JP3111610B2 - Ferroelectric liquid crystal composition and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal composition, and more particularly to a composition in which the sign of spontaneous polarization changes with temperature. The present invention further relates to a liquid crystal device constituted by using the liquid crystal composition.

[0002]

2. Description of the Related Art At present, a twisted nematic (TN) display system most widely used as a liquid crystal display device has many advantages such as low driving voltage and low power consumption. However, regarding the response speed,
It is significantly inferior to light-emitting display devices such as cathode ray tubes, electroluminescence, and plasma. The twist angle of the Super Twisted Nematic (STN) type is 180
The display method of -270 ° is also inferior in response speed. A display device using a ferroelectric liquid crystal has been proposed by Clark and the like as a display system that enables a significant improvement in response speed. Applications other than display using this ferroelectric liquid crystal have been attempted. These are, for example, harmonic generation elements, optical memories, optical amplifiers, and heat, light,
The possibility of sensors for temperature, pressure, etc. A compound in which the sign of spontaneous polarization (hereinafter abbreviated as Ps) changes with temperature among ferroelectric liquid crystals has been known so far. (Japanese, Journal, Ob, Applied, Physics (Jpn. J. Appl. Phys.
s. 25, L833 (1986) and Philosophy, Magazine, Letters.
cal Magazine Letters), 55 volumes,
283 (1987)).

The sign of the spontaneous polarization of this compound changes stepwise with temperature. This can be used for switching or sensing. However, the compounds reported earlier are insufficient for sensor applications in the following respects. (1) Since the region from room temperature to the temperature at which the sign of spontaneous polarization changes is not sufficiently wide, the temperature region that can be used as a sensor is narrow. (2) Since the reported temperature at which the sign of Ps of the compound changes (hereinafter abbreviated as Tps) is only about 25 ° C., Tps is set to a higher temperature range depending on the purpose of use. It is difficult to obtain a liquid crystal composition. (3) Since the value of Ps of the compound is small (about 3 nC / cm ² ), the response to sensing is not sufficient.

[0004]

As apparent from the above, the object of the present invention is to increase the absolute value of Ps,
Is to provide a liquid crystal composition having a temperature at which the sign changes.

[0005]

According to the present invention, there is provided a ferroelectric liquid crystal compound comprising at least one ferroelectric liquid crystal compound represented by the following general formula (I), wherein the content thereof is 60 to 100% by weight of the composition. A liquid crystal composition and a liquid crystal device using the composition.

[0006]

Embedded image

In the formula (I), R ¹ has 4 to 16 carbon atoms.
R ² represents an alkyl group having 2 to 12 carbon atoms, and * represents an incorrect carbon atom. As the compound of the formula (I) used in the composition of the present invention, R ^{1 in} the formula is 6
Preferably those which are over 12, also R ² is those preferably 4 -10. Further, compounds wherein R ² in the formula is 6-8 are more preferred. Table 1 shows the phase transition temperature and the temperature at which the sign of the spontaneous polarization changes of typical compounds among the compounds of the formula (I) used in the present invention.

[0008]

[Table 1]

In Table 1, the numerals represent the phase transition temperature and the temperature at which the sign of the spontaneous polarization changes (Tps) in degrees Celsius. C, Smectic A and isotropic liquid phase respectively. The symbol means that the phase abbreviated thereon is present, and the number in parentheses means that the phase transition is monomodal. In the composition of the present invention, the content of the compound represented by the formula (I) is 60-10% by weight of the composition.
0%, and more preferably 80-100%. If the proportion of the compound of the formula (I) contained is less than 60%, the phenomenon that the sign of spontaneous polarization changes is not observed, which is not preferable. Compounds of formula (I) have already been disclosed in
3-190842. Among the compounds disclosed therein, a phenomenon in which the sign of the spontaneous polarization is reversed is not observed in the compound of the formula (I) wherein R ¹ is an alkoxy group,
The phenomenon that the sign of Ps is inverted is limited only to the compound of the formula (I) wherein R ¹ is an alkyl group. In the present invention, in addition to the compound of the formula (I), compounds represented by the following formulas can be used as long as the object of the present invention is not impaired.

[0010]

Embedded image

In these formulas, R and R 'each independently represent an alkyl group having 4 to 20 carbon atoms. Among these compounds, compounds represented by the following formulas (II) and (III) are preferably used.

