JPH066556B2 - Fluorine-containing liquid crystalline compound - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ferroelectric liquid crystal compound as a material for a large-sized display device, which is required to have a high-speed response particularly in the property utilization of the electro-optical effect of liquid crystal. It is a thing.

[Prior Art] Most of the liquid crystals that have been put to practical use are nematic,
Among them, the twisted nematic type (TN) has been mainly used for displays with a small number of pixels such as a clock, a wristwatch and a calculator, but the number of pixels is large (for example, the number of signal electrodes is 100).
As described above, when a screen having a relatively large display area is used, the contrast is lowered and the viewing angle is narrowed, so that it becomes impractical.

Two measures were taken to solve this problem. In other words, the TN type with a twist angle of 90 ° is increased to 180-270 ° to increase the contrast, and the super twist nematic type (STN
It was the development of a new driving method called an active matrix method, which prevents the deterioration of contrast by incorporating a transistor or diode in each other pixel.

With these solutions, LCD TVs with a screen size of 2 to 3 inches and a pixel number of 50,000 to 80,000 appear on the market, which is a momentum on the extension of research and development, and a display having a larger display area, such as a CRT. The goal was to set a flat display that could replace the.

However, in the nematic liquid crystal device, since the anisotropy of the dielectric constant is simply used as the driving force by the electric field E, only a small force of the paraelectric material is used, and a high-speed response of m · sec or more is difficult. It has become clear that the display capacity, responsiveness, and display quality are inherently limited in spite of various efforts to meet the required level of detail. On the other hand, ferroelectric liquid crystals have recently attracted attention and expectations as new liquid crystals.

Ferroelectric liquid crystals were synthesized in 1975 by p-decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (DOBAMBC) by RB Meyer et al. (J. de Phys. Lett.,
36 , 69, 1975), it was confirmed that the chiral smectic C phase is a ferroelectric substance having spontaneous polarization.

In 1980, NA Clark et al. (Appl.Phys.Let
t., 36 , 899, 1980), DOBAMBC, which is one of the ferroelectric liquid crystal compounds in a thin film cell, exhibits high-speed switching characteristics of m.sec or less, and is also reported to have bistability. The potential as a material for display devices in the future was noted. Ferroelectric liquid crystals are characterized by high-speed response and memory property, but among them, the high-speed property showing a response time on the order of μ · sec is unprecedented in other liquid crystals. Ferroelectricity is 1) having a dipole moment or a dipole moment component in the direction perpendicular to the long axis direction of the molecule in view of the structure of liquid crystal molecules, 2) the molecule is a chiral molecule having an optically active group, 3) Smectic phase with tilt angle,
It is expressed with spontaneous polarization only when these three conditions are satisfied. The driving force of the element in the electric field E is the spontaneous polarization P
_s (nC / cm ² ), and its response speed τ is expressed as τ = η / P _s · E (η is the viscosity for precession movement with a constant tilt angle) (MAHandschy.; Appl.Phys .Lett., 41 , 39,198
2) It can be seen that spontaneous polarization must be large in order to obtain fast response.

Further, the following liquid crystal compounds are reported in JP-A-62-56444 and JP-A-62-111939. However,
It must be said that it is still insufficient from the viewpoint of high-speed response.

[Problems to be Solved by the Invention] For practical application to devices and devices that utilize the electro-optical effect of ferroelectric liquid crystals, there are still problems such as alignment technology, cell configuration and mass production technology, and driving method. Although there are various problems required, the most important thing is the development of a fast response liquid crystal having a large spontaneous polarization in a wide temperature range.
The present invention seeks to meet this expectation.

[Means for Solving Problems] The occurrence of spontaneous polarization is due to the permanent dipole moment in the direction perpendicular to the long axis of the molecule. Approximately 1/30 of the expected value when the binding moment of> C = O is perfectly oriented
Shows only 0D. This phenomenon is an internal motion of the molecule because the rotation of the molecule is not bound like a solid, so it rotates freely, and the asymmetric carbon and permanent dipole are distant from each other. It is said that the effective orientation of the dipole is canceled by the rotation and the vibration, and the spontaneous polarization is significantly reduced.

