JPH10330321A - Racemic compound and ferrielectric liquid crystal composition containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject liquid crystal composition excellent in response property and having high display quality by including a new racemic compound and ferrielectric liquid crystal. SOLUTION: This liquid crystal composition is obtained by adding a new racemic compound shown by formula I (X is H or F; (n) is 4-8) [e.g. 3-fluro-4-(1- methylheptyloxycarbonyl)phenyl 4-trifluoromethyoxybenzoate] to a ferrielectric liquid crystal shown by formula II (R is a 6-12C straight-chain alkyl; Y is H or F; (r) and (q) are each 2-4). It is preferable that the addition ratio of the compound shown by the formula I is 1-30 mol.% per the composition. The composition has transition temperature at 40 deg.C or higher in its high temperature side and at 0 deg.C or lower in its low temperature side of the ferrielectric phase, and a smectic A layer at a temperature higher than the ferrielectric phase, wherein a nonlinear active element is narrowly held between substrates placed for each pixel to make an active matrix liquid crystal display element, and driving by voltage is performed by switching to two ferrielectric states, two ferroelectric state, and an intermediate state of these.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel racemic compound, a novel ferrielectric liquid crystal composition containing the same, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Liquid crystal display devices (LCDs) are already becoming popular mainly in portable devices as flat panel displays replacing conventional CRT displays. With the recent expansion of the functions of personal computers and word processors and the increase in the amount of processing information, LC
D is also required to have higher functions, that is, large display capacity, full color display, wide viewing angle, high-speed response, high contrast, and the like.

As a liquid crystal display system (liquid crystal driving system) that meets such a demand, a thin film transistor (TFT) or a diode (MIM) is formed for each pixel of a screen, and a liquid crystal is independently driven for each pixel. Has been proposed and implemented. This display method has problems such as low production yield, low cost is difficult, and large screen is difficult.
Due to the high display quality, it has surpassed the STN display method which has been mainstream in the past, and is approaching the CRT.

[0004]

However, in such an AM display element, the following problem occurs because a TN (twisted nematic) liquid crystal is used as a liquid crystal material. (1) The TN liquid crystal is a nematic liquid crystal, and its response speed is generally slow (several tens of ms), and good image quality cannot be obtained when displaying a moving image. (2) The display angle is narrow because display is performed by using the twisted state (twist alignment) of liquid crystal molecules. In particular, when gradation display is performed, the viewing angle sharply decreases. In other words, depending on the viewing angle of the display,
The contrast ratio, color, etc. will change.

In order to solve these problems, an AM using a ferroelectric liquid crystal or an antiferroelectric liquid crystal instead of a TN liquid crystal has been proposed.
Panel proposals have also been made in recent years (Japanese Unexamined Patent Publication No.
5-150257, 6-95080, etc.) These liquid crystals also have the following problems, and the wall for practical use is currently thick.

(A) A ferroelectric liquid crystal has spontaneous polarization. However, since spontaneous polarization always exists, image burn-in easily occurs and driving is difficult. Further, when the ferroelectric liquid crystal is displayed in the surface stabilization mode, only binary display of black and white can be performed, so that gradation display is extremely difficult. A special device is required when performing gradation display (for example, a ferroelectric liquid crystal element using monostable; Keiichi NITO et.al, S
ID'94, Preprint, p48), requiring the development of advanced practical technology.

(B) Since the antiferroelectric liquid crystal does not have permanent spontaneous polarization, the problem of burn-in described in (A) is avoided. At least 10V for AM drive
A liquid crystal material driven below is required. However, the antiferroelectric liquid crystal generally has a large threshold voltage, and it is difficult to drive at a low voltage. In addition, there is a problem that gradation display is difficult due to a history (hysteresis) in optical response. An object of the present invention is to provide a new material suitable for AM driving that can solve the above problems,
A liquid crystal having a ferrielectric phase can be considered as this new material.

[0008] In 1989, a liquid crystal compound having a ferrielectric phase (SCγ * phase) was obtained from 4- (1-methylheptyloxycarbonyl) phenyl 4- (4'-octyloxybiphenyl) carboxylate (abbreviated as MHPOBC). First discovered
(Japanese Journal of AppliedPhysics, Vol.29, No.1,
pp.L131-137 (1990)).

