JPH0359884B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel substance that has positive dielectric anisotropy, low viscosity, and exhibits a liquid crystal phase over a wide temperature range, and a liquid crystal composition containing the same. Liquid crystal display elements utilize the optical anisotropy and dielectric anisotropy of liquid crystal materials, and can be divided into TN type (twisted nematic type), DS type (dynamic scattering type), and guest-host type depending on the display format. There are various types such as , DMP type, etc., and the properties of the liquid crystal materials suitable for each use are different. Both liquid crystal materials are free from moisture, air,
It is necessary to be stable to heat, light, etc., and there is also a need for something that exhibits a liquid crystal phase over as wide a temperature range as possible, centering on room temperature. At present, there is no single compound that satisfies these conditions, and liquid crystal compositions obtained by mixing several types of liquid crystal compounds and non-liquid crystal compounds are used. Especially recently -20℃
There is now a demand for liquid crystal display elements that operate over a wide temperature range of ~80°C. In order to satisfy such requirements, an effective means is to lower the viscosity, especially the viscosity at low temperatures. However, in general, those with a high clearing point (N-1 point) have a high viscosity;
Furthermore, those having low viscosity, such as alkylphenylcyclohexane derivatives, have a low clearing point. The present inventors previously reported in Japanese Patent Application Laid-Open No. 57-64626 that a liquid crystal compound with the general formula: 4-[trans-4′-(trans-
4″-alkylcyclohexyl)cyclohexyl]
The present invention discloses a compound of fluorobenzene that is effective for use in display elements that operate at lower to higher temperatures required by recent advances in liquid crystal display technology, and has particularly excellent thermal stability. This is what we provide. That is, the present invention is based on the general formula (In the above formula, R represents an alkyl group having 1 to 10 carbon atoms,

【ceremony

【formula】

[expression] or

[Formula] is shown. ) A 4-fluorobiphenyl derivative consisting of four rings and a liquid crystal composition containing the same. The compound of formula () of the present invention has a temperature of about 40 ~
Although it has a low viscosity of 50cp, its liquid crystal temperature range is wide from approximately 150℃ to over 300℃, and it has a high clearing point.
By adding a small amount of this compound, it is a very useful compound as a component of a liquid crystal composition used for liquid crystal display cells that operate in a wide temperature range from low to high temperatures. In addition, although the dielectric anisotropy Δε is about 2, the threshold voltage and saturation voltage of the liquid crystal composition to which the compound of the present invention is added do not increase much compared to the composition without the addition, and are almost the same. It is the rank.
Furthermore,

