JPH10147553A - Liquid crystal compound excellent in dependence of response speed on temperature and having stable antiferroelectric phase - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a new antiferroelectric liquid crystal compound free of possibility of showing defects, such as uneven display or the like, when working as a display and excellent in dependence of response speed on temperature by adequately positioning the fluorine-modified site in the main skeleton in the antiferroelectric liquid crystal compound. SOLUTION: This antiferroelectric liquid crystal compound is shown by formula I (R<1> is a 6-16C alkyl; R<2> is a 2-10C alkyl; Cf is CH3 or CF3 ; and *is optically active carbon), e.g. 4- 1-(trifluoromethyl) benzyloxycarbonyl} phenyl-4'-decyl-3-fluorobiphenyl-4-carboxylate. It has an index of temperature dependence of response time τ1<=1.7. A Grignard reaction liquor composed of 1-bromo-4-decylbenzene, Mg and tetrahydrofuran as the starting material is treated in two or more stages of reaction to produce a compound shown by formula II, which is converted into the corresponding chloride with a chlorinating agent and then reacted with 1-(trifluoromethyl) pentyl-4-hydroxybenzoate in a nitrogen atmosphere, to produce the objective compound after it is separated and purified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antiferroelectric liquid crystal compound which exhibits stable antiferroelectricity near room temperature and has excellent temperature dependence of response speed which is an essential property for display display.

[0002]

2. Description of the Related Art Liquid crystal display devices are 1) low-voltage operable 2).
Since it has excellent features such as low power consumption, 3) thin display, and 4) light receiving type, TN method, STN method,
A guest-host method has been developed and put into practical use.

However, those using nematic liquid crystals which are widely used at present have a response speed of several msec to several tens m.
There is a drawback of as slow as sec, and there are various restrictions in application.

In order to solve these problems, an STN method and an active matrix method using thin-layer transistors have been developed. However, STN-type display elements have excellent display quality such as display contrast and viewing angle. However, there is a problem that high accuracy is required for controlling the cell gap and the tilt angle, and that the response is slightly slow.

For this reason, there is a demand for the development of a new liquid crystal display system having excellent responsiveness, and the optical response time is μs
Attempts have been made to develop ferroelectric liquid crystals capable of realizing ultra-high-speed devices as short as c-orders.

[0006] Ferroelectric liquid crystals were introduced in 1975 by Meyer.
DOBMMBC (p-decyloxybenzylidene-p-amino-2-methylbutylcinnamate) was synthesized for the first time (Le Journal de Phys).
sque, 36, 1975, L-69).

Further, in 1980, Clark and Lag
Ferroelectric liquid crystals have attracted a great deal of attention since the reporting of characteristics on display devices such as the fast response time of DOBAMBC in sub-microseconds and memory characteristics by AWall [N. A. Clark, et al. , Appl.
Phys. Lett. 36.899 (1980)].

However, their methods have many technical problems for practical use. In particular, there is no material showing a ferroelectric liquid crystal at room temperature, and it is effective for controlling the alignment of liquid crystal molecules indispensable for a display. No practical method has been established.

Since this report, various attempts have been made from both sides of the liquid crystal material / device, and a display device utilizing switching between two twisted states has been prototyped. A high-speed electro-optical device using the same has also been disclosed in, for example, No. 107216, but high contrast and proper threshold characteristics have not been obtained.

[0010] From such a viewpoint, other switching methods have been searched, and a transient scattering method has been proposed.
Then, in 1988, the present inventors reported a three-state switching method of a liquid crystal having a tristable state [A.
D. L. Chandani, T .; Hagiwara,
Y. Suzuki et al. , Japan J .; of
Appl. Phys. , 27, (5), L729-L7
32 (1988)].

