CH640259A5 - LIQUID CRYSTAL SYSTEMS AND ELECTROOPTICAL DISPLAYS. - Google Patents

Description

The invention relates to combinations of pleochroic N-substituted cyclic derivatives of mono- or diaminoanthraquinones with dielectric positive nematic liquid crystals and electro-optical display systems in which these combinations are used.

Electro-optical devices using liquid crystals usually have two transparent flat plates with very thin transparent electrodes on their inwardly facing surfaces that are a few microns to a few tens of microns apart and include a liquid crystalline material. These plates are referred to below as the container wall. When an electrical field acts on the liquid crystal, the optical properties of the liquid crystal layer change. 30 Heilmeier and Zanoni, Applied Physics Letters, vol. 13, pp. 91-92 (1968) describe that when pleochroic dyes are combined with nematic liquid crystals in such a device, the pleochroic colors of the dyestuff when the electrical contact is applied and switched off Field occur. Here, the nematic liquid is referred to as the “host” and the pleochroic dye as the “guest”, so that a guest-host combination is present. Such systems are used in U.S. Patent Nos. 3,551,026,3,597,044 and 3,960,751 to manufacture 40 electro-optical displays.

So that an electro-optical device can be operated with nematic liquid crystals, the liquid crystal must have an oriented structure which is influenced by the direction of the applied electric field. 45 liquid crystals (mesomorphic substances) mostly have rod-like molecules. If the longitudinal axes of the liquid crystals are aligned perpendicular to the container walls, one speaks of a homeotropic structure. If, on the other hand, the longitudinal axes of the liquid crystal are aligned parallel to the container walls, one speaks of a homogeneous structure due to the homogeneous boundary conditions. If two homogeneously orienting walls are at right angles to the orientation lines, a twisted nematic liquid-crystalline structure is obtained.

55 Many nematic liquid crystals can be converted to a cholesteric phase by using a soluble optically active nematic liquid-crystalline material as a dopant or a chiral compound, e.g.

60 (-) CH3CH2C HCH20 - ^ - CN

CHs or

(-) CH3CH2CHCH2CH2 CH CN

ch3

3rd

640 259

wherein the alkyl radicals are optically active amyl and heptyl groups. In these cases the helix axis of the cholesteric phase is oriented homeotropically or homogeneously.

Homogeneous boundary conditions can be achieved in various known ways, e.g. by

1. rub, e.g. with an aqueous suspension of very fine zirconium oxide, in one direction; see. U.S. Patent 3,694,053;

2. mechanical surface marking or deforming; see. D.W. Bergman, Phys. Rev. Lett., Vol. 28, p. 1683 (1972)

3. Deposition of organic materials, e.g. Trimeth-oxysilane R-Si (OCH3) 3 and subsequent rubbing; see. F J. Kahn, Appi. Phys. Lett., Vol. 22, p. 11 (1973) and Appi. Phys. Lett., Vol. 22, p. 386 (1973);

4. Deposition of inorganic materials, e.g. Metal oxides or MgF2, which are evaporated at an angle of 1-30 ° to the coated surface [cf. J.L. Jan-ning. Appi. Phys. Lett., Vol. 21, p. 173 (1972)] or an angle of more than 30 ° and then rubbed.

Homeotropic boundary conditions are generally of less interest and are e.g. obtained by coating with metal oxides at an angle well above 30 ° or by treatment with surfactants.

Positive dielectric anisotropy occurs with liquid crystals that align in the longitudinal direction with an applied field. These connections are of particular interest for the guest-host combinations according to the invention. In general, it is only necessary that the overall effect corresponds to a positive dielectric aniostropy, so that the liquid-crystalline host component can consist to a high percentage of negative dielectric anisotropic materials and a smaller proportion of strongly positive dielectric anisotropic materials.

Numerous pleochroic dyes that can be used in the guest-host combinations usually also have molecules stretched in one direction, with little or no absorption taking place along their longitudinal axis and light from different regions of the visible spectrum being absorbed along the short axis. Other pleochroic dyes can align in opposite directions and are colorless along the short axis and colored along the long axis.

