JPH04290860A - 2,3-dicyanohydroquinone derivative, liquid crystal composition and liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the subject compound having extremely large negative dielectric anisotropy and useful as a component of a DS-type liquid crystal composition drivable at low voltage or a GH-type or DAP-type liquid crystal composition having perpendicular orientation. CONSTITUTION:The compound of formula I (R is 1-10C alkyl; m>=1; n>=0; m+n <=8), e.g. 4-allyloxy-2,3-dicyanophenyl 4'-propylbenzoate. The compound of formula I can be produced by reacting a 2,3-dicyano-4-hydroxyphenyl 4'-alkylbenzoate of formula II with an alkenyl alcohol of formula III in anhydrous THF in the presence of diethyl azocarboxylate and triphenyl phosphine. The compound of formula I is added to a liquid crystal composition in an amount of 1-30wt.%. It has high compatibility to conventional liquid crystal compositions and gives a composition having large negative dielectric anisotropy in high-frequency range in dual-frequency driving.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a compound having a very large negative dielectric anisotropy useful as a component of a liquid crystal composition used in a liquid crystal display element, a liquid crystal composition containing the same, and a liquid crystal composition thereof. This relates to the liquid crystal display element used.

0002

2. Description of the Related Art Liquid crystal display devices utilize the electro-optic effect of liquid crystals, in which the optical properties of a liquid crystal cell change when the arrangement of liquid crystal molecules changes by the application of an electric field, resulting in light modulation. Electro-optic effects used in liquid crystal display devices include dynamic scattering type (DS type), twisted nematic type (TN type), guest-host type (GH type), and birefringence control type (ECB type).
, super twisted nematic type (STN type), super twisted birefringent type (
SBE type), ferroelectric type, thermal effect type, etc. Driving methods for operating these liquid crystal display elements include a static driving method, a time division driving method (dynamic driving method), an active matrix driving method, a dual frequency driving method, and the like.

Furthermore, there are three types of liquid crystals used in liquid crystal display elements: smectic phase, cholesteric phase, and nematic phase, and these liquid crystals include compounds with positive dielectric anisotropy and compounds with negative dielectric anisotropy. exists. Liquid crystal display elements using liquid crystals with negative dielectric anisotropy include DS type and vertically aligned G type.
There are H type, vertical arrangement ECB type (DAP method), etc.
Further, there is a dual-frequency driving method that requires a liquid crystal with negative dielectric anisotropy.

In the DS type, nematic liquid crystals with negative dielectric anisotropy in which ionic substances are dissolved are arranged horizontally or vertically. When voltage is applied to this liquid crystal layer, a vortex is generated in the liquid crystal, and when the voltage is further increased, the vortex becomes turbulent, and the arrangement of liquid crystal molecules shifts to a disordered state, resulting in fine birefringence that differs from the surrounding arrangement. Innumerable regions are generated, and light is strongly scattered at the boundary surfaces of these regions, resulting in a cloudy state that can be displayed.

In the vertical alignment GH type, when a dichroic dye is added to a nematic liquid crystal or chiral nematic liquid crystal with negative dielectric anisotropy, the elongated molecules of the dichroic dye are aligned parallel to the liquid crystal molecules. When an electric field is applied to change the arrangement of liquid crystal molecules, the molecular arrangement of the dichroic dye also changes continuously. When no electric field is applied, it is colorless, and as the voltage increases, the color becomes darker. By using dichroic dyes of various colors, various color displays can be achieved.

In the DAP method, nematic liquid crystals with negative dielectric anisotropy are vertically aligned and placed between orthogonal polarizers. When no electric field is applied, the incident light does not undergo birefringence, so the light that has passed through the liquid crystal layer cannot pass through the second polarizer. When an electric field is applied, the liquid crystal molecules are tilted, so the incident light changes to elliptically polarized light, and as a portion of the light passes through the second polarizer, the transmitted light is colored due to interference effects. Various colors can be displayed depending on the magnitude of the applied voltage.

The dual-frequency driving method uses a nematic liquid crystal whose dielectric anisotropy sign changes from positive to negative as the frequency of the applied voltage increases, and uses a suitable combination of low and high frequencies. This is a driving method that displays images by changing the arrangement of molecules.

[0008] These liquid crystal display elements tend to have a higher driving voltage than the TN type, STN type, etc., which have conventionally been most widely used. For example, vertically arranged GH type and DAP
The threshold voltage (Vth) of the system is expressed by the following equation.

[Equation 1] (Here, ε0 is the vacuum permittivity, △ε is the dielectric anisotropy, and k3
3 represents the bend elastic constant. ) According to this formula, in order to lower the threshold voltage, the dielectric anisotropy is required to have a large negative value. The following compounds have been proposed to meet such demands.

