GB2024844A

GB2024844A - Pleochroic dyes and electro- optical displays therewith

Info

Publication number: GB2024844A
Application number: GB7917828A
Authority: GB
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1978-05-23
Filing date: 1979-05-22
Publication date: 1980-01-16
Also published as: GB2024844B; IT1115232B; DE2920730C2; IT7922892A0; DE2920730A1; JPS54157786A; JPH0116876B2; FR2426724A1; CH640259A5; KR850000050B1; FR2426724B1

Abstract

A composition suitable for use in electro-optical display devices has a positive dielectric anisotropy and comprises at least one nematic liquid crystal material having positive dielectric anisotropy and from 0.01 to 50 percent by weight of pleochroic dyestuff of the general formula: <IMAGE> wherein substituents (NRR') and Q may be in positions 1 through 8, Q is F, Cl, NO2, NH2, NH(Alk), OH, x is 0, 1, 2, 3, m is 1 or 2 R alone is H, R' alone is cyclohexyl, bicyclohexyl or -(CH2)DAr where p is 0, 1 or 2 and Ar is aryl of 6 to 10 carbon atoms substituted as in the 4 position by -NHCOCH3, CN, -CnH2n+1, cyclohexyl &lparstr& Alk &rparstr& cyclohexyl or <IMAGE> where y is 0 or 1, Y is CH2, O, S or OCH2, Z is a 4-substituted H, NO2, CN, -CnH2n+1, F, Cl or when y=0 also -C6H5, and in from 0 to 2 further position by CN, -CnH2n+>1, NH2 or OH wherein n is 1 to 20 and Alk is alkyl of 1 to 8 carbon atoms.

Description

SPECIFICATION Pleochroic dyes and electro-optical displays therewith This invention relates to guest-host combinations of pleochroic N-substituted cyclic derivatives of mono- and di-aminoanthraquinones with dielectrically positive nematic liquid crystals. This invention -further relates to electro-optical devices employing the said guest-host combinations.

Electro-optical devices in which liquid crystals are employed usually comprise two transparent flat plates having very thin transparent electrodes on their inwardly facing surfaces, separated by from a few microns to a few tens of microns and with a liquid crystalline composition filling the space between the plates. It is these plates which are referred to below as walls of the vessel. Impressing an electric field on the liquid crystal affects the optical properties of the layer of liquid crystal.

It was discovered by Heilmeier and Zanoni, Applied Physics Letters, Vol. 13, pages 91-92 (1 968) that, when pleochroic dyes are combined with nematic liquid crystals in a device such as above, the pleochroic colors of the dye are manifested as an electric field is applied and released. The nematic liquid is referred to as the "host" and the pleochroic dye as the "guest" so that the composition is referred to as a guest-host combination. The phenomenon has been utilized in U.S. Patents 3,551,026, 3,597,044 and 3,960,751 to produce electro-optical devices.

In order for an electro-optical device employing nematic liquid crystals to be operable the liquid crystal must have an oriented structure which is controlled by the direction of an applied electric field.

Liquid crystals (mesmorphic substances) tend to have rod-like molecules. When the long axes of the liquid crystals are perpendicular to the walls of the cell or vessel the structure is termed hemotropic.

When the long axes of the liquid are parallel to the,walls of the cell or vessel the structure is termed homogeneous because of the homogeneous boundary conditions. When two homogeneously orienting walls are at right angles of lines of orientation a twisted nematic liquid crystalline structure is achieved.

Many nematic liquid crystals can be altered to a cholesteric phase by addition of a soluble optically active nematic liquid crystalline material as a dopant, orchiral agent, such as:

wherein the alkyl groups are active amyl and active heptyl. In such cases it is the axis of the helix of the cholestric phase which is homeotropically or homogeneously oriented.

Homogeneous boundary conditions may be achieved by several techniques each of which offers advantages for certain purposes. These are well known in the art and do not need to be described in detail. Suitable techniques and references showing the procedure include: 1. rubbing, e.g., with aqueous suspension of very fine zirconium oxide in a single direction, cf. F. J.

Kahn "Nematic Liquid Crystal Device" U.S.3,694,053; 2. mechanical surface scribing or deformation, cf. D. W. Berrgman, Phys. Rev. Lett., Vol. 28, p.

1683,1972; 3. deposition of organic materials, such as trimethoxysilane, R-Si(OCH3) followed by rubbing as above, cf. F. J. Kahn, Appl. Phys. Lett., Vol. 22, p. (2/1/73) and idem. Appl. Phys. Lett., Vol.

