JPH09151166A - Antiferroelectric liquid crystal compound excellent in temperature dependence of response speed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a new compound, capable of manifesting stable antiferroelectricity at about ambient temperature and excellent in temperature dependence of response speed sufficiently usable for displays. SOLUTION: This compound is represented by formula I (R<1> is a 4-12C alkyl; R<2> is a 4C, a 6C, an 8C or a 10C alkyl; * indicates optically active carbon) and, e.g. 4-(2-octyloxycarbonyl)phenyl 4'-n-nonyloxy-2-fluorobiphenyl-4-carboxylate is cited. The compound represented by formula I is obtained by reacting a 4'-alkyloxy-3-fluoro-4-biphenylcarboxylic acid with a chlorinating agent and then reacting the resultant compound with a 2-alkyl 4-hydroxybenzoate represented by formula III in a solvent (e.g. methylene chloride) in the presence of triethylamine or dimethylaminopyridine as a catalyst at ambient temperature in a nitrogen atmosphere.

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 exhibiting stable antiferroelectricity at around room temperature and having excellent temperature dependence of response speed which is an essential property for displaying on a 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 to practical use. However, a nematic liquid crystal that is widely used at present has a response speed of several mse.
It has a drawback as slow as c to several tens of msec, and is subject to various restrictions in application. In order to solve these problems, an STN method and an active matrix method using a thin layer transistor have been developed, but the STN type display element has excellent display quality such as display contrast and viewing angle. However, there are problems that high accuracy is required for controlling the cell gap and the tilt angle and that the response is rather slow. For this reason, the development of a new liquid crystal display system having excellent responsiveness has been demanded, and the development of a ferroelectric liquid crystal capable of realizing an ultrahigh-speed device having an extremely short optical response time on the order of μsec has been attempted. Ferroelectric liquid crystal has 1
DOBAMBC (p-decyloxybenzylidene-p-amino-2-methylbutyl cinnamate) was first synthesized by Meyor et al. In 975 (Le Jour).
nal de Physique, vol. 36, 1975, L
-69). In addition, 1980, Clark and Laga
Since the characteristics of display devices such as sub-microsecond high-speed response of DOBAMBC and memory characteristics have been reported by WALL, ferroelectric liquid crystals have attracted great attention [N. A. Clark, et al. , Appl. P
hys. Lett. 36.899 (1980)]. However, their method has many technical problems for practical use. Especially, there is no material showing ferroelectric liquid crystal at room temperature, and it is effective and practical for the alignment control of liquid crystal molecules which is indispensable for display. The method was not established either. Since this report, various attempts have been made from both sides of liquid crystal materials / devices, prototype display devices utilizing switching between twisted two states have been produced, and high-speed electro-optical devices using the same have been disclosed, for example, in JP-A-56-107216. However, high contrast and proper threshold characteristics have not been obtained. From such a viewpoint, other switching schemes have been searched, and a transient scattering scheme 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 .; S
uzuki et al. , Japan. J. ofApp
l. Phys. , 27, (5), L729-L732
(1988)]. The above-mentioned “having three states” means a liquid crystal electro-optical device in which a ferroelectric liquid crystal is sandwiched between a first electrode substrate and a second electrode substrate which is arranged with a predetermined gap. A voltage for forming an electric field is applied to the first and second electrode substrates, and when the voltage is applied as the triangular wave shown in FIG. 1A, the ferroelectric liquid crystal is not present as shown in FIG. 1D. When the electric field is applied, the molecular orientation has a first stable state (1 in FIG. 1D), and when an electric field is applied, the molecular orientation is different from the first stable state in one electric field direction (the second stable state (FIG. 1)). 1D 2), and further has a third molecular orientation stable state (3 in FIG. 1D) different from the first and second stable states with respect to the other electric field direction. Regarding the liquid crystal electro-optical device utilizing the tri-stable state, that is, the tri-state, the applicant of the present application filed as Japanese Patent Application No. 63-70212 and disclosed in JP-A-2-153.
It is published as No. 322. The characteristics of the antiferroelectric liquid crystal exhibiting the tristable state will be described in more detail. Clerk/
