JPS6348259B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to liquid crystal ester compounds exhibiting low or negative dielectric anisotropy and liquid crystal materials and devices incorporating the compounds. It is now known that liquid crystal materials can be used to exhibit electro-optical effects in display devices such as digital computers or digital watches. One parameter of liquid crystal materials that is important in connection with electro-optic operation is the dielectric anisotropy (Δε) of the material. This is the difference between the average dielectric constant (ε) measured parallel to the molecules of a substance and the average dielectric constant (ε⊥) measured perpendicular to the molecules of a substance at a given frequency and temperature, for example when aligned in a straight line with each other. This is the difference minus . The sign and magnitude of the dielectric anisotropy of a given liquid crystal material is one of the main parameters that determines the type of electro-optic device that uses the material. For example, 4-alkyl- or alkoxy-
Substances with positive dielectric anisotropy (hereinafter referred to as positive substances) such as mixtures of 4′-cyanobiphenyl and 4″-alkyl- or alkoxy-4-cyano-para-terphenyl (hereinafter referred to as positive substances) are Ba)
It is used in known twisted nematic effect devices or (if in the cholesteric phase) in known cholesteric-nematic phase change effect devices in which the molecular alignment changes from a focal conic orientation to a homeotropic orientation. A substance having negative dielectric anisotropy (having an appropriate resistivity) (hereinafter referred to as negative substance) can be used as a known dynamic scattering effect device (if it is in a nematic phase) or a known dynamic scattering effect device (if it is in a cholesteric phase). Used in cholesteric memory effect devices. As well as materials with low dielectric anisotropy (negative or positive), materials with large negative dielectric anisotropy can also be mixed with materials with positive dielectric anisotropy to reduce the overall dielectric anisotropy. This results in a mixture with positive anisotropy (although the magnitude is smaller). According to the first feature of the present invention, the present invention provides the following structural formula () exhibiting low or negative dielectric anisotropy.
The present invention provides a novel liquid crystal ester compound. [In the formula, R ₁ represents an alkyl group, R ₂ represents an alkyl or alkoxy group,

[Formula] represents a 1,4-disubstituted-bicyclo(2,2,2)octane ring,

[Formula] represents a 1,4-disubstituted ring selected from the following: 1,4-disubstituted-bicyclo(2,2,2)octane ring; trans-1,4-disubstituted-cyclohexane ring; Side benzene ring with moiety substituted

[Formula] (wherein, at least one of Y and Z represents a halogen or a cyano group, the other represents hydrogen, a halogen, or a cyano group, and Y and Z
may be the same)] As mentioned above,