Structural formula of MHPOBC and phase transition temperature (° C.)
Is shown below. Structural formula: C ₈ H ₁₇ -O-Ph-Ph-COO-Ph-COO-C * H (CH ₃ ) -C ₆ H ₁₃ where Ph is 1,4-phenylene group and C * is asymmetric carbon Represent. Phase series: I (147) SA (122) SCα * (121) SC * (119) SCγ * (11
8) SCA * (65) SIA * (30) Cr where I is isotropic, SA is smectic A phase, SCα * is chiral smectic Cα phase, SC * is chiral smectic C phase (ferroelectric phase), SCγ * Is chiral smectic C
γ phase (ferrielectric phase), SCA * is chiral smectic C
A phase (antiferroelectric phase), SIA * is chiral smectic IA
The phase, Cr, indicates a crystalline phase.

In order to explain a ferrielectric liquid crystal, FIG.
2 shows the molecular arrangement state in the ferrielectric phase, and FIG. 2 shows the optical response of the ferrielectric phase to a triangular wave. In the ferrielectric phase, FI (+) (when the applied voltage is positive) or FI
The molecular arrangement is (-) (when the applied voltage is negative). In the absence of an electric field, FI (+) and FI (-) coexist because they are equivalent. Therefore, the average optical axis is in the direction of the normal to the layer, and is in a dark state under the conditions of the polarizing plate shown in FIG. This state corresponds to a state where the voltage is 0 in FIG.

Further, FI (+) and FI (-) have spontaneous polarizations, respectively, as evident from the molecular arrangement state. However, in the coexistence state, the spontaneous polarizations cancel each other, so that the average spontaneous polarization is zero. Becomes For this reason, the ferrielectric liquid crystal escapes the image sticking phenomenon observed in the ferroelectric liquid crystal, like the antiferroelectric liquid crystal.

In the ferrielectric phase, when a voltage is applied, a region (domain) having an extinction position appears at a voltage lower than the ferroelectric state. This region has an optical axis in a direction inclined from the normal direction, though not so much as in the ferroelectric state. This intermediate state is FI (+)
Or FI (-). In the present invention, at least the liquid crystal phase in which this intermediate state is always observed is referred to as a ferrielectric phase,
The liquid crystal compound whose ferrielectric phase is the broadest in the phase series is called a ferrielectric liquid crystal.

Further, when the applied voltage is increased, the ferroelectric phase FO (+) or FO (-) which is in a stable state according to the direction of the electric field is increased.
Phase transition. That is, in FIG. 2, the transmitted light intensity is in a saturated state (a flat portion on the left and right), and the intensity is FO (+) or FO
(-). In this ferroelectric state FO (+) or FO (-),
It can be seen from FIG. 1 that a spontaneous polarization larger than that of the ferrielectric state FI (+) or FI (-) appears. The response speed increases as the spontaneous polarization increases, and this results in high-speed response.

Conventional ferroelectric liquid crystals switch between FO (+) and FO (-), while ferrielectric liquid crystals have FO (+), FI (+), FI (-) and It has the great feature of switching between the four states of FO (-). Therefore, in the ferrielectric phase of FIG.
A stepped transmitted light intensity should be observed instead of a continuous change in transmitted light intensity between V and V. However,
In FIG. 2, a continuous change in transmitted light intensity was observed. This is the coexistence state of FI (+) and FI (-) → FI (+) → FO (+), or the coexistence state of FI (+) and FI (-) → FI (-) → FO (-) It is considered that the threshold voltage to is not clear.

In the ferrielectric phase, as shown in FIG. 2, the difference between the voltage that changes from the ferrielectric state to the ferroelectric state and the voltage that changes from the ferroelectric state to the ferrielectric state is generally small. That is, the width of the hysteresis tends to be very narrow, and is characterized by a V-shaped optical response.
It has properties suitable for gradation display in M drive and AM drive. Also, in the change due to the voltage in the ferrielectric phase, the voltage required to change from the ferrielectric state to the ferroelectric state tends to be much smaller than that of the antiferroelectric liquid crystal. It can be said that it is suitable.

In the ferrielectric phase, as shown in FIG. 2, the coexistence state of FI (+) and FI (-) and the ferroelectric state
The change between (FO (+), FO (-)) is continuous, and
The voltage required for the change is small. Further, by devising the alignment film, it is possible to further reduce the light transmittance in a state where FI (+) and FI (-) coexist at a voltage of 0. From these, in the ferrielectric phase, the coexisting state of FI (+) and FI (-) can be used as dark, the ferroelectric states FO (+) and FO (-) as light, and the intermediate state between them can be used as gray. All of the display principles use the birefringence of liquid crystal, and a display element with small viewing angle dependence can be manufactured.

