DE102007042414A1 - Liquid crystal medium, useful e.g. in electro-optical liquid crystal displays, preferably twisted nematic displays and thin-film transistor displays, televisions and videos, comprises 5-cyclohexyl-2-phenyl-tetrahydro-pyran compound - Google Patents

Abstract

Liquid crystal medium (A) comprises one or more 5-cyclohexyl-2-phenyl-tetrahydro-pyran compound (I). Liquid crystal medium (A) comprises one or more 5-cyclohexyl-2-phenyl-tetrahydro-pyran compounds of formula (I). R 0>halogenated or unsubstituted 1-15C alkyl- or alkoxy residue with 1 to 15 C atoms, where one or more CH 2-groups are substituted by -C?=C-, -CF 2O-, -CH=CH-, cyclobutane, spiro[3.3]heptane, -O-, -CO-O- or -O-CO- and the oxygen atoms are not connected directly; X 0>F, Cl, CN, SF 5, SCN, NCS, halogenated alkyl residue, halogenated alkenyl residue, halogenated alkoxy residue or halogenated up to 6C alkenyloxy residue; and Y 1>, Y 2>H or F. An independent claim is included for the preparation of (A) comprising mixing (I) with further 4-(difluoro-phenoxy-methyl)-bicyclohexyl compound of formula (II), 4-(difluoro-phenoxy-methyl)-biphenyl compound of formula (III), 4-phenyl-bicyclohexyl compound of formula (IV), 4-cyclohexyl-biphenyl compound of formula (V), [1,1';4',1'']terphenyl compound o of formula (VI) and cyclohexane-phenyl compound of formulae (VII) and (VIII), alkyl-cyclohexane compound of formula (IX) and alkenyl-cyclohexane compound of formula (X), alkenyl-cyclohexane-phenyl compound of formulae (XI) and (XII), and/or a biphenyl compound of formula (XIII), fluorophenyl-cyclohexane compounds of formulae (XX1a) and (XX1b) or with a further liquid crystal compounds and/or additives. Y 3>, Y 4>H or F; ring A : a cyclohexane ring or tetrahydro-pyran ring; Z 0>C 2H 4-, -(CH 2) 4-, -CH=CH-, -CF=CF-, -C 2F 4-, -CH 2CF 2-, -CF 2CH 2-, -CH 2O-, -OCH 2-, -COO- or -OCF 2-; alkyl : 1-7C alkyl; R1a : 1-7C alkyl, 1-6C alkoxy or 2-7C alkenyl; alkenyl, alkenyl1 : 2-7C alkenyl; R 1>, R 2>n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or up to 9C (preferably 2-9C) alkenyl; and r : 0 or 1. In formula (V):Z 0> = a single bond or -CF 2O-. In formula (VI):Z 0> = a single bond. In formula (VIII): Z 0>-CF 2O-. [Image] [Image] [Image] [Image] [Image] [Image] [Image] [Image] [Image].

Description

The The present invention relates to a liquid-crystalline medium (FK medium), and to the same Use for electro-optical purposes and displays containing this medium.

liquid Crystals are mainly used as dielectrics in display devices, because the optical properties of such substances by an applied Tension can be influenced. Electro-optical devices based on liquid crystals are well known to those skilled in the art and are capable of various effects based. Such devices are for example cells with dynamic scattering, DAP cells (Deformation of upright phases), guest / host cells, TN cells with twisted nematic ("twisted nematic ") structure, STN cells ("super-twisted nematic"), SBE cells ("superbirefringence effect ") and OMI cells ("optical mode interference"). The most common Display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.

The liquid crystal materials have to good chemical and thermal stability and good electrical stability Own fields and electromagnetic radiation. Furthermore, should the liquid crystal materials low viscosity have and in the cells short response times, low threshold voltages and give a high contrast.

Farther they should be at usual Operating temperatures, i. in the widest possible area below and have a suitable mesophase above room temperature, for example for the above cells a nematic or cholesteric mesophase. Because liquid crystals usually used as mixtures of several components, It is important that the components mix well with each other are. Other properties, such as electrical conductivity, the dielectric anisotropy and the optical anisotropy must each be according to cell type and field of application different requirements suffice. For example, materials for cells should be twisted nematic Structure has a positive dielectric anisotropy and a low one electric conductivity exhibit.

For example are for Matrix liquid crystal displays with integrated non-linear elements for switching individual Pixels (MFK displays) Media with large positive dielectric Anisotropy, broad nematic phases, relatively low birefringence, very high resistivity, good UV and temperature stability and low Steam pressure desired.

• 1. MOS (Metal Oxide Semiconductor) oder andere Dioden auf Silizium-Wafer als Substrat.
• 2. Dünnfilm-Transistoren (TFT) auf einer Glasplatte als Substrat.

Such 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 glass plate as a substrate.

The Use of single-crystal silicon as the substrate material restricts the Display size, as well the modular composition of various partial displays on the Bumps to problems leads.

at the more promising type 2, which is preferred, is considered electro-optical Effect usually the TN effect used. There are two technologies: TFTs made of compound semiconductors such as. CdSe or TFT's based on polycrystalline or amorphous silicon. At the latter Technology is being worked on worldwide with great intensity.

The TFT matrix is on the inside of a glass plate of the display upset while the other glass plate on the inside the transparent counter electrode wearing. Compared to the size of the pixel electrode is the TFT very small and disturbs the picture practically not. This technology can also be used for full color Image displays, with a mosaic of red, green and blue filters is arranged such that each one filter element lies opposite a switchable picture element.

The TFT displays usually work as TN cells with crossed polarizers in transmission and are illuminated from behind.