When combined with nematic liquid crystals with a homeotropic structure, i.e. Molecules perpendicular to the container wall, the first-mentioned pleochroic dye type aligns its molecules with those of the liquid crystal and no color is visible until an electric field is applied. If the same pleochroic dye is combined with a nematic liquid crystal with a twisted structure, the molecules align themselves parallel to the container walls and progressively at a right angle, so that the combination appears colored until an electric field is applied.

By combining the two pleochroic dye types, devices are possible in which one color converts to another. Another effect can be achieved by using an isotropic, i.e. non-pleochroic dye combined with a pleochroic dye so that the colors of both dyes add in one state and the isotropic dye emerges in the other state of the field cycle.

In order for a cycle between colorless and colored or between two colors to be obtained in a particular device, the dye must be used in amounts that can be aligned by the nematic liquid crystal, i.e. not in excess of the amount that can be aligned by the amount of liquid crystal present. This amount is usually up to about 5 percent by weight. In some cases, the solubility of the pleochroic dye in the liquid crystal is insufficient to achieve concentrations above 1 to 5 percent by weight. Known combinations enable contrasts 5 from 0 to the maximum electric field from approximately 2: 1 to approximately 4: 1. The object of the invention is to achieve greater solubilities and higher contrasts.

The invention relates to pleochroic dyes of the general formula which can be used for guest-host combinations

15

(NNR ') "Qx

2o in which the substituents (NRR ') and Q can be in positions 1 to 8 and the symbols have the following meanings: Q = F, Cl, -NO * -NH2, -NH (Alk) or -OH; X = 0,1,2 or 3;

m = 1 or 2;

25 R = H;

R '= cyclohexyl, bicyclohexyl or- (CH2) pAr;

in which:

p = 0.1 or 2;

Ar = aryl with 6 to 10 carbon atoms,

3o the in the 4-position by -NHCOCH3, -CN, -CnH2n + 1, -OCnH2n + ,, cyclohexyl,

4- (alk) -cyclohexyl or -Yy-

Z is substituted,

35 (where y = 0 or 1; Y = -CH2-, -O-, -S- or -OCH2-; Z = H, -N02, -CN, -CnH2n + I, -OCnH2n + i, F, Cl or if y = 0, also -C6H5)

and is substituted in 0 to 2 further positions by -CN, -C “H2n + 1, -OCnH2n + !, -NH2 or -OH; 40 n = Ibis 20 and

Alk = alkyl with 1 to 8 carbon atoms.

These substituted anthraquinones are particularly suitable for guest-host combinations with positive dielectric anisotropic nematic compounds or mixtures such as 45 n-pentylphenyl cyclohexyl cyanide or p-heptyl-4-cyanodiphenyl or mixtures which contain these compounds mainly, i.e. result in positive dielectric net anisotropy. In the following, positive anisotropy is understood to mean positive dielectric anisotropy. The compounds according to the invention can be used either alone or as combinations in up to equimolar proportions with the nematic compounds in order to obtain contrast ratios of up to about 20: 1 or above

55

The pleochroic dyes according to the invention also result in an extraordinarily high value for the optical size parameter S. This parameter is a measure of the degree of orientation of a dye. It is determined by measuring the light absorption as the reciprocal of the percent transmittance at ^ max through a liquid crystal solution of the dye, which is located between electrode-coated plates in a cell, in the presence or absence of an electrical field. The parameter S 65 is calculated using the following formula:

c _ Ao ~ Ai

A0 + 2A,

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Here A] and A0 mean the absorption in the presence of other current sources can also be used. The absence or presence of a field. S is given as a decimal number with a current source, with the coatings 16 of the cell above a value below 1. Depending on the switch 22 connected.

