JPH08109147A - 1,4-disubstituted-2,6-difluorobenzene derivative - Google Patents

Abstract

PURPOSE: To obtain a new compound useful as an electro-optical display material, having excellent compatibility with liquid crystal of parent material, high anisotropy of dielectric constant and high TN-1. CONSTITUTION: This compound is shown by formula I (R is a 1-10C alkyl; X and Y are H or F; Z is F, Cl, trifluoromethyl, trifluoromethoxy, etc.; cyclohexane ring is in trans-configuration) such as 1-[trans-4-(3,4,5-trifluorophenyl) cyclohexyl]-4-(trans-4-propylcyclohexyl)-2,6-difluorobenzene. The compound of formula I is obtained by catalytically reducing a compound of formula II in the presence of a catalyst such as palladium carbon and isomerizing the prepared cis-trans mixture in the presence of a strong base such as potassium butoxide. This compound is useful for a liquid crystal material for liquid crystal display attaching importance to lowvoltage drive for word processor, note personal computer, liquid crystal television, etc., especially for a liquid crystal material for driving an active matrix.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a liquid crystalline compound which is a novel 1,4-disubstituted-2,6-difluorobenzene derivative useful as an electro-optical display material, and a liquid crystal composition containing the same. A liquid crystal display device using this liquid crystal composition.

[0002]

2. Description of the Related Art Liquid crystal display devices have recently been used as information display devices such as watches and calculators, word processors, computer terminal displays, etc., and have become important as interfaces between electronic devices and people.

Display systems using liquid crystals are roughly classified into three types: (1) electric field effect (FEM) type, (2) dynamic scattering (DSM) type, and (3) thermal effect (TEM) type. . Of these, the display system based on the field effect type has been put into practical use so far. Field effect type includes twisted nematic (TN) type and super twisted nematic (STN)
Type, guest-host (GH) type, electric field controlled birefringence (EC
B) type, cholesteric-nematic phase transition (CN-P
There are T) type, surface-stabilized ferroelectric liquid crystal (SSFLC) type, etc., but at present, TN type and STN type are the mainstream. Further, in order to meet the demand for increasing the display capacity, conventional static drive, multiplex drive, and simple matrix drive have been put into practical use as a drive system. It was difficult to increase the capacity of the TN type even by using these driving methods, but the capacity could be increased to some extent by improving the STN type.

However, the STN type has also reached the limit of the recent demand for large display capacity. Therefore, MI using a non-linear element having a threshold characteristic for each display pixel
Active matrix methods such as M (Metal Insurator Metal) method and active element (TFT (Thin Film Transistor) method) have been developed. According to this, large capacity and high definition comparable to CRT are possible. It has been put to practical use as an LCD TV and a high-definition display, and is currently developing rapidly.

Liquid crystal materials used in these liquid crystal display systems are required to have various characteristics as in the case of ordinary display systems. In particular, (1) high specific resistance and excellent voltage holding ratio. (2) The threshold voltage (V _th ) is low,
It is important that (3) the temperature range of the liquid crystal phase is wide and (4) the response is excellent.

Usually, the threshold voltage (V
_th ) is the expression (p)

[0007]

[Equation 1]

(In the formula, k is a proportional constant, K is an elastic constant, and Δε is a dielectric anisotropy, respectively.) As can be seen from this formula, the threshold voltage is lowered. Therefore, it is necessary to reduce the elastic constant of the liquid crystal material or increase the dielectric anisotropy.

As a liquid crystal compound having a large dielectric anisotropy, a compound mainly having a cyano group as a polar terminal group has been used. However, with a compound having a cyano group, it is difficult to obtain a high specific resistance and a high voltage holding ratio in the active matrix driving method.

Therefore, as a compound having a large dielectric anisotropy and a high voltage holding ratio, a fluorine atom, a chlorine atom, a trifluoromethyl group, a trifluoromethyl group, a trifluoromethyl group, a trifluoromethyl group, or a trifluoromethyl group, instead of a cyano group as a polar terminal group, can be obtained. Methoxy group,
Alternatively, a compound having a difluoromethoxy group is used. However, the dielectric anisotropy of such a liquid crystal compound is considerably smaller than that of a compound having a cyano group, and thus it has been difficult to sufficiently reduce the threshold voltage.

