JPS6222889A - Ferroelectric liquid crystal composition for guest-host display element - Google Patents

Abstract

PURPOSE:To obtain the titled compsn. capable of providing a guest-host display element having an excellent contrast, by incorporating a (chiral)smectic liquid crystal compd. exhibiting no smectic A phase, as a main component, in a (chiral) smectic C phase at its high-temp. side. CONSTITUTION:At least one member selected from (chiral)smectic liquid compds. exhibiting no smectic A phase is incorporated as the main component in the high-temp. side of a (chiral)smectic C phase of formulae I-II [wherein formulae III-V area each independently formula VI-VII; L1-L2 are each independently a single bond, -N=N-, a group of formula VIII, -CH=N- or the like; X<1>-X<4> are each independently halogen, H or CN; Y is a single bond or a group of formula VIII; R<1> is 4-18C alkyl, alkyloxy, alkanoyloxy or alkoxycarbonyl; and R<2> is 4-10 alkyl(oxy) having an asymmetric carbon], thereby providing the titled compsn. exhibiting no smectic A phase and having a tilt angle of 30 deg.-60 deg. at the high-temp. side of the chiral smectic C phase.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a ferroelectric liquid crystal composition, and particularly to a ferroelectric liquid crystal material suitable for a guest-host type display element containing a dichroic dye. .

[Prior Art] Currently, liquid crystal compounds are widely used as display materials, but most of these liquid crystal display elements are FiT N (Tw
The liquid crystal material used belongs to the nematic phase. Display elements based on Hitoshi's TNII display system have rapidly come into use due to their features, such as eliminating eye strain from the viewer's eyes, extremely low power consumption, and being lightweight and compact. Although large products have been made, there are still unresolved shortcomings such as slow response and the display not being visible depending on the viewing angle.

In order to take advantage of the advantages of liquid crystal display elements and compensate for their drawbacks, it is essential to develop a new display system to replace the TNjlfi display system. One such attempt is N, A, C1ar.
There is a display element that utilizes the optical switching phenomenon of ferroelectric liquid crystal caused by k or the like.

(Abrid Physics Letters (Appl.

Phys, Latt, ) u, 899 (1980)
reference). Ferroelectric liquid crystal was developed in 1975 by R.B.Meye
Its existence was first revealed by r, etc. (
Jurnaldo Physique (J, d@Phys,) 36
L 69 (1975)), ferroelectricity is expressed only in a smectic phase having a helical structure (chiral smectic phase). As a chiral smectic phase,
Smectic C phase! phase, F phase, C phase and H phase (hereinafter referred to as
Sc* phase, SI* phase, SF* phase, S♂ phase and S, respectively.
(abbreviated as ♂phase) is known. In the chiral smectic phase, liquid crystal molecules form layers, and the molecules are tilted with respect to the layer plane, and the direction of tilt shifts little by little from layer to layer, forming a helical structure, and the helical axis is perpendicular to this layer plane. In the chiral smectic phase, spontaneous polarization occurs, so when a parallel DC electric field is applied to this layer, the molecules reverse around the helical axis as the rotation axis depending on the polarity. Display elements using ferroelectric liquid crystals utilize this switching phenomenon.

Among the chiral smectic phases, the Sc* phase is currently attracting particular attention. There are two possible display methods that utilize the switching phenomenon of the SC* phase. One method uses two polarizers to determine the amount of birefringence, and the other method uses a guest-host method that uses dichroic dyes.

The characteristics of these display methods include (1) very fast response speed, (2) good memory performance, and (3) low viewing angle dependence, and they have the potential for high-density display.
It is extremely attractive. In addition, since the guest-host display method uses only one polarizing plate, it has the excellent feature of (4) no coloration due to letter day shore. This means that there is no need to accurately control the thickness of the cell as a display element, and is a very convenient display method from an industrial perspective.

The main conditions required for a ferroelectric liquid crystal material as a guest-host type display element are (1) a tilt angle of 30° to 60', and (2) an SC* phase that can operate stably at room temperature. (3) large spontaneous polarization, and (4) long helical pitch. In particular, the tilt angle is an essential condition because if it is not within the above angle range, the contrast will deteriorate when used in a display element. The above angle range is calculated as follows. The absorption intensity by the dye of the guest-host type display element with the tilt angle θ is 5in2 (2θ
), and reaches its maximum at 0=45°. Here, even if the absorption intensity is 75% of the maximum absorption intensity, there is practically no difference in contrast from that of θ = 45°, so the range of θ that gives the absorption intensity of 75% of the maximum absorption intensity, that is, the contrast The allowable limit of θ between 30° and 60°
It can be calculated as °.