2 and 3 show, in an enlarged view, the end of sigrystal, S can change somewhat 5 for a given dye of cell 8 with a graphic representation of the molecules. Known pleochroic dyes result in S values for the nematic liquid-crystalline material 30 and the ge value of approximately 0.3 to 0.5. The dyes according to the invention redeemed pleochroic dye 40. The cell walls of FIG. 1 possible S values of 0.5 and above, preferred compounds 2 and 3 have been treated as described above, fertilize 0.7 and above. With a particularly suitable connection so that a homeotropic orientation takes place, if as in fertilization values of 0.9 and above are found. 3 a voltage is applied, and the molecules 30 and high values could not be aligned according to the prior art at right angles to the walls.

waiting. 4 and 5 is shown in front view. The

The unusual properties of the inner cell walls according to the invention have been oriented by coating the tin and / or pleochroic dyes, making them suitable for com- or indium oxide with MgF2 at a small angle in combinations with nematic liquid crystals of a positive arrangement. The orientation of net anisotropy, e.g. in display systems for computers Fig. 4 (no voltage applied) changes when applied egg-can. Furthermore, they can be an electronic voltage of approximately 5 volts and the molecules 30 and 40 see closures for devices, such as cameras or devices, as shown in FIG. 5, in the field.

ejectors, and can be used for mirror arrangements that FIGS. 6, 7 and 8 show the behavior in a cell with which can be switched from reflection to transparent and 20 twisted orientation. As in the figures, the cell walls are suitable for cameras or other mirror systems. 4 and 5, however, the orientation takes place without applied voltage

The drawing shows: on the rear wall in a vertical direction and

Fig. 1 in cross section an electro-optical Vertilvorrich- on the front wall in the horizontal direction. When the instructions in which guest-host combinations with the inventive voltage in FIGS. 7 and 8 are used, the corresponding pleochroic dyes are used; 25 molecules with the field. In Fig. 6, part of the cell and Fig. 2 are cut away in cross-section of a homeotropic guest-host content in order to show the orientation to the re-combination of the invention in the idle state without applied term wall.

Tension; To produce the guest-host

Fig. 3 the homeotropic guest-host combination of Fig. Combination it is necessary to di-electrically positive aniso-2 with applied voltage; 30 tropical nematic compounds or mixtures to be used

4 and 5 guest-host combinations from homogeneous. Specific examples of such compounds are in the positive anisotropic nematic liquid crystals and occur together with the temperature at which the dyes according to the invention with or without applied conversion from the crystalline to the nematic state

Tension; (C- »N) or from the nematic to the isotropic state

6, 7 and 8 the combinations of FIGS. 4 and 5, each 35 (N-> I), put together:

but with a right-angled cell wall orientation, so that twisted nematic liquid crystals are present. In Fig. 6 there is no voltage applied in Figs. 7 and 8; Table I

9, 10 and 11 permeability curves of 5 percent solutions of 1,5-bis- (4-cyclohexylphenyl) -anthrachi- 40 C-> N N-> I (° C)

non, 1-methylamino-2-undecyl-4- (4-octylanilino) anthrachi-

non or 1,4-bis (4-phenylanilino) anthraquinone; N-p-m-hexylbenzylidene-p'-amino

Fig. 12 comparative curves from which the decrease in the op-benzonitrile density with increasing the applied voltage arises - N-p - [(p-methoxybenzylidene) amino]. 45 benzonitrile

1 shows a cell 8 with walls 12 and 14, Np - [(ethoxybenzylidene) amino] - which are coated on the inside with conductive coatings 16 made of tin-benzonitrile and / or indium oxide and a guest-host Np -Cyanobenzylidene-p'-n-butoxy combination 18 from a positive anisotropic nematic aniline

Liquid crystal and a pleochroic dye contain 50 N-p-cyanobenzylidene-p'-octyloxy-ten. The cell 8 is between the light source 10 and the observatory 24 together with a polarizer 28 and given * conversion smectic to nematic.

if arranged an analyzer 26. Cell 8 is equipped with another usable positive anisotropic nematic flux DC source 20, e.g. a battery, however ^ sig crystals are the connections x "CM ^ ~ cn'r-C ^ ~ 0_ € ^ ~ ch and

-

51.5-52.5

105

125

106

118

70

93

83 *

107

where R = alkyl or alkoxy having 1 to 7 carbon atoms, the compounds mentioned standing up, and X = alkyl or alkoxy having 1 to 9 carbon atoms. Special eutectic mixtures of 4'-substituted 4-cyano-eutectic mixtures and combinations of the pre-4'-alkyldiphenyls are mentioned in Table II.

