JPH08311017A - Liquid crystal compound and liquid crystal composition containing the same - Google Patents

Abstract

(57) [Summary] [Object] To provide a novel liquid crystal compound, particularly a novel antiferroelectric liquid crystal compound exhibiting an antiferroelectric phase, and a liquid crystal composition containing the same. [Structure] General formula [1] (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, X ¹ and X ² are groups independently selected from the group consisting of H and F, and Y is a single bond. , independently from the group consisting of O and COO are selected groups, Cf is CH ₃
Alternatively, it represents CF ₃ , and * represents an optically active center. ) A liquid crystal compound comprising a compound represented by:

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel liquid crystal compound, particularly a novel liquid crystal compound exhibiting an antiferroelectric phase, and a liquid crystal composition containing the same.

[0002]

2. Description of the Related Art Liquid crystal display devices have 1) low voltage operability and 2)
It has excellent features such as low power consumption, 3) thin display, 4) light receiving type, etc., so far, 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 of being slow from c to several tens of msec, and is subject to various restrictions in application.

In order to solve these problems, an active matrix method using an STN method or a thin layer transistor method has been developed.
Although display qualities such as display contrast and viewing angle have been improved, problems such as high precision required for control of the cell gap and tilt angle and a rather slow response have become problems. The thin film transistor method has a complicated structure, has a low manufacturing yield, and is consequently expensive.

Therefore, there has been a demand for the development of a new liquid crystal display system having excellent responsiveness, and the optical response time is μse.
Attempts have been made to develop a ferroelectric liquid crystal that enables an extremely high speed device that is as short as c order.

Ferroelectric liquid crystals were first described in 1975 by Meyor.
DOBAMBC (p-decyloxybenzylidene-p-amino-2-methylbutyl cinnamate) was synthesized for the first time by (Le Journal de Phy).
sique, vol. 36, 1975, L-69).

Furthermore, 1980, Clark and Lag
Since AWALL reported on the characteristics of display devices such as sub-microsecond high-speed response of DOBAMBC and memory characteristics, ferroelectric liquid crystals have been receiving a lot of attention [N. A. Clark, et al. , Appl.
Phys. Lett. 36.899 (1980)].

However, their method has many technical problems for practical use, and there is almost no ferroelectric liquid crystal satisfying the practical characteristics required for a display at room temperature, which is essential for a display. An effective and practical method for controlling the alignment of liquid crystal molecules has not been established.

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

From this point of view, other switching systems have been searched and a transient scattering system has been proposed.
Then, in 1988, the inventors of the present invention reported a three-state switching method for a liquid crystal having three stable states [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 a tristable state" means a liquid crystal in which an antiferroelectric liquid crystal is sandwiched between a first electrode substrate and a second electrode substrate which is arranged with a predetermined gap. In the electro-optical device, a voltage for forming an electric field is applied to the first and second electrode substrates.
When a voltage is applied as a triangular wave indicated by, the molecular orientation of the antiferroelectric liquid crystal becomes the first stable state [Fig. 3 (a)] when there is no electric field, and the transmittance of the liquid crystal electro-optical device is the first. 2 (1 in FIG. 1D) and the molecular orientation becomes a second stable state [FIG. 3 (b)] different from the first stable state in one electric field direction when an electric field is applied. The transmittance of the electro-optical device shows the second stable state (2 in FIG. 1D), and the third molecular orientation stable state different from the first and second stable states with respect to the other electric field direction [FIG.
(C)], which means that the transmittance of the liquid crystal electro-optical device exhibits the third stable state (3 in FIG. 1D). Regarding the liquid crystal electro-optical device utilizing the tri-stable state, the present applicant has filed as Japanese Patent Application No. Sho 63-70212 and is disclosed as Japanese Patent Application Laid-Open No. 2-153322.

