DE19529106A1 - Liquid crystalline medium with very high resistivity and low threshold potential - based on polar cpds. with positive dielectric anisotropy contains cyclohexyl-cyclohexyl-di:fluoro-bi:phenyl cpds., useful for electro-optical purposes, pref. LCD, e.g. matrix or STN display - Google Patents

Abstract

Liquid crystalline (LC) medium based on a mixt. of polar cpds. with positive dielectric anisotropy contains 4'-(trans-cyclohexyl)-cyclohexyl-2,2'-difluorobiphenyl cpd(s). of formula (I); in which R = H or 1-15 C alk(en)yl, opt. mono-substd. by CN or CF3 or at least mono-substd. by halogen, in which CH2 gp(s). may be replaced by -O-, -S-,1,3-cyclobutylene, -CO-, -CO-O-, -O-CO- or -O-CO-O- without adjacent O atoms; Y = F, Cl or 1-6 C halogenated alkyl, alkenyl or alkoxy; L1 = H or F.

Description

The present invention relates to a liquid-crystalline medium, as well its use for electro-optical purposes and this medium containing ads.

Liquid crystals are mainly used as dielectrics in display devices used because the optical properties of such substances by a applied voltage can be influenced. Electro-optical Vorrich Solutions based on liquid crystals are well suited to the expert known and can be based on various effects. Such Vor directions are, for example, cells with dynamic scattering, DAP cells (upright phase deformation), guest / host cells, TN cells with twisted nematic structure, STN cells ("super twisted nematic "), superbirefringence effect (SBE) cells and OMI cells ("optical mode interference"). The most common display devices are based on the Schadt-Helfrich effect and have a twisted nema table structure.

The liquid crystal materials need a good chemical and thermal Stability and good stability to electric fields and have electromagnetic radiation. Furthermore, the liquid crystal should materials have low viscosity and short in the cells Speech times, low threshold voltages and high contrast result.

Furthermore, they should at normal operating temperatures, d. H. in one the widest possible range below and above room temperature have suitable mesophase, for example for the above Cells a nematic or cholesteric mesophase. Because liquid Crystals usually as mixtures of several components to the application It is important that the components are good with each other are miscible. Other properties, such as electrical conductivity, the dielectric anisotropy and the optical anisotropy, depending on  Cell type and application area meet different requirements For example, materials for cells should be twisted nematic Structure a positive dielectric anisotropy and a low elek have trical conductivity.

For example, for matrix liquid crystal displays with integrated non-linear elements for switching individual pixels (MFK display gen) media with high positive dielectric anisotropy, broad nema table phases, relatively low birefringence, very high specifi resistance, good UV and temperature stability and low Steam pressure desired.

Such matrix liquid crystal displays are known. As nonlinear Elements for individual switching of the individual pixels can For example, active elements (i.e., transistors) may be used. One speaks then of an "active matrix", whereby one two types can distinguish:

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

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

In the promising type 2, which is preferred, as electro optical effect commonly used the TN effect. Man under separates two technologies: TFTs made of compound semiconductors such. B. CdSe or TFTs based on polycrystalline or amorphous Silicon. At the latter technology is becoming worldwide with great intensity worked.  

The TFT matrix is on the inside of a glass plate of the display applied while the other glass plate on the inside the trans carries a parent counterelectrode. Compared to the size of the pixel Electrode, the TFT is very small and does not disturb the picture practically. These Technology can also be extended for fully color-capable image displays being a mosaic of red, green and blue filters like this is arranged that each filter element a switchable pixel is opposite.

The TFT displays usually work as TN cells with crossed ones Polarizers in transmission and are backlit.

