JP3092050B2 - Antiferroelectric liquid crystal composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a liquid crystal composition, particularly an anti-ferroelectric (chiral smectic C _A, below S
It relates to a liquid crystal composition so as to emerge mC _A ^* and for abbreviation) phase, more particularly antiferroelectric liquid crystal suitable for use in a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays have come to be widely used as display elements by making use of features such as thinness, light weight, and low power consumption. However, most of these display devices use a TN using a nematic liquid crystal. (Twisted Ne
matic) type is generally adopted. Since the TN type display method uses the anisotropy of the relative permittivity of the liquid crystal as a driving source, its response speed is slow, and it is necessary to improve the response speed.

On the other hand, a liquid crystal device using a chiral smectic C (abbreviated as SmC ^* ) liquid crystal which exhibits ferroelectricity, which was discovered by Meyer et al., Has a high speed response and memory performance which cannot be achieved with a nematic liquid crystal. Utilizing these characteristics, research on application to ferroelectric liquid crystal displays is being vigorously conducted. But,
It is difficult to realize good orientation and memory properties required for this display method in actual cells, and it has problems such as being vulnerable to external shocks.There are many problems to be solved. ing.

On the other hand, recently Chandani et al.
An antiferroelectric phase (SmC _A ^* phase) showing a tristable state was found on the low temperature side of the SmC ^* phase. This antiferroelectric liquid crystal exhibits a thermodynamically stable phase in which dipoles are arranged antiparallel in each adjacent layer, and is characterized by a distinct threshold value for applied voltage and a double hysteresis characteristic. An electric field-induced phase transition between the phase and the ferroelectric phase occurs. Also, studies have been started for realizing a new display method by applying this switching behavior.

[0005] Liquid crystal compounds having an antiferroelectric phase include:
JP-A-1-213390, JP-A-1-316339, JP-A-1-31667, and JP-A-2-28128 are already known, and newer antiferroelectric liquid crystal compounds have been announced. Increasing numbers. By the way, most of the antiferroelectric liquid crystal compounds manufactured up to now have a high melting point from a practical point of view, and the temperature range of the antiferroelectric phase is much higher than room temperature. Therefore,
It is difficult to fabricate a liquid crystal device using only one type of antiferroelectric liquid crystal compound, and usually, a mixture of several or more types of antiferroelectric liquid crystal compounds is used to balance practical physical properties. It is necessary to do.

[0006]

When the switching characteristics of the antiferroelectric phase are applied to a liquid crystal display, it is not impossible to fabricate a liquid crystal cell using a composition containing only an antiferroelectric liquid crystal. , Temperature range showing three stable states,
It is not always preferable in terms of liquid crystal driving voltage, crystallization temperature, orientation, and the like. In particular, regarding the liquid crystal drive voltage, the current antiferroelectric liquid crystal composition has a drive voltage of 35 to 4
It is as high as 5 V, and it is necessary to lower the liquid crystal driving voltage in view of the restrictions such as power consumption and withstand voltage conditions of the driving IC. In addition, high-speed response is required to obtain high contrast. In view of such circumstances, an object of the present invention is to provide an antiferroelectric liquid crystal composition which lowers the threshold voltage, enables low-voltage driving, and has a high-speed response.

[0007]

Means for Solving the Problems The present invention provides the following formula (1)
And an antiferroelectric liquid crystal composition containing at least one of the compounds represented by (2). R ¹ -A ¹ -A ² -X ¹ -A ³ -R ² (1) (where R ¹ is an alkyl group having 1 to 20 carbon atoms).
R ² is a linear alkoxyalkyl group having 2 to 18 carbon atoms. A ¹ , A ² and A ³ represent a cyclohexane ring or a benzene ring, and at least one of them represents a cyclohexane ring. X ¹ represents —COO— or a single bond. ) R ³ -B ¹ -X ² -B ² -CN (2) (where R ³ is an alkyl group having 1 to 20 carbon atoms).
B ¹ and B ²

Embedded image And X ² represents a single bond . )

Next, a method for synthesizing the compounds represented by the formulas (1) and (2) will be described. (1) In the formula (1), X ¹ is -CO
For O-:

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(2) When X ¹ is a single bond in the formula (1):

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[0010]

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[0011]

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[0012]

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(3) When X ² is a single bond in the formula (2):

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A preferred embodiment of the compound represented by the formula (1) is represented by the following formula (3), (4) or (5).

