DE10157670B4 - Four-ring compounds with negative DK anisotropy and liquid-crystalline medium - Google Patents

Abstract

Compounds of the formula Iworin R 1 and R 2 independently of one another denote an unsubstituted alkyl radical having 1-12 C atoms, A 1, A 2, A 3 and A 4 independently of one another are substituted in positions 2 and 3 twice by CN, F, Cl, CF 3 or OCF 3, 4-phenylene or 1,4-cyclohexenylene, and Z1, Z2 and Z3 represent a single bond, with the provisos that a) the compound substituted at least one in the 2- and 3-position with CN, F, Cl, CF3 or OCF3 Contains 1,4-phenylene radical, and b) three of the rings A1, A2, A3 and A4 trans-1,4-cyclohexylene mean.

Description

The invention relates to four-ring compounds with negative anisotropy of the dielectric constant (DK anisotropy), their use as components of liquid-crystalline media and liquid crystal and electro-optical display elements containing the liquid-crystalline media of the invention.

The compounds according to the invention can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell, the guest-host effect, the DAP (upright phase deformation), ECB (electrically controlled birefringence), CSH ( color super homeotropic), VA (vertically aligned), or IPS effect (In Plane Switching) or the effect of dynamic scattering.

The principle of electrically controlled birefringence, the ECB or DAP effect ("deformation of upright phases") was first described in 1971 (M: F. Schieckel and K. Fahrenschon, "Deformation of nematic liquid crystals with vertical orientation in electrical fields" Appl. Phys. Lett. 19 (1971), 3912). There followed work by J. F. Kahn (Appl Phys Lett 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869).

The work of J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982). , 244) have shown that liquid-crystalline phases have high values for the ratio of the elastic constants K ₃₃ / K ₁₁ , high values for the optical anisotropy Δn and values for the dielectric (DK) anisotropy Δε of about -0.5 to about 5 in order to be used for highly informative display elements based on the ECB effect. Electro-optical display elements based on the ECB effect have a homeotropic or vertical edge orientation when switched off, ie, an orientation largely perpendicular to the electrode surfaces.

Newer types of homeotropic edge-oriented ECB displays are those based on the CSH, VAN (vertically aligned nematic) or VAC (vertically aligned cholesteric) effect. CSH displays are known, inter alia, from H. Hirai, Japan Displays 89 Digest, 184 (1989), J.F. Clerc et al., Japan Displays 89 Digest, 188 (1989) and J.F. Clerc, SID 91 Digest, 758 (1991). VAN ads have become a. in S. Yamauchi et al., SID Digest of Technical Papers, p. 378ff (1989), VAC displays in K.A. Crabdall et al., Appl. Phys. Lett. 65, 4 (1994).

The newer VAN and VAC displays contain, like the previously known ECB displays, a layer of a liquid-crystalline medium between two transparent electrodes, the liquid-crystal medium having a negative value of DK anisotropy Δε. The molecules of this liquid crystal layer are homeotropically or tilted (English: "tilted") homeotropically oriented in the off state. Due to the negative DK anisotropy, a reorientation of the liquid crystal molecules takes place parallel to the electrode surfaces when switched on.

in contrast to the conventional ECB displays in which the liquid crystal molecules in the on state have a parallel orientation with a uniform direction over the whole liquid crystal cell, in the VAN and VAC displays this uniform parallel alignment is usually only on small domains within the cell limited. Between these domains, also referred to as tilt domains, declensions do exist.

As a result, VAN and VAC displays have greater viewing angle independence of contrast and grayscale as compared to the conventional ECB displays. In addition, such displays are easier to manufacture, as an additional treatment of the electrode surface for uniform orientation of the molecules in the on state, such. B. by rubbing, is no longer necessary.

In contrast to the VAN displays, the liquid crystal media in VAC displays additionally contain one or more chiral compounds, such as e.g. B. chiral dopants, which cause a helical twist of the liquid crystal molecules in the liquid crystal layer by an angle between 0 and 360 ° in the on state. The twist angle is in the preferred case about 90 °.

For displays with vertical edge orientation, the use of compensators, such. As optically uniaxial negative compensation films, proposed to compensate for unwanted translucency of the display in the off state at an oblique angle of observation.

In addition, it is possible to control the preferred direction of the tilt or tilt angle by a special configuration of the electrodes, without an additional surface treatment of the electrodes, such as by an orientation layer, would be necessary. A CSH display of this type is described, for example, in Yamamoto et al., SID 91 Digest, 762 (1991).

In IPS displays, the electrical signals are generated so that the electric fields have a significant component parallel to the liquid crystal layer (in-plane switching). In the international patent application WO 91/10936 Such a liquid crystal display is disclosed. The principles of operating such a display are e.g. As described by RA Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468 (1974). In the EP 0 588 568 various ways of driving such a display are disclosed.

These IPS displays can be operated with liquid-crystalline materials with either a positive or a negative dielectric anisotropy (Δε ≠ 0). With the materials known to date, however, relatively high threshold voltages and long switching times are achieved in IPS displays. In addition, in IPS displays with previously known materials, the problem of crystallization of the liquid crystal medium at low temperatures may occur.

The above-described displays may be of the active matrix or passive matrix (multiplex) type. For example, ECB and VA displays have been described as operating as active matrix or multiplexed displays, while CSH displays are commonly operated as multiplexed displays.

• 1. MOS (Metal Oxide Semiconductor) oder andere Dioden auf Silizium-Wafer als Substrat.
• 2. Dünnfilm-Transistoren (”thin film transistors”, TFT) auf einer Grasplatte als Substrat.