On the other hand, as a compound which has a large dielectric anisotropy and is capable of lowering the threshold voltage even though it is a fluorine-based compound, it has a terminal polarity such as having a 3,4,5-trifluorophenyl group. A compound in which a plurality of fluorine atoms are introduced in the same direction as the group has been reported. (JP-A-2
However, even with the liquid crystal compounds described above,
Its dielectric anisotropy is about +10, which is not sufficiently large compared with a compound having a cyano group.

Therefore, in order to further increase the dielectric anisotropy, it is conceivable to introduce a fluorine atom into the terminal phenyl group of the liquid crystal compound and another phenyl group in the same direction. Recently, formula (A) having a 4-substituted-2,6,3 ′, 4 ′, 5′-pentafluorobiphenyl skeleton

[0013]

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It has been reported that the compound (1) exhibits a very large dielectric anisotropy. (The 14th International Liquid Crystal Society,
A-P32) whereby the compound of formula (A) is +25
It has a large dielectric anisotropy.

The present inventors have also found that the formula (B) having a homologous pentafluorobiphenyl skeleton

[0016]

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It was found that the compound (1) has a large dielectric anisotropy, and the addition thereof lowers the threshold voltage of the composition. However, the above formula (A)
The compounds of formula (B) and (B) have poor liquid crystallinity, have a problem of compatibility with the host liquid crystal, and the amount that can be added is limited. Therefore, it was difficult to sufficiently bring out the characteristics of these compounds.

Furthermore, the present inventors have found that 2- (3,4,5-
Formula (C) having a trifluorophenyl) -1- (4-substituted-2,6-difluorophenyl) ethane skeleton

[0019]

[Chemical 4]

It was found that the compound (1) has a large dielectric anisotropy and, in addition to being a compound which lowers the threshold voltage of the composition, is also excellent in compatibility with the host liquid crystal. It was However, the compound of the formula (C) has a drawback that the maximum temperature of the nematic phase (T _NI ) is lowered.

On the other hand, in order to increase T _NI , it is effective to introduce a ring structure into a tetracyclic compound. Then, the present inventors reported the tetracyclic compounds of formula (D) and formula (E) into which a cyclohexane ring was further introduced, based on the idea of the compounds of formula (B) and formula (C). .

[0022]

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However, the compound of the formula (D) has a poor compatibility with the host liquid crystal like the compound of the formula (B), and the compound of the formula (E) has a sufficient effect of reducing the threshold voltage by addition. Was not.

[0024]

The problem to be solved by the present invention is to provide a liquid crystal compound which is excellent in compatibility with a host liquid crystal, has a very large dielectric anisotropy, and has a high T _NI. is there.

Further, an active matrix display containing the liquid crystalline compound, having a high specific resistance and a voltage holding ratio, a low threshold voltage, a wide temperature range of a liquid crystal phase, and capable of being driven in a wide temperature range. Another object of the present invention is to provide a liquid crystal composition and a liquid crystal display device using the same.

[0026]

In order to solve the above-mentioned problems, the present invention has the general formula (I)

[0027]

[Chemical 6]

(In the formula, R represents an alkyl group having 1 to 10 carbon atoms, preferably a linear alkyl group having 2 to 7 carbon atoms. X and Y are each independently.
It represents a hydrogen atom or a fluorine atom, preferably one is a fluorine atom, and more preferably both X and Y are fluorine atoms. Z represents a fluorine atom, a chlorine atom, a trifluoromethyl group, a trifluoromethoxy group or a difluoromethoxy group, preferably a fluorine atom or a trifluoromethoxy group, and more preferably a fluorine atom. The cyclohexane ring represents the trans configuration. ) A novel liquid crystal compound represented by

Furthermore, an active matrix display containing this liquid crystalline compound, having a high specific resistance and a voltage holding ratio, a low threshold voltage, a wide temperature range of a liquid crystal phase, and capable of being driven in a wide temperature range. Provided are a liquid crystal composition for use and a liquid crystal display device using the same.

The compound represented by the general formula (I) of the present invention can be produced, for example, as follows.