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More preferred embodiments of the compound represented by the formula (3), (4) or (5) are represented by the following formulas (8) and (8), respectively.
It is indicated by (9) or (10).

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A preferred embodiment of the compound represented by the formula (2) is represented by the following formula (7) .

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A preferred compound for producing an antiferroelectric liquid crystal composition in combination with at least one of the compounds represented by the above formulas (1) and (2) is represented by the following formula (13).

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This compound can be prepared as follows. Biphenylcarboxylic acid and optically active hydroxybenzoic acid ester are dissolved in a solvent such as chloroform or methylene chloride, and a dehydrating condensing agent such as N, N-dicyclohexylcarbodiimide and a base such as N, N-dimethyl-4-aminopyridine are used. Thus, the desired product can be obtained by carrying out the reaction. An outline of a method for synthesizing biphenylcarboxylic acids is shown below by taking an example in which an aromatic ring is not substituted.

(1) When X ³ is a single bond or —O—:

[0020]

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Here, R ⁸ is alkyl or alkoxy, and in reaction 1, a Grignard reagent prepared from 4-alkyl or alkoxy bromobenzene is reacted with 4-bromobenzonitrile. Reaction 2 is hydrolyzed as usual.

(2) When X ³ is —COO—:

[0023]

Embedded image Here, R ⁶ is alkyl, and in reaction 1, benzyl bromide is reacted with a base such as potassium hydrogen carbonate in a solvent such as DMF. In the reaction 2, esterification is carried out as usual. Reaction 3 is carried out by hydrogenolysis in the presence of a palladium catalyst to remove benzyl.

For producing a ferroelectric liquid crystal composition in combination with the compound represented by the formula (13), more preferred compounds of the formulas (1) and (2) are represented by the formula (3) ,
(4), (5), a compound represented by (7), further preferably formula (3), (4), (5), a compound represented by (7) the equation (8), (9 ), (10) and the following formula
It is a compound shown by (12) .

Embedded image Expression (7) and Expression (12) are the same, but for convenience of explanation, a description of Expression (12) is provided. In the formulas (8), (9) and (10), R ⁴ is preferably a methyl group, and in the formula (12) , R ³ is preferably an alkyl group having 1 to 6 carbon atoms.

The total content of the compounds represented by the formulas (1) and (2), preferably the formulas (3) to (7), more preferably the formulas (8) to (12) is preferably 1 to 49% by weight. . If this content exceeds 49% by weight, the antiferroelectricity is extremely reduced. On the other hand, if this content is less than 1 wt%,
Poor low-voltage drivability. More preferably, the content is 5 to 30 wt%.

[0026]

Examples (Examples 1 to 8, Comparative Example 1) Antiferroelectric liquid crystal compounds No. 1 to No. 4 shown in Table 1
Composition A (Comparative Example 1) was prepared as a reference liquid crystal using (all R bodies). Compound No. 5 to 10 shown in Table 2 were added to this composition A for 20
Compositions B to G ( Examples 1 to 6 ) were prepared by adding 10% by weight of Compound 12 to the composition (Table 3).
Compounds 5 to 12 are all commercial products, each of which was purchased from Kanto Chemical Co., Ltd., and the product number was NKV-3-151.
-1 (Compound No. 5), NKV-3-1444-1 (Compound No. 6), NKV-3-1277-1 (Compound No.
7), NKV-5-127-1 (Compound No. 8), NK
V-4-127-1 (Compound No.9), 3-CEN (of
Compound No. 10). And liquid crystal compositions A, B, C,
D, E, F, and G are respectively injected into a liquid crystal cell (gap: 2 μm) that has been subjected to an alignment treatment by rubbing, and after injection, the cell is heated to a temperature at which the liquid crystal composition changes into an isotropic liquid, and then the liquid is heated to 2 ° C. The mixture was cooled to room temperature at a rate of ° C / min to obtain an antiferroelectric liquid crystal device.