[Formula] is

[Formula] When Y is a halogen or a cyano group and Z is hydrogen. Or Z is halogen or cyano group and Y
is hydrogen. Alternatively, Z and Y are the same halogen or cyano group. When Z and/or Y are halogen, they are preferably F or Cl. Preferably R ₁ and R ₂ contain 18 or fewer carbon atoms, preferably 12 or fewer carbon atoms. These groups may be straight chain or branched. If branched, one or both have chiral centers and the compound is optically active. When R ₁ and R ₂ are linear, the compound is nematic. Preferably R ₁ is an n-alkyl group having between 1 and 12 carbon atoms (inclusive) and R ₂ is between 1 and 12 (if nematic). n-alkyl group having (including 1 and 12) carbon atoms or (if optically active) (+)-2-methylbutyl group. "Liquid crystal compounds" are compounds that belong to the following two known categories: (i) Compounds that normally exhibit a liquid crystal phase (ii) Compounds that exhibit some behavior as liquid crystals when dissolved in other liquid crystal compounds, even though they do not normally exhibit a liquid crystal phase. Compounds belonging to category (ii) exhibit a "monotropic" or "virtual" transition from liquid crystal to isotropic liquid at temperatures below the melting point of the solid phase.
The monotropic transition or the virtual transition is determined by rapidly cooling the liquid phase or by dissolving a compound in a substance exhibiting a liquid crystal phase and observing the change in the transition of the substance to an isotropic liquid phase by this addition, and the virtual transition, respectively. It can be detected by calculating the temperature by extrapolation. Compounds belonging to category (ii) may be used, for example, to extend or change the liquid crystal temperature range of the compound or (in the case of cholesteric liquid crystals).
It is useful to dissolve it in other liquid crystal compounds to change the molecular helical pitch. Compounds according to formula () are 1-alkyl-4-
Esters of carboxy-bicyclo(2,2,2)octane with variously substituted phenols or similar bicyclo(2,2,2)octane or cyclohexane compounds can be prepared by known techniques. Preferably in each case the carboxylic acid is converted into the acid chloride by conventional reaction with thionyl chloride.
The acid chloride is then reacted under certain conditions with a suitable phenol or similar compound to yield the ester. One or more compounds according to formula () may be used in any of the following applications (i) to (viii). (i) Mixed with a positive nematic material to form a positive nematic material as a whole and used in twisted nematic effect devices, especially diversified devices. An example of such a device will be described below. (ii) Alone (if Δε is large negative) or mixed (if Δε is small) with another preferably negative nematic substance and preferably a pleochroic dye to give an overall negative substance; Used in Friedericksz effect devices where the alignment changes from a homeotropic orientation (off state) to a homogeneous orientation (on state). An example of such a device will be described below. (iii) a nematic material, preferably mixed with a pleochroic dye, resulting in an overall positive nematic material, in a Friederick effect device in which the molecular arrangement changes from a homogeneous orientation (off-state) to a homeotropic orientation (off-state) by an electric field; used. (iv) mixed with an optically active substance to obtain a suitable resistivity (approximately
10 ⁹ ohm ^- cm), the molecular arrangement is twisted by the electric field and changes from a homogeneous orientation (off state) to a turbulent scattering focal cone orientation (turbulent scattering
used in cholesteric memory effect devices that change to a focal conic texture (on state). (v) Mixed with an optically active substance, preferably with a pleochroic dye, to form an overall negative cholesteric substance, the molecular arrangement of which is oriented in a weakly scattering surface linear homeotropic alignment by an electric field.
surface aligned hometropic texture (off state) to strongly scattered twisted homogeneous texture (off state) to strongly scattered twisted homogeneous texture (off state)
cholesteric texture (on state) - used in nematic phase change effect devices. (vi) mixed with an optically active substance, preferably with a pleochroic dye, resulting in an overall positive cholesteric substance whose molecular arrangement is changed by an electric field from a scattering focal cone orientation (off state) to an apparent homeotropic orientation (on state); It is used in cholesteric-nematic phase change effect devices. (vii) Mixed with a nematic material to form an overall negative nematic material with a suitable resistivity (approximately 10 ⁹ ohm ^- cm), where the molecular arrangement changes from an apparent homeotropic orientation (off state) to a turbulent scattering orientation due to an electric field. It is used in dynamic scattering effect devices that change. (viii) Mixed with a positive nematic material to form a positive nematic material as a whole, and the dielectric anisotropy of the material changes from positive (off state) at low frequencies to negative (on state) due to a high frequency electric field. two frequency switching effect device
switching effect devices). The structure and operation of the above devices and the general types of materials suitable for use in them are:
This is known per se. It is clear to those skilled in the art that in the above applications where a mixture is formed, by controlling the proportions of the substances mixed, the value and sign of the dielectric anisotropy of the mixture can be controlled as desired. . When a substance is added to one or more compounds according to formula (), the substance itself becomes a mixture of the two or more compounds. The mixture may be formed in a known manner. for example,
The component compounds are simply heated to form a collectively isotropic liquid, which is stirred and cooled. The compounds according to formula (formula) are effective for increasing the negativity or decreasing the positivity of the dielectric anisotropy and lowering the operating voltage in the above-mentioned applications. This effectively affects other properties. For example, it affects the diversity in a twisted nematic effect device or the switching frequency in a two-frequency switching effect device. According to a second feature of the invention, the invention provides:
There is provided a mixture of liquid crystal compounds comprising at least one compound according to formula () above. Depending on its composition and properties, the mixture can be used in any of the above applications (i) to (vii). An example of such a mixture for use in a diversified twisted nematic device includes at least one compound according to formula () above, and one or more 4'-alkyl- or 4'-alkoxy-
4-cyanobiphenyl and one or more of the following compounds () to (), optionally having low dielectric anisotropy, e.g.