[0012]

Embedded image

In the formula (II), R ³ and R ⁴ each independently represent an alkyl group or an alkoxy group having 6-16 carbon atoms, and in the formula (III), R ⁵ represents an alkyl group or an alkoxy group having 5-12 carbon atoms. R ⁶ is a group having 4-12 carbon atoms
Represents an alkyl group or an alkoxy group, respectively.
The compounds of formulas (II) and (III) have a smectic C
Many of the compounds exhibit a phase over a wide temperature range. These compounds are useful because a chiral smectic phase exhibiting ferroelectricity can be realized in a wide temperature range. The composition of the present invention has a high Tp by containing a compound of the formula (I) having a high Tps.
s is realized. The ferroelectric liquid crystal composition of the present invention has a Tp
In the temperature range higher than s, the sign of Ps is negative, and in the temperature range lower than Tps, the sign of Ps is positive. Where Ps
Is S. T. (Molecular Crystal and Liquid Crystal (Mol. Cryst. Liq. Crys)
t. 114, 151-187 (1984)). When such a liquid crystal composition is oriented in a liquid crystal phase exhibiting ferroelectricity (for example, a chiral smectic C phase) to form a ferroelectric liquid crystal cell, and when an electric field in a certain direction is applied to the cell, a high temperature side of Tps is obtained. On the low temperature side, the tilt direction of the liquid crystal molecules changes. The director of this liquid crystal molecule is Tp
By applying the fact that the optical response of the liquid crystal cell is changed by inverting above and below s, it is possible to perform sensing using Tps as the temperature to be detected. Further, since many of the compositions of the present invention are relatively stable even in a supercooled state, like ordinary liquid crystal compositions, they can be used as a material for a sensor that covers a wide temperature range on the low temperature side of Tps. it can.

The device according to the invention has a ferroelectricity with temperature,
It utilizes the change in properties during non-ferroelectricity. The liquid crystal composition of the present invention has a helical pitch in a ferroelectric state,
Physical properties such as spontaneous polarization exist, but in a non-ferroelectric state (when the temperature is Tps), the liquid crystal becomes a normal smectic liquid crystal, and no physical properties such as helical pitch and spontaneous polarization exist. Thus, a device utilizing the characteristics of the helical pitch can be configured. That is, in the ferroelectric liquid crystal state, the light is selectively reflected due to the spiral, and the reflected light is colored.
However, in the non-ferroelectric liquid crystal state, since no spiral is wound, selective reflection does not occur, and the liquid crystal is simply clouded. The temperature can be sensed by utilizing the difference in the scattered light. For example, when this is applied to an element, a temperature sensor corresponding to Tps of the composition can be obtained. When, for example, an AC electric field is applied to the composition of the present invention, an element utilizing spontaneous polarization can be formed. For example, in the ferroelectric state, switching according to the AC electric field occurs, but in the non-ferroelectric state, no switching occurs because spontaneous polarization does not exist. Therefore, it is possible to configure a temperature control mechanism using this.

Depending on the arrangement of the polarizer and the analyzer used in these elements, ON-OFF, ON-OFF,
-OFF-ON, OFF-ON, OFF-ON-OFF
It is possible to configure a temperature control element having a combination of the above. By using the composition of the present invention, an element having small temperature dependence of response speed can be formed. The small temperature dependence is more remarkable in a device using a composition in which components other than the compound of the formula (I) are mixed with a compound of the formula (I), as compared with a device using a composition including only a plurality of the compounds of the formula (I). is there.

[0016]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Various physical property values in the examples were measured by the following methods. Phase transition temperature: Determined by observation under a polarizing microscope equipped with a hot stage for temperature control. In the following examples, the phase transition temperature (° C.) is described between the abbreviations representing the phases. The symbols Cr, SC *, SA, and I mean the crystal, chiral smectic C, smectic A, and isotropic liquid phases, respectively. Spontaneous polarization (Ps): The magnitude of the spontaneous polarization is determined by the Sawyer-Tower method, and its sign is S.E. T. It was determined according to the definition of Lagall. Tilt angle (θ): The extinction position when the helical structure of the liquid crystal is eliminated by applying a voltage sufficiently higher than the critical voltage to the homogeneously aligned liquid crystal cell is obtained under orthogonal Nicols, and the polarity of the applied voltage is determined. The extinction position at the time of inversion was determined, and determined from the angle between the two extinction positions (corresponding to 2θ). Temperature at which the sign of spontaneous polarization changes (Tps): The temperature at which the value of Ps obtained by the Sawyer tower method becomes zero is obtained.