A 1 Hz, ± 40 V triangular wave was applied to this element, and the transmitted light intensity was measured under crossed Nicols.
A double hysteresis curve as shown in FIG. In this hysteresis, the liquid crystal driving voltage at which the relative transmittance becomes 90% when the voltage is increased is defined as the threshold voltage, and the compositions A, B, and
When the threshold voltages of C, D, E, F, and G were obtained and plotted against the measured temperatures, the results shown in FIG. 2 were obtained. Compound No. 5, No. 6, No. 7, No. 8, No.
By adding No. 9 and No. 10 , the compositions B, C,
The threshold voltages of D, E, F, and G could be significantly reduced as compared with the composition A. In other words, the threshold voltage at 30 ° C. for the phase transition from the SmC _A ^* phase to the electric field induced SmC ^* phase is 44.0 V for composition A, 21.7 V for composition B, and C is 24.5 V, Composition D is 22.7 V, Composition E is 23.2 V, Composition F
Is 22.6 V, and the composition G is as low as 15.2 V. Thus, the threshold voltage of the antiferroelectric liquid crystal composition can be reduced.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

The response time was measured as shown in FIG. 3 by applying a voltage of ± 50 V. Compositions A, B, C,
The response time of D, E, F, and G is 1 at 30 ° C.
00 μs, 30 μs, 30 μs, 45 μs, 50 μs,
The time was 45 μs and 25 μs, and the addition of Compound Nos. 5 to 10 made it possible to speed up the electric field response. JP-A-4-330048 and JP-A-4-30629 describe liquid crystal compositions having a similar structure.
3, Japanese Patent Publication No. 5-78596, etc., but none of them mention antiferroelectric liquid crystal.

[0032]

As described above, by adding the compound provided by the present invention to an antiferroelectric liquid crystal composition,
The liquid crystal can be driven by a low voltage and the electric field response can be speeded up, so that it can be used for manufacturing a liquid crystal display element having excellent practicality.

[Brief description of the drawings]

FIG. 1 is a graph showing a double hysteresis curve of a liquid crystal device manufactured using an antiferroelectric liquid crystal composition of an example.

FIG. 2 is a graph showing a change in threshold voltage with respect to temperature of a liquid crystal element made using the antiferroelectric liquid crystal compositions of Examples and Comparative Examples.

FIG. 3 is a graph showing a method for measuring a response time to a change in applied voltage of a liquid crystal element manufactured using the antiferroelectric liquid crystal compositions of Examples and Comparative Examples.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-218019 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09K 19/30 C09K 19/42-19 / 46

Claims (28)