It is a mixture that also contains other esters of the form (R, R' are n-alkyl groups). Preferably, the 4'-alkyl- or 4'-alkoxy-4-cyanobiphenyl is between about 10 and 90% by weight of the mixture, and the compound selected from formulas () to () is not more than about 20% by weight of the total. , the remainder being one or more compounds according to formula () above and optionally other esters. Preferably the 4'-alkyl or 4'-alkoxy-4'-cyanobiphenyl included in the mixture has 5 or fewer carbon atoms in the alkoxy or alkyl group. Preferably the number of carbon atoms is odd for alkoxy groups and even for alkyl groups. As a more general example, the mixture according to the second aspect of the invention may be used in one or more of the applications given above (the actual application depends on the properties of the mixture). A compound according to the above formula () mixed with one or more compounds belonging to

【formula】

【formula】

【formula】

【formula】

【formula】

【formula】

【formula】

【formula】

(In the formula,

[Formula] is a cyclohexane ring,

[Formula] is bicyclo(2,2,2)octane ring, X is 1,4-phenylene group

[Formula] or 4,4'-biphenylyl group

[Formula] or 2,6-naphthyl base

[Formula] Y is CN or R ¹ or OR ¹ or CO・O—X—Y ¹ , Y ¹ is CN or
R' or OR' is shown, and the definition of R' is the same as the definition of R. According to a third feature of the invention, the liquid crystal device of the invention comprises two dielectric substrates, at least one of which is optically transparent, and a layer of liquid crystal material sandwiched between the substrates. and has an electrode on the inner surface of the substrate so as to generate an electro-optic effect by applying an electric field across the liquid crystal material layer, and further, the liquid crystal material consists only of the compound according to the above formula () or contains the compound. It is characterized by containing. Devices according to the third aspect of the invention include twisted nematic effect devices, cholesteric-nematic phase change effect devices, Friederik effect devices, two-frequency switching effect devices, which may or may not be operated in various ways.
Either a cholesteric memory effect device or a dynamic scattering effect device, all of which are constructed in a known manner. Various ways in which compounds of formula () may be used in these devices are outlined above and will be further apparent to those skilled in the art. Examples regarding the preparation and properties of compounds according to the above formula () are shown below. Example 1 The intermediate compound 1-bromo-4-alkyl substituted bicyclo[2,2,2]octane is used to prepare the intermediate acid used in the preparation of the ester as described below. The bromo compound is prepared by the following route. Step A1: Generation of 3-acetyl-1,5-dicyano-trisubstituted pentane. Step B1: 3-acetyl-trisubstituted pentane-
Generation of 1,5-dicarboxylic acid. Step C1: Formation of 4-acetyl-tetrasubstituted cyclohexanone. Step D1: Formation of 1-hydroxy-tetrasubstituted bicyclo[2,2,2]octan-3-one. Step E1: Formation of 1-hydroxy-tetrasubstituted bicyclo[2,2,2]octane. Step F1: 1-bromo-tetrasubstituted bicyclo[2,
2,2] Synthesis of octane. All these steps are HDHoltz and LM
Preparation of 1-carboxy-tetrasubstituted bicyclo[2,2,2]octane by Stock, J.Am.Chem.
Soc., 86 , 5183 (1964) for R=methyl and ethyl groups. Example 2 In this example, 4-alkyl-2, which is an intermediate used for ester formation in Example 11 described later, was used.
- Describe the preparation of halogenated phenols.
The following routes are used. (In the formula, Z ₁ is fluorine, chlorine or bromine.) Step A2: Formation of 4-alkanoyl-2-halogenated anisole. Step B2: Generation of 4-alkyl-2-halogenated anisole. Step C2: Generation of 4-alkyl-2-halogenated phenol. All these steps are carried out essentially by the steps for Z ₁ =fluorine described in UK Patent Application No. 8,031,248. Example 3 In this example, 4-alkyl-3, which is an intermediate used for ester formation in Example 11 described later, was used.
-The preparation of halogenated phenol from commercially available 2-halogenated anisole by the following route is described. (In the formula, Y ₁ is fluorine, chlorine or bromine.) Step A3: Formation of 4-alkanoyl-3-halogenated anisole. Step B3: Generation of 4-alkyl-3-halogenated anisole. Step C3: Generation of 4-alkyl-3-halogenated phenol. All of these steps are essentially carried out by the steps for Y ₁ =F described in British Patent Application No. 8031248. Example 4 In this example, 4-alkyl-
The preparation of 2-cyanophenol by the following route will be described. Step A4: Generation of 4-alkyl-2-cyanophenol. This step is carried out by treating the product of step C2 with conventional cyanation, for example cuprous cyanide. Example 5 In this example, 4-alkyl-, which is an intermediate used in the preparation of ester in Example 11 described later, was used.
The preparation of 3-cyanophenol by the following route will be described. Step A5: Generation of 4-alkyl-3-cyanophenol. This step is carried out by treating the product of step C3 with conventional cyanation, for example cuprous cyanide. Example 6 This example describes the preparation of trans-1-alkyl-4-cyclohexanol from the corresponding commercially available 4-alkylphenol by the following route. Step A6: Generation of 1-alkyl-4-cyclohexanone. This step is based on J. Pines and V. Ipatieff.
The method described in JACS, 61, 2728 (1939) is used. Step B6: Production of trans-1-alkyl-4-cyclohexanol. This step is based on ELEliel, R., J.L.Martin and D.Nasyuri, Organic Synthesis, 47, 16.
(1967). trans-1-alkyl- produced in this example
4-Cyclohexanol is an intermediate used in the production of esters as in Example 11 below. Example 7 This example describes the preparation of various alkoxyphenols used as intermediates in the preparation of liquid crystal esters such as the ester formed in Example 11 below. It will be carried out in the following steps. (In the formula, Y' is F, Cl, Br or CN and Z' is H, or Y' is H and Z' is F, Cl, Br or
CN, or Y' and Z' are both Cl, and R' ₂ is an alkoxy group. ) Steps A7 to D7 are steps known to those skilled in the art of organic chemistry. starting compound

