JP2902398B2 - Liquid crystal compound and liquid crystal for optical element showing optical response between three stable states using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a ferroelectric chiral smectic liquid crystal compound, and the liquid crystal compound relates to a liquid crystal compound used for a display element or an electro-optical element utilizing a response to an electric field. It is. Further, the present invention relates to a ferroelectric liquid crystal compound showing three stable molecular alignment states. The liquid crystal compound is used for a display element or an electro-optical element utilizing a response to an electric field.

Further, the present invention relates to a liquid crystal for an optical element which shows an optical response between three stable states to an electric field application.

[0003]

2. Description of the Related Art As an electro-optical device using a liquid crystal, D is used.
Electro-optical devices using nematic liquid crystals such as SM type, TN type, GH type and STN type have been developed and put to practical use. However, those using such a nematic liquid crystal have a drawback that the response speed is extremely slow, from several meters to several tens of msec. The reason that the response speed of the device using the nematic liquid crystal is slow is that the torque for moving the molecules is basically not based on the anisotropy of the dielectric constant, so that the force is not so strong.
In such a background, since it has spontaneous polarization (Ps) and the torque is based on Ps × E (E is an applied electric field), the force is strong, and a high-speed response of several μsec to several + μsec is possible. A dielectric liquid crystal was developed by Meyer et al. (L
e Journal de Physique, 36
Vol., 1975, L-69) and JP-A-63-3078.
No. 37 discloses a newer ferroelectric liquid crystal, but does not disclose a "three state" described later.

Some high-speed electro-optical devices using ferroelectric liquid crystals have already been proposed.

[0005] A typical example is one in which the twisted structure is solved by the force of the wall surface and the two molecular orientations parallel to the wall surface are changed by the polarity of the applied electric field (see, for example, Japanese Patent Application Laid-Open No. Sho 56-56).
107216).

The foregoing is based on the premise that there is a compound exhibiting ideal two states as shown in the electric field response waveform of FIG. However, in reality, no compound exhibiting the ideal two-state has been found, and the electric field response waveform of the two-state liquid crystal synthesized so far is as shown in FIG. 2, and the response waveform as shown in FIG. Has not been obtained. For example, when a response waveform as shown in FIG. 2 is used for an optical switching circuit, the transmittance changes gradually as the applied voltage changes from-to +, so that it is simply turned on and off. In fact, the change in the applied voltage cannot sufficiently achieve the purpose. Furthermore, it is difficult for the two-state liquid crystal synthesized so far to create a monodomain state, which is an ideal molecular alignment state, in the S ^* c phase stage in the absence of an electric field, causing disclination (defects),
Distortion of molecular orientation called twist occurs. Therefore, it is difficult to realize the ideal two-state orientation in a large area. Further, since the threshold (voltage at which the luminance changes by a predetermined value) is low, the contrast is reduced or the viewing angle range is narrowed when the dynamic drive is performed. Also,
The two-state liquid crystal synthesized so far cannot exhibit the hysteresis as shown in FIG. 1, but has only the hysteresis as shown in FIG. 2, and thus has no memory effect. Therefore, in order to hold the response of the liquid crystal into a stable S ^* c phase, either continuously applying a voltage of the upsilon ₃ 2, or must be kept continue over frequency, energy loss in any event Is big.

After all, although a high-speed liquid crystal electro-optical device that effectively utilizes the strong coupling between an applied electric field and a molecular orientation obtained by a ferroelectric liquid crystal is desired, the conventional ferroelectric liquid crystal electro-optical device still does not. In fact, many problems remain.

Therefore, in the present invention, a stable molecular orientation state with a clear contrast between light and dark is realized without an electric field, a clear threshold characteristic and a clear hysteresis as shown in FIG. It is an object of the present invention to provide a novel liquid crystal compound which can be used in a liquid crystal electro-optical device utilizing three states which can realize a high-speed response.

[0009]

SUMMARY OF THE INVENTION The first object of the present invention is as follows.
Is to provide a novel liquid crystal compound. A second object of the present invention is to provide a ferroelectric liquid crystal exhibiting a chiral smectic phase and a chiral smectic C which is a conventional bistable state phase.
An object of the present invention is to provide a novel ferroelectric liquid crystal having a completely new three state different from the phase (S ^* c phase).