Matrix liquid crystal displays are known. As non-linear elements for individual switching of the individual pixels, for example, active elements (ie transistors) can be used. One speaks then of an "active matrix", whereby one can distinguish two types:

• 1. MOS (Metal Oxide Semiconductor) or other diodes on silicon wafer as a substrate.
• 2. Thin film transistors (TFT) on a grass plate as a substrate.

The use of monocrystalline silicon as a substrate material limits the display size, since the modular composition of various partial displays on the joints leads to problems.

In the more promising type 2, which is preferred, the TN effect is usually used as the electro-optical effect. A distinction is made between two technologies: TFTs made of compound semiconductors such as. B. CdSe or TFTs based on polycrystalline or amorphous silicon. The latter technology is being worked on worldwide with great intensity.

The TFT matrix is applied on the inside of one glass plate of the display, while the other glass plate on the inside carries the transparent counter electrode. Compared to the size of the pixel electrode, the TFT is very small and practically does not disturb the image. This technology can also be extended to fully color-capable image representations, wherein a mosaic of red, green and blue filters is arranged such that each one filter element is opposite to a switchable picture element. TFT displays are usually backlit.

The term MFK displays here includes any matrix display with integrated nonlinear elements, i. H. in addition to the active matrix also displays with passive elements such as varistors or diodes (MIM = metal-insulator-metal).

Such MFK displays are particularly suitable for TV applications (eg pocket televisions) or for high-information displays for computer applications (laptops) and in the automotive or aircraft industry. In addition to problems with regard to the angle dependence of the contrast and the switching times, difficulties arise in MFK displays due to insufficiently high resistivity of the liquid-crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K. , TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, Sept. 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Liquid Crystal Displays, p. 145 ff, Paris]. As the resistance decreases, the contrast of a MFK display degrades and the problem of "old image elimination" can arise. As the resistivity of the liquid crystal mixture, through interaction with the internal surfaces of the display, generally decreases over the life of a MFK display, high (initial) resistance is very important for displays that must have acceptable resistance values over a long period of operation.

Furthermore, it is important that the resistivity shows the lowest possible decrease with increasing temperature and after temperature and / or UV exposure. Also particularly disadvantageous are the low-temperature properties of the mixtures of the prior art. It is required that no crystallization and / or smectic phases occur even at low temperatures and that the temperature dependence of the viscosity is as low as possible. The MFK displays from the prior art thus do not meet today's requirements.

For the technical application of the effects described above in electro-optical display elements FK phases are needed, which must meet a variety of requirements. Particularly important here are the chemical resistance to moisture, air and physical influences such as heat, radiation in the infrared, visible and ultraviolet range such as electric alternating and alternating fields.

Furthermore, technically usable LC phases require a liquid-crystalline mesophase in a suitable temperature range and a low viscosity.

In none of the previously known series of compounds with liquid-crystalline mesophase there is a single compound that meets all these requirements. As a rule, mixtures of 2 to 25, preferably 3 to 18, compounds are prepared in order to obtain substances which can be used as LC phases. However, optimum phases could not easily be produced in this way, since liquid crystal materials with clearly negative dielectric anisotropy were not sufficiently available to date.

Out EP 0 474 062 MFK ads are known based on the ECB effect. However, the FK mixtures described there, based on 2,3-difluorophenyl derivatives which contain an ester, ether or ethyl bridge, have low values of the "voltage holding ratio" (HR) after UV exposure. They are therefore poorly suited for use in the ads described above.

Thus, there is still a great need for MFK displays, in particular of the ECB, VA and CSH types, with very high resistivity combined with a large operating temperature range, short switching times even at low temperatures and low threshold voltage, providing a variety of grayscale levels , high contrast and wide viewing angle and the disadvantages described above do not or only to a small extent.

The invention had the object of providing MFK displays that do not have the disadvantages mentioned above, or only to a lesser extent, and preferably at the same time have very high resistivities and low threshold voltages.

Another object was to provide new stable, liquid-crystalline or mesogenic compounds with negative DK anisotropy, which are suitable as components of liquid-crystalline media, in particular for the ECB, VA, CSH, DAP and IPS displays described above.

The substances used hitherto for this purpose always have certain disadvantages, for example too little stability to the action of heat, light or electric fields, unfavorable mesophases, elastic and / or dielectric properties.

It has now been found that this object can be achieved by using compounds and media according to the invention in LC displays.

It has thus been found, in particular, that the compounds according to the invention are outstandingly suitable as components of liquid-crystalline media. With their help, stable liquid-crystalline media are obtained which are particularly suitable for the FK displays described above. The new compounds are characterized above all by a high thermal stability, which is advantageous for a high "holding ratio", and show a pronounced negative DK anisotropy as well as favorable values of the clearing points and the birefringence.

With the provision of the four-ring compounds according to the invention, the range of liquid-crystalline substances which are suitable for the production of liquid-crystalline mixtures from a variety of application-technical points of view is widened considerably.

The compounds according to the invention are colorless in the pure state and form liquid-crystalline mesophases in a temperature range which is favorably located for electro-optical use. Chemically, thermally and against light, they are stable.

worin
R¹ und R² unabhängig voneinander einen unsubstituierten Alkylrest mit 1-12 C-Atomen,
A¹, A², A³ und A⁴ unabhängig voneinander ein in den Positionen 2 und 3 zweifach mit CN, F, Cl, CF₃ oder OCF₃ substituiertes 1,4-Phenylen oder 1,4-Cyolohexylen, und
Z¹, Z² und Z³ eine Einfachbindung
bedeuten,
mit den Maßgaben, daß

• a) die Verbindung mindestens einen in 2- und 3-Position mit CN, F, Cl, CF₃ oder OCF₃ substituierten 1,4-Phenylenrest enthält, und
• b) drei der Ringe A¹, A², A³ und A⁴ trans-1,4-Cyclohexylen bedeuten.

