JPH0726102B2 - Ferroelectric liquid crystal composition and optical switching element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is capable of assuming a stable ferroelectric liquid crystal state.
For displays such as LCD TVs, optical printer heads,
The present invention relates to a liquid crystal composition and an optical switching element which are useful as materials for optoelectronic-related elements used for light valves and the like.

(Prior Art) At present, liquid crystal compounds are applied as display materials in various devices and put to practical use in watches, calculators, small televisions and the like. These use a nematic liquid crystal material as a main component, and a display method called TN type or STN type is adopted.

The device in this case utilizes the effect based on the interaction between the dielectric anisotropy of the liquid crystal compound and the electric field, and has a drawback that the optical response to the electric field is as slow as a few msec.

On the other hand, the simple matrix drive method is considered to be the most advantageous in terms of productivity, cost, and reliability in terms of increasing the size of the display, but a liquid crystal that does not have bistability such as TN type or STN type liquid crystal is used. However, there is a problem in that the number of scanning lines cannot be increased sufficiently when the simple matrix driving method is used.

In order to improve such a defect of the conventional liquid crystal element, a display method utilizing an optical switching phenomenon of a ferroelectric liquid crystal was proposed by NAClark and ST Lagerwall (Ap
plied Phys. Lett., 1980, vol.36, p.899). The existence of ferroelectric liquid crystals was first reported in 1975 by RB Meyer et al. A device using a ferroelectric liquid crystal has bistability and has an optical response of μ in comparison with conventional liquid crystal devices.
It has excellent features such as sec order and high speed.

In order for these ferroelectric liquid crystal materials to be used as actual device materials, some physical properties and characteristics are required. Among them, the basic one is that chiral smectic C in a wide temperature range including room temperature. It can be mentioned that it exhibits a (Sc ^* ) phase and that it responds quickly. In addition to this, a large number of physical properties and characteristics are required for ferroelectric liquid crystal materials, but at present, it is not possible to meet the requirements for these physical properties and characteristics with a single compound, and several compounds are mixed. It is necessary to use a ferroelectric liquid crystal composition.

In order to obtain a ferroelectric liquid crystal composition, it is not necessary to mix using only a ferroelectric liquid crystal compound, and it is a liquid crystal which is a non-chiral compound and exhibits a smectic C (Sc) phase or a liquid crystal mixture (a base liquid crystal and a liquid crystal mixture). (Also referred to as), can be obtained by adding a chiral compound.

(Problems to be solved by the invention) However, until now, regarding the base liquid crystal and the chiral compound,
Although many studies have been carried out and proposals have been made for both, the present situation is that there is no ferroelectric liquid crystal composition having sufficient high-speed response.

The present inventors previously mentioned the following general formula (III), It was found that the compound represented by the formula (wherein R ₅ and R ₆ are alkyl groups and C ^* is an asymmetric carbon in which optically active is induced) has large spontaneous polarization and is excellent in high-speed response. Has proposed a liquid crystal composition containing (Japanese Patent Application No. 1-287994). However, since this compound has a high temperature range in which it takes a ferroelectric liquid crystal phase, it cannot be put to practical use by itself.

On the other hand, the following general formula (I), The compound represented by (in the formula, R ₁ and R ₂ represent an alkyl group) has a temperature region of liquid crystal on a low temperature side and has a low viscosity, and is therefore widely used as a base liquid crystal. Then, the compound of the general formula (III) was added to this base liquid crystal, but there was a drawback that the temperature range in which the ferroelectric liquid crystal phase could be formed was narrow.

The present invention is to solve the above problems, and the object of the present invention is to
It is an object of the present invention to provide a ferroelectric liquid crystal composition having a sufficiently wide Sc ^* phase temperature range and a high-speed response, and an optical switching element using the liquid crystal composition.