Currently known ferroelectric liquid crystal compounds are illustrated in Table 1. These reporters and sources are Martino, P.H.
t-Lagarde @ta1. ．． Mol, Cry@t
.

Lig, Cryst, 75.249 (1981):
Takashi Inukai et al., Proceedings of the 1st O LCD Symposium, pp164. p
p166 (1984): Yoshiyako Hori, Proceedings of the 10th Liquid Crystal Conference ppH2 (1984), etc.

As can be seen from Table 1, most of the compounds have an inclination angle of 30° or less at lc~.

Also, those with 45° have a very short helical pitch (for example, M, F, Bone at al: Mo1.cryat
, Liq.

(See Cryst, 102 (1984) 331)
.

Furthermore, many of them have a temperature range in which they exhibit ferroelectricity higher than room temperature, and this range is narrow, so they cannot be used as they are as guest-host type display element materials.

[Problem to be solved by the invention 3 As is clear from the above description, the main object of the present invention is to provide a ferroelectric chiral smectic liquid crystal composition whose tilt angle is in the range of 30 to 60°. That's true. Other objects of the invention will become apparent from the following description.

[Means for solving problems]

The present inventors conducted research on ferroelectric liquid crystal compounds and liquid crystal compositions containing such compounds, focusing on the correlation between the mode of phase transition and the tilt angle in the S-phase. The invention has been completed.

Among ferroelectric liquid crystal compounds or compositions, the tilt angle of the Sc* phase of a ferroelectric liquid crystal compound or composition having an SA phase on the high temperature side of the Sc phase is smaller than 30°C, while the SA phase is on the high temperature side of the Sc* phase. The present inventors have discovered the surprising fact that the inclination angle is greater than 30°C in the case of a material that does not exhibit this.

That is, on the high temperature side of the ferroelectric chiral smectic C phase of the present invention (1),
The main component is a chiral smectic liquid crystal compound that does not exhibit a smectic physiognomy, or a smectic liquid crystal compound that does not exhibit a smectic physiognomy on the high temperature side of the smectic C phase. A ferroelectric chiral smectic liquid crystal composition exhibiting no The strong vj electron-N=CH-1-C according to item (1) above, which contains at least one compound that does not exhibit smectic physiognomy on the high temperature side of the smectic C phase.
H20-1 or 10CH2-, Xl, X2, X3 and X4 are each a halogen atom, a water X atom and a cyan group, Y is a single bond or -OC-, and R1 has 4 carbon atoms.
~18 alkyl group, alkyloxy group, alkanoyloxy group or alkoxycarbonyl group; 12 represents an alkyl group having 4 to 10 carbon atoms or an alkyloxy group having an asymmetric carbon atom, respectively; ). The second aspect of the present invention is (3) a liquid crystal compound that does not exhibit smectic physiognomy on the high temperature side of the ferroelectric C phase, or does not exhibit smectic physiognomy on the high temperature side of the smectic C phase. This is an optical switching element characterized by using a ferroelectric chiral smectic liquid crystal composition which has a smectic liquid crystal compound as a main component and which does not exhibit a smectic human phase on the high temperature side of the chiral smectic C phase.

The compound preferably used as a component of the ferroelectric liquid crystal composition of the present invention is a compound represented by the above general formula (1) or (II), which has an Sl or Sc phase, and whose phase transition mode is S'' It does not show the KSA phase or the KSA phase on the high temperature side of the Sc phase.

Examples of these compounds are the high-temperature phase of the st phase or the Sc phase, and the transition temperature (Tc) to the high-temperature phase.
It is shown below along with the value of the inclination angle at a temperature R(T) that is lower in degrees Celsius.

In addition, in addition to the compounds exemplified below, S! A compound that does not have an SA phase as a phase on the high temperature side of the Sc phase or the Sc phase can be used as a component of the liquid crystal composition of the present invention in the same manner as the exemplified compounds.

In the following, ch represents a cholesteric phase, N represents a nematic phase, and ■ represents an isotropic liquid phase.

*As mentioned above, the tilt angle of the ferroelectric liquid crystal phase differs depending on the type of phase on the high temperature side of the SC phase*.If the SA phase is on the high temperature side of the SC phase, the tilt angle is small (θ 30°)
, on the other hand, when the S physiognomy is not shown, the inclination angle is large (
θ≧300). Next, it will be explained using an example that this also applies to a liquid crystal composition having an S-benign phase.