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

Such MFK displays are particularly suitable for TV applications (eg pocket TV) or for high-information displays for computer applications (laptop) and in the automotive or aircraft. In addition to problems with regard to the angle dependence of the contrast and the switching times, difficulties arise with MFK displays due to the insufficiently high specific resistance 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 ]. With decreasing resistance, the contrast of a MFK display deteriorates and the problem of "after image elimination" may occur. Since the resistivity of the liquid crystal mixture decreases by interaction with the internal surfaces of the display, generally over the lifetime of an MFK display, high (initial) resistance is very important in order to obtain acceptable service lives. In particular, in low-volt mixtures, it has not been possible to realize very high resistivities. Furthermore, it is important that the resistivity shows the smallest possible increase 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.

In addition to liquid crystal displays which use backlighting, ie are operated transmissively and optionally transflectively, reflective liquid crystal displays are also of particular interest. These reflective liquid crystal displays use the ambient light for information presentation. Thus, they consume significantly less energy than backlit liquid crystal displays of appropriate size and resolution. Since the TN effect is characterized by a very good contrast, such reflective displays are still easy to read even in bright ambient conditions. This is already from simple reflective TN displays, as they are in z. As watches and calculators are used known. However, the principle is also on high-quality, higher-resolution active matrix driven displays such. B. TFT displays applicable. Here, as with the general conventional transmissive TFT-TN displays, the use of liquid crystals with low birefringence (Δn) is necessary in order to achieve a small optical delay (d · Δn). This small optical delay leads to a mostly acceptable low viewing angle dependence of the contrast (cf. DE 30 22 818 ). For reflective displays, the use of liquid crystals with low birefringence is even more important than for transmissive displays, because with reflective displays the effective layer thickness through which the light passes is approximately twice that of transmissive displays with the same layer thickness.

It There is still a great need for MFK ads with very high specific resistance and at the same time a large operating temperature range, short switching times even at low temperatures and low threshold voltage, which do not show these disadvantages or only to a lesser extent.

• – erweiterter nematischer Phasenbereich (insbesondere zu tiefen Temperaturen)
• – Schaltbarkeit bei extrem tiefen Temperaturen (out-door-use, Automobil, Avionik)
• – erhöhte Beständigkeit gegenüber UV-Strahlung (längere Lebensdauer)
• – kleine Schwellenspannung

In TN (Schadt-Helfrich) cells, media are desired which allow the following advantages in the cells:

• - extended nematic phase range (especially at low temperatures)
• - Switchability at extremely low temperatures (out-door-use, automotive, avionics)
• - increased resistance to UV radiation (longer life)
• - small threshold voltage

With It is the media available from the prior art not possible, to realize these advantages while maintaining the other parameters.

at twisted higher Cells (STN) are media desirable the one higher Multiplexibility and / or smaller threshold voltages and / or wider nematic phase ranges (especially at low temperatures) enable. For this purpose, a further expansion of the available parameter space (clearing point, transition smectic-nematic or melting point, viscosity, dielectric sizes, elastic sizes) urgently he wishes.

In particular, in FK displays in devices for mobile video applications (eg mobile phones, PDAs or notebooks with multimedia features such as movies or video games), a significant reduction in switching times is desired. At the same time, the operating voltage should be as low as possible in order to reduce the total energy consumption of the device. However, it has been found that the LC media used for this purpose in the prior art often have an insufficient voltage holding ratio (HR) under light and temperature loading, and low low temperature stability (LTS). This leads to defects such as streaks and the so-called "Mura" in the FK ads (see "Automatic blemish detection in liquid crystal flat panel displays" by William K Pratt et al., SPIE Proceedings 3306-01, pp. 2-13 ).

Of the Invention is based on the object media in particular for such Provide MFK, TN, or STN displays that conform to the above Do not show disadvantages or only to a lesser extent, and preferably at the same time high HR values, high low-temperature stability, low Threshold voltage, high clearing point and low birefringence exhibit. In addition, the FK media should have a low rotational viscosity, to enable fast switching times.

It It has now been found that this task can be solved when looking at FK media containing one or more compounds of the formula I used. The compounds of formula I lead to mixtures with the desired properties indicated above.

enthält, worin
R⁰ einen halogenierten oder unsubstituierten Alkyl- oder Alkoxyrest mit 1 bis 15 C-Atomen, wobei in diesen Resten auch eine oder mehrere CH₂-Gruppen jeweils unabhängig voneinander durch -C≡C-, -CF₂O-, -CH=CH-,

-O-, -CO-O- oder -O-CO- so ersetzt sein können, dass O-Atome nicht direkt miteinander verknüpft sind,
X⁰ F, Cl, CN, SF₅, SCN, NCS, halogenierter Alkylrest, halogenierter Alkenylrest, halogenierter Alkoxyrest oder halogenierter Alkenyloxyrest mit bis zu 6 C-Atomen, und
Y^1,2 jeweils unabhängig voneinander H oder F bedeuten.The invention relates to a liquid-crystalline medium, characterized in that it contains one or more compounds of the formula I.

contains, in which
R ^{0 is} a halogenated or unsubstituted alkyl or alkoxy radical having 1 to 15 C atoms, wherein in these radicals also one or more CH ₂ groups each independently of one another by -C≡C-, -CF ₂ O-, -CH = CH -

-O-, -CO-O- or -O-CO- may be replaced so that O atoms are not directly linked to one another,
X ^{0 is} F, Cl, CN, SF ₅ , SCN, NCS, halogenated alkyl radical, halogenated alkenyl radical, halogenated alkoxy radical or halogenated alkenyloxy radical having up to 6 C atoms, and
Y ^1,2 each independently represent H or F.