[C4] (Refer to Japanese Patent Application Laid-open No. 52-118450)

[C5] (Refer to Special Publication No. 61-26898)

[C6] (Refer to Special Publication No. 61-26899)

[0009]

[Problems to be Solved by the Invention] Among the above compounds, compound (II) has a dielectric anisotropy of -4, which is a relatively large negative value, but because its liquid crystal temperature range is higher than room temperature, the threshold voltage is low. If it is added to the mother liquid crystal to a sufficient extent to lower the viscosity, crystals will precipitate, and the high viscosity will slow down the response speed. Moreover, compound (III) has a dielectric anisotropy of -
20 or more, and has a very large negative value, but because of its high melting point and high viscosity, it is not possible to increase the proportion of addition to the mother liquid crystal, and the threshold voltage cannot be lowered sufficiently, and the response It has the disadvantage of slow speed. Compound (IV) has improved the drawbacks of compounds (II) and (III), and has a large dielectric anisotropy of -17 to -18, a fairly low melting point and a small viscosity, and is suitable for mother liquid crystals. By increasing the addition ratio, the threshold voltage can be further lowered, and the response speed is also relatively fast.

However, the melting point of compound (IV) is 80°C or higher, and as a component of a practical liquid crystal that must maintain a liquid crystal state at -20°C, it is necessary to increase the addition ratio to the extent that the threshold voltage is sufficiently lowered. I couldn't.

[0011] Accordingly, an object of the present invention is to provide a 2,3-dicyanohydroquinone derivative which has a large negative dielectric anisotropy value and a low melting point, so that the addition ratio to the mother liquid crystal can be increased. . Another object of the present invention is to provide a liquid crystal composition that contains the 2,3-dicyanohydroquinone derivative, maintains a liquid crystal state at low temperatures, and has large negative dielectric anisotropy. Furthermore, another object of the present invention is to provide a liquid crystal display element that can be driven at low voltage using the liquid crystal composition.

0012

[Means for Solving the Problems] The present invention provides the general formula

[C7
] (Here, R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m≧1, n≧0, m+n≦8.) 2,3- A liquid crystal composition containing a dicyanohydroquinone derivative and a 2,3-dicyanohydroquinone derivative, and a liquid crystal display element using the liquid crystal composition.

The 2,3-dicyanohydroquinone derivative of the present invention has a very negative dielectric anisotropy value of -17 to -19, and is characterized by a low melting point. The compounds of the present invention can be obtained, for example, according to the scheme shown in Table 1 below.

[Table 1] (Here, R is a linear alkyl group having 1 to 10 carbon atoms, and m and n are integers satisfying m≧1, n≧0, and m+n≦8.) That is, Step 1 In , 4-alkylbenzoic acid, chloride (V) and 2,3-dicyanohydroquinone (VI) were esterified in anhydrous pyridine to obtain 2.
, 3-dicyano-4-hydroxyphenyl 4'-alkyl benzoate (VII). In Step 2, the compound (VII) obtained in Step 1 and the alkenyl alcohol (VIII) are reacted in anhydrous tetrahydrofuran using diethyl azocarboxylate and triphenylphosphine to obtain the 2,3-dicyanohydroquinone derivative (I) of the present invention. ).

In the case of DS type, vertically aligned GH type and DAP type liquid crystal display elements, the components of the base liquid crystal to which the 2,3-dicyanohydroquinone derivative (I) of the present invention is added have dielectric anisotropy. Small liquid crystal compounds, whether negative or positive, such as the following compounds, are used.

[Chemical formula 8]

[Chemical formula 9]

[Chemical formula 10]

embedded image In addition to the above-mentioned compounds, the following compounds are used as components of a liquid crystal composition used in a dual-frequency drive type liquid crystal display element.

[Chemical formula 12]

[Chemical formula 13] The compound of the present invention (
When adding I), it is possible to add only one component, but in order to increase the addition ratio to the mother liquid crystal and more effectively obtain the characteristics of water, it is possible to combine several components. It is more preferable to add it. In that case, the addition ratio of the compound (I) of the present invention to the mother liquid crystal is 1 to 30
The range is 1 to 20% by weight, but a practical range is 1 to 20% by weight when compatibility with the mother liquid crystal is considered.

The liquid crystal composition obtained in this manner has a large negative dielectric anisotropy compared to conventional liquid crystal compositions, and the liquid crystal composition using this liquid crystal composition is of the GH type, DAP type, etc. The display element can be driven at low voltage.

[0016]

EXAMPLES Hereinafter, the 2,3-dicyanohydroquinone derivative of the present invention, a liquid crystal composition containing the same, and a liquid crystal display device using the liquid crystal composition will be explained in more detail with reference to Examples. [Example 1] (Compound) 4-allyloxy-2,3-dicyanophenyl 4'
-propyl benzoate (m=1, n=0, R=C3H7 in compound (I)
Step 1: Dissolve 16.0 g of 2,3-dicyanohydroquinone (manufactured by Aldrich) in 500 cm3 of anhydrous pyridine, and add 18.2 g of 4-propylbenzoic acid chloride for 30 minutes while stirring this solution on an ice-water bath. The mixture was added dropwise, and the mixture was further stirred at room temperature overnight. Add the reactant to 1500c of water
Pour into m3, filter the precipitated result and wash with water,
It was dried at 0°C. The crystals were recrystallized from 500 cm3 of toluene and aqueous methanol to give 2,3-dicyano-4-
Hydroxyphenyl 4'-propyl benzoate 2
3g was obtained.

