CA1040411A

CA1040411A - Electro-optical display element

Info

Publication number: CA1040411A
Application number: CA209,501A
Authority: CA
Inventors: Akio Moriyama; Masakazu Fukai; Hiroaki Takahashi; Hiroshi Tatsuta
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1973-09-19
Filing date: 1974-09-18
Publication date: 1978-10-17
Also published as: DE2445164A1; FR2243980B1; US3960751A; DE2445164C3; DE2445164B2; FR2243980A1; GB1482542A

Abstract

ABSTRACT OF THE DISCLOSURE

An electro-optical element comprising a nematic liquid crystal composition and at least one compound represented by the formula:

or wherein R is an alkyl radical having from 4 to 20 carbon atoms.
Said compound is a pleochroic dye having a special function which differs from hitherto known dyes in its inter-action with nametic liquid crystal molecules. The electro-optical element makes it possible to obtain a liquid crystal display device which can exhibit the desired figure in colors differing from background colors.

Description

1()4041~
B~CKGROUND OF THE I~ENTI~N
: ~ ~ .
; ~
Field of the Invention . I
The present invention relates to an electro-optical element composed of nematic liquid crystal composition having pleochroic dyes dissolved therein.
More particularly, it pertains to an electro-optical element making use of compositions of nematic liquid crystals containing at least one species of dyestuff represented by the undermentioned chemical formulae:

~ R RNM O

¦ ~ or O I-INR O

wherein R is a radical chosen from the group consisting of alkyl radical having from 4 to 20 carbon atoms.

Description of the Prior Art . - ,~
In general, a liquid crystal device is usually composed of two parallel flat plates whose inner surfaces are coated with thin electrodes. Said plates are held at a distance of several microns, e.g. several tens of microns, and in the space between said plates there is contained a liquid crystal composition.
The opticalcharacteristics of this device may be controlled by .j .
means of electric or magnetic field.
When an electric fieldis applied on a layer of a nematic , liquid crystal having a pleochroic dye dissolved therein, the ' layer exhibits turbulent motion or the molecules in the layer are orientated along the direction of the electric field and at this time, the dye molecules exhibit co-operative behavior : . , :`

with the nematic liquid crystal molecules, whereby a change in the optical absorption of the device is obtained.
In order to increase the optical absorption change of the device, it is desirable that nematic liquid crystal layer have a homeotropic, homogeneous or twisted structure, wherein the arrangement of nematic liquid crystal is selected, according to the difference in the dielectric anisotropy of the nematic liquid crystal and the direction of the applied electric field.
For example, when using nematic liquid crystals having negative dielectric anisotropy, the dye molecules are placed in homeotropic or twisted structure (a structure in which the long axis of the liquid crystal molecules is aligned perpen-dicular to the vessel wall), and when using nematic liquid crystals having positive dielectric anisotropy, they are placed in the homogenous or twisted structure (a structure in which the long axis of the liquid crystal molecules is aligned parallel to the vessel wall).
In the liquid crystal device, where the nematic liquid crystal molecules are arranged in a predetermined direction, the molecularaxis of the liquid crystal can be controlled to turn a maximum of90 degrees by applying an electric field.
As the dye molecules are oriented co-operatively with the alignment of the nematic liquid crystal materials-in the electric field, a display with high contrast can be obtained in the aligned phase of a nematic liquid crystal.
As dyes, azo, anthraquinone, azine, xanthene and related coloring matter and other various dyes which are soluble in the liquid crystalline substances are available.
Of these dyes, some induce a change of optical absorption of the device, but some do not, when they are placed in the aligned phase of the liquid crystal, and then, an electric field is imposed on them.

104~411 The dyes may be further classified by 4 different functions based on the way in which the change of optical ab-sorption of the device (the change of state from when the electric field is not applied to the state when the electric field is applied) takes place as follows:
(~) Dyes which change from the colorless state to colored state.

(2) Dyes which change from the colored state to colorless state.

(3) Dyes which change from a colored state to another colored state showing a different hue.