5

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Tables

^ ■ substituent

connection

(Mol%) C- * N N-> I

(° C)

nC5H "

59

3rd

37.5

nC7H15

41.

nC7Hn

55 '

nC5H "0

15

nC7H150

13

0

57.5

nCgHi70

17th

nC6H17

36

nC3H70

18th

nC5HnO

15

0

61

nC7H150

12

nCgH ^ O

12

The above compounds with positive anisotropy can be used, for example, together with the specific examples of nematic liquid crystals with negative anisotropy mentioned in Table III.

Table III

C-> N N-> (° C) N-p-methoxybenzylidene- 19 45

p'-n-butylaniline p- [N- (p-methoxybenzylidene) - 120 166 amino] phenyl benzoate

N-p-methoxybenzylidene- 79 102

p'-aminophenylacetate p-azoxyanisole 119 133

p-n-Butylbenzoic acid-p'- 56 87

n-hexyloxyphenyl ester p- (p'-ethoxyphenoxycarbonyl) - 73 127

phenylcarboxylic acid

butyl ester p- (p'-ethoxyphenyl- 73 127

azo) phenylheptanoate p- (p'-ethoxyphenylazo) - 64 107

phenylundecylenate p-methoxybenzylidene 20 44.5

p'-butylaniline

N- (p-Butyloxybenzylidene) - 41 80

p'-pentylaniline p-athoxybenzylidene-38 78-9

p'-n-butylaniline

Special compounds have the formula wherein R and R1 are C, 4-alkyl radicals;

mO ^ - <H £ K

and wherein R is a C1_7 alkyl group and R1 is a Q.ralkoxy group or R is a C] _7 alkoxy group and R1 is a C] _7 alkyl group;

0 0

R - ^ - o-c - ^ - o-c - ^ - a1

10 wherein R and R1 are C ^ alkoxy and a or b are hydrogen or one is chlorine;

A

B (%:

57.3

51

32.7

29

10.0

20th

where R is an alkyl or alkoxy radical having 1 to 10 carbon atoms, and eutectic mixtures of these compounds.

If nematic compounds from Table III are combined with those from Table I or II, the 20 combinations must have a positive net anisotropy. This can be achieved by using only relatively small percentages of materials with high positive anisotropy if the other materials have a relatively low negative anisotropy. Examples of such combinations are combinations A and B in Table IV, both of which are nematic from at least -10 to + 50 ° C.

Table IV

N-p-methoxybenzylidene-p'-n-butyl-aniline

N-p-ethoxybenzylidene-p'-n-butyl-35 aniline and N-p-hexylbenzylidene-p'-aminobenzo-nitrile

A commercially available nematic liquid crystalline mixture contains approximately

13.9% n-Pentylphenylcyclohexyldiphenylcyanid 26.1% n-Propylphenylcyclohexylcyanid 35.9% n-Pentylphenylcyclohexylcyanid 24.1% n-Heptylphenylcyclohexylcyanid.

45

The N-substituted aminoanthraquinones used in the guest-host combinations according to the invention, in which R = H, are prepared by methods known per se for converting groups on anthraquinone molecules. Some of these reactions are illustrated in the following examples. In the examples, the melting points are measured with a Kahn electrothermal melting point determination device in a capillary tube on a heated block using an NBS-calibrated Ther-55 mometer (not corrected).

example 1

5 parts of 1,5-dichloroanthraquinone are added to 20 parts of 60 4-amino-1-cyclohexylbenzene, which contains 5 parts of sodium acetate and 0.1 part of copper metal. The mixture is heated under reflux for 2 hours, with stirring, giving a light red slurry which is cooled and mixed with petroleum ether. The deposited 1,5-bis (4-cyclo-65 hexylphenyl) anthraquinone is recrystallized as a dark red powder.