Step 2 2,3-dicyano-4-hydroxyphenyl 4'-propyl benzoate6.
1 g, allyl alcohol 1.8 g and triphenylphosphine 7.9 g in 100 cm3 of anhydrous tetrahydrofuran.
5.3 g of diethyl azocarboxylate was added dropwise to the solution while stirring, and the mixture was further left at room temperature overnight. Tetrahydrofuran in the reaction solution was distilled off, and the residue was treated with a silica gel column using chloroform as a solvent. The chloroform in the effluent was distilled off, and the residue was recrystallized from methanol to give colorless crystals of 4-allyloxy-2,3-dicyanophenyl 4'-propylbenzoate 3.2
I got g. The phase transition temperature of this compound was measured using DSC and the results were as follows.

[Chemical formula 14] (Here, C represents a crystal, S represents a smectic phase, and I represents an isotropic liquid.) [Examples 2 to 6] (Compounds) The following compounds were prepared by the same manufacturing method as Example 1. Manufactured. In addition, the measurement results of the phase transition temperatures of these compounds are also listed.

4-(trans-2'-butenyloxy)
-2,3-dicyanophenyl 4″-propylbenzoate

embedded image 4-(trans-2'-hexenyloxy)-2,3-
Dicyanophenyl 4″-propyl benzoate

[Chemical formula 16] 4-allyloxy-2,3-dicyanophenyl 4″
-butyl benzoate

[Chemical formula 17] 4-(3'-butenyloxy)-2,3-dicyanophenyl 4''-butylbenzoate

embedded image 4-(trans-3'-pentenyloxy)-2,3-
Dicyanophenyl 4″-butylbenzoate

[Example 7] (Liquid crystal composition and liquid crystal display element) The liquid crystal composition shown in Table 2 has a dielectric anisotropy of -1.3 and a nematic isotropic liquid phase transition temperature (N -I point) is 70.3℃
Even when stored at -20°C, no crystal precipitation or phase change was observed. Using this liquid crystal composition as a mother liquid crystal, its 0
．． 0.10 g of 4-allyloxy-2,3-dicyanophenyl 4'-propylbenzoate from Example 1
A liquid crystal composition was prepared by mixing g. N of this liquid crystal composition
-I point was 72.8°C, and no crystal precipitation was observed even when stored at -20°C. Further, the dielectric anisotropy of this liquid crystal composition was -17.

Dichroic dye D-
35 (manufactured by BDH Co., Ltd.) added as a guest at 1 wt% was sealed in a vertically aligned liquid crystal cell with a thickness of 9 μm.
When voltage-light transmittance characteristics were measured, the threshold voltage was 3.75V and the saturation voltage was 6.20V. Here, the threshold voltage and the saturation voltage indicate voltages at which the light transmittance becomes 90% and 10%, respectively, in a voltage-light transmittance curve.

[0020] Next, D
-Threshold voltage with 1wt% addition of 35 is 2.1V
, the saturation voltage was 3.3V.

[Table 2] [Example 8] (Liquid crystal composition and liquid crystal display element) The liquid crystal compositions shown in Table 3 were prepared and the dielectric constant single frequency characteristics were measured at 25°C, and the crossover frequency was approximately 4kHz.
The dielectric anisotropy in the low frequency range was 6.0, and that in the high frequency range was -2.0.

Next, a liquid crystal composition prepared by mixing 0.90 g of the liquid crystal composition shown in Table 3 and 0.1 g of the compound of Example 1 has a crossover frequency of about 2 kHz and a dielectric anisotropy of 5 in the low frequency region. .0, and that in the high frequency region was -4.0.

[Table 3]

[0022]

As described above, it has been revealed that the 2,3-dicyanohydroquinone derivative of the present invention has negative and very large dielectric anisotropy. Furthermore, the compound of the present invention has good compatibility with conventional liquid crystal compositions, and the liquid crystal composition obtained by mixing them shows no crystal precipitation at low temperatures.
It was found that the dielectric anisotropy was large and negative. Furthermore, vertically aligned G using a liquid crystal composition containing the compound of the present invention
It was confirmed that liquid crystal display elements such as H type and DAP type can be driven at low voltage, and in dual frequency driving, the dielectric anisotropy in the high frequency region can be made negative and large.

Therefore, the 2,3-dicyanohydroquinone derivatives of the present invention are of the DS type, vertically aligned GH type, DAP type.
This method is very useful for lowering the driving voltage of systems, etc., and increasing the negative value of dielectric anisotropy in the high frequency region of dual-frequency driving.

Claims (3)

[Claims] Claim 1: General formula [Formula 1] (wherein, R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m≧1, n≧0, m+n≦8 2,3-
Dicyanohydroquinone derivative. Claim 2: General formula [Formula 2] (wherein, R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m≧1, n≧0, m+n≦8 1. A liquid crystal composition comprising at least one 2,3-dicyanohydroquinone derivative represented by: Claim 3: General formula [Formula 3] (wherein, R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m≧1, n≧0, m+n≦8 A liquid crystal display element characterized by using a liquid crystal composition containing at least one type of 2,3-dicyanohydroquinone derivative represented by the following formula.