(Means for Solving the Problems) The present invention provides the following general formula (I): (Wherein, R ₁ and R ₂ represent an alkyl group), and at least one compound represented by the following general formula (II): (In the formula, R ₃ and R ₄ are alkyl groups, X is a single bond or —O—
And at least one compound represented by the following general formula (III): (Wherein R ₅ and R ₆ are alkyl groups, and C ^* is an asymmetric carbon in which optical activity is induced) and at least one compound represented by the formula The present invention relates to a liquid crystal composition (hereinafter referred to as "first invention").

The present invention also includes at least one compound represented by the general formula (I), at least one compound represented by the general formula (III), and the following general formula (IV): (Wherein, R ₇ and R ₈ represent an alkyl group), and at least one compound represented by the following general formula (V): A ferroelectric liquid crystal composition containing at least one compound represented by the formula (wherein R ₉ and R ₁₀ represent an alkyl group) (hereinafter referred to as “second invention”)
It is about.

Furthermore, the present invention provides at least one of the compounds represented by the general formula (I), at least one of the compounds represented by the general formula (II), and the general formula (II
At least one compound represented by the general formula (IV), at least one compound represented by the general formula (IV), and at least one compound represented by the general formula (V); The present invention relates to a ferroelectric liquid crystal composition (hereinafter referred to as "third invention") characterized by containing.

Furthermore, the present invention relates to an optical switching element characterized by using any one of the above ferroelectric liquid crystal compositions as a constituent element.

In the general formulas (I) to (V), the number of carbon atoms of the alkyl group represented by R _{1 to} R ₁₀ is not particularly limited, but from the viewpoint of practical production such as availability of raw materials, Those having up to 18 carbon atoms are preferable.

The compound represented by the general formula (I) can be obtained by the method of H. Zaschke (Journal f. Prakt. Chem. 317, 617 (197).
According to 5)), it can be synthesized from a commercially available reagent by the following scheme.

Next, the compound represented by the general formula (II) is, for example, an intermediate of the following formula obtained by a method similar to the synthetic method of the general formula (I), (In the formula, X represents a single bond or —O—) and can be obtained by esterification with the corresponding carboxylic acid (R ₃ COOH).

The compound represented by the general formula (III) can be obtained, for example, by the synthetic method described in Japanese Patent Application No. 1-287994.

The compound represented by the general formula (IV) can be prepared according to the method of H. Zaschke [Z. Chem., 15, 441 (1975), or Journal f. Prakt. Chem. 323, 199 (1981)].
It can be synthesized by the following scheme using alkyl-4'-cyanobiphenyl as a raw material.

The compound represented by the general formula (V) can be synthesized by the following scheme, for example, by a method similar to the synthetic method of the general formula (IV).

The liquid crystal composition of the first invention of the present invention comprises: at least one of the compounds represented by the general formula (I), and at least one of the compounds represented by the general formula (III).
The response speed prepared by adding it as a chiral dopant is fast, but the chiral smectic C is available only in a relatively narrow temperature range.
To the ferroelectric liquid crystal that does not exhibit a liquid crystal phase of
By adding the compound represented by, the temperature range on the low temperature side where the chiral smectic C phase is taken is widened without deteriorating the response speed.

Therefore, it is necessary to select the mixing ratio of these compounds so that such an effect can be effectively exhibited. For example, (I)
/ (II) is mixed in a ratio of 50/50 to 98/2, and the above general formula (III) is added so as to be 2 to 34% by weight as a whole.
It is preferable to add at least one of the above compounds in order to more effectively achieve the above object.

On the other hand, the liquid crystal composition of the second invention of the present invention comprises at least one of the compounds represented by the general formula (I) and at least one of the compounds represented by the general formula (III). The ferroelectric liquid crystal composition is mixed with at least one compound represented by the general formula (IV) and at least one compound represented by the general formula (V) to obtain a response speed. The temperature range on the high temperature region side where the chiral smectic C phase is taken is widened without deteriorating. In this case, unless both the compounds represented by the general formula (IV) and the general formula (V) are mixed, the temperature range on the high temperature side cannot be expanded without deteriorating the response speed. The mixing ratio of these compounds is such that (I) / {(IV) + (V)} is 50/50 to 98/2 and (IV) / (V) is 10/90 to 90/10. In order to achieve the above-mentioned object more effectively, it is more effective to add at least one of the compounds of the general formula (III) to the mixture in a ratio of 2 to 34% by weight as a whole. preferable.