10 mg of the bis (1,5-cyclohexylphenyl) anthraquinone obtained are, with gentle heating, in 1.0 g of a mixture

640 259

6

of n-pentyl, n-propyl and n-heptylphenylcyclohexyl cyanide (35.9, 36.1 and 24.1% respectively) dissolved in 13.9% n-pentylphenyl cyclohexyldiphenyl cyanide, which has a positive dielectric anisotropy .

In order to determine the optical S parameter of the guest-host combination obtained, a cell for orienting the nematic medium is produced. Two approximately 5 x 7 cm large and 5 mm thick glass plates are thoroughly cleaned by washing them successively with acid, alcohol, aqueous ammonia and distilled water and drying them in an oven at 65 ° C. Each plate is then coated on a surface with indium oxide so that the surface is electrically conductive. The indium oxide surfaces are oriented, i.e. made anisotropic by rubbing it under light to moderate pressure about 20 times with a cotton cloth soaked in an aqueous suspension of zirconium oxide. Each plate is rinsed carefully with distilled water, placed in an oven and dried at 65 ° C for 1 hour. Two strips of a polytetrafluoroethylene film approximately 12 cm thick are cut to a length of approximately 5 cm and applied to the oriented surface of one plate at a distance of approximately 5 cm, after which the other plate is placed in the direction of orientation perpendicular thereto. The arrangement is then firmly connected.

A solution of the pleochroic dye to be tested is prepared by heating approximately 0.5 g (10 drops) of the nematic combination of Table IV to 65 ° C (i.e. above the isotropic melting temperature) and dissolving approximately 50 mg of the dye therein. An optical density of about 2 is obtained at 655 nm. As long as the solution is still above the isotropic melting point, an edge of the cell is introduced into the dye solution, which fills the cell with capillary action. When cooling, the temperature of the solution drops below the isotropic point into the nematic range after some time and the experiment can be continued.

Optionally, about 0.1 to 50% of a chiral compound such as cholesteryl nonanoate can be added at this time. The amount used depends on the intended effect. Smaller amounts (up to about 5 to 10%) are used to improve the spontaneous response of such guest-host combinations to the switching off of the electric field. Larger amounts result in a more cholesteric structure of the system instead of the more common twisted nematic structure, so that a polarizer is no longer required.

Using frog clamps, electrical contacts are made to the indium oxide coatings on the exposed ends of the glass plates that form the cell, and these are connected to a DC power source that is 50 to 100 nA over a range of 0.8 to 10 volts or can provide a sufficiently high fixed voltage. The cell is then placed in the sample beam of a spectrophotometer (e.g. Perkin Elmer Model 350), which has polarization filters in both the reference and sample beams and analyzers arranged in parallel. When crossed, the filters produce a neutral gray color. The permeability is graphically recorded over a range of 400 to 750 nm, with no voltage (switch off) or a voltage above the threshold value for the respective host component (switch on) being applied to the cell. The S values are calculated from the permeability or absorption curves obtained. The color shifts from light red to colorless are shown in FIG. 9 on the basis of the absorption maximum at 555 nm.

Example 2

In a procedure similar to that in Example 1, 5 parts of 1-butylamino-4-chloroanthraquinone are added to 20 parts of 4-aminodiphenyl, 0.1 g of copper and 5 g of sodium acetate and 100 5 parts of nitrobenzene. After heating under reflux for about 2 hours, the blue-green dye 1-butylamino-4-diphenylaminoanthraquinone, which has an S value of 0.7, is obtained.

Example 3

5 parts of l- (n-pentylanilino) -4-hydroxyanthraquinone are heated under reflux in 20 parts of cyclohexylamine in the presence of a small amount of sodium hydrosulfite, the light blue dye l- (n-pentylanilino-4-cyclohexylamino-

15 anthraquinone arises.

