CH643291A5 - LIQUID CRYSTAL COMPOSITION FOR ELECTRO-OPTICAL DEVICE. - Google Patents

Description

The present invention relates to a composition based on liquid crystal containing in solution an anthraquinone pleochroic dye and usable in electro-optical devices, more particularly in display devices.

For a colorant to be suitable for use in solution in a liquid crystal for display devices, it must have at least the following properties:

- be sufficiently soluble in the liquid crystal;

- be perfectly stable chemically (especially inert vis-à-vis the liquid crystal) and especially photochemically (stable to UV light);

- have a sufficient absorption intensity; and

- not contain ionic or ionizable groups.

In addition, such a dye must have a high “S” order parameter, this parameter corresponding to the measurement of the orientation power of the dye by the molecules of the liquid crystal, so that a high contrast display can be obtained. Finally, the basic structure of the envisaged compounds must of course correspond to a color suitable for use in a display device, preferably blue and red.

In patent application FR 8 016 662 from the same holder, this describes a composition based on liquid crystal containing in solution an anthraquinone derivative having the following general formula,

Y

0

R

R

R

usable as plechroic dye and having in particular a high order parameter, as well as a high light stability, this composition also being intended to be used in electro-optical devices in particular in display devices.

By continuing their research, the present inventors have found that other anthraquinone dyes of the same type but with an ester substituent are also s

10

15

20

25

30

35

40

45

50

55

60

65

3

643,291

valuable pleochroic dyes, usable in compositions based on liquid crystal.

The object of the present invention therefore consists of a composition based on liquid crystal containing at least one pleochroic dye of formula (I),

Y

R

O

R

wherein R1 is an amino group which can be alkylated or acylated, or a substituted or unsubstituted hydroxy group; R2, R3 and R4, identical or different, are each a hydrogen atom, an amino group which may be alkylated or acylated, a substituted or unsubstituted hydroxy group, a nitro group, a halogen atom, or a cyano group; X is a group -COOR-5 or a group -OOCR5, where Rs is a linear, branched or cyclic alkyl chain, an alkoxyalkyl chain, a cyanoalkyl chain, the alkyl residue having from 1 to 16 carbon atoms, or a group

Z

n where Re is a hydrogen atom, an alkyl chain, an alkoxy chain, a cyano group, an amino group, a dialkylamino group, the alkyl residue having from 1 to 16 carbon atoms, Z is a hydrogen atom, a halogen atom, a hydroxy group, a lower alkyl group or a lower alkoxy group, and n is an integer from 1 to 4; and Y has the same meaning as X or is a hydrogen atom.

Preferably, the group Y is in position 6 when X is substituted in position 2 on the anthraquinone nucleus, and in position 7 when X is substituted in position 3.

The order parameter, measured in a liquid crystal, of the dye of formula (I) is generally higher when Y = X than when Y = H. This is particularly true when the mixture of liquid crystals used is based on esters or contains an ester component.

As regards the length of the side chain (s) (), it partly determines at least the solubility of the compound of formula (I) and should therefore not exceed approximately 24 carbon atoms. The substituents Rs and Re each preferably have a maximum of 10 carbon atoms, but when several of these groups are present simultaneously, the total of the carbon atoms does not in principle exceed about 24. Above, the compound (I) risks not to be sufficiently soluble in the liquid crystal and therefore unusable as a dye for the latter.

The anthraquinone dyes described in the patent CH (application 7543/79 of August 17, 1979) mentioned above, have a high order parameter in mixtures of liquid crystals based on biphenyl, pyrimidine or phenylcyclohexane. However, the order parameter values of these same dyes decrease significantly when dissolved in a mixture containing an ester liquid crystal. However, liquid crystals of negative dielectric anisotropy, essentially consisting of esters, have found applications in particular in dichroic display devices with positive contrast such as those described for example in the CH patent (application 1272/78 of February 6 1978).

The ester derivatives represented by the following general formula,

OH

OCR

O

NH

HO

where R is an alkyl chain or a substituted phenyl group, also described in the aforementioned CH patent, however, are exceptions, as are the ester derivatives represented by the general formula (I). These are therefore of great practical interest, especially since they are relatively easy to synthesize.

The invention will now be illustrated by means of an example of a compound of formula (I), the properties of which are studied are listed in the table below. More particularly, the solubility and the order parameter of this compound were measured using the following known techniques.

- Solubility measurement (by colorimetry)

A saturated solution of the compound (I) is prepared in a liquid crystal, and the solution obtained is filtered. Then, 100 μl of the filtrate are removed and dissolved in 50 cc of chloroform.

Then, the optical density of this solution is measured spectroscopically, and the concentration of the saturation dye is deduced from this measurement, the absorption coefficient being known in chloroform.

The result obtained is shown in the Table below. Regarding the value given for solubility, it should be noted that the solution was considered to be saturated when it contained dye grains after heating in the isotropic phase and stirring for 3 minutes.