In the surface-stabilized ferroelectric liquid crystal device proposed by Clark-Lagawall, the ferroelectric liquid crystal molecules are uniformly aligned in one direction in the S ^* C phase as shown in FIGS. 2 (a) and 2 (b). One of two stable states is shown, and depending on the direction of the applied electric field, it is stabilized in either one of the states, and that state is maintained even when the electric field is cut off. However, in reality, the alignment state of the ferroelectric liquid crystal molecules shows a twisted two-state in which the director of the liquid crystal molecules is twisted, or the layer has a chevron structure in which the layers are bent. With the Sieblon layer structure, the switching angle becomes small, which causes low contrast, which is a major obstacle to practical use. On the other hand, "anti" ferroelectric liquid crystal shows S which shows tristable state.
^{* In the} phase (3), in the above liquid crystal electro-optical device, when there is no electric field, the molecules in each adjacent layer are tilted in opposite directions and antiparallel to each other as shown in FIG. Cancel each other out. 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, the liquid crystal molecules shown in FIGS. 3B and 3C 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 when there is no electric field and the two ferroelectric phases depending on the polarity of the applied electric field are stable, and the “anti” ferroelectric liquid crystal is stable. Switching between the three stable states is performed with a DC threshold value between the phase and the 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. In this double hysteresis,
As shown in FIG. 4A, a memory effect can be realized by applying a bias voltage 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 a 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 hysteresis on the plus side and the hysteresis on the minus side alternately, so that an afterimage phenomenon of an image due to accumulation of an internal electric field based on spontaneous polarization can be prevented. As described above, the “anti” ferroelectric liquid crystal is a very useful liquid crystal compound that can achieve 1) high-speed response, 2) high contrast and wide viewing angle, and 3) good alignment characteristics and memory effect. Can be said. Regarding the liquid crystal phase showing the tristable state of "anti" ferroelectric liquid crystal, 1) A. D. L. Chandani eta
L., Japan J. Appl. Phys., 28 , L
-1265 (1989), 2) H.M. Orihara e
tal., Japan J. Appl. Phys., 29 ,
L-333 (1990), S ^* CA phase (Antiferroel) associated with "anti" ferroelectric properties.
It is named as electric Sictic C ^* phase). The present inventors have defined this liquid crystal phase as the S ^* (3) phase because it switches between the three stable states. The liquid crystal compounds having the "anti" ferroelectric phase S ^* (3) showing a tristable state in the phase series are disclosed in Japanese Patent Application Laid-Open Nos. 1-331667, 1-316372, and 1-316339. issue,
JP-A-2-28128 and JP-A-1-213 of Ichihashi
No. 390, and as a liquid crystal electro-optical device utilizing the tristable state, the present applicant discloses in Japanese Patent Laid-Open No. 2-40625.
JP-A-2-153322, JP-A-2-17372
We are making a new proposal in issue 4. When applying “anti” ferroelectric liquid crystal to a liquid crystal display, it is difficult to satisfy all of 1) operating temperature range, 2) response speed, 3) spontaneous polarization, 4) hysteresis characteristics, etc. with a single liquid crystal.
Usually, it is prepared as a mixed liquid crystal of more than ten kinds. At present, the antiferroelectric liquid crystal compound, which is generally known as an antiferroelectric liquid crystal material, has a large temperature dependence of the response speed, and therefore, when displayed on a display, defects such as display unevenness may occur. That is a concern.

[0003]

The object of the present invention is to modify the main skeleton of a conventionally known antiferroelectric liquid crystal compound, and more specifically, to select the fluorine modification site of the main skeleton. Another object of the present invention is to provide a novel antiferroelectric liquid crystal compound that exhibits stable antiferroelectricity and is excellent in temperature dependence of response speed that can be sufficiently used in displays.

[0004]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present inventors have specifically discovered the optimum position of a fluorine modification site in the main skeleton of an antiferroelectric liquid crystal compound having a specific structure. As a result of earnest efforts, the inventors have found an antiferroelectric liquid crystal compound having a temperature dependence of response speed superior to that of a conventional antiferroelectric liquid crystal compound, and completed the present invention.