[0031]

[Chemical 7]

[0032]

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(In the formula, R, X, Y and Z have the same meanings as in formula (I).) First step: 1-bromo-3,5-difluorobenzene is reacted with magnesium to obtain a Grignard reagent. By reacting with a cyclohexanone derivative represented by the general formula (II) to obtain 3,5 represented by the general formula (III).
Obtaining a difluorobenzene derivative. Second step: The compound of general formula (IV) is obtained by dehydrating the compound of general formula (III) in the presence of an acid catalyst. Step 3: Catalytic reduction of the compound of general formula (IV) in the presence of a catalyst such as palladium carbon, and the resulting cis-trans mixture is isomerized to the trans form in the presence of a strong base such as potassium t-butoxide. To obtain a compound of the general formula (V). Fourth step: after the compound of the general formula (V) is lithiated with an alkyllithium such as n-butyllithium, the compound of the general formula (V
I) by reacting with a compound of general formula (VII)
To obtain the compound of Fifth step: The compound of general formula (VII) is obtained by dehydrating the compound of general formula (VII) in the presence of an acid catalyst. Step 6: Catalytic reduction of the compound of general formula (VIII) in the presence of a catalyst such as palladium carbon, and the resulting cis-trans mixture is isomerized to the trans form in the presence of a strong base such as potassium t-butoxide. To give a compound of the general formula (I)
To obtain the compound of

Table 1 shows typical examples of the compounds thus obtained.

[0035]

[Table 1]

(In the table, C represents a crystalline phase, N represents a nematic phase, I represents an isotropic liquid phase, and the phase transition temperature represents a transition temperature between a phase on the left side and a phase on the right side of the numeral, for example, , C1
42N represents that the transition temperature between the crystal phase and the nematic phase is 142 ° C. The liquid crystal composition containing the compound of the general formula (I) according to the present invention has excellent characteristics as shown below, as shown in Examples below.

Liquid crystal composition (a), which is a composition for active matrix having low viscosity and excellent high-speed response.

[0038]

[Chemical 9]

T _NI (upper limit temperature of nematic phase) is 11
The temperature is 6 ° C., and the dielectric anisotropy is +4.8. A liquid crystal display device was manufactured by enclosing this composition in a TN cell having a cell thickness of 4.5 μm, and the threshold voltage at 20 ° C. was measured and found to be 1.88V.

Next, 90% by weight of this liquid crystal composition (a) and (No. 1) in Table 1

[0041]

[Chemical 10]

When a liquid crystal composition (M-1) comprising 10% by weight of the compound of (1) was prepared, T _NI was hardly changed to 116 ° C. and the dielectric anisotropy was increased to +6.1,
A liquid crystal display device was prepared in the same manner, and the threshold voltage was measured. Further, the specific resistance value of this liquid crystal composition was 10 ¹² Ωcm or more, and the voltage holding ratio was as high as 99%.

For comparison, equation (D)

[0044]

[Chemical 11]

10% by weight of the compound of and the liquid crystal composition (a)
When a liquid crystal composition (N-1) containing 90% by weight was prepared, T _NI rose to 125 ° C., and the dielectric anisotropy was +.
It was a little bigger, 6.3. However, when a liquid crystal display device was prepared in the same manner and the threshold voltage was measured, it was 1.71 V, which was slightly lower than that of the liquid crystal composition containing the liquid crystalline compound of the present invention. . Further, crystals were precipitated at room temperature.

Further, the formula (E)

[0047]

[Chemical 12]

10% by weight of the compound of and liquid crystal composition (a)
When a liquid crystal composition (N-2) consisting of 90 wt% was prepared, T _NI rose to 119 ° C. However, when a liquid crystal display element was similarly prepared and the threshold voltage was measured, it was 1.77 V, and the decrease was slight compared with the liquid crystal composition containing the liquid crystalline compound of the present invention.

Thus, the general formula (I) according to the present invention is
By using the compound (1), a liquid crystal composition for active matrix which has a low threshold voltage and can be driven in a wide temperature range can be easily prepared.