The above-mentioned "having three states" refers to a liquid crystal electro-optical device in which a ferroelectric liquid crystal is sandwiched between a first electrode substrate and a second electrode substrate arranged with a predetermined gap. Wherein a voltage for forming an electric field is applied to the first and second electrode substrates, and when a voltage is applied as a triangular wave shown in FIG. 1A, the ferroelectric liquid crystal is applied as shown in FIG. 1D. Has a second stable state in which the molecular orientation has a first stable state (1 in FIG. 1D) when no electric field is applied, and the molecular orientation is different from the first stable state in one electric field direction when an electric field is applied. State (2 in FIG. 1D) and a third molecular orientation stable state (3 in FIG. 1D) different from the first and second stable states in the other electric field direction. The applicant of the present invention discloses a three-stable state, that is, a liquid crystal electro-optical device utilizing the three states.
No. 3-70212 and Japanese Patent Application Laid-Open No. Hei 2-15332.
Published as Issue 2.

The characteristics of the antiferroelectric liquid crystal exhibiting a tristable state will be described in more detail. Clark / Ragaval (Cla
In the surface-stabilized ferroelectric liquid crystal device proposed by rk-Lagawall, two stable liquid crystal molecules in which the ferroelectric liquid crystal molecules are uniformly aligned in one direction in the S ^* C phase as shown in FIGS. A state is shown, and the state is stabilized to one of the states depending on the direction of the applied electric field, and the state is maintained even when the electric field is cut off.

However, in practice, the orientation state of the ferroelectric liquid crystal molecules shows a twisted two state in which the director of the liquid crystal molecules is twisted, or shows a Chevron structure in which the layer is bent in a square shape. In the case of the Chevron layer structure, the switching angle becomes small and causes a low contrast, which is a major obstacle for practical use.

On the other hand, in the S ^* (3) phase in which the "anti" ferroelectric liquid crystal exhibits a tristable state, in the above-mentioned liquid crystal electro-optical device, when there is no electric field, as shown in FIG. The molecules are tilted in opposite directions and arranged antiparallel, and the dipoles of the liquid crystal molecules cancel each other. Therefore, the spontaneous polarization is canceled in the entire liquid crystal layer. The liquid crystal phase exhibiting this molecular arrangement corresponds to 1 in FIG. 1D.

Further, when a voltage sufficiently higher than the threshold value of (+) or (-) is applied, FIGS.
Are arranged in parallel in the same direction. In this state, the dipoles of the molecules are also aligned in the same direction, so that spontaneous polarization occurs and a ferroelectric phase is formed.

That is, in the S ^* (3) phase of the “anti” ferroelectric liquid crystal, the “anti” ferroelectric phase in the absence of an electric field and the two ferroelectric phases depending on the polarity of the applied electric field become stable, and the “anti” ferroelectric phase becomes stable. "Switching between three stable states with a DC threshold value between a ferroelectric phase and two ferroelectric phases. Due to the change in the liquid crystal molecule arrangement accompanying the switching, the light transmittance changes in a double hysteresis shown in FIG.

As shown in FIG. 4A, a memory effect can be realized by applying a bias voltage to the double hysteresis and further superimposing a pulse voltage.

Further, the layer of the ferroelectric phase is stretched by the application of an electric field, and a bookshelf structure is formed. On the other hand, the "anti" ferroelectric phase in the third stable state has a similar bookshelf structure. Since the layer structure switching by the application of the electric field gives dynamic shear to the liquid crystal layer, alignment defects are improved during driving, and good molecular alignment can be realized.

In the "anti" ferroelectric liquid crystal, image display is performed by using both the positive and negative hysteresis alternately, so that the afterimage phenomenon of the image due to the accumulation of the internal electric field based on the spontaneous polarization is prevented. Can be.

As described above, the "anti" ferroelectric liquid crystal is
It can be said that this is a very useful liquid crystal compound capable of 1) high-speed response, 2) high contrast and a wide viewing angle, and 3) excellent alignment characteristics and a memory effect.

