JPH0229072B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to novel nematic liquid crystal compounds of ester derivatives useful as electro-optic display materials. The novel nematic liquid crystal provided by the present invention has the general formula [In the formula, R represents a linear alkyl group having 1 to 10 carbon atoms] 4-n-alkylcyclohexanecarbonyloxy-3'-fluoro-4'-cyanobenzene. One of the representative liquid crystal display cells is M.Schadt etc. [APPLIED PHYSICS
LETTERS, 18 , 127-128 (1971)] is a field-effect cell (feed-effect mode cell). This field effect cell has two transparent electrode plates arranged in parallel,
A nematic liquid crystal material with positive dielectric anisotropy is filled between the electrode plates, and the liquid crystal molecules form a spiral arrangement twisted at a certain angle between the electrode plates with their long axes parallel to the electrode plates. , which gives it a certain degree of optical rotation power for the incident light. When a voltage is applied to the electrode plates, the liquid crystal molecules align with their long axes perpendicular to the electrode plates, thereby eliminating optical rotation power. This change in optical rotation power is converted into a change in optical transmittance of the cell using a polarizing plate. in this way,
Nematic liquid crystal materials used in field-effect cells must have positive dielectric anisotropy. The compound of formula () is a nematic liquid crystal compound with strong positive dielectric anisotropy. Therefore, various nematic liquid crystal materials can be applied to field effect cells by containing a small amount of the compound of formula (). Driving a field effect cell at a low voltage is considered to be one of the important issues in this technical field, and for this purpose it is necessary to lower the threshold voltage of the nematic liquid crystal material used as much as possible. The compound of formula (1) is a highly effective liquid crystal compound that meets this purpose. That is, since the compound of formula () has a strong positive dielectric constant anisotropy, by mixing it with various nematic liquid crystal materials, the threshold voltage of the material can be lowered. Even if the compound to be added and mixed has extremely strong positive dielectric anisotropy, if the compound does not have properties as a nematic liquid crystal, such a compound can be used in various nematic liquid crystal materials. When mixed, the nematic phase monoisotropic liquid phase (N-I) transition temperature is significantly lowered, which narrows the usable temperature range. However, since the compound of formula () has a nematic phase, it is Even if a large amount is mixed into a liquid crystal material, the NI transition temperature thereof will not be significantly lowered. Therefore, by using the compound of formula (), a mixed liquid crystal for low voltage driving can be easily produced without significantly narrowing the nematic temperature range. Furthermore, the compound of formula () has very good performance with 4,4'-substituted cyclohexylcarboxylic acid phenyl ester, which was reported as a nematic liquid crystal material with excellent time-division driving characteristics in JP-A-54-83694. Since they have excellent compatibility, a practically excellent mixed liquid crystal can be produced by mixing them with these compounds. The compound of formula () of the present invention has the reaction formula As shown, it can be produced by a two-step reaction. In the first step, a halogenating agent is reacted with a compound of formula () (wherein R has the above meaning. The same applies hereinafter) to form a compound of formula (') (wherein, X is a halogen atom). ) is manufactured. In the compound of formula ('), X is preferably a chlorine atom, and thionyl chloride may be used as the halogenating agent. The reaction is carried out at normal pressure and the reflux temperature of the reaction mixture. It is not necessary to isolate the compound of formula (') from the mixture produced by the reaction, it is only necessary to remove excess halogenating agent. In the second step, the crude compound of formula (') prepared in the first step and the compound of formula () are reacted in an inert organic solvent. As the inert organic solvent, for example, diethyl ether, tetrahydrofuran, dimethylformamide, benzene, etc. may be used. In order to remove hydrogen halide liberated during the reaction from the reaction system, it is desirable to include a basic substance such as pyridine, tertiary amine, etc. in the above-mentioned inert organic solvent. The reaction is carried out at normal pressure and at a temperature ranging from room temperature to the reflux temperature of the reaction mixture. The desired compound of formula () can be isolated by subjecting the reaction product to a series of purification treatments such as solvent extraction, water washing, drying, and recrystallization. The transition temperatures of representative compounds of formula () thus produced are shown in the table below. In the table below, C represents a crystalline phase, N represents a nematic phase, and I represents an isotropic liquid phase.

【table】

[Table] Next, as a typical comparative example compound having a chemical structure similar to that of the compound of formula () and which can be added to a nematic liquid crystal material to make the material applicable to a field effect cell, Compound and formula of Select compounds of the formula that are these compounds or representative compounds of the present invention. , respectively, for typical mixed nematic liquid crystal materials, i.e. Compound (a), compound (a') and compound (b) are added in various proportions to a mixed nematic liquid crystal material consisting of
The difference in the effect of the nematic liquid crystal materials on the threshold voltage and NI transition temperature was tested. The threshold voltage was measured using a field effect cell with a liquid crystal layer thickness of 10 μm filled with a sample. The threshold voltage was the voltage at which a variable voltage of 1KHz sine wave was applied to the liquid crystal cell and the amount of transmitted light was 90%. Here, the standard for the amount of transmitted light (%) is that the amount of transmitted light when no voltage is applied is 100%, and the amount of transmitted light when the light from the light source is completely blocked is 0%. The results are shown in Figures 1 and 2. The compound of formula (a) above is described in JP-A-54-90144 and has strong positive dielectric anisotropy;
It is a compound that does not have the properties of a nematic liquid crystal. Moreover, the compound of the above formula (a') is
It is a nematic liquid crystal compound that has strong positive dielectric anisotropy.
From FIG. 1 and FIG. 2, the compound (b) of the present invention can be added in the same amount as the known compounds (a) and (a').
It will be understood that the threshold voltage can be lowered to a lower value, and the decrease in the NI transition temperature can be suppressed to a smaller extent than in the known compound (a). Example 1 Formula

30 c.c. of thiol chloride was added to 2.28 g (0.0146 mol) of the compound of the formula, and the mixture was reacted under reflux for 30 minutes, and then excess thionyl chloride was distilled off. Next, the reaction product obtained has the formula

2.0 g (0.0146 mol) of the compound of [formula], 50 c.c. of toluene and 4.0 g of pyridine
were added and reacted under reflux for 30 minutes. Next, the reaction solution was washed with 1% hydrochloric acid and water to make it neutral, and then toluene was distilled off from the reaction solution. The obtained reaction product was recrystallized from methanol,
3.0 g (0.0075 mol) of a compound having the following formula was obtained. Yield 70% Transition temperature 55°C (C→I) -15°C (NI) Examples 2 to 6 In the same manner as in Example 1, compounds of the following formulas were produced, respectively.

[Table] 30℃ (N〓I)

[Table] 49℃ (N〓I)
Example 7 We investigated a mixed liquid crystal consisting of . This mixed liquid crystal is 29
It exhibits a nematic phase at temperatures between ℃ and 46℃, and the dielectric anisotropy is
It exhibits a nematic phase at 29°C to 46°C, the dielectric anisotropy is +11.4, and the threshold voltage (measured by the above method) is
It was 1.1 volts.

[Brief explanation of drawings]

FIGS. 1 and 2 are charts showing the relationship between the amount of the compound of the present invention or a known compound added to a nematic liquid crystal material, threshold voltage, and NI transition temperature.

Claims (1)

[Claims] 1. General formula [In the formula, R represents a linear alkyl group having 1 to 10 carbon atoms] A compound represented by the following formula.