The Compounds of the formula I have a high clearing point, a high positive dielectric anisotropy, a low birefringence and a broad nematic phase range. Surprisingly, it was found that LC media comprising compounds of the formula I have a high LTS and a high HR with simultaneously low threshold voltage, high clearing point, low rotational viscosity and thereby have fast switching times. you are therefore especially good for FK ads suitable for mobile and video applications.

The Compounds of the formula I have a wide range of applications. Dependent on from the selection of substituents they can be used as base materials serve, from which liquid crystalline Media for the most part Part are composed; it can but also the compounds of the formula I liquid-crystalline base materials be added from other classes of compounds, for example the dielectric and / or optical anisotropy of such a dielectric to influence and / or its threshold voltage and / or its viscosity to optimize.

The Compounds of the formula I are colorless in the pure state and form liquid crystalline Mesophases in a for the electro-optical use favorable located temperature range. Chemical, thermal and against light they are stable.

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

If in the above and below formulas R ^{0 is} an alkyl radical and / or an alkoxy radical, this may be straight-chain or branched. Preferably, it is straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and thus preferably 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 tetradedoxy.

oxaalkyl preferably denotes straight-chain 2-oxapropyl (= methoxymethyl), 2 - (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6-, or 7-oxo-octyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadexyl.

If R ^{0 is} an alkyl radical in which one CH ₂ group has been replaced by -CH = CH-, this may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 C atoms. It therefore means especially 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 ^{0 is} an alkyl or alkenyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain and halogen is preferably F or Cl. In the case of multiple substitution, halogen is preferably F. The resulting radicals also include perfluorinated radicals. For single substitution, the fluoro or chloro substituent may be in any position, but preferably in the ω position.

In the formulas above and below X ^{0 is} preferably F, Cl or mono- or polyfluorinated alkyl or alkoxy having 1, 2 or 3 C atoms or mono- or polyfluorinated alkenyl having 2 or 3 C atoms. X ⁰ is particularly preferably F, Cl, CF ₃ , CHF ₂ , OCF ₃ , OCHF ₂ , OCFHCF ₃ , OCFHCHF ₂ , OCFHCHF ₂ , OCF ₂ CH ₃ , OCF ₂ CHF ₂ , OCF ₂ CHF ₂ , OCF ₂ CF ₂ CHF _2, OCF ₂ CF ₂ CHF _2, OCFHCF ₂ CF _3, OCFHCF ₂ CHF _2, OCF ₂ CF ₂ CF _3, OCF ₂ CF ₂ CClF _2, OCClFCF ₂ CF ₃ or CH = CF _2, very particularly preferably F or OCF ₃ ,

worin R⁰ und X⁰ die in Formel I angegebene Bedeutung haben. Vorzugsweise bedeutet R⁰ geradkettiges Alkyl mit 1 bis 8 C-Atomen, ferner Alkenyl mit 2 bis 7 C-Atomen. X⁰ bedeutet vorzugsweise F oder OCF₃, besonders bevorzugt F.Particularly preferred compounds of the formula I are selected from the following sub-formulas

wherein R ⁰ and X ^{0 have} the meaning given in formula I. Preferably, R ^{0 is} straight-chain alkyl having 1 to 8 carbon atoms, further alkenyl having 2 to 7 carbon atoms. X ⁰ is preferably F or OCF ₃ , more preferably F.

• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen der Formel II und/oder III:
  
  
  worin R⁰, X⁰, Y¹ und Y² die in Formel I angegebene Bedeutung besitzen, Y³ und Y⁴ H oder F und
  
• – Die Verbindungen der Formel II sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet R⁰ Alkyl mit 1 bis 8 C-Atomen und X⁰ F. Besonders bevorzugt sind Verbindungen der Formel IIa und IIb;
• – Die Verbindungen der Formel III sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet R⁰ Alkyl mit 1 bis 8 C-Atomen und X⁰ F. Besonders bevorzugt sind Verbindungen der Formel IIIa;
• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen ausgewählt aus folgenden Formeln:
  
  worin R⁰, X⁰ und Y^1-4 die in Formel II angegebenen Bedeutungen besitzen, Z⁰ -C₂H₄-, -(CH₂)₄-, -CH=CH-, -CF=CF-, -C₂F₄-, -CH₂CF₂-, -CF₂CH₂-, -CH₂O-, -OCH₂-, -COO- oder -OCF₂-, in Formel V und VI auch eine Einfachbindung, in Formel V und VIII auch -CF₂O-, und r 0 oder 1 bedeutet;
• – Die Verbindungen der Formel IV sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet R⁰ Alkyl mit 1 bis 8 C-Atomen und X⁰ F oder OCF₃;
• – Die Verbindungen der Formel V sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet R⁰ Alkyl mit 1 bis 8 C-Atomen und X⁰ F;
• – Die Verbindungen der Formel VI sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet R⁰ Alkyl mit 1 bis 8 C-Atomen und X⁰ F;
• – Die Verbindungen der Formel VII sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet R⁰ Alkyl mit 1 bis 8 C-Atomen und X⁰ F;
• – Das Medium enthält ein oder mehrere Verbindungen ausgewählt aus folgenden Formeln:
  
  worin L und X⁰ die oben angegebene Bedeutung besitzen,

"Alkyl" C_1-7-Alkyl, R' C_1-7-Alkyl, C_1-6-Alkoxy oder C_2-7-Alkenyl, und "Alkenyl" und "Alkenyl*" jeweils unabhängig voneinander C_2-7-Alkenyl bedeuten.

• – Die Verbindungen der Formeln IX-XII sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  
  worin "Alkyl" die oben angegebene Bedeutung hat;
• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen ausgewählt aus folgenden Formeln:
  
  
  worin R¹ und R² jeweils unabhängig voneinander n-Alkyl, Alkoxy, Oxaalkyl, Fluoralkyl oder Alkenyl mit jeweils bis zu 9 C-Atomen bedeuten, und vorzugsweise jeweils unabhängig voneinander Alkyl mit 1 bis 8 C-Atomen bedeuten;
• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen der folgenden Formel:
  
  worin R⁰, X⁰ und Y^1,2 die in Formel I angegebenen Bedeutungen besitzen, und
  
  bedeuten, wobei A und B nicht gleichzeitig Cyclohexylen bedeuten;
• – Die Verbindungen der Formel XV sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet R⁰ Alkyl mit 1 bis 8 C-Atomen und X⁰ F;
• – Das Medium enthält eine oder mehrere Verbindungen der folgenden Formel:
  
  worin R¹ und R² die oben angegebene Bedeutung besitzen, und vorzugsweise jeweils unabhängig voneinander Alkyl mit 1 bis 8 C-Atomen bedeuten, und L H oder F bedeutet;
• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen ausgewählt aus folgenden Formeln:
  
  worin R^1,2 und Y^1,2 die oben angegebenen Bedeutungen haben;
• – Das Medium enthält eine oder mehrere Verbindungen der Formel XVIII, worin R¹ und/oder R² Alkenyl mit 2 bis 7 C-Atomen bedeuten, vorzugsweise solche ausgewählt aus folgenden Formeln:
  
  worin "Alkyl" die oben angegebene Bedeutung hat;
• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen ausgewählt aus folgenden Formeln:
  
  
  worin R⁰ und X⁰ jeweils unabhängig voneinander eine der oben angegebenen Bedeutungen haben und Y^1-4 jeweils unabhängig voneinander H oder F bedeuten. X⁰ ist vorzugsweise F, Cl, CF₃, OCF₃ oder OCHF₂. R⁰ bedeutet vorzugsweise Alkyl, Alkoxy, Oxaalkyl, Fluoralkyl oder Alkenyl mit jeweils bis zu 8 C-Atomen. Besonders bevorzugt sind Verbindungen der Formel XXI.
• – Die Verbindungen der Formel XXI sind vorzugsweise ausgewählt aus folgenden Formeln:
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet R⁰ Alkyl mit 1 bis 8 C-Atomen und X⁰ F;
  
• – R⁰ ist geradkettiges Alkyl oder Alkenyl mit 2 bis 7 C-Atomen;
• – X⁰ ist F;
• – Das Medium enthält eine, zwei oder mehr Verbindungen der Formel I, insbesondere der Formel Ia, Ib oder Ic;
• – Das Medium enthält 2-40 Gew.%, bevorzugt 3-30 Gew.%, besonders bevorzugt 3-20 Gew.%, an Verbindungen der Formel I;
• – Das Medium enthält Verbindungen ausgewählt aus den Formeln I, II, III, IV, VI, IX-XII, XVIII und XXI;
• – Der Anteil an Verbindungen der Formeln II, III, IV, VI, IX-XII, XVIII und XXI im Gesamtgemisch beträgt 40 bis 95 Gew.%;
• – Das Medium enthält 5-60 Gew.%, besonders bevorzugt 10-50 Gew.% an Verbindungen der Formel II;
• – Das Medium enthält 2-40 Gew.%, besonders bevorzugt 5-30 Gew.% an Verbindungen der Formel III;
• – Das Medium enthält 1-30 Gew.%, besonders bevorzugt 2-20 Gew.% an Verbindungen der Formel IV;
• – Das Medium enthält 2-30 Gew.%, besonders bevorzugt 3-20 Gew.% an Verbindungen der Formel VI;
• – Das Medium enthält 2-40 Gew.%, besonders bevorzugt 3-30 Gew.% an Verbindungen der Formeln IX-XII und XVIII;
• – Das Medium enthält 1-20 Gew.%, besonders bevorzugt 1-15 Gew.% an Verbindungen der Formel XXI.

Further preferred embodiments are given below:

• The medium additionally contains one or more compounds of the formula II and / or III:
  
  
  wherein R ⁰ , X ⁰ , Y ¹ and Y ^{2 have} the meaning given in formula I, Y ³ and Y ⁴ H or F and
  
• The compounds of the formula II are preferably selected from the following formulas:
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, R ^{0 is} alkyl having 1 to 8 carbon atoms and X ⁰ F. Particularly preferred are compounds of formula IIa and IIb;
• The compounds of the formula III are preferably selected from the following formulas:
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, R ^{0 is} alkyl having 1 to 8 carbon atoms and X ⁰ F. Particularly preferred are compounds of formula IIIa;
• - The medium additionally contains one or more compounds selected from the following formulas:
  
  wherein R ⁰ , X ⁰ and Y ^{1-4 have} the meanings given in formula II, Z ⁰ -C ₂ H ₄ -, - (CH ₂ ) ₄ -, -CH = CH-, -CF = CF-, -C ₂ F ₄ -, -CH ₂ CF ₂ -, -CF ₂ CH ₂ -, -CH ₂ O-, -OCH ₂ -, -COO- or -OCF ₂ -, in formula V and VI also a single bond, in formula V and VIII are also -CF ₂ O-, and r is 0 or 1;
• The compounds of the formula IV are preferably selected from the following formulas:
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, R ^{0 is} alkyl having 1 to 8 C atoms and X ⁰ F or OCF ₃ ;
• The compounds of the formula V are preferably selected from the following formulas:
  