[Formula] is the corresponding anisole if not commercially available.

Obtained from [Formula]. Example 8 This example describes the preparation of 4-alkoxy-2,3-dicyanophenol, which is used as an intermediate in the preparation of the ester described in Example 11 below, by the following route. Step A8: This step is carried out using a conventional cyanation treatment, for example cuprous cyanide. The starting material has both Y′ and Z′
This is the product of step D7 for Cl. Example 9 Used as an intermediate in Example 11 below

1-Hydroxy-4-substituted bicyclooctane of the formula is prepared in the same manner as in Example 1 above (Steps A1 to E1). Example 10 This example describes the preparation of 4-alkyl-2,3-dichlorophenol and 4-alkyl-2,3-dicyanophenol by the following route. Step A10: Generation of 4-alkanoyl-2,3-dichloroanisole. Step B10: Generation of 4-alkyl-2,3-dichloroanisole. Step C10: Generation of 4-alkyl-2,3-dichlorophenol. Step D10: Generation of 4-alkyl-2,3-dicyanophenol. Steps A10-C10 are each performed in essentially the same manner as steps A2-C2. Step D10 is carried out using a conventional cyanation treatment, for example cuprous cyanide. The products of steps C10 and D10 are used as intermediates in the preparation of esters in Example 11 below. Example 11 An ester derivative of 1-carboxy-4-alkyl-substituted-bicyclo[2,2,2]octane is produced by the following route. (In the formula,

