DE102004062962B4 - Liquid crystalline medium and its use in a high-twist liquid crystal display - Google Patents

Abstract

Liquid-crystalline medium with a helically twisted structure containing a nematic component and an optically active component, characterized in that the optically active component contains one or more chiral compounds of the formula XVII, wherein B 1,4-phenylene, which is also mono-, di- or may be trisubstituted, or 1,4-cyclohexylene, LH, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1-7 carbon atoms, b 0, 1 or 2, Z5 -COO -, -OCO-, -CH2CH2- or a single bond, and R5 is alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy with 1-12 carbon atoms, the nematic component is one or more compounds selected from the following formulas I1a, I2a and IIa , wherein R1 is H, an unsubstituted, an alkyl or alkenyl radical which is monosubstituted by CN or CF3 or an at least monosubstituted by halogen and has 1 to 20 carbon atoms, in these radicals also an ode r several CH2 groups each independently of one another by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -CC- can be replaced in such a way that O atoms are not directly linked, ...

Description

The present invention relates to a high-twist liquid crystalline medium, and its use for electro-optical purposes and in displays.

Liquid crystal displays are known in the art. The most common display devices are based on the Schadt-Helfrich effect and include a twisted nematic structure liquid crystal medium such as twisted nematic (TN) cells with twist angles of typically 90 ° and STN cells ("super-twisted nematic") Twist angles of typically 180 to 270 °. Further, ferroelectric liquid crystal displays containing a liquid crystal medium having a twisted smectic structure are known. The twisted structure is usually achieved in these displays by adding one or more chiral dopants to a nematic or smectic liquid crystal medium.

In addition, for example, out DE 102 21 751 A1 Liquid crystal displays containing liquid crystal (FK) media of chiral nematic or cholesteric structure are known. These media have TN and STN cells as compared to the media, such as in DE 195 32 292 A1 described, a significantly higher twist on.

Cholesteric liquid crystals exhibit selective reflection of circularly polarized light, with the direction of rotation of the light vector corresponding to the direction of rotation of the cholesteric helix. The reflection wavelength λ results from the pitch p of the cholesteric helix and the mean birefringence n of the cholesteric liquid crystal according to equation (1): λ = n × p (1)

The terms "chiral nematic" and "cholesteric" are used side by side in the prior art. "Chiral nematic" often refers to FK materials consisting of a nematic host mixture doped with an optically active component that induces a helically twisted superstructure. In contrast, "cholesteric" often refers to chiral FK materials, for example cholesteryl derivatives, which have a "natural" cholesteric phase with helical twist. Both terms are also used in parallel to the name of the same object. In the present application, the term "cholesteric" is used for both of the abovementioned types of LC materials, which term is intended to encompass the broadest meaning of "chiral nematic" and "cholesteric".

Examples of common cholesteric liquid crystal (CFRP) displays are the so-called SSCT (surface stabilized cholesteric texture) and PSCT (polymer stabilized cholesteric texture) displays. SSCT and PSCT displays usually contain a CFRP medium which, for example, in the initial state has a planar, light of a specific wavelength-reflecting structure, and can be switched to a focal conical, light-scattering structure by applying an AC electrical pulse, or vice versa. When a stronger voltage pulse is applied, the CFRP medium is converted into a homeotropic, transparent state, from where it relaxes into the focal conical state after rapidly switching off the voltage to the planar or, after a slow turn-off, into the focal conical state.

The planar orientation of the CFRP medium in the initial state, d. H. before applying a voltage, in SSCT displays, for example, it is achieved by surface treatment of the cell walls. In PSCT displays, the CFRP medium additionally contains a phase-separated polymer or polymer network, which stabilizes the structure of the CFRP medium in the respectively activated state.

SSCT and PSCT displays generally do not require backlighting. The CFK medium in a pixel shows in the planar state selective light reflection of a certain wavelength according to the above equation (1), so that the pixel z. B. appears in front of a black background in the corresponding reflection color.

The reflection color disappears when switching to the focal-conical, scattering or homeotropic, transparent state.

SSCT and PSCT displays are bistable, ie after switching off the electric field, the respective state is retained and is only returned to the initial state by applying a new field. To generate a pixel, therefore, a short voltage pulse is sufficient, in contrast z. B. to electro-optical TN or STN displays in which the FK medium in a controlled pixel after Switching off the electric field immediately returns to the initial state, so that for the permanent generation of a pixel maintenance of the drive voltage is necessary.

For the reasons mentioned above, CFRP displays consume significantly less power than TN or STN displays. Moreover, in the scattering state, they show little or no dependence on viewing angles. In addition, they do not require active matrix control as with TN displays, but can be operated in the simpler multiplex or passive matrix method.

WO 92/19695 and US 5,384,067 describe, for example, a PSCT display comprising a CFRP medium having positive dielectric anisotropy and up to 10 wt% of a phase-separated polymer network dispersed in the liquid crystal material. US 5,453,863 describes, for example, an SSCT display comprising a polymer-free CFK medium having positive dielectric anisotropy.

Other known from the prior art displays in which CFRP materials are used, the so-called flexoelectric displays, especially those that are operated in "uniformly lying helix mode" (ULH mode). The flexoelectric effect and CFRP materials that exhibit this effect are e.g. By Chandrasekhar in "Liquid Crystals", 2nd Ed., Cambridge University Press (1992), P.G. deGennes et al. in The Physics of Liquid Crystals, 2nd edition, Oxford Science Publications (1995), Patel and Meyer, Phys. Rev. Lett. 58 (15), 1538-1540 (1987) and Rudquist et al., Liq. Cryst. 22 (4), 445-449 (1997).

Flexoelectric CFRP materials typically have an asymmetric molecular structure and a strong dipole moment. Upon application of an electric field perpendicular to the cholesteric helical axis, the permanent dipoles are oriented in the direction of the field. At the same time, the FK director is distorted due to the asymmetric molecular structure, while the orientation of the cholesteric helix axis remains unchanged. This leads to a macroscopic polarization of the CFRP material in the field direction, and to a shift of the optical axis relative to the helical axis.

Flexoelectric displays are usually operated in the so-called "uniformly lying helix" (ULH) mode, such as. In P. Rudquist et al., Liq. Cryst. 23 (4), 503 (1997). For this purpose, a layer of flexo-electric CFRP material with high twist and short helical pitch, typically in the range of 0.2 μm to 1.0 μm, in particular smaller than 0.5 μm, is oriented between two transparent parallel electrodes such that the cholesteric helical axis aligned parallel to the electrodes and the CFK layer has a macroscopically uniform orientation. When an electric field is applied to the cell perpendicular to the CFRP layer, the LC director and thus the optical axis of the sample rotate in the layer plane. If the CFRP layer is placed between two linear polarizers, this leads to a change in the transmission of the linearly polarized light in the CFRP material, which can be exploited in electro-optical displays. The flexoelectric effect is characterized u. a. due to very fast switching times, typically from 6 μs to 100 μs, as well as good contrast with a high number of gray levels.

Flexoelectric displays can be operated as transmissive or reflective displays, with active matrix control or in multiplex or passive matrix processes.

High twist CFRP materials for use in flexoelectric displays are e.g. In EP 0 971 016 and GB 2 356 629 described. EP 0 971 016 proposes chirally liquid-crystalline estradiol derivatives for this purpose, GB 2 356 629 the so-called bimesogenic compounds containing two mesogenic groups linked by flexible hydrocarbon chains in combination with chiral dopants.

A CFK medium for the above-mentioned displays can be produced, for example, by doping a nematic FK mixture with a high-twisting chiral dopant. The pitch p of the induced cholesteric helix then results from the concentration c and the twisting power HTP (helical twisting power) of the chiral dopant according to equation (2): p = (HTP * c) ^-1 (2)

It is also possible to use two or more dopants, for example to compensate for the temperature dependence of the HTP of the individual dopants and thus to achieve a low temperature dependence of the helical pitch and the reflection wavelength of the CFC medium.

For use in the above displays, the chiral dopants should have the highest possible twistability with low temperature dependence, high stability, and good solubility in the liquid crystalline host phase. In addition, they should as far as possible not adversely affect the liquid-crystalline and electro-optical properties of the liquid-crystalline host phase. A high twisting capacity of the dopants is among other things to achieve small pitches z. B. desired in cholesteric displays, but also to lower the concentration of the dopant can. As a result, on the one hand, a possible impairment of the properties of the liquid-crystal medium by the dopant is reduced, and on the other hand the scope for the solubility of the dopant is increased, so that z. B. also dopants with lower solubility can be used.

In addition, CFRP materials should have a sufficiently strong flexoelectric effect for use in flexoelectric displays.

Generally, CFRP materials for use in the above displays must have good chemical and thermal stability and good stability to electric fields and electromagnetic radiation. Further, the liquid crystal materials should have a wide cholesteric liquid crystal phase with a high clearing point, sufficiently high birefringence, high positive dielectric anisotropy, and low rotational viscosity.

The CFRP materials should also be such that different reflection wavelengths, especially in the visible range, can be realized by simple and targeted variation. Furthermore, they should have a low temperature dependence of the reflection wavelength.

Since liquid crystals are generally used as mixtures of several components, it is important that the components are readily miscible with each other. Other properties, such as dielectric anisotropy and optical anisotropy, must meet different requirements depending on the type of cell.

However, with the media available from the prior art, it is not possible to realize favorable values for all the parameters mentioned above.

EP 0 450 025 describes, for example, a cholesteric liquid crystal mixture consisting of a nematic liquid crystal with two or more chiral dopants. However, the mixtures shown therein have only low clearing points. In addition, they contain a high proportion of 26% of chiral dopants. However, high concentrations of dopant generally lead to an impairment of the liquid-crystalline and electro-optical properties of the CFRP medium.

The materials known in the art for flexoelectric and CFRP displays often do not have sufficiently wide FK phases, sufficiently low viscosity values, and sufficiently high dielectric anisotropy values. In addition, they require high switching voltages and often have no matched to the required FK layer thickness birefringence values.

So z. For example, many CRP displays require a CFRP medium with high birefringence Δn to achieve high reflectivity while other CRP displays, eg. For example, if your priority is high color saturation (multicolour CFRP displays), you need low values of Δn. However, it has been shown that a reduction in the birefringence while maintaining the high polarity of the CFRP medium, which is necessary for low switching voltages, could not be realized sufficiently with the CFK media known from the prior art.

There is thus a great need for CFRP media with high twist, high operating temperature range, short switching times, low threshold voltage, low temperature dependence of the reflection wavelength, and in particular low values of birefringence, which do not or only in the disadvantages of the known from the prior art media have smaller dimensions.

For use in CFRP displays, especially in SSCT displays, the CFRP media should also have good dielectric behavior, a wide operating temperature range, and good color saturation.

The object of the invention is to provide CFRP media, in particular for use in flexoelectric displays, CFRP displays such as SSCT and PSCT displays and other bistable CFRP displays. Displays which have the above-mentioned required properties and do not or only to a lesser extent have the disadvantages of the media known from the prior art.