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, R ^{0 is} alkyl of 1 to 8 carbon atoms and X ⁰ F;
• The compounds of the formula VI are preferably selected from the following formulas:
  
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, R ^{0 is} alkyl of 1 to 8 carbon atoms and X ⁰ F;
• The compounds of the formula VII are preferably selected from the following formulas:
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, R ^{0 is} alkyl of 1 to 8 carbon atoms and X ⁰ F;
• - The medium contains one or more compounds selected from the following formulas:
  
  wherein L and X ^{0 have} the abovementioned meaning,

"Alkyl" C _1-7 alkyl, R ' C _1-7 alkyl, C _1-6 alkoxy or C _2-7 alkenyl, and "Alkenyl" and "alkenyl *" each independently of one another C _2-7 alkenyl mean.

• The compounds of the formulas IX-XII are preferably selected from the following formulas:
  
  
  wherein "alkyl" has the meaning given above;
• - The medium additionally contains one or more compounds selected from the following formulas:
  
  
  wherein R ¹ and R ^{2 are} each independently n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl each having up to 9 C atoms, and preferably each independently of one another are alkyl having 1 to 8 C atoms;
• The medium additionally contains one or more compounds of the following formula:
  
  wherein R ⁰ , X ⁰ and Y ^{1.2 have} the meanings given in formula I, and
  
  where A and B are not simultaneously cyclohexylene;
• The compounds of the formula XV are preferably selected from the following formulas:
  
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, R ^{0 is} alkyl of 1 to 8 carbon atoms and X ⁰ F;
• The medium contains one or more compounds of the following formula:
  
  wherein R ¹ and R ^{2 have} the meaning given above, and preferably each independently of one another are alkyl having 1 to 8 C atoms, and L is H or F;
• - The medium additionally contains one or more compounds selected from the following formulas:
  
  wherein R ^1,2 and Y ^{1,2 have} the meanings given above;
• The medium contains one or more compounds of the formula XVIII in which R ¹ and / or R ^{2 are} alkenyl having 2 to 7 C atoms, preferably those selected from the following formulas:
  
  wherein "alkyl" has the meaning given above;
• - The medium additionally contains one or more compounds selected from the following formulas:
  
  
  wherein R ⁰ and X ⁰ each independently have one of the meanings given above and Y ^1-4 each independently represent H or F. X ⁰ is preferably F, Cl, CF ₃ , OCF ₃ or OCHF ₂ . R ⁰ is preferably alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 8 carbon atoms. Particular preference is given to compounds of the formula XXI.
• The compounds of the formula XXI are preferably selected from the following formulas:
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, R ^{0 is} alkyl of 1 to 8 carbon atoms and X ⁰ F;
  
• R ⁰ is straight-chain alkyl or alkenyl having 2 to 7 C atoms;
• - X ⁰ is F;
• The medium contains one, two or more compounds of the formula I, in particular of the formula Ia, Ib or Ic;
• The medium contains 2-40% by weight, preferably 3-30% by weight, particularly preferably 3-20% by weight, of compounds of the formula I;
• The medium contains compounds selected from the formulas I, II, III, IV, VI, IX-XII, XVIII and XXI;
• The proportion of compounds of the formulas II, III, IV, VI, IX-XII, XVIII and XXI in the total mixture is 40 to 95% by weight;
• The medium contains 5-60% by weight, more preferably 10-50% by weight, of compounds of the formula II;
• The medium contains 2-40% by weight, more preferably 5-30% by weight, of compounds of the formula III;
• The medium contains 1-30% by weight, more preferably 2-20% by weight, of compounds of the formula IV;
• The medium contains 2-30% by weight, more preferably 3-20% by weight, of compounds of the formula VI;
• The medium contains 2-40% by weight, more preferably 3-30% by weight, of compounds of the formulas IX-XII and XVIII;
• The medium contains 1-20% by weight, more preferably 1-15% by weight, of compounds of the formula XXI.

It was found to already have a relatively low proportion of compounds of the formula I in admixture with conventional Liquid crystal materials, but especially with one or more compounds of the formulas II to XXIII increase the light stability and too low values for the birefringence leads, where at the same time broad nematic phases with low transition temperatures smectic-nematic be observed, whereby the storage stability is improved. simultaneously the mixtures show very low threshold voltages and very good values for the VHR at UV exposure.

Of the The term "alkyl" or "alkyl *" includes straight-chain and branched alkyl groups of 1-7 carbon atoms, especially the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, Hexyl and heptyl. Groups of 1-6 carbon atoms are in general prefers.

The term "alkenyl" or "alkenyl *" includes straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight-chain groups. Preferred alkenyl groups are C ₂ -C ₇ -1E-alkenyl, C ₄ -C ₇ 3E-alkenyl, C ₅ -C ₇ -alkenyl, C ₆ -C ₇ -5-alkenyl and C ₇ -6-alkenyl, in particular C ₂ -C ₇ -1E-alkenyl, C ₄ -C ₇ -EE-alkenyl and C ₅ -C ₇ -alkenyl. Examples of particularly 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 of up to 5 carbon atoms are generally preferred.

Of the The term "fluoroalkyl" preferably includes straight-chain groups with terminal Fluorine, i. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions However, the fluorine are not excluded.

The term "oxaalkyl" or "alkoxy" preferably comprises straight-chain radicals of the formula C _n H _{2n + 1} -O- (CH ₂ ) _m , in which n and m are each independently of one another from 1 to 6. m can also mean 0. Preferably, n = 1 and m is 1-6 or m = 0 and n = 1-3.

