GB2027026A

GB2027026A - Aromatic azines and nematic liquid crystal materials of positive dielectric anisotropy containing them

Info

Publication number: GB2027026A
Application number: GB7926746A
Authority: GB
Original assignee: AMERICAN LIQUID XTAL CHEM
Current assignee: AMERICAN LIQUID XTAL CHEM
Priority date: 1978-08-04
Filing date: 1979-08-01
Publication date: 1980-02-13
Also published as: JPS5525481A

Abstract

A mixture suitable for use in a twisted nematic liquid crystal display comprising at least three different liquid crystal compounds having the general formula: <IMAGE> in which in two of the compounds, Y represents an imine and an ester linkage and X and Z represent monovalent radicals, and a third compound is of positive dielectric anisotropy and has the formula: <IMAGE> in which R<1> represents a saturated aliphatic radical containing 1 to 12 carbon atoms, R<2> represents a saturated aliphatic radical containing 1 to 7 carbon atoms, R<3> represents a hydrogen atom or a saturated aliphatic radical containing 1 to 7 carbon atoms, and R<4> represents a hydrogen atom, an alkoxy group or a saturated aliphatic radical containing 1 to 12 carbon atoms. The third compound has a high degree of stability, is not subject to hydrolysis and may be readily synthesized by reacting an appropriate aromatic ketone and, if required, an appropriate aromatic aldehyde with hydrazine hydrochloride. A sharper turn-on threshold voltage is achieved by its presence.

Description

SPECIFICATION Nematic liquid crystal material of positive dielectric anisotropy This invention relates to compositions suitable for use in a twisted nematic liquid crystal display.

As is known, with the advent of field-effect liquid crystal light shutters and alpha-numeric displays, a need has arisen for liquid crystal materials which are colourless, of positive dielectric anisotropy and at the same time nematic at room temperature. In the past, the liquid crystal material employed in fieldeffect light shutters usually consisted of a mixture of at least three different liquid crystal compounds having the general formula:

in two of the three compounds, the Y moiety comprises an ester linkage while the X and Z moieties comprise a saturated alkyl group or an alkoxy group having a chain of 1 to 18 carbon atoms. The third compound, which usually imparts positive dielectric an isotropy to the mixture, can be an ester or an aniline.United States Patent Specification No. 3 795 436 discloses that the third compound may comprise a cyano compound present in the mixture of the three compounds in the range of 3 to 40 weight percent and preferably 10 weight percent of the total mixture of the three compounds. One difficulty with cyano compounds of this type, however, is that they are somewhat unstable and subject to hydrolysis. The third compound may also comprise, for example, p-ethoxyalbenzylidene-pmethoxybenzylidine-p-butylaniline.

The present invention resides in the discovery that azine compounds can be formulated which are nematic and which have positive dielectric anisotropy but which do not contain a cyano group. The compounds have a high degree of chemical stability, meaning that they are not subject to hydrolysis.

At the same time, they provide for a sharper turn-on threshold voltage and are less expensive to synthesize.

The compounds for use in the invention have a positive dielectric anistropy and are of the formula:

in which R' represents a saturated aliphatic radical containing 1 to 12 carbon atoms, R2 represents a saturated aliphatic radical containing 1 to 7 carbon atoms, R3 represents a hydrogen atom or a saturated aliphatic radical containing 1 to 7 carbon atoms, and R4 represents a hydrogen atom, an alkoxy group or a saturated aliphatic radical containing 1 to 12 carbon atoms.

The present invention provides a mixture suitable for use in a twisted liquid crystal display comprising at least three different liquid crystal compounds having the general formula:

in which in two of the compounds, Y represents an imine and an ester linkage and X and Z represent monovalent radicals and a third compound is of positive dielectric anistropy and has the formula:

in which R1 to R4 are as defined above.