The characteristics of the antiferroelectric liquid crystal exhibiting the tristable state will be described in more detail. Clark / Ragawell (Cla
In the surface-stabilized ferroelectric liquid crystal device proposed by rk-Lagawall, two stable liquid crystal molecules in which ferroelectric liquid crystal molecules are uniformly oriented in one direction as shown in FIGS. 2 (a) and 2 (b) in the S * C phase. State, and depending on the direction of the applied electric field,
It is stabilized in 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 a chevron structure in which the layers are bent in a V shape. 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, in the SmC * A phase (indicated as S * (3) phase in the present specification) in which the "anti" ferroelectric liquid crystal shows a tristable state, in the above liquid crystal electro-optical device, there is a As shown in FIG. 3 (a), the molecules in each adjacent layer are tilted in the 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 showing this molecular arrangement is shown in FIG.
Corresponds to 1 in D.

Further, when a voltage sufficiently higher than the threshold value of (+) or (-) is applied, FIGS. 3B and 3C are obtained.
Liquid crystal molecules are tilted in the same direction and arranged in parallel as shown in FIG. In this state, the dipoles of the molecules are also aligned in the same direction, so spontaneous polarization occurs and a ferroelectric phase is formed.

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 due to the polarity of the applied electric field are stable, and the "anti" ferroelectric phase is stable. High-speed microsecond order switching is performed between three stable states with a DC threshold between the dielectric phase and two ferroelectric phases.

That is, the molecular alignment of the liquid crystal changes depending on the polarity and magnitude of the applied electric field, and the optical axis of the liquid crystal can be changed into three states. Such three states of the liquid crystal are sandwiched between a pair of polarizing plates. By incorporating it, it can be used as an electro-optical display device. When the light transmittance is plotted against the applied voltage of the AC triangular wave, the double hysteresis as shown in FIG. 4 is shown.

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

In the "anti" ferroelectric liquid crystal, since the image display can be performed by alternately using the hysteresis on both the plus side and the minus side, the afterimage phenomenon of the image due to the accumulation of the internal electric field due to the spontaneous polarization is caused. Can be prevented.

Further, by applying an electric field, the layer of the ferroelectric phase is stretched to form a Bookshelf structure. On the other hand, the first stable state “anti” ferroelectric phase 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.

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

Regarding the liquid crystal phase showing the tristable state of "anti" ferroelectric liquid crystal, 1) A. D. L. Chandani
et al., Japan J. Appl. Phys., 2
8, L-1265 (1989) and 2) H. Orih
ara et al., Japan J. et al. Appl. Ph
Ys., 29, L-333 (1990), the S * CA phase (Anti) associated with the "anti" ferroelectric property.
ferroelectric Smatic C *
The present inventors defined this phase as the S * (3) phase because the liquid crystal phase switches between tristable states.

"Anti" ferroelectric phase S * (3) showing tri-stable state
Liquid crystal compounds having a phase in a phase series are disclosed in Japanese Patent Application Laid-Open Nos. 1-31667 and 1-316372.
JP-A-1-316339, JP-A-2-28128
And Japanese Patent Laid-Open No. 1-213390, such as Ichihashi,
Further, regarding the liquid crystal electro-optical device utilizing the tristable state, the present applicant has disclosed in Japanese Patent Application Laid-Open Nos. 2-40625 and 2-1533.
No. 22, JP-A-2-173724, and new proposals are made.

The material characteristics required for the antiferroelectric liquid crystal used in the above-mentioned display device are mainly 1) operating temperature range, 2) response speed, 3) hysteresis characteristic, and 4) display contrast.

Regarding the display contrast of 4), light leakage occurs as a precursor phenomenon of switching from the antiferroelectric phase to the ferroelectric phase, and when the display is driven using such an antiferroelectric liquid crystal, only a low contrast is obtained. Absent. The value obtained by quantitatively evaluating the light leakage in the antiferroelectric phase is called the pot bottom rate. The smaller the pot bottom rate, the less the light leak and the display contrast is improved. Therefore, in order to improve the display contrast, it is necessary to improve the pan bottom rate. However, at present, no antiferroelectric liquid crystal having an excellent pan bottom ratio has been obtained.

