DE10151913B4 - Nematic liquid-crystal mixture and its use in liquid-crystal displays - Google Patents

Abstract

worin
R⁰ eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, und
L¹ bis L⁴ unabhängig voneinander H oder F bedeuten,
dadurch gekennzeichnet, daß sie mindestens eine Verbindung der Formel II und/oder II* enthält

worin
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen,
R⁴ eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind,
a O oder 1,
L¹ und L² jeweils unabhängig voneinander H oder F,
Q CF₂, OCF₂, CFH, OCFH oder eine Einfachbindung, und
Y F oder Cl...Liquid-crystal mixture containing at least one compound of the formula I.

wherein
R ^{0 is} an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH ₂ groups by -O-, -CH = CH-, -CO-, -OCO- or -COO - can be replaced so that O atoms are not directly linked, and
L ¹ to L ⁴ independently of one another denote H or F,
characterized in that it contains at least one compound of formula II and / or II *

wherein
R ^{3 is} an alkenyl group having 2 to 7 C atoms,
R ^{4 is} an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH ₂ groups by -O-, -CH = CH-, -CO-, -OCO- or -COO - can be replaced so that O atoms are not directly linked,
a O or 1,
L ¹ and L ^{2 are} each independently H or F,
Q CF ₂ , OCF ₂ , CFH, OCFH or a single bond, and
YF or Cl ...

Description

The Invention relates to novel liquid-crystal mixtures, their use in liquid crystal displays, especially in twisted and highly twisted nematic liquid crystal displays (English: Twisted Nematic, short: TN or Supertwisted Nematic, short: STN) with very short switching times and good slopes and Angle dependencies.

TN displays are known, e.g. From M. Schadt and W. Helfrich, Appl. Phys. Lett., 18, 127 (1971). STN ads are known, for. B. off EP 0 131 216 B1 ; DE 34 23 993 A1 ; EP 0 098 070 A2 ; M. Schadt and F. Leenhouts, 17th Freiburger Workshop on Liquid Crystals (8.-10.04.87); K. Kawasaki et al., SID 87 Digest 391 (20.6); M. Schadt and F. Leenhouts, SID 87 Digest 372 (20.1); K. Katoh et al., Japanese Journal of Applied Physics, Vol. 11, L 1784-L 1786 (1987); F. Leenhouts et al., Appl. Phys. Lett. 50 (21), 1468 (1987); HA van Sprang and HG Koopman, J. Appl. Phys. 62 (5), 1734 (1987); TJ Scheffer and J. Nehring, Appl. Phys. Lett. 45 (10), 1021 (1984), M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (5), 236 (1987) and EP Raynes, Mol. Cryst. Liq. Cryst. Letters Vol. 4 (1), pp. 1-8 (1986). The term STN here includes any higher twist display element with a twist angle in the amount between 160 ° and 360 °, such as the display elements according to Waters et al. (CM Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd International Display Conference, Kobe, Japan), the STN-LCDs ( DE OS 35 03 259 SBE-LCD's (TJ Scheffer and J. Nehring, Appl. Phys. Lett., 45: 1021 (1984)), OMI-LCD's (M. Schadt and F. Leenhouts, Appl. Phys., Lett., 50: 236 (1987)) , DST-LCD's ( EP OS 0 246 842 ) or BW-STN-LCD's (K.Kawasaki et al., SID 87 Digest 391 (20.6)).

STN displays stand out compared to standard TN displays by substantially better slopes of the electro-optical characteristic curve and, at medium and higher Multiplexing rates, for example 32 to 64 and higher, through better contrast values out. In contrast, in TN displays, in general, the contrast is due to the better dark value higher and the angle dependence the contrast is lower than in STN displays with low multiplex rates for example, less than 16.

From Of particular interest are TN and STN displays with very short switching times especially at lower temperatures. To achieve short Switching times have been optimized so far the rotational viscosities of the liquid crystal mixtures using mostly monotropic additives with relatively high vapor pressure. However, the achieved switching times were not sufficient for every application.

To achieve a steep electro-optical characteristic curve in the displays, the liquid-crystal mixtures should have relatively large values for the ratio of the elastic constants K ₃₃ / K ₁₁ and relatively small values for Δε / ε _⟘ , where Δε is the dielectric anisotropy and ε _{⟘ is} the dielectric constant perpendicular to the molecular axis.

• 1. Breites d/p-Fenster
• 2. Hohe chemische Dauerstabilität
• 3. Hoher elektrischer Widerstand
• 4. Geringe Frequenz- und Temperaturabhängigkeit der Schwellenspannung.

In addition to optimizing the contrast and the switching times, further important requirements are placed on such mixtures:

• 1. Wide d / p window
• 2. High chemical stability
• 3. High electrical resistance
• 4. Low frequency and temperature dependence of the threshold voltage.

The achieved parameter combinations are far from sufficient, especially for high-multiplex STN displays (at a multiplex rate greater than or equal to equal to 1/128), but also for Medium and low-multiplex STN (with multiplex rates in the range of approx. 1/64 or 1/16), and TN displays. In part, this is due to the fact that the various Requirements are influenced by material parameters in opposite directions.

It Thus, there is still a great need for liquid-crystal mixtures, especially for Medium and low-multiplex STN displays, with very short switching times and at the same time a large operating temperature range, high slope, good angle dependence of contrast and low threshold voltage meeting the above requirements satisfy.

The invention has for its object to provide liquid crystal mixtures for use in liquid crystal displays, especially in TN and STN displays that not or only to a lesser extent at the same time short switching times, especially at low temperatures, and very good slopes and improved the above-mentioned disadvantages Temperature dependence of the operating voltage due to a have improved frequency dependence of the dielectric constant.

worin
R⁰ eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, und
L¹ bis L⁴ unabhängig voneinander H oder F bedeuten.It has now been found that this object can be achieved by using nematic liquid-crystal mixtures which contain one or more compounds of the formula I,

wherein
R ^{0 is} an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH ₂ groups by -O-, -CH = CH-, -CO-, -OCO- or -COO - can be replaced so that O atoms are not directly linked, and
L ¹ to L ⁴ independently of one another denote H or F.