The liquid crystal phase showing a tristable state of the "anti" ferroelectric liquid crystal is described in 1) A. D. L. Chandani
et al., Japan J. et al. Appl. Phys., 2
8 , L-1265 (1989), 2) H.E. Orihar
a et al., JapanJ. Appl. Phys.,
29 , L-333 (1990);
S ^* CA phase (Antifer) for its “anti” ferroelectric properties
(selective Sectic C ^* phase). The present inventors have defined this liquid crystal phase as the S ^* (3) phase because it switches between the three stable states.

Liquid crystal compounds having an "anti" ferroelectric phase S ^* (3) exhibiting a tristable state in a phase series are disclosed in JP-A-1-316367, JP-A-1-316372 and JP-A-1-316372, filed by the present inventors. There are JP-A-1-316339, JP-A-2-28128, and JP-A-1-213390 such as Ichihashi. As a liquid crystal electro-optical device utilizing a tristable state, the applicant of the present invention discloses JP-A-2-40625. Kaihei 2-153322
And Japanese Patent Application Laid-Open No. 2-173724.

When an "anti" ferroelectric liquid crystal is applied to a liquid crystal display, 1) operating temperature range, 2) response speed, 3).
It is difficult to satisfy all of spontaneous polarization and 4) hysteresis characteristics etc. with a single liquid crystal, and it is usually prepared as a dozen or more kinds of mixed liquid crystal.

At present, antiferroelectric liquid crystal compounds, which are generally known as antiferroelectric liquid crystal materials, have a large temperature dependence of the response speed, and may cause defects such as display unevenness when displayed on a display. There is concern that there is.

[0025]

SUMMARY OF THE INVENTION An object of the present invention is to modify the main skeleton of a conventionally known antiferroelectric liquid crystal compound, specifically, to optimize the fluorine-modified site of the main skeleton. Accordingly, it is an object of the present invention to provide a novel antiferroelectric liquid crystal compound which exhibits a stable antiferroelectric property and is excellent in temperature dependency of a response speed which can be sufficiently used for a display.

[0026]

Means for Solving the Problems In order to achieve the above object, the present inventors have specifically proposed an antiferroelectric liquid crystal compound in which the main skeleton of a conventional antiferroelectric liquid crystal compound is modified with an appropriate fluorine modification site. As a result of diligent research on the synthesis of a crystalline liquid crystal compound, Japanese Patent Application Nos. 7-334122 and 8-12656 have already been published.
The invention of No. 2 has been completed. The present inventors have made further detailed molecular design and worked diligently on synthesis, and as a result, have found an antiferroelectric liquid crystal compound that has a higher temperature dependence of response speed than conventional antiferroelectric liquid crystal compounds. Thus, the present invention has been completed.

That is, the present invention provides a compound represented by the general formula

Embedded image (In the formula, R ¹ is an alkyl group having 6 to 16 carbon atoms, R ²
Is an alkyl group having 2 to 10 carbon atoms, Cf is CH ₃ or CF ₃ , and * indicates an optically active carbon. )).

Particularly, among the antiferroelectric liquid crystal compounds, the following formula (A)

ΤI = log (τ ₁₀ ) / log (τ ₃₀ ) (A) (where, τ ₁₀ ; response speed at 10 ° C. when 50 V is applied; τ ₃₀ ;
It is preferable that τI (index indicating the temperature dependency of the response speed) expressed by the response speed at 30 ° C. when a voltage of 50 V is applied is 1.7 or less.

One example of the compound of the present invention is listed in the following table.

[Table 1]

[0030]

[Table 2]