Mixing this pleochroic dye into the positive nematic liquid crystal mixture from Example 1 gives a blue guest-host combination in which the dye has an S value of 0.65.

20th

Example 4

5 parts of leucoquinizarin are condensed with 20 parts of 4-n-butylcyclohexylamine to give the sky-blue dye bis- (1,4-n-butylcyclohexylamino) anthraquinone.

25 A 1% solution of this dye in a mixture of the nematic liquid crystals from Example 1 gives a blue guest-host mixture which becomes colorless. The S value is 0.7.

see example 5

Leucoquinizarin is converted to leuko-1-amino-4-hydroxyanthraquinone with ammonia and then reacted with two amine bases, e.g. n-butylamine and p-toluidine. After heating for 2 hours at 90 ° C and oxidizing with air and

35 copper sulfate gives 1-n-butylamino-4-p-toluidinoan-thrachinone as a clear blue pleochroic dye with an S value of 0.7.

Example 6

40 1,5-diaminoanthraquinone is dissolved in o-dichlorobenzene and reacted with sulfuryl chloride to give 3,4,7,8-tetrachloroanthraquinone as an intermediate, which is then condensed with two equivalents of p-n-hexylaniline. When the chlorine atoms are split off, 4,8-bis-p-hexylphenylamino-l, 5-diami-

15 no-2,6-dichloroanthraquinone as a pure blue dye with an S value of 0.75.

Example 7

so 1-methylamino-2-undecyl-4-octylanilinoanthraquinone is by condensation of 1 equivalent of pn-octylamino-aniline with 4-bromo-l-methylaminoanthraquinone, Cu and sodium acetate and subsequent alkylation of this dye with undecylaldehyde in a mixture of nitrobenzene 55 and piperidine produced. This purple dye has an S value of 0.7. The transmittance curves of the color shift are shown in FIG. 10.

Example 8

60 1 -Nitroanthraquinone is converted under reflux with excess cyclohexylamine in o-dichlorobenzene to 1-cyclohexylaminoanthraquinone, which is then brominated in aqueous pyridine to give the corresponding l-cyclohexylamino-4-bromoanthraquinone. This compound is then further condensed with p-aminoacetanilide, giving the blue-green pleochroic dye l-cyclohexylamino-4- (p-acetaminoanilino) anthraquinone with an S value of 0.7.

7

640 259

Example 9

1 equivalent (2.4 g) of 1,4-dihydroxyanthraquinone is placed in a flask equipped with a reflux condenser and stirrer, which contains 1 g of boric acid and 0.5 g of stannous chloride and 30 g of 2-phenylethylamine. Then it is stirred for 2 hours at 130 ° C. and the contents are then poured into 10% hydrochloric acid. This gives rise to the blue pleochroic dye bis- (1,4-phenethylamino) anthraquinone with an S value of 0.78.

Examples 10 to 19 A series of pleochroic dyes, the meanings of Q, x, R 'and m and the position on the anthraquinone core 5 together with the color and the S value in Table V are prepared by the process of Example 1 are. The 1,4-cyclohexylene group is indicated by an H in the ring.

Table V

Example color

10th

11

12th

13

14

15

16

17th

18th

19th

red blue violet red brown red red red blue reddish blue red

R 'positions

1.5

1.5

1.8 1.8

1.8 1.5 1.5 1.4 1.8

R '

c5HU £> @ - "-

H

H

° 12H25- <5> N-

H

no2 @ -S ^ O) -N-

H

P ^ Zy-N-

H

GX ^ -

c5Hu <g> -N-

H

° 8 »17 °

m

2 2

S value 0.75

0.80

0.75 0.8

0.75

> 0.8

0.7

0.7 0.85

0.8

Examples 20 to 28 Further pleochroic dyes which can be used for guest-host combinations are refluxed in an inert solvent by condensation of substituted dichloroanthraquinones with various amines.

65 tel, such as nitrobenzene, in the presence of sodium acetate and copper acetate. The dyes are listed in Table VI. The intermediates are known or can be prepared in a known manner.