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

Such MFK displays are particularly suitable for TV applications (eg pocket TV) or for high-information displays for computers applications (laptop) and in automotive or aircraft construction. Next Problems with the angular dependence of the contrast and the Switching times result in MFK displays due to difficulties Insufficient 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 Transistor for Matrix Addressing of Tele vision Liquid Crystal Displays, p. 145 ff, Paris]. With decreasing cons The contrast of a MFK display deteriorates and it can the problem of "after image elimination" occur. Because the specific Resistance of the liquid crystal mixture by interaction with the internal surfaces of the display generally over the lifetime MFK display decreases, a high (initial) resistance is very high important to maintain acceptable service life. Especially at low  Volt mixtures were previously not possible to very high specific To realize resistances. Furthermore, it is important that the specific Resistance the smallest possible increase with increasing temperature as well as after temperature and / or UV exposure. Especially after also the low temperature properties of the mixtures from the State of the art. It is required that even at low temperatures no crystallization and / or smectic phases occur and the tem Temperature dependence of the viscosity is as low as possible. The MFK ads from the prior art thus do not meet today's requirements requirements.

There is thus still a great need for MFK displays very high specific resistance with at the same time big work temperature range, short switching times even at low temperatures and low threshold voltage, these disadvantages are not or only in show a lesser degree.

For TN (Schadt-Helfrich) cells, media are desired, the following Benefits in the cells allow:

• - extended nematic phase range (especially to deep temperatures)
• - Switchability at extremely low temperatures (out-door-use, Automobile, avionics)
• - increased resistance to UV radiation (longer life period).

With the media available from the prior art It does not allow these benefits while preserving the rest To realize parameters.

For higher-twisted cells (STN), media are required, those higher Multiplexibility and / or lower threshold voltages and / or porridge tern nematic phase ranges (especially at low temperatures)  enable. For this purpose, a further expansion of the available standing parameter space (clearing point, transition smectic-nematic or melting point, viscosity, dielectric values, elastic sizes) urgently desired.

The invention is based, media especially for the task provide MFK, TN, or STN displays similar to those listed above give disadvantages or only to a lesser extent, and preferably at the same time very high resistivities and low thresholds have voltages.

It has now been found that this problem can be solved if one uses in ads inventive media.

The invention thus relates to a liquid-crystalline medium on the Base of a mixture of polar compounds with positive dielectrics shear anisotropy, characterized in that it has one or more Compounds of the general formula I

contains, in which
RH, an unsubstituted, a simple by CN or CF₃ or at least one halogen-substituted alkyl or alkenyl radical having 1 to 15 carbon atoms, wherein in these radicals also one or more CH₂ groups each independently

may be replaced so that O atoms are not directly linked to each other,
YF, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 carbon atoms, and
L 1 H or F
mean.

The compounds of the formula I have a broad application Area. Depending on the choice of substituents, these may Compounds serve as base materials from which liquid crystalline Media are composed for the most part; but it can also compounds of formula I liquid-crystalline base materials be added to other classes of compounds, for example, the dielectric and / or optical anisotropy of such a dielectric to influence and / or the threshold voltage and / or to optimize its viscosity.

The compounds of the formula I are colorless in the pure state and form liquid-crystalline mesophases in one for electro-optical use conveniently located temperature range. Chemical, thermal and against Light are they stable.

Compounds of the formula

X = F, Cl, CF₃, CHF₂, OCHF₂, OCF₃
with r = 0 or 1, Z = H or F and ring A = 1,4-cyclohexylene or 1,4-phenylene
are already known from WO 91/13850.

In the media according to the invention containing compounds of the formula I. Y is preferably F, Cl, OCF₃, OCHF₂, CF₃, CHFCF₃, CF₂CHF₂, C₂H₄CHF₂, CF₂CH₂CF₃, CHF₂, OCH₂CF₃, OCH₂CHF₂, OCF₂CHF₂, O (CH₂) ₃CF₃, OCH₂C₂F₅, OCH₂CF₂CHF₂, OCH₂C₃F₇, OCHFCF₃, OC₂F₅, OCF₂CHFCF₃, OCH = CF₂, OCF = CF₂, OCF = CFCF₃, OCF = CF-C₂F₅, CH = CHF, CH = CF₂, CF = CF₂, CF₂OCF₃, in particular F, OCHFCF₃, OCF₃, OCHF₂, OC₂F₅, OC₃F₇, OCH = CF₂, and CF₂OCF₃.