[Formula] R ₁ and R ₂ are the same as defined in the above formula ()) Step A11: HD Holtz and LMStock's above paper J.Am.Chem.Soc, 86, 5183
(1964) for R = methyl and ethyl groups, Example 1
1-bromo-4-substituted-bicyclo[2,2,2]octane prepared by
Carboxy-4-substituted-bicyclo[2,
2,2] Prepare octane. Step B11: 4-substitution-1-bicyclo [2,
2,2] Production of octanoyl chloride. 1-carboxy-4-substituted-bicyclo[2,
A solution of 2,2] octane (0.0018 mol) in dry toluene (10 cm ³ ) is heated under reflux with thionyl chloride (1 cm ² ) for 1 hour under anhydrous conditions and then cooled. After the mixture was evaporated to dryness under reduced pressure, dry toluene (10 cm ³ ) was added once again and the resulting solution was evaporated to dryness under reduced pressure again. The acid anhydride fraction is used in the next step C11 without being purified. Step C11: 1, 4-bicyclo [2, 2, 2]
MJSDewar for the preparation of octylene-di-4-methoxy-bicyclo[2,2,2]octane-1-carboxylate
and RSGoldberg, “The role of para-phenylene groups in nematic liquid crystals,” J.Am.Chem.Soc, 92, 1582.
(1970) with appropriate modifications,
An ester derivative of 1-carboxy-4-substituted-bicyclo[2,2,2]octane is prepared using the acid chloride prepared in Step B11. This is the usual esterification of acid chlorides with substituted phenols or similar compounds. Acid chloride is the product of step B11, phenol or similar compound is the product of step A5, C2, C3,
A4, A5, B6, D7, A8, C10 or D10
Any product of the following is suitable. Examples of the products of Example 11 are listed in Tables 1-10. The following symbols are used in Tables 1-10. N-I = Nematic substance - Isotropic liquid transition temperature C - I = Crystalline solid - Isotropic liquid transition temperature S _B - I = Smectic B - Isotropic liquid transition temperature C - S _B = Crystalline solid - Smetic B transition temperature C--N = crystalline solid--nematic transition temperature Ch--I = cholesteric-isotropic liquid transition temperature C--Ch = crystalline solid--cholesteric transition temperature () represents the monotropic transition temperature. [ ] represents the virtual transition temperature. (+)- represents an optically active isomer having a positive angle of optical rotation. + is a smectic, but other
In order to make a possible comparison with the T _N-1 values, a series of mixtures of compounds with a strong suppression of the properties of the smectic B phase and a known nematic system (BDH mixture E7)
represents a compound used to obtain a virtual NI value from the properties of

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

[Table] Specific examples of materials and devices embodying the present invention will be described based on the accompanying drawings. The display of Figures 1 to 4 consists of cells formed from front and rear glass slides 2, 3 held apart by spacers 4 at a distance of approximately 7 μm and held together by epoxy adhesive. Consists of 1. The liquid crystal material 12 is placed on the slide 2,
3 and spacer 4 is filled. Front polarizers 5 are arranged in front of the windshield slide 2 so that their polarization axes are horizontal. Reflector plate 7
Place it behind slide 3. A rear polarizer 6 or analyzer is placed between the slide 3 and the reflector 7. a tin oxide electrode 8, typically 100 Å thick;
9 is applied as a complete film to the inner surface of the slides 2, 3 and etched in the shape shown in FIGS.
The display has seven bars for each digit 10, plus 11 decimal points between each digit.
As shown in FIG. 3, the rear electrode structure consists of three electrodes X ₁ , X ₂ , X ₃ . Similarly, the front electrode structure has three electrodes Y ₁ , Y 2 , Y ₂ for each number and decimal point.
Y ₃ It consists of... By examining the six electrodes for each number and applying the appropriate voltages to the appropriate X, Y electrodes, each of the eight elements is shown to have an independently applied voltage. Before assembling, slide 2 with electrodes attached,
3. After cleaning, soak it in a 0.2% by weight polyvinyl alcohol (PVA) aqueous solution. When dry, the slides are rubbed in a certain direction with a soft cloth, and then assembled so that the rubbing directions are perpendicular to each other and parallel to the optical axes of the adjacent polarizers, that is, the polarizers intersect. Slide the nematic liquid crystal substance 12 2,
When introduced between 3 and 3, the molecules line up on the slide surface along the rubbing direction of each slide and gradually twist between the slides. When no voltage is applied to the cell 1, the light passes through the front polarizer 5, through the cell 1 (during which the plane of polarization rotates 90°), through the rear polarizer 6, and through the reflective surface 7.
It is reflected and reaches the observer. (See Figure 1. The observer is at an angle of 45° to the Z axis perpendicular to the X and Y axes in the plane of the slides 2 and 3.) When a high voltage is applied,
In the liquid crystal layer 12, molecules that do not lose their optical activity are rearranged perpendicularly to the slides 2, 3, ie along the Z axis. In this state, the light no longer reaches the reflector 7 and therefore does not reach the observer, and the observer sees only a dark display of one or more numeric bars. As shown in Figures 5, 6 and 7, 3
The voltage is applied in a line scanning manner at continuous time intervals.
Each X electrode is set to a potential of 3V/2 in turn, while the remaining X electrodes are set to -V/2. Meanwhile, the Y electrode is -
Set it to 3V/2 or V/2. 3V at the crossing point/
When 2 and -3V/2 match, a voltage of 3V will be applied to the liquid crystal layer 12. At other points the voltage is V or -V. Thus, by applying -3V/2 to the appropriate Y electrode when 3V/2 is scanned to the X electrode, the selected crossing point is turned on (indicated by a black circle in the figure). The voltage V is, for example, a 100 Hz square wave alternating current signal, and the sign represents the phase. It will be apparent to those skilled in the art that the devices shown in Figures 1-7 are diversified displays because the electrodes are distributed between on and off cross-points or display elements. Materials embodying the invention suitable for use in material 12 of the above device are those shown in Table 11 below. (Mixture 1)