An example of a method for synthesizing the compound of the present invention and a flow sheet thereof are shown below. Grignard reagent (II) prepared from 1-bromo-4-decylbenzene (I), magnesium, tetrahydrofuran (THF)
Was added to ethyltrichlorosilane at 0 ° C. and stirred at room temperature. The solvent, THF and unreacted ethyltrichlorosilane were distilled off under reduced pressure, hexane was added to the residue, and the mixture was filtered through a glass filter. The filtrate is concentrated and then distilled to obtain a crude product of (4-decylphenyl) dichloroethylsilane (III)
I got (4-decylphenyl) was added to a suspension of anhydrous potassium fluoride in dimethylformamide (DMF) at 0 ° C.
A DMF solution of the dichloroethylsilane crude product (III) was added, and the mixture was stirred at 60 ° C. To this, methyl 4-bromo-2-fluorobenzoate (IV) and dichlorobis (triisopropylphosphine) palladium were added at room temperature, and 1
Stirred at 20 ° C. A saturated saline solution and ethyl acetate were added to the reaction solution, and the mixture was filtered through celite. The filtrate was extracted with ethyl acetate and concentrated. The residue was purified by silica gel column chromatography, and 4'-decyl-3-fluorobiphenyl-4-
Methyl carboxylate (V) was obtained. An aqueous solution of potassium hydroxide was added to an ethanol solution of methyl 4'-decyl-3-fluorobiphenyl-4-carboxylate at room temperature, and the mixture was heated under reflux. After distilling off ethanol under reduced pressure, 2M
Hydrochloric acid was added, and the mixture was extracted with ether and concentrated. The residue was recrystallized from a mixed solvent of hexane / ether to give 4'-decyl-3-.
Fluorobiphenyl-4-carboxylic acid (VI) was obtained.

[0032]

Embedded image

Next, the 4'-decyl-
By reacting 3-fluoro-4-biphenylcarboxylic acid (VI) with a chlorinating agent such as thionyl chloride, 4 ′
-Decyl-3-fluoro-4-biphenylcarboxylic acid chloride is prepared. In addition, 1-adjusted by the conventional method
(Trifluoromethyl) pentyl 4-hydroxybenzoate is reacted overnight at room temperature under a nitrogen atmosphere using dichloromethane as a solvent and triethylamine (hereinafter abbreviated as TEA) and dimethylaminopyridine (hereinafter abbreviated as DMAP) as catalysts. The reaction solution is washed with a hydrochloric acid solution, dried over anhydrous magnesium sulfate, and dichloromethane is distilled to obtain a crude product. The crude product was separated and purified using a mixed solution of hexane / ethyl acetate using silica gel, and 4- {1- (trifluoromethyl) pentyloxycarbonyl} phenyl 4′-decyl-3-fluorobiphenyl-4-carboxylate was obtained. Get. It can be further purified using ethanol. The separation and purification of the crude product, the synthesis of the ester, and the recrystallization of the liquid crystal can be replaced by known methods other than the methods described above.

The method for measuring the response speed will be described below. In the same manner as in the above method, the liquid crystal property measurement cell was set on a hot stage, and this was placed in a polarizing microscope equipped with a photomultiplier tube in which two polarizing plates were orthogonal to each other so as to have a dark field without an electric field. When the liquid crystal in the cell is in the antiferroelectric phase, the response time τ can be determined from the change in the relative transmittance of light when a rectangular wave of ± 50 V as shown in FIG. 5 is applied to the cell. τ is the state of the ferroelectric phase (at the end of the rectangular wave voltage on the minus side), the state of the next ferroelectric phase via the state of the antiferroelectric phase (the relative transmittance is 90% by applying the rectangular wave voltage on the plus side). Is reached).

Examples of the present invention will be described below, but the present invention is not limited by these examples.

Example 1 4- {1- (trifluoromethyl) pentyloxycarbonyl} phenyl 4'-decyl-3 represented by the following formula:
Synthesis of -Fluorobiphenyl-4-carboxylate