640 259

Table VI

Example color

Q position

R position

R '

m x

S value

20 yellow-green

21 blue

OH

22

23

24th

25th

26

27th

28

red red red purple blue red

1.4 2.6

1.5 1.5 1.5

C8H17

1.4

1.5

1.5

© - * ■

2 2

NO

C15H31

C20 »

C5B1Ï

H

N-

0.7

0.68

0.85

0.8

0.75

0.85

0.8 0.85

0.9

Example 29

The procedure used in Examples 20 to 28 is illustrated by the preparation of 1,5-bis (benzylamino) anthraquinone:

20 g of benzylamine, 0.1 g of copper acetate, 2.0 g of sodium acetate and 10 g of nitrobenzene are mixed with 277 g of 1,5-dichloroanthraquinone in a suitable vessel. The mixture is heated under reflux for 2 hours and then poured into methanol. The crude dye is separated and treated with hot nitrobenzene, which contains a small amount of piperidine. The red dye is cleaned from alcohol and washed with ether. It has an S-value of 0.75.

Example 30

A useful method for introducing a substituted amino group instead of a hydroxyl group is to heat the hydroxyl-substituted anthraquinone with the amine in the presence of boric acid, usually in an inert solvent such as nitrobenzene. This process also enables the production of anthraquinone 45 with two different substituents; see. Examples 19 and 30.

1-Hydroxy-4-chloroanthraquinone is condensed with 1 equivalent of p- (n-decyl) aniline in the presence of boric acid to l- [p- (n-decyl) anilino] -4-chloroanthraquinone, which is then so condensed with 1 equivalent of 2-aminonaphthalene in the presence of copper acetate / sodium acetate. After cleaning, the blue-green pleochroic dye l-p- (n-decyl) anilino-4-naphthylaminoanthraquinone with an S value of 0.72 is obtained.

55

Examples 31 to 39 Using the boric acid condensation described in Example 29, the 60 pleochroic dyes listed in Table VII are prepared. In Examples 37 and 38, the asterisk means that tin (II) chloride is used as in Example 9.

640 259

Table VII

At

Q position

game color lung

Q

31 reddish blue

5.8

Cl

32 blue-green

5.8

Oh

33 green

5.8

no2

5

no2

34 bluish green

8th

Oh

1

qh

35 blue

-

-

36 blue

-

-

37 reddish blue

5.8

Cl

38 * bluish-green 39 * blue-green

R position

H

1.4

1.4

1.4 1.4

R '

C8k17-0- <0> - ^

H

N0 ^ D "S- <O" N "

H

»Oï © -« - © - «-

C8H17_0 ^ 0> "N"

H

cioh21- ° - <Oi-N- <0 ^ CH2 "®" CK2. * -

m

S value

0.75 0.75 0.68

0.72

0.8

0.8

2 2 0.75

2 - 0.75 2 - 0.8

Example 40

The guest-host combinations according to the invention are distinguished by an unusual light fastness. A field effect device is produced to demonstrate this property. As a nematic guest-host component, a mixture of the nematic liquid crystals from Example 1, which contains 1% 1,4-bis (4-phenylanilino) anthraquinone (prepared like the 1,5-isomer in Example 11), used. The test sample is placed in an Atlas weathering apparatus at 60 ° C. for 100 hours, using a xenon UV light source with an output power of 0.115 nm / cm 2 at 340 nm. After 100 hours, the absorption spectra show no decrease in> »max of the pleochroic dye and a current increase of less than 10% is measured over the electrode surfaces. The

Permeability curves with respect to the color shift 55 are shown in FIG. 11.