Now, as a preferable representative example of the nematic liquid crystal compound which can be used as a liquid crystal composition by mixing with the compound represented by the general formula (I) according to the present invention, for example, 4- Substituted benzoic acid 4-substituted phenyl ester, 4-substituted cyclohexanecarboxylic acid 4-substituted phenyl ester, 4-substituted cyclohexanecarboxylic acid 4′-substituted biphenylyl ester,
4- (4-Substituted cyclohexanecarbonyloxy) benzoic acid 4-substituted phenyl ester, 4- (4-substituted cyclohexyl) benzoic acid 4-substituted phenyl ester, 4-
(4-Substituted cyclohexyl) benzoic acid 4-substituted cyclohexyl ester, 4,4′-substituted biphenyl, 1- (4
-Substituted phenyl) -4-substituted cyclohexane, 4,4 "
-Substituted terphenyl, 1- (4'-substituted biphenylyl)
-4-substituted cyclohexane, 1- (4-substituted cyclohexyl) -4- (4-substituted phenyl) cyclohexane, 2
-(4-Substituted phenyl) -5-substituted pyrimidine, 2-
(4-Substituted biphenylyl) -5-substituted pyrimidine, 1-
(4-Substituted cyclohexyl) -2- (4-substituted cyclohexyl) ethane, 1- (4-substituted cyclohexyl) -2
-(4-Substituted phenyl) ethane, 1- [4- (4-substituted cyclohexyl) cyclohexyl] -2- (4-substituted phenyl) ethane, 1- [4- (4-substituted phenyl) cyclohexyl] -2- ( 4-substituted cyclohexyl) ethane, 1- (4-substituted phenyl) -2- (4-substituted phenyl) ethyne, 1- [4- (4-substituted cyclohexyl)]
2- (4-substituted phenyl) ethyne etc. can be mentioned.

Especially for active matrix, 4,4'-substituted biphenyl, 1- (4-substituted phenyl) -4-substituted cyclohexane, 4,4 "-substituted terphenyl, 1- (4'-substituted biphenylyl ) -4-Substituted cyclohexane, 1- (4-substituted cyclohexyl) -4-
(4-substituted phenyl) cyclohexane, 1- (4-substituted cyclohexyl) -2- (4-substituted cyclohexyl) ethane, 1- (4-substituted cyclohexyl) -2- (4-substituted phenyl) ethane, 1- [4 -(4-Substituted cyclohexyl) cyclohexyl] -2- (4-substituted phenyl) ethane, 1- [4- (4-substituted phenyl) cyclohexyl] -2- (4-substituted cyclohexyl) ethane, 1-
(4-Substituted phenyl) -2- (4-substituted phenyl) ethyne, 1- [4- (4-substituted cyclohexyl)]-2-
(4-Substituted phenyl) ethyne and the like are preferable.

[0052]

EXAMPLES The present invention will be further described below by showing Examples of the present invention. However, the present invention is not limited to these examples. (Example 1) 1- [trans-4- (3,4,5-
Synthesis of trifluorophenyl) cyclohexyl] -4- (trans-4-propylcyclohexyl) -2,6-difluorobenzene (1) 1- (3,5-difluorophenyl) -4-
Synthesis of propylcyclohexene

[0053]

[Chemical 13]

6.9 g of magnesium was suspended in 10 ml of tetrahydrofuran (THF), and 3,5-difluoro-
A solution of 50.0 g of 1-bromobenzene in 200 ml of THF was added dropwise at a rate at which THF continued to gently reflux. After the dropping was completed, the mixture was further stirred for 1 hour at room temperature. In this solution, 4-
Propylcyclohexanone 29.0 g THF 80 ml
The solution was added dropwise at room temperature over 30 minutes, and further stirred at room temperature for 1 hour. 10% Hydrochloric acid was added until it became weakly acidic, the reaction product was extracted with 300 ml of toluene, the organic layer was washed with saturated brine, dried over anhydrous sodium sulfate, and the solvent was distilled off. The obtained oily substance was dissolved in 300 ml of toluene, and p
-Toluenesulfonic acid monohydrate 2.0g was added and it heated and refluxed for 3 hours. The mixture is allowed to cool to room temperature, washed successively with saturated aqueous sodium hydrogen carbonate solution, water and saturated brine, dried over anhydrous sodium sulfate, and the solvent is distilled off to give 1- (3,5-difluorophenyl) -4-propyl. Cyclohexene 4
8.6 g was obtained. (2) Synthesis of 1- (trans-4-propylcyclohexyl) -3,5-difluorobenzene