Particular preference is given to compounds of the formula I in which Y = L¹ = F mean.

If R is an alkyl radical and / or an alkoxy radical, then this may straight-chain or branched. Preferably it is straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and therefore preferably denotes ethyl, propyl, Butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, Tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, Undecoxy, dodecoxy, tridecoxy or tetradecoxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (= methoxy methyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxa heptyl, 2-, 3-, 4-, 5-, 6- or 7-oxo-octyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxa nonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R is an alkyl radical in which a CH₂ group is replaced by -CH = CH- is replaced, it may be straight-chain or branched. Preferably it is straight-chain and has 2 to 10 carbon atoms. He therefore means special vinyl, prop-1, or prop-2-enyl, but-1, 2- or but-3-enyl, pent-1, 2-, 3- or pent-4-enyl, hex-1, 2-, 3-, 4- or hex-5-enyl, hept-1, 2-, 3-,  4-, 5- or hept-6-enyl, oct-1, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, Dec-1, 2-, 3-, 4-, 5-, 6-, 7-, 8- or Dec-9-enyl.

If R is an alkyl radical in which a CH₂ group by -O- and one replaced by -CO-, these are preferably adjacent. Thus These include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. Preferably, these are straight-chain and have 2 to 6 C atoms.

They therefore mean especially acetyloxy, propionyloxy, butyryloxy, Pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, Butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxy ethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, Butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxy carbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxy carbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl, 4- (methoxycarbonyl) -butyl.

If R is an alkyl radical in which a CH₂ group by unsub substituted or substituted -CH = CH- and an adjacent CH₂ group replaced by CO or CO-O or O-CO, this can be straight-chain or be branched. Preferably, it is straight-chain and has 4 to 13 C atoms. He therefore means especially acryloyloxymethyl, 2-acrylic oxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyl oxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxy ethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyl oxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryl oyloxyoctyl, 9-methacryloyloxynonyl.

If R is a substituted by CN or CF₃ alkyl or Alkenyl means, this radical is preferably straight-chain. The Substitution by CN or CF₃ is in any position.  

If R is an alkyl or at least monosubstituted by halogen Alkenyl radical, this radical is preferably straight-chain and Halogen is preferably F or Cl. When multiple substitution is halogen preferably F. The resulting radicals also include perfluorinated Leftovers. For single substitution, the fluorine or chlorine substituent may be in be any position, but preferably in the ω position.

Compounds of the formula I which are suitable for polymerization reactions have appropriate wing groups R, are suitable for the representation of liquid crystal liner polymer.

Compounds of formula I with branched wing groups R ge occasionally because of better solubility in the usual liquid crystal linen base materials, but especially as a chiral Dopants when they are optically active. Smectic compounds of this Art are suitable as components for ferroelectric materials.

Compounds of the formula I with S _A phases are suitable, for example, for thermally addressed displays.

Branched groups of this type usually contain no more than one Chain branching. 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, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methyl butoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methyl hexoxy, 1-methylheptoxy.

If R represents an alkyl radical in which two or more CH₂ groups replaced by -O- and / or -CO-O-, it may be straight-chain or be branched. Preferably, it is branched and has 3 to 12 carbon atoms. It means that especially bis-carboxy-methyl, 2,2-bis-carboxy ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxybutyl, 5,5-bis-carboxy pentyl, 6,6-bis-carboxyhexyl, 7,7-bis-carboxyheptyl, 8,8-bis-carboxy octyl, 9,9-bis-carboxy-nonyl, 10,10-bis-carboxy-decyl, bis (methoxy carbonyl) -methyl, 2,2-bis (methoxycarbonyl) -ethyl,  3,3-bis- (methoxycarbonyl) -propyl, 4,4-bis (methoxycarbonyl) -butyl, 5,5-bis (methoxycarbonyl) pentyl, 6,6-bis (methoxycarbonyl) hexyl, 7,7-bis (methoxycarbonyl) heptyl, 8,8-bis (methoxycarbonyl) octyl, Bis (ethoxycarbonyl) methyl, 2,2-bis (ethoxycarbonyl) ethyl, 3,3-bis (ethoxycarbonyl) propyl, 4,4-bis (ethoxycarbonyl) butyl, 5,5-bis- (ethoxycarbonyl) -hexyl.