(57) [Claims] 1. An antiferroelectric liquid crystal composition comprising at least one compound represented by the following formulas (1) and (2). R ¹ -A ¹ -A ² -X ¹ -A ³ -R ² (1) (where R ¹ is an alkyl group having 1 to 20 carbon atoms).
R ² is a linear alkoxyalkyl group having 2 to 18 carbon atoms. A ¹ , A ² and A ³ represent a cyclohexane ring or a benzene ring, and at least one of them represents a cyclohexane ring. X ¹ represents —COO— or a single bond. ) R ³ -B ¹ -X ² -B ² -CN (2) (where R ³ is an alkyl group having 1 to 20 carbon atoms).
B ¹ and B ² are And X ² represents a single bond . ) 2. The antiferroelectric substance according to claim 1, wherein the equation (1) is represented by the following equation (3), (4) or (5), and the equation (2) is represented by the following equation (7) . Liquid crystal composition. Embedded image (However, R ¹ and R ² have the same meaning as described above, and are independent of formulas (3) to (5).) (However, R ³ has the same meaning as described above . ) 3. The equations (3), (4), (5) and (7)
Are the following equations (8), (9), (10), and (12), respectively.
3. The antiferroelectric liquid crystal composition according to claim 2, wherein Embedded image (However, R ¹ has the same meaning as described above; R ⁴ is a linear alkyl group having 1 to 17 carbon atoms;
(10) is independent of each other. ) (However, R ³ has the same meaning as described above.) 4. The antiferroelectric liquid crystal composition according to claim 3, comprising a compound represented by the formula (8). 5. The antiferroelectric liquid crystal composition according to claim 3, comprising a compound represented by the formula (9). 6. The antiferroelectric liquid crystal composition according to claim 3, comprising a compound represented by the formula (10). 7. The antiferroelectric liquid crystal composition according to claim 3, comprising a compound represented by the formula (12). 8. The expression (8), (9), (10) according to claim 3.
And an antiferroelectric liquid crystal composition comprising at least one compound represented by the following formula (13) and at least one compound represented by the following formula (13). Embedded image (Where R ⁶ is an alkyl group having 4 to 14 carbon atoms, X ³ is a single bond, —O— or —COO—, and D ¹ ,
D ² and D ³ are (However, these may be substituted by F, Cl, Br, CH ₃ groups), and Rf is CH ₃ or CF ₃ ,
R ⁷ is mainly composed of a hydrocarbon group and has 2 to 16 carbon atoms.
Which is a hydrocarbon group having 2 to 16 carbon atoms which may contain an oxygen atom, such as an ether group or a carbonyl group. ) 9. The antiferroelectric liquid crystal composition according to claim 8 , comprising at least one kind of the compound represented by the formula (8) and at least one kind of the compound represented by the formula (13). 10. The antiferroelectric liquid crystal composition according to claim 8 , comprising at least one kind of the compound represented by the formula (9) and at least one kind of the compound represented by the formula (13). 11. The antiferroelectric liquid crystal composition according to claim 8 , comprising at least one kind of the compound represented by the formula (10) and at least one kind of the compound represented by the formula (13). 12. antiferroelectric liquid crystal composition according to claim 8 comprising at least one compound represented by at least one and the formula of the compound represented by the formula (12) (13). 13. The expression (8), (9), (10) and
The total content of the compound represented by (12) is from 1 to 49
The antiferroelectric liquid crystal composition according to claim 8 , which is in wt%. 14. The antiferroelectric liquid crystal composition according to claim 9 , wherein the content of the compound represented by the formula (8) is 1 to 49 wt%. 15. The antiferroelectric liquid crystal composition according to claim 10 , wherein the content of the compound represented by the formula (9) is 1 to 49 wt%. 16. The antiferroelectric liquid crystal composition according to claim 11 , wherein the content of the compound represented by the formula (10) is 1 to 49% by weight. 17. The antiferroelectric liquid crystal composition according to claim 12 , wherein the content of the compound represented by the formula (12) is 1 to 49 wt%. 18. The expression (8), (9), (10) and
The total content of the compound represented by (12) is 5 to 30.
The antiferroelectric liquid crystal composition according to claim 8 , wherein the composition is wt%. 19. The antiferroelectric liquid crystal composition according to claim 9 , wherein the content of the compound represented by the formula (8) is 5 to 30% by weight. 20. The antiferroelectric liquid crystal composition according to claim 10 , wherein the content of the compound represented by the formula (9) is 5 to 30% by weight. 21. The antiferroelectric liquid crystal composition according to claim 11 , wherein the content of the compound represented by the formula (10) is 5 to 30% by weight. 22. The antiferroelectric liquid crystal composition according to claim 12 , wherein the content of the compound represented by the formula (12) is 5 to 30% by weight. 23. The antiferroelectric liquid crystal composition according to claim 9, 14 or 19 , wherein R ^{4 in the} compound represented by the formula (8) is a methyl group. 24. The antiferroelectric liquid crystal composition according to claim 10 , wherein R ^{4 in the} compound represented by the formula (9) is a methyl group. 25. the formula among the compounds represented by (10), anti-ferroelectric liquid crystal composition according to claim 11, 16 or 21 R ⁴ is a methyl group. 26. The antiferroelectric liquid crystal composition according to claim 8 , wherein R ³ is an alkyl group having 1 to 6 carbon atoms containing at least one compound represented by the formula (12) . 27. The compound represented by the structural formula (12)
13. The antiferroelectric liquid crystal composition according to claim 12 , wherein ³ is an alkyl group having 1 to 6 carbon atoms. (28) A liquid crystal display device using the composition according to any one of (1) to ( 27 ).