[0017]

However, the number of ferrielectric liquid crystals synthesized to date is extremely small,
Further, a conventionally known ferrielectric liquid crystal alone is AM
Considering the application to the driving element, there are the following problems. That is, in the active matrix drive, the TFT
In the driving method, the driving voltage is 5 V or less. No single ferrielectric liquid crystal having practical characteristics at such a low voltage and exhibiting a high-speed response has been found. The present invention is directed to improving these points, and relates to an additive for improving responsiveness and a ferrielectric liquid crystal composition containing the additive, which is preferably used for AM driving and containing the additive.

[0018]

That is, the present invention provides a racemic compound represented by the following general formula (1),
In (1), it is preferable that m is 9 and that the compound does not have a liquid crystal phase, since a material having excellent properties when obtained as a ferrielectric liquid crystal composition is obtained. Further, the present invention provides a racemic compound represented by the following general formula (1) represented by the following general formula (2)
A ferrielectric liquid crystal composition obtained by adding to a ferrielectric liquid crystal represented by the formula:

[0019]

Embedded image (In the formula (1), X is a hydrogen atom or a fluorine atom, and n is 4 to
It is an integer of 8. In the formula (2), R is a straight-chain alkyl group having 6 to 12 carbon atoms, X is an H atom or an F atom, r is an integer of 2 to 4, and q is an integer of 2 to 4. )

The amount of the racemic compound represented by the general formula (1) is preferably from 1 to 50 mol%, more preferably from 1 to 30 mol% of the composition. As the ferrielectric liquid crystal composition, the transition temperature on the high temperature side of the ferrielectric phase is 40 ° C. or more, and the transition temperature on the low temperature side is 0 ° C. or less. It is preferred to have. Then, the ferrielectric liquid crystal liquid crystal composition of the present invention is sandwiched between substrates on each of which a non-linear active element such as a thin film transistor or a diode is provided to form an active matrix liquid crystal display element. Driving of the used liquid crystal by voltage is performed by switching between two ferrielectric states, two ferroelectric states, and an intermediate state between them.

The ferrielectric liquid crystal in the present invention can be easily manufactured by the present inventors in Japanese Patent Application No. 8-91235.
The outline of the production method is as follows for a compound in which r = 3 and q = 2 in the general formula (2). (1) AcO-Ph (3X) -COOH + SOCl ₂ → AcO-Ph (3X) -COCl (2) (1) + CF ₃ C * H (OH) (CH ₂ ) ₃ OC ₂ H ₅ → AcO- Ph (3X) -COO-C * H (CF ₃ ) (CH ₂ ) ₃ OC ₂ H ₅ (3) (2) + (Ph-CH ₂ NH ₂ ) → HO-Ph (3X) -COO-C * H (CF ₃ ) (CH ₂ ) ₃ OC ₂ H ₅ (4) RO-Ph-Ph-COOH + SOCl ₂ → RO-Ph-Ph-COCl (5) (3) + (4) → Desired ferrielectricity In the formula, AcO- is an acetyl group, -Ph- is a 1,4-phenylene group, -P
h (3X)-represents a 1,4-phenylene group which may be F-substituted at the 3-position, Ph- represents a phenyl group, and C * represents an asymmetric carbon.

The above-mentioned manufacturing method is briefly described as follows. (1) is a chlorination reaction of fluorine-substituted or unsubstituted p-acetoxybenzoic acid with thionyl chloride. (2)
Is the formation of an ester by the reaction of chloride (1) with an optically active alcohol. (3) is the deacetylation of ester (2). (4) is the chlorination of 4'-alkyloxybiphenyl-4-carboxylic acid. (5) is phenol (3) and chloride
(4) to produce a liquid crystal.

[0023]

The present invention provides a novel racemic compound and a ferrielectric liquid crystal composition containing the same. The novel ferrielectric liquid crystal composition provided by the present invention has excellent responsiveness. Therefore, a ferrielectric liquid crystal display element having high display quality can be realized.

[0024]

Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is of course not limited thereto. Example 1 (General formula (1): n = 6, X = F (E1)) Production of 3-fluoro-4- (1-methylheptyloxycarbonyl) phenyl = 4-trifluoromethoxybenzoate.

