JP3078664B2 - Ferroelectric liquid crystal composition and optical switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can provide a stable ferroelectric liquid crystal state, and is useful as a material for optoelectronics-related elements used for displays such as liquid crystal televisions, optical printer heads and light valves. , A liquid crystal composition and an optical switching element.

[0002]

2. Description of the Related Art At present, a liquid crystal compound is applied as a display material in various devices and has been put to practical use in watches, calculators, small televisions and the like. These use a nematic liquid crystal material as a main component and adopt a display method called a TN type or STN type. 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 several milliseconds. On the other hand, the simple matrix drive method requires productivity,
Although it is considered to be the most advantageous in terms of cost and reliability, when a liquid crystal having no bistability such as a TN type or STN type liquid crystal is driven by a simple matrix driving method, the number of scanning lines cannot be sufficiently increased. There was a problem.

As a solution to the drawbacks of such conventional liquid crystal devices, a display system utilizing the optical switching phenomenon of ferroelectric liquid crystal has been proposed by NAClark and STLagerwall (Applied Phys. Lett., 1980, vol. , 36, p.89
9). The existence of a ferroelectric liquid crystal was first reported by RBMeyer et al. In 1975. An element using a ferroelectric liquid crystal has bistability, and has an excellent feature that an optical response is faster, on the order of μsec, than a conventional liquid crystal element.

In order to use these ferroelectric liquid crystal materials as actual device materials, several physical properties and characteristics are required. Among them, basic ones are to exhibit a chiral smectic C (S _C ^* ) phase in a wide temperature range including room temperature, and to provide a high-speed response. Many other physical properties and properties are required for ferroelectric liquid crystal materials, but at present, these properties and properties cannot be met by a single compound, and some 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, but it is necessary to use a non-chiral compound which exhibits a smectic C (S _C ) phase or a liquid crystal mixture. (Called base liquid crystal)
It can also be obtained by adding a chiral compound.

[0006]

However, a number of studies have been made on both the base liquid crystal and the chiral compound and proposals have been made so far. However, a ferroelectric liquid crystal composition having a sufficient high-speed response has been proposed. It is not yet.

The present inventors have found that a compound represented by the following general formula has a large spontaneous polarization and excellent high-speed response, and has proposed a ferroelectric liquid crystal composition containing this compound. (JP-A-3-151368). However, since this compound has a high temperature range in which the compound takes a ferroelectric liquid crystal phase, this compound alone cannot be put to practical use.

Embedded image [R ₅ and R ₆ each represent an alkyl group. C
^* Represents an asymmetric carbon atom. ]

On the other hand, compounds represented by the following general formula [I] are widely used as base liquid crystals because the temperature range of liquid crystals is on the low temperature side and the viscosity is low.

Embedded image [In the general formula [I], R ₁ and R ₂ each represent an alkyl group. ]

Therefore, the above-mentioned optically active compound is added to a base liquid crystal comprising a compound represented by the general formula [I],
A liquid crystal composition was manufactured. However, it has been found that there is a problem that the temperature range in which a ferroelectric liquid crystal phase can be obtained is narrow. In order to obtain a good orientation in the chiral smectic C phase (S _C ^* ), the liquid phase (I _SO ) -cholesteric phase (C
h) -Smectic A phase (S _A ) -Chiral smectic C
A liquid crystal composition having a phase sequence of phases (S _C ^* ) is desirable. However, in a system in which the above-mentioned optically active compound is added to a base liquid crystal composed of the compound represented by the general formula [I], the cholesteric phase disappears when the added amount of the optically active compound is increased to a practical level. There was found.

It is an object of the present invention, I _SO -Ch -S _A -S _C
^* Indicates phase sequence of a wide temperature range showing the S _C ^* phase, and to provide a ferroelectric liquid crystal composition having high-speed response.