22, p. 386 (4/1 5/73); 4. deposition of inorganic materials such as metal oxides or MgF2, vapor deposited at angles of 130 to the coated surface, cf. J. L. Janning, Appl. Phys. Lett., Vol.21, p. 173 (1972) or deposition at angles above 30C followed by rubbing.

Homeotropic boundary conditions, which are generally of less interest, are obtained, for example by coating with metal oxides at angles well above 30C or treatment with surfactants.

Dielectrically positive anisotropy is exhibited by liquid crystals which tend to align longitudinally with an impressed field. Such compounds are of particular significance for guest-host combinations of the invention. It is usually only necessary that the overall effect is that of dielectrically positive anisotropy so that the liquid crystalline host may be composed of high percentages of dielectrically negative anisotropic materials with smaller amounts of highly dielectrically positive anisotropic materials.

Many pleochroic dyes which are useful in guest-host combinations also tend to have molecules elongated in one direction with little or no absorption along their long axis and absorpiton of light in various portions of the visible spectrum along the short axis. Other pleochroic dyes may align oppositely being colorless on the short and colored along the long axis. They are thus of two types.

When combined with nematic liquid crystals having a homeotropic structure, i.e. molecules perpendicular to walls of vessel, the first above type of pleochroic dye then aligns its rods with those of the host liquid crystal and no color is seen until an electric field is imposed. CorrespondinRly, when the same pleochroic dye is combined with a nematic liquid crystal having the twisted structure, the molecules are aligned parallel to the walls of the vessel and progressively at right angles and the combination appears colored until an electric field is applied.

By combining two pleochroic dyes, one each of the above two types, devices which change from one color to another are evidently possible. A further effect is obtained by incorporating an isotropic, i.e., non-pleochroic, dyestuff with a pleochroic dyestuff so that the colors of the two are additive at one stage and the isotropic dyestuff appears at the other stage of cycling the electric field.

In order that there be a cycle between colorless and colored or between two colors for a given device it is obviously imperative to employ the dye in amounts which are alignable by the nematic liquid crystal, i.e., not in excess of the proportions which are within the capabilities of alignment by the amount of liquid crystal pressent. This is usually found to be up to about 5% by weight. In some cases the solubility of the plechroic dye in the liquid crystal is indadequate to achieve concentrations above 1-5% by weight. Combinations of the prior art are capable of achieving contrasts from zero to maximum electric field of about 2:1 up to about 4:1. It would be desirable to have greater solubilities and higher contrasts and these are therefore aims and objects of the inventions.

In accordance with these aims and objects it has been found that a very useful group of pleochroic dyes for use in guest-host combinations are provided by anthraquinones of the general formula:

wherein substituents (NRR') and Q may be in positions 1 through 8, Q is F, Cl, No2, NH2, NH(Alk), OH, x is 0, 1, 2, 3, misl or2, R alone is H, R' along is cyclohexyl, bicyclohexyl or -(CH2)Ar where p is 0, 1 or 2 and Ar is aryl of 6 to 10 carbon atoms substituted la in the 4position by -NHCOCH3, CN, -CnH2n+1, -OCnH2n+1, cyclohexyl, 4-(-Alk-)-cyclohexyl or

Where y is O or 1, Y is CH2, O, S, or OCH2, Z is a 4-substituted H, NO2, CH2+1, -0C0H 2n+1' F, Cl, or when y = 0 also-C6H5, and in from O to 2 further positions by Cn, -CnH2n+1, -OCnH2n+1, NH2, or OH wherein n is 1 to 20 and Alk is aikyi of 1 to 8 carbon atoms.

The substituted anthraquinones of the above general formula are found to form particularly useful guest-host combinations with dielectrically positive anisotropic, nematic compounds or compositions, such as n-pentyl phenyl cyclohexyl cyanide or p-heptyl-4-cyanobiphenyl, or compositions including these compounds in dominating amounts, i.e., providing net dielectrically positive anisotrophy. It will be understood herein that positive anisotropy refers to dielectrically positive anisotropy. Compounds of the invention can be employed alone and in combinations at up to equimolar proportions with the nematic compounds to obtain contrast ratios up to about 20:1 or more.