Therefore, in order to increase the spontaneous polarization, it is conceivable to bring the positions of the asymmetric carbon and the permanent dipole as close as possible, or to directly insert a halogen atom or a bond having a large polarization into the asymmetric carbon.

In view of such circumstances, the present inventors have conducted various studies on the molecular structure including an optically active group with respect to a liquid crystal compound having a large spontaneous polarization, which is effective, and a compound as represented by the following general formula (I). Has been found to have a relatively large spontaneous polarization over a wide range, and the present invention has been completed based on such findings.

That is, the present invention is a general formula that exhibits ferroelectricity and is excellent in high-speed response. (In the formula, R ₁ represents an alkoxy group having 6 to 12 carbon atoms, R ₂ represents a lower alkyl group, l represents 0 or 1, m represents 0 or 1, and n represents 1 or 2.). A liquid crystal compound is provided.

Next, a general production method will be briefly described for the synthesis of the compound of the general formula (I).

A. When l = 1 and m = 1 First, the carbonyl group of trifluoromethylacetofatty acid ester (II) is hydrogen-reduced to a hydroxyl group, and then the ester is saponified, followed by optical resolution, and then esterification to obtain optically active trifluoromethylhydroxy fatty acid. The ester (IV) is obtained. The hydroxy group of the ester of (IV) is protected with a pyran derivative, the carboxylic acid ester portion is methylolated with lithium aluminum hydride, and then trifluoromethylhydroxyalkyl is etherified with sodium hydride and alkyl iodide. Obtain the ether (VI).

Next, separately from this, acetylbenzoic acid was prepared, which was chlorinated with thionyl chloride and then reacted with (VI) (V
The compound of II) is obtained.

Next, the acetoxy group of (VII) is reduced with benzylamine to form a hydroxyl group, and finally the compound is dehydrated and condensed with an alkoxyarylcarboxylic acid with a condensing agent to obtain the crude product of (I). This is purified by column purification and recrystallization to obtain the compound (I).

B. When l = 0 and m = 0 In the same manner as in A, trifluoromethylhydroxyalkyl ether (VI) is obtained, and this is subjected to a condensation reaction with alkoxybiphenylcarboxychloride to obtain the target compound (I).

Representative examples of the liquid crystal compound represented by the general formula (I) are shown below.

The liquid crystalline compound according to the present invention is used as a mixture with an existing ferroelectric liquid crystal or a compound that does not exhibit ferroelectricity and goes through a simple S _c phase to expand the temperature range of the S _c ^* phase and to display it. A practical liquid crystal composition can be obtained. In addition, even if the compound according to the present invention has poor liquid crystallinity, the compound having the S _c phase or S _c ^* phase is
By adding about 20%, a ferroelectric liquid crystal composition having a large spontaneous polarization can be obtained.

[Examples] Hereinafter, the present invention will be described more specifically with reference to Examples.

Example 1 Synthesis of optically active trifluoromethylhydroxybutyric acid ethyl ester 162.5 g of trifluoromethylacetoacetic acid ethyl ester
Was hydrogenated with Raney nickel to quantitatively obtain a hydroxy group-reduced product of a carboxyl group. Caustic soda 42.2
g, 170 ml of water was added, and the mixture was heated under reflux for 2 hours for saponification, and then ethanol was distilled off. 90 ml of concentrated hydrochloric acid was added thereto and reacted for 30 minutes. After completion of the reaction, ether was added for extraction, and the ether was removed to obtain 132 g of trifluoromethylhydroxybutyric acid. 65.25g of this acid was added to methanol 27
The product was dissolved in 0 ml and optically resolved using 50 g of 1-phenethylamine by a conventional method to obtain 34.0 g of an amine salt of optically active R-trifluoromethylhydroxybutyric acid. Concentrated hydrochloric acid (14 ml) was added to this, and it was reacted at room temperature for 30 minutes to decompose the amine salt, then extracted with ether, and the ether was distilled off to give a concentrate.
17 g was obtained.

