JPH0717904B2 - Ferroelectric liquid crystal composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a strongly inductive smectic liquid crystal composition.

[Prior Art] In recent years, an electro-optical device using a strongly inductive liquid crystal has attracted attention. (For example, NAClark, STLagerwall, Appl.Phy
s.Lett. 36, 899 (1980) ) strongly induced crystal is a chiral smectic -C phase, in the liquid crystal phase of the chiral smectic -H equality, having spontaneous polarization, i.e. strong display conventionally by showing inductive element It has different characteristics from the nematic phase or cholesteric phase that has been used for the above.

Although several phases are known as the strongly inductive smectic phase, the phase expected to be applied to applications such as optical shutters is the chiral smectic phase-C phase (hereinafter referred to as SmC ^* ). Will be described for the SmC ^* phase example.

In the SmC ^* phase, liquid crystal molecules form a layered structure, and the major axis direction of the molecules is an orientation inclined with respect to the layer normal direction.
Further, it usually contains at least an optically active compound having an asymmetric carbon in the molecular structure, and has a helical structure in which the tilt direction of the molecule is shifted for each layer. Furthermore, in the SmC ^* phase, the spontaneous polarization is perpendicular to the long axis of the molecule and parallel to the plane of the layer, and the orientation of the molecules changes so that the polarity of the spontaneous polarization and the electric field match the external electric field. And can cause optical changes. As a feature of this electro-optical effect,
10-1000 compared to the effect using conventional nematic liquid crystal
It has been found that the response is twice as fast and that it exhibits a memory property, and is expected to be applied to an optical shutter element, a dot matrix display element and the like. However, there are also numerous technical problems with these excellent features.

The biggest problem is that it is difficult to fabricate the device. The SmC ^* liquid crystal is a phase closer to a crystal than the conventionally used nematic liquid crystal, and uniform alignment on the substrate has a difficulty similar to single crystal growth.

As a result of various investigations by the present inventors, it was found that liquid crystals having a cholesteric phase in a temperature range higher than the strongly inductive smectic liquid crystal phase temperature are effective in lengthening the helical pitch of the liquid crystal material and uniformizing the alignment. I found it. The pitch length is more preferably at least four times the substrate gap.

For such a purpose, by coexisting a left helix compound and a right helix compound to form a pitch compensation composition,
A method for increasing the pitch is already known for cholesteric materials. On the other hand, when producing an SmC ^* liquid crystal device, the magnitude of spontaneous polarization is an important physical property for lowering the driving voltage or increasing the response speed. From this viewpoint, the SmC ^* liquid crystal composition preferably has a sufficiently long helical pitch and a large spontaneous polarization. Therefore, an attempt was made for pitch compensation in which a left helix compound and a right helix compound coexist.

As a result, it has been reported that a liquid crystal with a small pitch can be obtained, but on the other hand, spontaneous polarization becomes small, which is impractical. For example, if the d-form and the l-form are allowed to coexist as optically active compounds, helix formation is possible. However, there is a contradiction that spontaneous polarization also becomes zero at the same time.

[Problems to be Solved by the Invention] Therefore, a left helix compound and a right helix compound are allowed to coexist,
There has been a demand for a method of increasing the pitch and not adversely affecting the magnitude of spontaneous polarization.

[Means for Solving Problems] As a result of studies to solve the above problems, the present inventors have found that the polarities of spontaneous polarization differ depending on the type of the optically active compound. As a result, it was found that the direction of the helix and the polarity of the spontaneous polarization are independent physical properties, and the above-mentioned problems can be solved by selecting an appropriate combination.

That is, the present invention comprises at least one kind of optically active compound which produces a left helix when added to a cholesteric phase or a nematic phase and at least one kind of an optically active compound which produces a right helix (however, the following composition 1 and (Except composition 2), and the spontaneous polarization of the optically active compound in the ferroelectric smectic phase must have polarities in the same direction with respect to the smectic layer normal direction and the tilt direction of the molecule from the layer normal direction. A ferroelectric liquid crystal composition characterized by the above is provided, and by having such a constitution, a long pitch can be achieved without adversely affecting spontaneous polarization.