- Determination of the order parameter (S)

A 0.5% solution of the compound studied in a liquid crystal is introduced into a 30 µm thick glass cell coated with an alignment film (SiOx tangentially evaporated in rubbed polyimide). Then the optical density of this solution is measured at its maximum absorption in polarized light on the one hand when the direction of the polarizer is parallel (D //), on the other hand perpendicular (D -), to the direction alignment, and the order parameter is calculated from the following relationship:

where r is the dichroic ratio, corresponding to the Bi7 ratio • The result obtained is also reported in the Table below.

s

10

15

20

25

30

35

40

45

50

55

60

643 291 4

Board

Properties of the compounds of formula (I)

Compound (I) Physical properties Optical properties A. max (nm) Order parameter

Solubility Point Tn-i (CHCta CL CL solution

fusion (° C) in CL (%) 0.5% in CL)

0 NH,

@ ^ Iorcoo- <ö}

O NH,

261-262.7 0.6

60.0 ° C

596,628

605

643

605,641

0.64 0.65

0.67 .0.68

NB. The liquid crystal (LC) in which the measurements of solubility, of the nematic-isotropic transition temperature (Tn-i) and of the order parameter were carried out is “E7” from BDH Chemical Limited (mixture of cyanobiphenyl and cyanoterphenyl with positive dielectric anisotropy), except for values accompanied by an asterisk (*), the measurements of which were carried out in "Lixon EN 17 H" by Chisso Corp. (mixture of ester and Schiff base with negative dielectric anisotropy).

The compounds of formula (I) which can be used as dyes in solution in liquid crystals for display devices can be prepared by the conventional methods of synthesis of anthraquinone compounds described in the literature.

In the composition according to the invention, it is possible to use a single type of liquid crystal or preferably a mixture of liquid crystals such as those sold for example by BDH Chemicals Limited under the references E3, E7, E8 or E9 and whose respective compositions are mentioned in published European patent application No. 78 300487.2, or by Chisso Corp. under the references "EN 17" or "EN 18" (see Takashi Innukai, J.E.E. Sept. 1979, p. 84). They are preferably nematic liquid crystals with positive or negative anisotropy, which may or may not additionally contain an optically active agent.

In addition, the composition according to the invention may comprise several dyes of formula (I) or optionally other types of anthraquinone dyes, as well as a cholesterization agent and / or alignment agent. As cholesteric agent, there may be mentioned that sold by BDH 25 Chemicals Limited under the reference "CB 15", which is preferably added in an amount of approximately 3% relative to the total composition. As an alignment agent for dispersing the molecules of the liquid crystals perpendicular to the walls of the electro-optical device, about 2% of a surfactant can be used, for example a sorbitol monoester, sorbitol monolaurate being particularly suitable.

Finally, the pleochroic dye of formula (I) is generally present in the composition according to the invention in an amount corresponding to approximately 0.5 to 5% of the total composition, for example preferably approximately 1.5%.

Of course, the composition according to the invention may contain several compounds represented by formula (I), as well as one or more anthraquinone dyes of different form.

Claims (10)

643291 2. Composition according to claim 1, characterized in that Y is in position 6 or 7 of the anthraquinone nucleus when X is substituted in position 2 and in position 6 or 7 when X is substituted in position 3. 2 CLAIMS 1. Composition based on liquid crystal containing a pleochroic dye and intended to be used in an electro-optical device, characterized in that the dye is an anthraquinone compound represented by the general formula (I), R 0 R wherein R 1 is an amino group which may be alkylated or acylated, or a substituted or unsubstituted hydroxy group; R2, R3 and R4, identical or different, are each a hydrogen atom, an amino group which may be alkylated or acylated, a substituted or unsubstituted hydroxy group, a nitro group, a halogen atom, or a cyano group; X is a group -COOR5, or a group -OOCR5, is a linear, branched or cyclic alkyl chain, an alkoxyalkyl chain, a cya-noalkyl chain, the alkyl residue having from 1 to 16 carbon atoms, or a group "n where R" is a hydrogen atom, an alkyl chain, an alkoxy chain, a cyano group, an amino group, a dialkylamino group, the alkyl residue having from 1 to 16 carbon atoms, Z is a hydrogen, a halogen atom, a hydroxy group, a lower alkyl group or a lower alkoxy group, and n is an integer from 1 to 4; and Y has the same meaning as X or is a hydrogen atom. 3. Composition according to claim 1 or claim 2, characterized in that the anthraquinone base structure substituted in position 2 or 2 and 6/7 or 3, or 3 and 6/7, is chosen from the group comprising amino-1-anthraquinone, diamino-1,4-anthraquinone, diamino-1,5-anthraquinone, diamino-1,8-anthraquinone, amino-1-hydroxy-4-anthraquinone, diamino-1, 8-dihy-droxy-4,5-anthraquinone, diamino-l, 4-nitro-5-anthraqui-none, tetramino-1,4, -5,8-anthraquinone, dia-mino-l, 5- dihydroxy-4,8-anthraquinone and amino-1-nitro-4-anthraquinone. 4. Composition according to claim 1, characterized in that the dye is represented by the formula: NH 0 NH 5. Composition according to claim 1, characterized in that it comprises one or more nematic liquid crystals with positive or negative anisotropy. 6. Composition according to claim 5, characterized in that it comprises an optically active agent inducing a cholesteric structure and / or an alignment agent. 7. Composition according to claim 1, characterized in that it contains a solution of 0.5 to 5% of an anthraquinone dye of formula (I). 8. Composition according to Claims 6 and 7, characterized in that it comprises approximately 0.5% of an anthraquinone dye of formula (I), approximately 3% of a cholesteric agent and approximately 2% of an agent alignment. 9. Composition according to claim 1, characterized in that it comprises at least one other anthraquinone dye of formula (I). 10. Composition according to claim 1, characterized in that it comprises at least one other anthraquinone dye different from those represented by formula (I).