DE4130660A1 - New 1,2-bis:acyloxy-1-phenyl-ethane cpds. used in large LCD - e.g. for lap-top personal computer, with aromatic or cycloaliphatic acyl gps., to avoid chromatographic defect - Google Patents

Abstract

Liquid crystal (LC) cell with a large surface area has a twisted nematic LC layer with positive dielectric anisotropy between 2 substrates with electrode and surface orientation coatings. The LC layer consists of a nematic LC material and, as optically active component, 1,2-bis-acyloxy-1-phenylethane cpd(s)., having aromatic or cycloaliphatic acyl gps., of formula (I) and the 1,2-bis-acyloxy-1-phenylethane cpds. (I) are new: (where R1-3 indpendently = H, halogen, CF3, CN or linear or branched 1-7C alkyl, opt. with -O- or -CH=CH- in place of one or 2 nonadjacent CH2 gps. and at least one of R1 and R2 must = H; Y = H, halogen, CN or a (fluoro)alkyl or alkenyl gp. with up to 12; gp. (A) where the 1,4-phenylene gp. can be 1 or 2 lateral F substit(s). (I) is prepd. by standard methods, e.g. as described in Houben-Weyl, Methoden de Organischen Chemie, Georg-Thiema-Verlag, Stuffgart, and esp. in EP 168043. USE/ADVANTAGE - (I) are used as chiral depants. The LC layer has high twist, with a twist angle of at least 100 deg. and the substrate surface area is at least 16 sq.cm. (I) are used in LCDs, esp. STN cells. Their optical properties are not or only slightly impaired by chromatographic effects, making them useful e.g. as displays for laptop PCs.

Description

The invention relates to large-area liquid crystal cells the

• an electrically controllable, dielectrically positive, twisted nematic liquid crystal layer between 2 Contains substrates that border a cell form,
• - Electrode layers with overlying orientation has layers on the insides of the substrates, wherein by the orientation layers one in wesentli Chen parallel edge orientation of the liquid crystal Molecules take place and
• - At least one device for linear polarization of Contains light in such an arrangement that the Light before entering the liquid crystal layer and after leaving this at least once each one Polarization device happens.

Liquid crystal cells with twist angles y between about 80 ° and 100 ° are commonly referred to as TN cells (twi sted nematic); the structure of such cells is z. In Thermotropic Liquid Crystals, G.W: Gray [ed.], S. 77 ff  described. Liquid crystal cells with y <100 ° i. a. STN cells (supertwisted nematic) while using for cells ψ <80 ° in P 40 10 503 the designation LTN cell (low-twisted nematic) has been proposed. A short description of STN displays can be found z. In B.S. Scheuble, Liquid Crys tal Displays with high Information Content, Contacts, 1/88, Pp. 34-38, Darmstadt.

In LTN and TN liquid crystal cells, the twist angle ψ usually by aligning the Orientierungsschich defined. For setting higher twist angle ψ <90 ° contains the liquid crystal i. a. a doping component, the consists of one or more chiral dopants. It But it is also possible that smaller test angle ψ by a cholesteric pitch p of the liquid crystal are given. Even if the twist angle does not exceed the pitch of the Liquid crystal is adjusted, i. a. a chiral one Dopant in low concentrations to avoid Reverse twist and reverse tilt added as z. In DE 25 07 524 is described.

The twisting power of dopants (helical twisting power) is usually defined as

where p is the pitch of the liquid crystal, d. H. the distance, along which the helix axis is rotated by 2π, and c is the  Concentration of the doping component means. The Konzentra tion is usually given in mass percentages, so that HTP has the dimension of a reciprocal length.

The HTP of chiral dopants is typically 1-100 μm ^-1 . Dopants with high HTP of z. B. more than 15 microns ^-1 , are particularly desirable for STN applications, as a high twist angle can be obtained at relatively small or smaller layer thicknesses of the liquid crystal layer, resulting in a reduction of the switching times.

Chiral dopants with high HTP are z. As described in EP 01 68 043. So z. B. the there specified (S) -1,2-bis (p-trans-4-pentylcyclohexylbenzoyloxy) -1-phenyl-ethane in the liquid crystal mixture ZLI-2806 (E. Merck, Darmstadt) for the Verdrillungsvermögen a value of HTP = 32.6 μm ^-1 , on.