The pleochroic dye compounds of the present invention are further remarkable in providing exceptionally high value of the optical order parameter S. The parameter is a measure of the efficiency of orientation of a dye. It is determined by measuring absorption of light as the reciprocal of percent transmission at max through a liquid crystal solution of the dye between electrode-coated plates in a cell as described above with and without an impressed field. Where A, and A. are the absorption with and without field respectively, A0-A1 S= Ao+2At The parameter S is given as a decimal number less than 1. For a given dye it may vary somewhat depending on the particular nematic liquid crystal employed as host. Pleochroic dyes of the prior art provided values of S of the order of about 0.3 to 0.5. Compounds of the above formula have optical order parameters of 0.5 and higher and in preferred compounds are 0.7 and higher. Values of 0.9 and higher are found for some particularly useful compounds. This is a very high range of values not to be expected from any prior art teachings.

The unusual properties of the instant pleochroic dyestuffs renders them of value in combinations with nematic liquid crystals of net positive anisotropy in display devices as for calculators, watches, etc.

and also for use as electronic shutters for devices such as cameras and projectors and by use in a specular arrangement they assist in providing mirrors which can pass from specular to transparent and can be employed in cameras or wherever mirrors are used.

Reference is now made to the several drawings herewith wherein Figure 1 shows diagrammatically an electro-optical valve device employing guest-host combinations of pleochroic dyes of the invention.

Figure 2 shows in diagrammatic fashion a homeotropic guest-host combination of the invention in the quiescent state with no impressed voltage.

Figure 3 shows the homeotropic guest-host combination of Figure 2 with impressed voltage.

Figures 4 and 5 show combinations in guest host relationship of homogeneous positive anisotropic nematic liquid crystals and dyesf the invention without and with impressedvoltage respectively.

Figure 6, 7 and 8 show combinations of Figures 4 and 5 but with orientation of walls of cell at right angles giving twisted nematic liquid crystals. Figure 6 is without and Figures 7 and 8 with impressed voltage.

Figures 9, 10, and 11 show transmittance curves of 5% solutions of 1,5-bis(4 cyclohexylphenyl)anthraquinone, 1 -methylamino-2-undecyl-444-octylanilino)anthraquinone and 1 ;4bis(4-phenylanilino)anthraquinone, respectively. Figure 12 shows comparative curves of decrease of optical density with increasing applied voltage in a test cell.

In Figure 1 a cell (8) is showh having walls (12) and (14) inwardly coated with conductive coatings of tin and/or indium oxide (16) and containing guest-host combination (18) of positive anisotropic nematic liquid crystal and pleochroic dye (not indicated in this figure). Cell (8) is placed between light source (10) and observer (24) with polarizer (28) and, for certain uses, analyzer (26). Cell (8) is provided with a source of direct current (20) shown as a battery but any source is the equivalent thereof.

The source of current is connected to coatings 116) of the cell with switch (22) interposed.

Figures 2 and 3 show an enlarged view of the end of cell (8) with diagrammatic representation of the molecules of nematic liquid crystalline material (30) and dissolved pleochroic dye (40). The cell walls of Figures 2 and 3 have been treated as described above so that homeotropic orientation oqcurs when a voltage is applied as indicated in Figure 3 and molecules (30) and (40) tend to orient at right angles to the walls as shown.

The cell of Figures 4 and 5 is shown in facial view. The inner cell walls have been oriented in parallel arrangement as described herein suitably by coating with MgF2 at low angle over the tin and/or indium oxide. The orientation of Figure 4 with 0 impressed voltage is changed by.an applied voltage of about 5 volts and molecules (30) and (40) aligh with the field as shown in Figure 5.

Figures 6, 7 and 8 shows the behavior in a cell with twisted orientation. The cell walls are as for Figures 4 and 5 but with orientation in a vertical direction at the rearward wall and horizontally at the forward wall with no impressed voltage. When a voltage is impressed as in Figures 7 and 8 it is seen that molecules are oriented with the field In Figure 6 a portion of cell and contents are cut away to show orientation on the rearward wall.

As indicated above it is necessary in forming guest-host combinations of the invention to employ dielectrically positive anisotropic nematic compounds or compositions. Included in typical compounds with positive anisotropy are the following with temperature at which conversion of crystalline to nematic state (C N) and nematic to isotropic state (N I) occurs: TABLE 1 - CN Nl N-p-n-hexylbenzylidene-p'-a minobenzonitrile - 51.5-52.5 N-p-[(p-methoxybenzylidene)-amino]benzonitrile 105 125 N-p-[(ethoxybenzylidene)amino]benzonitrile 106 118 N-p-cyanobenzyl idene-p'-n-butoxyaniline 70 93 N-p-cyanobenzylidene-p'-octyloxyaniline 83* 107 * Smectic to nematic transition.

Other useful positive anisotropic nematic liquid crystals are included in compounds

wherein R = alkyl or alkoxy of 1-7 carbon and X is alkyl or alkoxy of 1-9 carbon atoms.

Eutectic mixtures and combinations of all the above are also useful. Illustrative eutectic mixtures of 4'-substituted 4-cyano-4"-alkyl biphenyls are included in Table 2.

Table 2

comp OC 4'sub (Mol%) CN N3I nC5H11 591 3 37.5 nC7H15 41 nC7H1l 551 nC5 H 110 15 nC7E3150 13 { 0 57.5 nC8H.1 70 17 nC7td17 36 nC3H70 18 nC5H110 15 0 61 nC7 50 12 nC8H17C 12 The above compounds with positive anisotropy can be employed with compounds such as the representative species of several useful groups of nematic liquid crystals with negative anisotropy shown in Table 3.

TABLE 3 C C#N N#I N-p-methoxybenzyl idene-p'-n-butyla niline 19 45 p-[N-(p-meth oxybenzylidene)-ami no]-phenylbenzoate 120 166 N-p-methoxybenzylidene-p'-aminophenylacetate 79 102 p-azoxyanisole 119 133 p-n-butylbenzoic acid p'-n-hexyloxyphenyl ester 56 87 butyl-p-(p'-ethoxyphenoxycarbonyl)phenylcarbonate 73 127 p(p'-ethoxyphenylazo)phenyl heptanoate 73 127 p(p'-ethoxyphenylazo) phenyl undecylenate 64 107 p-methoxybenzylidene-p'-butylanlline 20 44.5 N-(p-butyoxybenzylidene)-p'-pentylanlline - 41 80 p-ethoxybenxylidene-p'-n-butylaniline 38 78-9 Some groups of included compounds are

wherein R and RX are lower alkyl of C,C4; ;

wherein R is alkyl of C1-C7 and R1 is alkoxy of C1-C7 or wherein R is alkoxy of C1-C7 and R' is alkyl C1-C7;

wherein R and R1 are alkyl of C1-C7 and a orb are H or one can be-Cl.

wherein R is alkyl or alkoxy of 1 to 10 carbon atoms and eutectic mixtures of such compounds. When combined nematic compounds of Table 3 are with those of Tables 1 or 2 the combinations must have a net positive anisotropy. This may be achieved using only relatively low percentages of materials with high positive anisotropy when the other materials have relatively low negative anisotropy. Such combinations include, for example A and B shown in Table 4, as percentages, both of which are nematic from at least -1 00C to +500 C.

TABLE 4 A B N-p-methoxybenzylidene-ptn-butylaniline 57.3 51 N-p-ethoxybenzylidene-p'-n-butylanil ine 32.7 29 and N-p-hexylbenzylidene-p'-aminobenzonitrile 10.0 20 One useful commercially available nematic liquid crystalline composition contains approximately: 13.9% n-pentyl phenyl cyclohexylbiphenyl cyanide 26.1% n-propyl phenyl cyclohexyl cyanide 35.9% n-pentyl phenyl cyclohexyl cyanide 24.1% n-heptyl phenylcyclohexyl cyanide The N-substituted aminoanthraquinones in which R is H employed in guest-host compositions of the invention are made by reactions well known in the art for effecting transformations of groups on anthraquinone molecules. Several of these reactions are illustrated in the following examples. Other reactions will be evident to those familiar with the chemistry of such molecules.

The following examples will illustrate the present invention wherein temperatures are in degrees centigrade and melting points are determined on a Kahn Electro-thermal Melting Point Apparatus in a capillary tube on a heated block with National Bureau of Standards calibrated thermometer (uncorrected).

EXAMPLE 1 Five parts of 1 ,5-dichloroanthraquinone are added to 20 parts 4amino1 -cyclohexylbenzene containing 5 parts sodium acetate and 0.1 part copper metal. The mixture is stirred and refluxed for two hours to give a bright red slurry which is cooled and mixed with petroleum ether. The precipitated 1,5 bis(4-cyclohexylphenyl)anthraquinone is recrystallized as a dull reddish powder.