In the pamphlets DE 40 37 154 A1 . WO 92/06148 A1 . WO 92/05230 A2 . EP 0 738 709 A2 and EP 0 728 830 A2 For example, ester compounds of the formula I and liquid-crystalline mixtures with such compounds have already been disclosed.

• • geringe Frequenzabhängigkeit der Dielektrizitätskonstanten,
• • geringe Temperaturabhängigkeit der Betriebsspannung und der Schwellenspannung, und
• • sehr schnelle Schaltzeiten, insbesondere bei tiefen Temperaturen.

The use of the compounds of formula I in the mixtures for TN and STN displays according to the invention

• Low frequency dependence of the dielectric constant,
• • low temperature dependence of the operating voltage and the threshold voltage, and
• • very fast switching times, especially at low temperatures.

The Shorten compounds of the formula I. especially the switching times of TN and STN mixtures, especially at low temperatures, while increasing the Steepness and reduction of the temperature dependence of the threshold voltage, especially at temperatures between -20 and + 20 ° C.

• – sie besitzen eine niedrige Viskosität,
• – sie besitzen eine niedrige Schwellenspannung und Betriebsspannung,
• – sie bewirken lange Lagerzeiten in der FK-Anzeige bei tiefen Temperaturen.

Furthermore, the mixtures according to the invention are distinguished by the following advantages

• They have a low viscosity,
• They have a low threshold voltage and operating voltage,
• - They cause long storage times in the FK display at low temperatures.

worin
R⁰ eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, und
L¹ und L² unabhängig voneinander H oder F bedeuten,
eine oder mehrere Alkenylverbindungen der Formel II und/oder II*:

worin
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen,
R⁴ eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, und
a 0 oder 1,

worin
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen,
Q CF₂, OCF₂, CFH, OCFH oder eine Einfachbindung,
Y F oder Cl, und
L¹ und L² jeweils unabhängig voneinander H oder F bedeuten,
und mindestens eine Verbindung der Formel IV24:

worin R¹ Alkenyl mit 2 bis 7 C-Atomen und R² Alkyl oder Alkoxy mit 1 bis 6 C-Atomen bedeutet.The invention thus relates to a liquid-crystal mixture containing at least one compound of the formula I.

wherein
R ^{0 is} an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH ₂ groups by -O-, -CH = CH-, -CO-, -OCO- or -COO - can be replaced so that O atoms are not directly linked, and
L ¹ and L ² independently of one another denote H or F,
one or more alkenyl compounds of the formula II and / or II *:

wherein
R ^{3 is} an alkenyl group having 2 to 7 C atoms,
R ^{4 is} an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH ₂ groups by -O-, -CH = CH-, -CO-, -OCO- or -COO - can be replaced so that O atoms are not directly linked, and
a 0 or 1,

wherein
R ^{3 is} an alkenyl group having 2 to 7 C atoms,
Q CF ₂ , OCF ₂ , CFH, OCFH or a single bond,
YF or Cl, and
L ¹ and L ^{2 are} each independently H or F,
and at least one compound of the formula IV24:

wherein R ^{1 is} alkenyl having 2 to 7 carbon atoms and R ^{2 is} alkyl or alkoxy having 1 to 6 carbon atoms.

object The invention also relates to corresponding liquid crystal mixtures for Use in liquid crystal displays, especially in TN and STN ads, particularly preferably in medium- and low-multiplex STN displays.

• – zwei Trägerplatten, die mit einer Umrandung eine Zelle bilden,
• – einer in der Zelle befindlichen nematischen Flüssigkristallmischung mit positiver dielektrischer Anisotropie,
• – Elektrodenschichten mit Orientierungsschichten auf den Innenseiten der Trägerplatten,
• – einem Anstellwinkel zwischen der Längsachse der Moleküle an der Oberfläche der Trägerplatten und den Trägerplatten von 0 Grad bis 30 Grad, und
• – einem Verdrillungswinkel der Flüssigkristallmischung in der Zelle von Orientierungsschicht zu Orientierungsschicht dem Betrag nach zwischen 22,5° und 600°,
• – einer nematischen Flüssigkristallmischung bestehend aus a) 15–80 Gew.% einer flüssigkristallinen Komponente A, bestehend aus einer oder mehreren Verbindungen mit einer dielektrischen Anisotropie von über +1,5; b) 20–85 Gew.% einer flüssigkristallinen Komponente B, bestehend aus einer oder mehreren Verbindungen mit einer dielektrischen Anisotropie zwischen –1,5 und +1,5; c) 0–20 Gew.% einer flüssigkristallinen Komponente D, bestehend aus einer oder mehreren Verbindungen mit einer dielektrischen Anisotropie von unter –1,5 und d) gegebenenfalls einer optisch aktiven Komponente C in einer Menge, daß das Verhältnis zwischen Schichtdicke (Abstand der Trägerplatten) und natürlicher Ganghöhe der chiralen nematischen Flüssigkristallmischung etwa 0,2 bis 1,3 beträgt, dadurch gekennzeichnet, daß die nematische Flüssigkristallmischung mindestenste eine Verbindung der Formeln I, in 24, II und/oder II* enthält.