The method used for the preparation of both symmetrical and unsymmetrical azines involves reaction of one moe of ketone with one moe of hydrazine monohydrochloride in methanol, with the addition of acetic acid as a catalyst, to form an intermediate hydrazone hydrochloride. The hydrazone is purified by recrystallisation from methanol. The purificed material is then reacted with a second mole of ketone (or aldehyde) in methanol with the addition of sodium acetate to free the hydrazone hydrochloride for reaction. After a brief reflux period, the reaction mixture is chilled in ice water or liquid nitrogen and the resulting precipitate is filtered and purified by recrystallization.

The reaction is illustrated by the following equation:

By using hydrazine monohydrochloride, the usual mixture of symmetrical and unsymmetrical azines obtained when hydrazine is employed can be avoided and nearly pure unsymmetrical azine can be obtained. Also, the acetic acid catalyst necessary for the reaction is produced in situ by the action of sodium acetate on the hydrazone hydrochloride.

If symmetrical azines are desired, it is often more convenient to combine two moles of the carbonyl compound with one mole of hydrazine in methanol with a small amount of acetic acid catalyst:

After a brief reflux period, the reaction mixture is chilled and the precipitate is filtered and purified by recrystallization.

The invention will now be illustrated by the following Examples.

EXAMPLE 1 4,4'-Dibutyl-,'-dimethylbenzal azine 7.24 g (40 mmol) of p-butylacetophenone, 0.64 g (20 mmol) of hydrazine, 25 ml of methanol and a small amount of acetic acid were added to a 100 ml round-bottom flask. The reaction mixture was allowed to refluxfor one half-hour. Upon cooling, the product separated out of solution as an oil, which crystallized upon further cooling. The solid product was recrystallized twice from hexane.

EXAMPLE 2 4'-Pentyl--ethyl-a'-methylbenzal azine 3.9 g (20 mmol) ofp-pentylacetophenone and 1.2 g (20 mmol) of acetic acid followed by 100 ml of methanol were added to a 250 ml round-bottom flask. Hydrazine monohydrochloride (1.36 g, 20 mmol) dissolved in water was then added. The reaction mixture was stirred at OOC until a yellow precipitate was formed. The precipitate was filtered by suction and washed successively with cold methanol and water. The hydrochloride was recrystallized once from methanol.

The purified hydrazone (4.9 g, 20 mmol) was added to a 250 ml round-bottom flask.

Propiophenone (2.7 g, 20 mmol), 100 ml of methanol and 1.64 g (20 mmol) of sodium acetate were added and the reaction mixture was refluxed for one-half hour. Upon cooling, the product separated from solution. The precipitate was filtered by suction, and washed successively with cold methanol and water. The material was purified by recrystallization from hexane.

MIXTURES For use in a liquid crystal display, a mixture of an azine with other liquid crystal materials is employed. The other materials are preferably at least two in number and have the general formula:

The moietyY is an amine or an ester linkage. The azine is present in the mixture of the compounds in the range of 3 to 40 weight percent and preferably about 10 weight percent of the total mixture.

Three mixtures, each containing 10% by weight of an azine were prepared. The composition of the base material is as follows: Base p-Ethoxybenzylidine-p-butylaniline 36% p-Pentylphenyl-p-methoxy-benzoate 19% p-Cyanobenzylidine-p-butylaniline 10% p-Cyanophenyl-p-meth oxy-benzoate 5% p-Cya nophenyl-p-pentyl-benzoate 5% p-Cyanophenyl-p-heptyl-benzoate 7% p-Cyanophenyl-p-heptyloxy-benzoate 3% p-Cyanophenyl-p-octyloxy-benzoate ' 5% The azine materials that were used are listed as follows:: A1 = 4,4'-dibutyl-α,α'-dimethylbenzal azine

A2 = 4'-pentyl-α-ethyl-α'-methylbenzal azine

A3 = 4'-butyl-cg-butylbenzal azine

The resulting clearing points of the three mixtures are summarized in the following Table I.