Example 1 A compound represented by the formula (I), a compound represented by the formula (II), a compound represented by the formula (III) and a compound represented by the formula (III):
The following ferroelectric composition comprising the compound was prepared.

[0018]

Embedded image

Embedded image

The phase transition temperature of this ferroelectric composition is Cr 10.6 SC * 52.0 SA 81.1
I. Table 2 shows the temperature dependence of the spontaneous polarization and the tilt angle. In Table 2 and in Tables 3-5 below,
Tc means the upper limit temperature of the SC * phase, and T means the measured temperature. The Tps of this composition was 35.1 ° C.
Met.

Example 2 The following ferroelectric liquid crystal composition comprising four compounds of the general formula (I), one compound of the general formula (II) and four compounds of the general formula (III) has a phase transition temperature Cr 15.1 SC * 53.5 SA 84.7
I was indicated. Table 3 shows the temperature dependence of Ps and the tilt angle. The temperature at which the sign of Ps of this composition changes is 30.7 ° C.
Met.

[0021]

Embedded image

Example 3 A ferroelectric liquid crystal composition described below comprising five compounds of the formula (I) and four compounds of the formula (II) was prepared. Its phase transition temperature is Cr 13.3 SC * 53.3 SA 82.2.
I. Table 4 shows the temperature dependence of Ps and the tilt angle. The Tps of this composition was 25.5 ° C.

[0023]

Embedded image

Example 4 A ferroelectric liquid crystal composition described below comprising four compounds of the formula (I) and four compounds of the formula (II) was prepared. The phase transition temperature of this composition is Cr 14.3 SC * 56.0 SA 85.1.
I. Table 5 shows the temperature dependence of Ps and the tilt angle. The Tps of this composition was 29.5 ° C.

[0025]

Embedded image

Example 5 A ferroelectric liquid crystal composition described below consisting of only four compounds represented by the formula (I) was prepared. The phase transition temperature of this composition was Cr24SC * 49SA79.3I. Further, Tps of this composition was 42 ° C.

[0027]

Embedded image

Example 6 The composition shown in Example 1 was injected into a cell provided with a transparent electrode having a cell thickness of 2 μm, which was coated with PVA as an aligning agent, rubbed on the surface and subjected to a parallel alignment treatment. A liquid crystal element was created. This element was placed on a hot stage and sandwiched between two polarizing plates arranged in a crossed Nicols state at 40 ° C.
A DC voltage of 0 V was applied, and the positions of the element and the polarizing plate were adjusted so that light was blocked. Next, when the temperature of the hot stage was lowered to 30 ° C. without changing the polarity of the applied voltage, light transmission was observed. When the temperature of the hot stage was gradually increased and decreased, light blocking and transmission were observed at about 35 ° C.

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

The ferroelectric liquid crystal composition provided by the present invention has a temperature Tps at which the sign of spontaneous polarization is inverted in a temperature range higher than room temperature and 25 ° C. A liquid crystal element using this composition can be used for a sensor or the like by applying the change of the sign of spontaneous polarization of a ferroelectric liquid crystal.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-190842 (JP, A) JP-A-63-216878 (JP, A) JP-A-3-205487 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C09K 19/34 C09K 19/42-19/46

Claims (6)

(57) [Claims] 1. A ferroelectric liquid crystal composition comprising at least two components, which contains at least one compound represented by the following general formula (I) and has a mixing ratio of 60 to 100% by weight. Embedded image In the formula (I), R ¹ represents an alkyl group having 4 to 16 carbon atoms, and R ² represents an alkyl group having 2 to 12 carbon atoms. 2. A ferroelectric material comprising at least one compound selected from the group consisting of compounds represented by the following general formulas (II) and (III) as a component other than the compound represented by the formula (I) in claim 1. Liquid crystal composition. Embedded image In the formula (II), R ³ and R ⁴ each independently represent an alkyl group or an alkoxy group having 6 to 16 carbon atoms,
In the formula (III), R ⁵ represents an alkyl group or an alkoxy group having 4 to 12 carbon atoms, and R ⁶ represents an alkyl group or an alkoxy group having 4 to 12 carbon atoms. 3. The ferroelectric liquid crystal composition according to claim 1, comprising only a plurality of compounds represented by formula (I). 4. A liquid crystal device comprising the ferroelectric liquid crystal composition according to claim 1. 5. A liquid crystal device comprising the ferroelectric liquid crystal composition according to claim 2. 6. A liquid crystal device comprising the ferroelectric liquid crystal composition according to claim 3.