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

The compounds of the invention can be z. B. as follows produce:

scheme 1 scheme 2 scheme 3 scheme 4 scheme 5 scheme 6 scheme 7 scheme 8 scheme 9

The invention also provides electro-optical displays (esp STN or MFK displays with two plane-parallel support plates, the forming a cell with a border, integrated non-linear elements for switching individual pixels on the carrier plates and an in the cell nematic liquid crystal mixture with positive dielectric anisotropy and high resistivity), which is the like media and the use of these media for electro optical purposes.

The liquid-crystal mixtures according to the invention enable a be significant extension of the available parameter space.

The achievable combinations of clearing point, viscosity at low temperature temperature, thermal and UV stability and dielectric anisotropy meet by far previous materials from the prior art.  

The demand for high clearing point, nematic phase at lower Temperature and a high Δε has so far met only insufficient become. Systems such. Although ZLI-3119 have comparable clearing point and comparable favorable viscosities, but have a Δε of only +3.

Other mixing systems have comparable viscosities and Values of Δε, however, have only clearing points in the region of 60 ° C.

The liquid-crystal mixtures according to the invention make it possible with Retention of the nematic phase to -20 ° C and preferably to -30 ° C, particularly preferably to -40 ° C, clearing points above 80 °, preferably above 90 °, more preferably above 100 ° C, simultaneously dielek trical anisotropy values Δε 6, preferably 8 and a high value to achieve the specific resistance, resulting in excellent STN and MKF displays can be achieved. In particular, the Mixtures characterized by small operating voltages. The TN thresholds are below 2.0 V, preferably below 1.5 V, more preferably <1.3 V.

It is understood that by suitable choice of components of the inventions mixtures according to the invention also have higher clearing points (eg above 110 ° C.) at higher threshold voltage or lower clearing points at low ren threshold voltages to obtain the other advantageous properties can be realized. Likewise, in accordance with little increased viscosities mixtures with larger Δε and thus lower thresholds are obtained. The invention MFK displays preferably work in the first transmission minimum Gooch and Tarry [C.H. Gooch and H.A. Tarry, Electron. Lett. 10, 2-4, 1974; C.H. Gooch and H.A. Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], Here, in addition to particularly favorable electro-optical properties such as B. high slope of the curve and low angle dependence of the Contrast (DE-PS 30 22 818) at the same threshold voltage as in an analog display in the second minimum a smaller dielectric  Anisotropy is sufficient. This can be done using the Mixtures according to the invention in the first minimum significantly higher specific resistances realize than with mixtures with Cyanver bonds. The skilled person can by suitable choice of the individual Components and their proportions by simple routine the required for a given layer thickness of the MFK display Set birefringence.

The viscosity at 20 ° C is preferably <60 mPa · s, especially before zugt <50 mPa · s. The nematic phase range is preferably min at least 90 °, in particular at least 100 °. Preferably, it extends this range at least from -20 ° to + 80 °.

Measurements of the Capacity Holding Ratio (HR) [p. Matsumoto et al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); G. Weber et al., Liquid Crystals 5, 1381 (1989)] have shown that inventive mixtures enthal tend compounds of formula I have a significantly smaller decrease in HR with increasing temperature than analogous mixtures containing instead of the compounds of formula I.
Cyanophenylcyclohexanes of the formula

or esters of the formula

The UV stability of the mixtures according to the invention is considerable better, d. H. they show a much smaller decrease in HR UV exposure.