The invention thus four-membered compounds with negative DK anisotropy of the formula

wherein
R ¹ and R ² independently of one another represent an unsubstituted alkyl radical having 1-12 C atoms,
A ¹ , A ² , A ³ and A ⁴ independently of one another in the positions 2 and 3, twice with CN, F, Cl, CF ₃ or OCF ₃ substituted 1,4-phenylene or 1,4-cyolohexylene, and
Z ¹ , Z ² and Z ³ a single bond
mean,
with the provisos that

• a) the compound contains at least one in the 2- and 3-position with CN, F, Cl, CF ₃ or OCF ₃ substituted 1,4-phenylene, and
• b) three of the rings A ¹ , A ² , A ³ and A ^{4 are} trans-1,4-cyclohexylene.

Another object of the invention is the use of compounds of formula 1 as components of liquid-crystalline media.

Another object of the invention is a liquid-crystalline medium having at least two liquid-crystalline components, which contains at least one compound of formula I.

Another object of the invention is the use of a liquid-crystalline medium according to the invention in a liquid crystal display element, in particular an electro-optical display element, as a dielectric.

Particularly preferred is the use in liquid crystal display elements with homeotropic edge orientation in the off state, in particular ECB, VA, CSH and DAP displays, also in IPS displays.

The meaning of the formula includes all isotopes of the chemical elements bound in the compounds of formula I. In enantiomerically pure or enriched form, the compounds of the formula I are also suitable as chiral dopants and in general for obtaining chiral mesophases.

Above and below, R ¹ , R ² , A ¹ A ² , A ³ , A ⁴ , Z ¹ , Z ² and Z ^{3 have} the meaning given, unless expressly stated otherwise. If a remainder occurs several times, it can assume the same or different meanings.

Double substituted 1,4-phenylene means 2 and 3 position substitution unless otherwise specified.

• – A¹, A², A³ und A⁴ zweifach mit CN, F, Cl oder CF₃ substituiertes 1,4-Phenylen bedeuten.
• – R¹ und R² geradkettiges Alkyl mit 1 bis 10 C-Atomen bedeuten,
• – einer der Reste A¹, A², A³ und A⁴ zweifach mit CN oder CF₃ substituiertes 1,4-Phenylen bedeuten,

Particular preference is given to compounds of the formula I in which

• A ¹ , A ² , A ³ and A ^{4 are} double-substituted by CN, F, Cl or CF ₃ substituted 1,4-phenylene.
• R ¹ and R ² denote straight-chain alkyl having 1 to 10 C atoms,
• One of the radicals A ¹ , A ² , A ³ and A ⁴ denotes double-substituted by CN or CF ₃ substituted 1,4-phenylene,

insbesondere solche, worin L¹ und L² F bedeuten, sowie solche, worin R¹ und R² Alkyl mit 1 bis 8 C-Atomen bedeuten.Very particular preference is given to the following compounds

in particular those in which L ¹ and L ² denote F, and those in which R ¹ and R ^{2 are} alkyl having 1 to 8 C atoms.

If R ¹ and / or R ² in the above and following formulas denotes an alkyl radical, this may be straight-chain or branched. Preferably, it is straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and therefore preferably ethyl, propyl, butyl, pentyl, hexyl or heptyl, furthermore methyl, octyl, nonyl, decyl, undecyl or dodecyl.

Compounds of the formula I having a branched wing group R ¹ and / or R ² may occasionally be of importance for better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are useful as components of ferroelectric materials.

Branched groups of this type usually contain no more than one chain branch. Preferred branched radicals R ¹ and / or R ² are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl , 2-butylhexyl, 2-propylpentyl,

Formula I includes both the racemates of these compounds and the optical antipodes and mixtures thereof.

Preferred among these compounds of the formula I and the sub-formulas are those in which at least one of the radicals contained therein has one of the preferred meanings given.

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart) under reaction conditions which are known and suitable for the said reactions. One can make use of known per se, not mentioned here variants.

R, R' = C_1-12-Alkyl, -Alkenyl, -Oxaalkyl, -Oxaalkenyl Schema 2

R, R¹ = C_1-12-Alkyl, Alkenyl, -Oxaalkyl, -Oxaalkenyl Die Ausgangsstoffe können gewünschtenfalls auch in situ gebildet werden, derart, daß man sie aus dem Reaktionsgemisch nicht isoliert, sondern sofort weiter zu den Verbindungen der Formel I umsetzt.The compounds of formula I may, for. Example, according to the following reaction schemes or in analogy to be prepared. Further synthetic methods can be found in the examples. Scheme 1

R, R '= C _1-12 -alkyl, -alkenyl, -oxaalkyl, -oxaalkenyl Scheme 2

R, R ¹ = C _1-12 -alkyl, alkenyl, -oxaalkyl, -oxalkenyl If desired, the starting materials can also be formed in situ, such that they are not isolated from the reaction mixture but immediately further reacted to give the compounds of the formula I. ,

Nitriles can be obtained by exchanging halogens with copper cyanide or alkali cyanide.

For the preparation of the laterally substituted fluorine or chlorine compounds of the formula I, corresponding aniline derivatives with sodium nitrite and either with tetrafluoroboric acid (to introduce an F atom) or with copper (I) chloride (to introduce a Cl atom) to the Diazonium salts are reacted, which are then thermally decomposed at temperatures of 100-140 ° C.

The organometallic compounds are prepared, for example, by metal-halogen exchange (for example according to Org. React. 6, 339-366 (1951)) between the corresponding halogen compound and an organolithium compound, preferably tert-butyllithium or lithium naphthalenide. or by sales of magnesium turnings.