(4) Dyes which do not undergo the change of state when the electric field is applied.
Displays with color to color contrast can be achieved by mixing a plurality of dyes which have different hue and different function in display performance.
Most of the customary pleochroic dyes are usually long cylindrically shaped molecules and show little or no absorption of light in the direction along its long axis and absorption oflight by the dye itself in the direction along its short axis.
When such dyes are placed in the nematic liquid crystal layer having a homeotropic structure at an appropriate concentration .such that no unoriented molecules are left behind, the transmitted light comes to the eyes of the observer in the colorless state with no applied field and in the colored state when an orientating field is applied.
Moreover, when they are placed in the nematic liquid crystal layer having a homogeneous or twisted structure, the transmitted light comes to the eyes of the observer in the colored state with no applied field and in the colorle-ss state when an orienting field is applied.
The dyes of this kind include compounds suah as:

~04Q411 011 i.
~N--N~--OH (Orange), I1 ~N
eN~ (Yellow), 1:10 = N~N--N~ ed), OII OC~H ~ OCH3 H,O
(Sca rlet red), =~ Nl~ /CI13 NI-~ CH 3 i~ (Bl~ ~C113 IN--~-- Cl13 O (Violet), or ~ (Green), etc O HN ~--CH3 i . :

~04V411 Objects of the Invention The dyes employed for the element of this invention are dyes having a different function contrasting with the above-listed dyes. Thus, when the dye molecule is palced in the aligned phase of the liquid crystal, the transmitted light along the long axis of the liquid crystal molecule comes into the eyes of the observer in the colored state with no applied field, while the transmitted light along the short axis of the liquid crystal molecule is observed in the colorless state with no applied field.
No dyes of this kind have ever been discovered. They are truly novel dyes.
Therefore, it is an object of the present invention to provide an electro-optical element comprising a,nematic liquid crystal and a novel pleochroic dye to control the color dis-played in the electro-optical device under conditions different from the use of a conventional dye.
It is another object of the present invention to provide electro-optical element comprising a nematic liquid crystal and mixture of the novel pleochroic dye and the conventional one to display the background and the figure of the electro-,optical device in the different colors.
A further object of the present invention is to control the color exhibited by a pleochroic dye in polarized light.
A further object of the present invention is to provide novel display device.

A further object of the present invention is to provide novel display systems.
Those objects are cachieved by providing an electro-optical eIement and an electro-optical display device according to the present invention. The electro-optical element comprising ~04~411 a nematic liquid crystal and at least one compound rep-resented by the formula:

~ or O HNRl O

wherein Rl is an n-alkyl radical having from 5 to 20 carbon atoms and R2 is an n-alkyl radical having from 4 to 20 carbon atoms in an amount of from 0.5 to 5~ by weight.
. ~he electro-optical' display device comprises two parallel transparent members whose inner surfaces have been coated with transparent electrodes; an electro-optical element comprising a nematic liquid crystal composition con-taining at least one compound represented by the formula [~ ~
O H Rl wherein Rl is an n-alkyl radical having from 5 to 20 carbon atoms and R2 is an n-alkyl radical having from 4 to 20 B~

104~)411 carbon atoms, in an amount of 0.5 to 5 percent by weight, said eleOEtro-opt.ical element being interposed between said electrodes and having all its moleaules in their quiescent state, non-electrically aligned perpendicular or parallel to such facing surfaces, and means for selectively applying an electric field across said electro-optical element through said electrodes to exceed a threshold electric field.

Brief Descripti n of the Drawings Other objects and advantageous features of the present invention will become apparent from the following description of some embodiments thereof, taken together with the accompanying drawing, in which:
Fig. 1, (A), diagramatically shows the spatial - 6a -:31`

.

104~411 arrangement of a dye molecule in the liquid crystal, as a typical example of conventional dyes.
Figure 1, (B) and (C), diagramatically show the spatial arrangement of the dye molecule of this invention in a liquid crystal.
Figure 2 represents change of optical absorption characteristics of the liquid crystal device which has the homeotr-opic structure of a nematic liquid crystal composition consisting of the nematic liquid crystal with negative dielectric aniso-tropy and one of the dyes of this invention, where the field isapplied and not applied.
Figure 3 represents change of the absorption character-istics of the liquid crystal device which has the homogeneous structure of a nematic liquid crystal composition consisting of nematic liquid crystal with positive dielectric anisotropy and one of the dyes of this invention, where the field is applied and not applied.
Figure 4 represents change of the absorption character-istics of the liquid crystal device which has the homeotropic structure of liquid crystal composition consisting of nematic liquid crystal with negative dielectric anisotropy and mixture of functionally different dyes in combination with the dyes of this invention.
Figure 5 shows a display device according to this invention, which is effective to obtain a high contrast ratio.