Example 41

The improvements achieved by the compounds according to the invention compared to unsubstituted bis-phenylaminoanthraquinones in 60 guest-host combinations result from a comparison of a system (A) according to the invention in which the anthraquinone from Example 30 is used, in which each phenyl group is substituted by an octyloxy group (in the 4-position of Ar), with a system (B), 65 which has no substituent in the same position. Using the dielectric positive nematic liquid crystal mixture of Example 1, solutions are prepared in the same concentration, followed by the passage

640 259

liquid curves with increasing voltage. The results are shown in Fig. 12. The higher S value of system B (approximately 0.7) demonstrates the increased contrast ratio, the less colored background and the increased brilliance that can be achieved with electro-optical devices in which the combinations according to the invention are used. S values similar to those in Examples 1 to 39 be10

are obtained if chiral compounds, such as cholesteryl pelargonate, are added to the nematic liquid-crystalline materials in various amounts. When using small amounts, e.g. about 0.5%, you get a faster reorientation when switching off the voltage.

C.

3 sheets of drawings

Claims (12)

640 259 2. Systems according to claim 1, characterized in that they additionally contain about 0.1 to 10 percent by weight of an isotropic dye with a color contrast with respect to the normal color of the pleochroic dye. 2nd PATENT CLAIMS 1. Liquid crystal systems with positive dielectric anisotropy, containing at least one nematic liquid crystalline material with positive dielectric anisotropy and 0.01 to 50 percent by weight of a pleochroic dye of the general formula 0 in which the substituents (NRR ') and Q can be in positions 1 to 8 and the symbols have the following meaning: Q = F, Cl, -N02, -NH2, -NH (Alk) or -OH; X = 0,1,2 or 3; m = 1 or 2; R = H; R '= cyclohexyl, bicyclohexyl or- (CH2) pAr; where p = 0.1 or 2; Ar = aryl with 6 to 10 carbon atoms, which in the 4-position by --nhcoch3, -CN, -CnH2n + 1, -OCnH2n + 1, cyclohexyl, 3. Systems according to claim 1, characterized in that the nematic liquid-crystalline material comprises 10 to 20 weight percent N-p-alkoxybenzylidene-p'-aminobenzonitrile. 4. Systems according to claim 1, characterized in that the nematic liquid-crystalline material comprises n-pentylphenyl-cyclohexyldiphenyl cyanide in a combination of n-propyl, n-pentyl and n-heptylphenylcyclohexyl cyanide. 4- (alk) -cyclohexyl or -Yy - ^ _ ^ - Z is substituted, (where Y = 0 or 1; Y = -CHo-, -O-, -S- or -OCH2-; Z = H, -no * -CN, -CnH2n + J-OCnH2n + 1, F, Cl or, if Y = 0, also -C6HS) and in 0 to 2 further positions by-CN, -cnh2n + 1, -ocnh2n + 1, -nh2 or -oh is substituted; n = 1 to 20 and Alk = alkyl with 1 to 8 carbon atoms. 5. Systems according to claim 1, characterized in that the nematic liquid-crystalline material comprises combinations of 4-cyano-4'-alkyl-diphenylene. 6. Systems according to claim 4, characterized in that the pleochroic dye is 1,5-bis- [p- (4-n-pentylcy-clohexyl) phenylamino] anthraquinone. 7. Systems according to claim 4, characterized in that the pleochroic dye is 1,5-bis (diphenylamino) anthraquinone. 8. Systems according to claim 4, characterized in that the pleochroic dye is bis- [4- (p-nitrophenylthio) phenylaminoj-anthraquinone, in which the substituents are in the positions 1,4,1,5 or 1,8 . 9. Systems according to claim 4, characterized in that the pleochroic dye is 1,4-bis (4-n-decyloxyphe-nylamino) anthraquinone. 10. Systems according to claim 1, characterized in that they also contain about 0.1 to 50 percent by weight, based on the nematic liquid-crystalline material, of a chiral agent. 11. Systems according to claim 10, characterized in that the chiral agent is cholesterylplargonate. 5 12. Electro-optical displays in which an electric field can be switched off acting on a cell that contains a liquid-crystalline material in which a pleochroic dye is dissolved between transparent glass plates provided with electrodes, characterized in that the liquid-crystal material is a liquid crystal system having positive dielectric anisotropy according to any one of claims 1 to 11.