Moreover, the compounds of the formula I can be prepared by reducing a compound which otherwise corresponds to the formula I but contains one or more reducible groups and / or C-C bonds instead of H atoms.

As reducible groups are preferably carbonyl groups, in particular keto groups, also z. B. free or esterified hydroxy groups or aromatically bound halogen atoms. Preferred starting materials for the reduction are compounds corresponding to the formula I, but instead of a cyclohexane ring, a cyclohexene ring or cyclohexanone ring and / or instead of an H atom a free OH or a functional OH (modified, for example, in the form of its p-toluenesulfonate) Group included.

The reduction can z. Example, by catalytic hydrogenation at temperatures between about 0 ° C and about 200 ° C and pressures between about 1 and 200 bar in an inert solvent, eg. An alcohol such as methanol, ethanol or isopropanol, an ether such as tetrahydrofuran (THF) or dioxane, an ester such as ethyl acetate, a carboxylic acid such as acetic acid or a hydrocarbon such as cyclohexane. Suitable catalysts are suitably noble metals such as Pt or Pd, which are in the form of oxides (eg PtO ₂ , PdO), can be used on a support (for example Pd on carbon, calcium carbonate or trontium carbonate) or in finely wedged form.

Ketones can also be prepared by the methods of Clemmensen (with zinc, amalgamated zinc or tin and hydrochloric acid, expediently in aqueous-alcoholic solution or in heterogeneous phase with water / toluene at temperatures between about 80 and 120 ° C.) or Wolff-Kishner (with hydrazine, expediently in the presence of alkali such as KOH or NaOH in a high boiling solvent such as diethylene glycol or triethylene glycol at temperatures between about 100 and 200 ° C) to the corresponding compounds of formula I containing alkyl groups and / or -CH ₂ CH ₂ bridges ,

Furthermore, reductions with complex hydrides are possible. For example, arylsulfonyloxy groups can be removed by reduction with LiAlH ₄ , in particular p-toluenesulfonyloxymethyl groups can be reduced to methyl groups, expediently in an inert solvent such as diethyl ether or THF at temperatures between about 0 and 100 ° C. Double bonds can be hydrogenated with NaBH ₄ or tributyltin hydride in methanol.

The starting materials are either known or can be prepared in analogy to known compounds.

The liquid-crystalline media according to the invention preferably contain, in addition to one or more compounds according to the invention, as further constituents 2 to 40, in particular 4 to 30 components. With very particular preference these media contain, in addition to one or more compounds according to the invention, 7 to 25 components. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, cyclohexanecarboxylic acid phenyl or cyclohexyl esters, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, Phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexyl phenyl esters of benzoic acid, of cyclohexanecarboxylic acid or of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1,4-biscyclohexylbenzenes, 4,4'-biscyclohexylbiphenyls, 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-phenyl-cyclohexyl) -ethanes, 1-cycl ohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexyl-phenylethanes, optionally halogenated stilbenes, benzylphenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds can also be fluorinated.

The most important compounds which may be used as further constituents of inventive media can be characterized by the formulas 1, 2, 3, 4 and 5: R'-LE-R '' 1 R'-L-COO-E-R "2 R'-L-OOC-E-R "3 R'-L-CH ₂ CH ₂ -E-R "4 R'-LC≡CE-R "5

In formulas 1, 2, 3, 4 and 5, L and E, which may be the same or different, each independently represents a bivalent radical selected from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe- Cyc, -Cyc-Cyc, -Pyr-, -Dio, -G-Phe- and -G-Cyc- and their mirror images formed group, wherein 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 L and E is Cyc, Phe or Pyr. E is preferably Cyc. Phe or Phe-Cyc. The media according to the invention preferably comprise one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which L and E are selected from the group Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the Formulas 1, 2, 3, 4 and 5, wherein one of the radicals L and E is selected from the group Cyc, Phe and Pyr and the other radical 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 radicals L and E are selected from the group -Phe-Cyc- , -Cyc-Cyc, -G-Phe and -G-Cyc-.

R 'and / or R "each independently represent alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 C atoms, -F, -Cl, -CN, -NCS, - (O) _i CH _{3 - (k + 1)} F _k Cl _l , where i is 0 or 1 and k and 1, 2 or 3.

R 'and R "in a smaller subgroup of the compounds of formulas 1, 2, 3, 4 and 5 are each independently alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy of up to 8 carbon atoms. In the following, this smaller subgroup will be called Group A and the compounds will be referred to as Partial Formulas 1a, 2a, 3a, 4a and 5a. In most of these compounds R 'and R "are different from each other, one of these radicals is usually alkyl, alkenyl, alkoxy or alkoxyalkyl.

In a smaller subgroup of compounds of formulas 1, 2, 3, 4 and 5, other than group B, R '' is -F, -Cl, -NCS or - (O) _i CH ₃ - _{(k + 1)} F _k Cl _l , where i is 0 or 1 and k and l are 1, 2 or 3; the compounds in which R "has this meaning are designated by the subformulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the subformulae 1b, 2b, 3b, 4b and 5b in which R "has the meaning -F, -Cl, -NCS, -CF ₃ , -OCHF ₂ or -OCF ₃ .

In the compounds of sub-formulas 1b, 2b, 3b, 4b and 5b, R 'has the meaning given for the compounds of sub-formulas 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller subgroup of the compounds of formulas 1, 2, 3, 4 and 5, R "is -CN; this subgroup is referred to below as group C and the compounds of this subgroup are described respectively with sub-formulas 1c, 2c, 3c, 4c and 5c. In the compounds of sub-formulas 1c, 2c, 3c, 4c and 5c, R 'has the meaning given for the compounds of sub-formulas 1a-5a and is preferably alkyl, alkoxy or alkenyl.