Embedded image 1-bromo-4-decylbenzene (2 g, 6.7 mmol
l), magnesium (220 mg, 9.0 mmol),
A Grignard reactant prepared from tetrahydrofuran (THF) (12 ml) was added to ethyltrichlorosilane (2.3 ml) at 0 ° C., and the mixture was stirred at room temperature for 11 hours. The solvent, THF and unreacted ethyltrichlorosilane were distilled off under reduced pressure, hexane was added to the residue, and the mixture was filtered through a glass filter. After concentration of the filtrate, distillation (130 to 140 ° C /
0.1 Torr) to obtain a crude product of (4-decylphenyl) dichloroethylsilane (1.85 g, about 80%). 0 ° C. was added to a suspension of anhydrous potassium fluoride (2 g, 34 mmol) in dimethylformamide (DMF) (5 ml).
Then, a solution of the crude product of (4-decylphenyl) dichloroethylsilane (1.8 g) in DMF (3 ml) was added, and
Stirred at C for 6 hours. To this, at room temperature, 4-bromo-2
-Methyl fluorobenzoate (1.0 g, 4.6 mmol
l) and dichlorobis (triisopropylphosphine) palladium (60 mg, 0.09 mmol), and 12
Stirred at 0 ° C. for 20 hours. A saturated saline solution and ethyl acetate were added to the reaction solution, and the mixture was filtered through celite. The filtrate was extracted with ethyl acetate and concentrated. The residue was purified by silica gel column chromatography (hexane / ethyl acetate = 20/1),
Methyl 4'-decyl-3-fluorobiphenyl-4-carboxylate (1.15 g, 71% yield) was obtained. Methyl 4'-decyl-3-fluorobiphenyl-4-carboxylate (1.3 g, 3.5 mmol) in ethanol (70 m
l) Add potassium hydroxide aqueous solution (KOH 1
g, H ₂ O 10 ml) was added, and the mixture was heated under reflux for 30 minutes.
After about 30 ml of ethanol was distilled off under reduced pressure, 2 M
Hydrochloric acid was added, and the mixture was extracted with ether and concentrated. The residue was recrystallized from a mixed solvent of hexane / ether (9/1), and 4'-decyl-3-fluorobiphenyl-4-carboxylic acid (1.
1 g, 88%).

The identification data of the present compound are as follows. ¹ H-NMR (CDCl ₃ ) δ 0.88 (t, J = 6.8 Hz, 3H), 1.32
~ 1.40 (m, 14H), 1.65 (broad q
uintet, J = 7.5 Hz, 2H), 2.66 (b
load t, J = 7.5 Hz, 2H), 7.29
(D, J = 8.2 Hz, 2H), 7.40 (dd, J =
12.2 and 1.6 Hz, 1H), 7.47 (d
d, J = 8.1 and 1.6 Hz, 1H), 7.5
4 (d, J = 8.2 Hz, 2H), 8.09 (t, J =
8.1 Hz, 1 H), 11.5 (broad s, 1
H)

The 3-fluoro-4'-prepared by the above method
By reacting n-decyl-4-biphenylcarboxylic acid with a chlorinating agent such as thionyl chloride, 3-fluoro-4'-n-decyl-4-biphenylcarboxylic acid chloride is prepared. This 3-fluoro-4'-n-decyl-
0.27 g of 4-biphenylcarboxylic acid chloride (0.7
mmol) to 1- (trifluoromethyl) pentyl 4-hydroxybenzoate 0.2 prepared by a conventional method.
0 g (0.7 mmol) using methylene chloride as a solvent and T
EA 0.07 g (0.7 mmol), DMAP 0.02
Using g (0.2 mmol) as a catalyst, the reaction is carried out at room temperature overnight or more in a nitrogen atmosphere. The reaction solution is washed with a hydrochloric acid solution, dried over anhydrous magnesium sulfate, and dichloromethane is distilled to obtain a crude product. This crude product was separated and purified using a 20/1 (v / v) mixed solution of hexane / ethyl acetate using silica gel, and 4- {1- (trifluoromethyl) pentyloxycarbonyl} phenyl
0.39 g (88%) of 4'-decyl-3-fluorobiphenyl-4-carboxylate is obtained. It can be further purified using ethanol.

¹ H-NMR of this compound (CDCl ₃ , T
MS standard, δ value ppm) are 8.3 to 7.1 (m, 11H) and 5.7 to 5.5 (m, 11H).
1H), 2.8-2.6 (t, 2H), 2.1-0.8
(M, 28H).