Ten milligrams of the above bis( 1 ,5-cyclohexylphenyl)anthraquinone are dissolved with gentle heating in 1.0 gm of a mixture of n-pentyl, n-propyl and n-heptylphenylchclohexyl cyanides (35.9, 36.1 and 24.1% respectively) in 13.9% of n-pentylphenylcyclohexylbiphenyl cyanide which has dielectrically positive anisotropy to yield a guest-host composition.

In order to determine the optical order parameter a cell is constructed to provide orientation of a host nematic medium. Two glass plates 5 mm thick and about 5 x 7 cm are cleaned thoroughly by washing successively in acid, alcohol, aqueous ammonia and distilled water and dried at 65"C in an oven. Each plate is then coated on one surface by vapor deposition of indium oxide which makes the surface electrically conductive. The indium oxide surfaces are oriented, i.e., rendered anisotropic, by unidirectional rubbing under slight moderate pressure for about 20 strokes with a cotton pad impregnated with an aqueous suspension of zirconium oxide.Each plate is carefully rinsed with distilled water, placed on edge in an oven and dried for one hour at 650 C. Two strips of polytetrafluoroethylene sheets about 12 thick are cut about 5 cm long and applied to the oriented surface of one plate at a distance of about 5 cm and the other plate applied with orientation directions of the two plates at right angles. The assembly is then fastened together.

A solution of the pleochroic dye to be tested is prepared by warming about 0.5 g (10 drops) of the nematic combination of Table 4 to 650C (i.e., above the isotropic melting temperature) and dissolving about 50 mg of the dyestuff therein. This should provide an optical density of approximately 2 and 655 nm. With the solution still above the isotropic melting point one edge of the cell is applied to-thedyestuff solution which is drawn up to fill the cell by capillary action. After cooling for a period of time the temperature of the solution drops below the isotropic point into the nematic region and testing can continue.

If desired from about 0.1 to about 50% of chiral agent such as chloesteryl nonanoate can be incorporated at this time if desired. The amount used is determined by the effect desired. Smailer amounts (up to about 510%) are used to improve the spontaneous response of such guest-host mixtures to withdrawal of an electrical field. Largeramounts influence the composition to have a colesteric structure instead of the more usual twisted nematic structure so that the use of a polarizer is not required. This phenomenon is well known in the art.

Electrical contacts are made to the indium oxide coatings on the exposed ends of the glass plates forming the cell using alligator clips and these are connected to direct current capable of providing 50-100 microamperes over the range of 0.8 to 1 0 volts or of sufficiently high fixed voltage. The cell is then placed in the sample beam of a spectrophotometer (such as Perkin Elmer Model 350) having polarizing filters in both reference and sample beams and parallelly arranged analyzers. The filters give a neutral gray color when crossed. The transmittance is scanned over the range of 400-750 nm. and recorded graphically with no voltage applied to the cell (switch off) and with a voltage exceeding the threshold for the particular host (switch on).Values of S are calculated from these transmission (or absorption) curves as explained herein above. The color shifts from bright red to colorless with transmittance curves as shown in Figure 9 with absorption maximum at 555 nm.

EXAMPLE 2 In a procedure somewhat similar to that of Example 1 , five parts of 1 -butylamino-4chloroanthraquinone are added to 20 parts 4-aminodiphenyl, 0.1 gm copper and 5 gm sodium acetate and 100 parts nitrobenzene. After refluxing for about 2 hours the blue green dye (1 -butylamino-4biphenylamino)anthraquinone which has an optical order parameter of 0.7 is recovered. The optical order parameter is 0.7.

EXAMPLE 3 Five parts of 1 -(n-pentylanilino)-4-hydroxyanthraquinone are refluxed in 20 parts cyclohexylamine in the presence of a minor amount of sodium hydrosulfite to yield 1 -(n-pentylanilino-4-cyclohexylamino anthraquinone as a bright blue dye.

Incorporation of this pleochroic dyestuff in a positive nematic liquid crystal mixture as in Example 1 above provides a blue guest-host mixture in which the dye has an optical order parameter of 0.65.

EXAMPLE 4 Five parts of leucoquinizarin are condensed with 20 parts of 4-n-butylcyclohexylamine to yield bis( 1 ,4-n-butylcyclohexylamino)anthraquinone as a bright sky blue dye.

A 1% solution of this dye in a mixture of nematic liquid crystals as in Example 1 gives a blue guesthost mixture which becomes colorless. The optical order parameter os 0.7.