Detailed Description of this Invention That the dyes used according to this invention, i.e., the 1,4-bisalkyl-amino-anthraquinone dye or 1,8-bisalkyl-amino-anthraquinone dye, have special functions i5 attrlbutable to the special molecular configuration of these dyes~
- These dyes are believed to show slight absorption in 1~4~)411 the direction along the long axis of the anthraquinone ring, being the chromogen, and have the main absorption axis in the direction along the short axis of the ring.
In the oriented structure of the nematic liquid crystal, it may be supposed that the molecular chain of the alkylamino radical, being the auxochrome in these dyes, is arranged parallel to the long axis of the liquid crystal molecule, while the long axis of the anthraquinone ring extends in the per-pendicular direction thereto, so that a stable spatial arrangement may be achieved.
For this reason, transmitted light along the long axis of the liquid crystal molecules comes to the eyes of the observer in the colored state, after being absorbed by this dye.
Figure 1, (A), diagramatically shows the spatial arrangement of a red dye in the liquid crystal, MQ

~ N=N ~ N - N ~ , as a ~picalexampleof a conventional dye. Its long molecular axis is aligned parallel to the long molecular axis of the liquid crystal, and for this reason, the light transmitted along this axial direction is observed in the colorless state when white incident light is irradiated thereon.
In contrast, Figure 1, (B) and (C), diagramatically show the spatial arrangment of the dyes of this invention in the liquid crystal (B) illustarates, 1,4-bisalkylamino-anthraquinone, and (C) 1,8-bisalkylaminoanthraquinone. The long molecular axis of anthraquinone ring is aligned in the direction perpendicular to the long molecular axis of the liquid crystal molecule. For this reason, the light transmitted along the molecular axis the liquid crystal molecule is observed in .. . ~ ,. ...

the colored state. 1040411 In the following, examples of dyes used in the electro-optical element of this invention and embodiments of the liquid crystal devices making use of such an element are described:
Embodiment 1:
First of all, examples of dyes used according to this invention are listed in Tables 1 and 2, giving the colors and melting points thereof.

Table 1. 1,4-bisalk~laminoanthraquinone R H~R

O IlNR

Melting Compound point No. R Color of dye lC) 1. Butyl n-C4Hg Light reddish violet 120 2. Pentyl n-C H Light reddish v~olet 117 3. Hexyl n C6H12 Dark reddish vi~olet 95 4. Heptyl n C7H15 Dark blue 93

5. Octyl n-C8H17 Dark blue 77

6. ~onyl n-CgHlg Bluish violet 81

7. Dodecyl n-C12H25 Blue 85

8. Octadecyl n C18H37 Blue 96 Table 2. 1,8-bisalkylaminoanthraquinone R~H ~ III K
e~ , O

104~411 Melting Compound point No. R ~ Color of dye (C) 1. Butyl n-C4Hg Reddish yi~let 110 2. Hexyl n-C6H13 Blackish yiolet 97 3. Heptyl n C7H15 Blackish Violet 84 4. Octyl n C8H17 Dark reddish violet 70 5. Decyl n C10 21 Reddish violet 83 6. Dodecyl n C12H25 Dark reddish violet 88 7- Octadecyl n-C18H37 Reddish violet 96 These dyes may be manufactured in the following ways:

(Manufacture of 1,4-bisalkylaminoanthraquinone.) For example, in manufacturing 1,4-bisdodecylamino-anthraquinone, 2.7 g (0.01 mol) of leucoquinizaline and 9 g of n-dodecylamine in 30 ml of pyridine is refluxed overnight.
Initially the solution is brown in color. It turns blue after being refluxed. The reaction mixture is poured into 10% aqueous solution of hydrochloric acid. The separated product is filtered off, and then, is refined by recrystallizing it with the use of methyl Cellosolve (Cellosolve is a Trademark of Union Carbide Co., Ltd. for ethyleneglycolmonoethylether).

