JPH0680968A - Ferroelectric liquid crystal composition and optical switching element - Google Patents

Abstract

(57) [Summary] [Structure] The ferroelectric liquid crystal composition of the present invention comprises one or more compounds represented by the general formula [I] and one or more compounds represented by the general formula [II]. It contains one or more compounds represented by the general formula [III]. [Chemical 1] [Chemical 2] [Chemical 3] [R ₁ , R ₂ , R ₃ , R ₄ , 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.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can be in a stable ferroelectric liquid crystal state and is useful as a material for optoelectronic-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, liquid crystal compounds are applied as display materials in various devices and put to practical use in watches, calculators, small televisions and the like. For these, a nematic liquid crystal material is used 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 has a
Although it is considered to be the most advantageous in terms of cost and reliability, the number of scanning lines cannot be increased sufficiently when a liquid crystal having no bistability such as TN type or STN type liquid crystal is driven by a simple matrix driving method. There was a problem.

In order to improve such a drawback of the conventional liquid crystal device, a display system utilizing the optical switching phenomenon of a ferroelectric liquid crystal was proposed by NAClark and ST Lagerwall (Applied Phys. Lett., 1980, vol. , 36, p.89
9). 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 excellent feature that the optical response is faster than the order of μsec as compared with the conventional liquid crystal device.

In order to use these ferroelectric liquid crystal materials as actual device materials, some physical properties and characteristics are required. Among them, the basic ones are that they exhibit a chiral smectic C (S _C ^* ) phase in a wide temperature range including room temperature and that they have a high-speed response. 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.

[0005] strength to obtain a ferroelectric liquid crystal composition, the strength is not necessary to mix using only ferroelectric liquid crystal compounds, liquid crystal or liquid crystal mixture showing the a non-chiral compound smectic C (S _C) Phase (Called the base liquid crystal)
It can also be obtained by adding a chiral compound.

[0006]

However, a lot of researches have been conducted on both the base liquid crystal and the chiral compound up to now, and proposals have been made, but a ferroelectric liquid crystal composition having a sufficient high-speed response has been proposed. The current situation is that there is not yet.

The present inventors have found that the compound represented by the following general formula has large spontaneous polarization and is excellent in 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 it takes a ferroelectric liquid crystal phase, it cannot be put to practical use by itself.

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

On the other hand, the compound represented by the following general formula [I] is widely used as a base liquid crystal since the temperature range of the liquid crystal is on the low temperature side and the viscosity is low.

[Chemical 6] [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 the base liquid crystal composed of the 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 the ferroelectric liquid crystal phase can be taken is narrow. Further, in order to obtain 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 the phase (S _C ^* ) is desirable. However, in the system in which the above-mentioned optically active compound is added to the base liquid crystal composed of the compound represented by the general formula [I], the cholesteric phase disappears when the amount of the optically active compound added 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]

The present invention has the general formula [I]
A ferroelectric liquid crystal containing one or more compounds represented by, one or more compounds represented by general formula [II], and one or more compounds represented by general formula [III] It relates to the composition.

[Chemical 7] [In the general formula [I], R ₁ and R ₂ each represent an alkyl group].

[Chemical 8] [In the general formula [II], R ₃ and R ₄ each represent an alkyl group].

[Chemical 9] [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. ]

Further, the present invention is represented by one or more compounds represented by the general formula [I], one or more compounds represented by the general formula [II], and represented by the general formula [III]. The present invention relates to a ferroelectric liquid crystal composition, which comprises one or more compounds and one or more compounds represented by the general formula [IV].

[Chemical 10] [In the general formula [IV], R ₇ and R ₈ each represent an alkyl group. Z represents a single bond or an oxygen atom. ]

Furthermore, the present invention relates to an optical switching element characterized by including 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
Although the carbon number of the alkyl group represented by is not particularly limited, an alkyl group having 18 or less carbon atoms is preferable from the viewpoint of practical production such as availability of raw materials.

The compound represented by the above 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 by the following scheme.

[0016]

[Chemical 11]

Next, as the compound represented by the general formula [II], for example, an intermediate obtained by the synthetic method described in Japanese Patent Application No. 3-138682 is used, which is combined with 4-alkylbenzoic acid. It is obtained by condensing.

[0018]

[Chemical 12]

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

[0020]

[Chemical 13]

As described in the section [Problems to be Solved by the Invention], the inventor of the present invention provides a base liquid crystal containing at least one of the compounds represented by the general formula [I].
At least one of the compounds represented by the general formula [III] was added as a chiral dopant to prepare a ferroelectric liquid crystal composition. However, this composition has a high response speed, but is chiral smectic C only in a relatively narrow temperature range.
It was found that there is a problem that the liquid crystal phase of the phase is not exhibited and the cholesteric phase easily disappears.

[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
Shows the _A -S _C ^* phase sequence of, and was able to extend the temperature range of the high temperature zone side to take S _C ^* phase.

Therefore, the mixing ratios of these compounds must be selected so that such effects can be effectively exhibited. 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 70/30 to 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
] It is preferable that the addition amount of the compound represented by the following is from 2 to 34% by weight in order to more effectively achieve the above object.

Further, the present inventor further added to the base liquid crystal composed of one or more compounds represented by the general formula [I],
By mixing one or more compounds represented by the general formula [II] and one or more compounds represented by the general formula [IV], _ISO-
Indicates Ch -S _A -S _C ^* phase series of succeeded in extending the temperature range of the high temperature zone side and the low temperature range side take S _C ^* phase.

In this case, the proportion of each compound is preferably as follows. First, the base liquid crystal showing no smectic C phase without optical activity is composed of 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 this 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,
The content ratio of the compound represented by the general formula [III] is preferably 2 to 34% by weight in the entire liquid crystal composition.

[0026]

EXAMPLES Next, the present invention will be specifically described by way of 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 at the time of heating. 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 a smectic X phase, S _C ^* is a chiral smectic C
Phase, Ch is cholesteric phase and I is liquid.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

(Example 1) Of the compounds shown in Table 1,
35 parts by weight of compound No. (I-1), 10 parts by weight of compound No. (I-4), 25 parts by weight of compound No. (I-5), compound No. (I-7) To
A liquid crystal composition A was manufactured by mixing 30 parts by weight. Next, 90 parts by weight of this 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. To 85 parts by weight of the base liquid crystal composition B thus obtained,
15 parts by weight of 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 when the temperature is lowered is shown below.

[0032]

[Table 5] Thus, the liquid crystal composition of Example 1, 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 −22 nC / cm ² and tilt angle 31 °.

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

Example 2 The above base liquid crystal composition B was added.
15 parts by weight of compound No. (III-7) shown in Table 3 was mixed with 85 parts by weight to produce 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] Thus, the liquid crystal composition of Example 1, I → Ch → S _A
→ It was confirmed that the S _C ^* phase sequence was shown and that the S _C ^* phase was shown in a wide temperature range. The physical properties at 25 ° C. were spontaneous polarization −18 nC / cm ² and tilt angle 29 °. 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 (t _10-90 ) required for changing the amount of transmitted light from 10% to 90% was measured. As a result, it was as high as 33 μsec.

(Example 3) Further, the compound (IV-5) shown in Table 4 was added to 80 parts by weight of the liquid crystal composition B shown in Example 1.
Was mixed with 20 parts by weight to prepare a base liquid crystal composition E. Further, Table 3 shows the amount based on 85 parts by weight of the base liquid crystal composition E.
The ferroelectric liquid crystal composition F of Example 3 was manufactured by mixing 15 parts by weight of the compound (III-2) shown in (3). The phase transition temperatures of liquid crystal composition F are shown below.

[0037]

[Table 7] Thus, the liquid crystal composition of Example 1, 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 inclination angle of 29 degrees. In addition, by following the same procedure as described in Example 1 and injecting the liquid crystal composition F into the cell, the time (t _10-90 ) required for changing the transmitted light amount from 10% to 90% was measured. As a result, the speed was as high as 37 μsec.

Example 4 The compound No. (III-) shown in Table 3 was added to 85 parts by weight of the base liquid crystal composition E shown in Example 3.
The liquid crystal composition G of Example 4 was manufactured by mixing 15 parts by weight of 7). The phase transition temperatures of liquid crystal composition G are shown below.

[0039]

[Table 8] As described above, the liquid crystal composition of Example 4 had a composition of I → Ch → S _A.
→ It was confirmed that the S _C ^* phase sequence was shown and that the S _C ^* phase was shown in a wide temperature range. The physical properties at 25 ° C. were spontaneous polarization −19 nC / cm ² and tilt angle 27 °. In addition, 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 (t _10-90 ) required for the amount of transmitted light to change from 10% to 90% was measured.

Comparative Example 1 The compound No. (III-) shown in Table 3 was added to 85 parts by weight of the base liquid crystal composition A shown in Example 1.
15 parts by weight of 2) were mixed 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 exhibits a cholesteric phase unlike 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.
A liquid crystal composition H was manufactured by mixing 50 parts by weight of the compound No. (I-4) with 50 parts by weight. 40 parts by weight of this liquid crystal composition H, 20 parts by weight of compound No. (IV-1) shown in Table 4
A liquid crystal composition I was produced by mixing 20 parts by weight of No. (IV-6) and 20 parts by weight of compound No. (IV-7).

90 parts by weight of this liquid crystal composition I was mixed with 10 parts by weight of the compound No. (II-1) shown in Table 2 to prepare a liquid crystal composition J. Then, the base liquid crystal composition J
The 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 was I → Ch → S.
_A → S _C ^* of indicates phase series, and a wide temperature range S _C ^*
It was confirmed that the phases were shown. The physical properties at 25 ° C are
The spontaneous polarization was −7 nC / cm ² , and the tilt angle was 22 degrees. Also,
According to the same operation as described in Example 1, the liquid crystal composition K was injected into the cell, and the time (t _10-90 ) required for changing the transmitted light amount from 10% to 90% was measured. , 55 μsec
And was fast.

Example 6 Base liquid crystal composition L was prepared by mixing 8 parts by weight of compound No. (II-1) shown in Table 2 with 92 parts by weight of liquid crystal product I shown in Example 5. Was manufactured. Next, 89 parts by weight of this base liquid crystal composition L was used in Table 3
The liquid crystal composition M of Example 6 was obtained by mixing 11 parts by weight of the compound (III-8) shown in (3). The phase transition temperature of the liquid crystal composition M when the temperature is lowered is shown below.

[0046]

[Table 11] As described above, the liquid crystal composition M of Example 6 was I → Ch → S.
_A → S _C ^* of indicates phase series, and a wide temperature range S _C ^*
It was confirmed that the phases were shown. The physical properties at 25 ° C are
The spontaneous polarization was 13 nC / cm ² , and the tilt angle was 22 degrees. In addition, 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 (t _10-90 ) required for the transmitted light amount to change from 10% to 90% was measured, and it was as fast as 33 μsec.

(Example 7) Base liquid crystal composition L was prepared by mixing 8 parts by weight of compound No. (II-1) shown in Table 2 with 92 parts by weight of liquid crystal product I shown in Example 5. Was manufactured. Then, the base liquid crystal composition L was added to 92 parts by weight of Table 3.
4 parts by weight of compound (III-2) and 4 parts of compound (III-8)
The liquid crystal composition N of Example 7 was manufactured by mixing with a weight part. 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 has a composition of I → Ch → S.
_A → S _C ^* of indicates phase series, and a wide temperature range S _C ^*
It was confirmed that the phases were shown. 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 Example 1, the liquid crystal composition N was injected into the cell, and the time (t _10-90 ) required for changing the transmitted light amount from 10% to 90% was measured. , 48 μsec
And was fast.

[0049]

As described above, the ferroelectric liquid crystal composition of the present invention exhibits a phase sequence of liquid phase-cholesteric phase-smectic A phase-chiral smectic C phase and temperature at which 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 and extremely effective as a material for optical switching elements such as display devices, optical printer heads and light valves.

[Procedure amendment]

[Submission date] October 15, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029]

[Table 3]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

[0035]

[Table 6] Thus, the liquid crystal composition of Example 2, I → Ch → S _A
→ It was confirmed that the S _C ^* phase sequence was shown and that the S _C ^* phase was shown in a wide temperature range. The physical properties at 25 ° C. were spontaneous polarization −18 nC / cm ² and tilt angle 29 °. 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 (t _10-90 ) required for changing the amount of transmitted light from 10% to 90% was measured. As a result, it was as high as 33 μsec.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

[0037]

[Table 7] Thus, the liquid crystal composition of Example 3, 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 inclination angle of 29 degrees. In addition, by following the same procedure as described in Example 1 and injecting the liquid crystal composition F into the cell, the time (t _10-90 ) required for changing the transmitted light amount from 10% to 90% was measured. As a result, the speed was as high as 37 μsec.

Front Page Continuation (72) Inventor Toshihiro Hirai 3-17-35, Niizominami, Toda City, Saitama Prefecture Japan Mining Co., Ltd.

Claims (4)

[Claims] 1. One or more compounds represented by general formula [I], and one or more compounds represented by general formula [II],
A ferroelectric liquid crystal composition comprising one or more compounds represented by the general formula [III]. [Chemical 1] [In the general formula [I], R ₁ and R ₂ each represent an alkyl group. ] [Chemical 2] [In the general formula [II], R ₃ and R ₄ each represent an alkyl group. ] [Chemical 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 constituent element. 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, which further comprises one or more compounds represented by the general formula [IV]. [Chemical 4] [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.