The present invention has the following general formula

Embedded image (In the formula, R ¹ is a group independently selected from the group consisting of alkyl groups having 4 to 12 carbon atoms, R ² is 4, 6 carbon atoms,
It is a group independently selected from the group consisting of 8 and 10 alkyl groups, and * represents an optically active carbon. )). It is interesting that R ² selectively exhibits antiferroelectricity.

The compounds of the present invention are listed in the following table. The compounds having R ¹ of C ₉ or C ₁₀ have excellent characteristics, R ¹ is C ₉ H ₁₉ -and R ² is C ₆ H _13-. The combination of is preferable.

[Table 1]

Among those having the above structural formula, τI (index indicating the temperature dependence of response speed) represented by the following formula is 1
It is preferably an antiferroelectric liquid crystal compound of No. 2 to No. 2.

[Formula 2] τI = log ₁₀ (τ ₃₀ ) ÷ log ₁₀ (τ ₆₀ ) ... (i) τ ₃₀ ; response speed at 30 ° C. τ ₆₀ ; response speed at 60 ° C.

A general method for synthesizing the compound of the present invention is shown below. As shown in the following reaction formula, by reacting 4'-alkyloxy-3-fluoro-4-biphenylcarboxylic acid with a chlorinating agent such as thionyl chloride, 4'-
Prepare alkyloxy-3-fluoro-4-biphenylcarboxylic acid chloride. In addition to this, 2-alkyl-4-hydroxybenzoate prepared by a conventional method using methylene chloride as a solvent, triethylamine (hereinafter abbreviated as TEA), dimethylaminopyridine (hereinafter abbreviated as DMAP)
Is used as a catalyst and reacted overnight at room temperature in a nitrogen atmosphere. By washing this reaction solution with a hydrochloric acid solution, dehydrating it with anhydrous magnesium sulfate, and distilling methylene chloride,
A crude product is obtained. The crude product was separated and purified on silica gel with a mixed solution of hexane / ethyl acetate to give 4- (2
-Alkoxycarbonyl) phenyl-4'-alkyloxy-2-fluorobiphenyl-4-carboxylate is obtained. It can be further purified using ethanol. The separation and purification of the crude product, ester synthesis, and recrystallization of liquid crystal can be replaced by known methods other than the above method.

[0009]

Embedded image

The method of measuring the response speed is as follows. The compound was injected into a cell with a thickness of 2 μm made of glass with a transparent electrode which was coated with polyimide and subjected to rubbing treatment,
The liquid crystal physical property measuring cell was set on a hot stage, and the cell was placed in a polarization microscope with a photomultiplier tube in which two polarizing plates were orthogonal to each other so as to have a dark field in the absence of 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). ), And the unit is μsec.

[0011]

EXAMPLES The following examples show that the antiferroelectric liquid crystal compound of the general formula (1) gives superior results in the temperature dependence of the response speed than the conventional antiferroelectric liquid crystal compounds. However, the present invention is not limited thereto.

Example 1 The following formula

Embedded image Synthesis of 4- (2-octyloxycarbonyl) phenyl-4'-n-nonyloxy-2-fluorobiphenyl-4-carboxylate represented by 3-fluoro-4'-n-nonyloxy-4-biphenylcarboxylic acid and chloride 3-Fluoro-4'-n-nonyloxy-4-biphenylcarboxylic acid chloride is prepared by reacting with a chlorinating agent such as thionyl. 0.20 g (0.8 mmol) of 2-octyl-4-hydroxybenzoate prepared by a conventional method was added to 0.27 g (0.7 mmol) of this compound using methylene chloride as a solvent, and 0.08 g (0.8 mmol) of TEA was added. DMAP
Using 0.03 g (0.2 mmol) as a catalyst, the reaction is performed overnight at room temperature under a nitrogen atmosphere. The reaction solution is washed with a hydrochloric acid solution, dehydrated with anhydrous magnesium sulfate, and methylene chloride is distilled to obtain a crude product. This crude product was mixed with hexane / ethyl acetate 20/1 (vol / vo).
l) Separation and purification using silica gel with the mixed solution, 4-
0.43 g (92%) of (2-octyloxycarbonyl) -4'-n-nonyloxy-2-fluorobiphenyl-4-carboxylate is obtained. It can be further purified using ethanol.