[0011]

According to the present invention, there is provided a compound represented by the general formula [I]:
A ferroelectric liquid crystal comprising at least one compound represented by the general formula [II], and at least one compound represented by the general formula [III] It relates to the composition.

Embedded image [In the general formula [I], R ₁ and R ₂ each represent an alkyl group.]

Embedded image [In the general formula [II], R ₃ and R ₄ each represent an alkyl group.]

Embedded image [In the general formula [III], R ₅ and R ₆ each represent an alkyl group. X represents a single bond or an oxygen atom.
Y represents a hydrogen atom or a fluorine atom, and C ^* represents an asymmetric carbon atom. ]

The present invention also relates to a compound represented by the general formula [I], one or more compounds represented by the general formula [II], and a compound represented by the general formula [III]: The present invention relates to a ferroelectric liquid crystal composition containing at least one compound and at least one compound represented by the general formula [IV].

Embedded image [In the general formula [IV], R ₇ and R ₈ each represent an alkyl group. Z represents a single bond or an oxygen atom. ]

Further, the present invention relates to an optical switching element comprising any one of the above ferroelectric liquid crystal compositions as a constituent element.

In the above general formulas [I] to [IV], R _{1 to} R ₈
The carbon number of the alkyl group represented by is not particularly limited, but from the viewpoint of practical production such as availability of raw materials, an alkyl group having 18 or less carbon atoms is preferable.

The compound represented by the general formula [I] is H.
Zaschke's method (Journal of.Prakt.Chem. 317, 617 (19
According to 75)), it can be synthesized from a commercially available reagent in the following scheme.

[0016]

Embedded image

Next, as the compound represented by the general formula [II], for example, an intermediate obtained by a synthesis method described in Japanese Patent Application No. Hei 3-138682 is used, and this compound is combined with a 4-alkylbenzoic acid. By condensation.

[0018]

Embedded image

The compound represented by the general formula [III] is
For example, JP-A-3-151368 and Japanese Patent Application No. 3-080
No. 641. In order to obtain the compound represented by the general formula [IV], for example, the following intermediate is synthesized according to the above-described synthesis scheme of the compound of the general formula [I], and the intermediate is subjected to a condensation reaction with a carboxylic acid to form an ester. Become

[0020]

Embedded image

As described in the section of [Problems to be Solved by the Invention], the present inventor has proposed that a base liquid crystal comprising at least one of the compounds represented by the general formula [I]
A ferroelectric liquid crystal composition was prepared by adding at least one compound represented by the general formula [III] as a chiral dopant. However, this composition has a high response speed but has a chiral smectic C over a relatively narrow temperature range.
It was found that there was a problem that no liquid crystal phase was exhibited and that the cholesteric phase was easily lost.

[0022] The present inventors have further advanced the research, by adding a compound of formula (II) in the above composition, without degrading the response speed of the composition, I _SO -Ch -S
_It showed the _A- S _C ^* phase sequence and succeeded in expanding the temperature range on the high temperature side where the S _C ^* phase is taken.

Therefore, it is necessary to select the mixing ratio of these compounds so that such an effect can be exhibited effectively. First, in the base liquid crystal, the weight of the compound of the general formula [I] / the weight of the compound of the general formula [II] is calculated as 70 / 30-98.
It is preferable to set the ratio to / 2. One or more compounds represented by the general formula [III] are added to the base liquid crystal. For the entire liquid crystal composition, the general formula [III
The amount of the compound represented by the formula (1) is preferably from 2 to 34% by weight in order to more effectively achieve the above object.

Further, the present inventors further provided a base liquid crystal comprising one or more compounds represented by the general formula [I],
By mixing one or more compounds represented by least one compound represented by the general formula [II] and formula [IV], without degrading the response speed of the composition, I _SO -
It shows the phase sequence of Ch-S _A -S _C ^* , and succeeded in expanding the temperature range on the high temperature side and the low temperature side, which take the S _C ^* phase.

