system is characterized in particular by a low threshold voltage, an advantageous value for the steepness of the electro-optical characteristic curve and by a high UV stability.

Claims (15)

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, regardless of the polarization of the incident light, has a reduced transmission compared to the other state,

characterized in that the liquid crystal contains one or more compounds of the formula I. wherein Q-A¹- (A²) _m -Z- or -A¹-Z-A²-,
Z -CH₂CH₂- or a single bond,
one of the radicals A¹ and A² present in the molecule of the formula I. where X is CH or N and the other radical A¹ or A², if present, 1,4-phenylene or trans-1,4-cyclohexylene,
m 0 or 1 and
R is 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 contains one or more compounds selected from the compounds of the formulas II-IV, 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-,
Y is a single bond, -COO- or -OOC-, and mean. 3. System according to claim 2, characterized in that the proportion of those consisting of compounds I-IV Base mixture on the liquid crystal is 15-100%. 4. System according to at least one of claims 1-3, characterized in that the liquid crystal contains further connections from the classes of azoxybenzenes, benzylidene anilines, biphenyls, Terphenyls, phenyl- or cyclohexylbenzolates, cyclo hexane-carboxylic acid phenyl or cyclohexyl ester, Phenyl or cyclohexyl ester of cyclohexylbenzoe acid, phenyl or cyclohexyl ester of cyclohexyl cyclohexane carboxylic acid, cyclohexylphenyl ester of Benzoic acid, cyclohexane carboxylic acid or Cyclohexylcyclohexane carboxylic acid, phenylcyclohexane, Cyclohexylbiphenyls, phenylcyclohexylcylohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-bicyclohexylbenzenes,  4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylprimidines, phenyl- or cyclohexylpyridines, Phenyl- or cyclohexyldioxane, phenyl- or cyclo hexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclo hexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclo hexyl-2- (4-phenyl-cyclohexyl) ethane, 1-cyclohexyl- 2-biphenylethane, 1-phenyl-2-cyclohexylphenyl- ethane, halogenated stilbene, benzylphenyl ether, Tolanes and substituted cinnamic acids selected be, the 1,4-phenylene groups in these Compounds can also be fluorinated. 5. System according to at least one of claims 1-4, 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) where L and E each independently of one another are a bivalent radical from the from -Phe- , -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- as well as their mirror images, where Phe unsubstituted or substituted by fluorine-substituted 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 are 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 denote alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy each with 1-8 C atoms or CN, CF₃, F, Fl or NCS. 6. System according to at least one of claims 1-5, characterized in that the liquid crystal is based on one of the mixtures 1-6, wherein the mass fraction of mixtures 1-6 in the liquid crystal is between 10% and 98%. 7. System according to at least one of claims 1-6, characterized in that the liquid crystal additionally contains a compound of formula V, wherein
one of the rings and the other n and o 1 or 2 and
(n + o) 2, 3 or 4 mean and R have the meaning given above. 8. System according to at least one of claims 1-7, characterized in that the liquid crystal has a dielectric anisotropy Δε <3. 9. System according to at least one of claims 1-8, characterized in that the liquid crystal at least contains a pleochroic dye.   10. System according to at least one of claims 1-9, characterized in that the liquid crystal in Form of microdroplets in the optically transparent Medium is embedded. 11. System according to at least one of claims 1-10, characterized in that the optically transparent Medium forms a 3-dimensional network in which The liquid crystal is located in the pores. 12. Liquid crystal, characterized in that it has the liquid crystal in an electro-optical system is identical according to at least one of claims 2-9. 13. Use of a liquid crystal containing at least a compound of formula I, in one system according to claim 10 or 11. 14. Use of a liquid crystal according to claim 11 in a system according to claim 10 or 11.