Preferably, the media of the invention are based on several (preferably two or more) compounds of formula I, d. H. the amount of these compounds is 5-95%, preferably 10-60% and especially preferably in the range of 20-50%.  

The individual compounds of the formulas I to XII and their sub-formulas, which can be used in the media according to the invention are either known, or they can analogously to the known Verbindun be prepared.

Preferred embodiments are given below:

• - Medium contains one or more compounds of the formula wherein R has the meaning given in claim 1, but is preferably a straight-chain alkyl radical;
• - Medium additionally contains one or more compounds selected from the group consisting of the general formulas II to VI: in which the individual radicals have the following meanings:
  R °: n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms
  X °: F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 C atoms,
  Y¹ and Y² are each independently H or F
  r: 0 or 1.

The compound of formula IV is preferred

• - Medium additionally contains one or more compounds selected from the group consisting of the general formulas VII to XII: wherein R °, X °, Y¹ and Y² each independently have one of the meaning given in claim 2, preferably F, Cl, CF₃, OCF₃, OCHF₂, alkyl, oxaalkyl, fluoroalkyl or alkenyl each having up to 6 carbon atoms.
• - The proportion of compounds of formulas I to VI is taken together at least 50% by weight in the total mixture;
• - The proportion of compounds of formula I is in the total mixture 10 to 50% by weight;
• the proportion of compounds of the formulas II to VI in the total mixture is 30 to 70% by weight
• - The medium contains compounds of the formulas II, III, IV, V or VI
• R ° is straight-chain alkyl or alkenyl having 2 to 7 C atoms
• - The medium consists essentially of compounds of Formulas I to VI
• the medium contains further compounds, preferably selected from the following group consisting of the general formulas XIII to XVI: wherein R ° and X ° have the abovementioned meaning and the 1,4-Phe nylenringe may be substituted by CN, chlorine or fluorine. Preference, the 1,4-phenylene rings are mono- or polysubstituted by fluorine atoms.
• The weight ratio I: (II + III + IV + V + VI) is preferred 1:10 to 10: 1.
• - Medium consists essentially of compounds selected from the group consisting of the general formulas I to XII.

It has been found that even a relatively low proportion of Verbindun of the formula I in admixture with conventional liquid crystal materials, esp but especially with one or more compounds of the formula II, III, IV, V and / or VI to a considerable lowering of thresholds voltage and low values for birefringence, where at the same time broad nematic phases with low transition temperatures be observed smectic-nematic, whereby the storage stability is improved. Furthermore, such mixtures are characterized by their favorable values for the rotational viscosity γ₁. The connections of the Formulas I to VI are colorless, stable and mutually and with others Liquid crystal materials readily miscible.

The term "alkyl" includes straight-chain and branched alkyl groups with 1-7 carbon atoms, in particular the straight-chain groups methyl, Ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups of 2-5 coals Atoms are generally preferred.

The term "alkenyl" includes straight-chain and branched alkenyl groups pen with 2-7 carbon atoms, in particular the straight-chain groups. Especially alkenyl groups are C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, in particular C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl. Examples preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups up to 5 carbon atoms are generally preferred.  

The term "fluoroalkyl" preferably includes straight-chain groups terminal fluorine, d. H. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluoro butyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions However, the fluorine are not excluded.

The term "oxaalkyl" preferably includes straight-chain radicals of the formula C _n H _{2n + 1} -O- (CH₂) _m , wherein n and m are each independently 1 to 6. Preferably, n = 1 and m is 1 to 6.

By a suitable choice of the meanings of R ° and X °, the An Speech times, the threshold voltage, the steepness of the transmissions characteristics, etc. are modified in the desired manner. For example lead 1 E-alkenyl, 3E-alkenyl, 2E-Alkenyloxyreste and the same usually to shorter response times, improved nemati tendencies and a higher ratio of elastic constancy th k₃₃ (bend) and k₁₁ (splay) compared to alkyl or alkoxy. 4-alkenyl radicals, 3-alkenyl radicals and the like generally result lower threshold voltages and smaller values of k₃₃ / k₁₁ in comparison to alkyl and alkoxy radicals.

A -CH₂CH₂ group generally leads to higher values of k₃₃ / k₁₁ compared to a simple covalent bond. Higher values of k₃₃ / k₁₁ allow z. B. flatter transmission characteristics in TN cells with 90 ° twist (to achieve shades of gray) and steeper transmissions characteristics in STN, SBE and OMI cells (higher multiplexability) and vice versa.

The optimum ratio of the compounds of the formulas I and II + III + IV + V + VI depends largely on the desired properties, on the choice of the components of the formulas I, II, III, IV, V and / or VI and from the choice of other optional components. Suitable proportions within the Be realms can easily be determined on a case-by-case basis.  

The total amount of compounds of formulas I to XII in the inventions The mixtures according to the invention are not critical. The mixtures can therefore one or more other components included for optimization different properties. The observed effect on the response times and the threshold voltage, however, is generally greater higher is the total concentration of compounds of formulas I to XII.

In a particularly preferred embodiment, the inventions contain According to the invention media compounds of formula II to VI (preferably II, III and / or IV, in particular IVa), wherein X ° F, OCF₃, OCHF₂, F, OCH = CF₂, OCF = CF₂ or OCF₂-CF₂H means. A cheap synergi tical effect with the compounds of formula I leads to particular advantageous properties. In particular, mixtures containing Ver Compounds of the formula I and the formula IVa are characterized by their low threshold voltages.

The structure of the MFK display of polarizers according to the invention, Electrode base plates and electrodes with surface treatment corresponds to the usual for such displays construction. It is the Concept of customary construction here broad and includes all Modifications and modifications of the MFK display, in particular also matrix display elements based on poly-Si TFT or MIM.

A significant difference of the displays according to the invention to the hitherto customary on the basis of the twisted nematic cell however, in the choice of the liquid crystal parameters of the liquid crystal layer.

The preparation of the liquid crystal which can be used according to the invention Mixtures takes place in a conventional manner. In general, the ge desired amount of components used in lesser amount the components constituting the main component are solved, purpose moderately at elevated temperature. It is also possible solutions of the Kom components in an organic solvent, e.g. In acetone, chloroform or methanol, and the solvent after mixing to remove again, for example by distillation.  

The dielectrics may also other, known in the art and in the Literature described additives contain. For example, 0-15% pleochroic dyes or chiral dopants are added.

C is a crystalline, S is a smectic, S _{c is} a smectic C, N is a nematic and I is the isotropic phase.

V₁₀ denotes the voltage for 10% transmission (view perpendicular right to the disk surface). t _on denotes the switch-on time and t _off the switch-off time at an operating voltage corresponding to 2.5 times the value of V₁₀. Δn denotes the optical anisotropy and n₀ the refractive index. Δε denotes the dielectric anisotropy (Δε = ε _|| -ε _┴ , where ε _|| the dielectric constant parallel to the _longitudinal molecular _axes and ε _┴ the dielectric constant perpendicular to it). The electro-optical data were measured in a TN cell in the 1st minimum (ie at a d · Δn value of 0.5) at 20 ° C, unless expressly stated otherwise. The optical data were measured at 20 ° C, unless expressly stated otherwise.

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. The coding according to Table B is self-evident. In Table A, only the acronym for the basic body is given. In the individual case, 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:

Preferred mixture components are given in Tables A and B.  