Furthermore, the liquid crystal composition of the third invention of the present invention is the same as the liquid crystal composition of the first invention of the present invention, except that at least one of the compounds represented by the general formula (IV) and the general formula (V) is used. By mixing with at least one of the compounds described above, without deteriorating the response speed and without narrowing the temperature range on the low temperature side where the chiral smectic C phase is taken,
The temperature range on the high temperature side is widened. In this case, unless the compound represented by the general formula (IV) and the compound represented by the general formula (V) are mixed, the temperature range on the high temperature side cannot be sufficiently widened without lowering the response speed.

The mixing ratio of these compounds in this case is (I)
/ {(I) + (II) + (IV) + (V)} = 30/100 to 95/1
00, (II) / {(I) + (II) + (IV) + (V)} = 2 /
100 to 40/100, (IV) / (V) = 10/90 to 90/10, and at least one of the compounds of the general formula (III) is added to the mixture in a ratio of 2 to 34 weight. It is preferable to add it so that the content becomes%.

(Examples) Next, the present invention will be specifically described with reference to Examples.

Tables 1 to 5 below specifically show the phase transition temperatures of some of the compounds that can be used in the present invention at the time of heating. In the table, Cr is a crystal, Sc is a smectic C phase,
S _A is a smectic A phase, N is a nematic phase, S _X is a smectic X phase, Sc ^* is a chiral smectic C phase, Ch is a cholesteric phase, and I is a liquid.

Example 1 Liquid crystal composition A was prepared by mixing the following compounds No. out of the compounds exemplified in Table 1 above in the following proportions.

Further, the liquid crystal composition B was prepared by mixing the liquid crystal composition A with the following compounds No. out of the compounds exemplified in Table 2 at the following ratios.

Further, with respect to this liquid crystal composition B, among the compounds exemplified in Table 3 above, the following compound No. was mixed at the following ratio to prepare a liquid crystal composition C.

The phase transition temperatures of liquid crystal composition C are shown below.

Phase transition temperature (℃): As a result, it was confirmed that the Sc ^* phase was exhibited in a wide temperature range including room temperature.

Next, the liquid crystal composition C was injected into a cell having a thickness of 2 μm and made of glass with a transparent electrode, which was subjected to a rubbing treatment coated with polyimide, and an electric field was applied in the Sc ^* phase, and observed under a crossed Nicols polarization microscope. However, a clear switching operation was observed. Moreover, when a rectangular wave of 10 Vpp / μm was applied at 25 ° C and the change in the transmitted light amount at that time was observed with a photodiode, the time required for the transmitted light amount to change from 10% to 90% (t _10-90 ) Was as high as 33 μsec.

Example 2 A liquid crystal composition D was prepared by mixing, with the composition A shown in Example 1, the following compounds No. out of the compounds illustrated in the fourth and fifth examples at the following ratios.

Further, with respect to this liquid crystal composition D, among the compounds exemplified in Table 3 above, the following compound No. was mixed at the following ratio to prepare a liquid crystal composition E.

The phase transition temperatures of liquid crystal composition E are shown below.

Transition temperature (℃): As a result, Sc ^* phase was shown in a wide temperature range including room temperature.

The liquid crystal composition E was put into a cell in the same manner as in Example 1 and the time required for the change in the amount of transmitted light (t _10-90 ) was measured.

Example 3 A liquid crystal composition F was prepared by mixing the composition A shown in Example 1 with the compounds shown below in Tables 2, 4, and 5 at the following ratios. did.

Further, the liquid crystal composition G was prepared by mixing the liquid crystal composition F with the following compounds No. out of the compounds exemplified in Table 3 above.

The phase transition temperatures of liquid crystal composition G are shown below.