Other compounds may also be obtained by reacting leucoquinizaline with the corresponding alkylamines in the similar way.
These dyes all give their maximum absorption at 652 nanometers in benzene and their solutions are colored blue.
(Manufacturing of 1,8-bisalkylaminoanthraquinone).
For example, in manufacturing 1,8-bisbutylamino-anthraquinone, 4.8 g (0.0173 mols) of 1,8-dichloroanthra-quinone, 0.112 g of copper, 4.3 g of sodium acetate and 33 g (0.451 mols) of n-butylamine are mixed. The mixture is boiled while stirring for 2 hours, and after letting it cool down, it is poured into 10% aqueous solution of hydrochloric acid.

Al~

104~)411 The separated product is filtered off, and recrystallized with the use of glacial acetic acid.
Other c~mpounds may be obtained by reacting l,8-dichloroanthraquinone with the corresponding n-al'~-.ylamines in the similar way.
These dyes all give their maximum absorption at 560 nanometers in benzene and their solutions are colored reddish violet.
Embodiment 2:

Firstly, the combination of a composition of a nematic liquid crystal having negative dielectric anisotropy and the ~yestuffs based on this invention is described.
The layer of above mentioned composition may be ar-ranged to have a homeotropic structure.
This liquid crystal device was composed of two transparent glass plates with a transparent electrode of indium oxide put thereon, held parallel to each other at a distance of about lO microns, and disposing the element of this invention in this space.

The composition of the nematic liquid crystal having negative dielectric anisotropy employed in this embodiment was a mixture of, CI-130 ~ CI1= N ~ C7Hl5 C2H50 ~ CH= N ~ c~-lg, an~

C3 7 ~ C~= N ~ C51I~1, , being a composition of them l : l : l in weight ratio (de-; signated mixted liquid crystal A). Into this composition, about l weight percent of any one of the dyes listed in TabLes l and 2 was mixed. Furthermore, in order to provide a phase of homeotropic structure, two weight percent of a commercially _ _ . . , . . _ . .

1~4~411 available surface active agent Nonion LP -20R (a trademark of Hihon Yushi, Ltd., Japanl comprising sorbitan monolaurate was added for controlling the molecular arrangement.
The display device of the liquid crystal containing the composition of 1,4-bisalkylanthraquinone or 1,8-bisalkyl-anthraquinone respectively gives a blue or reddish violet color in the absence of electric field. Under an electric field which induces no dynamic scattering, as when an electric field of 20 volts and 1 KHz was applied, the color disappeared, and the colorless state was brought about in all cases.
Such a change of state in the device has never been recognized with hitherto known dyes.
This composition gives a colored scattering state of emulsion when an electric field which induces the dynamic scattering is applied.
Figure 2 shows the change of the absorption character-istic of the liquid crystal device when it contained 1,8-bisheptyl-aminoanthraquinone. The solid line indicates the absorption wave form; and the broken line, the absorption wave form when an electric field of 15 volts and 1 KHz was applied.
Embodiment 3:
In the following, a combination of a composition of a nematic liquid crystal having positive dielectric anisotropy and the dyestuff of this invention is described:
This liquid crystal layer is used to form a homo-geneous structure.
The liquid crystal device was composed by holding parallel to each other two glass plates having transparent electrodes of indium oxide placed thereon, with their surfaces rubbed with a cotton cloth in one direction for the purpose of obtaining homogeneous structure orientation in the liquid crystal layer, so disposed that the rubbing direction of the surface of the first plate and the rubbing direction of the surface .