TABLE I

Clearing points Clearing points Mixture Composition of compounds of mixtures I Base 60 59.2 Base II Base 60 62.0 A2 82.4 III Base 60 63.8 A3 71.8 Examples of pentylacetophenone derivatives, butylacetophenone derivatives, acetophenone, propiophenone derivatives, valerophenone derivatives and butyrophenone derivatives are given in the following Table II together with their transition temperatures in degrees centigrade.

Table II Examples of nematic liquid crystal compounds of positive dielectric anisotropy having the general formula:

Compound Crystalline Nematic Crystalline to to to nematic OC isotropic isotropic OC OC C5Hll O) 68.2-71.3 78.5 I C5H1N-C- O -CqHg 70.2 75 I (super It cools to 50.3) C5H11NŏaI3o 110-175 CH3 CE3 OC"'N-O II + 4hug 73.5 cr I 4 9 67.3 (super CH3 CH3 cools to 56.7) C4E9&num; rN=C1o41119 53 (s6uper C1l13Cll3 3 CH3 cools to 35) C5H110 110 CiN-N=C &commat; C5H11 110 117.3 CH3 H CEȮ 59.5 CI&num;N-NiC 1 C3H70 59.5 64 CH3 H C4Hg &commat; O N=CI &commat; C4Hg 50,5 (s6u9pe9r 013 H (super 34) When mixing the azines of Table II with the base material described above, one selects the temperature range for the material, and the percentage of such material used, so as to obtain the desired temperature range for the nematic liquid crystal phase for any particular intended use of the liquid crystal system.

Claims

1. A mixture suitable for use in a twisted nematic liquid crystal display comprising at least three different liquid crystal compounds having the general formula:

in which in two of the compounds, Y represents an imine and an ester linkage and X and Z represent monovalent radicals, and a third compound is of positive dielectric anisotropy and has the formula:

in which R1 represents a saturated aliphatic radical containing 1 to 12 carbon atoms, R2 represents a saturated aliphatic radical containing 1 to 7 carbon atoms, R3 represents a hydrogen atom or a saturated aliphatic radical containing 1 to 7 carbon atoms, and R4 represents a hydrogen atom, an alkoxy group or a saturated aliphatic radical containing 1 to 1 2 carbon atoms.

2. A mixture as claimed in Claim 1 in which in said two of the compounds, X and Z independently represent an alkyl group having 1 to 1 8 carbon atoms or an alkoxy group having 1 to 1 8 carbon atoms.

3. A mixture as claimed in Claim 1 or Claim 2 in which said third compound is present in the mixture in the range from 3 to 40 weight percent.

4. A mixture as claimed in any one of claims 1 to 3 in which the third compound has the formula:

5. A mixture as claimed in any one of claims 1 to 3 in which the third compound has the formula:

6. A mixture as claimed in any one of claims 1 to 3 in which the third compound has the formula:

7. A mixture as claimed in any one of claims 1 to 3 in which the third compound has the formula:

8.A mixture as claimed in any preceding claim containing, by weight percent, 36% p ethoxybenzylidine-p-butylan iline, 19% p-pentylphenyl-p-methoxy-benzoate, 10% p-cyanobenzylidine-p butylaniiine, 5% p-cyanophenyl-p-methoxy-benzoate, 5% p-cyanophenyl-p-pentyl-benzoate, 7% pcyanop henyl-p-heptyl-benzoate, 3% p-cyanophenyl-p-heptyloxy-benzoate, 5% p-cyanophenyl-poctyloxybenzoate, and ten percent of said compound having the formula:

9. A mixture as claimed in Claim 1 suitable for use in a twisted nematic liquid crystal display substantially as herein described with reference to the Examples.

10. A compound having a positive dielectric anisotropy of the general formula:

in which R' represents a saturated aliphatic radical containing 1 to 12 carbon atoms, R2 represents a saturated aliphatic radical containing 1 to 7 carbon atoms, R3 represents a hydrogen atom or a saturated aliphatic radical containing 1 to 7 carbon atoms, and R4 represents a hydrogen atom, an alkoxy group or a saturated aliphatic radical containing 1 to 1 2 carbon atoms.