JP2946792B2 - 2,3-dicyanohydroquinone derivative, liquid crystal composition and liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound having a very large negative dielectric anisotropy useful as a component of a liquid crystal composition used for a liquid crystal display device, a liquid crystal composition containing the compound and a liquid crystal composition containing the compound. The present invention relates to a used liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device utilizes the electro-optical effect of a liquid crystal, in which the optical properties of a liquid crystal cell change due to the change in the arrangement of liquid crystal molecules due to the application of an electric field. Electro-optical effects used in liquid crystal display devices include dynamic scattering type (DS type), twisted nematic type (TN type),
Guest-host type (GH type), birefringence control type (ECB
Type), super-twisted nematic type (STN type), super-twisted birefringent type (SBE type), ferroelectric type, heat effect type, and the like. 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, and a dual frequency driving method.

There are three types of liquid crystals used in liquid crystal display devices: smectic phase, cholesteric phase, and nematic phase. These liquid crystals have a compound having a positive dielectric anisotropy and a compound having a negative dielectric anisotropy. Exists. A liquid crystal display element using a liquid crystal having a negative dielectric anisotropy has a DS type and a vertical alignment G
H type, ECB type (DAP method) of vertical arrangement, etc.
In addition, there is a dual frequency driving method in which a liquid crystal having a negative dielectric anisotropy is required.

In the DS type, nematic liquid crystals having a negative dielectric anisotropy in which an ionic substance is dissolved are arranged horizontally or vertically. When a voltage is applied to this liquid crystal layer, a eddy current is generated in the liquid crystal, and when the voltage is further increased, the eddy current becomes a turbulent state,
The arrangement of the liquid crystal molecules shifts to a disordered state, and a myriad of fine birefringent regions differing from the surrounding arrangement are generated. At the boundary between these regions, light is strongly scattered and the display becomes a cloudy state and can be displayed.

In a vertically arranged GH type, when a dichroic dye is added to a nematic liquid crystal or a chiral nematic liquid crystal having a negative dielectric anisotropy, elongated molecules of the dichroic dye are arranged in parallel with the liquid crystal molecules. When an electric field is applied to change the arrangement of liquid crystal molecules, the arrangement of dichroic dye molecules also changes continuously. When no electric field is applied, the color is colorless and the color becomes darker as the voltage is increased. Various color displays can be performed by using dichroic dyes of various colors.

In the DAP method, nematic liquid crystals having negative dielectric anisotropy are vertically arranged and arranged between orthogonal polarizers. When no electric field is applied, incident light does not receive birefringence, so that 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 that the incident light changes to elliptically polarized light, and a part of the light passes through the second polarizer, so that the transmitted light is colored by the interference effect. Various color displays can be performed according to the magnitude of the applied voltage.

The two-frequency driving method uses a nematic liquid crystal in which the sign of the dielectric anisotropy changes from positive to negative as the frequency of the applied voltage is increased. This is a driving method for changing the arrangement of molecules for display.

[0008] These liquid crystal display elements tend to have a higher driving voltage than TN type, STN type and the like which have been most widely used in the past. For example, vertical arrangement of GH type and DAP
The threshold voltage (V _th ) of the system is expressed by the following equation.

(Equation 1) (Where ε ₀ is the vacuum permittivity, △ ε is the dielectric anisotropy, k ₃₃
Represents the elastic constant of bend. From this equation, it is required that the dielectric anisotropy have a large negative value in order to lower the threshold voltage. The following compounds have been proposed as compounds meeting such demands.

Embedded image (See JP-A-52-118450)

Embedded image (See Japanese Patent Publication No. 61-26898)

Embedded image (See Japanese Patent Publication No. 61-26899)

[0009]

Among the above compounds, compound (II) has a relatively large negative value with a dielectric anisotropy of -4, but its threshold voltage is higher because its liquid crystal temperature range is higher than room temperature. When the compound is added to the mother liquid crystal to the extent that is sufficiently reduced, crystals are precipitated, and the response speed is reduced due to the high viscosity. Compound (III) has a dielectric anisotropy of-
It has a very large negative value of 20 or more, but its melting point is high and its viscosity is so high that the addition ratio to the mother liquid crystal cannot be increased so much, the threshold voltage cannot be lowered sufficiently, and the response It has the disadvantage of slowing down. The compound (IV) is an improvement over the disadvantages of the compounds (II) and (III). The compound (IV) has a large dielectric anisotropy of -17 to -18, a considerably low melting point and a small viscosity, and is suitable for mother liquid crystals. The threshold voltage can be further reduced by increasing the addition ratio of, and the response speed is relatively fast.