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. 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. 4A, the ferroelectric liquid crystal is turned off as shown in FIG. 4D. In the absence of an electric field, the molecular orientation has a first stable state (shown in FIG. 4D), and when an electric field is applied, the molecular orientation in one electric field direction is different from the first stable state (see FIG. 4D). 4D, and a third molecular orientation stable state (of FIG. 4D) different from the first and second stable states with respect to the other electric field direction. It should be noted that the present applicant has disclosed a liquid crystal electro-optical device utilizing the three stable states, that is, the three states, in Japanese Patent Application No. 63-7 / 1988.
No. 0212.

On the other hand, "a commercially available nematic liquid crystal"
In addition, the two-state liquid crystals synthesized so far do not have three stable states as seen in FIGS. 4B and 4C.

The new three-state ferroelectric liquid crystal exhibits an epoch-making effect when used in a liquid crystal display as compared with a conventional nematic liquid crystal.

The conventional type requires a very complicated structure in which the driving method is an active matrix type, whereas the three-state ferroelectric liquid crystal requires only a simple matrix type display. For this reason, in the case of the conventional type, the production process is complicated, it is difficult to increase the size of the screen, and the production cost is high, whereas in the case of the three-state ferroelectric liquid crystal, the production process is simple, and the screen is This is an epoch-making thing that can be made larger and the manufacturing cost can be reduced.

[0014]

Means for Solving the Problems A first aspect of the present invention is as follows.

Embedded image [In the formula, R ₁ is an alkyl group having 5 to 18 carbon atoms, R ₂ is an alkyl group having 4 to 15 carbon atoms, and * indicates an optically active center. And a liquid crystal compound exhibiting a tristable state.

A second aspect of the present invention relates to a liquid crystal for an optical element, which comprises the liquid crystal compound according to the first aspect and exhibits an optical response between three stable states when an electric field is applied.

The following are examples of the synthesis of the compounds of the present invention. The 4-benzyloxybenzoic acid compound is reacted with an optically active 2-alkanol to give 4-benzyloxybenzoic acid-1-methylalkyl ester, which is hydrogenolyzed to give 4-hydroxybenzoic acid-1 To obtain a methylalkyl ester. The resulting ester,
Reaction with 4'-alkanoyloxybiphenyl-4-carboxylic acid in the presence of dicyclohexylcarbodiimide (DCC) gives 1-methylalkyl 4'-alkanoyloxybiphenyl-4-carboxylate.

[0017]

The compounds of the present invention will be described below by way of examples, which should not be construed as limiting the invention.

Example 1 1) Synthesis of 1-methylheptyl 4-benzyloxybenzoate

Embedded image 1.23 g of 4-benzyloxybenzoic acid chloride is dissolved in 10 ml of methylene chloride, and then 0.59 g of optically active 2-octanol and 0.59 g of dimethylaminopyridine are dissolved.
5 g and 0.48 g of triethylamine were dissolved in methylene chloride 2
The solution dissolved in 0 ml was added little by little under ice cooling. The reaction mixture was returned to room temperature and reacted overnight.The reaction solution was poured into ice water, extracted with methylene chloride, and the methylene chloride phase was washed successively with dilute hydrochloric acid, water, a 1N aqueous solution of sodium carbonate and water, and then dried over anhydrous magnesium sulfate. Dry and evaporate the solvent,
A crude product was obtained. This was treated with a toluene-silica gel column chromatograph, and further recrystallized with ethanol to obtain 1.48 g of the desired product.

2) Synthesis of 1-methylheptyl 4-hydroxybenzoate

Embedded image The compound obtained in 1) is dissolved in 15 ml of ethanol,
0.36 g of 10% supported Pd-carbon was added, and a hydrogenation reaction was performed in a hydrogen atmosphere to obtain 1.29 g of a target compound.