¹ H-NMR of this compound (T in CDCl ₃
MS standard, δ value ppm) is 8.3 to 6.9 (m, 11
H), 5.3-5.1 (m, 1H), 4.1-3.9.
(T, 2H) and 1.9 to 0.8 (m, 33H).

The above compound is coated with polyimide and rubbed to form a glass with a transparent electrode having a thickness of 2 μm.
Table 2 shows the phase transition temperatures obtained by injecting into a m cell and observing with a polarizing microscope with a hot stage. Table 2 also shows response speeds at 60 ° C. and 30 ° C. and τI represented by the formula (i).

Comparative Example 1 The following formula

Embedded image Of 4- (2-octyloxycarbonyl) phenyl-4'-n-nonyloxy-3'-fluorobiphenyl-4-carboxylate represented by 2μ
Table 2 shows the phase transition temperatures obtained by injecting into the m cell and observing with a polarizing microscope with a hot stage. Also, 60 ℃, 3
Table 2 also shows the response speed at 0 ° C. and τI represented by the formula (i).

Comparative Example 2 The following formula

[Chemical 6] 4- (2-octyloxycarbonyl) -3 represented by
-Fluorophenyl-4'-n-nonyloxybiphenyl-4-carboxylate made of glass with a transparent electrode, which was coated with polyimide and rubbed, and had a thickness of 2 μm.
Table 2 shows the phase transition temperatures obtained by observing with a polarizing microscope with a hot stage. Also, 60 ℃, 30
Table 2 also shows the response speed at ° C and τI represented by the formula (i).

Comparative Example 3 The following formula

Embedded image 4- (2-octyloxycarbonyl) -2 represented by
-Fluorophenyl-4'-n-nonyloxybiphenyl-4-carboxylate made of glass with a transparent electrode, which was coated with polyimide and rubbed, and had a thickness of 2 μm.
Table 2 shows the phase transition temperatures obtained by observing with a polarizing microscope with a hot stage. Also, 60 ℃, 30
Table 2 also shows the response speed at ° C and τI represented by the formula (i).

[0018]

[Table 2] ^{* 1 No} antiferroelectricity at 30 ° C ^{* 2} Response speed cannot be measured at 50V

[0019]

[Effect] By modifying the optimum position of the main skeleton of the antiferroelectric liquid crystal compound with a specific structure with fluorine, it exhibits more stable antiferroelectricity at room temperature than conventional fluorine-modified antiferroelectric liquid crystal compounds. In addition, it was possible to provide an antiferroelectric liquid crystal compound having a small temperature dependence of response speed.

[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 a ferroelectric liquid crystal molecule proposed by Clark / Ragawell.

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.

 ─────────────────────────────────────────────────── --Continued front page (72) Inventor Toshio Yamauchi 3-5 Kasumigaseki, Chiyoda-ku, Tokyo Showa Shell Sekiyu Co., Ltd.

Claims (2)

[Claims] [Claim 1] The following general formula: (In the formula, R ¹ is a group independently selected from the group consisting of alkyl groups having 4 to 12 carbon atoms, R ² is 4, 6 carbon atoms,
It is a group independently selected from the group consisting of 8 and 10 alkyl groups, and * represents an optically active carbon. An antiferroelectric liquid crystal compound represented by the formula: 2. A temperature dependence (τI) represented by the following equation: τI = log ₁₀ (τ ₃₀ ) ÷ log ₁₀ (τ ₆₀ ) ... (i) τ ₃₀ ; 30 ° C. response speed τ ₆₀ ; The antiferroelectric liquid crystal compound according to claim 1, which has a response speed of 1 to 2 at 60 ° C.