EXAMPLE 5 Leucoquinizarin is converted to leuco-1-amino-4-hydroxy anthraquinone with ammonia and then reacted with two amine bases, e.g. n-butylamine and p-toluidine. After heating to 900 for two hours and oxidation with air and copper sulfate, 1-n-butylamino 4-p-toluidino anthraquinone is obtained as a clear blue pleochroic dye with an optical order parameter of 0.7.

EXAMPLE 6 1,5-Diaminoanthraquinone is dissolved in o-dichlorobenzene and treated with sulfuryl chloride to yield the 3,4,7,8-tetrachloroanthraquinone intermediate which is then condensed with 2 equivalents of p-n-hexyiailine and the -chlorine atoms are displaced leaving the 4,8-bis-p-hexylphenylamino, 1,5 diamino-2,6-dichloroanthraquinone as a pure blue dye with an optical order parameter of 0.75.

EXAMPLE 7 1 -Methylamino-2-undecyl-4-octylanilino anthraquinone is prepared by condensing 1 equivalent p-n-octylaminoaniline with 4-bromo-1 -methylamino anthraquinone Cu and NaOAC -followed by alkylation by reacting this dye with undecyl aldehyde in nitrobenzene-piperidine. This blue red dye has an optical order parameter of 0.7. The transmittance curves of the color shift are shown in Figure 10.

EXAMPLE 8 1 -Nitroanthraquinone is refluxed with an excess of cyclohexylamine in o-dichlorobenzene to yield 1 -cyclohexylamino anthraquinone which is further brominated in aqueous pyridine to yield the corresponding 1 -cyclohexylamino-4-bromoanthraquinone. This compound is further condensed with pamino acetanilide to yield 1 -cyclohexylamino-4-(p-acetaminoanilino)anthraquinone as a bright green pleochroic dye having an optical order parameter 0.7.

EXAMPLE 9 One equivalent (2.4 g) 1 ,4-dihydroxyanthraquinone is added to a flask fitted with a reflux condenser, stirrer, containing 1 g boric acid and 0.5 g stannous chloride and 30 g 2-penylethylamine.

Stirring and heating ta 1300 for two hours and pouring into a 10% HCI solution yieldsbis(1,4- phenethylamino)anthraquinone as a pleochroic blue dye with an optical order parameter of 0.78.

EXAMPLES 10-19 A series of pleochroic dyes are produced by the procedure of Example 1 in which 0 and color, x, B', m of the general formula above and positions on anthraquinone nucleus are as indicated in Table 5 together with optical order parameter. The 1 ,4-cyclohexylene radical is indicated by S in the ring.

Table 5

Optical R' Order Example Color Positions R' m Parar,le,ter H 10 red 1,5 5 11 9 H 2 0.75 lit blue 1,5 OO N- 2 0.80 H 12 bluish red 1 8 C12H25N- 2 0.75 13 rnaroori 1,8 NO2sNH 2 14 red 1,8 FNH 2 0.75 15 red 1,5 C4H9ONHO 2 2 > 0.8 H 16 red 1,5 0N- 2 0.7 H 17 blue b b 2 0-7 18 reddish blue 1,8 9 N 2 0.85 fl cgi H 19 red 4 C5HilNH 2 0.8 5 C8Hl7OHN EXAMPLES 2S28 Further pleochroic dyes useful in guest-host combinations are prepared by condensing substituted dichloroanthraquinones with various amines by refluxing in an inert solvent such as nitrobenzene in the presence of sodium acetate and cupric acetate. Such deystuffs are shown in Table 6. Intermediates are known or readily available by known reactions.

Table 6

LI ar d d Order o Color 0 Position 0 R'Position o rn x Parameter c( al o yellow green 5,8 z H xl lue I I I I 1 I I H 22 red - -- 1,5 NO2S-N- 2 - 0.85 H 23 red z Z 1,5 NCSN- 2 z 1 m z W 1 m z red m -- 1,5 NCN- 10 25 purple - -- 1,8 CISH3INH 2 - 0.85 26 blue Z Z 1,4 V V V U H 27 red - -- 1,5 C5H11mffSON- 2 - 0.85 (n X o H N ~ H H H H H H P tr: I I I I I I I I 1 0 o ,l av v I I I I I í I I o un Pt 1 v s4 o o 3 a U o H H o z a > n v v v z n c c: H N n v tn W rW U N O1 N t N N N N x EXAMPLE 29 The procedure of Examples 20-28 is illustrated by the formation of 1,5bis(benzylamino)anthraquinone: To 20 g benxylamine with 0.1 g cupric acetate and 2.0 g sodium acetate and 10 g nitrobenzene in a suitable vessel is added 2.77 g of 1 ,5-dichloroanthraquinone. The mixture is refluxed 2 hours and the reaction mixture poured into methanol. The crude dye is collected and treated with hot nitrobenzene containing a small amount of piperidine. The red dye is purified from alcohol and washed with ether. The optical order parameter is 0.75.