By suitably selecting the meanings of R ⁰ and X ⁰ , the response times, the threshold voltage, the transconductance of the transmission characteristics etc. can be modified in the desired manner. For example, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxy radicals and the like generally lead to shorter response times, improved nematic tendencies and a higher ratio of the elastic constants k ₃₃ (bend) and k ₁₁ (splay) compared to alkyl or alkoxy. 4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and smaller values of k ₃₃ / k ₁₁ compared to alkyl and alkoxy radicals. The mixtures according to the invention are distinguished in particular by high K ₁ values and thus have significantly faster switching lines than the mixtures from the prior art.

The optimal ratio The compounds of the above formulas depends largely on the desired Properties, from the choice of components of the above formulas and the choice of other optionally present components.

suitable proportions within the range given above can be easy from case to case be determined.

The Total amount of compounds of the above formulas in the mixtures according to the invention is not critical. The mixtures can therefore one or more other components are included to optimize various properties. The observed effect on the desired improvement of the properties however, the higher the total concentration, the larger the mixture is usually to compounds of the above formulas.

In a particularly preferred embodiment, the media of the invention comprise compounds of the formula II to VIII (preferably II, III, IV and VI, in particular IIa, IIIa and Via), wherein X ⁰ is F, OCF _3, OCHF _2, OCH = CF _2, OCF = CF ₂ or OCF ₂ -CF ₂ H means. A favorable synergistic effect with the compounds of the formula I leads to particularly advantageous properties. In particular, mixtures containing compounds of the formulas I, IIa, IIIa and Via are distinguished by their low threshold voltage.

The individual compounds of the above formulas and their sub-formulas, in the media of the invention can be used are either known or they can be analogous to the known ones Connections are made.

object The invention also electro-optical displays, such. B. STN or MFK displays with two plane-parallel support plates, with one border forming a cell, integrated non-linear elements to the circuit individual pixels on the carrier plates and a nematic liquid crystal mixture in the cell with positive dielectric anisotropy and high specificity Resistance) containing such media and the use this media for electro-optical purposes.

The Liquid crystal mixtures according to the invention enable a significant extension of the available parameter space. The achievable combinations of clearing point, viscosity at low temperature, thermal and UV stability and high optical anisotropy by far previous materials from the prior art.

The mixtures according to the invention are in particular for mobile applications and low Δn TFT applications, such as As mobile phones and PDAs suitable.

The liquid-crystal mixtures according to the invention make it possible to maintain the nematic phase at -20 ° C. and preferably at -30 ° C., more preferably at -40 ° C., and at the clearing point ≥ 70 ° C., preferably ≥ 75 ° C., more preferably ≥ 80 ° C at the same time to achieve dielectric anisotropy values Δ∈ ≥ +8, preferably ≥ +10 and a high value for the resistivity, whereby excellent MFK displays can be achieved. In particular, the blends are small in operation marked.

The Threshold voltage of the liquid crystal mixtures according to the invention preferably ≤ 1.5 V, more preferably ≤ 1.3 V.

The Birefringence Δn the liquid crystal mixtures according to the invention is preferably ≤ 0.11, especially preferably ≤ 0.10.

The rotational viscosity γ _{1 of} the liquid-crystal mixtures according to the invention at 20 ° C. is preferably ≦ 180 mPa · s, more preferably ≦ 140 mPa · s.

Of the nematic phase range of the liquid crystal mixtures according to the invention preferably at least 90 °, in particular at least 100 ° wide. Preferably, this range extends at least from -20 ° to + 75 ° C.

It is understood that by suitable choice of the components of the mixtures according to the invention also higher clearing points (eg above 100 ° C) can be realized at higher threshold voltages or lower clearing points at lower threshold voltages to obtain the other advantageous properties. Likewise, with correspondingly low viscosities, mixtures with a larger Δε and thus lower thresholds can be obtained. The MFK displays according to the invention preferably operate in the first transmission minimum according to Gooch and Tarry [ CH Gooch and HA Tarry, Electron. Lett. 10, 2-4, 1974; CH Gooch and HA Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975 ], where in addition to particularly favorable electro-optical properties, such as high slope of the characteristic 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. As a result, significantly higher specific resistances can be achieved using the mixtures according to the invention in the first minimum than in the case of mixtures with cyano compounds. By suitable choice of the individual components and their proportions by weight, the person skilled in the art can set the birefringence required for a given layer thickness of the MFK display with simple routine methods.

Measurements of the Voltage Holding Ratio (HR) [ S. 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 mixtures according to the invention comprising compounds of the formula I have a significantly lower decrease in HR under UV exposure than analogous mixtures comprising instead of the compounds of the formula I cyanophenylcyclohexanes of the formula

The light stability and UV stability the mixtures according to the invention is considerably better, i. e. they show a much smaller decrease of the HR under light or UV exposure. Already low concentrations of compounds (<10 % By weight of the formula I in the mixtures increase the HR compared to mixtures the prior art by 6% and more.

Of the Structure of the MFK display according to the invention made of polarizers, electrode base plates and electrodes with surface treatment corresponds to the for Such ads usual Construction. The term of the usual construction is here far including all modifications and modifications of the MFK display, in particular also matrix display elements based on poly-Si TFT or MIM.

One significant difference of the displays of the invention to the usual however, based on the twisted nematic cell, there exists the choice of liquid crystal parameters the liquid crystal layer.