The invention also relates to the use of the liquid-crystal mixtures for a liquid-crystal display

• Two support plates, which form a cell with a border,
• An in-cell nematic liquid-crystal mixture having positive dielectric anisotropy,
• Electrode layers with orientation layers on the insides of the carrier plates,
• An angle of attack between the longitudinal axis of the molecules on the surface of the carrier plates and the carrier plates of 0 degrees to 30 degrees, and
• A twist angle of the liquid-crystal mixture in the cell from orientation layer to orientation layer in the amount between 22.5 ° and 600 °,
• A nematic liquid-crystal mixture consisting of a) 15-80% by weight of a liquid-crystalline component A consisting of one or more compounds having a dielectric anisotropy of more than +1.5; b) 20-85% by weight of a liquid-crystalline component B consisting of one or more compounds having a dielectric anisotropy between -1.5 and +1.5; c) 0-20 wt.% Of a liquid-crystalline component D, consisting of one or more compounds having a dielectric anisotropy of less than -1.5 and d) optionally an optically active component C in an amount such that the ratio between layer thickness (distance of Support plates) and natural pitch of the chiral nematic liquid-crystal mixture is about 0.2 to 1.3, characterized in that the nematic liquid-crystal mixture contains at least one compound of the formulas I, in 24, II and / or II *.

Particular preference is given to liquid-crystal mixtures which contain one or more compounds of the formula I in which R ⁰ denotes straight-chain 1 E or 3 E alkenyl having 2 to 7 C atoms.

Preference is furthermore given to liquid-crystal mixtures which comprise one or more compounds of the formula I in which R ⁰ denotes straight-chain alkyl having 1 to 8 C atoms.

Preference is furthermore given to liquid-crystal mixtures which comprise one or more compounds of the formula I. in which L ¹ and L ^{2 are} H, and liquid-crystal mixtures which contain a plurality of compounds of the formula I in which one or two of the radicals L ¹ and L ^{2 is} F.

Preference is furthermore given to liquid-crystal mixtures which contain one or more compounds of the formula I in which L ³ and L ^{4 are} H, and liquid-crystal mixtures which contain one or more compounds of the formula I in which one or two of the radicals L ³ and L ^{4 are} F. ,

worin R⁰⁰ H, CH₃, C₂H₅ oder n-C₃H₇, besonders bevorzugt CH₃, und alkyl eine Alkylgruppe mit 1 bis 8 C-Atomen bedeuten.Particularly preferred compounds of the formula I are selected from the following formulas

wherein R ^{00 is} H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ , more preferably CH ₃ , and alkyl is an alkyl group having 1 to 8 carbon atoms.

The Use of compounds of the formula I results in the liquid-crystal mixtures according to the invention to particularly low values of rotational viscosity and to TN and STN displays with high slope and fast switching times especially at low temperatures.

The Compounds of the formula I have low viscosities, in particular low rotational viscosities, and lead therefore in the ads too short switching times.

worin R^3a und R^4a jeweils unabhängig voneinander H, CH₃, C₂H₅ oder n-C₃H₇ und alkyl eine Alkylgruppe mit 1 bis 8 C-Atomen bedeuten.Particularly preferred compounds of the formula II are selected from the formulas IIa to IIg

wherein R ^3a and R ^{4a are} each independently H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ and alkyl is an alkyl group having 1 to 8 carbon atoms.

Particular preference is given to compounds of the formula IIa, in particular those in which R ^3a and R ^{4a are} CH ₃ , and also compounds of the formulas IIe, IIf and IIg, in particular those in which R ^{3a is} H.

The Use of compounds of the formula II leads in the liquid-crystal mixtures according to the invention to particularly low values of rotational viscosity and to TN and STN displays with high slope and fast switching times especially at low temperatures.

Particularly preferred compounds of the formula II * are those in which L ¹ and / or L ^{2 are} F and QY is F or OCF ₃ .

Preference is furthermore given to compounds of the formula II * in which R ^{3 is} 1E-alkenyl or 3E-alkenyl having 2 to 7, in particular 2, 3 or 4, C atoms.

The polar compounds of the formula II * with a dielectric anisotropy of more than + 1.5 are assigned to the component A defined above.

worin
R eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, und
L¹ bis L³ jeweils unabhängig voneinander H oder F bedeuten.
R bedeutet in diesen Verbindungen besonders bevorzugt Alkyl oder Alkoxy mit 1 bis 8 C-Atomen oder Alkenyl mit 2 bis 7 C-Atomen.Component A preferably contains one or more cyano compounds of the following formulas

wherein
R is an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, whereby also one or two non-adjacent CH ₂ groups are represented by -O-, -CH = CH-, -CO-, -OCO- or -COO- may be replaced so that O atoms are not directly linked, and
L ¹ to L ³ each independently represent H or F.
R in these compounds particularly preferably denotes alkyl or alkoxy having 1 to 8 C atoms or alkenyl having 2 to 7 C atoms.

Particular preference is given to mixtures comprising one or more compounds of the formulas IIIb and / or IIIc, furthermore IIIf, in particular those in which L ¹ and / or L ^{2 are} F.

worin R^3a H, CH₃, C₂H₅ oder n-C₃H₇, in Formel IIIb-1 und IIIb-2 bevorzugt H oder CH₃, in Formel IIIc-1 und IIIc-2 bevorzugt H oder C₂H₅, bedeutet.Very particular preference is given to mixtures which contain one or more compounds of the formula IIIb and / or IIIc in which R is alkenyl having 2 to 7 C atoms and L ¹ and L ^{2 are} H or F, preferably both H. Particularly preferred are compounds of the following formulas

in which R ^{3a is} H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ , in formula IIIb-1 and IIIb-2 preferably H or CH ₃ , in formula IIIc-1 and IIIc-2 preferably H or C ₂ H ₅ , means.

Preference is furthermore given to mixtures which comprise one or more compounds of the formula IIIh in which L ^{2 is} H and L ^{1 is} H or F, in particular F.

sowie gegebenenfalls eine oder mehrere Verbindungen mit polarer Endgruppe der folgenden Formeln

worin R eine der oben angegebenen Bedeutungen besitzt und L³ und L⁴ jeweils unabhängig voneinander H oder F bedeuten. R bedeutet in diesen Verbindungen besonders bevorzugt Alkyl oder Alkoxy mit 1 bis 8 C-Atomen.In a specific embodiment, component A preferably contains one or more 3,4,5-trifluorophenyl compounds of the following formulas

and optionally one or more compounds having a polar end group of the following formulas

wherein R has one of the meanings given above and L ³ and L ^{4 are} each independently H or F. R in these compounds particularly preferably denotes alkyl or alkoxy having 1 to 8 C atoms.

Especially preferred are compounds of the formulas IVa, IVb, IVc, IVd, IVm and Vi, in particular compounds of the formulas IVa, IVm and Vi.

preferred liquid crystal mixtures contain one or more compounds of component A preferably in a proportion of 15% to 80%, more preferably from 20% to 70%. These compounds have a dielectric anisotropy Δε ≥ +3, in particular Δε ≥ +8, especially preferably Δ∈ ≥ +12.

Preferred liquid-crystal mixtures comprise one or more compounds of component B, preferably in a proportion of 20 to 85%, particularly preferably in a proportion of 30 to 75%. The compounds of group B, in particular those having alkenyl groups, are distinguished in particular by their low values for the rotational viscosity γ ₁ .

und/oder eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Dreiringverbindungen der folgenden Formeln

und/oder eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Vierringverbindungen der folgenden Formeln

worin
R¹ und R² jeweils unabhängig voneinander eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, und
L H oder F bedeuten.In addition to one or more compounds of the formula II, component B preferably contains one or more compounds selected from the group consisting of the two-ring compounds of the following formulas

and / or one or more compounds selected from the group consisting of the three-membered compounds of the following formulas

and / or one or more compounds selected from the group consisting of the four-membered compounds of the following formulas

wherein
R ¹ and R ² each independently represent an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, whereby also one or two non-adjacent CH ₂ groups are represented by -O-, -CH = CH-, -CO-, -OCO- or -COO- can be replaced so that O atoms are not directly linked, and
Mean LH or F.

The 1,4-phenylene groups in IV10 to IV19 and IV23 to IV32 may each be independently also be substituted by fluorine mono- or polysubstituted.

Particular preference is given to compounds of the formulas IV 25 to IV 31 in which R ^{1 is} alkyl and R ^{2 is} alkyl or alkoxy, in particular alkoxy, in each case having 1 to 7 C atoms. Preference is furthermore given to compounds of the formulas IV 25 and IV 31 in which L is F.

All Particular preference is given to compounds of the formulas IV25 and IV27.

R ¹ and R ² in the compounds of the formulas IV1 to IV30 particularly preferably denote straight-chain alkyl or alkoxy having 1 to 12 C atoms.

The liquid crystalline Mixtures optionally contain an optically active component C in an amount that that relationship between layer thickness (distance of the carrier plates) and more natural Pitch of the chiral nematic liquid-crystal mixture greater than 0.2 is. For the components are available to a person skilled in the art, in part commercially available chiral dopants available z. B. Cholesterylnonanoat, S-811 Merck KGaA, Darmstadt and CB15 (BDH, Poole, UK). The choice of dopants is not per se critical.

Of the Proportion of the compounds of the component C is preferably 0 to 10%, in particular 0 to 5%, particularly preferably 0 to 3%.

worin R¹ und R² die oben angegebene Bedeutung besitzen,
Z⁴ -CO-O-, -CH₂CH₂- oder eine Einfachbindung, und
L¹ bis L⁶ jeweils unabhängig voneinander H oder F bedeuten.In addition to the compounds of the formula I, the mixtures according to the invention preferably contain one or more liquid-crystalline tolane compounds. Due to the high birefringence Δn of the tolan compounds, it is possible to work with lower layer thicknesses, as a result of which the switching times become significantly shorter. The tolan compounds are preferably selected from the group consisting of Ta to Th

in which R ¹ and R ^{2 have} the abovementioned meaning,
Z ⁴ -CO-O-, -CH ₂ CH ₂ - or a single bond, and
L ¹ to L ⁶ each independently represent H or F.

Especially preferred are compounds of the formula Ta, Tb and Th.

Particularly preferred compounds of the formula Te are those in which one, two or three of the radicals L ¹ to L ^{6 are} F and the other H, where L ¹ and L ² or L ³ and L ⁴ or L ⁵ and L ⁶ not both mean F at the same time.

Of the Proportion of the compounds from the group containing Ta and Tb preferably 5 to 50%, in particular 10 to 40%. The share of Compounds of the formula Th is preferably 2 to 35%, in particular 4 to 25%.

Of the Proportion of the compounds of the formulas Ta to Th is preferably 2 to 55%, especially 5 to 35%.

The mixtures according to the invention can also optionally up to 20% of one or more compounds with a dielectric anisotropy of less than -2 (component D) included.

If the mixtures contain compounds of component D, these are preferably one or more compounds having the structural element 2,3-difluoro-1,4-phenylene, eg. B. compounds according to DE-OS 38 07 801 . 38 07 861 . 38 07 863 . 38 07 864 or 38 07 908 , Particularly preferred are tolans with this structural element according to the International Patent Application PCT / DE 88/00133 ,

gemäß DE-OS 32 31 707 bzw. DE-OS 34 07 013 .Other known compounds of component D are, for. B. derivatives of 2,3-Dicyanhydrochinone or cyclohexane derivatives with the structural element

according to DE-OS 32 31 707 respectively. DE-OS 34 07 013 ,

Preferably contain the liquid crystal displays no compounds of component D.

The term "alkenyl" in the meaning of R, R ¹ , R ² , R ³ and R ⁴ includes straight-chain and branched alkenyl groups, in the case of R, R ¹ and R ² with 2-12, in the case of R ³ and R ⁴ with 2-7 carbon atoms, in particular the straight-chain groups. Particularly preferred alkenyl groups are C ₂ -C ₇ -1E-alkenyl, C ₄ -C ₇ 3E-alkenyl, C ₅ -C ₇ -alkenyl, C ₅ -C ₇ -5-alkenyl, and C ₇ -6- Alkenyl, in particular C ₂ -C ₇ -1E-alkenyl, C ₄ -C ₇ 3E-alkenyl and C ₅ -C ₇ -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 of up to 5 carbon atoms are generally preferred.

The individual compounds of the formulas I, II, III, IV, V, VI and T or their sub-formulas as well as other compounds which are included in the TN and STN ads can be used are either known or you can be prepared analogously to the known compounds.

• – eine oder mehrere Verbindungen ausgewählt aus den Formeln Ia, Ib und Ic,
  
  worin R⁰⁰ und alkyl die oben angegebene Bedeutung besitzen, insbesondere worin R⁰⁰ H und alkyl C₂H₅, n-C₃H₇ oder n-C₄H₉ bedeuten,
• – eine, zwei oder drei Verbindungen der Formel I,
• – 3 bis 40%, insbesondere 5 bis 25%, besonders bevorzugt 6 bis 16% einer oder mehrerer Verbindungen der Formel I,
• – 5 bis 60%, insbesondere 12 bis 50% einer oder mehrerer Alkenylverbindungen der Formel II und II*,
• – wenigstens eine Verbindung der Formel IIe und/oder IIf,
• – wenigstens eine Alkenylverbindung ausgewählt aus der folgenden Gruppe
  
  worin alkyl eine Alkylgruppe mit 1 bis 8 C-Atomen und R^3a H oder CH₃ bedeutet,
• – eine oder mehrere Verbindungen der Formel IV9, worin R¹ Alkenyl mit 2 bis 7 C-Atomen bedeutet und R² die oben angegebene Bedeutung hat und insbesondere Alkyl oder Alkoxy mit 1 bis 6 C-Atomen bedeutet, insbesondere eine oder mehrere Verbindungen der Formeln IV9a und/oder IV24a
  
  worin R^3a H, CH₃, C₂H₅ oder n-C₃H₇, insbesondere H oder CH₃ bedeutet, und R² die oben angegebene Bedeutung hat, vorzugsweise Alkyl oder Alkoxy mit 1 bis 6, insbesondere 1, 2 oder 3 C-Atomen bedeutet. Der Anteil dieser Verbindungen in den Flüssigkristallmischungen liegt vorzugsweise bei 2 bis 30%, insbesondere bei 3 bis 20%,
• – eine oder mehrere, insbesondere zwei bis fünf Verbindungen der Formel IIIb, IIIc und/oder IIIh,
• – wenigstens zwei Verbindungen der Formel IIIc, und gegebenenfalls zusätzlich wenigstens eine Verbindung der Formel IIIb, worin L¹ und/oder ¹² F bedeuten. Der Anteil dieser Verbindungen in den Flüssigkristallmischungen liegt vorzugsweise bei 7 bis 50%, insbesondere bei 10 bis 40%,
• – eine oder mehrere Verbindungen der Formel IIIc-1
  
  worin R^3a H oder CH₃, besonders bevorzugt H bedeutet. Der Anteil dieser Verbindungen in den Flüssigkristallmischungen liegt vorzugsweise bei 2 bis 20%, insbesondere bei 3 bis 9%,
• – eine oder mehrere, besonders bevorzugt eine, zwei oder drei Tolan-Verbindungen der Formel Ta oder Tb,
• – eine oder mehrere, besonders bevorzugt eine, zwei oder drei Tolan-Verbindungen der Formel Th,
• – eine oder mehrere Verbindungen der Formel IV25 und/oder IV27, wobei L in Formel IV 25 H oder F, besonders bevorzugt F bedeutet. Der Anteil dieser Verbindungen in den Flüssigkristallmischungen liegt vorzugsweise bei 10 bis 45%, insbesondere bei 15 bis 40%,
• – mehr als 20% an Verbindungen mit positiver dielektrischer Anisotropie, insbesondere mit Δε ≥ +12,

In particularly preferred embodiments, the mixtures contain

• One or more compounds selected from the formulas Ia, Ib and Ic,
  
  in which R ⁰⁰ and alkyl have the abovementioned meaning, in particular in which R ^{00 is} H and alkyl is C ₂ H ₅ , nC ₃ H ₇ or nC ₄ H ₉ ,
• One, two or three compounds of the formula I,
• From 3 to 40%, in particular from 5 to 25%, particularly preferably from 6 to 16% of one or more compounds of the formula I,
• From 5 to 60%, in particular from 12 to 50%, of one or more alkenyl compounds of the formula II and II *,
• At least one compound of the formula IIe and / or IIf,
• At least one alkenyl compound selected from the following group
  
  wherein alkyl is an alkyl group having 1 to 8 C atoms and R ^{3a is} H or CH ₃ ,
• - One or more compounds of formula IV9, wherein R ^{1 is} alkenyl having 2 to 7 carbon atoms and R ^{2 has} the meaning given above and in particular alkyl or alkoxy having 1 to 6 carbon atoms, in particular one or more compounds of the formulas IV9a and / or IV24a
  
  wherein R ^{3a is} H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ , in particular H or CH ₃ , and R ^{2 has} the meaning indicated above, preferably alkyl or alkoxy having 1 to 6, in particular 1, 2 or 3 C. -Atoms means. The proportion of these compounds in the liquid-crystal mixtures is preferably from 2 to 30%, in particular from 3 to 20%,
• One or more, in particular two to five compounds of the formula IIIb, IIIc and / or IIIh,
• - At least two compounds of formula IIIc, and optionally additionally at least one compound of formula IIIb, wherein L ¹ and / or ^{12 is} F. The proportion of these compounds in the liquid-crystal mixtures is preferably from 7 to 50%, in particular from 10 to 40%,
• One or more compounds of the formula IIIc-1
  
  wherein R ^{3a is} H or CH ₃ , more preferably H means. The proportion of these compounds in the liquid-crystal mixtures is preferably from 2 to 20%, in particular from 3 to 9%,
• One or more, more preferably one, two or three tolan compounds of the formula Ta or Tb,
• One or more, more preferably one, two or three tolan compounds of the formula Th,
• - One or more compounds of formula IV25 and / or IV27, wherein L in formula IV 25 H or F, particularly preferably F means. The proportion of these compounds in the liquid-crystal mixtures is preferably from 10 to 45%, in particular from 15 to 40%,
• More than 20% of compounds with positive dielectric anisotropy, in particular Δε ≥ +12,

The mixtures according to the invention are distinguished, in particular when used in TN and STN displays with high layer thicknesses, by very low sum switching times (t _ges = t _on + t _off ).

The are liquid crystal mixtures used in the TN and STN cells dielectrically positive with Δε ≥ 1. Especially preferred are liquid crystal mixtures with Δε ≥ 3, in particular with Δ∈ ≥ 5.

The liquid-crystal _{mixtures according} to the invention have favorable values for the threshold voltage V _10/0/20 and for the rotational _viscosity γ ₁ . If the value for the optical path difference d · Δn is predetermined, the value for the layer thickness d is determined by the optical anisotropy Δn. In particular, at relatively high values for Δn, the use of liquid crystal mixtures according to the invention having a relatively high value for the optical anisotropy is generally preferred since then the value for d can be chosen to be relatively small, which leads to more favorable values for the switching times. However, even liquid crystal displays containing liquid crystal mixtures according to the invention with smaller values for Δn are characterized by advantageous values for the switching times.

The Liquid crystal mixtures according to the invention are further characterized by advantageous values for the steepness of the electro-optical Characteristic curve, and can especially at temperatures above 20 ° C with operated at high multiplex rates. In addition, the liquid-crystal mixtures according to the invention have a high stability and cheap Values for the electrical resistance and the frequency dependence of the threshold voltage on. The liquid crystal displays have a big one Working temperature range and a good angle dependence of the contrast.

The structure of the liquid crystal display elements of polarizers, electrode base plates and Elek electrodes with such a surface treatment that the preferred orientation (director) of each adjacent liquid crystal molecules from one to the other electrode is usually rotated by 160 ° to 720 ° relative to each other, corresponds to the usual for such display elements construction. The term of the usual construction is here broadly and includes all modifications and modifications of the TN and STN cell, in particular matrix display elements and the additional magnets containing display elements.

Of the surface tilt on the two carrier plates can be the same or different. Same tilt angles are preferred. Preferred TN displays have angles of attack between the longitudinal axis of the molecules at the surface the carrier plates and the carrier plates from 0 ° to 7 °, preferably 0.01 ° to 5 °, in particular 0.1 to 2 °. In the STN ads is the angle of attack at 1 ° to 30 °, preferably at 1 ° to 12 ° and in particular at 3 ° to 10 °.

Of the Twist angle of the TN mixture in the cell is the amount after between 22.5 ° and 170 °, preferably between 45 ° and 130 ° and especially between 80 ° and 115 °. Of the Twist angle of the STN mixture in the cell from orientation layer to orientation layer is the Amount after between 100 ° and 600 °, preferably between 170 ° and 300 ° and in particular between 180 ° and 270 °.

The Preparation of the invention usable liquid crystal mixtures takes place in per se usual Wise. In general, the desired Amount of components used in lesser amount in the Main component making up components solved, expedient at elevated temperature. It is also possible, solutions the components in an organic solvent, e.g. In acetone, Chloroform or methanol, to mix and the solvent after mixing to remove again, for example by distillation.

The liquid-crystal mixtures according to the invention are also suitable for use as liquid-crystal (FK) media in cholesteric liquid crystal (CFRP) displays, in particular SSCT (surface stabilized cholesteric texture) and PSCT (polymer stabilized cholesteric texture ") Ads, such as in WO 92/19695 . US 5,384,067 . US 5,453,863 . US 6,172,720 or US 5,661,533 described. CFRP displays typically contain a cholesteric FK medium consisting of a nematic component and an optically active component which has a significantly higher helical twist compared to TN and STN displays and exhibits selective reflection of circularly polarized light. The reflection wavelength corresponds to the product of the pitch of the cholesteric helix and the mean refractive index of the CFRP medium.

For this purpose, one or more chiral dopants whose twisting power and concentration are chosen such that the LC medium has a cholesteric phase at room temperature and has a reflection wavelength, preferably in the visible, UV or IR, are added to the LC mixtures according to the invention. Range of the electromagnetic spectrum, in particular between 400 and 800 nm. Suitable dopants are known to the person skilled in the art and are commercially available, for example cholesteryl nonanoate (CN), CB15, R / S-811, R / S-1011, R / S-2011, R / S-3011 or R / S-4011 ( Merck KGaA, Darmstadt). Particularly suitable are highly twisting dopants with a chiral sugar residue, in particular sorbitol derivatives as in WO 98/00428 described. If two or more dopants are added, they may have the same or opposite directions of rotation and the same or opposite temperature dependence of the twist.

CLC media, containing as nematic component of an inventive FK mixture and as optically active component one or more chiral dopants, are another object of the present invention. object The present invention further includes CFRP displays, in particular SSCT and PSCT displays containing CFRP media as described above.

The Dielectrics can also further, known in the art and described in the literature additions contain. For example, you can 0-15% pleochroic dyes are added.

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 the 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 alkenyl radicals have the trans configuration. 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 separate line from the acronym for the main body follows with a dash of the code given in the table below for the sub substituents R ¹ , R ² , L ¹ , L ² and L ³ . 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:

The TN and STN displays preferably contain liquid crystalline mixtures which are composed of one or more compounds from Tables A and B. Table A: (L ¹ , L ² , L ³ = H or F)

Table B:

• Klp. Klärpunkt (Phasenübergangs-Temperatur nematisch-isotrop),
• S-N Phasenübergangs-Temperatur smektisch-nematisch,
• Visk. Fließviskosität (soweit nicht anders angegeben bei 20°C),
• Δn optische Anisotropie (589 nm, 20°C)
• n_o ordentlicher Brechungsindex (589 nm, 20°C)
• Δε dielektrische Anisotropie (1 kHz, 20°C)
• ε_⟘ Dielektrizitätskonstante senkrecht zur Moleküllängsachse (1 kHz, 20°C)
• γ₁ Rotationsviskosität
• S Kennliniensteilheit = V₉₀/V₁₀
• V₁₀ Schwellenspannung = charakteristische Spannung bei einem relativen Kontrast von 10%,
• V₉₀ charakteristische Spannung bei einem relativen Kontrast von 90%,
• t_ave
  
  (mittlere Schaltzeit)
• t_on Zeit vom Einschalten bis zur Erreichung von 90% des maximalen Kontrastes,
• t_off Zeit vom Ausschalten bis zur Erreichung von 10% des maximalen Kontrastes,
• Mux Multiplexrate
• t_store Tieftemperatur-Lagerstabilität in Stunden (–20°C, –30°C, –40°C)

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

• Klp. Clearing point (phase transition temperature nematic-isotropic),
• SN phase transition temperature smectic-nematic,
• Visc. Flow viscosity (unless otherwise stated at 20 ° C),
• Δn optical anisotropy (589 nm, 20 ° C)
• n _o ordinary refractive index (589 nm, 20 ° C)
• Δε dielectric anisotropy (1 kHz, 20 ° C)
• ε _⟘ Dielectric constant perpendicular to the molecular axis (1 kHz, 20 ° C)
• γ ₁ rotational viscosity
• S characteristic steepness = V ₉₀ / V ₁₀
• V ₁₀ threshold voltage = characteristic voltage at a relative contrast of 10%,
• V ₉₀ characteristic stress at a relative contrast of 90%,
• t _ave
  
  (middle switching time)
• t _on from switching on until reaching 90% of maximum contrast,
• t _off time from switching off to reaching 10% of the maximum contrast,
• Mux multiplex rate
• t _store low-temperature storage stability in hours (-20 ° C, -30 ° C, -40 ° C)

In front- and below, all temperatures are in ° C. The percentages are weight percent. All values refer to 20 ° C, as far as not stated otherwise. The display is activated as far as possible not stated otherwise, at a multiplex rate of 1/64 and a Bias of 1/9. The twist is 240 °, unless stated otherwise.

Comparative Example 1

A TN and STN mixture consisting of PCH 3N.FF 10.00% klp .: 102.0 ° C PZU-V2-N 5.00% .DELTA.n: 0.1620 ME2N.F 2:00% n _o : 1.5038 ME3N.F 3:00% V ₁₀ : 1.58V ME4N.F 5:50% S: 1,065 CC-5-V 3:50% t _on + t _off (20 ° C): 250 ms CCG-VF 8:00 pm% t _on + t _off (-20 ° C): 4100 ms CCP-V-1 13.00% CCP-V2-1 9.00% CVCP-V-1 5.00% PTP 102 3:00% PTP 201 2:00% PPTUI-3-2 16:00% CCPC-33 3:00%

example 1

• weist gegenüber Vergleichsbeispiel 1 ein deutlich kürzere Schaltzeit, vor allem bei –20°C, und eine niedrigere Schwellenspannung auf.

A TN and STN mixture consisting of PCH 3N.FF 10.00% klp .: 100.0 ° C PZU-V2-N 5.00% .DELTA.n: .1631 ME2N.F 2:00% n _o : 1.5015 ME3N.F 3:00% V ₁₀ : 1.56V ME4N.F 2:00% S: 1.066 CC-5-V 2:00% t _on + t _off (20 ° C): 230 ms CCG-VF 15.00% t _o + t _off (-20 ° C): 2200 ms CCP-V-1 13.00% CCP-V2-1 9.00% CVCP-V-1 5.00% PTP 102 3:00% PPTUI-3-2 17.00% CCPC-33 4:00% PZP-V2-OT 10.00%

• Compared to Comparative Example 1 has a significantly shorter switching time, especially at -20 ° C, and a lower threshold voltage.

Example 2

• weist gegenüber Vergleichsbeispiel 1 ein deutlich kürzere Schaltzeit, vor allem bei –20°C, und eine niedrigere Schwellenspannung auf.

A TN and STN mixture consisting of PCH 3N.FF 10.00% klp .: 99.0 ° C PZU-V2-N 5.00% .DELTA.n: .1622 ME2N.F 2:00 %% n _o : 1.5011 ME3N.F 3:00% V ₁₀ : 1.55V ME4N.F 2:00% S: 1,074 CC-5-V 2:00% t _on + t _off (20 ° C): 230 ms CCG-VF 15.00% t _on + t _off (-20 ° C): 2700 ms CCP-V-1 13.00% CCP-V2-1 9.00% CVCP-V-1 5.00% PTP 102 3:00% PPTUI-3-2 17.00% CCPC-33 4:00% PZP-3-OT 10.00%

• Compared to Comparative Example 1 has a significantly shorter switching time, especially at -20 ° C, and a lower threshold voltage.

Comparative Example 2

A TN and STN mixture consisting of PCH 3N.FF 13.00% klp .: 88.0 ° C ME2N.F 2:00% .DELTA.n: .1374 ME3N.F 3:00% Δε: 14.4 ME4N.F 6:00 am% V ₁₀ : 1.56V ME5N.F 4:00% S: 1.063 CC-5-V 10.00% t _on + t _off (20 ° C): 502 ms CC-3-V1 5.00% t _on + t _off (-20 ° C): 3866 ms CCG-VF 24.00% CCP-V-1 8.00% CCP-V2-1 4:00% CVCP V O1 5.00% PPTUI-3-2 14.00% CCPC-33 2:00%

Example 3

• weist gegenüber Vergleichsbeispiel 2 ein deutlich kürzere Schaltzeit auf.

