JPS61174294A - Ferroelectric liquid crystal composition - Google Patents

Abstract

PURPOSE:To provide the titled liquid crystal compsn. containing an optically active compd. which produces a counterclockwise spiral and an optically active compd. which produces a clockwise spiral, and having a higher pitch of the spiral without decrease in spontaneous polarization. CONSTITUTION:The liquid crystal compsn. contains an optically active compd. of formulae I, II, etc. and an optically active compd. of formula III or IV (where A is of formula V) which produce a counterclockwise spiral and a clockwise spiral, respectively, when added to cholesteric or nematic phase. In a ferroelectric smectic phase, these optically active compds. show spontaneous polarization (60) which has a polarity in the same direction as a direction (10) perpendicular to smectic layer and a tilting direction (50) of molecule from the perpendicular line direction. EFFECT:Enable realizing low voltage driving, high speed response or uniform orientation control.

Description

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

[Prior Art] In recent years, electro-optical devices using strongly inductive liquid crystals have been attracting attention. (For example, N, A, flakk, S, T.

Lagerwall, Appl, Phys, Lett,
3B, 899 (1980)) Strongly inductive liquid crystals have been traditionally used in display elements, etc. because they have spontaneous polarization, that is, exhibit strong inductivity, in liquid crystal phases such as chiral smectic-〇 phase and chiral smectic-H phase. It has characteristics different from the nematic phase or cholesteric phase.

Several phases are known as strongly inductive smectic phases, but the phase that is expected to be applied to applications such as optical shutters is the chiral smectic phase-C phase (hereinafter referred to as SmCψ
Therefore, the following explanation will be made regarding the example of the SmC'' phase.

In the SmC* phase, liquid crystal molecules form a layered structure, and the long axis direction of the molecules is oriented obliquely with respect to the layer perpendicular direction. Further, it usually contains at least an optically active compound having an asymmetric carbon in its molecular structure, and has a helical structure in which the direction of inclination of the molecules is shifted from layer to layer. Furthermore, the SmG" phase has spontaneous polarization perpendicular to the long axis direction of the molecules and parallel to the layer plane, and the orientation direction of the molecules changes so that the polarity of spontaneous polarization matches the electric field with respect to the external electric field. This electro-optic effect is characterized by a 10% improvement in the effect compared to the effect using conventional nematic liquid crystals.
It has been found that the response is up to 1,000 times faster, or that it exhibits memory properties, and is expected to be used in optical shutter devices, dot matrix display devices, etc. However, despite these excellent features, there are also many technical problems.

The biggest problem is that it is difficult to create devices. SmC”
Liquid crystal has a phase closer to a crystal than conventionally used nematic liquid crystal, and it is difficult to arrange it uniformly on a substrate, similar to ILT crystal growth.

As a result of various studies, the present inventors have found that increasing the helical pitch of the liquid crystal material and liquid crystal having a cholesteric phase at a temperature higher than the ferroconductive smectic liquid crystal phase temperature are effective in making alignment uniform. I found it. Further, the length of the pitch is more preferably at least four times the substrate gap or more.

For this purpose, a method is already known for cholesteric materials in which a left-handed helical compound and a right-handed helical compound are made to coexist to form a pitch compensation composition, thereby increasing the length of the pitch. On the other hand, when creating an SmC" liquid crystal element, the magnitude of spontaneous polarization is an important physical property in order to lower the driving voltage or increase the response speed to V. From this point of view, as for the SmC" liquid crystal composition, It is preferable that the helical pitch is sufficiently long and the spontaneous polarization is large. Therefore, attempts were made to achieve pitch compensation in which left-handed helical compounds and right-handed helical compounds coexist.

As a result, it is possible to increase the pitch length, but on the other hand, it has been reported that the spontaneous polarization becomes small, resulting in a liquid crystal that is not practical. For example, helicalization is possible if hexagonal and text coexist as optically active compounds. However, a contradiction arises in that the spontaneous polarization also becomes zero at the same time.

[Problems to be solved by the invention] Therefore, a left helical compound and a right helical compound are made to coexist,
There was a need for a method that would allow for longer pitches while at the same time not adversely affecting the magnitude of spontaneous polarization.

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

That is, the present invention provides at least one optically active compound that produces a left-handed helix when added to a cholesteric phase or a nematic phase.

and contains at least one optically active compound that produces a right-handed helix, and the spontaneous polarization in the ferroelectric smectic phase of the optically active compound is in the direction perpendicular to the smectic layer and in the tilt direction of the molecule from the direction perpendicular to the layer. On the other hand, we provide a ferroelectric smectic liquid crystal composition characterized by having polarities in the same direction, and by configuring it in this way, it is possible to increase the pitch length without adversely affecting the spontaneous polarization.

Figure 1 shows the spiral direction (70-73), the layer normal direction (10
-13), and (d), which schematically shows the tilt direction of the molecule (50-53) and the polarity of spontaneous polarization (60-63). Helical direction in the cholesteric phase and SmC: “Depending on the spontaneous polarization direction in the layer,
In Fig. 1(a), if we assume that the layer perpendicular direction (10), the tilt direction (50), and the polarity of spontaneous polarization (60) are left-handed, then (b) is also left-handed, while (c) and (d ) indicates right-handed properties.