The liquid crystal mixtures which can be used according to the invention are prepared in a conventional manner, for example by mixing one or more compounds of the formula I with one or more compounds of the formulas II-XXIII or with further liquid-crystalline compounds and / or additives. 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 solutions of the components in an organic solvent, for example in acetone, chloroform or Me ethanol, and to remove the solvent again after thorough mixing, for example by distillation.

The dielectrics may also other, known in the art and described in the literature additives such. As UV stabilizers such as Tinuvin ^® Fa. Ciba, antioxidants, radical scavengers, nanoparticles, etc. included. For example, 0-15% pleochroic dyes or chiral dopants may be added. Suitable stabilizers and dopants are mentioned below in Tables C and D.

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 and are preferably 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. The coding according to Table B is self-evident. In Table A is only the acronym given for the basic body. In individual cases, followed by acronym for the main body with a dash followed by a code for the substituents R ^{1 *} , R ^{2 *} , L ^{1 *} and L ^{2 *} : Code for R ^{1 *} , R ^{2 *} , L ^{1 *} , L ^{2 *} , L ^{3 *} R ^{1 *} R ^{2 *} L ^{1 *} L ^{2 *} nm C _n H _{2n + 1} C _m H _{2m + 1} H H n Om C _n H _{2n + 1} OC _m H _{2m + 1} H H nO.m OC _n H _{2n + 1} C _m H _{2m + 1} H H ⁿ C _n H _{2n + 1} CN H H nN.F C _n H _{2n + 1} CN F H nN.FF C _n H _{2n + 1} CN F F nF C _n H _{2n + 1} F H H n Cl C _n H _{2n + 1} Cl H H nOF OC _n H _{2n + 1} F H H nF.F C _n H _{2n + 1} F F H nF.FF C _n H _{2n + 1} F F F nOCF ₃ C _n H _{2n + 1} OCF ₃ H H nOCF ₃ .F C _n H _{2n + 1} OCF ₃ F H n-Vm C _n H _{2n + 1} -CH = CH-C _m H _{2m + 1} H H nV-Vm C _n H _{2n + 1} -CH = CH -CH = CH-C _m H _{2m + 1} H H

Tabelle B

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

Table B

Particular preference is given to liquid-crystalline mixtures which, in addition to the compounds of the formulas I contain at least one, two, three, four or more compounds from Table B.

Table C

In Table C becomes possible Specified dopants, which are usually the mixtures of the invention be added. Preferably, the mixtures contain 0-10% by weight, in particular 0.01-5% by weight and particularly preferably 0.01-3% by weight Dopants.

Table D

stabilizers, For example, the inventive mixtures in amounts of 0-10% by weight can be added are mentioned below.

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

• – Δn die optische Anisotropie bei 589 nm und 20°C),
• – γ₁ die Rotationsviskosität (mPa·s) bei 20°C,
• – V₁₀ die Spannung (V) für 10% der Transmissionsänderung (Blickrichtung senkrecht zur Plattenoberfläche), (Schwellenspannung),
• – V₉₀ die Spannung (V) für 90% der Transmissionänderung (Blickrichtung senkrecht zur Plattenoberfläche),
• – Δε die dielektrische Anisotropie bei 20°C und 1 kHz (Δε = ε_∥⁣ – ε_⊥ wobei ε_∥⁣ die Dielektrizitätskonstante parallel zu den Moleküllängsachsen und ε_⊥ die Dielektrizitätskonstante senkrecht dazu bedeutet),
• – HR die "voltage holding ratio" [%] und
• – LTS die "low temperature stability" (Phase), bestimmt in Testzellen.

Above and below, percentages are by weight. 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 information between these symbols represents the transition temperatures

• Δn the optical anisotropy at 589 nm and 20 ° C),
• - γ ₁ the rotational viscosity (mPa · s) at 20 ° C,
• V ₁₀ the voltage (V) for 10% of the transmission change (viewing direction perpendicular to the plate surface), (threshold voltage),
• V ₉₀ the voltage (V) for 90% of the transmission change (viewing direction perpendicular to the plate surface),
• Δε is the dielectric anisotropy at 20 ° C. and 1 kHz (Δε = ε _∥⁣ -ε _⊥ where ε _{∥⁣ means} the dielectric constant parallel to the _longitudinal molecular _axes and ε _⊥ the dielectric constant perpendicular thereto),
• - HR the "voltage holding ratio" [%] and
• - LTS the "low temperature stability" (phase), determined in test cells.

The electro-optical data are measured in a TN cell in the 1st minimum (ie at a d · Δn value of 0.5 microns) at 20 ° C, unless expressly stated otherwise. The optical data are measured at 20 ° C, unless expressly stated otherwise. All physical properties will be after "Merck Liquid Crystals, Physical Properties of Liquid Crystals" Status Nov. 1997, Merck KGaA, Germany determined and are valid for a temperature of 20 ° C, unless explicitly stated otherwise. Comparative Example 1 CC-4-V 18.00% Clearing point [° C]: 80.0 PP 1-2V1 4.00% Δn [589 nm, 20 ° C]: 0.1000 CCQU-3-F 13.00% Δε [20 ° C, 1 kHz]: +10.5 CCQU-5-F 12.00% γ ₁ [mPa.s, 20 ° C]: 107 CCP 20CF3 6.00% V ₁₀ [V]: 1.28 CCP 30CF3 2.00% LTS Bulk -30 [h]: 24 PUQU-3-F 14.00% BCH 3F.FF 16.00% CCP-V-1 8.00% CCGU-3-F 7.00% Comparative Example 2 CC-4-V 14.00% Clearing point [° C]: 80.5 CC-3-V1 2.00% Δn [589 nm, 20 ° C]: 0.1000 CCQU-2-F 2.00% Δε [20 ° C, 1 kHz]: +11.4 CCQU-3-F 10.00% γ ₁ [mPa.s, 20 ° C]: 100 CCQU-5-F 10.00% V ₁₀ [V]: 1.24 CCP 20CF3 7.00% LTS Bulk -30 [h]: 48 CCP 30CF3 6.00% PUQU-2-F 9.00% PUQU-3-F 12.00% PGU-3-F 7.00% CCG-VF 4.00% CCP-V-1 15.00% CCGU-3-F 2.00% example 1 CC-4-V 13.00% Clearing point [° C]: 80.0 CC-3-V1 4.00% Δn [589 nm, 20 ° C]: 0.0987 PP 1-2V1 1.00% Δε [20 ° C, 1 kHz]: +10.7 CCQU-3-F 10.00% γ ₁ [mPa.s, 20 ° C]: 99 CCQU-5-F 10.00% V ₁₀ [V]: 1.28 CCP 20CF3 4.00% LTS Bulk -30 [h]: 1000 PUQU-2-F 7.00% HR [5 min, 100 ° C]: 97.5% PUQU-3-F 13.00% PGU-3-F 6.00% CCG-VF 7.00% CCP-V-1 13.00% CCGU-3-F 2.00% CAP-3-F 10.00%

The Mixture faces the mixtures of Comparative Examples 1 and 2 a significantly higher LTS on, at comparable values for the clearing point, birefringence, dielectric anisotropy, rotational viscosity and Threshold voltage. Furthermore it shows a high HR value.

Claims (13)

Liquid-crystalline medium, characterized in that it contains one or more compounds of the formula I.

in which R ⁰ denotes a halogenated or unsubstituted alkyl or alkoxy radical having 1 to 15 C atoms, where in these radicals also one or more CH ₂ groups are each independently denoted by -CC-, -CF ₂ O-, -CH = CH, - ♢ -, - ♢♢ -, -O-, -CO-O- or -O-CO- can be replaced so that O atoms are not directly linked together, X ⁰ F, Cl, CN, SF ₅ , SCN, NCS, halogenated alkyl radical, halogenated alkenyl radical, halogenated alkoxy radical or halogenated alkenyloxy radical having up to 6 C atoms, and Y 1, ² each, independently of one another, denote H or F. Liquid-crystalline medium according to claim 1, characterized in that it contains one or more compounds selected from the following formulas

wherein R ⁰ and X ^{0 have} the meanings given in claim 1. Liquid-crystalline medium according to claim 1 or 2, characterized in that it additionally contains one or more compounds selected from the following formulas

wherein A, R ⁰ , X ⁰ , Y ¹ and Y ^{2 have} the meanings given in claim 1 and Y ³ and Y ^{4 are} each independently H or F. Liquid-crystalline medium according to claim 3, characterized in that it contains one or more compounds selected from the following formulas

wherein R ⁰ and X ^{0 have} the meanings given in claim 1. Liquid-crystalline medium according to one or more of claims 1 to 4, characterized in that it additionally contains one or more compounds selected from the following formulas

wherein R ⁰ , X ⁰ and Y ^{1-4 have} the meanings given in claim 3, Z ⁰ -C ₂ H ₄ -, - (CH ₂ ) ₄ -, -CH = CH-, -CF = CF-, -C ₂ F ₄ -, -CH ₂ CF ₂ -, -CF ₂ CH ₂ -, -CH ₂ O-, -OCH ₂ -, -COO- or -OCF ₂ -, in formula V and VI also a single bond, in formula V and VIII also -CF ₂ O-, and r is 0 or 1. Liquid-crystalline medium according to claim 5, characterized in that it contains one or more compounds selected from the following formulas

wherein R ⁰ and X ^{0 have} the meanings given in claim 1. Liquid-crystalline medium according to claim 5 or 6, characterized in that it contains one or more compounds selected from the following formulas

wherein R ⁰ and X ^{0 have} the meanings given in claim 1. Liquid-crystalline medium according to one or more of claims 1 to 7, characterized in that it additionally contains one or more compounds selected from the following formulas

wherein L and X ^{0 have} the abovementioned meaning, "Alkyl" C _1-7 alkyl, R ' C _1-7 alkyl, C _1-6 alkoxy or C _2-7 alkenyl, and "Alkenyl" and "alkenyl *" each independently of each other C _2-7 alkenyl, and R ¹ and R ² each independently of one another n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms mean, wherein at least one of the radicals R ¹ and R ² alkenyl having 2 to 9 carbon atoms. Liquid-crystalline medium according to one or more of claims 1 to 8, characterized in that it additionally contains one or more compounds selected from the following formulas

wherein R ⁰ and X ^{0 have} the meaning given in claim 1. liquid-crystalline Medium according to one or more of claims 1 to 9, characterized in that it 2-40% by weight of compounds of the formula I, 20-90% by weight to compounds of the formula II, 2-30% by weight of compounds of Formula III, optionally 2-30% by weight of compounds of the formula IV, optionally 2-30% by weight of compounds of the formulas IX-XII, possibly 4-30% by weight of compounds of the formula XIV contains. Use of a liquid-crystalline medium after one or more of the claims 1 to 10 for electro-optical Purposes. Electro-optical liquid crystal display containing a liquid crystalline Medium according to one or more of claims 1 to 10. Process for the preparation of a liquid-crystalline medium according to one or more of Claims 1 to 10, characterized in that one or more compounds of the formula I as in Claim 1 defined with one or more compounds according to one or more of claims 3 to 9 or mixed with other liquid crystalline compounds and / or additives.