In the currently developed anti-ferroelectric liquid crystal display, the display quality is not sufficient in terms of high definition and high quality as compared with the display performance of the TFT liquid crystal display, and the above-mentioned important driving characteristics There is a strong demand for improvement methods. It has been found that it is extremely difficult to satisfy these performances with a single compound antiferroelectric liquid crystal compound.

[0026]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a novel liquid crystal compound, particularly a novel antiferroelectric liquid crystal compound exhibiting an antiferroelectric phase and a liquid crystal composition containing the same. .

[0027]

The first aspect of the present invention is the general formula [1].

Embedded image (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, X ¹ and X ² are groups independently selected from the group consisting of H and F, and Y is a single bond. , independently from the group consisting of O and COO are selected groups, Cf is CH ₃
Alternatively, it represents CF ₃ , and * represents an optically active center. ) A liquid crystal compound comprising a compound represented by

A second aspect of the present invention relates to a liquid crystal composition containing at least one liquid crystal compound of the first aspect. In particular, the antiferroelectric liquid crystal compound of the first invention,
Improving the pan bottom rate by adding 0.1 wt% or more, preferably 1.0 to 50 wt%, particularly preferably 5.0 to 40 wt% to the total amount of the liquid crystal composition, particularly the antiferroelectric liquid crystal composition. can do.

An example of the method for synthesizing the liquid crystal compound of the present invention is shown below. In the formula,

Embedded image R ¹ represents C _m H _{2m + 1 and} R ² represents C _n H _{2n + 1} .

[0030]

[Chemical 4]

As shown in the above reaction formula, 3-fluoro-
4-alkyloxybiphenylcarboxylic acid (1) was added to SO
After conversion to the acid chloride (2) with a chlorinating agent such as Cl ₂ or (COCl) ₂ , it is reacted with 4-mercaptobenzoic acid in the presence of a base such as pyridine or triethylamine to give a thioester compound (3). Induce. Further, this is converted to the acid chloride (4), and then esterified with an optically active alkyl-2-alkanol in the presence of a base to produce the target compound (5).

The following method may be mentioned as another manufacturing method. In the formula,

Embedded image R ¹ represents C _m H _{2m + 1 and} R ² represents C _n H _{2n + 1} .

[0033]

[Chemical 6]

As shown in the above reaction formula, 4-mercapto-aromatic carboxylic acid (6) is derivatized to disulfide (7) with hydrogen peroxide or the like. This compound was added to SOCl ₂ ,
The acid chloride (8) is converted with a chlorinating agent such as (COCl) ₂ and subjected to an esterification reaction with an optically active alkyl-2-alkanol in the presence of a base to obtain an ester compound (9). In the presence of phenylphosphine, 3
-Fluoro-4-alkyloxybiphenylcarboxylic acid is reacted to give the desired thioester compound (10).
To manufacture.

The compounds shown by the present invention are exemplified below.

[Chemical 7]

Embedded image In the formula, R ¹ represents C _m H _{2m + 1 and} R ² represents C _n H _{2n + 1} .

The reason why the two components are necessary is that the first component (antiferroelectric liquid crystal composition) and the second component (C
The presence of both H ₃ -based thioester compounds) keeps the pot bottom ratio low. If only the first component (antiferroelectric liquid crystal composition) is used (that is, the second component is not contained), the pan bottom ratio becomes large, which is not desirable.

[0037]

[Table 1]

A liquid crystal cell having a cell thickness of 2.0 μm having a rubbing-treated polyimide alignment film on a transparent electrode substrate was filled with a liquid crystal compound or a liquid crystal composition obtained in an example to be described later in an isotropic phase to form a liquid crystal thin film. A cell was prepared. The manufactured liquid crystal cell was heated at 0.1 to 1.0 ° C./min. The mixture was gradually cooled with a temperature gradient of 2 to deposit. This liquid crystal cell was placed in a polarizing microscope with a photomultiplier tube in which two polarizing plates were orthogonal to each other so as to provide a dark field at a voltage of 0V.