of the second plate are parallel to each other, and then, placing the element of this invention in this interspace.
The nematic liquid crystal having the Eositive di-electric anisotropy employed in this instance is a composition formed by adding lO weight percent of C4H90 - ~ CII= N ~ CN
to the aforementloned mixture composition ~of a nematic liquid crystal having negative dielectric anisotropy.
Into this composition, about 1 weight percent of any one of the dyes listed in Table 1 or Table 2 was mixed.
The liquid crystal device in which is housed the element containing 1,4-bisalkylaminoanthraquinone and 1,8-bisalkyl-aminoanthraquinone shows the colorless state in the absence of electric field, but produces the color of blue or reddish violet when the electric field is applied.
Figure 3 shows the change of the absorption character-istic of the liquid crystal device when it contains 1,4-bisheptylalkylaminoanthraquinone. The solid line indicates the absorption wave form in the absence of the electric field;
and the broken line, the absorption wave form when an electric field of 20 volts and 50 Hz was applied.
Embodiment 4:
~ Liquid crystal devices using a liquid nematic crystal ; into which at least two dyes which have different hue and dif-ferent function in display performance are mixed in combination with the dyes of this invention are described:
Into the liquid crystal device of Embodiment 1, were mixed the dyes of Table 3 in combinations as indicated in Table 4. The colors listed in these Tables indicate the colors of the devices produced in the absence of the electric field and when the electric field is applied. The applied electric field is 20 volts and 1 KHz.

......

104~)411 Table 3. The effect of the dyes mi~ed on the operation characteristic.
In the When the Compound absence of electric the electric field is No, Dye field applied INC4Hg l. ~ Blue Colorless O HNC4Hg Cll HNI C 1 2H 2 5 2. ~ Blue Colorless O I~NCl 2H25 O~I
3, ~ Color less Red . 4. ~N=N~N(CH3)2 Colorless Yellow H17C8 NII (j~ HNC8H17 ~b E~eddish Colorless . , .

:
Bi . .

In the When the absence of electric Compound the electric field is No. Dye field applied o HN ~ ~s.

6. ~ Colorless Blue O :EIN ~

~. .
,, Table 4. The effect of the combination of dyes on the operation characteristic.

Mixing proportion of dyes In the absence of When the electric Sample (Weight percent) the electric field field is applied ~,~
No.l 2 3 4 5 6 (Color backgrouncl) (Color indication) a 1 0 l 0 violet Red b 0 2 0 1 Green Yellow c2. 5 0 l 0 . Blue Red d 1 0 l 1 Brown Red e l 0 l 3 Green Orange f 0 0 0 3 0. 5 0. 5 Orange Green ." .

, .. , .... . . _ .. . .. . _ .

' ~04~)411 Ths display in d'ifferent colors made for the background and the indication as shown in Table 4 is achieved by making - use of the dyes of this invention.
Figure 4 shows the change of the absorption characteristic ofthe liquid crystal device housing the sample C. The real line indicates the absorption wave form in the absence of the electric field; the broken line, when an electric field of 20 volts and 1 KHz was applied.
Embodiment 5:
Another example of the liquid crystal device in which the electro-optical element of this invention is used is described hereunder:
A significant display system may be obtained when a linear polarizer is placed in the light path of a liquid crystal device which houses the element consisting of the dyestuffs and the nematic liquid crystals having the positive dielectric anisotropy with their molecules so arranged as to provide the homogeneous structure therein.
Figure 5 represents a schematic diagram of this device in which: 1 and 2 denote the transparent members, on the inside surfaces ofwhich transparent electrodes 3 and 4 are put.
They are held parallel to each other at a distance of from several to,several 10~, interposed by insulative spacers 5 and 6, and in that interspace, the electro-optical element 7 of this invention (8 designates the liquid crystal molecule, and 9 the dy~ molecule)is inserted. A means 10 for applying the electric field on the layer of this element from outside is provided.
A linear polarizer 11 is placed adjacent to this device~ 12 indicates the light source; and 13, the observer~
The liquid crystal device obtained by disposing the nematic liquid crystals containing pleochroic dyes in such a way as to hold their molecular axis in parallel and in a certain direction to their contacting surfaces, itself possesses the function of a polarizer and is disposed in such a way that the polarization plane of the polarizer is held perpendicular or parallel to the direction of the arrangement of the liquid crystal molecules. The color of the device tinted with the dye turns deeper or weaker, for the benefit of enhanced contrast of indications.
Similar objectivesmay be achieved by disposing the aforementioned device in the interspace of a pair of polarizers in the similar way.

Furthermore, when a linear color polarizer having a spectroscopic characteristic such as to absorb light other than those of specific colors is put in the light path of the device, a color toned by the absorption characteristic of this polarizer and the absorption characteristic of the dyes in the liquid crystal device may be used for display purposes.
This is described hereunder more in detail in con-nection with the following embodiment:
The employed element has 3 wt %, 1 wt % and 1 wt~
respectively of dyes of, Il HNCBH17 (a) ~
O HNC8Hl7 OH
(~) ~ N = ~ ~=N~ , an~

.