In this case, the ratio of each compound is preferably as follows. First, it is assumed that the base liquid crystal having no optical activity and exhibiting a smectic C phase is composed of the compounds represented by the general formulas [I], [II] and [IV], and the total weight thereof is 100 parts by weight. . In 100 parts by weight of the base liquid crystal, the content of the compound represented by the general formula [I] is preferably 20 to 95 parts by weight,
The content of the compound represented by the general formula [II] is preferably 2 to 30 parts by weight, and the content of the compound represented by the general formula [IV] is preferably 2 to 80 parts by weight. Also,
It is preferable that the content of the compound represented by the general formula [III] is 2 to 34% by weight in the whole liquid crystal composition.

[0026]

Next, the present invention will be described in detail with reference to examples. Tables 1 to 4 below specifically show the phase transition temperatures of some of the compounds that can be used in the present invention when the temperature is raised. In the table, _Cr is a crystal, S _C is a smectic C phase, S _A is a smectic A phase, N is a nematic phase, S
_X is smectic X phase, S _C ^* is chiral smectic C
Phase, cholesteric phase, I, liquid.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

Example 1 Among the compounds shown in Table 1,
Compound No. (I-1) 35 parts by weight, Compound No. (I-4) 10 parts by weight, Compound No. (I-5) 25 parts by weight, Compound No. (I-7) To
The mixture was mixed with 30 parts by weight to produce a liquid crystal composition A. Next, 90 parts by weight of the liquid crystal composition A and 10 parts by weight of the compound No. (II-1) shown in Table 2 were mixed to obtain a liquid crystal composition B. Based on 85 parts by weight of the base liquid crystal composition B thus obtained,
15 parts by weight of the compound No. (III-2) shown in Table 3 was mixed to obtain a liquid crystal composition C of Example 1 of the present invention. The phase transition temperature (° C.) of the liquid crystal composition C of Example 1 at the time of cooling is shown below.

[0032]

[Table 5] As described above, the liquid crystal composition of Example 1 has I-Ch-S _A
It indicates -S _C ^* phase sequence of, and in a wide temperature range was confirmed to exhibit S _C ^* phase. The physical properties at 25 ° C. were spontaneous polarization of −22 nC / cm ² and an inclination angle of 31 degrees.

Next, the liquid crystal composition C was injected into a 2 μm thick cell made of rubbed glass with a transparent electrode coated with polyimide, and an electric field was applied in the S _C ^* phase. When observed below, a clear switching operation was observed. 10 Vpp / μ at 25 ° C
When a square wave of m was applied and the change in the amount of transmitted light at that time was observed with a photodiode, the amount of transmitted light was 10% to 90%.
The time required to change to (t _10-90 ) was as fast as 51 μsec.

Example 2 The above base liquid crystal composition B was
15 parts by weight of the compound No. (III-7) shown in Table 3 was mixed with 85 parts by weight to prepare a liquid crystal composition D of Example 2. The phase transition temperature (° C.) of the liquid crystal composition D when the temperature is lowered is shown below.

[0035]

[Table 6] As described above, the liquid crystal composition of Example 2 was obtained from I → Ch → S _A
→ indicates the S _C ^* phase sequence of, and in a wide temperature range was confirmed to exhibit S _C ^* phase. The physical properties at 25 ° C. were spontaneous polarization of −18 nC / cm ² and a tilt angle of 29 degrees. Further, according to the same operation as described in the section of Example 1, the liquid crystal composition D
Was injected into the cell, and the time required for the amount of transmitted light to change from 10% to 90% (t _10-90 ) was measured.

Example 3 The compound (IV-5) shown in Table 4 was used with respect to 80 parts by weight of the liquid crystal composition B shown in Example 1.
Was mixed in an amount of 20 parts by weight to produce a base liquid crystal composition E. Further, based on 85 parts by weight of the base liquid crystal composition E,
Was mixed with 15 parts by weight of the compound (III-2) shown in (1) to produce a ferroelectric liquid crystal composition F of Example 3. The phase transition temperature of the liquid crystal composition F is shown below.