The above compound was injected into a 2 μm-thick cell made of glass with a transparent electrode which had been coated with polyimide and subjected to rubbing treatment. The phase transition temperature as observed by a polarizing microscope equipped with a hot stage is shown in Table 3. Table 3 also shows the response speed at 30 ° C. and 10 ° C. and τI represented by the formula (A).

Comparative Example 1 4- {1- (trifluoromethyl) pentyloxycarbonyl} phenyl 4'-decylbiphenyl-4-carboxylate

Embedded image In addition, the above compound was injected into a 2 μm-thick cell made of glass with a transparent electrode which had been coated with polyimide and rubbed, and the phase transition temperature measured by observation with a polarizing microscope equipped with a hot stage is shown in Table 3. Table 3 also shows the response speed at 30 ° C. and 10 ° C. and τI represented by the formula (A).

[0042]

[Table 3]

The embodiments of the present invention are listed below. (1) General formula

Embedded image (In the formula, R ¹ is an alkyl group having 6 to 16 carbon atoms, R ²
Is an alkyl group having 2 to 10 carbon atoms, Cf is CH ₃ or CF ₃ , and * indicates an optically active carbon. An antiferroelectric liquid crystal compound represented by the formula: (2) The following formula (A)

ΤI = log (τ ₁₀ ) / log (τ ₃₀ ) (A) (where, τ ₁₀ ; response speed at 10 ° C. when 50 V is applied. Τ ₃₀ ;
The antiferroelectric liquid crystal compound according to the above item (1), wherein τI (index indicating the temperature dependence of the response speed) represented by the response speed at 30 ° C. when 50 V is applied is 1.7 or less.

[0044]

[Effect] By optimizing the location of fluorine modification of the main skeleton of the conventional antiferroelectric liquid crystal compound, it shows stable antiferroelectricity near room temperature and low temperature range, and has fast response and temperature dependence of response speed. Can be provided. Specifically, comparing Example 1 with Comparative Example 1, 1) The response speed at 10 ° C. was increased by about 73%. 2) τI was also improved by about 5%.

[Brief description of the drawings]

1 (A) shows an applied triangular wave, (B) shows a commercially available nematic liquid crystal, (C) shows a two-state liquid crystal, and (D) shows a tristable state liquid crystal. .

FIG. 2 shows two stable alignment states of ferroelectric liquid crystal molecules proposed by Clark / Ragaval.

FIG. 3 (A) shows three stable alignment states of the “anti” ferroelectric liquid crystal molecules of the present invention, and (B) shows each of (A), (b) and (c) of A. The corresponding three-state switching and the change of the liquid crystal molecule arrangement are shown.

FIG. 4 is an applied voltage-light transmittance characteristic diagram showing that the “anti” ferroelectric liquid crystal molecules change their light transmittance by drawing a double hysteresis with respect to an applied voltage.

FIG. 5A shows a relationship between applied voltage and time, and FIG.
Is a graph showing a response state of liquid crystal molecules when the applied voltage is applied.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuo Kusumoto 1-9-1-102, Minamidai, Sagamihara-shi, Kanagawa (72) Inventor Emiko Hagiwara 1-9-1-302, Minamidai, Sagamihara-shi, Kanagawa (72) Inventor Tanijiro Hiyama 4-29-3-101 Kamizuruma, Sagamihara City, Kanagawa Prefecture

Claims (2)

[Claims] 1. A compound of the general formula (In the formula, R ¹ is an alkyl group having 6 to 16 carbon atoms, R ²
Is an alkyl group having 2 to 10 carbon atoms, Cf is CH ₃ or CF ₃ , and * indicates an optically active carbon. An antiferroelectric liquid crystal compound represented by the formula: 2. The following equation (A): τI = log (τ ₁₀ ) / log (τ ₃₀ ) (A) (where, τ ₁₀ ; response speed at 10 ° C. when 50 V is applied; τ ₃₀ ;
2. The antiferroelectric liquid crystal compound according to claim 1, wherein τI (index indicating the temperature dependence of the response speed) expressed by a response speed at 30 ° C. when a voltage of 50 V is applied is 1.7 or less.