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

worin
B 1,4-Phenylen, welches auch durch L mono-, di- oder trisubstituiert sein kann, oder 1,4-Cyclohexylen,
L H, F, Cl, CN oder optional halogeniertes Alkyl, Alkoxy, Alkylcarbonyl, Alkoxycarbonyl, Alkylcarbonyloxy oder Alkoxycarbonyloxy mit 1–7 C-Atomen,
b 0, 1 oder 2,
Z⁵ -COO-, -OCO-, -CH₂CH₂- oder eine Einfachbindung, und
R⁵ Alkyl, Alkoxy, Alkylcarbonyl, Alkoxycarbonyl oder Alkylcarbonyloxy mit 1-12 C-Atomen
bedeuten,
die nematische Komponente eine oder mehrere Verbindungen ausgewählt aus den folgenden Formeln I1a, I2a und IIa,

worin
R¹ H, einen unsubstituierten, einen einfach durch CN oder CF₃ oder einen mindestens einfach durch Halogen substituierten Alkyl- oder Alkenylrest mit 1 bis 20 C-Atomen, wobei in diesen Resten auch eine oder mehrere CH₂-Gruppen jeweils unabhängig voneinander durch -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH=CH- oder -C=C- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind,
X⁰ F, Cl, halogeniertes Alkyl, Alkenyl oder Alkoxy mit 1 bis 6 C-Atomen, und
eine oder mehrere Verbindungen ausgewählt aus den Formeln IV6, IV26, IV32 und V

worin R¹ und R² jeweils unabhängig voneinander eine der vorstehenden Bedeutung für R¹ haben, enthält.The invention relates to a liquid-crystalline medium having a helically twisted structure comprising a nematic component and an optically active component, characterized in that the optically active component contains one or more chiral compounds of the formula XVII

wherein
B is 1,4-phenylene, which may also be mono-, di- or trisubstituted by L, or 1,4-cyclohexylene,
LH, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1-7 C atoms,
b 0, 1 or 2,
Z ^{5 is} -COO-, -OCO-, -CH ₂ CH ₂ - or a single bond, and
R ^{5 is} alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy having 1-12 C atoms
mean,
the nematic component comprises one or more compounds selected from the following formulas I1a, I2a and IIa,

wherein
R ^{1 is} H, an unsubstituted, an alkyl or alkenyl radical having 1 to 20 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, where one or more CH ₂ groups in these radicals are also each independently O, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -C = C- can be replaced so that Atoms are not directly linked,
X ⁰ F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 carbon atoms, and
one or more compounds selected from the formulas IV6, IV26, IV32 and V

wherein R ¹ and R ² each independently have one of the above meanings for R ¹ contains.

Another object of the invention is the use of the CFRP media according to the invention for electro-optical purposes, in particular in bistable CFRP displays, CFRP displays such as SSCT and PSCT displays, and in flexoelectric displays.

Another object of the invention is the use of the CFRP media according to the invention for an electro-optical display, in particular a bistable, CFK, SSCT, PSCT or flexoelectric display, with two plane-parallel support plates, which form a cell with a border, and a in CFK medium, wherein the CFK medium is a medium according to claim 1.

Surprisingly, it has been found that it is possible to provide a CFRP medium according to the present invention having a reflection wavelength in the visible range and / or a cholesteric phase at room temperature which has medium to low levels of birefringence and yet sufficiently high levels of dielectric anisotropy Δε to realize low switching times. This is achieved in the CFRP media according to the invention in particular by using compounds of the formula I1a, I2a and IIa, together with highly twisting chiral dopants as described below.

Thus, the use of the compounds of formula I1a, I2a and IIa in the blends for CFRP displays leads to a high polarity, i. H. low threshold voltages, short switching times and a wide operating temperature range.

In addition, the CFRP media according to the invention show outstanding properties with regard to color saturation and UV stability by the combination of the compounds of the formula I1a, I2a and IIa when used in CFRP displays. In particular, CFRP and SSCT displays can thereby be realized, which can also represent the color red without appearing orange due to the high yellow and green fractions of the previously known SSCT media.

Surprisingly, the achievement of the high polarity, which is necessary for acceptable switching voltages, not adversely affected.

• – sie besitzen einen breiten cholesterischen Phasenbereich insbesondere bei tiefen Temperaturen und einen hohen Klärpunkt,
• – sie besitzen eine hohe UV-Stabilität.

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

• They have a broad cholesteric phase range, especially at low temperatures and a high clearing point,
• - they have a high UV stability.

The compounds of formulas I1a, I2a and IIa have a wide range of applications. Depending on the choice of substituents, these compounds may serve as base materials from which liquid crystalline media are predominantly composed; However, it is also possible to add compounds of the formulas I1a, I2a and IIa to liquid-crystalline base materials from other classes of compounds For example, to influence the dielectric and / or optical anisotropy of such a dielectric and / or to optimize its threshold voltage and / or its viscosity. The compounds of the formulas I1a, I2a and IIa are colorless in the pure state and form liquid-crystalline mesophases in a temperature range which is favorably located for the electro-optical use. Chemically, thermally and against light, they are stable.

Particular preference is given to CFRP media in which the nematic component contains more than 20%, in particular more than 40%, particularly preferably more than 50%, very particularly preferably more than 60% of one or more compounds having a 3,4,5-trifluorophenyl group ,

Further preferred CFK media containing at least one compound of formula I1a or I2a, wherein X ^{0 is} F.

worin
A³ 1,4-Phenylen oder trans-1,4-Cyclohexylen,
c 0 oder 1,
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-, -C≡C-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind,
Q CF₂, OCF₂, CFH, OCFH oder eine Einfachbindung,
Y F oder Cl, und
L¹ und L² jeweils unabhängig voneinander H oder F
bedeuten.In addition to the compounds according to claim 1, the mixtures according to the invention preferably comprise one or more alkenyl compounds selected from the formulas III1 and III2

wherein
A ^{3 is} 1,4-phenylene or trans-1,4-cyclohexylene,
c 0 or 1,
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, whereby also one or two non-adjacent CH ₂ groups are represented by -O-, -CH = CH-, -C≡C-, -CO-, -OCO- or -COO- can be replaced so that O atoms are not directly linked to one another,
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
mean.

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.Particular preference is given to compounds of the formula III1 in which c denotes 1. Further preferred compounds of formula III1 are selected from the following formulas

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 IIIa, in particular those in which R ^3a and R ^{4a are} CH ₃ , compounds of the formula III1e, in particular those in which R ^{3a is} H, and compounds of the formulas III1f, III1g, III1h and IIIl, in particular those in which R is ^3a H or CH _3.

worin R^3a H, CH₃, C₂H₅ oder n-C₃H₇, insbesondere H oder CH₃ bedeutet.Particularly preferred compounds of formula III2 are those in which L ¹ and / or L ^{2 are} F and QY is F or OCF ₃ . Further preferred compounds of the formula III2 are those in which R ^{3 is} 1E-alkenyl or 3E-alkenyl having 2 to 7, in particular 2, 3 or 4 C atoms. Further preferred compounds of formula III2 are those of formula III2a

wherein R ^{3a is} H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ , in particular H or CH ₃ .

The use of compounds of the formula III1 and III2 leads in the liquid-crystal mixtures according to the invention to particularly low values of the rotational viscosity and to CFRP displays with fast switching times, in particular at low temperatures.

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 der vorstehenden Bedeutung von R¹ haben, und vorzugsweise jeweils unabhängig voneinander eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen bedeuten, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -C≡C-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, und 11 H oder F bedeutet.Preferred liquid-crystal mixtures contain, in addition to the compounds according to claim 1, preferably one or more compounds selected from the group consisting of the Zweiringverbindungen 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

in which R ¹ and R ² each independently have one of the above meanings of R ¹ , and preferably in each case independently of one another denote an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, where one or two non-adjacent CH ₂ - Groups can be replaced by -O-, -CH = CH-, -C≡C-, -CO-, -OCO- or -COO- so that O atoms are not directly linked together, and 11 is H or F. ,

The 1,4-phenylene groups in IV10 to IV19 and IV23 to IV25 can each independently be substituted one or more times by fluorine.

Particular preference is given to compounds of the formulas IV27 to IV31 and IV33 in which R ^{1 is} alkyl and R ^{2 is} alkyl or alkoxy, in each case having 1 to 7 C atoms. Preference is furthermore given to compounds of the formulas IV25 and IV31 in which L ^{1 is} F. Very particular preference is given to compounds of the formulas IV27.

R ¹ and R ² in the compounds of the formulas IV1 to IV5, IV7 to IV25, IV27 to IV31 and IV33 particularly preferably denote straight-chain alkyl or alkoxy having 1 to 12 C atoms.

• – eine oder mehrere Verbindungen der Formel I1a, worin X⁰ F ist,
• – eine oder mehrere Verbindungen der Formel I2a, worin X⁰ F ist,
• – eine oder mehrere Verbindungen der Formel IIa,
• – 1 bis 20, insbesondere 5 bis 15 Verbindungen der Formel I1a und/oder I2a,
• – mehr als 20%, insbesondere mehr als 30%, besonders bevorzugt mehr als 35% einer oder mehrerer Verbindungen der Formel I1a und/oder I2a,
• – 5 bis 50%, bevorzugt 10 bis 45% an Verbindungen der Formel I1a,
• – 10 bis 65%, bevorzugt 20 bis 55% an Verbindungen der Formel I2a,
• – 5 bis 60%, bevorzugt 15 bis 50% an Verbindungen der Formel IIa,
• – eine oder mehrere Verbindungen ausgewählt aus den Formeln IV6, IV26 und IV32,
• – eine oder mehrere Verbindungen der Formel V,

In particularly preferred embodiments, the nematic component of the media according to the invention contains

• One or more compounds of the formula I1a in which X ^{0 is} F,
• - one or more compounds of formula I2a in which X ⁰ is F,
• One or more compounds of the formula IIa,
• 1 to 20, in particular 5 to 15 compounds of the formula I1a and / or I2a,
• More than 20%, in particular more than 30%, more preferably more than 35% of one or more compounds of the formula I1a and / or I2a,
• From 5 to 50%, preferably from 10 to 45%, of compounds of the formula I1a,
• From 10 to 65%, preferably from 20 to 55%, of compounds of the formula I2a,
• From 5 to 60%, preferably from 15 to 50%, of compounds of the formula IIa,
• One or more compounds selected from the formulas IV6, IV26 and IV32,
• One or more compounds of the formula V,

In a further particularly preferred embodiment, the nematic component consists essentially of compounds selected from the formulas I1a, I2a, IIa, IV6, IV26, IV32 and V.

By suitable choice of the terminal radicals R ⁰ , R ¹ , R ² , R ³ , R ⁴ and X ⁰ in the compounds of the above formulas, the response times, the threshold voltage and other properties 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 ₃ (bend) and K ₁ (splay) in comparison to alkyl or alkoxy. 4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and smaller K ₃ / K ₁ values compared to alkyl and alkoxy radicals.

The optimum ratio of the individual compounds of the above formulas depends largely on the desired properties, on the choice of the compounds of the above formulas and on the choice of further optional components. Suitable proportions within the range given above can be easily determined on a case-by-case basis.

In the formulas mentioned above and below, the term "fluorinated alkyl or alkoxy having 1 to 3 C atoms" preferably denotes CF ₃ , OCF ₃ , CFH ₂ , OCFH ₂ , CF ₂ H, OCF ₂ H, C ₂ F ₅ , OC ₂ F ₅ , CFHCF ₃ , CFHCF ₂ H, CFHCFH ₂ , CH ₂ CF ₃ , CH ₂ CF ₂ H, CH ₂ CFH ₂ , CF ₂ CF ₂ H, CF ₂ CFH ₂ , OCFHCF ₃ , OCFHCF ₂ H, OCFHCFH ₂ , OCH ₂ CF ₃ , OCH ₂ CF ₂ H, OCH ₂ CFH ₂ , OCF ₂ CF ₂ H, OCF ₂ CFH ₂ , C ₃ F ₇ or OC ₃ F ₇ , in particular CF ₃ , OCF ₃ , CF ₂ H, OCF ₂ H, C ₂ F ₅ , OC ₂ F ₅ , CFHCF ₃ , CFHCF ₂ H, CFHCFH ₂ , CF ₂ CF ₂ H, CF ₂ CFH ₂ , OCFHCF ₃ , OCFHCF ₂ H, OCFHCFH ₂ , OCF ₂ CF ₂ H , OCF ₂ CFH ₂ , C ₃ F ₇ or OC ₃ F ₇ , more preferably OCF ₃ or OCF ₂ H.

The term "alkyl" includes straight-chain and branched alkyl groups having 1-7 carbon atoms, especially the straight-chain groups of methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups of 2-5 carbon atoms are generally preferred.

The term "alkenyl" includes straight-chain and branched alkenyl groups having 2-7 carbon atoms, especially 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 -4-alkenyl, C ₆ -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 of 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 term "fluoroalkyl" preferably includes straight-chain fluoro-end-capped groups, i. H. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions of the fluorine are not excluded.

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

Halogen is preferably F or Cl, in particular F.

If one of the abovementioned radicals denotes 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 tetradecoxy.

Oxaalkyl is preferably 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-oxadecyl.

If one of the abovementioned radicals denotes 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 one of the abovementioned radicals denotes an alkyl radical in which one CH ₂ group has been replaced by -O- and one by -CO-, these are preferably adjacent. Thus, they include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. Preferably, these are straight-chain and have 2 to 6 carbon atoms.

They therefore particularly mean acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, Propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl, 4 - (methoxycarbonyl) butyl.

If one of the abovementioned radicals denotes an alkyl radical in which one CH ₂ group has been replaced by unsubstituted or substituted -CH =CH- and one adjacent CH ₂ group has been replaced by CO or CO-O or O-CO, this may be straight-chain or be branched. Preferably, it is straight-chain and has 4 to 13 carbon atoms. It therefore particularly means acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3 Methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyl-oxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl, 9-methacryloyloxynonyl.

If one of the abovementioned radicals is an alkyl or alkenyl radical which is monosubstituted by CN or CF ₃ , this radical is preferably straight-chain. The substitution by CN or CF ₃ is in any position.

If one of the abovementioned radicals 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 ones Leftovers. For single substitution, the fluoro or chloro substituent may be in any position, but preferably in the ω position.

Branched wing group compounds may occasionally be of importance for better solubility in the common liquid crystalline base materials. But they may be particularly suitable as chiral dopants, if they are optically active.

Branched groups of this type usually contain no more than one chain branch. Preferred branched radicals are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2 Propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy.

If one of the abovementioned radicals represents an alkyl radical in which two or more CH ₂ groups have been replaced by -O- and / or -CO-O-, this may be straight-chain or branched. Preferably, it is branched and has 3 to 12 carbon atoms. It therefore particularly denotes bis-carboxymethyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxypentyl, 6, 6-bis-carboxy-hexyl, 7,7-bis-carboxyheptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl, 10,10-bis-carboxydecyl, bis (methoxycarbonyl) - methyl, 2,2-bis (methoxycarbonyl) ethyl, 3,3-bis (methoxycarbonyl) propyl, 4,4-bis (methoxycarbonyl) butyl, 5,5-bis (methoxycarbonyl) pentyl, 6,6-bis (methoxycarbonyl) hexyl, 7,7-bis (methoxycarbonyl) heptyl, 8,8-bis (methoxycarbonyl) octyl, bis (ethoxycarbonyl) methyl, 2,2-bis (ethoxycarbonyl) -ethyl, 3,3-bis (ethoxycarbonyl) -propyl, 4,4-bis (ethoxycarbonyl) -butyl, 5,5-bis (ethoxycarbonyl) -hexyl.

The optically active component of the CFRP media according to the invention contains one or more chiral dopants whose twisting power and concentration are chosen such that the helical pitch of the LC medium is less than or equal to 1 .mu.m.

The proportion of the optically active component in the CFRP media according to the invention is preferably ≦ 20%, in particular ≦ 10%, particularly preferably from 0.01 to 7%, very particularly preferably from 0.1 to 5%. The optically active component preferably contains 1 to 6, in particular 1, 2, 3 or 4 chiral dopants.