When manufacturing a liquid crystal cell, first the front and rear substrate with functional layers So each with a possibly structured electrode layer and an overlying orientation layer; Occasionally, other layers such. B. Insulating layers or dye-containing layers in colored Ads applied. One of the two substrates will then usually provided with a Kleberandstreifen while on the other substrate in a horizontal position small distance holder (spacer) are applied. That with the glue edge Striped substrate is transferred to the other, with spacers the substrate is pressed on and the glue is applied in one Tempering process cured. It should be noted that the  Kleberandstreifen is not completely closed, so that the Interior between the substrates and the adhesive edge strip communicates with the outside space via a small hole. The assembly thus produced is placed in a vacuum vessel evacuated, to the opening in the adhesive edge strip is a vessel prepared with liquid crystal and then is vented. Thereby the liquid crystal is in the evacuated interior pressed. Subsequently, the vessel is closed. This one described preparation and filling of the liquid crystal cell is to be understood as an example and is intended to be the invention explain without limiting it; modified filling methods are z. Example described in EP 03 91 143.

However, it has been shown that when filling cells after with the described method or also with modified methods Liquid-crystal mixtures, with the usual doping are offset substances to observe chromatographic effects are, which lead to an enrichment of the dopants at the Phase boundary liquid crystal / substrate lead; will continue in many cases a particularly low dopant concentration in observed near the filling hole. Due to the inhomogeneity of Dopant concentration in the liquid crystal layer resul causes a significant deterioration of the electro-optical Properties of the liquid crystal cell. This Chromatogra phieeffekt occurs particularly disadvantageous in large areas Cells and / or cells with highly twisted nematic Liquid crystals on.

Since large-area STN cells with an area of z. B. more than 10 cm × 10 cm increasingly, z. B. as displays of laptop PC's There was an urgent need for new ones Dopants and liquid crystal containing them  mixtures, which when filling cells no or one much lower chromatographic effect than conventional ones Effect liquid crystal mixtures.

The object of the present invention was to Indicate liquid crystal displays and in particular STN cells, their optical properties are not or only to a lesser extent Dimensions are affected by the chromatographic effect. Another object of the present invention was in the provision of new dopants and these contain the liquid crystal mixtures used in the filling of Liquid crystal cells no or a much lower Chromatography effect result than conventional Materials.

It has been found that these tasks are solved by the Provision of liquid crystal displays with doped nematic liquid crystals whose doping component is reduced at least one chiral component of the formula I contains, as well as by the provision of the new dopants of the formula I.

The invention thus relates to a large area Liquid crystal cell and in particular a STN cell one between two substrates, which with electrode and provided overlying surface orientation layers are, and polarizing devices arranged twisted nematic liquid crystal layer with positive dielectric shear anisotropy, consisting of a nematic Liquid crystal material and an optically active Kompo nente, characterized in that the optically active Kompo component contains one or more compounds of the formula I.  

wherein
R¹, R² and R³ are each independently H, halogen, CF₃, CN or a straight or branched chain alkyl group having 1-7 C atoms, wherein also one or two non-adjacent CH₂ groups be replaced by -O- or CH = CH- with the proviso that at least one of R¹ and R² is H,
Y is H, halogen, CN or an alkyl, alkenyl or fluoroalkyl group having up to 12 C atoms and

wherein the 1,4-phenylene groups laterally by 1 or 2 F atoms can be replaced mean.

The invention further relates to the new chiral Dopants of the formula I and these containing Liquid crystal mixtures.  

The invention further relates to a method for verrin with the filling of liquid crystal cells with doped nematic liquid crystals observed chroma tographieeffekts, characterized in that the liquid crystal to produce the twist one or more Compounds of formula I are added.

The compounds of formula I include chiral ethane derivatives of the formulas Ia-Id, which have 2 rings in the main chain:

wherein

means.  

The compounds of formula I further include chiral ethane derivatives of the formulas Ie-Iq, which contain 3 rings in the main chain respectively:

The compounds of formula I further include chiral ethane derivatives of the formulas Ir-Iz, which are 4 rings in the main chain respectively:

In the compounds of the formula Ia-Iz, at least one of R¹ and R² is H. The other is preferably H or n-alkyl or n-alkoxy having 1-7 C atoms, in addition also n-alkoxymethyl or n-alkoxyethyl with 1-6 C atoms and n-Al  kenyl with 1-8 C atoms. Particularly preferred is the other H, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, Methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, Methoxymethyl, ethoxymethyl, propoxymethyl, methoxyethyl, ethoxyethyl, propoxyethyl, vinyl, prop-1 or prop-2-enyl, But-1, 2- or 3-enyl or pent-1, 2-, 3- or 4-enyl.

Furthermore, that of the two radicals R ¹ and R ² , which is not H, also a polar radical F, Cl, CF ₃ or CN and in particular F, Cl or CF ₃ . If this non-H radical is an optionally substituted alkyl group, this is preferably straight-chain; However, it can also be branched and usually contains nothing more than a chain branching. Compounds of the formulas Ia-Id which, in addition to the asymmetric C atom in the ethylene group, contain a further asymmetric C atom in that of the two radicals R ¹ and R ² which does not denote H, can be a largely temperature-independent HTP and / or higher Have values for the HTPs as the corresponding single-chiral compounds.

In the compounds of the formulas Ia-Iz, this means that Asymmetric carbon atom of the ethylene group bound radical Q a Group of formula

R³ is preferably H or an alkyl, alkoxy or alkenyl group having 1-7 C atoms, but in particular H, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy , Vinyl, prop-1- or 2-enyl, but-1, 2- or 3-enyl or pent-1-, 2-, 3- or 4-enyl. In addition, R ^{3 can} also be F, Cl, CF ₃ or CN and in particular F, Cl or CN. Particularly preferably, R ^{3 is} H or methyl.

The 1,4-phenylene group of the radical Q can be unsubstituted or substituted in the 2- or 3-position by halogen, CN or an alkyl, alkenyl or fluoroalkyl group having up to 12 C atoms and in particular 1-5 C atoms. The 1,4-phenylene group of the radical Q is preferably unsubstituted or substituted by F, Cl, C, CH ₃ , OCH ₃ or CF ₃ in the 2- or 3-position.

In the following table, the meaning of R¹, R², R³ and Y in particularly preferred compounds of the formulas Ia-Id where Y.2 or Y.3 is a substitution of the phenylene group of Q in the 2- or 3-position means:

Particular preference is given to chiral dopants of the formula I in which both R ¹ and R ^{2 are} H. It has surprisingly been found that liquid crystal mixtures whose dopant contains at least one compound of formula I with R ¹ = R ² = H, cause virtually no or only a very small Chromatogra phieeffekt when filling liquid crystal cells. These dopants of the formula I where R ¹ = R ² = H are also characterized by favorable values for the HTP and their temperature dependence.

Very particular preference is given to compounds of the formula Ia-Id which have 2 rings in the main chain and for which R¹ = R² = H.

Preference is furthermore given to compounds of the formula I in which R ³ , Y.2 and Y.3 are H.

Of particular interest is the following single compound of the formula Id, by favorable own and manufacturability is characterized and can be purified by recrystallization:

The compounds of the formula I structurally closely adjacent compounds are given in EP 01 68 043. However, the wing groups of the compounds given therein can not be H, while the gist of the present invention is the recognition that compounds of formula I in which at least one of the two wing groups R ¹ and R ² signifies H, have particularly favorable properties, and that when filling liquid crystal cells with liquid crystal mixtures whose doping component comprises at least one compound of the formula I, a chromatographic effect is not or only to a small extent observed.

The compounds of the formula I are known per se Methods described in the literature (eg Houben Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart Bd IX, p. 867 ff.) Are described, under  Reaction conditions for the reactions mentioned are known and suitable.

Preferably, the compounds of the formula I according to the in. In EP 01 68 043 described methods.

It has been found that the avoidance or at least clearly reduce the chromatographic effect independently of the special filling technique is. So was both at the initially briefly outlined filling method as well as in the EP 03 81 142 modifications no Chromatogra observed phieeffekt.

The liquid crystal cells according to the invention, the active component of which contains one or more compounds of the formula I and in particular one or more of the compounds of the formula I which are indicated as preferred, have twist angles between 0 ° and 600 °. A particularly significant reduction in the chromatographic effects was observed in highly twisted and / or large-area cells according to the invention. For example, liquid crystal cells according to the invention which have a twist angle ψ 100 ° and in particular ψ 180 ° are preferred. The substrate surface of inventive liquid crystal cells is preferably A 25 cm ² , in particular A 36 cm ² and most preferably A 49 cm ² .

The used in the liquid crystal cells according to the invention th liquid crystal mixtures contain a dielectric positive nematic liquid crystal material, to the Dotie tion, an optically active component containing at least a compound of formula I is added. The selection of the nematic liquid crystal material, which is usually  2-45 and especially 3-39 components is not very critical. The components are preferably selected from nematic or nematogenic (monotropic or isotropic) Substances, in particular substances from the classes of Biphenyls, terphenyls, phenyl or cyclohexyl benzoates, Cyclohexane-carboxylic acid phenyl or cyclohexyl esters, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or Cyclohexyl ester of cyclohexylcyclohexanecarboxylic acid, cyclo hexylphenyl ester of benzoic acid, cyclohexane carboxylic acid or cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, Cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexyl cyclohexanes, cyclohexylcyclohexenes, cyclohexylcyclohexyl cyclohexenes, 1,4-biscyclohexylbenzenes, 4,4'-biscyclohexyl biphenyls, phenyl or cyclohexylpyrimidines, phenyl or Cyclohexyl-1,3-dithiane, 1,2-diphenylethanes, 1,2-dicyclohexylethane, 1,2-dicyclohexylethane, 1-phenyl-2- cyclohexylethane, 1-cyclohexyl-2- (4-phenylcyclohexy) ethane, 1-Cyclohexyl-2-biphenylethane, 1-phenyl-2-cyclohexylphenyl ethane and tolane.

The 1,4-phenylene groups in these compounds can also be fluorinated.

It is furthermore preferably possible to use according to the invention compounds which can be characterized by the formulas 1, 2, 3, 4 and 5:
R'-LER '' (1)

R'-L-COO-E-R '' (2)

R'-L-OOC-E-R '' (3)

R'-L-CH₂CH₂-E-R '' (4)

R'-L-CC-E-R '' (5)

In formulas 1, 2, 3, 4 and 5, L and E are the same or may be different, each independently -Cyc, -Phe-Phe, -Phe-Cyc, -Cyc-Cyc, -pyr-, -Dio, -G-Phe- and G-Cyc and their mirror images formed group, wherein Phe unsubstituted or substituted by fluorine 1,4- Phenylene, cyc trans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio 1,3-diox an-2,5-diyl and G 2- (trans-1,4-cyclohexyl) -ethyl, pyrimi din-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl mean.

Preferably, one of L and E is Cyc, Phe or Pyr. e is preferably Cyc, Phe or Phe-Cyc. Preferably ent th the materials of the invention one or more Components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein L and E are selected from the group cyc, Phe and Pyr and at the same time one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein one of L and E is selected from the group Cyc, Phe and Pyr and the other radical is selected from the Group -Phe-Phe, -Phe-Cyc, -Cyc-Cyc, -G-Phe and -G-Cyc-, and optionally one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein the Radicals L and E are selected from the group -Phe-Cyc-, -Cyc-Cyc, G-Phe and -G-Cyc.

R 'and R "in the compounds of sub-formulas 1a, 2a, 3a, 4a and 5a are each independently of one another alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. In most of these compounds R 'and R "are different from each other, one of these radicals is usually alkyl or alkenyl. In the compounds of part formulas 1b, 2b, 3b, 4b and 5b, R "is -CN, -CF ₃ , -OCF ₃ , F, Cl or -NCS; R has the meaning given in the compounds of sub-formulas 1a to 5a and is preferably alkyl or alkenyl. More preferably R "is selected from the group consisting of -F, Cl, CF ₃ and -OCF ₃ . But other variants of the proposed Substi tuenten in the compounds of formulas 1, 2, 3, 4 and 5 are in use. Many such substances or mixtures thereof are commercially available. All of these substances are available by methods known from the literature or in analogy thereto.

The liquid-crystal materials used in the systems according to the invention preferably also contain, in addition to components from the group of compounds 1a, 2a, 3a, 4a and 5a (group 1), components from the group of compounds 1b, 2b, 3b, 4b and 5b (group 2) whose shares are preferably as follows:
Group 1: 20 to 90%, in particular 30 to 90%,
Group 2: 10 to 80%, especially 10 to 50%.

The dielectrically positive, nematic liquid crystal mixtures contain in addition to the nematic liquid crystal material is an optically active Component consisting of one or more chiral mesogenic or non-mesogenic compounds, of which minde at least one is a compound of formula I. The invention According to used liquid crystal mixtures contain preferential example, 0.5-25% and especially 2.5-20 mass percent Compounds of the formula I.  

Liquid crystal mixtures containing 1-8 and in particular 1, 2 or 3 compounds of formula I are preferred.

The optically active component of the invention used Liquid-crystal mixtures can, in addition to compounds of the formula I contain further chiral compounds. The relationship out the mass fraction of the compounds of formula I to the Liquid crystal mixture to the mass fraction of the optical active component is preferably 0.1 and in particular 0.2-1; this ratio is not particularly preferred less than 0.25.

The liquid crystal mixtures used according to the invention can add other additives to modify and optimize the electro-optical properties of the cells according to the invention z. B. with regard to the particular application. Such additives are known in the art and in the Lite described. So z. B. pleochroic dyes for the production of colored electro-optical systems or sub punching to change the dielectric anisotropy, the Viscosity and / or the temperature dependence elektroopti shear parameters of the liquid crystals are added. Derar tige substances are z. In H. Kelker, R. Hatz, Handbook of Liguid Crystals, Verlag Chemie, Weinheim, 1980 and in the DE-OS 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430, 28 53 728 and 29 02 177 described.

The preparation of erfindungsgmäß usable liquid crystal mixtures is carried out in a conventional manner. In the Usually, the desired amount will be in lesser quantity used components in the main component  Components dissolved, expedient at elevated temperature. It is also possible solutions of the components in an organi rule solvent, for. In acetone, chloroform or metha nol, to mix and the solvent after mixing to remove again, for example by distillation.

The electrooptical cells according to the invention are distinguished by good electro-optic, not by chromatographic effect impaired properties. These cells come with it as well as the inventive method for filling Liquid crystal cells because of the significantly reduced Aus shot at the filled displays a considerable economic economic significance.

The following examples are intended to explain the invention, without limiting it. Above and below mean percent The information is percent by weight and all temperatures are in degrees Celsius indicated. "Usual processing" means: one gives Water, extracted with methylene chloride, The organic phase is dried, evaporated and purified Product by crystallization and / or by chromatography.

example 1

According to Example 2 of EP 01 68 043 is optically active 1,2-Bis-benzoyloxy-1-phenylethane from benzoic acid chloride and (S) -phenyl-1,2-ethanediol. The melting point is Mp = 83.0 ° C.  

Analog are produced:
1,2-bis-benzoyloxy-1- (4-methylphenyl) -ethane
1,2-bis-benzoyloxy-1- (4-fluorophenyl) ethane
1,2-bis-benzoyloxy-1- (3,4-difluorophenyl) -ethane
1-benzoyloxy-1-phenyl-2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-ethylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-propylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-butylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-pentylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-hexylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-heptylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-octylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-nonylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-decylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-undecylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-dodecylbenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-methoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-ethoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-propoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-butoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-pentoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-hexoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-heptoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-octoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-nonoxybenzoyloxy) ethane
1-benzoyloxy-1-phenyl-2- (p-decoxybenzoyloxy) ethane