[Formula] is

【formula】

Formula
It is stable against heat, air, moisture, etc., and has a wide range of applications. Next, a method for producing the compound of the present invention will be described. 4-Fluoro-4'-bromobiphenyl is first reacted with magnesium in tetrahydrofuran to give 4-fluorobiphenyl-4'-magnesium bromide and then with 4-substituted cyclohexanone to form 4-(4-substituted cyclohexane-1- ol-1-yl)-4'-fluorobiphenyl ()
get. Compound () is then subjected to a dehydration reaction in the presence of sodium hydrogen sulfate to form 4-(4-substituted cyclohexen-1-yl)-4'-fluorobiphenyl (a), and this (a) is dehydrogenated with chloranyl. Possibly 4-substituted-4″-fluoro-
p-terphenyl (b).
In addition, (a) is catalytically reduced to give 4-(trans-4-
Substituted cyclohexan-1-yl)-4'-fluorobiphenyl (c). The above is expressed as a chemical formula as follows. (In the above formula, R is the same as above.) The present invention will be explained in more detail with reference to the following examples. In the example, the liquid crystal-smectic point is C-Sm point,
The smectic-nematic point is abbreviated as the Sm-N point, and the nematic-clear point is abbreviated as the N-point. Example 1: Production of compound (a) 4-[4-(trans-4-propylcyclohexyl)cyclohexen-1-yl)-4'-fluorobiphenyl 1.3 g of magnesium turnings was placed in a three-necked flask, and nitrogen Under a gas atmosphere, 13.4 g of 4-fluoro-4'-bromobiphenyl was added to 200 ml of tetrahydrofuran.
was gradually added with stirring, and the reaction temperature was kept below 40°C. It took 2 hours for the dropwise addition, and after refluxing for 1 hour, the reaction solution became homogeneous. The 4-fluorobiphenyl-4'-magnesium bromide thus produced was cooled to below 10°C, and a solution of 8.9 g of 4-(trans-4-propylcyclohexyl)cyclohexanone, prepared separately, dissolved in 200 ml of tetrahydrofuran was added. After adding all at once, the mixture was allowed to react at room temperature for 30 minutes, and then refluxed for 3 hours. Then, after cooling, 100 ml of 3N hydrochloric acid was added, followed by 1 portion of water. This solution was extracted three times with 100 ml of toluene, the toluene was combined, and the toluene layer was washed with water until neutral. The toluene layer was concentrated under reduced pressure to obtain oily 4-[4-(trans-4-propylcyclohexyl)cyclohexan-1-ol-1-yl]-4'-fluorobiphenyl ().
I got it. The compound () was kept in a nitrogen atmosphere together with 2 g of potassium hydrogen sulfate and subjected to a dehydration reaction at 200° C. for 2 hours. After cooling, add 300ml of toluene,
The toluene layer was washed off with hot water. The toluene layer was concentrated to 100 ml under reduced pressure and recrystallized to give 4-[4-
Crystals of (trans-4-propylcyclohexyl)cyclohexen-1-yl]-4'-fluorobiphenyl (a) were obtained. The yield of compound (a) was 3.4 g. The C-Sm point of this product is 171℃,
The Sm-N point was 201°C and the N-I point was 277°C. Example 2: Compound (b) 4-(trans-4-propylcyclohexyl)
-4″-Fluoro-p-terphenyl 4-[4-(trans-4-
propylcyclohexyl)cyclohexene-1-
7.6 g of [yl]-4'-fluorobiphenyl (a) was dissolved in 250 ml of xylene, and 10.9 g of chloranil was added to this solution, followed by refluxing for 15 hours. After cooling, 100 ml of toluene was added, and the organic solvent layer was washed three times with 100 ml of 2N sodium hydroxide. After washing with hot water until the washing liquid became neutral, the organic solvent layer was distilled off under reduced pressure. The remaining solid substance was dissolved in toluene, activated carbon was added, and the mixture was filtered while hot, and then left as is to obtain the desired 4-(trans-4-propylcyclohexyl)-4″-fluoro-p-terphenyl (b). The yield of compound (b) was 2.1 g.The C-Sm point of this product was 192°C, and the Sm-N
The point was 257°C, and the N-I point was 300°C or higher. Example 3: Preparation of compound (c) 4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]-4'-fluorobiphenyl 4-[4-(trans-4- −
propylcyclohexyl)cyclohexene-1-
[Il]-4'-fluorobiphenyl (a) (3.4 g) was dissolved in 250 ml of toluene, 1 g of platinum oxide catalyst was added, the mixture was heated to 60°C, and catalytic reduction was carried out at normal pressure to produce the calculated amount of hydrogen in 7 hours. was absorbed. After filtering off the catalyst, toluene was distilled off under reduced pressure, and the remaining solid was recrystallized three times with toluene to obtain 4-[trans-4
-(trans-4-propylcyclohexyl)cyclohexyl]-4'-fluorobiphenyl (c)
I got it. The yield of compound (c) was 0.7 g, and its C-Sm point was 154°C, its Sm-N point was 190°C, and its N-
The temperature at point I was 300°C or higher. The physical properties of a compound (hereinafter referred to as c') having the same structure as the compound (c) of the present invention obtained above except that the substituent on the terminal phenyl ring is iodine instead of fluorine are as follows.
-Sm: 170℃, Sm-N: 216.3℃, N-I: 293
℃ (Japanese Unexamined Patent Publication No. 58-59930, page 231, No. 1)
(See the column for Example 5 in the table). In order to compare the thermal stability of both compounds, both were left on a hot plate heated to 300° C. for 2 hours in an air atmosphere, and then their respective transition temperatures were measured, and the following results were obtained. C-Sm Sm-N N-I c 154℃ 190℃ 300℃ or more c' 132℃ 168℃ 212℃ From the above results, it is known that the thermal stability of the comparative compound c' is extremely poor, but this It was found that c, which is an example of the compound of the invention, does not substantially undergo thermal changes and is extremely stable. Usage example 1 Trans-4-propyl-(4'-cyanophenyl)cyclohexane 28% by weight Trans-4-pentyl-(4'-cyanophenyl)cyclohexane 42% by weight Trans-4-heptyl-(4'-cyanophenyl)cyclohexane 30% by weight %, the N-I point is 52°C, Δε is +11.2, and the viscosity at 20°C is 23 cp.
This liquid crystal composition is used in a cell with a thickness of 10 μm and a counter electrode.
The threshold voltage of the device sealed in a TN cell (twisted nematic cell) was 1.5V and the saturation voltage was 2.1V. 4 produced in Example 1 to 95 parts by weight of liquid crystal composition (A)
-[4-(trans-4-propylcyclohexyl)cyclohexen-1-yl]-4'-fluorobiphenyl (a) was added to the liquid crystal composition (B) in an amount of 5 parts by weight, and the N-I point was 61°C. Δε was +11.0, the viscosity at 20° C. was 25 cp, the threshold voltage of the cell sealed in the cell was 1.6 V, and the saturation voltage was 2.2 V. Usage example 2 4 produced in Example 3 was added to 95 parts by weight of liquid crystal composition (A).
-N- of a composition consisting of 5 parts by weight of [trans-4-(trans-4-propylcyclohexyl)cyclohexyl]-4'-fluorobiphenyl (c)
Point I is 60℃, Δε is +11.1, viscosity at 20℃ is 24cp,
The threshold voltage of the one sealed in the cell is 1.6V,
The saturation voltage was 2.2V.

Claims (1)

[Claims] 1. General formula (In the above formula, R represents an alkyl group having 1 to 10 carbon atoms, and [Formula] represents [Formula] [Formula] or [Formula].) A 4-fluorobiphenyl derivative consisting of four rings represented by: 2 General formula (In the above formula, R represents an alkyl group having 1 to 10 carbon atoms, and [Formula] represents [Formula] [Formula] [Formula].) Contains a 4-fluorobiphenyl derivative consisting of 4 rings represented by liquid crystal composition.