[Table] The last compound is partially or completely 1 in the mixture.
One or more of the other fluorine compounds mentioned above may be substituted. A small amount of cholesteric material may be added to the nematic material to create a favorable twist in the molecules of the liquid crystal layer. Using this treatment and appropriate slide surface preparation, the display patch problems taught in UK Patent Application Nos. 1,472,247 and 1,478,592 can be avoided. Suitable cholesteric substances are: About 0.1-0.5% by weight C15 and about 0.01-0.05% by weight CB15. Small amounts of polychromatic dyes e.g. British Patent Application No. 42810/
One of the anthraquinone dyes described in No. 77 may be added to enhance display contrast. Other specific mixtures embodying the second aspect of the invention may be used in Friedericksz effect cells. The cell consists of a sandwich of liquid crystal material between glass slides having an electrode film on the inner surface, as in the device described above. However, in this case, a polarizer is not necessarily necessary, and the inner surface of the glass slide is coated with lecithin, and the liquid crystal material is a negative substance, and the lecithin coating ensures that all molecules are perpendicular to the slide substrate (homeotropic orientation). Arranged in the off state. When an appropriate electric field is applied to the material in the on state, the molecules rearrange parallel to the slide surface (homogeneous orientation). Pleochroic dyes may be incorporated into the liquid crystal material to enhance the contrast between the on and off states. Freedericksz effect cells made as described above may incorporate mixture 2 below.

Table: The preparation of compound E is described in UK Patent Application No. 7934129. 1.2% by weight of known pleochroic dyes such as 1,5-
Add bis-4′-n-butylphenylaminoanthraquinone to mixture 2 to create a colored mixture (mixture 2a)
You can also do this. When a voltage is applied to the cell, the color changes from a weakly absorbing state to a strongly absorbing state. Another embodiment of the invention incorporates the above-mentioned materials into a phase change effect device (cholesteroleptic-nematic). A cell is prepared containing a long helical pitch of cholesteric material sandwiched between electrodes having a glass slide, similar to the twisted nematic cell described above. However, in this case surface preparation for homogeneous arrays e.g.
Treatment of the glass slide surface with SiO and polarizers are not used. If the glass slide is untreated and the liquid crystal material has a positive dielectric anisotropy (Δε), the liquid crystal material has a twisted focal conic molecular orientation in the off state which scatters light. The effect of an electric field applied between a pair of electrodes on the internal surface of each glass slide is to turn the region of liquid crystal material between the electrodes into an on state into a homeotropic nematic orientation with less scattering than an off state. be. This is a negative contrast phase change effect device. If the internal surface of the glass slide is treated with a coating of lecithin, for example, so that the liquid crystal material has a negative Δε and is aligned perpendicular to the surface, then the material in the off state is in a homeotropic orientation with a small scattering effect on the incident light. . Applying an electric field between a pair of electrodes on the interior surface of each glass slide changes the region of liquid crystal material between the electrodes (in the on state) into a twisted homogeneous orientation that scatters light. This is a positive contrast phase change effect device. The contrast between the two states in each case is determined by adding a small amount of a suitable pleochroic dye to the liquid crystal material (e.g. 1% by weight of 1,5-bis-4'-n- if Δε is positive).
butylphenylaminoanthraquinone). Suitable positive dielectric anisotropic materials embodying the invention for use in phase change effect devices include:

Suitable negative dielectric anisotropy materials embodying the invention for use in phase change effect devices, Mixture 4, are:

Table Compound E in mixtures 2 and 4 may be replaced by one of the above-mentioned di-cyano compounds (the product of Example 10 where both Y and Z are CN). The specified fluoro-esters present in the compositions in mixtures 1 to 4 may be replaced by suitable known non-fluorinated esters of the form:

【formula】

[Formula] or

(R = alkyl group, R ¹ = alkyl or alkoxy group) (see, for example, the esters used in the diversified twisted nematic device described in GB 2031010A).

[Brief explanation of drawings]

Figure 1 is a partial view of a twisted nematic type digital display, Figure 2 is a cross-sectional view of the display in Figure 1, Figure 3 is a diagram of the shape of the rear electrode in Figure 1, and Figure 4 is a diagram of the shape of the front electrode in Figure 1. , 5, 6 and 7 are illustrations of the device of FIGS. 1-4 showing typical voltages. 1... Cell, 2, 3... Glass slide, 4...
...Spacer, 5, 6... Polarizer, 7... Reflector, 8, 9... Electrode, 12... Liquid crystal material.

[Claims]

1 General formula (In the above formula, R represents an alkyl group having 1 to 10 carbon atoms, and X represents F or Cl.) 4-halogenobenzoic acid 4'-(4''-alkylphenyl) phenyl ester. 2 general formula (In the above formula, R represents an alkyl group having 1 to 10 carbon atoms, and X represents F or Cl.) Tomo1
A liquid crystal composition characterized by containing the following ingredients:

Claims (1)

Side-substituted benzene ring [Formula] (In the formula, at least one of Y and Z represents a halogen or a cyano group, and the other represents hydrogen, a halogen, or a cyano group, and Y and Z may be the same) A liquid crystal ester compound having a low or negative dielectric anisotropy. 2. The compound according to claim 1, wherein R ₁ and R ₂ represent an n-alkyl group having from 1 to 12 carbon atoms. 3. The compound according to claim 2, wherein [Formula] represents a trans-1,4-disubstituted-cyclohexane ring. 4. The compound according to claim 2, wherein [Formula] represents a 1,4-disubstituted-bicyclo(2,2,2)octane ring. 5. A compound according to claim 2, wherein [formula] represents [formula] (wherein Y and Z have the same meanings as in claim 1). 6. The compound according to claim 5, wherein [Formula] represents [Formula]. 7. The compound according to claim 5, wherein [Formula] represents [Formula]. 8. The compound according to claim 5, wherein [Formula] represents [Formula]. 9. The compound according to claim 1, wherein R ₁ represents an n-alkyl group having 1 to 12 carbon atoms, and R ₂ represents a (+)-2-methylbutyl group. 10. A liquid crystal composition comprising a mixture of liquid crystal compounds, wherein at least one compound is a compound according to claim 1. 11 Two dielectric substrates, at least one of which is optically transparent, a layer of liquid crystal material sandwiched between the substrates, and an electric field capable of being applied to the layer of liquid crystal material to produce an electro-optic effect. 11. A liquid crystal electro-optic effect display comprising: an electrode disposed on the inner surface of the substrate, and wherein the liquid crystal material is a liquid crystal compound according to claim 10.