[0055]

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48.6 g of 1- (3,5-difluorophenyl) -4-propylcyclohexene obtained in the above (1)
Was dissolved in 250 ml of ethyl acetate, 5 g of 5% palladium carbon was added, and the mixture was reacted under a hydrogen pressure of 3 atm for 3 hours. The catalyst was filtered off and the solvent was distilled off to obtain 44 g of a mixture of cis isomer and trans isomer. This is N, N-dimethylformamide 2
It was dissolved in 50 ml, 24.3 g of potassium t-butoxide was added, and the mixture was stirred at room temperature for 3 hours to isomerize to the trans form. 250 ml of water was added, and the reaction product was mixed with hexane 200
extracted with ml, the organic layer was washed with water and saturated saline solution in that order,
It was dried over anhydrous sodium sulfate. The solvent was distilled off and the residue was purified by silica gel column chromatography (hexane) to obtain 1- (trans-4-propylcyclohexyl) -3,5-difluorobenzene (30.2 g). (3) 1- [4- (3,4,5-trifluorophenyl) cyclohexen-1-yl] -4- (trans-
Synthesis of 4-propylcyclohexyl) -2,6-difluorobenzene

[0057]

[Chemical 15]

6.3 g of 1- (trans-4-propylcyclohexyl) -3,5-difluorobenzene obtained in (2) above was dissolved in 30 ml of THF, cooled to -50 ° C or lower, and n-butyllithium hexane solution was added. (1.68mo
16 ml of 1 / l) was added dropwise at a rate to keep the temperature below -50 ° C. Furthermore, 4- (3,4,5-trifluorophenyl)
A solution of 5.0 g of cyclohexanone in 25 ml of THF was added to -5
The solution was added dropwise at a rate that kept it at 0 ° C or lower. After returning to room temperature, 10 ml of 10% hydrochloric acid was added to the reaction product, and after completion of the reaction, extraction with 100 ml of toluene was performed. The organic phase was washed twice with saturated saline, dried over anhydrous sodium sulfate, and the solvent was distilled off.
It was dissolved in 100 ml of toluene, 1 g of p-toluenesulfonic acid monohydrate was added, and the mixture was heated under reflux for 1 hour. After the reaction was completed, the mixture was allowed to cool to room temperature, saturated aqueous sodium hydrogen carbonate solution,
It was washed successively with water and saturated saline, dried over anhydrous sodium sulfate, and the solvent was distilled off, followed by purification using silica gel column chromatography (hexane), 1- [4-
9.7 g of (3,4,5-trifluorophenyl) cyclohexen-1-yl] -4- (trans-4-propylcyclohexyl) -2,6-difluorobenzene was obtained. (4) 1- [trans-4- (3,4,5-trifluorophenyl) cyclohexyl] -4- (trans-
Synthesis of 4-propylcyclohexyl) -2,6-difluorobenzene

[0059]

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1- [4- (3,4,5) obtained in (3) above
-Trifluorophenyl) cyclohexen-1-yl]
-4- (trans-4-propylcyclohexyl)-
Toluene 100 was added to 9.7 g of 2,6-difluorobenzene.
It was dissolved in ml, 1 g of 5% palladium carbon was added, and the mixture was stirred under a hydrogen pressure of 2 atm for 7 hours. After the reaction was completed, the catalyst was filtered off and the solvent was distilled off to obtain a mixture of cis and trans 9.8.
g was obtained. This is N, N-dimethylformamide 100
Dissolve in ml, add 0.5 g of potassium t-butoxy,
The mixture was stirred at room temperature for 2 hours and isomerized to the trans form. 10
% Hydrochloric acid (20 ml) was added, and the reaction product was mixed with ethyl acetate (100).
extracted with ml, the organic layer was washed with water and saturated saline solution in that order,
It was dried over anhydrous sodium sulfate. The solvent was distilled off, and the residue was purified by silica gel column chromatography (hexane), 1- [trans-4- (3,4,5-trifluorophenyl) cyclohexyl] -4- (trans-4-).
7.6 g of propylcyclohexyl) -2,6-difluorobenzene was obtained. The phase transition temperature is shown in Table 1. Example 2 1- [trans-4- (3,4-difluorophenyl) cyclohexyl] -4- (trans-
Synthesis of 4-propylcyclohexyl) -2,6-difluorobenzene