When the liquid crystal in the cell is in the antiferroelectric phase,
When a graph is plotted against the applied voltage of the relative transmittance of light when a triangular wave (1 Hz) of ± 50 V or ± 40 V is applied to the cell, double hysteresis is shown as shown in FIG. As shown in the figure, in the process of increasing (decreasing) the applied positive voltage (minus voltage), the voltage at which the relative transmittance becomes 10% is V1, and the applied positive voltage (minus voltage) is increased. Do (decrease)
In the process, the voltage at which the relative transmittance becomes 90% is V2,
The voltage at which the relative transmittance becomes 90% in the process of passing (increasing) the plus voltage (minus voltage) past the peak of the triangular wave is defined as V3, and these are referred to as threshold voltages V1, V2, and V3. Define.

In the process of applying a voltage from the antiferroelectric phase state (no electric field) to the plus (or minus) side,
There is a phenomenon that the relative transmittance gradually increases before the transition to the ferroelectric phase. Light leakage in the state of the antiferroelectric phase causes a decrease in contrast. The light leakage in this antiferroelectric phase state is quantitatively evaluated as follows. Hysteresis curve obtained by the above method (relative transmittance-
Applied voltage curve) with no voltage (antiferroelectric phase)
Then, the relative transmittance in the process of applying the voltage to the plus (or minus) side is second-ordered from the applied voltage to obtain the voltage when the value at this time becomes 2. Then, the relative transmittance at a corresponding voltage is obtained from the relative transmittance-applied voltage curve, and this is defined as the pan bottom rate. The smaller the pan bottom rate, the less light leakage. Therefore, it means that the smaller the pan bottom rate is, the higher the contrast is, and the better the display performance is.

[0041]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 3-Fluoro-4-n-decyloxybiphenyl-4 '
-Carboxylic acid 4- (2-octyloxycarbonyl)
Synthesis of phenylthioester

[Chemical 9]

1) Synthesis of bis (4-hydroxycarbonylphenyl) disulfide

[Chemical 10] 4-mercaptobenzoic acid 35g ethanol 800ml
Was dissolved in 100 ml of 35% hydrogen peroxide, and the mixture was stirred at room temperature for 8 hours, and the precipitated crystals were collected by filtration, washed with hydrous ethanol and water in that order, and dried to give bis (4-
Hydroxycarbonylphenyl) disulfide 28.7
g was obtained.

2) Synthesis of bis [4- (2-octyloxycarbonyl) phenyl] disulfide

[Chemical 11] 10 g of the compound obtained in 1) was added to 200 ml of methylene chloride.
And dissolved in 100 ml of thionyl chloride, a few drops of dimethylformamide were added, and the mixture was heated under reflux for 2 hours. Unreacted thionyl chloride and methylene chloride solvent were distilled off under reduced pressure to obtain an acid chloride.

Optically active 2-octanol (8.9 g), triethylamine (6.9 g) and a catalytic amount of dimethylaminopyridine were dissolved in 100 ml of methylene chloride.
A solution prepared by dissolving the above acid chloride in 100 ml of methylene chloride was gradually added dropwise at 0 ° C. with stirring. After the dropping was completed, the reaction was carried out at room temperature for 12 hours. Then the reaction solution is 1N
After washing with hydrochloric acid and saturated saline in this order, the solvent was distilled off under reduced pressure, and the obtained residue was purified by silica gel chromatography to obtain bis [4- (2-octyloxycarbonyl)].
14.9 g of phenyl] disulfide was synthesized.

3) Synthesis of 3-fluoro-4-n-decyloxybiphenyl-4'-carboxylic acid 4- (2-octyloxycarbonyl) phenylthioester

[Chemical 12] 7.4 g of the compound obtained in 2), 3-fluoro-4-n
-Decyloxybiphenyl-4'-carboxylic acid 10.5
g and 1.3 g of triphenylphosphine were heated and stirred in 390 ml of acetonitrile. The crystals precipitated by cooling were collected by filtration and further purified by silica gel chromatography to give 3-fluoro-4-n-decyloxybiphenyl-4'-carboxylic acid 4- (2-octyloxycarbonyl) phenylthioester 1 0.8 g was obtained.