The chiral dopants should preferably have high helical twisting power (HTP) with low temperature dependence. Furthermore, they should have a good solubility in the nematic component and not impair the liquid crystalline properties of the LC medium or only to a slight extent. They may have the same or opposite sense of rotation and the same or opposite temperature dependence of the twist.

Particular preference is given to chiral dopants having an HTP of 20 μm ^-1 or more, in particular of 40 μm ^-1 or more, particularly preferably of 70 μm ^-1 or more.

ausgewählt aus folgenden Formeln

worin B, b, R⁵ und Z⁵ die in Formel XVII angegebene Bedeutung haben und Z⁵ insbesondere -OCO- oder eine Einfachbindung bedeutet.Particularly, chiral binaphthyl derivatives of the formula XVII

selected from the following formulas

wherein B, b, R ⁵ and Z ^{5 have} the meaning given in formula XVII and Z ^{5 is} in particular -OCO- or a single bond.

sind besonders bevorzugt.The dopants of the following formula

are particularly preferred.

• – einen oder mehrere Dotierstoffe der Formel XVII,
• – nicht mehr als einen Dotierstoff, vorzugsweise ausgewählt aus Formel XVII, vorzugsweise in einem Anteil von weniger als 8%, insbesondere weniger als 5% der Gesamtmischung (d. h. der Summe des Massenanteile aus nematischer und optisch aktiver Komponente).

In particularly preferred embodiments, the optically active component of the media according to the invention

• One or more dopants of the formula XVII,
• No more than one dopant, preferably selected from formula XVII, preferably in an amount of less than 8%, in particular less than 5% of the total mixture (ie the sum of the mass fractions of nematic and optically active component).

In a further particularly preferred embodiment, the media according to the invention contain 20% or less, in particular 0.01 to 10%, of the optically active component.

In particular, the chiral dopants of the above-mentioned formula XVII have a good solubility in the nematic component, and induce a cholesteric structure with high twist and low temperature dependence of the helical pitch and the reflection wavelength. As a result, even with the use of only one of these dopants, CFK media according to the invention having reflection colors in the visible wavelength range of high brilliance and low temperature dependency can be obtained in small amounts, which are particularly suitable for use in SSCT and PSCT displays.

This is a significant advantage over the CFRP media of the prior art, in which usually at least two dopants with the same sense of rotation and opposite temperature dependence of the twist are needed (for example, a dopant with positive temperature dependence, ie increase in twist with increasing temperature, and a dopant with negative temperature dependence) to achieve temperature compensation of the reflection wavelength. In addition, large amounts of dopants are often required in the known CFRP media to achieve reflection in the visible range.

A particularly preferred embodiment of the invention therefore relates to a CFRP medium and its use in CFRP displays as described above and below, wherein the chiral component contains not more than one chiral compound, preferably in an amount of less than 15%, in particular less than 10%, more preferably 5% or less. A CFRP medium of this preferred embodiment has a low dependence of the reflection wavelength λ on the temperature T over a wide temperature range.

The helical pitch of the medium is preferably from 130 nm to 1000 nm, in particular from 200 nm to 750 nm, particularly preferably from 300 nm to 450 nm.

Preferably, the helical pitch is selected so that the medium reflects light in the visible wavelength range. The term "visible wavelength range" or "visible spectrum" typically covers the range of wavelengths from 400 to 800 nm. However, in the preceding and following, this term is also intended to cover the range of wavelengths from 200 to 1200 nm, including the UV and infrared ( IR) range as well as the far UV and far IR range.

The reflection wavelength of the FK medium according to the invention is preferably in the range from 200 to 1500 nm, in particular 300 to 1200 nm, particularly preferably from 350 to 900 nm, very particularly preferably from 400 to 800 nm. Further preferred are FK media having a reflection wavelength of 400 to 700, in particular 400 to 600 nm.

The wavelengths given above and below refer to the half-width of the reflection band, unless otherwise specified.

Particular preference is given to CFRP media according to the invention having a temperature dependence dλ / dT of 0.6 nm / ° C. or less, in particular 0.3 nm / ° C. or less, very particularly preferably 0.15 nm / ° C. or less, preferably in the range between 0 and 50 ° C, in particular between - 20 and 60 ° C, more preferably between - 20 and 70 ° C, most preferably in the range of - 20 ° C up to a temperature of 10 ° C, in particular 5 ° C, below the clearing point.

Unless otherwise indicated, dλ / dT means the local slope of the function λ (T), where a nonlinear function λ (T) is approximately described by a 2nd or 3rd degree polynomial.

Another object of the invention is the use of the CFRP media according to the invention for electro-optical purposes.

Another object of the invention is also the use of CFRP media according to the invention for electro-optical display, in particular in SSCT, PSCT or flexoelectric displays with two plane-parallel support plates, which form a cell with a border, and an in-cell cholesteric liquid crystal mixture.

Another object of the invention is the use of the CFRP media according to the invention for electro-optical active matrix displays, in particular in AM-CFK displays, preferably an AM-SSCT or PSCT displays, with two plane-parallel support plates, which form a cell with a border , integrated non-linear elements for switching individual pixels on the carrier plates, and an in-cell cholesteric liquid crystal mixture, which preferably has a positive dielectric anisotropy and a high resistivity.

The construction of bistable SSCT and PSCT cells is, for example, in WO 92/19695 . WO 93/23496 . US 5,453,863 or US 5,493,430 described. The structure of active matrix CFRP displays is, for example, in WO 02/086855 and US 2002-0149552 described.