(1) Production of 4-acetoxy-2-fluoro-1- (1-methylheptyloxycarbonyl) benzene. 4-acetoxy-2-fluorobenzoic acid 10.8 g (0.06 mol)
Then, 60 ml (milliliter) of thionyl chloride was added thereto, and the mixture was reacted under reflux for 7 hours. Next, after removing excess thionyl chloride, 10 ml of pyridine and 5.2 g (0.0402 mol) of 2-octanol were added dropwise. After the dropwise addition, the mixture was stirred at room temperature for one day and night, and then diluted with 200 ml of ether. The organic layer was washed with diluted hydrochloric acid, a 1N aqueous sodium hydroxide solution and water in that order, and dried over magnesium sulfate. The solvent was distilled off, and the crude target product was purified by silica gel column chromatography using hexane / ethyl acetate as a solvent to obtain the target product in a yield of 90%.

(2) Production of 2-fluoro-4-hydroxy-1- (1-methylheptyloxycarbonyl) benzene. 11.3 g (0.036 mol) of the compound prepared in the above (1) was dissolved in 250 ml of ethanol, and 7.7 g (0.07
72 mol) was added dropwise. Furthermore, after stirring at room temperature for 24 hours,
Dilute with 300 ml of ether, wash with diluted hydrochloric acid and water in that order,
Dried over magnesium sulfate. After evaporating the solvent, the residue was isolated and purified by silica gel column chromatography to obtain the desired product in a yield of 98%.

(3) Production of 3-fluoro-4- (1-methylheptyloxycarbonyl) phenyl 4-trifluoromethoxybenzoate 15 ml of thionyl chloride was added to 6.4 g (0.031 mol) of commercially available p-trifluoromethoxybenzoic acid, and the mixture was heated under reflux for 5 hours.
After distilling off excess thionyl chloride, 2 ml of pyridine was added.
2.12 mmol of the compound prepared in (2) was added, and
Allowed to react for hours. After completion of the reaction, the reaction mixture was diluted with 300 ml of ether, washed with diluted hydrochloric acid, a 1N aqueous solution of sodium carbonate and water in that order, and the organic layer was dried over magnesium sulfate. Next, after distilling off the solvent, the residue was isolated by silica gel chromatography to obtain the desired product in a yield of 87%.

Example 2 (general formula (1): n = 6, X = H
(E2)) Production of 4- (1-methylheptyloxycarbonyl) phenyl = 4-trifluoromethoxybenzoate. The desired product was obtained in the same manner as in Example 1 except that p-hydroxybenzoic acid was used instead of 4-acetoxy-2-fluorobenzoic acid in Example 1. 1H-NMR data of the target compound (E1, E2) obtained in Examples 1 and 2 are shown in Table 1, and its chemical formula is shown in Chemical Formula 4. The liquid crystal phase was identified by texturer observation and DSC (differential scanning calorimetry) measurement. The melting point was determined by DSC. As a result, the melting points of these compounds were −50 ° C. or lower, and did not have a liquid crystal phase.

[0029]

Embedded image

[0030]

[Table 1] Proton No. 1 2 3 4 5 6 Example 1 (E1) 7.4 8.2 7.1 7.1 8.0 5.2 Example 2 (E2) 7.3 8.2 7.2 8.1 5.2

Example 3 A ferrielectric liquid crystal (2A) represented by the following formula was used in Example 1
The ferric dielectric liquid crystal composition was obtained by adding 15 mol% of the racemic compound (E1) obtained in the above. Table 2 shows the results of measurement of the phase series and orientation. 2A: C ₉ H ₁₉ -O-Ph-Ph-COO-Ph (3F) -COO-C * H (CF ₃ ) (CH ₂ )
_{In the} formula ₃ OC ₂ H ₅ , -Ph- is a 1,4-phenylene group, -Ph (3F)-is a 1,4-phenylene group substituted with fluorine at the 3-position, and C * is an asymmetric carbon.

The liquid crystal phase was identified by texture observation, observation of a conoscopic image, and measurement by DSC (differential scanning calorimeter). Observation of a conoscopic image is a powerful tool for identifying a ferrielectric phase. Observation of conoscopic images is literature
(J. Appl. Phys. 31, 793, (1992)).