[0037]

[Table 7] Thus, the liquid crystal composition of Example 3 is I-Ch-S _A
It indicates -S _C ^* phase sequence of, and in a wide temperature range was confirmed to exhibit S _C ^* phase. Physical properties at 25 ° C. were spontaneous polarization of −22 nC / cm ² and an inclination angle of 29 °. Further, in accordance with the same operation as described in the section of Example 1, the liquid crystal composition F was injected into the cell, and the time (t _10-90 ) required for the amount of transmitted light to change from 10% to 90% was measured. As a result, the speed was as fast as 37 μsec.

Example 4 Compound No. (III-III) shown in Table 3 was added to 85 parts by weight of the base liquid crystal composition E shown in Example 3.
7) was mixed in an amount of 15 parts by weight to produce a liquid crystal composition G of Example 4. The phase transition temperature of the liquid crystal composition G is shown below.

[0039]

[Table 8] As described above, the liquid crystal composition of Example 4 was obtained from I → Ch → S _A
→ indicates the S _C ^* phase sequence of, and in a wide temperature range was confirmed to exhibit S _C ^* phase. The physical properties at 25 ° C. were spontaneous polarization of −19 nC / cm ² and a tilt angle of 27 degrees. Further, according to the same operation as described in the section of Example 1, the liquid crystal composition G
Was injected into the cell, and the time required for the amount of transmitted light to change from 10% to 90% (t _10-90 ) was measured.

(Comparative Example 1) Compound No. (III-II) shown in Table 3 was added to 85 parts by weight of the base liquid crystal composition A shown in Example 1.
2) was mixed by 15 parts by weight to obtain a liquid crystal composition a of Example 1.
The phase transition temperature (° C.) of this liquid crystal composition a is shown below.

[0041]

[Table 9] As can be seen from the above results, each of the liquid crystal compositions of Examples 1 to 4 of the present invention shows a cholesteric phase different from the liquid crystal composition a, and has a wider temperature range of the S _C ^* phase than the liquid crystal composition a. And has excellent characteristics.

Example 5 Compound No. (I-3) shown in Table 1 was used
50 parts by weight of Compound No. (I-4) and 50 parts by weight of Compound No. (I-4) were mixed to produce a liquid crystal composition H. 40 parts by weight of the liquid crystal composition H, 20 parts by weight of the compound No. (IV-1) shown in Table 4,
20 parts by weight of No. (IV-6) and 20 parts by weight of compound No. (IV-7) were mixed to produce a liquid crystal composition I.

A liquid crystal composition J was produced by mixing 90 parts by weight of the liquid crystal composition I and 10 parts by weight of the compound No. (II-1) shown in Table 2. Next, this base liquid crystal composition J
A liquid crystal composition K of Example 5 was obtained by mixing 7 parts by weight of the compound (III-7) shown in Table 3 with 93 parts by weight. The phase transition temperature of the liquid crystal composition K when the temperature is lowered is shown below.

[0044]

[Table 10] As described above, the liquid crystal composition K of Example 5 has I → Ch → S
_A → S _C ^* of indicates phase series, and a wide temperature range S _C ^*
Phase. The physical properties at 25 ° C are
The spontaneous polarization was −7 nC / cm ² and the tilt angle was 22 degrees. Also,
In accordance with the same operation as described in the section of Example 1, the liquid crystal composition K was injected into the cell, and the time (t _10-90 ) required for the amount of transmitted light to change from 10% to 90% was measured. , 55μsec
And was fast.

Example 6 92 parts by weight of the liquid crystal product I shown in Example 5 and 8 parts by weight of the compound No. (II-1) shown in Table 2 were mixed. Was manufactured. Next, based on 89 parts by weight of the base liquid crystal composition L, Table 3
11 parts by weight of the compound (III-8) shown in the following was mixed to obtain a liquid crystal composition M of Example 6. The phase transition temperature of the liquid crystal composition M when the temperature is lowered is shown below.