Phase transition temperature (℃): As a result, Sc ^* phase was shown in a wide temperature range including room temperature.

The liquid crystal composition G was put into the cell in the same manner as in Example 1 and the time required for the change in the amount of transmitted light (t _10-90 ) was measured. As a result, the speed was 24 μsec.

Comparative Example 1 Instead of the liquid crystal composition B used in Example 1, the compound (II-4) was not mixed with the liquid crystal composition A, but instead, the following exemplified compound (ii-1), (Ii-2), (ii-
3) and (ii-4) were mixed in the ratio shown below to prepare a liquid crystal composition b.

Further, with respect to this liquid crystal composition b, the following compounds No. out of the compounds exemplified in Table 3 above were mixed at the following ratio to prepare a liquid crystal composition c.

This liquid crystal composition c was put into a cell in the same manner as in Example 1 and the time required (t _10-90 ) for a change in the amount of transmitted light was measured and found to be 69 μsec. As a result, Example 1
It was found that the liquid crystal composition C of No. 1 had a faster response time and was preferable.

Comparative Example 2 Instead of the liquid crystal composition E used in Example 2, the exemplified compound (V-2) was not mixed with the liquid crystal composition A, but the compounds (III-1) and (IV-1) were used. , (IV-2) were mixed in the following proportions to prepare a liquid crystal composition e.

The liquid crystal composition e was put into a cell in the same manner as in Example 1 and the time required (t _10-90 ) for a change in the amount of transmitted light was measured and found to be 59 μsec. As a result, Example 2
It can be seen that the liquid crystal composition E of (1) has a faster response time and is preferable.

Comparative Example 3 Instead of the liquid crystal composition G used in Example 3, the compounds (IV-1), (IV-2), (V-
2), without mixing (II-4), the compound (III-
Liquid crystal composition g was prepared by mixing only 1) in the following proportions.

The phase transition temperature of this liquid crystal composition g is shown below.

Phase transition temperature (℃): As a result, the liquid crystal composition G of Example 3 has a wider temperature range of the chiral smectic C phase than the liquid crystal composition g, which is preferable.

(Effects of the Invention) As described above, the liquid crystal composition of the present invention has a sufficiently wide temperature range of the chiral smectic C phase and a high-speed response, and is excellent as a material for display devices and other optical switching elements. It is very useful and has the effect.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor ▲ Yoshi ▼ Sawa Atsushi 3-17-35, Nisoni, Toda City, Saitama Prefecture Japan Mining Co., Ltd. No. 35 in Japan Mining Co., Ltd. (56) Reference JP-A-3-151368 (JP, A)

Claims (4)

[Claims] 1. The following general formula (I): (Wherein R ₁ and R ₂ represent an alkyl group), and at least one compound represented by the following general formula (II): (In the formula, R ₃ and R ₄ are alkyl groups, X is a single bond or —O—
And at least one compound represented by the following general formula (III): (Wherein R ₅ and R ₆ are alkyl groups, C ^* is an asymmetric carbon in which optical activity is induced), and at least one compound represented by the formula Liquid crystal composition. 2. At least one compound represented by the general formula (I) described in claim 1, and at least one compound represented by the general formula (III) described in claim 1. One of the following general formula (IV), (Wherein, R ₇ and R ₈ represent an alkyl group), and at least one compound represented by the following general formula (V): A ferroelectric liquid crystal composition containing at least one compound represented by the formula (wherein R ₉ and R ₁₀ represent an alkyl group). 3. At least one of the compounds represented by the general formula (I) described in claim 1 and at least one of the compounds represented by the general formula (II) described in claim 1. One, at least one of the compounds represented by the general formula (III) described in claim 1, and at least one of the compounds represented by the general formula (IV) described in claim 2. A ferroelectric liquid crystal composition containing at least one of the compounds represented by formula (V) according to claim 2. 4. An optical switching element comprising the ferroelectric liquid crystal composition according to any one of claims 1 to 3 as a constituent element.