The ratio d / p between the layer thickness of the liquid crystal cell d (distance between the carrier plates) in a CFRP display and natural helical pitch p of the CFRP medium is preferably greater than 1, in particular in the range from 2 to 20, particularly preferably from 3 to 15, very particularly preferably from 4 to 10.

The CFRP media according to the invention enable a significant expansion of the available parameter space. Thus, the achievable combinations of reflection wavelength, birefringence, clearing point, viscosity, thermal and UV stability and dielectric anisotropy far exceed previous materials from the prior art and make the media according to the invention particularly suitable for use in CFRP displays.

The CFRP media of the invention preferably have a cholesteric phase to -20 ° C and preferably to -30 ° C, more preferably to -40 ° C, and clearing points above 70 ° C, preferably above 90 ° C, more preferably above 110 ° C. , The dielectric anisotropy Δε is preferably ≥ 5, in particular ≥ 10, very particularly preferably ≥ 15. The birefringence Δn is preferably ≦ 0.15, in particular ≦ 0.10 and preferably ≥ 0.03, in particular ≥ 0.05, preferably between 0 , 04 and 0.08.

At the same time, the CFRP media according to the invention have low viscosity values and high resistivity values, which means that excellent CFRP displays, in particular AM CFRP displays, can be achieved. In particular, the mixtures are characterized by low operating voltages.

It is understood that by suitable choice of the components of the mixtures according to the invention also higher clearing points (eg above 120 ° C) can be realized at higher threshold voltages or lower clearing points at lower threshold voltages to obtain the other advantageous properties. Likewise, mixtures can be obtained with a larger Δε and thus lower thresholds at correspondingly little increased viscosities.

The width of the cholesteric phase region is preferably at least 90 ° C., in particular at least 100 ° C. Preferably, this range extends at least from -20 ° to + 60 ° C, more preferably at least from -20 ° to + 70 ° C, most preferably at least from -20 ° to + 80 ° C.

The UV stability of the CFRP media according to the invention is considerably better, d. H. they show a much smaller change in the reflection wavelength and operating voltage under UV exposure.

A further preferred embodiment of the present invention relates to a CFRP medium according to the invention which contains one or more compounds having at least one polymerizable group. Such CFRP media are particularly suitable for use in, for example, polymer gel or PSCT displays. The polymerizable compounds may be part of the nematic and / or chiral component or form an additional component of the medium.

Suitable polymerizable compounds are known in the art and described in the prior art. The polymerizable compounds may additionally be mesogenic or liquid-crystalline. They may contain one or more, preferably two polymerizable groups. Typical examples of non-mesogenic compounds having two polymerizable groups are alkyl diacrylates or alkyl dimethacrylates having alkyl groups of 1 to 20 carbon atoms. Typical examples of non-mesogenic compounds having more than two polymerizable groups are trimethylolpropane trimethacrylate or pentaerythritol tetraacrylate. Typical examples of mesogenic or liquid crystalline polymerizable compounds are, for example, in WO 93/22397 . EP 0 261 712 . DE 195 04 224 . WO 95/22586 and WO 97/00600 described.

Examples of particularly suitable and preferred chiral and achiral polymerizable mono- and di-reactive mesogenic compounds (reactive mesogens) are shown in the following list, which is intended to illustrate the invention without limiting it

In the formulas shown above, P is a polymerisable group, preferably acrylic, methacrylic, vinyl, vinyloxy, propenyl ether, epoxy, oxetane or styryl, x and y are each independently an integer from 1 to 12, D and E are each independently 1, 4-phenylene, which may also be substituted by L ¹ mono-, di-, tri- or tetra-substituted, or 1,4-cyclohexylene, u and v are each independently 0 or 1, Z ⁰ -COO-, -OCO-, - CH ₂ CH ₂ -, -CH = CH-, -C≡C- or a single bond, R ^{0 is} a polar or nonpolar group, Ter a terpene residue such. Menthyl, Chol a cholesteryl group, r 0, 1, 2, 3 or 4, L, L ¹ and L ^{2 are} each independently H, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy with 1 to 7 carbon atoms. The phenyl rings in the formulas shown above are optionally substituted by L 1, 2, 3 or 4 times.

The term "polar group" in this context means a group selected from F, Cl, CN, NO ₂ , OH, OCH ₃ , OCN, SCN, optionally fluorinated alkylcarbonyl, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy having up to 4 C atoms or mono -, oligo- or polyfluorinated alkyl or alkoxy having 1 to 4 carbon atoms. The term "non-polar group" in this context means optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy having 1 or more, preferably 1 to 12, carbon atoms, which does not fall under the above definition "polar group".

In addition to the compounds of the above formulas, the CFRP media may contain one or more other components to optimize various properties.

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

The preparation of the liquid crystal mixtures which can be used according to the invention is carried out in a conventional manner. In general, the desired amount of the components used in lesser amount is dissolved in the constituent of the main component, expediently at elevated temperature. It is also possible to use solutions of the components in an organic solvent, e.g. B. in acetone, chloroform or methanol, to mix and remove the solvent after mixing again, for example by distillation.