3) 4- (1-methylheptyloxycarbonyl) phenyl 4'-n-nonanoylbiphenyl-
Synthesis of 4-carboxylate and measurement of phase transition temperature

Embedded image 4'-nonanoylbiphenyl-4-carboxylic acid 5.00
g and 6.76 g of 1-methylheptyl 4-hydroxybenzoate synthesized in 2) are dissolved in 330 ml of dehydrated tetrahydrofuran. In it, 6.18 g of dicyclohexylcarbodiimide (DCC) and 0.24 g
Of dimethylaminopyridine and stir all day and night. The reaction solution is filtered, and tetrahydrofuran in the filtrate is distilled off. The residue is dissolved in methylene chloride and washed with a small amount of water. The methylene chloride layer is collected and dehydrated with anhydrous magnesium sulfate. The methylene chloride is distilled off, and the residue is purified by silica gel chromatography and recrystallized from ethanol to obtain 2.83 g of the desired product. The following phase transition temperature (° C.) was obtained by observation with a polarizing microscope using a hot stage.

[Table 1]

The infrared absorption spectrum (KB) of the target compound
r) is shown in FIG. The specific rotation of the target compound is shown below. [Α] _D ²⁵ = -21.2 °

Example 2 A 2.9 μm thick liquid crystal cell having a rubbed polyimide alignment film on an ITO electrode substrate was filled with the liquid crystal compound obtained in Example 1 in an isotropic phase to form a liquid crystal thin film cell. did. 0.1 ~
After slowly cooling at a temperature gradient of 1.0 ° C. for 1 minute, orienting the SA phase, applying a ± 30 V, 10 Hz rectangular wave, and detecting the electro-optical response operation with a polarizing microscope equipped with a photomultiplier. As shown in FIG. 6, an electroclinic effect (b) that optically responds to an applied electric field (a) in the SA phase was observed.

Example 3 A liquid crystal cell prepared in exactly the same manner as in Example 2 was placed on a polarizing microscope equipped with a photomultiplier in which two polarizing plates were orthogonal to each other. Were placed in a state of overlapping. This liquid crystal cell is kept at 0.1 to
/ Slowly cooled to S ^* (3) phase with a temperature gradient of 1 minute. FIG. 7 shows a case where the temperature was further cooled and a triangular wave voltage (a) of ± 30 V and 10 Hz was applied in a temperature range of 103.0 ° C. to 62.6 ° C. The applied voltage changes to a dark state in a negative range, an intermediate state in a 0 volt range, a bright state in a positive range, and a light transmittance in three states (c). (B) was observed, and it was confirmed that there were three stable alignment states of liquid crystal molecules.

[0024]

The novel liquid crystal of the present invention exhibits three stable states, and has a wide range of applications such as display devices and switching devices using the same.

[Brief description of the drawings]

FIG. 1 shows the hysteresis of an ideal two-state liquid crystal that is not actually obtained.

FIG. 2 shows the hysteresis of a two-state liquid crystal actually synthesized so far.

FIG. 3 shows a hysteresis of a three-state liquid crystal according to the present invention.

FIG. 4 shows optical response characteristics of a triangular wave to which A is applied; B, a commercially available nematic liquid crystal; C, a two-state liquid crystal synthesized so far; and D, a three-state liquid crystal.

FIG. 5 shows an infrared absorption spectrum of the compound of Example 1 of the present invention.

6A and 6B show the electroclinic effect, wherein FIG. 6A shows an alternating voltage applied to the liquid crystal electro-optical element, and FIG. 6B shows a change in light transmittance with respect to the alternating voltage shown in FIG. It is shown.

7A and 7B show three-state switching of the compound of the present invention. FIG. 7A shows a triangular wave voltage applied to a liquid crystal electro-optical element, FIG. 7B shows a domain inversion current, and FIG. c) shows the change in light transmittance with respect to the triangular wave voltage shown in FIG.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-30740 (JP, A) JP-A-63-250348 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] [Claim 1] [In the formula, R ₁ is an alkyl group having 5 to 18 carbon atoms, R ₂ is an alkyl group having 4 to 15 carbon atoms, and * indicates an optically active center. ] A liquid crystal compound exhibiting a tristable state, characterized by comprising a compound represented by the formula: 2. A liquid crystal for an optical element, comprising the liquid crystal compound according to claim 1 and exhibiting an optical response between three stable states with respect to application of an electric field.