HO ~ N 2 M

IIO

1~)40411 :
- mixed into a smiliar nematic liquid crystal composition as that of ~mbodiment 3, consisting of 90 wt~ of the mixed liquid crystal t A and 10 wt ~ of . .
C Il O ~ CII ~ N ~ CN.~

This elemcnt is placed in the liquid crystal device in such a way that it forms the homogeneous structure in the absence of the electric field.
Table 5 shows the states of the display operation ,~
obtained wi~h this liquid crystal device:

Table 5 In the absence When thee:lecitri~
Type of polarizer of the electric field field is applied p t 1. Without a polarizer Brown Green 2. Neutral color linear Reddish brown Green polarizer 3. Green lin~ar Black Green polarizer The results of Table 5 were obtained, when the linear polarizer is placed in such a way that its polarization plane ~s held perpendicular to the direction of the arranyement of . the liquid crystal molecules in the liquid crystal device.
2Q As is evident from the.results, different colors of the device from that produced without the polarizer are displaced as the : result of the color of the polarizer being mixed with the color of the dyes.
This liquid crystal device is characterized by its capability of makiny a display with hiyh color contrast and wide visual angle.
As described hereinabove, the electro-optical element 104041~
of this invention is of high industrial value, for it makes it possible to produce liquid crystal devices capable of providing a display effect heretofore not attainable.

~ " ' . , .

Claims

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. An electro-optical element comprising a nematic liquid crystal composition containing at least one compound represented by the formula or wherein R1 is an n-alkyl radical having from 5 to 20 carbon atoms and R2 is an n-alkyl radical having from 4 to 20 carbon atoms in an amount of from 0.5 to 5% by weight.

2. The electro-optical element according to claim 1, wherein at least one of said compounds has the formula where R1 is an n-alkyl radical having from 5 to 12 carbon atoms and is added to said nematic liquid crystal composition in an amount of from 0.5 to 5% by weight.

3. The electro-optical element according to claim 1, wherein at least one of said compounds having the formula where R2 is an n-alkyl radical having from 4 to 8 carbon atoms, and is added to said nematic liquid crystal composition in an amount of from 0.5 to 5% by weight.

4. The electro-optical element according to claim 1 wherein said compound is 1,4-bisdodecylaminoanthraquinone and further comprising 4-(dimethylamino)azobenzene.

5. The electro-optical element according to claim 1 wherein said compound is 1,8-bisoctylaminoanthraquinone and further comprising 1,4-bisphenylaminoanthraquinone and 4-(dimethylamino)azobenzene.

6. The electro-optical element according to claim 1 wherein said compound is 1,4-bisoctylaminoanthraquinone and further comprising 2-hydroxynaphthalene-1-azo-1'-benzene-4'-azobenzene and phenylazoresorcine.

7. An electro-optical display device comprising two parallel transparent members whose inner surfaces have been coated with transparent electrodes; an electro-optical element comprising a nematic liquid crystal composition con-taining at least one compound represented by the formula wherein R1 is an n-alkyl radical having from 5 to 20 carbon atoms and R2 is an n-alkyl radical having from 4 to 20 carbon atoms, in an amount of 0.5 to 5 percent by weight, said electro-optical element being interposed between said electrodes and having all its molecules in their quiescent state, non-electrically aligned perpendicular or parallel to such facing surfaces, and means for selectively applying an electric field across said electro-optical element through said electrodes to exceed a threshold electric field.

8. An electro-optical display device according to claim 7, wherein said electro-optical element comprises a nematic liquid crystal composition with net positive dielectric anisotropy which has a homogeneous arrangement and a mixture of dyes consisting of 1,4-bisoctylaminoanthraquinone, 2-hydroxynaphthalene-1-azo-1'-benzene-4'-azobenzene and phenyl-azoresorcine and further comprising at least one polarizer located adjacent to said transparent members, said nematic liquid crystal comprising a nematic liquid crystal with negative dielectric anisotropy and a nematic liquid crystal with positive dielectric anisotropy.