EXAMPLE 30 A convenient method for introduction of a substituted amino group in place of a hydroxy group is to heat the hydroxy substituted anthraquinone with the amine in the presence of boric acid usually in an inert solvent such as nitrobenzene. This also facilitates the formation of anthraquinones having two different substituents, e.g., Example 1 9 above and 30 below.

1-Hydroxy-4-chloroanthraquinone is condensed with 1 equivalent p-(n-decyl)aniline in the presence of boric acid to yield 1-p(n-decyl)anilino)-4-chloroanthraquinone which is then condensed with 1 equivalent 2-aminoaphthalene in the presence of copper acetate-sodium acetate and when purified yields 1-p(n-decyl)anilino-4-nahthylamino-anthraquinone as a blue green pleochroic dye having an optical order parameter of 0.72.

EXAMPLES 31-39 A series of pleochroic dyes is prepared using the boric acid condensation reaction described in Example 29 as set forth in Table 7. In Examples 37 and 38 marked with asterisks, stannous chloride is also included as in Example 9 above.

Table 7

LI Optical Order ar o a35 QD Ut o o o O o o o (3 0 3 0 0 c( Color 0 Position 0 RP9sition m x Parameter CIL O reddish blue 5,8 v 32 blue green 5,8 OH m CH3NHj 2 2 tt) H 33 green 5,8 N N C8H17-ON- 2 2 0.68 5 NO2 m 34 bluish green 8 OH Z r,. Z H 1 C5H11N H 35 blue - mo m a o o co u u u z P U o ol "I 51 f P P o v z ,{ H mt tr H H v p, cz N N ,J et v o o m tn Ol U O z o U l Z e o St v at v X X o ur et to S' otl o tX < c &commat; ; tb4 C,t o ti o O m H < i4 o tn xm s t) ot c u,* U o O ot Q o X n n xJ N tN elç UZ tD mt n n m X n rr3 Table 7 (continued)

LI att rs b H v o O kl V1 CO al rl C)( 0 nr QI 0 0 xl Order EY.amole Color 0 Position 0 R'POSitiOfl m x Parameter H 37 reddish blue 5,8 Cl m z H m '1uish green z - 1,4 | 2 - 0.75 N H XI blue green - - Ci) I N o d v v v v o X X X P4 H ~I ~tt otl u o S 4 H c: u, X o un P4 al o r ot o t: , n k O o > o x < b4 o u. z > U H H o &commat; x v n n o g b O 5 n n i EXAMPLE 40 The guest-host combinations of this invention are especially useful because of their unusual fastness to light. To show the stability of these combinations a field effect device was constructed and a guest-host mixture of nematic liquid crystals of Example 1 containing 1% 1 ,4-bis(4-phenylanilino)anthraquinone (prepared as for the 1,5 isomer in Example 11) was used as the guest-host nematic component. The test sample was placed in an Atlas Weatherometer for 100 hrs. at 600C using a zenon U.V. light source with output at 340 nm of 0.1 5 nm/cm2.Absorption spectra show no decrease in max of the pleochroic dyestuff after 100 hous and less than 10% increase in current as measured across the electrode surfaces. The transmittance curves for the color shift are shown in Figure 11.

EXAMPLE 41 The improvement achieved by compositions of the invention over unsubstituted bis-phenylamino anthraquinone in guest-host combinations is illustrated by comparison of a composition of the invention (A) using the anthraquinone of Example 30 in which each phenyl group is substituted by an octyoxy group (in the 4 position of Ar of the general formula) with a composition (B) in which no substituent is present in the same position. Solutions are prepared in the dielectrically positive nematic liquid crystal mixture used in Example 1 at the same concentration and the transmittance curves measured as voltage is increased. The results are shown in Figure 12. The higher optical order parameter of about 0.7 of composition B demonstrates the increased contrast ratios, lower colored backgrounds and increase brilliance attainable in electro-optical devices using compositions of the invention.

Similar optical order parameter to those described above in Examples 1-39 are obtained when chiral agents such as cholesteryl nononoate are included in the nematic liquid crystalline materials in various amounts. When the amounts are small, i.e., about 0.5% it is found that there is more rapid reordering when an impressed voltage is removed.