The liquid-crystal mixtures according to the invention may also contain other additives such as, for example, one or more stabilizers or antioxidants.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, wherein the transformation into chemical formulas according to following Tables A and B takes place. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m C atoms. The coding according to Table B is self-evident. In Table A, only the acronym for the main body is given. In the individual case, a code for the substituents R ¹ , R ² , L ¹ L ² and L ³ follows separately from the acronym for the main body with a dash: Code for R ¹ , R ¹ R ² , L ¹ , L ² , L ³ R ² L ¹ L ² L ³ nm C _n H _{2n + 1} C _m H _{2m + 1} H H H n Om C _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 / nOT 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:

Tabelle C (Dotierstoffe):

Preferred mixture components are given in Tables A, B and C. Table A: (L ¹ , L ² , L ³ = H or F)

Table B:

Table C (dopants):

Table D

Suitable stabilizers and antioxidants for LC mixtures are mentioned below (n = 0-10, terminal methyl groups are not shown):

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

Above and below, percentages are by weight. All temperatures are in degrees Celsius. Mp means melting point, bp = clearing point. Furthermore, K = crystalline state, S = smectic phase, N = nematic phase, Ch = cholesteric phase and I = isotropic phase. The information between these symbols represents the transition temperatures.

Δn

optische Anisotropie bei 589 nm und 20°C

n_e

außerordentlicher Brechungsindex bei 589 nm und 20°C

Δε

dielektrische Anisotropie bei 20°C

ε_||

Dielektrizitätskonstante parallel zu den Moleküllängsachsen

γ₁

Rotationsviskosität [mPa·sec], soweit nicht anders angegeben bei 20°C

λ

Reflektionswellenlänge [nm], soweit nicht anders angegeben bei 20°C

Δλ

maximale Schwankung der Reflektionswellenlänge [nm] im angegebenen Temperaturbereich, soweit nicht anders angegeben zwischen –20 und +70°C

Furthermore, the following abbreviations are used

.DELTA.n

optical anisotropy at 589 nm and 20 ° C

n _e

extraordinary refractive index at 589 nm and 20 ° C

Δε

dielectric anisotropy at 20 ° C

ε _||

Dielectric constant parallel to the molecular axes

γ ₁

Rotational viscosity [mPa.sec] unless otherwise stated at 20 ° C

λ

Reflection wavelength [nm], unless otherwise stated at 20 ° C

Δλ

maximum fluctuation of the reflection wavelength [nm] in the specified temperature range, unless otherwise specified between -20 and + 70 ° C

The twisting power HTP ("helical twisting power") of a chiral compound which generates a helically twisted superstructure in a liquid crystalline mixture is given by the equation HTP = (p · c) ^-1 [μm ^-1 ].

In this formula, p denotes the helical pitch of the helically twisted phase in μm and c the concentration of the chiral compound (a value of 0.01 for c corresponds to a concentration of 1% by weight, for example). Unless otherwise stated, the preceding and following HTP values refer to a temperature of 20 ° C and the commercially available neutral nematic TN-host mixture MLC-6260 (Merck KGaA, Darmstadt).

For the experimental determination of the physical parameters, according to "Licristal, Physical Properties of Liquid Crystals, Description of the Measurement Methods", ed. W. Becker, Merck KGaA, Darmstadt, revised edition, 1998, proceeded.

example 1

und besitzt eine Reflektionswellenlänge λ von 400 nm.A cholesteric mixture C1 contains 96.98% of a nematic component N1 consisting of CCH 501 7.0% Kp. 86 CH-33 3.0% .DELTA.n 0.0645 CH-35 3.0% n _e 1.5325 CH-43 3.0% Δε +10.2 CCP 2F.FF 7.0% CCP 3F.FF 5.0% CCZU-2-F 6.0% CCZU-3-F 15.0% CCZU-5-F 6.0% CDU-2-F 9.0% CDU-3-F 9.0% CDU-5-F 16.0% CCH 3CF3 7.0% CCH 5CF3 8.0% CCPC-34 3.0% CCPC-33 3.0% and 3.02% of the chiral dopant R-5011 of the following formula

and has a reflection wavelength λ of 400 nm.

Claims (8)

A liquid-crystalline medium having a helically twisted structure comprising a nematic component and an optically active component, characterized in that the optically active component contains one or more chiral compounds of the formula XVII

wherein B is 1,4-phenylene, which may also be mono-, di- or trisubstituted by L, or 1,4-cyclohexylene, LH, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1-7 C atoms, b is 0, 1 or 2, Z ^{5 is} -COO-, -OCO-, -CH ₂ CH ₂ - or a single bond, and R ^{5 is} alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy with 1- 12 C atoms, the nematic component denotes one or more compounds selected from the following formulas I1a, I2a and IIa,

wherein R ^{1 is} H, an unsubstituted, an alkyl or alkenyl radical having 1 to 20 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, in which radicals also one or more CH ₂ groups are each independently of one another -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -CC- may be replaced so that O atoms are not directly linked together, X ⁰ F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 carbon atoms, and one or more compounds selected from the formulas IV6, IV26, IV32 and V

wherein R ¹ and R ² each independently have one of the meanings given for R ¹ contains. Medium according to claim 1, characterized in that it contains more than 50% of one or more compounds with a 3,4,5-trifluorophenyl group. Medium according to one of Claims 1 and 2, characterized in that the nematic component contains 5 to 50% of compounds of the formula I1a, 10 to 65% of compounds of the formula I2a, 5 to 60% of compounds of the formula IIa. Medium according to one or more of Claims 1 to 4, characterized in that it has a reflection wavelength in the range from 400 to 800 nm. Use of a medium according to one or more of claims 1 to 4 for electro-optical purposes. Use of a medium according to claim 5 in an electro-optical liquid crystal display. Use of a medium according to claim 6, in a cholesteric, SSCT, PSCT or flexoelectric display. Use of a medium according to one or more of claims 6 and 7 in an active matrix display.