Table A

Table B

The following examples are intended to illustrate the invention without being limits. Above and below mean percentages by weight center. All temperatures are in degrees Celsius. Mp means Melting point, bp. = Clearing point. Furthermore, K = crystalline state,  N = nematic phase, S = smectic phase and I = isotropic phase. The Indications between these symbols represent the transition temperatures Δn means optical anisotropy (589 nm, 20 ° C) and viscosity (mm² / sec) was determined at 20 ° C.

"Usual workup" means: if necessary, add water, extracted with dichloromethane, diethyl ether or toluene, separated, dried the organic phase is evaporated and the product is purified by distillation under reduced pressure or crystallization and / or chromato graphy. The following abbreviations are used:

DAST diethylaminosulfur DMEU 1,3-dimethyl-2-imidazolidinone KOT Potassium tert-butoxide PdCl₂dppt Palladium bis (triphenylphosphine) dichloride THF tetrahydrofuran pTsOH p-toluenesulfonic acid

example 1 Step 1.1

4 mmol of bis (triphenylphosphine) palladium (II) chloride in 24 ml of THF at 55 ° C in a nitrogen atmosphere with 4 mmol sodium borohydride added. The mixture is refluxed for 0.5 h and then the suspension is allowed to rise  Cool to 40 ° C. The catalyst solution becomes a reaction at 50 ° C mixture consisting of 0.27 mol I, 0.27 mol II, 600 ml of toluene and 0.56 mol Sodium carbonate added dropwise. It is allowed to stir overnight at 50 ° C, mixed with water and worked up as usual.

Step 1.2

In a nitrogen atmosphere, to 0.02 mol IV dissolved in 100 ml of toluene / THF (4: 1), 5.1 g of zinc bromide and 0.56 g of lithium granules are added, and the reaction mixture is treated with stirring for 4 h with ultrasound. At 15-20 ° C, 0.02 mol III and 0.6 g PdCl₂dppt be added to the reaction mixture. The mixture is stirred for 48 h at 25 ° C, treated with an ammonium chloride solution and the reaction mixture was filtered through kieselguhr. The filtrate is worked up as usual.
K 91 N 237.3 I; Δn = +0.150; Δε = 14.83.

Analogously, the following compounds of the formula

manufactured:

Examples mix Example A example B

Claims (10)

1. Liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, characterized in that it contains one or more compounds of general formula I. contains, in which
RH, an unsubstituted, a simply by CN or CF₃ or at least one substituent by halogen sub stituted alkyl or alkenyl radical having 1 to 15 C-Ato, wherein in these radicals also one or more CH₂ groups each independently may be replaced so that O atoms are not directly linked to each other,
YF, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 carbon atoms, and
L 1 H or F
means. 2. Medium according to claim 1, characterized in that it additionally contains one or more compounds selected from the group consisting of the general formulas II, III, IV, V and VI: in which the individual radicals have the following meanings:
R⁰: n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 7 C atoms,
X⁰: F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 C atoms,
Y¹ and Y² are each independently H or F,
r: 0 or 1. 3. Medium according to claim 2, characterized in that the proportion to compounds of the formulas I to VI together in the total mixture at least 50 wt .-% is. 4. Medium according to claim 1 or 2, characterized in that the Proportion of compounds of the formula I in the total mixture 3 to 80% by weight is. 5. Medium according to at least one of claims 2 to 3, characterized characterized in that the proportion of compounds of the formulas II to VI in the total mixture is 20 to 80 wt .-%. 6. Medium according to one of claims 1 to 5, characterized in the compound of the formula I Y F, OCF₃, OCHF₂, OCHFCF₃, OCH₂CF₃, OCH = CF₂ or OC₂F₅ means. 7. Medium according to one of claims 1 to 6, characterized that in the compound of the formula I Y = L¹ = F. 8. Medium according to claim 1, characterized in that it additionally contains a compound of formula IVa contains
wherein R ° and X ° have the meaning given in claim 2. 9. Use of the liquid-crystalline medium according to claim 1 for electro-optical purposes. 10. Electro-optical liquid crystal display containing a liquid crystal Lines Medium according to claim 1.