The composition 1 Compound _{C 8 H 17 O-Ph-} CO-O-Ph-Y 1 ( left spiral), the compound _{C 8 H 17 O-Ph-} Ph-CO-Y 1 composition comprising (right helix) Composition 2 Compound C ₈ H ₁₇ O-Ph-CO-O-Ph-Y ₁ (left helix), Compound C ₉ H ₁₉ O-Ph-CO-O-Ph-Y ₁ (left helix), Compound _{C 6 H 13 O-Ph-} Ph-CO-O-Ph-Y 1 ( left spiral)
And the compound C ₈ H ₁₇ O-Ph-CO-O-Ph-CO-Y ₁ (right helix)
When, wherein the composition comprising the compound _{C 8 H 17 O-Ph-} Ph-CO-O-Ph-CO-Y 1 ( right helix), Ph is a paraphenylene group.

Figure 1 shows the spiral direction (70 to 73) and the layer normal direction (10 to 1).
3), the tilt direction of the molecule (50 to 53) and the polarity of spontaneous polarization (60 to 63) are schematically shown. The optically active compound is classified into any of FIGS. 1 (a) to (d).
Depending on the helical direction in the cholesteric phase and the spontaneous polarization direction in the SmC ^* layer, assuming that the layer normal direction (10), the tilt direction (50) and the spontaneous polarization polarity (60) are left-handed in FIG. 1 (a). , (B) also show left-handed characteristics, while (c) and (d) show right-handed characteristics.

In FIG. 1, preferable combinations are (a) and (b) or (c) and (d), the spiral directions are opposite, and the spontaneous polarizations have the same polarity. On the other hand, in each of the systems (a) to (d) alone, the means for achieving a long pitch is only to reduce the concentration of the optically active compound added, and the magnitude of spontaneous polarization decreases almost in proportion to the concentration. . Also,
In the combination of (a) and (c) or (b) and (d),
It is possible to make the pitch longer, but this has an adverse effect on the magnitude of self polarization.

The following are optically active compounds having a strongly inductive smectic phase.

In the following examples, R ^* represents an alkyl group or an alkoxy group having an asymmetric carbon or halogen, R represents a linear alkyl group or a linear alkoxy group, and one compound has the same R ^* , R
Is not necessarily the same group.

Further, even optically active substances other than the substances exhibiting the strongly inductive smectic phase as described above can be used by adding other smectic liquid crystals to improve their characteristics. A liquid crystal additive of liquid crystal can be used, and examples thereof include the following.

Although some strongly inductive smectic phases are known, the SmC ^* phase is preferable in consideration of practical properties such as responsiveness.

Further, the concentration of the optically active compound affects the magnitude of spontaneous polarization, so that the total concentration is preferably at least 1% by weight or more.

Furthermore, as a condition for easier orientation control, a composition exhibiting a cholesteric phase in a higher temperature region than the SmC ^* phase is preferable, and a method such as a rubbing method used for a conventional nematic liquid crystal can be used. Further, when it is used while being held between two substrates, it is preferable that the pitch is at least 4 times or more the gap between the substrates. The control of the substrate gap is not practical when it is 1 μm or less in consideration of the smoothness of the substrate, the likelihood of a short circuit, and the like. Therefore, it is preferable that at least the cholesteric phase has a pitch of 4 μm or more.

[Operation] Table 1 shows examples of optically active compounds classified according to the direction of helix and the polarity of spontaneous polarization. In Table 1,
The self-confidence was able to independently know the direction of spontaneous polarization for a compound exhibiting the SmC ^* phase, but if it did not exhibit such a phase, it was considered as a material exhibiting the SmC phase. It was determined by adding 5 to 30% by weight, sandwiching it between transparent electrode substrates, applying an electric field, and examining the direction of the electric field and the orientation direction of molecules. Since there is no known definition of the polarity of spontaneous polarization, (S +)-2-methylbutyl-p- (pn-decyloxybenzylideneamino) cinnamate (Compound No11), which is usually diversified, is defined as the left.