In addition to the preferred compounds of groups A, B and C, other compounds of formulas 1, 2, 3, 4 and 5 with other variants of the proposed substituents are also used. All of these substances are available by methods known from the literature or in analogy thereto.

In addition to compounds of the formula I according to the invention, the media according to the invention preferably contain one or more compounds which are selected from the group A and / or group B and / or group C. The mass fractions of the compounds from these groups on the media according to the invention are preferably: Group A: 0 to 90%, preferably 20 to 90%, in particular 30 to 90% Group B: 0 to 80%, preferably 10 to 80%, in particular 10 to 65% Group C: 0 to 80%, preferably 5 to 80%, in particular 5 to 50% wherein the sum of the mass fractions of the compounds of the groups A and / or B and / or C contained in the respective inventive media is preferably 5% -90% and in particular 10% to 90%.

The media according to the invention preferably contain 1 to 40%, in particular preferably 5 to 30%, of the compounds according to the invention. Also preferred are media containing more than 40%, in particular 45 to 90%, of compounds according to the invention. The media preferably contain three, four or five compounds according to the invention.

• a) zusätzlich eine oder mehrere Verbindungen der Formel II enthält:
  
  worin R⁴ und R⁵ unabhängig voneinander eine Alkyl- oder Alkenylgruppe mit bis zu 12 C-Atomen, worin auch eine oder mehrere nicht benachbarte CH₂-Gruppen durch -O-, -S- und/oder -C≡C- ersetzt sein können, B trans-1,4-Cyclohexylen oder 1,4-Phenylen, und m 0 oder 1 bedeuten.
• b) zusätzlich eine oder mehrere Verbindungen der Formel III enthält:
  
  worin R⁴ und R⁵ unabhängig voneinander die in Formel II angegebene Bedeutung besitzen, C 1,4-trans Cyclohexylen oder in 2- oder 3-Position optional fluoriertes 1,4-Phenylen, und k 1 oder 2 bedeuten.
• c) eine oder mehrere Verbindungen ausgewählt aus den Formeln IIa bis IIe enthält
  
  
  worin alkyl jeweils unabhängig voneinander eine geradkettige Alkylgruppe mit 1 bis 6 C-Atomen bedeutet.
• d) eine oder mehrere Verbindungen ausgewählt aus den Formeln IIIa bis IIIg enthält
  
  
  worin alkyl jeweils unabhängig voneinander eine geradkettige Alkylgruppe mit 1 bis 6 C-Atomen, alkenyl eine geradkettige Alkenylgruppe mit 2 bis 7 C-Atomen, n 0 oder 1 und L H oder F bedeuten.

Particular preference is given to a liquid-crystal medium which, in addition to the compounds of the formula I

• a) additionally contains one or more compounds of the formula II:
  
  wherein R ⁴ and R ^{5 are} independently an alkyl or alkenyl group having up to 12 C atoms, wherein also one or more non-adjacent CH ₂ groups are replaced by -O-, -S- and / or -C≡C- may be B, trans-1,4-cyclohexylene or 1,4-phenylene, and m is 0 or 1.
• b) additionally contains one or more compounds of the formula III:
  
  wherein R ⁴ and R ⁵ independently of one another have the meaning given in formula II, C is 1,4-trans cyclohexylene or in the 2- or 3-position optionally fluorinated 1,4-phenylene, and k is 1 or 2.
• c) one or more compounds selected from the formulas IIa to IIe contains
  
  
  wherein each alkyl independently represents a straight-chain alkyl group having 1 to 6 carbon atoms.
• d) one or more compounds selected from the formulas IIIa to IIIg contains
  
  
  in which each alkyl independently of one another is a straight-chain alkyl group having 1 to 6 C atoms, alkenyl is a straight-chain alkenyl group having 2 to 7 C atoms, n is 0 or 1 and L is H or F.

• e) Medium, welches eine oder mehrere, bevorzugt 2 bis 5 Verbindungen der Formel I enthält, vorzugsweise ausgewählt aus den Formeln Ia und Ib.
• f) Medium, welches mindestens eine Verbindung der Formel IIa, mindestens eine Verbindung der Formel IIb, und gegebenenfalls mindestens eine Verbindung der Formel IIc und/oder IIIa enthält.
• g) Medium, welches mindestens eine Verbindung der Formel IIIa und/oder IIIb und/oder IIIe enthält.
• h) Medium, welches mindestens eine Verbindung der Formel IIIc und/oder IIId und/oder IIIg enthält.
• i) Medium, worin der Anteil an Verbindungen der Formel I im Gesamtgemisch mindestens 5 Gew.-%, bevorzugt 8 bis 35 Gew.-%, besonders bevorzugt 10 bis 25 Gew.-% beträgt.
• k) Medium, worin der Anteil an Verbindungen der Formel II im Gesamtgemisch mindestens 30 Gew.-%, bevorzugt 30 bis 95 Gew.-%, besonders bevorzugt 45 bis 85 Gew.-% beträgt.
• L) Medium, worin der Anteil an Verbindungen der Formel III im Gesamtgemisch mindestens 2 Gew.-%, bevorzugt 3 bis 35 Gew.-%, besonders bevorzugt 5 bis 30 Gew.-% beträgt.

Also particularly preferred are the following media:

• e) Medium which contains one or more, preferably 2 to 5, compounds of the formula I, preferably selected from the formulas Ia and Ib.
• f) medium containing at least one compound of formula IIa, at least one compound of formula IIb, and optionally at least one compound of formula IIc and / or IIIa.
• g) medium containing at least one compound of formula IIIa and / or IIIb and / or IIIe.
• h) medium containing at least one compound of formula IIIc and / or IIId and / or IIIg.
• i) Medium in which the proportion of compounds of the formula I in the total mixture is at least 5% by weight, preferably 8 to 35% by weight, particularly preferably 10 to 25% by weight.
• k) medium in which the proportion of compounds of formula II in the total mixture is at least 30 wt .-%, preferably 30 to 95 wt .-%, particularly preferably 45 to 85 wt .-%.
• L) medium, wherein the proportion of compounds of formula III in the total mixture at least 2 wt .-%, preferably 3 to 35 wt .-%, particularly preferably 5 to 30 wt .-% is.

The preparation of the liquid crystal mixtures which can be used according to the invention is carried out in a conventional manner. In general, the desired amount of the components used in lesser amount is dissolved in the constituent of the main component, expediently at elevated temperature. It is also possible to use solutions of the components in an organic solvent, e.g. B. in acetone, chloroform or methanol, to mix and remove the solvent after mixing again, for example by distillation. Furthermore, it is possible the mixtures in other conventional ways, eg. B. by Uses of premixes, e.g. B. homolog mixtures or using so-called "multi-bottle" systems to produce.

The dielectrics may also contain further additives known to the person skilled in the art and described in the literature. For example, 0-15%, preferably 0-10%, pleochroic dyes and / or chiral dopants may be added. The individual added compounds are used in concentrations of 0.01 to 6%, preferably from 0.1 to 3%. However, the concentration data of the other constituents of the liquid-crystal mixtures ie the liquid-crystalline or mesogenic compounds are given, without taking into account the concentration of these additives.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, wherein the transformation into chemical formulas according to following Tables A and B takes place. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m C atoms. n and m are integers, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12, where n = m or n ≠ m. The coding according to Table B is self-evident. In Table A, only the acronym for the main body is given. In individual cases, a code for the substituents R ^{1 *} , R ^{2 *} , L ^{1 *} and L ^{2 *} follows separately from the acronym for the main body with a dash: Code for R ¹ , R ² , L ¹ , L ² , L ³ R ¹ R ² L ¹ L ² L ³ nm C _n H _{2n + 1} C _m H _{2m + 1} H H H n Om OC _n H _{2n + 1} C _m H _{2m + 1} H H H nO.m C _n H _{2n + 1} OC _m H _{2m + 1} H H H n C _n H _{2n + 1} CN H H H nN.F C _n H _{2n + 1} CN H H F nN.FF C _n H _{2n + 1} CN H F F nF C _n H _{2n + 1} F H H H nOF OC _n H _{2n + 1} F H H H nF.F C _n H _{2n + 1} F H H F NMF C _n H _{2n + 1} C _m H _{2m + 1} F H H nOCF ₃ C _n H _{2n + 1} OCF ₃ H H H n-Vm C _n H _{2n + 1} -CH = CH-C _m H _{2m + 1} H H H nV-Vm C _n H _{2n + 1} -CH = CH -CH = CH-C _m H _{2m + 1} H H H

Tabelle B:

Preferred mixture components are given in Tables A and B. TABLE A

Table B:

Table C:

In Table C possible dopants are given, which are usually added to the mixtures of the invention.

Particular preference is given to mixtures according to the invention which, in addition to one or more compounds of the formula I, contain two, three or more compounds selected from Table B.

The following examples are intended to illustrate the invention without limiting it. Above and below, percentages are by weight. All temperatures are in degrees Celsius. Mp means melting point Clp. = Clearing point. Furthermore, K = crystalline state, N = nematic phase, Sm = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures. Δn means optical anisotropy (589 nm 20 ° C) and Δε the dielectric anisotropy (1 kHz, 20 ° C).

Δn and Δε values of the compounds according to the invention were obtained by extrapolation from liquid-crystalline mixtures which consisted of 10% of the respective compound according to the invention and 90% of the commercially available liquid crystal ZLI 4792 (Merck, Darmstadt).

"Conventional workup" means: water is optionally added, extracted with methylene chloride, diethyl ether or toluene, separated, the organic phase is dried, evaporated and the product is purified by distillation under reduced pressure or crystallization and / or chromatography. RT means room temperature.

example 1

Compound 1 is prepared according to Scheme 1 above as follows

1-1) Preparation of the Tercyclohexanone (1a)

113.7 g (0.5 mol) of ZnBr ₂ and 14 g (2 mol) of Li are added simultaneously to 345.8 g (1 mol) of 4'-bromo-4-pentyl-bicyclohexyl in 2 l of THF and 4 hours at 0 to 10 ° C treated with ultrasound. After removal of the cooling, 263.7 g (1 mol) of 4-bromophenol benzyl ether and 14.6 g of PdCl ₂ dppf are added and the mixture is stirred at RT for 72 hours. Then it is worked up as usual. The product 4 '- (4-benzyloxyphenyl) -4-pentylbicyclohexyl is hydrogenated with Pd-C (5%) in THF. The obtained 4- (4'-pentyl-bicyclohexyl-4-yl) -phenol (yield 83.1%) is then hydrogenated to the ketone with Rh-C (5%) in THF. Conventional work-up gives 4-pentyl- [1,1 ', 4', 1 ''] tercyclohexan-4 '' - one (1a) (yield 66.8%).

1-2) Preparation of (1)

15 ml (0.025 mol) of BuLi (15% in n-hexane) are added dropwise at -70 ° C. to a solution of 3.2 g (0.025 mol) of 2,3-difluorotoluene in 70 ml of THF. After stirring for 30 minutes, a solution of 8.1 g (0.025 mol) (1a) in 30 ml of THF is added dropwise and stirred for 1 hour. After warming to RT is hydrolyzed and worked up as usual. The obtained 4 '' - (2,3-difluoro-4-methylphenyl) -4-ethyl- [1,1 ', 4', 1 ''] tercyclohexan-4 '' - ol (yield 93.2%). ) is heated for dehydration with 300 mg of p-toluenesulfonic acid in toluene for 5 hours on a water boil and the mixture worked up as usual. The obtained 4 '' - (2,3-difluoro-4-methylphenyl) -4-ethyl- [1,1 ', 4', 1 ''] tercyclohexan-3 '' - ene (yield 69.8%) ) is hydrogenated at 50 ° C and 5.8 bar with Ra-Ni / ion exchanger in ethanol / ethyl acetate. After usual work-up, compound (1) (HPLC: 98.9%) is obtained.
K 62 SmB 286 N 317.3 I; Δε = -2.8; Δn = 0.1254

R L¹ L² R' C₅H₁₁ F F OC₂H₅ CH₂=CH F F CH₃ C₃H₇ F F OC₂H₅ CH₃-CH=CH₂ F F CH₃ CH₂=CH-(CH₂)₂ F F OC₂H₅ C₃H₇ CF₃ CF₃ OC₂H₅ C₅H₁₁ CF₃ CF₃ OC₂H₅ CH₂=CH CF₃ CF₃ OC₂H₅ CH₃-CH=CH₂ CF₃ CF₃ CH₃ ^C5^H11 CN CN OC₂H₅ CH₂=CH CN CN CH₃ CH₃-CH=CH₂ CN CN CH₃ CH₂=CH-(CH₂)₂ CN CN OC₂H₅ In an analogous manner, the following compounds are prepared:

R L ¹ L ² R ' C ₅ H ₁₁ F F OC ₂ H ₅ CH ₂ = CH F F CH ₃ C ₃ H ₇ F F OC ₂ H ₅ CH ₃ -CH = CH ₂ F F CH ₃ CH ₂ = CH- (CH ₂ ) ₂ F F OC ₂ H ₅ C ₃ H ₇ CF ₃ CF ₃ OC ₂ H ₅ C ₅ H ₁₁ CF ₃ CF ₃ OC ₂ H ₅ CH ₂ = CH CF ₃ CF ₃ OC ₂ H ₅ CH ₃ -CH = CH ₂ CF ₃ CF ₃ CH ₃ ^C 5 ^H 11 CN CN OC ₂ H ₅ CH ₂ = CH CN CN CH ₃ CH ₃ -CH = CH ₂ CN CN CH ₃ CH ₂ = CH- (CH ₂ ) ₂ CN CN OC ₂ H ₅

Example 2

Compound 2 is prepared according to Scheme 2 above as follows

2-1) Preparation of 1,2-Difluoro-3- (4-propylcyclohexylbenzene (2a)

344 ml (0.55 mol) of BuLi (15% in n-hexane) are added dropwise at -70 ° C. to a solution of 57 g (0.5 mol) of 2,3-difluorobenzene in 750 ml of THF. After stirring for 30 minutes, a solution of 84.2 g (0.6 mol) of 4-propylcyclohexanone in 250 ml of THF is added dropwise. After warming to RT is hydrolyzed, with halbkonz. HCl acidified and worked up as usual. The resulting 1- (2,3-difluoro-4-methyl-phenyl) -4-propyl-cyclohexanol (crude yield 100%) is heated to dehydration with 10 g of p-toluenesulfonic acid in toluene for 4 hours on a water to boiling and the approach as worked up usual. This gives 2,3-difluoro-1-methyl-4- (4-propyl-cyclohex-1-enyl) benzene (yield 97.3%). After hydrogenation with Pd-C (5%) in THF, 1,2-difluoro-3- (4-propylcyclohexyl) benzene is obtained. For the isomerization is stirred with the equimolar amount of potassium tert-butoxide in 500 ml of 1-methyl-2-pyrrolidone at 5 ° C overnight and worked up as usual (yield 65.2%).

2-2) Preparation of (2)

To 23.8 g (0.1 mol) of 1,2-difluoro-3- (4-propylcyclohexyl) benzene (2a) in 250 ml of THF at -70 ° C 68.8 ml (0.11 mol ) BuLi (15% in n-hexane) was added dropwise and stirred for 30 minutes. Subsequently, a solution of 24.5 g (0.11 mol) of 4'-propyl-bicyclohexyl-4-one in 100 ml of THF is added dropwise. After warming to RT is hydrolyzed, with halbkonz. HCl acidified and worked up as usual (crude yield). Thereafter, analogously to 2-1), the resulting cyclohexanol derivative (2b) is converted by elimination of water to the cyclohexene derivative, followed by catalytic hydrogenation. Compound (2) is obtained (yield after hydrogenation 98.9%).
K 85 SmB 188 N 297.1 I; Δε = -2.7; Δn = 0.0936

R L¹ L² R' C₂H₅ F F C₃H₇ K 69 SmB 184 N 279,3 I; Δε –2,6; Δn 0,1035 ^C5^H11 F F C₂H₅ CH₂=CH F F C₂H₅ CH₃-CH=CH₂ F F C₂H₅ CH₂=CH-(CH₂)₂ F F C₂H₅ C₃H₇ CF₃ CF₃ C₂H₅ ^C5^H11 CF₃ CF₃ C₃H₇ CH₂=CH CF₃ CF₃ C₂H₅ CH₃-CH=CH₂ CF₃ CF₃ CH₃ C₃H₇ CN CN C₃H₇ C₅H₁₁ CN CN C₂H₅ CH₂=CH CN CN C₂H₅ CH₃-CH=CH₂ CN CN CH₃ In an analogous manner, the following compounds are prepared:

R L ¹ L ² R ' C ₂ H ₅ F F C ₃ H ₇ K 69 SmB 184 N 279.3 I; Δε -2.6; Δn 0.1035 ^C 5 ^H 11 F F C ₂ H ₅ CH ₂ = CH F F C ₂ H ₅ CH ₃ -CH = CH ₂ F F C ₂ H ₅ CH ₂ = CH- (CH ₂ ) ₂ F F C ₂ H ₅ C ₃ H ₇ CF ₃ CF ₃ C ₂ H ₅ ^C 5 ^H 11 CF ₃ CF ₃ C ₃ H ₇ CH ₂ = CH CF ₃ CF ₃ C ₂ H ₅ CH ₃ -CH = CH ₂ CF ₃ CF ₃ CH ₃ C ₃ H ₇ CN CN C ₃ H ₇ C ₅ H ₁₁ CN CN C ₂ H ₅ CH ₂ = CH CN CN C ₂ H ₅ CH ₃ -CH = CH ₂ CN CN CH ₃

Comparative example

A liquid crystal mixture containing PCH-53 8:00 pm Clearing point [° C]: 111.6 PCH-502FF 12:00 CCP 302FF 14:00 Δn [589 nm, 20 ° C]: 0.1012 CCP 502FF 14:00 Δε [1 kHz, 20 ° C]: -4.0 CCP 21FF 12:00 γ ₁ [mPa.s]: 247 CCP 31ff 12:00 CPYC-2-3 4:00 CYYC-2-3 4:00 CCYY-2-O2 4:00 CCYY-3-1 4:00

Example 3

A liquid crystal mixture containing PCH-53 13:00 Clearing point [° C]: 112.6 PCH-502FF 13:00 CCP 302FF 14:00 Δn [589 nm, 20 ° C]: 0.0930 CCP 502FF 14:00 Δε [1 kHz, 20 ° C]: -4.1 CCP 21FF 12:00 γ ₁ [mPa.s]: 241 CCP 31ff 12:00 CCCY-5-1 5:00 CYCC-3-3 5:00 CYCC-2-3 3:00 PCH-504FF 9:00 Compared to the comparative example has a significantly reduced birefringence at comparable values of the clearing point, the DK anisotropy and the rotational viscosity.

Example 4

A liquid crystal mixture containing PCH-53 2:50 Clearing point [° C]: 114.1 PCH-502FF 13:00 CCP 302FF 14:00 Δn [589 nm, 20 ° C]: 0.0947 CCP 502FF 14:00 Δε [1 kHz, 20 ° C]: -4.7 CCP 21FF 12:00 y ₁ [mPa.s]: 264 CCP 31ff 12:00 CCCY-5-1 5:00 CYCC-3-3 5:00 CYCC-2-3 2:00 PCH-504FF 18:00 PCH-304 2:50 Compared to the comparative example has a significantly reduced birefringence and a more negative DK anisotropy at comparable values of the clearing point and the rotational viscosity.

Claims (11)

Compounds of the formula I

wherein R ¹ and R ² are each independently an unsubstituted alkyl radical having 1-12 C atoms, A ¹ , A ² , A ³ and A ⁴ independently of one another in the positions 2 and 3 twice with CN, F, Cl, CF ₃ or OCF ₃ substituted 1,4-phenylene or 1,4-cyclohexenylene, and Z ¹ , Z ² and Z ^{3 is} a single bond, with the proviso that a) the compound at least one in the 2- and 3-position with CN, F, Cl, CF ₃ or OCF _{3 contains} substituted 1,4-phenylene radical, and b) three of the rings A ¹ , A ² , A ³ and A ^{4 are} trans-1,4-cyclohexylene. Compounds of the formula I according to claim 1, characterized in that the compounds contain at least one 2- and 3-position with CN, F or CF ₃ substituted 1,4-phenylene radical. Compounds of the formula I according to claim 1 or 2, characterized in that the compounds contain at least one 2- and 3-position with F-substituted 1,4-phenylene radical. Compounds of the formula I according to one or more of Claims 1 to 3, characterized in that the compounds of the formula I are selected from the formulas Ia or Ib,

wherein L ¹ and L ² F, and R ¹ and R ² independently represent an unsubstituted alkyl radical having 1 to 8 carbon atoms Use of compounds of the formula I according to one or more of claims 1 to 4 as components of liquid-crystalline media. Liquid-crystalline medium containing at least one compound according to one or more of claims 1 to 4. Flüssigkristllines medium according to claim 6, characterized in that it contains one or more compounds of formula II in addition to at least one compound of formula I,

wherein R ⁴ and R ^{5 are} independently an alkyl or alkenyl group having up to 12 C atoms, wherein also one or more non-adjacent CH ₂ groups are replaced by -O-, -S- and / or -C≡C- may be B, trans-1,4-cyclohexylene or 1,4-phenylene, and m is 0 or 1. Liquid-crystalline medium according to claim 6 or 7, characterized in that it contains one or more compounds of formula III,

wherein R ⁴ and R ⁵ independently of one another have the meaning given in formula II, C is 1,4-trans cyclohexylene or in the 2- or 3-position optionally fluorinated 1,4-phenylene, and k is 1 or 2. Use of a liquid-crystalline medium according to one or more of claims 6 to 8 in a liquid-crystal display element. Use of a liquid-crystalline medium according to claim 9, characterized in that the liquid-crystal display element is an ECB, VA, CH, DAP or IPS display element. Use of a liquid-crystalline medium according to claim 9 as a dielectric in an electro-optical display element.