This was dissolved in ethanol, 1 ml of concentrated sulfuric acid was added, and the mixture was heated under reflux for 2.5 hours for esterification to obtain 21.0 g of a crude ester. Distillation refined 16.1 g of the target compound (theoretical yield 19.8
%) Was obtained.

Example 2 Synthesis of optically active trifluoromethylhydroxybutyric acid ethyl ether 14.8 g of the ester obtained in Example 1 was taken and dissolved in 90 ml of ether, and 8.0 g of 2,3-dihydropyran and 0.12 g of p-toluenesulfonic acid were added. The reaction was carried out at room temperature for 6 hours. After completion of the reaction, the ether was distilled off and distilled to obtain 19.2 g of a protected body, and 19.0 g of this protected body was taken.
dissolved in ml. Separately, 2.1 g of lithium aluminum hydride was previously dissolved in 150 ml of tetrahydrofuran, and the temperature was 5 ° C.
A cooled solution was prepared, and the tetrahydrofuran solution of the above-mentioned protector was added to this solution over about 15 minutes, and then the reaction was carried out at room temperature for 5 hours. Remove the solvent from the separated liquid under reduced pressure.
16.2 g of alcohol was obtained. This alcohol body 10.0g
A solution of 60% sodium hydride (3.55 g) dissolved in 100 ml of tetrahydrofuran was added to the solution while keeping it at room temperature, and the mixture was reacted at room temperature for 1 hour. Then ethyl iodide 1
3.9 g was added and the reaction was continued at room temperature for another 3 hours. After completion of the reaction, the solvent was distilled off to obtain 8.7 g of ether compound. The ether group (8.5 g) was dissolved in methanol (20 ml), p-toluenesulfonic acid (10 mg) was added, and the mixture was reacted at 50 ° C. for 1 hour to remove the protecting group. After neutralization, distilled, ether compound
6.9 g (theoretical yield 36.3%) was obtained.

Example 3 Synthesis of p-hydroxybenzoic acid ester 6.9 g of the ether compound obtained in Example 2 was dissolved in 40 ml of toluene, and 1.64 g of pyridine was added thereto, followed by cooling to 5 ° C.
p-acetoxybenzoyl chloride 3.5g toluene 10m
The solution was added and reacted overnight at room temperature. The pyridine salt formed was separated and neutralized, and then toluene was distilled off to obtain 6.0 g of crude acetoxybenzoic acid ester. Next, dissolve it in 20 ml of ethanol and keep it at 15 ℃, and then add 3.82 g of benzylamine.
Was added, the mixture was reacted at room temperature for 5 hours, and 10 g of the composition obtained by distilling off ethanol was column-purified to obtain 2.9 g of the target p-hydroxybenzoic acid ester (theoretical yield: 49.4%).

Example 4 4- (4'-n-octyloxybiphenyl-4-carbonyloxy) benzoic acid (1-trifluoromethyl-3
Synthesis of -ethoxy) propyl ester 1.56 g of the ester obtained in Example 3 in 70 ml of dichloroethane
And n-octyloxybiphenyl-4-carboxylic acid 1.5
g was dissolved, 1.23 g of N, N′-dicyclohexylcarbodiimide and 58 mg of dimethylaminopyridine were added, and the mixture was reacted for 2 hours while maintaining the temperature at 15 to 20 ° C.
The produced amine salt was separated, and then dichloroethane was distilled off. The obtained crude product was purified by column and recrystallized with ethanol to give 4- (4'-n-octyloxybiphenyl-4-carbonyloxy) benzoic acid (1-trifluoromethyl-3) having a melting point of 93.1 ° C. 0.8 g (theoretical yield 29%) of -ethoxy) propyl ester was obtained. (Exemplified Compound 2) The analytical values of this compound are shown below.

