JPH0571579B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel liquid crystal compound. In the field of display devices, electro-optical devices with low power consumption are desired. Liquid crystal display cells are attracting attention as a device that can electrically control the orientation of liquid crystal molecules and have extremely high electrical resistance, thus meeting such requirements. Among liquid crystal display cells, liquid crystal dot matrix display cells are used in electronic desktop calculators, etc.
It is beginning to be used in office equipment, computer terminal display devices, etc. As a result, liquid crystal display cells that are easier to see and have a larger number of display pixels are required. A dot matrix display is one that displays information such as figures or characters as a collection of dots.
Multiplex driving becomes necessary as the number of display pixels increases. Initially, single-line display cells driven at 1/7 or 1/8 duty were common, but recently there has been a demand for 1/32 duty or 1/64 duty, and the multiplex drive characteristics of TN cells have changed. Improving this has become an important issue. Therefore, as a result of various studies to find a liquid crystal composition with excellent multiplex drive characteristics, we found that
General formula ()

4-(trans-4′-alkylcyclohexyl)benzoic acid 3″-fluoro-4″-alkoxyphenyl ester represented by

[Formula] represents a trans-1,4-disubstituted cyclohexane ring, and R and R' represent a straight-chain alkyl group having 1 to 6 carbon atoms) is colorless and transparent and has a temperature at which it transitions from a liquid crystal to an isotropic liquid. is 100℃
It has been found that a nematic liquid crystal composition having positive dielectric anisotropy, which is an excellent liquid crystal compound having the above properties, and furthermore, containing a compound represented by the general formula () has excellent multiplex drive characteristics. The multiplex drive characteristics of a TN cell are often expressed in terms of drive voltage, voltage margin, response speed, etc., but the voltage margin is the most important characteristic that directly affects display contrast. Voltage margin (M) is a value that expresses how much variation in drive voltage can be tolerated, and it is defined as the lowest voltage (Von) for sufficient lighting with the selected waveform and the highest voltage (Voff) at which crosstalk begins to occur with the half-selected waveform. ) is defined as the ratio of the difference between M=(Voff-Von)/VD×100% (1) VD=(Von+Voff)/2 (2) The larger the voltage margin, the more the number of scanning lines can be increased, and the better the display contrast. In equations (1) and (2), Von and Voff are the applied waveforms,
Since the meaning changes depending on the viewing angle, temperature, or the definition of the lighting state and crosstalk state, in the following explanation, the following definitions will be used in accordance with the usual method. First, as is known from the past, TN cells operate according to the effective value of the applied voltage, so even if the duty ratio or bias of the waveform used changes.
Comparison using one type of waveform is sufficient for relative comparison between TN cells. Therefore, we will compare the voltage margin when using a 1/8 duty 1/4 bias waveform. The viewing angle (θ) is assumed to be in the range of 10° to 40° from the normal direction of the TN cell toward the low visual angle clear vision direction. Also, the temperature is 25°C, and the brightness change due to voltage application at θ = 10° is 50% of its saturation value.
Von is defined as Von when the voltage reaches %, and Voff is defined as crosstalk occurs at 25% at θ = 40°. The lengths of the alkyl groups R and R' of the compound of the general formula () of the present invention are each 1 to 6, but the smaller the total number of carbon atoms in X, the higher the melting point, and the larger the total number of carbon atoms, the higher the viscosity. It is preferably 8 or less. The compound of formula () of the present invention is used in combination with other liquid crystal compounds to widen the usable temperature range,
Furthermore, it improves multiplex drive performance, and is usually 1% to 50% compared to other liquid crystal compounds.
More preferably, they may be used in a mixture of 3% to 30%. The dielectric anisotropy of the compound () is about -2 at 25°C, and in order to be used in TN cells, it must be used in conjunction with liquid crystals that have positive dielectric anisotropy. Examples of compounds with positive dielectric anisotropy (referred to as Np materials) that are suitable for these purposes are described below.

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[Formula] (R″, R is a straight-chain alkyl group having 1 to 8 carbon atoms,
X means a halogen group such as F, Cl, Br, etc. ) The preferred physical property for Np materials is large dielectric anisotropy. Therefore, it is common to use a compound having a CN group at the end, and these compounds are particularly preferred among those having a CN group.

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[Formula] etc. In addition, even though the dielectric anisotropy is not as large as that of the above-mentioned compounds, Np materials with excellent compatibility are

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[Formula] etc. Further, it can also be used in combination with a material whose dielectric anisotropy is negative or close to zero. The purpose is to match the physical properties of the liquid crystal composition, such as dielectric anisotropy, nematic temperature range, and refractive index anisotropy, to the required specifications.

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[Formula] (R″, R is a straight-chain alkyl group having 1 to 8 carbon atoms)
etc. are used. Note that these compounds are merely examples, and substitution of a hydrogen atom with a halogen atom, cyano group, methyl group, etc., substitution of a cyclohexane ring or benzene ring with another six-membered ring, five-membered ring, etc., substitution of a ring with a halogen atom, a cyano group, a methyl group, etc. Various materials can be selected and used, such as changing the bonding group between them. The composition of the present invention is used by being injected into a liquid crystal cell. A typical liquid crystal cell is a twisted nematic (TN) type liquid crystal cell, in which transparent electrodes such as In ₂ O ₃ -SnO ₂ are formed in a desired pattern on the inner surface of a transparent substrate such as glass or plastic. Overcoat with SiO ₂ , polyimide, etc. as necessary.
The substrates on which the horizontal alignment layer has been formed are placed facing each other, the periphery is sealed, liquid crystal is injected, and the injection port is sealed, and polarizing plates are laminated on both outer surfaces.
Further, the external phase transition type, the guest host type, the dynamic scattering type, or a combination thereof may be used. In the present invention, TN such as dot matrix display, etc.
It is suitable for multiplex driving of cells, especially for high duty ratio multiplex driving. Furthermore, the cell structure includes providing an undercoat layer such as SiO ₂ or Al ₂ O ₃ between the transparent substrate and the transparent electrode, using a reflective electrode, and using a two-layer electrode.
Various applications are possible, such as using a color polarizing plate, using a color filter, using a semiconductor substrate, and using a two-layer element, and it can be used in various applications such as watches, home appliances, measuring instruments, automobile instruments, games, computer terminals, etc. Can be used for various purposes. General formula () of the present invention
The compound can be produced, for example, by the method shown below.