The phase transition temperatures measured by observation with a polarizing microscope equipped with a hot stage were as follows. The S * (3) phase is as described on page 5, the S * (2) phase is a ferroelectric phase exhibiting two-state switching, and the SA phase is a smectic A phase.
It is a phase.

[Table 2]

Example 2 3-Fluoro-4-n-nonyloxybiphenyl-4 '
-Carboxylic acid 4- (2-octyloxycarbonyl)
Phenylthioester

[Chemical 13] 3-Fluoro-4-n-decyloxybiphenyl-4′-carboxylic acid in Example 1, 3) was replaced with 3-fluoro-
It was synthesized by a similar method using 4-n-nonyloxybiphenyl-4'-carboxylic acid.

The phase transition temperatures (° C.) measured by observation with a polarizing microscope equipped with a hot stage are as follows.

[Table 3]

Example 3 A basic antiferroelectric liquid crystal composition was prepared by mixing the compounds shown below in the proportions shown below.

Embedded image

The basic antiferroelectric liquid crystal compositions were blended with the compounds of Examples 1 and 2 in the proportions shown below to prepare antiferroelectric liquid crystal compositions A and B, respectively.

[Equation 1] The pot bottom rate measured by the above-mentioned measuring method is shown in FIG.

The embodiments of the present invention will be listed below. 1. General formula [1]

[Chemical 15] (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, X ¹ and X ² are groups independently selected from the group consisting of H and F, and Y is a single bond. , independently from the group consisting of O and COO are selected groups, Cf is CH ₃
Alternatively, it represents CF ₃ , and * represents an optically active center. ) A liquid crystal compound comprising a compound represented by: 2. An antiferroelectric liquid crystal compound exhibiting an optical tristable state, characterized by comprising a compound represented by the above general formula [1]. 3. The following general formula [2]

Embedded image (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, Cf is CH ₃ or CF ₃ , and * is an optically active center.). Characteristic liquid crystal compound. 4.

[Chemical 17] (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, Cf is CH ₃ or CF ₃ , and * is an optically active center.). An antiferroelectric liquid crystal compound exhibiting a characteristic optical tristable state. 5.

Embedded image (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, and * represents an optically active center.) A liquid crystal compound. 6.

[Chemical 19] (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, and * represents an optically active center.) The compound has the optical tristable state. Antiferroelectric liquid crystal compound. 7. A liquid crystal composition comprising one or more liquid crystal compounds according to the above 1, 3 or 5. 8. A liquid crystal composition comprising one or more antiferroelectric liquid crystal compounds exhibiting the optical tristable state according to the above item 2, 4 or 6.

[0053]

[Effect] The present invention improves the contrast in the display by improving the pan bottom rate.

[Brief description of drawings]

FIG. 1A is an applied triangular wave, B is a commercially available nematic liquid crystal, C is a two-state liquid crystal, and D is a three-stable state liquid crystal.
The respective optical response characteristics are shown.

FIG. 2 shows two stable alignment states of a ferroelectric liquid crystal molecule proposed by Clark / Ragawell.

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

FIG. 4 is an applied voltage-light transmittance characteristic diagram showing that the “anti” ferroelectric liquid crystal molecule draws double hysteresis with respect to the applied voltage and the light transmittance changes.

FIG. 5 shows a model of a hysteresis curve of relative transmittance with respect to a triangular wave applied voltage.

FIG. 6 is a graph showing the relationship between the temperatures of the basic composition of Examples 3 and Compositions A to B and the pan bottom rate.

Claims (2)

[Claims] 1. A general formula [1]: (In the formula, m is an integer of 4 to 14, n is an integer of 4 to 14, X ¹ and X ² are groups independently selected from the group consisting of H and F, and Y is a single bond. , independently from the group consisting of O and COO are selected groups, Cf is CH ₃
Alternatively, it represents CF ₃ , and * represents an optically active center. ) A liquid crystal compound comprising a compound represented by: 2. A liquid crystal composition comprising at least one liquid crystal compound according to claim 1.