A TN and STN mixture consisting of PCH 3N.FF 13.00% klp .: 84.1 ° C ME2N.F 2:00% Δ _n: 0.138 ME3N.F 3:00% _Δ ε: 12.6 ME4N.F 3:00% V ₁₀ : 1.7V ME5N.F 3:00% S: 1,073 CC-5-V 19:50% t _on + t _off (20 ° C): 304 ms CC-3-V1 5.00% t _on + t _off (-20 ° C): 2442 ms CCP-V-1 8.00% CCP-V2-1 4:00% CVCP V O1 5.00% PPTUI-3-2 15.00% CCPC-33 3:00% CCPC-34 4:00% PZP-V2-OT 12.50%

• Compared to Comparative Example 2 has a significantly shorter switching time.

Example 4

• weist gegenüber Vergleichsbeispiel 2 ein deutlich kürzere Schaltzeit auf.

A TN and STN mixture consisting of PCH 3N.FF 13.00% klp .: 85 ° C ME2N.F 2:00% Δ _n: .1381 ME3N.F 3:00% _Δ ε: 13.1 ME4N.F 5:50% V ₁₀ : 1.65 V CC-5-V 10:50% S: 1,065 CC-3-V1 5.00% t _on + t _off (20 ° C): 374 ms CCG-VF 15.00% t _on + t _off (-20 ° C): 3676 ms CCP-V-1 8.00% CCP-V2-1 4:00% CVCP V O1 5.00% PPTUI-3-2 14.00% CCPC-33 4:50% PZP-V2-OT 10:50%

• Compared to Comparative Example 2 has a significantly shorter switching time.

Example 5

• weist gegenüber Vergleichsbeispiel 2 ein deutlich kürzere Schaltzeit auf.

A TN and STN mixture consisting of ME2N.F 3:00% klp .: 86.3 ° C ME3N.F 4:00% .DELTA.n: .1374 ME4N.F 6:00 am% _Δ ε: 13.2 ME5N.F 5.00% V ₁₀ : 1.66 V CC-5-V 9:50% S: 1,072 CC-3-V1 5.00% t _on + t _off (20 ° C): 377 ms CCG-VF 24.00% t _on + t _off (-20 ° C): 2973 ms CCP-V-1 8.00% CCP-V2-1 5.00% CVCP V O1 5.00% PPTUI-3-2 11:50% CCPC-33 1:00% PZP-V2-OT 13.00%

• Compared to Comparative Example 2 has a significantly shorter switching time.

Claims (9)

Liquid-crystal mixture containing at least one compound of the formula I.

in which R ^{0 is} an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, where also one or two non-adjacent CH ₂ groups is represented by -O-, -CH = CH-, -CO-, -OCO- or - COO- can be replaced so that O atoms are not directly linked to one another, and L ¹ to L ⁴ independently of one another denote H or F, characterized in that it contains at least one compound of formula II and / or II *

wherein R ^{3 is} an alkenyl group having 2 to 7 C atoms, R ^{4 is} an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH ₂ groups by -O-, -CH = CH, -CO-, -OCO- or -COO- can be replaced so that O atoms are not directly linked to each other, a O or 1, L ¹ and L ^{2 are} each independently H or F, Q is CF ₂ , OCF ₂ , CFH, OCFH or a single bond, and YF or Cl, and at least one compound of formula IV24

wherein R ^{1 is} alkenyl having 2 to 7 carbon atoms and R ^{2 is} alkyl or alkoxy having 1 to 6 carbon atoms. Liquid-crystal mixture according to Claim 1, characterized in that it contains at least one compound of the formula IV9

wherein R ^{1 is} alkenyl having 2 to 7 carbon atoms and R ^{2 is} alkyl or alkoxy having 1 to 6 carbon atoms. A liquid-crystal mixture according to claim 1 or 2, characterized in that it contains one or more compounds of the following formulas

wherein R is an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH ₂ groups by -O-, -CH = CH-, -CO-, -OCO- or -COO - may be replaced so that O atoms are not directly linked, and L ¹ and L ^{2 are} each independently H or F. Liquid-crystal mixture according to one or more of claims 1 to 3, characterized in that it contains one or more compounds of the following formulas

in which R ¹ and R ² each independently of one another are an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, whereby also one or two non-adjacent CH ₂ groups are represented by -O-, -CH = CH-, -CO- , -OCO- or -COO- can be replaced so that O atoms are not directly linked to one another, and denote LH or F. Liquid-crystal mixture according to one or more of claims 1 to 4, characterized in that it contains one or more tolan compounds selected from the following formulas.

wherein R ¹ and R ^{2 have} the meaning given in claim 4. liquid crystal mixture according to one or more of claims 1 to 6, characterized in that it 3 contains up to 40% of one or more compounds of the formula I. Use of a liquid-crystal mixture according to one or more of the claims 1 to for a liquid crystal display. Use according to claim 7 for a TN or STN liquid crystal display With - two Carrier plates, that form a cell with a border, - one in the cell nematic liquid-crystal mixture with positive dielectric anisotropy, - Electrode layers with orientation layers on the insides of the carrier plates, - one Angle of attack between the longitudinal axis of the molecules on the surface the carrier plates and the carrier plates from 0 degrees to 30 degrees, and - a twist angle the liquid crystal mixture in the cell from orientation layer to orientation layer Amount after between 22.5 ° and 600 °, - one nematic liquid-crystal mixture consisting of a) 15-80 % By weight of a liquid-crystalline Component A, consisting of one or more compounds with a dielectric anisotropy of over +1.5; b) 20-85% by weight a liquid crystalline Component B, consisting of one or more compounds with a dielectric anisotropy between -1.5 and +1.5; c) 0-20% by weight a liquid crystalline Component D, consisting of one or more compounds with a dielectric anisotropy of less than -1.5 and d) if appropriate an optically active component C in an amount such that the ratio between Layer thickness (distance of the carrier plates) and more natural pitch the chiral nematic liquid crystal mixture about 0.2 to 1.3, thereby characterized in that nematic liquid-crystal mixture a liquid crystal mixture according to one of the claims 1 to 6 is. Use according to claim 7 for a cholesteric liquid crystal display, SSCT or PSCT display containing as optically active component one or more chiral dopants and as a nematic component the liquid crystal mixture according to one of the claims 1 to 6.