However, the melting point of compound (IV) is 80 ° C. or higher, and as a practical liquid crystal component which must maintain a liquid crystal state at −20 ° C., it is necessary to increase the addition ratio to such an extent that the threshold voltage is sufficiently reduced. Could not.

Accordingly, an object of the present invention is to provide a 2,3-dicyanohydroquinone derivative which has a large negative value of dielectric anisotropy, a low melting point, and a high addition ratio to a mother liquid crystal. . Another object of the present invention is to provide a liquid crystal composition containing the 2,3-dicyanohydroquinone derivative, maintaining a liquid crystal state at a low temperature, and having a large negative dielectric anisotropy. Still another object of the present invention is to provide a liquid crystal display device using the liquid crystal composition, which can be driven at a low voltage.

[0012]

According to the present invention, there is provided a compound of the general formula

Embedded image (Where R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m ≧ 1, n ≧ 0, and m + n ≦ 8). A liquid crystal composition containing a hydroquinone derivative and its 2,3-dicyanohydroquinone derivative, and a liquid crystal display device using the liquid crystal composition.

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

[Table 1] (Where R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m ≧ 1, n ≧ 0, and m + n ≦ 8). Esterification of the alkyl benzoic acid, chloride (V) and 2,3-dicyanohydroquinone (VI) in anhydrous pyridine gives 2,3-dicyano-4-hydroxyphenyl 4'-alkylbenzoate (VII). In step 2, the compound (VII) obtained in step 1 is reacted with alkenyl alcohol (VIII) in anhydrous tetrahydrofuran using diethyl azocarboxylate and triphenylphosphine to prepare the 2,3-dicyanohydroquinone derivative (I) of the present invention. Get)

In the case of DS-type, GH-type and DAP-type liquid crystal display elements of vertical alignment, the component of the base liquid crystal for adding the 2,3-dicyanohydroquinone derivative (I) of the present invention has a dielectric anisotropy. A liquid crystal compound which is small even if it is negative or positive, for example, the following compound is used.

Embedded image

Embedded image

Embedded image

Embedded image In addition, as the components of the liquid crystal composition used in the dual frequency driving type liquid crystal display device, the following compounds are used in addition to the above compounds.

Embedded image

Embedded image When the compound (I) of the present invention is added to the mother liquid crystal obtained by mixing the above liquid crystal compounds, it is possible to add only one component thereof. In order to more effectively obtain the properties possessed, it is more preferable to add several components in combination. In this case, the addition ratio of the compound (I) of the present invention to the mother liquid crystal is 1 to 3
Although it is in the range of 0% by weight, the range of 1 to 20% by weight is practical when compatibility with the mother liquid crystal is considered.

The liquid crystal composition thus obtained has a large negative value of dielectric anisotropy as compared with a conventional liquid crystal composition, and a GH type or DAP type liquid crystal using the liquid crystal composition. The display element can be driven at a 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 of the present invention will be described in more detail with reference to Examples. [Example 1] (Compound) 4-allyloxy-2,3-dicyanophenyl 4'-
Propyl benzoate (m = 1, n = 0, R = C ₃ H _{7 in} compound (I))
Step 1 16.0 g of 2,3-dicyanohydroquinone (manufactured by Aldrich) was dissolved in 500 cm ³ of anhydrous pyridine, and 18.2 g of 4-propylbenzoic acid chloride was added to this solution for 30 minutes while stirring the solution on an ice water bath. Over and dripping,
The mixture was further stirred at room temperature overnight. The reaction was poured into 1500 cm ³ of water, and the precipitated result was filtered, washed with water and dried at 80 ° C. The crystals were recrystallized from 500 cm ³ of toluene and hydrated methanol to obtain 23 g of 2,3-dicyano-4-hydroxyphenyl 4′-propylbenzoate.

Step 2 2,3-dicyano-4-hydroxyphenyl 4'-propylbenzoate 6.1
g, 1.8 g of allyl alcohol and 7.9 g of triphenylphosphine were dissolved in 100 cm ³ of anhydrous tetrahydrofuran, and 5.3 g of diethyl azocarboxylate was added dropwise while stirring the solution, and the solution 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. Chloroform in the effluent was distilled off, and the residue was recrystallized from methanol to obtain 3.2 g of colorless crystals of 4-allyloxy-2,3-dicyanophenyl 4'-propylbenzoate.
I got The result of measuring the phase transition temperature of this compound using DSC was as follows.