[0046]

[Table 11] Thus, the liquid crystal composition M of Example 6 has I → Ch → S
_A → S _C ^* of indicates phase series, and a wide temperature range S _C ^*
Phase. The physical properties at 25 ° C are
The spontaneous polarization was 13 nC / cm ² and the tilt angle was 22 degrees. Further, according to the same operation as described in the section of Example 1, the liquid crystal composition M
Was injected into the cell, and the time required for the amount of transmitted light to change from 10% to 90% (t _10-90 ) was measured. The result was a high speed of 33 μsec.

Example 7 92 parts by weight of the liquid crystal product I shown in Example 5 and 8 parts by weight of the compound No. (II-1) shown in Table 2 were mixed. Was manufactured. Then, 92 parts by weight of the base liquid crystal composition L was added to Table 3
4 parts by weight of compound (III-2) and 4 parts of compound (III-8)
And the liquid crystal composition N of Example 7 was manufactured. The phase transition temperature of the liquid crystal composition N when the temperature is lowered is shown below.

[0048]

[Table 12] As described above, the liquid crystal composition N of Example 7 was obtained from I → Ch → S
_A → S _C ^* of indicates phase series, and a wide temperature range S _C ^*
Phase. The physical properties at 25 ° C are
The spontaneous polarization was −7 nC / cm ² and the tilt angle was 21 degrees. Also,
According to the same operation as described in the section of Example 1, the liquid crystal composition N was injected into the cell, and the time (t _10-90 ) required for the amount of transmitted light to change from 10% to 90% was measured. , 48μsec
And was fast.

[0049]

As described above, the ferroelectric liquid crystal composition of the present invention exhibits a liquid crystal-cholesteric phase-smectic A phase-chiral smectic C phase sequence and a temperature at which the chiral smectic C phase is exhibited. It has a wide range and high-speed response. Therefore, the ferroelectric liquid crystal composition of the present invention is excellent as a material for an optical switching element such as a display device, an optical printer head, and a light valve, and is very effective.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshihiro Hirai 3-17-3 Nishinaminami, Toda City, Saitama Prefecture Inside Japan Mining Co., Ltd. (56) References JP 4-25591 (JP, A) JP JP-A-3-151368 (JP, A) JP-A-4-89455 (JP, A) JP-A-2-272091 (JP, A) JP-A-4-290875 (JP, A) JP-A-5-320140 (JP) JP-A-5-112779 (JP, A) JP-A-5-320649 (JP, A) JP-T-62-502901 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) C09K 19/34

Claims (4)

(57) [Claims] (1) one or more compounds represented by the general formula (I) and one or more compounds represented by the general formula (II):
A ferroelectric liquid crystal composition comprising at least one compound represented by the general formula [III]. Embedded image [In the general formula [I], R ₁ and R ₂ each represent an alkyl group. [Chemical formula 2] [In the general formula [II], R ₃ and R ₄ each represent an alkyl group. [Chemical formula 3] [In the general formula [III], R ₅ and R ₆ each represent an alkyl group. X represents a single bond or an oxygen atom.
Y represents a hydrogen atom or a fluorine atom. C ^* represents an asymmetric carbon atom. ] 2. An optical switching element comprising the ferroelectric liquid crystal composition according to claim 1 as a component. 3. One or more compounds represented by the general formula [I], one or more compounds represented by the general formula [II], and one or more compounds represented by the general formula [III] 2. The ferroelectric liquid crystal composition according to claim 1, wherein the ferroelectric liquid crystal composition comprises: and a compound represented by the general formula [IV]. Embedded image [In the general formula [IV], R ₇ and R ₈ each represent an alkyl group. Z represents a single bond or an oxygen atom. ] 4. An optical switching element comprising the ferroelectric liquid crystal composition according to claim 3 as a constituent element.