* Figures 1 and 2 show the KSA phase on the high temperature side of the SC phase as a compound with a small tilt angle, and the compound with a large tilt angle that does not show the SA phase on the high temperature side of the S" phase. The graphs show the concentration dependence of the tilt angle and the phase position* degree in the system.As the concentration of Compound B, which does not exhibit the KSA phase on the high temperature side of the SC phase, increases, the tilt angle increases, and the yield of Compound B becomes approximately 40 molti S
The A phase disappears, and the tilt angle increases accordingly, and 3
00 or more.

* Figures 3 and 4 show the SA phase on the high temperature side of the SC phase as a compound with a small tilt angle; * As the compound with a large tilt angle that does not show the SA phase on the high temperature side of the SC phase; The concentration dependence of the tilt angle and phase transition temperature in a mixed component system is shown. As in the above example *, when the concentration of the compound that does not show the SA phase on the high temperature side of the SC phase is about 80 molt, the SA phase disappears, and the tilt angle increases rapidly.

* Figures 5 and 6 show the above-mentioned compound A, which shows the Ic5A phase on the high temperature side of the SC phase and has a small tilt angle, and compound A, which does not show the SA phase on the high temperature side of the SC phase and has a large tilt angle. The concentration dependence of the tilt angle and phase transition temperature in a mixed component system is shown. A similar trend to the previous two examples can be seen, with compound Riku.

As mentioned above, the composition is the same as the compound * <, and the SA phase is shown on the high temperature side of the SC phase, and even if a compound with a small tilt angle is used, the composition will have the SA phase on the high temperature side of the SC phase. If it is not shown, it can be seen that the tilt angle becomes large.

In this way, among the group of compounds represented by the general formula (1) or (II)*, the main component is a compound that does not show the SA phase on the high temperature side of the SC phase, and the composition is the S''!' phase. This is an example of a mixed system of ferroelectric liquid crystal compositions that is suitable as a guest-host display element material by adjusting the composition ratio. The same can be said for a mixed system of a chiral smectic liquid crystal compound and a smectic liquid crystal compound that does not have an asymmetric center.In other words, the SA phase is placed on the high temperature side of the SC phase, as in the case of * Kana, on the high temperature side of the SC phase. In the mixed yarn of compound and compound G shown below, the SA phase appears on the high-temperature side of the Sc phase in any composition*, and the inclination* angle does not exceed 30', and the SA phase appears on the high-temperature side of the Sc phase. If present, it is considered unsuitable as a guest-host type display element material.

〔Effect of the invention〕

As is clear from the examples explained above, by applying the present invention, a ferroelectric chiral smectic liquid crystal composition with a tilt angle of 30' to 60' can be obtained, and it is possible to obtain a ferroelectric chiral smectic liquid crystal composition with a tilt angle of 30' to 60'. A guest-host type display element with excellent contrast can be obtained.

〔Example〕

The present invention will be explained in more detail by way of examples below.
The present invention is not limited to these examples.

In addition, the magnitude of spontaneous polarization (Ps) was measured by the Sawyer-Tower method, and the helical pitch (P) was measured using a homogeneously oriented cell with a cell thickness of about 200 μm, and a striped pattern (large pattern) corresponding to the helical pitch was measured. It was determined by directly measuring the spacing between the ralization lines). and the tilt angle (
θ) is the shift angle (20 (corresponding to) The composition was prepared by weighing a predetermined weight of the liquid crystalline compound and mixing the compound while heating and dissolving it in a sample bottle.

Example 1 * A chiral smectic liquid crystal compound that does not exhibit an S phase on the high temperature side of the Sc phase.A chiral smectic liquid crystal composition consisting of a liquid crystal compound that exhibits an SC phase in the temperature range of 28°C to 82°C and its It does not form a ch phase on the high temperature side, and becomes an isotropic liquid at 96°C.

The spontaneous polarization, helical pitch, and tilt angle of this liquid crystal composition were 20 nC/j, 4 μm, and 38' at 30°C, respectively.
A ferroelectric chiral smectic liquid crystal composition having a very large tilt angle and highly suitable for a guest-host display system was obtained.