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[Chemical formula] First step: The compound of formula () is chlorinated using a chlorinating agent such as thionyl chloride or phosphorus oxychloride to produce the compound of formula (). Second Step The compound of formula () produced in the first step is reacted with the compound of formula () in the presence of a basic substance such as pyridine to produce the desired compound of formula (). Next, the present invention will be specifically explained with reference to Examples. Example 1 Compound where R is n-C ₃ H ₇ in general formula ()
After heating a mixture of 24.6 g (0.1 mol), 100 ml of carbon tetrachloride, and 15 ml of thionyl chloride under reflux for 6 hours, the solvent and excess thionyl chloride were distilled off, and the residue was formed by the general formula () where R is n-C A compound _{of 3H7} was obtained. Dissolve this in 50 ml of toluene, and add 16.8 mL of a compound of general formula () where R' is n-C ₄ H ₉ .
After adding 10 g of pyridine and stirring at room temperature for 3 hours, the precipitated pyridine hydrochloride was filtered off, the filtrate was washed with dilute hydrochloric acid and water in that order, and then magnesium sulfate was added and dried. death,
Distill the solvent of the filtrate to obtain the desired general formula ()
A crude crystal of a compound in which R is n-C ₃ H ₇ and R' is n-C ₄ H ₉ was obtained. This was recrystallized twice from methanol. Yield: 24.7g, yield: 64%. Observation under a polarizing microscope with a hot stage shows that this compound melts at 94.9°C;
It shows a smectic phase between 128.0℃ and 128.0℃.
It exhibits a nematic phase between ~178.8°C. ¹ HNMR of this compound (CDCl ₃ solvent, TMS internal standard) δ (ppm) 0.80-2.06 Complex m. 25H 2.57 tJ=9Hz 1H 4.0 tJ=6Hz 2H 6.86-7.07 Complex m. 3H 7.26, 8.03 A ₂ B ₂ qualtet 4H The first IR spectrum of this compound (KBr tablet)
As shown in the figure. Example 2 In Example 1, except that a compound in which R′ is C ₂ H ₅ is used as the compound of general formula ().
Similarly, in the general formula (), R is n-C ₃
A compound in which H ₇ and R′ are C ₂ H ₅ was obtained. Example 3 In the same manner as in Example 1, except that a compound in which R' is n-C ₃ H ₇ is used as the compound in general formula (), R
A compound in which C ₃ H ₇ and R′ is n-C ₃ H ₇ was obtained. Example 4 In Example 1, a compound _of general formula () in which R is _n-
A compound in which C ₃ H ₇ and R′ is C ₅ H ₁₁ was obtained. Example 5 In Example 1, a compound in which R' is n-C ₄ H ₉ was used as the compound of the general formula (), and the compound of the general formula ()
A compound in which R is n-C ₄ H ₉ and R' is C ₂ H ₅ in the general formula () was obtained in the same manner as in Example 1 except that a compound in which R' is C ₂ H ₅ was used as the compound. . Example 6 In Example 5, in the same manner as in Example 5, except that a compound in which R' is n-C ₃ H ₇ is used as the compound of general formula (), R is n- in the general formula ().
A compound in which C ₄ H ₇ and R′ is n-C ₃ H ₇ was obtained. Example 7 _In Example 5, in _the general formula (), R is n-
A compound in which C ₄ H ₉ and R′ is n-C ₃ H ₇ was obtained. Examples 8 to 10 Table 1 shows VD and M when a TN cell using a nematic liquid crystal containing the compound of the present invention was driven at 25° C. with a 1/8 duty and 1/14 bias waveform. Compounds are represented by the following abbreviations. A (Example 1)

[ka] B

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【formula】 Equal weight of mixed liquid crystal C

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【formula】 Equal weight of mixed liquid crystal D

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[Table] One or more compounds of the present invention are mixed with other nematic, cholesteric, smectic liquid crystals, dichroic dyes, etc. as necessary, and the compound is sealed between transparent substrates having electrodes of a desired shape as a liquid crystal. It is used as a liquid crystal display element. Moreover, this element may have various undercoats, overcoats for alignment control, polarizing plates, filters, reflective layers, etc. as necessary, and may be used as a multilayer cell or in combination with other display elements. There are various types that use a semiconductor substrate or a light source. In addition, the driving methods for liquid crystal display elements include dynamic scattering (DSM) method, twisted nematic (TN) method, guest host (GH) method, dual frequency method, smectic phase electric and/or thermo-optical method. Any method known in the field of liquid crystal display elements can be adopted. The liquid crystal compound of the present invention has a high clearing point, and the liquid crystal composition containing the liquid crystal compound of the present invention has excellent multiplex drive characteristics, and can be used in various applications in the future.

[Brief explanation of drawings]

Figure 1 shows the IR of the liquid crystal compound of the example of the present invention.
Spectrum diagram.

Claims (1)

[Scope of Claims] 1. A liquid crystalline compound represented by the general formula () [Chemical formula] (where [Formula] represents a 1,4-disubstituted transcyclohexane ring, and R and R' have 1 to 6 carbon atoms. (indicates a straight-chain alkyl group)