[0061]

[Chemical 17]

In Example 1, 4- (3,4,5-trifluorophenyl) cyclohexanone was replaced with 4-
1- [trans- was prepared in the same manner as in Example 1 except that (3,4-difluorophenyl) cyclohexanone was used.
4- (3,4-difluorophenyl) cyclohexyl]
-4- (trans-4-propylcyclohexyl)-
2,6-difluorobenzene was obtained. The phase transition temperature is shown in Table 1. Example 3 Preparation of Liquid Crystal Composition Liquid crystal composition for active matrix (a) having low viscosity and excellent high-speed response

[0063]

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Was prepared. T _{NI of} this composition (a),
The dielectric anisotropy (Δε) and the threshold voltage (V _th ) at 20 ° C. of the liquid crystal display device manufactured by enclosing the liquid crystal display device in a TN cell having a cell thickness of 4.5 μm were measured and the results were as follows.

T _NI : 116 ° C. Δε: +4.8 V _th : 1.88 V 90% by weight of this composition (a) and Example 1 (No. 1 in Table 1)

[0066]

[Chemical 19]

Liquid crystal composition comprising 10% by weight of the compound of
(M-1) was prepared and its T _NIAnd V_thTo
The measurement results were as follows. T_NI: 116 ° C. Δε: +6.1 V_th: 1.62V Therefore, by adding the compound of (No. 1),
Dielectric anisotropy increases and nematic phase is generated in wide temperature range
Liquid crystal whose threshold voltage is greatly reduced while maintaining
It can be seen that a composition is obtained. Also, this composition
Has a specific resistance of 10¹²Ωcm or more, voltage holding ratio is 9
It was as high as 9%. (Comparative Example 1) Formula (D)

[0068]

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10% by weight of the compound of and the liquid crystal composition (a)
A liquid crystal composition (N-1) consisting of 90% by weight was prepared, and its T _NI , Δε and V _th were measured in the same manner.

T _NI : 125 ° C. Δε: +6.3 V _th : 1.71 V Therefore, the compound of formula (D) can increase T _NI and Δε, but contains the compound of (No. 1). It can be seen that the decrease in threshold voltage is slight when compared to the composition. Moreover, when left at room temperature, precipitation occurred within 1 day. (Comparative Example 2) Formula (E)

[0071]

[Chemical 21]

10% by weight of the compound of and the liquid crystal composition (a)
A liquid crystal composition (N-2) consisting of 90% by weight was prepared, and its T _NI , Δε and V _th were measured in the same manner.

T _NI : 119 ° C. Δε: +5.7 V _th : 1.77 V Therefore, the compound of formula (E) can increase T _NI and Δε, but contains the compound of (No. 1). It can be seen that the decrease in threshold voltage is slight when compared to the composition.

[0074]

The compound represented by the general formula (I) of the present invention has excellent compatibility with the host liquid crystal, has a very large dielectric anisotropy, and has a high T _NI . Therefore, by adding this compound, it is possible to obtain a composition in which the nematic phase is maintained in a wide temperature range and the threshold voltage is effectively lowered. Further, since there is no cyano group, it is possible to obtain a high voltage holding ratio. Therefore, the present invention
It is useful as a liquid crystal material useful for liquid crystal displays such as word processors, notebook computers, and liquid crystal televisions that emphasize low voltage driving, particularly as an active matrix driving liquid crystal material.

Claims (5)

[Claims] 1. A compound of the general formula (I) (In the formula, R represents an alkyl group having 1 to 10 carbon atoms, X and Y each independently represent a hydrogen atom or a fluorine atom, and Z is a fluorine atom, a chlorine atom, a trifluoromethyl group, or a trifluoromethyl group. A compound represented by a methoxy group or a difluoromethoxy group, and a cyclohexane ring having a trans configuration.). 2. The compound according to claim 1, wherein at least one of X and Y is a fluorine atom. 3. The compound according to claim 2, wherein X and Y are both fluorine atoms. 4. The compound according to claim 1, 2 or 3, wherein Z is a fluorine atom. 5. A liquid crystal composition containing the compound represented by formula (I) according to claim 1, 2, 3 or 4.