1-benzoyloxy-1- (p-methylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-ethylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-propylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-butylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-pentylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-hexylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-heptylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-octylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-nonylphenyl) -2- (p-methylbenzoyloxy) ethane
1-benzoyloxy-1- (p-decylphenyl) -2- (p-methylbenzoyloxy) ethane
1- (p-methylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Ethylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Propylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-butylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Pentylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Hexylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Heptylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Octylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Nonylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Decylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Undecylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Dodecylbenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-methoxybenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Ethoxybenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Propoxybenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Butoxybenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Pentoxybenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Hexoxybenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Heptoxybenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-Octoxybenzoyloxy) -1-phenyl-2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-methylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-ethylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-propylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-butylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-pentylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-hexylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-heptylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-octylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-nonylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-decylbenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-methoxybenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-ethoxybenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-propoxybenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-butoxybenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-hexoxybenzoyloxy) -2-benzoyloxy-ethane
1- (p-methylphenyl) -1- (p-octoxybenzoyloxy) -2-benzoyloxy-ethane

example 2

A liquid crystal mixture containing the following components contains

5.0% of 4- (trans-4-ethylcyclohexyl) benzonitrile
15.0% of 4- (trans-4-propylcyclohexyl) benzonitrile
11.0% of 4- (trans-4-butylcyclohexyl) benzonitrile
21.0% of 4- (trans-4-pentylcyclohexyl) benzonitrile
11.0% of 4- (trans-4-heptylcyclohexyl) benzonitrile
5.0% of 4- (trans-4-propylcyclohexyl) -1-ethylbenzene
12.0% of 4- (trans-4-propylcyclohexyl) -4'-ethylbiphenyl
10.0% of 4- (trans-4-pentylcyclohexyl) -4'-ethylbiphenyl
4.0% of 4- (trans-4-propylcyclohexyl) -4 '- (trans-4-propylcyclohexyl) -biphenyl
6.0% of 4- (trans-4-pentylcyclohexyl) -4 '- (trans-4-propylcyclohexyl) biphenyl

and having the following physical parameters

Melting point | -21 ° C clearing point 85 ° C viscosity 21 mm²s ^-1 (20 ° C) birefringence 0.14 (20 ° C, 589 nm)

is in the experimental part A with 0.26% (S) -1,2-bis (p-trans-4-pen tylcyclohexylbenzoyloxy) -1-phenylethane (described in EP 01 68 043) and in Experimental Part B with 0.38% (S) -1,2-bis (ben zoyloxy) -1-phenylethane.

The mixtures obtained in test parts A and B were in cells with rectangular substrates of dimensions 4 cm × 20 cm filled, wherein in both experimental parts STN-Zel received with the following parameters:

Twist angle | 240 ° cell thickness 6.5 μm

The two experimental parts A and B were each 10 times carried out. It was found in experiment part A that about 70-80% of conventional cells so distinct electro-optical Deficiencies (formation of striped domains in the Area around the filling opening, optical inhomogeneities) that  they are to be described as unusable. In contrast, revealed in test part B for the cells according to the invention only a committee of about 10%.

Claims (5)

1. A large-area liquid crystal cell of a sandwiched between two substrates, which are provided with electrode and overlying surface orientation layers, and polarizing devices arranged ver twisted nematic liquid crystal layer with positive dielectric anisotropy consisting of a nematic liquid crystal material and an optically active component, characterized in that contains optically active component one or more compounds of formula I, wherein
R¹, R² and R³ are each independently H, halogen, CF₃, CN or a straight or branched chain alkyl group having 1-7 C atoms, wherein also one or two non-adjacent CH₂ groups be replaced by -O- or CH = CH- with the proviso that at least one of R¹ and R² is H,
Y is H, halogen, CN or an alkyl, alkenyl or fluoroalkyl group having up to 12 C atoms and wherein the 1,4-phenylene groups may laterally be substituted by 1 or 2 F atoms,
mean. 2. Cell according to claim 1, characterized in that the nematic liquid crystal layer hochverdrillt with a twist angle ψ 100 °. 3. Cell according to claim 1, characterized in that the Substrate area A is 16 cm². 4. Chiral compounds of the formula I. 5. liquid crystal mixtures containing a Dotierkompo which at least one chiral compound of the Formula I has.