Table 2 shows the results of examining the optical response of the obtained ferrielectric liquid crystal composition. The cell was produced according to the following procedure. After polyimide coating on a glass substrate with an insulating film (SiO ₂ , film thickness 50 nm) and ITO electrode (film thickness approx.
m) Only one of the pair of glass substrates was rubbed.
A pair of glass substrates were bonded via a spacer having a particle size of 1.6 μm to form a test cell. The cell thickness was 2 μm. The liquid crystal was heated to a temperature at which the liquid crystal became an isotropic phase, and injected into a test cell by capillary action. Thereafter, the liquid crystal was gradually cooled at a rate of 1 ° C./min to parallel align the liquid crystal.

At 30 ° C., ± 10 V, 50 mHz
The driving was performed by applying the triangular wave voltage, and the change in transmitted light was examined. As for the light transmittance, an empty cell was placed between orthogonal polarizing plates, and the amount of transmitted light was determined, and the amount of transmitted light was set to 0%. next,
The test cell was placed between polarizing plates, and the amount of transmitted light in the ferroelectric state (when the amount of transmitted light was the highest) was determined. The amount of transmitted light was defined as 100%. The phase transition voltage is defined as a voltage at which the transmitted light intensity becomes 90% due to a phase transition from a ferrielectric phase to a ferroelectric phase. The response time was defined as the time required for the transmitted light intensity to change by 90% when a step voltage of ± 8 V, 10 Hz was applied. For comparison, Table 2 shows the results of evaluating the characteristics of the ferrielectric liquid crystal (2A) in the same manner as described above except that the measurement temperature was 40 ° C.

[0035]

[Table 2] Phase transition Response time Measurement temperature Phase sequence Voltage (V) (μsec) (° C) Example 3 Cr (<-20) SCγ * (77) SA (86) I 2.4 203 30 Liquid crystal 2A Cr ( 34) SCγ * (101) SA (103) I 2.9 * 1 40 * 1; High phase transition voltage and no response. In the above phase series, the numbers in parentheses indicate the phase transition temperature (° C.), Cr indicates the crystal phase, SCγ * indicates the chiral smectic Cγ phase (ferrielectric phase), SA indicates the smectic A phase, and I indicates the isotropic phase. .

[Brief description of the drawings]

FIG. 1 shows a molecular arrangement state in a ferrielectric phase. FI
(+) And FI (-) indicate a ferrielectric state, and FO (+) and FO (-) indicate a ferroelectric state.

FIG. 2 shows an optical response of a ferrielectric phase to a triangular wave voltage.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takahiro Matsumoto 22nd Wadai, Tsukuba, Ibaraki Pref. Mitsubishi Gas Chemical Company, Ltd.

Claims (10)

[Claims] 1. A racemic compound represented by the following general formula (1). Embedded image (Where X is a hydrogen atom or a fluorine atom, and n is 4-8
Is an integer. ) 2. The racemic compound according to claim 1, wherein n is 6 in the general formula (1). 3. The racemic compound according to claim 1, wherein X is F in the general formula (1). 4. A ferrielectric liquid crystal composition obtained by adding a racemic compound represented by the following general formula (1) to a ferrielectric liquid crystal represented by the following general formula (2). Embedded image (In the formula (1), X is an H atom or a F atom, n is an integer of 4 to 8. In the formula (2), R is a straight-chain alkyl group having 6 to 12 carbon atoms, and Y is an H atom or a F atom. Atom, r is an integer of 2 to 4, and q is an integer of 2 to 4.) 5. In the general formula (2), R has 9 carbon atoms.
The ferrielectric composition according to claim 4, which is: 6. The ferrielectric liquid crystal composition according to claim 4, wherein the amount of the racemic compound represented by the general formula (1) is 1 to 50 mol% of the composition. 7. The ferrielectric liquid crystal liquid crystal composition according to claim 4, wherein the amount of the racemic compound represented by the general formula (1) is 1 to 30 mol% of the composition. 8. The ferrielectric phase having a transition temperature on the high temperature side of 40.
The ferrielectric liquid crystal composition according to claim 4, which has a transition temperature on the low temperature side of 0 ° C or higher at 0 ° C or higher and a smectic A phase on the higher temperature side than the ferrielectric phase. 9. An active matrix liquid crystal display device comprising the ferrielectric liquid crystal composition according to claim 4 sandwiched between substrates on which a non-linear active device such as a thin film transistor or a diode is provided for each pixel. 10. The active matrix liquid crystal display device according to claim 9, wherein switching is performed between two ferrielectric states, two ferroelectric states, and an intermediate state by a voltage.