Embedded image (Here, C represents a crystal, S represents a smectic phase, and I represents an isotropic liquid.) [Examples 2 to 6] (Compound) The following compounds were produced by the same production method as in Example 1. The measurement results of the phase transition temperatures of those compounds are also shown.

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

Embedded image 4- (trans-2'-hexenyloxy) -2,3-
Dicyanophenyl 4 "-propylbenzoate

Embedded image 4-allyloxy-2,3-dicyanophenyl 4 ″-
Butyl benzoate

Embedded image 4- (3'-butenyloxy) -2,3-dicyanophenyl 4 "-butylbenzoate

Embedded image 4- (trans-3'-pentenyloxy) -2,3-
Dicyanophenyl 4 "-butylbenzoate

Embedded image [Example 7] (Liquid crystal composition and liquid crystal display device) The liquid crystal composition shown in Table 2 has a dielectric anisotropy of -1.3 and a nematic isotropic liquid phase transition temperature (NI point). Was stored at -7O <0> C and no precipitation of crystals and no phase change were observed even at -20 <0> C. Using this liquid crystal composition as a mother liquid crystal, 0.90 g of the 4-allyloxy-
A liquid crystal composition was prepared by mixing 0.10 g of 2,3-dicyanophenyl 4'-propylbenzoate. The NI point of this liquid crystal composition was 72.8 ° C, and no crystals were precipitated even when stored at -20 ° C. The dielectric anisotropy of this liquid crystal composition was -17.

In the liquid crystal composition shown in Table 2, a dichroic dye D-
35 (manufactured by BDH) added as a guest at 1 wt% is sealed in a vertically oriented liquid crystal cell having a thickness of 9 μm,
When the voltage-light transmittance characteristics were measured, the threshold voltage was 3.75 V and the saturation voltage was 6.20 V. Here, the threshold voltage and the saturation voltage indicate voltages at which the light transmittance is 90% and 10%, respectively, in a voltage-light transmittance curve.

Next, a liquid crystal composition obtained by mixing 0.10 g of the compound of Example 1 with 0.90 g of the liquid crystal composition shown in Table 2 was added with D
Threshold voltage of 2.1 wt.
V and the saturation voltage were 3.3V.

[Table 2] [Example 8] (Liquid crystal composition and liquid crystal display element) When a liquid crystal composition shown in Table 3 was prepared and its dielectric constant-frequency characteristic was measured at 25 ° C, the crossover frequency was about 4 kHz and the low frequency region The dielectric anisotropy at 6.
0, that in the high frequency region was -2.0.

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

[Table 3]

[0022]

As described above, it has been clarified that the 2,3-dicyanohydroquinone derivative of the present invention has a very large negative dielectric anisotropy. Further, the compound of the present invention has good compatibility with the conventional liquid crystal composition, and the liquid crystal composition obtained by mixing them does not show crystal precipitation at low temperature,
It was found that the dielectric anisotropy was negative and large. Further, a vertically aligned G using a liquid crystal composition containing the compound of the present invention.
It was confirmed that the liquid crystal display element of the H type, the DAP mode or the like can be driven at a low voltage, and that the dielectric anisotropy in the high frequency region can be increased negatively in the dual frequency drive.

Therefore, the 2,3-dicyanohydroquinone derivative of the present invention is DS-type, GH-type having a vertical arrangement, DAP
This method is very useful for lowering the driving voltage of the system or the like and increasing the value of the dielectric anisotropy in the high frequency region of the dual frequency driving to a negative value.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Miho Yudazaka 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation (58) Field surveyed (Int. Cl. ⁶ , DB name) CA ( STN) CAOLD (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] 1. A compound of the general formula (Where R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m ≧ 1, n ≧ 0, and m + n ≦ 8). Two, three
-Dicyanohydroquinone derivatives. 2. A compound of the general formula (Where R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m ≧ 1, n ≧ 0, and m + n ≦ 8). A liquid crystal composition comprising at least one hydroquinone derivative. 3. A compound of the general formula (Where R is a linear alkyl group having 1 to 10 carbon atoms, m and n are integers satisfying m ≧ 1, n ≧ 0, and m + n ≦ 8). A liquid crystal display device comprising a liquid crystal composition containing at least one hydroquinone derivative.