Example 2 *Chiral smectic liquid crystal composition consisting of a chiral smectic liquid crystal compound that exhibits a KSA phase on the high temperature side of the SC phase* and a chiral smectic liquid crystal compound that does not exhibit an SA phase on the high temperature side of the SC phase* - The material was heated at 25°C. It enters the SC phase in the temperature range from 75°C to 75°C, becomes the CH phase on the high temperature side, and becomes an isotropic liquid at 130°C.

The spontaneous polarization, helical pitch, and tilt angle of this liquid crystal composition are 2nC/j, 3μm, and 34°, respectively, at 30°C)
A ferroelectric chiral smectic liquid crystal composition very suitable for the W display system was obtained.

Example 3 * 20% by weight of a chiral smectic liquid crystal compound that does not exhibit an SA phase on the high temperature side of the SC phase 20% by weight - * A composition consisting of a chiral smectic liquid crystal compound and a nematic liquid crystal compound that exhibit a KS phase on the high temperature side of the SC phase The chiral smectic liquid crystal composition* exhibits an SC phase in a temperature range of 0°C to 66°C, changes to a CH phase on the high temperature side, and becomes an isotropic liquid at 82°C. The spontaneous polarization, helical pitch and tilt angle of this liquid crystal composition are 25
12 n C/ui, 8 μm and 39° at °C, respectively.
Finally, a guest-host type display type liquid crystal composition was obtained.

Example 4 To the ferroelectric chiral smectic liquid crystal composition prepared in Example 3, 3 wt. The composition used for display was injected into a cell equipped with a transparent electrode having a cell thickness of 8 μm, which had been coated with PVA as an alignment agent and subjected to parallel alignment treatment by rubbing the surface. When a low frequency current of 0.5 Hz and 30 V was applied to the device so that it was parallel to the molecular axis, a clear switching phenomenon with very good contrast was observed. When the response time at this time was determined from the change in transmitted light intensity, a guest-host display element was obtained which had a very fast response of about 2 m5 ec at 25°C.

[Brief explanation of drawings]

Figures 1 to 8 show the aforementioned compound and compound B1, respectively.
Compound C and Compound D1 Compound A and Compound R and Compound A
This is a diagram showing the concentration dependence of the tilt angle and phase transition temperature in a binary mixture system of compound @a and compound @a. In the figure, SC, SA, Ch, and ISO represent chiral smectic C phase, smectic A phase, cholesteric phase, and isotropic liquid phase, respectively. that's all

Claims (3)

[Claims] (1) The main component is a chiral smectic liquid crystal compound that does not exhibit a smectic A phase on the high temperature side of the chiral smectic C phase, or a smectic liquid crystal compound that does not exhibit a smectic A phase on the high temperature side of the smectic C phase. A ferroelectric chiral smectic liquid crystal composition that does not exhibit a smectic A phase on the high temperature side of a chiral smectic C phase. (2) General formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (I) or ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (II) (In formulas (I) and (II), ▲ mathematical formulas, chemical formulas, tables, etc. ▼, ▲There are mathematical formulas, chemical formulas, tables, etc.▼ and ▲There are mathematical formulas, chemical formulas, tables, etc.▼ are each independently ▲There are mathematical formulas, chemical formulas, tables, etc.▼, ▲There are mathematical formulas, chemical formulas, tables, etc. ▼、▲Mathematical formula, chemical formula,
There are tables, etc. ▼, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼
, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ or ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼, L^1 and L ^2 each independently has a single bond, -N=N-, ▲There are mathematical formulas, chemical formulas, tables, etc.▼, ▲There are mathematical formulas, chemical formulas, tables, etc.▼, ▲There are mathematical formulas, chemical formulas, tables, etc.▼, -CH =N-, -N=
CH-, -CH_2O- or -OCH_2-,
1. 4 to 18 alkyl groups, alkyloxy groups, alkanoyloxy groups or alkoxycarbonyl groups,
^2 represents an alkyl group having 4 to 10 carbon atoms or an alkyloxy group having an asymmetric carbon atom. ) and contains at least one compound that does not exhibit a smectic A phase on the chiral smectic C phase or the high temperature side of the smectic C phase,
The ferroelectric liquid crystal composition described in item 1). (3) A high temperature chiral smectic C phase whose main component is a chiral smectic liquid crystal compound that does not exhibit a smectic A phase on the high temperature side of the chiral smectic C phase or a smectic liquid crystal compound that does not exhibit a smectic A phase on the high temperature side of the smectic C phase. An optical switching element characterized by using a ferroelectric chiral smectic liquid crystal composition that does not exhibit a smectic A phase on its side.