Specific rotation: [α] ▲ ²⁵ _P ▼ 46.37 ° M _s : 600 (M ⁺ ) NMR: 0.91 (3H, t, J = 6.9Hz), 1.14 (3H, t, J = 7.0Hz), 1.33 ~ 1.5 (10H, m), 1.83 (2H, m), 2.16 (2H, m), 3.45 (3H, m), 3.58 (1H, m), 4.03 (2H, t, J = 6.58Hz), 5.78 (1H, m), 7.01 (2H, m), 7.36 (2H, m), 7.6 (2H, m), 7.7 (2H, m), 8.13 (2H, m), 8.23 (2H, m) Example 5 4- ( 4'-n-decyloxybiphenyl-4-carbonyloxy) benzoic acid (1-trifluoromethyl-3-
Synthesis of ethoxy) propyl ester 1.21 g of n-decyloxybiphenyl-4-carboxylic acid and 1.0 g of the parahydroxybenzoic acid derivative obtained in Example 3 were reacted according to Example 4 and then purified and recrystallized. Go melting point 65.0 ℃ 4-
0.45 g (theoretical yield 21.0%) of (4'-n-decyloxyphenyl-4-carbonyloxy) benzoic acid (1-trifluoromethyl-3-ethoxy) propyl ester (Exemplary compound 3) was obtained.

Example 6 Synthesis of 4- (4'-n-decyloxybiphenyl) benzoic acid (1-trifluoromethyl-3-ethoxy) propyl ester In 1.52 g of n-decyloxybiphenyl-4-carboxylic acid chloride and Example 2. The obtained trifluoromethyl hydroxypropyl ethyl ether (0.93 g) was reacted in pyridine at room temperature and then purified and recrystallized to give a melting point of 35.0 ° C.
-(4'-n-decyloxybiphenyl) benzoic acid (1
-Trifluoromethyl-3-ethoxy) propyl ester 0.74 g (theoretical yield 34.3%) (Exemplary compound 10) was obtained.

Example 7 Liquid crystal properties of 4- (4′-n-octyloxybiphenyl-4-carbonyloxy) benzoic acid (1-trifluoromethyl-3-ethoxy) propyl ester obtained in Example 4 were measured. A transparent electrode is provided on the glass plate, a polymer is further coated on it, and it is rubbed in a certain direction. Then, the rubbing directions of the two substrates are made parallel, and a certain thickness is used by using a spacer. The assembled liquid crystal cell was used as a liquid crystal cell. The thickness of the cell is 3 μm.

The present compound was injected into this cell, a square wave AC of ± 20 V was applied using a helium-neon laser and a photomultiplier, and the electro-optical effect of the liquid crystal was observed. A high-speed response was confirmed, and it was confirmed that the material could be used as a liquid crystal display device.

On the other hand, the phase transition temperature was determined by observation with a differential scanning calorimeter and a polarizing microscope. Note that S ₁ is an undetermined liquid crystal phase. The measurement results are shown in Table-1 and Table-2.

Examples 8 to 9 The phase transition temperature and various characteristic values of the compound of the present invention of Example 5 and the phase transition temperature of the compound of Example 6 were measured in the same manner as in Example 7. The results are shown in Table-1 and Table-
Shown in 2.

Examples 10 to 11 In the display device, in order to obtain a liquid crystal composition exhibiting a high-speed response over a wider range of the actual operating temperature, the liquid crystal compound obtained in Example is mixed with other various liquid crystal compounds, Using this, the response characteristics as a liquid crystal display device were evaluated. The measurement method was the same as in Example 7. The results are shown in Table-1 and Table-2.

The liquid crystal composition of Example 10 had the compound of Example 6 of 9.8 mol%.
And 90.2% of 4-decyloxybiphenylcarboxylic acid butyl ester having no optically active group and exhibiting no ferroelectricity. The liquid crystal composition of Example 11 is the following mixture.

[Effects of the Invention] The liquid crystalline compound of the present invention exhibits high-speed response in image display and exhibits ferroelectricity in a wide temperature range, and thus meets future needs for high-density and large-sized displays. It is possible.

Claims (1)

[Claims] 1. A general formula (In the formula, R ₁ represents an alkoxy group having 6 to 12 carbon atoms, R ₂ represents a lower alkyl group, l is 0 or 1, m is 0 or 1,
n represents 1 or 2. ) A liquid crystal compound represented by: