JP3458401B2 - Smectic A liquid crystal composition having electroclinical effect - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal composition, and more particularly to a smectic A liquid crystal composition having an electroclinic effect and an optical switching device using the composition.

[0002]

2. Description of the Related Art The electroclinic effect (hereinafter sometimes abbreviated as ECE) is first described in S. Garoff and R.G. B. Meye
studied by r. (Physical Revi
ewLetters 38 , 845 (1977),
And Physical Review A19 , 3
38 (see 1979)) The electroclinic effect is observed in the smectic phase parallel to the normal of the layer in the smectic liquid crystal phase exhibited by the chiral liquid crystal compound or the liquid crystal mixture containing the chiral compound. . Such a smectic phase is generally a smectic A phase. When an electric field is externally applied to such a smectic A phase, the director of the liquid crystal molecules tilts from the direction normal to the layer. This phenomenon is called the electroclinic effect. A liquid crystal element in which this electroclinic effect is applied to a display element is described in G. Anderson et al. (Appl. Phys. Lett.
51 , 640 (1987) and EP-0 263.
225)

Regarding the compounds in which ECE is found, Ni
shiyama et al. (Jap. J. Appl. Phy
s. 26 , 1787 (1987)) and C
h. Bahr and Heppke (Liq. Crys
t. 2 , 825 (1987)), and liquid crystal mixtures having ECE are disclosed in JP-A-64-9286 and JP-A-2-504433. However, almost none of these exhibit ECE at room temperature. For example, according to the description of Example 3 in JP-A-2-50433, although the ECE was obtained at room temperature, the tilt angle induced at 20 ° C. was such that the applied electric field was 5 V / μm.
When the electric field is 25 V / μm, it is 9 °. Since the inclination angle generally tends to be smaller as the temperature is higher, it is expected to be smaller at 25 ° C. A display element using ECE has an inclination angle of 45 ° under crossed Nicols.
When, the amount of transmitted light increases and the contrast is good. The tilt angle at room temperature needs to be at least 10 ° and is preferably 15 ° or more for use in a practical ECE mode display element.

[0004]

As described above, the first object of the present invention is to provide a smectic A liquid crystal composition exhibiting a smectic A phase at room temperature and having an inclination angle of 15 ° or more induced by application of an electric field. To provide things,
A second object is to provide an ECE type optical switching element with good contrast.

[0005]

The first object of the present invention is achieved by the following item (1). Aspects of the present invention are shown in the following items (2) to (4). The second object of the present invention is achieved by the second term (5). (1) contains the components A, B, C and D described below,
The mixing ratio of each component is 30 to 50% for the A component, 15 to 30% for the B component, and C for the total weight thereof.
A smectic A liquid crystal composition having an electroclinic effect, in which the component is 15 to 40%, the D component is 10 to 30%, and the tilt angle of liquid crystal molecules induced by application of an electric field is 15 ° or more at room temperature. However, the component A is at least one compound represented by the general formula (A), and the component B is the general formula (B).
Is at least one optically active compound represented by
The component is at least one optically active compound represented by the general formula (C), and the component D is at least one optically active compound represented by the general formula (D).

[0006]

[Chemical 5]

In the formula (I), R ¹ and R ² each independently represent an alkyl group having 1 to 18 carbon atoms, and R ³ and
R ⁵ and R ⁷ each independently represent an alkyl group or an alkoxy group having 1 to 18 carbon atoms, and R ⁴ , R ⁶ and R ⁸
Each independently represents an alkyl group having 2 to 18 carbon atoms or an alkoxy group having 1 to 18 carbon atoms, and a six-membered ring A or B
Represents 1,4-phenylene, pyridine-2,5-diyl or pyrimidine-2,5-diyl, X is a single bond,
-COO -, - OCO -, - OCH 2 - or -CH ₂ O
- indicates, Y and W independently represent H or F, Z represents a -CH ₃ or -CF _3, m is 0 or 1
Indicates.

(2) In the above item (1), the component B is at least one compound selected from the optically active compounds represented by the following general formula (BI) or (B-II). Smectic A liquid crystal composition.

[0009]

[Chemical 6]

In the formulas (BI) and (B-II),
R ³ and R ⁴ each have the above-mentioned meaning.

(3) The above item (1) or (2)
In the item, the smectic A liquid crystal composition, wherein the component C is at least one compound selected from the optically active compounds represented by the following general formula (C-I) or (C-II).

[0012]

[Chemical 7]

In the formulas (C-I) and (C-II),
R ⁵ and R ⁶ each have the above-mentioned meaning. (4) The smectic according to any one of the above items (1) to (3), wherein the component D is at least one compound selected from the optically active compounds represented by formula (DI). A liquid crystal composition.

[0014]

[Chemical 8]

In the formula (DI), R ⁷ and R ⁸ have the above-mentioned meanings. (5) An optical switching device comprising the smectic A liquid crystal composition according to any one of items (1) to (4).

The compound of the component A in the present invention is an achiral compound, and a compound showing a smectic A phase (hereinafter sometimes abbreviated as SA phase) in a relatively high temperature region is preferably used. The component A is a main component for developing the smectic A phase in the present invention. For example, the phase transition temperature of the compound (A-1) represented by the following formula is

[0017]

[Chemical 9] Cr 27 SC 67.5 SA 84.2 I, where I, SC and Cr mean an isotropic liquid phase, a smectic C phase and a crystalline phase, respectively, and the numbers indicate the Celsius temperature. The phase transition temperatures mentioned above and below are all values measured during the temperature rising process, unless otherwise specified in the present specification. Preferred examples of the component A include compounds of the formula (I) in which R ¹ is a linear alkyl group having 6 to 14 carbon atoms, and R ^{2 in} the formula is 7 to 15 carbon atoms.
Those which are straight chain alkyl of are preferred.

Compounds more preferable as the component A in the present invention are shown in Table 1.

[Table 1]

In the present invention, it is preferable to use at least two compounds as the component A, and it is more preferable to mix three or more compounds to form the component A because the melting point of the obtained composition is lowered. preferable. In the present invention, the mixing ratio of the component A is 30 to 50% based on the total weight of the components A, B, C and D. The ratio of A component is 30
If it is less than%, the temperature range of the obtained SA phase becomes extremely narrow, or the SA phase may develop in a region not containing room temperature, which is not suitable. When the content of the component A exceeds 50%, the mixing ratio of the chiral component in the obtained composition becomes relatively small, and the tilt angle may not be increased, which is not suitable. The mixing ratio of the component A is 30 to
It is more preferably 45%, further preferably 30-40%.

As the component B of the present invention, a compound in which the six-membered ring A is 1,4-phenylene, pyridine-2,5-diyl or pyrimidine-2,5-diyl in the formula (B) is preferable, and X is a single bond or -OCH ₂ - in which ones are preferred. Among these compounds, compounds of the formula (BI) or formula (B-II) in which R ³ is an alkyl group or an alkoxy group having 5 to 12 carbon atoms, and R ⁴ is 2 carbon atoms
Compounds having linear alkyl groups of 10 to 10 are preferred. In these formulas, compounds in which R ³ is a linear alkyl group having 6 to 8 carbon atoms and compounds in which R ⁴ is a linear alkyl group having 4 to 8 carbon atoms are preferably used as the B component. The compounds preferable as the component B are shown in Tables 2 and 3.

[0021]

[Table 2]

[0022]

[Table 3]

The mixing ratio of the component B in the present invention is 15 to 30%, more preferably 15 to 25%, based on the total weight of each component. When the mixing ratio of the B component is less than 15%, the SA phase region of the obtained composition may not be expanded to the temperature region including room temperature, which is not preferable. B
As shown in the examples below, many of the compounds of the component show the SA phase in a relatively high temperature range, but when this is combined with the component A, it works to lower the minimum temperature of the smectic A phase of the resulting mixture. It is a component that does.

[0024]

[Chemical 10] Cr 57 SH * 79.0 SCA * 99.2 SC * 94.0 SA 118.5 I where SH *, SCA * and SC * represent the antiferroelectric phase and chiral smectic C phase of the chiral smectic H phase and chiral smectic C phase, respectively Means the phase transition temperature according to the Celsius temperature.

Many of the C component compounds represented by the formula (C) have a SC * phase by themselves, and these compounds have a large spontaneous polarization in the SC * phase. Further, even if the compound of the formula (C) does not exhibit an SC * phase by itself, it is mixed with a compound or a mixture exhibiting a smectic C phase to give a chiral smectic C phase having a large spontaneous polarization. Is induced. That is, it can be said that the compound of the component C is a compound having a large spontaneous polarization either explicitly or potentially. As an example, the following compound (C-1) exhibits a large spontaneous polarization of 378 nC / cm ² at a temperature 10 ° C. lower than the upper limit of SC * phase.

[0026]

[Chemical 11] The phase transition temperature (° C) of this compound (C-1) is Cr 88 SC * 103.8 N * 112.8 I. Here, N * means a cholesteric phase.

In the present invention, the mixing ratio of the C component is A,
It is 15 to 40%, and more preferably 15 to 30%, based on the total weight of the B, C and D components. When the mixing ratio of the C component is less than 15%, the inclination angle of the obtained composition may not be the desired value, which is not preferable.
When the mixing ratio of the component C exceeds 40%, the SA phase temperature range of the obtained composition may be narrowed, which is not preferable.

The compound of the component C in the present invention is as follows:
In the formula (C), a compound in which R ⁵ is a linear alkyl group or alkoxy group having 3 to 12 carbon atoms is preferable, and
In the formula, R ⁶ is preferably a straight-chain alkyl or alkoxy group having 2 to 8 carbon atoms. Among these compounds, in the formula (C-I), R ⁵ has 3 to 10 carbon atoms.
A compound having a linear alkyl group of ⁶ or a compound having R ^{6 as} an alkoxy group having 2 to ⁶ carbon atoms, or a compound of the formula (C-I
A compound in which R ⁵ is an alkoxy group having 6 to 10 carbon atoms or a compound in which R ⁶ is an alkoxy group having 2 to ⁶ carbon atoms is more preferably used in I). Compounds preferable as the C component are exemplified in Tables 4 and 5.

[0029]

[Table 4]

[0030]

[Table 5]

In the present invention, in addition to the C component, the D component is also used as a component useful for increasing the tilt angle. As the compound of component D, a compound having the same potential or apparent direction of spontaneous polarization as that of the compound of component C is used. If the spontaneous polarization directions of the C component and the D component compounds are different from each other, the inclination angle of the obtained composition may not be increased, which is not preferable. As the D component, a compound of the formula (DI) in which W is F in the formula (D) is preferably used. These compounds have relatively low melting points as exemplified by the following compound (D-1), and when mixed with other components, they function to lower the melting point of the resulting composition.

[0032]

[Chemical 12]

A compound in which R ⁷ in the formula is a linear alkyl group or an alkoxy group having 3 to 12 carbon atoms is preferable, and R ^{8 in} the formula is a linear alkyl group having 2 to 10 carbon atoms. The compound of is preferably used. Among these compounds, a compound of the formula (DI) in which R ⁷ is a straight chain alkyl group having 6 to 10 carbon atoms, or R ⁸ is a straight chain alkyl group having 4 to ⁸ carbon atoms in the formula Certain compounds are more preferably used. Among these, preferred compounds are shown in Table 6.

[0034]

[Table 6]

In the present invention, the mixing ratio of the D component is A,
It is 10 to 30%, preferably 10 to 20%, based on the total weight of the B, C and D components. If the mixing ratio of the D component is less than 10%, the inclination angle of the obtained composition may not be increased, which is not preferable. The optical switching element of the present invention is the smectic A of the above item (1).
It is characterized by using a liquid crystal composition. This optical switching element has a feature that the contrast ratio can be increased since the director of liquid crystal molecules makes a large tilt angle at room temperature due to the electroclinic effect.

[0036]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. % In the following examples means weight percentage. The tilt angle (θ) in the examples was measured by applying an electric field to an object enclosed in a cell having a cell gap of 2 μm in which a liquid crystal composition was homogeneously aligned, and determining an extinction position under observation with a polarizing microscope. The other extinction position was found by reversing and determined from the angle (2θ) formed by these two extinction positions.

Example 1 A smectic A liquid crystal composition comprising the following compounds was prepared.

[0038]

[Chemical 13]

The phase transition temperature (° C.) of this composition was Cr-11 SA 76.1 I. In addition, this product is 25V / μm at 25 ℃
The tilt angle when the electric field was applied was 15.3 °.

Example 2 A smectic A liquid crystal composition having the following composition was prepared using the above compound. Compound (A-1) 18% by weight Compound (A-2) 14.5% by weight Compound (A-3) 5% by weight Compound (B-1) 17% by weight Compound (C-2) 23% by weight Compound (C -3) 7.5% by weight Compound (D-1) 15% by weight

The phase transition temperature (° C.) of this composition was Cr-6 SA 70.1 I. The tilt angle is 25 at an applied voltage of 25 V / μm.
It was 15.8 ° at 0 ° C.

Example 3 A smectic A liquid crystal composition having the following composition containing the following compound (B-2) and compound (E-1) was prepared.

[0043]

[Chemical 14]

18% by weight of compound (A-1) 14.5% by weight of compound (A-2) 5% by weight of compound (A-3) 17% by weight of compound (B-2) 15% by weight of compound (C-2) Compound (C-3) 7.5% by weight Compound (D-1) 15% by weight Compound (E-1) 8% by weight The phase transition temperature (° C) of this composition is Cr -4 SC * 20.3 SA 73. It was 0.5 I. The tilt angle when an electric field of 10 V / μm was applied to this product was 16.8 ° at 25 ° C.
It was 14.7 ° at 0 ° C.

Example 4 The liquid crystal composition prepared in Example 3 was provided with an ITO transparent electrode and had a set of substrates coated with polyimide and subjected to a homogeneous alignment treatment. The cell gap was 2 μm.
A liquid crystal element was prepared by enclosing the liquid crystal element in a cell. This liquid crystal cell exhibited a contrast ratio of 20: 1 at 25 ° C.

[0046]

As shown in the above examples, the smectic A liquid crystal composition of the present invention exhibits an electroclinic effect in a wide temperature range including room temperature, and the tilt angle induced by application of an electric field at room temperature. Is 15 ° or more. An optical switching device using this composition exhibits a high contrast ratio at room temperature.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C09K 19/00-19/46

Claims (5)

(57) [Claims] 1. The composition contains the components A, B, C and D described later, and the mixing ratio of each component is 30 to 50% of the component A and 15 to 30 of the component B with respect to the total weight thereof.
%, The C component is 15 to 40%, the D component is 10 to 30%, and the tilt angle of liquid crystal molecules induced by the application of an electric field is 15 ° or more at room temperature, and a smectic A liquid crystal having an electroclinic effect. Composition. However, the component A is at least one compound represented by the general formula (A), the component B is at least one optically active compound represented by the general formula (B), and the component C is the general formula (C). Is at least one optically active compound, and the D component is at least one optically active compound represented by the general formula (D). [Chemical 1] In formula (I), R ¹ and R ² each independently represent an alkyl group having 1 to 18 carbon atoms, and R ³ , R ⁵ and R ⁷
Each independently represents an alkyl group or an alkoxy group having 1 to 18 carbon atoms, R ⁴ , R ⁶ and R ⁸ each independently represent an alkyl group having 2 to 18 carbon atoms or an alkoxy group having 1 to 18 carbon atoms, Six-membered rings A and B represent 1,4-phenylene, pyridine-2,5-diyl or pyrimidine-2,5-diyl, and X is a single bond, -COO-,-.
OCO -, - OCH ₂ - or -CH ₂ O-are shown, Y and W each independently represents H or F, Z is -CH
₃ or indicates -CF _3, m is 0 or 1. 2. The smectic A liquid crystal composition according to claim 1, wherein the component B is at least one compound selected from the optically active compounds represented by the following general formulas (BI) or (B-II). . [Chemical 2] In formulas (BI) and (B-II), R ³ and R ⁴
Have the meanings described above. 3. The smectic according to claim 1 or 2, wherein the C component is at least one compound selected from the optically active compounds represented by the following general formula (C-I) or (C-II). A liquid crystal composition. [Chemical 3] In formulas (C-I) and (C-II), R ⁵ and R ⁶
Have the meanings described above. 4. The smectic A liquid crystal composition according to claim 1, wherein the component D is at least one compound selected from the optically active compounds represented by formula (DI). . [Chemical 4] In formula (D-I), R ⁷ and R ⁸ each have the above-mentioned meaning. 5. An optical switching device comprising the smectic A liquid crystal composition according to any one of claims 1 to 4.