In addition, regarding the direction of the spiral, ZLI-1565 manufactured by Merck
2 to 20% by weight was added to the nematic liquid crystal, etc., and the direction of the helix was determined.

As mentioned above, the preferred combination in Table 1 is N
o.01 ~ 05 compound group and No. 21 ~ 25 compound group, or No. 11 ~ 16 compound group and No. 31 ~ 34 compound group,
In these combinations, the spiral pitch can be lengthened without canceling the spontaneous polarization with each other.

Table 2 shows the spontaneous polarization and the helical pitch of the liquid crystal composition according to the present invention. The compound with No. 01 as the right material for both the spiral direction and the polarity of spontaneous polarization, and the compound with No. 22 (5.5 wt%) as the left material for both A mixed liquid crystal (hereinafter referred to as No. 220) was used. The spontaneous polarization was measured at a temperature 10 ° C lower than the upper limit temperature of the SmC ^* phase. The pitch was measured at 70 ° C.

FIG. 2 illustrates the results of Table 2. There is a composition in which the pitch becomes infinite, and the spontaneous polarization is always the same polarity.

Table 3 shows No. 15 (5.0% by weight) It is a comparative example of a mixed liquid crystal of No. 150 and a mixed liquid crystal of No. 220. The contents of Table 3 are shown in FIG. 3, and it can be seen that the spontaneous polarization becomes smaller at the same time as the pitch is increased.

[Effect of the Invention] As described above, the present invention makes it possible to increase the helical pitch without reducing the spontaneous polarization by coexisting a left-helix and a right-helix optically active compound having the same polarity of the spontaneous polarization. As a result, low voltage driving, high-speed response, or uniform alignment control can be realized.

In addition, the helical pitch of the SmC ^* phase can be lengthened as well, and improved memory performance can be expected.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the main concept of the present invention. FIG. 2 is a diagram showing the physical properties of the embodiment according to the present invention. FIG. 3 illustrates a comparative example. 10,11,12,13: Layer normal direction 30,31,32,33: Liquid crystal molecule 50,51,52,53: Tilt direction 60,61,62,63: Spontaneous polarization direction 70,71,72,73: Spiral direction

Claims (5)

[Claims] 1. An optically active compound which produces a left helix when added to a cholesteric phase or a nematic phase, and at least one optically active compound which produces a right helix (provided that composition 1 and (Except composition 2), and the spontaneous polarization of the optically active compound in the ferroelectric smectic phase must have polarities in the same direction with respect to the smectic layer normal direction and the tilt direction of the molecule from the layer normal direction. A ferroelectric liquid crystal composition characterized by: The composition 1 Compound _{C 8 H 17 O-Ph-} CO-O-Ph-Y 1 ( left spiral), the compound _{C 8 H 17 O-Ph-} Ph-CO-Y 1 composition comprising (right helix) Composition 2 Compound C ₈ H ₁₇ O-Ph-CO-O-Ph-Y ₁ (left helix), Compound C ₉ H ₁₉ O-Ph-CO-O-Ph-Y ₁ (left helix), Compound _{C 6 H 13 O-Ph-} Ph-CO-O-Ph-Y 1 ( left spiral)
And the compound C ₈ H ₁₇ O-Ph-CO-O-Ph-CO-Y ₁ (right helix)
When, wherein the composition comprising the compound _{C 8 H 17 O-Ph-} Ph-CO-O-Ph-CO-Y 1 ( right helix), Ph is a paraphenylene group. 2. The ferroelectric liquid crystal composition according to claim 1, wherein the phase exhibiting ferroelectricity is a chiral smectic-C phase. 3. The ferroelectric liquid crystal composition according to claim 2, wherein the total concentration of the optically active compound is 1% by weight or more. 4. The ferroelectric liquid crystal composition according to claim 3, which exhibits a cholesteric phase in a temperature range between a smectic phase exhibiting ferroelectricity and an isotropic phase. 5. The ferroelectric liquid crystal composition according to claim 4, wherein the helical pitch in the cholesteric phase is 4 μm or more.