Claims

1. As a composition of matter the combination having dielectrically positive anisotropy comprising at least one nematic liquid crystalline material having dielectrically positive anisotropy and from 0.01 to 50 percent by weight of pleochroic dyestuff of the general formula:

wherein substituents (NRR') and Q may be in positions 1 through 8, Q is F, Cl, NO2, NH2, NH(Alk), OH, xis 1,2,3, mis1 or2, R alone is H, R' alone is cyclohexyl, bicyclohexyl or -(CH2)Ar where pisO, 1 or2and Ar is aryl of 6 to 10 carbon atoms substituted as in the 4 position by -NHCOCH3,CN, -CnH2n+1, -OCnH2n+1, cyclohexyl, 4-(-Alk-)-cyclohexyl or

where y is O or 1, YisCH2, 0, S orOCH2 Z is a 4-substituted H, NO2, -CnH2n+1, -OCnH2n+1, F, Cl, or when y = 0 also C6Ha, and in from 0 to 2 further positions by CN, --C,H,,,,, --OC,H,,,,, N H2 or OH wherein n is 1 to 20 and Alk is alkyl of 1 to 8 carbon atoms.

2. The composition of matter according to claim 1 wherein there is additionally present from about 0.1 to 10 percent by weight of isotropic dyestuff having color contrast with respect to the normal color of the pleochroic dyestuff.

3. The composition of matter according to claim 1 wherein the nematic liquid crystalline material comprises from 10 to 20 percent by weight of N-p-alkoxybenxylidene-p'-amino-benzonitrile.

4. The composition according to claim 1 wherein the nematic liquid crystalline material comprises n-pentyl phenyl cyclohexylbiphenyl cyanide in a combination of n-propyl-, n-pentyl- and n-heptyl phenylcyclohexyl cyanide.

5. The composition according to claim 1 wherein the nematic liquid cryatalline material comprises combinations of 4-cyano-4'-alkyl biphenyls.

6. The composition according to claim 4 wherein the pleochroic dyestuff is 1 ,5-bis(p-(4-npentylcyclohexyl)-phenylamino)anthraquinone.

7. The composition according to claim 4 wherein the pleochroic dyestuff is 1,5 bis(biphenylamino)anthraquinone.

8. The composition according to claim 4 wherein the pleochroic dyestuff is bis(4-(pnitrophenylthio)phenyl-amino)anthraquinone in which the groups are in 1 4-, 1,5- or 1,8-positions.

9. The composition according to claim 4 wherein the pleochroic dyestuf is 1 ,4-bis(4-ndecyloxyphenylamino)anthraquinone.

10. The composition according to claim 1 comprising additionally chiral agent in an amount of about 0.1 to about 50% by weight based on the nematic liquid crystalline material.

11. The composition according to claim 10 wherein the chiral agent is chloesteryl nonanoate.

12. In an electro-optical device wherein an electrical field is imposed or withdrawn from action on a cell comprising liquid crystalline material having dissolved therein a pleochroic dye between transparent electroded glass plates, characterized in that the liquid crystalline material has dielectrically positive anisotropy and comprises at least one nematic liquid crystalline material having dielectrically positive anisotropy and the dissolved pleochroic dye has the general formula::

wherein substituents (NRR') and Q may be In positions 1 through 8, Q is F, Cl, NO2, NH2, NH(Alk), OH, x is 0, 1, 2, 3, mis 1 or 2, R alone is H, R' alone is cyclohexyl, bicyclohexyl or-(CH2)Ar where p is 0, 1 or 2 and Ar is aryl of 6 to 10 carbon atoms substituted as in the 4 position by-NHC0CH3, C N, -CnH2n+1, -OCnH2n+1, cyclohexyl, 4+AlkAcyclohexyl or

where y is O or 1, YisCH2, 0, Sor OCH2 Z is a 4-substituted H, NO2, CH, -CnH2n+1, -OCnH2n+1, F F, dl, or when y =0 also-C6H5, a and in from 0 to 2 further positions by CN, -CnH2n+1, # NH2, or OH wherein n is 1 to 20 and Alk is alkyl of 1 to 8 carbon atoms.

13. A composition as claimed in Claim 1 substantially as herein described with reference to any one of the Examples.

14. An optical device as claimed in Claim 12 substantially as herein described with reference to the accompanying drawings.