In FIG. 1, preferred combinations are (a) and (b) or (c) and (d), in which the helical directions are opposite, [
One shot polarization becomes the same polarity. On the other hand, in systems in which each of (a) to (d) is used alone, the only way to achieve a long pitch is to reduce the concentration of the optically active compound added, and the magnitude of the spontaneous polarization is small approximately in proportion to the la degree. Become. Also,
In the combination of (a) and (c) or (b) and (d),
It is possible to lengthen the pitch, but it has a negative effect on the magnitude of spontaneous polarization.

Examples of optically active compounds having a strongly inductive smectic phase include the following.

In the following examples, the R umbrella represents an asymmetric carbon or halogen-containing alkyl group or a bamboo □□□oxy group; ', R are not necessarily the same group.

In addition, non-liquid crystal additives can be used for optically active substances other than substances that exhibit a strongly inductive smectic phase as described above by adding other smectic liquid crystals to improve their properties. There is something like.

Although several strongly inductive smectic phases are known, the 5tnC◆ phase is preferred in consideration of practical properties such as responsiveness.

Since the concentration of the optically active compound influences the magnitude of spontaneous polarization, a total concentration of at least 1% by weight is preferred.

Furthermore, under conditions such as easier alignment control, a composition that exhibits a stiff/steric phase in a higher temperature range than the SmG'' phase is preferable, and methods conventionally used for nematic liquid crystals such as rubbing methods can be used. When used while being held between two substrates, the pitch is preferably at least four times the substrate gap.The substrate gap is controlled by taking into account the smoothness of the substrates, the susceptibility to short circuits, etc. If the pitch is less than 1pm, it is not practical.Therefore, it is preferable that at least the cholesteric phase exhibits a pitch of 4pm or more.

[Function] Table 1 shows examples of optically active compounds classified according to the helical direction and the polar direction of spontaneous polarization. In Table 1,
For compounds that show a 5llG" phase, we were able to determine the direction of spontaneous polarization by themselves; however, in cases where such a phase is not shown, 5 to 30% by weight of the compound that shows an SmC phase is added to make the crystal clear. Sandwiched between electrode substrates,
This was determined by applying an electric field and examining the direction of the electric field and the orientation of the molecules. There is no known definition regarding the polarity of spontaneous polarization, so (S+)-2-methylbutyl-p-(p-n-desyloxyhenzylideneamino) is commonly used.
Cinnamate (compound Mail) was defined as left.

Also, regarding the direction of the helix, ZLI-1 manufactured by Merck & Co.
2 to 20% by weight was added to a nematic liquid crystal such as No. 565, and the direction of the helix was determined.

-7 n') - As mentioned above, the happy combinations in Table 1 are positive, old - 05 compound group and No, compound group 21-25, or M, compound group 11-16. and teeth, 31-34
are a group of compounds, and in these combinations, the helical pitch can be lengthened without mutually canceling out the spontaneous polarizations.

Table 2 shows the spontaneous polarization and helical pitch of the liquid crystal composition according to the invention. Compound No. 01 is the material with both the helical direction and the polarity of spontaneous polarization on the right, while the compound No. 01 is the material with both the polarities on the left, and a mixed liquid crystal of compound No. 22 (5.5% by weight) and CRH+106COOGOCb HI3 (
(hereinafter abbreviated as 22Q) was used. The measurement of spontaneous polarization was carried out at a temperature 10°C lower than the upper limit temperature of the SmC'' phase. Also, the IIIJ constant of pitch was carried out at 70°C.

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

This is a comparative example of a mixed liquid crystal (abbreviated as No. 150) of the third tooth, 15 (5, O double star %) and as HI70/coo@oca HI3, and a mixed liquid crystal of as, 220. The contents of Table 3 are illustrated in FIG. 3, and it can be seen that as the pitch increases, the spontaneous polarization also decreases.

Table 2 Table 3 [Effects of the Invention] As described above, the present invention enables the helical pitch to be reduced without reducing the spontaneous polarization by coexisting left helical and right helical optically active compounds with the same polarity of spontaneous polarization. As a result, low-voltage driving, high-speed response, and uniform orientation control can be realized.

Furthermore, the helical pitch of the Sac" phase can be similarly increased, and an improvement in memory properties can be expected.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the main concept of the present invention. FIG. 2 is a diagram illustrating the physical properties of an example according to the present invention. FIG. 3 is a diagram of a comparative example. 10.11.12,13: Layer normal direction 30.31,3
2, 33: Liquid crystal molecules 50.51, 52.53: Tilt direction Bo, s2. s
2. g3: Spontaneous polarization direction? 0,71,72.73:
Helical direction fcl +d) second
U statement 2 1z town NO, Q I 7'! (v amount%)th
3 Figure 1゛°・. ~ ″.

Claims (1)

[Scope of Claims] 1. At least one optically active compound that produces a left helix when added to a cholesteric phase or a nematic phase, and at least one optically active compound that produces a right helix when added to a cholesteric phase or a nematic phase, and the optically active compound A ferroelectric smectic liquid crystal composition characterized in that the spontaneous polarization in the ferroelectric smectic phase of the compound has polarity in the same direction with respect to the direction perpendicular to the smectic layer and the direction of tilt of molecules from the direction perpendicular to the layer. . 2. The ferroelectric liquid crystal composition according to claim 1, wherein the phase exhibiting ferroelectricity is a chiral smectic-C phase. 3. The ferroelectric smectic liquid crystal composition according to claim 2, wherein the total concentration of optically active compounds 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. In the cholesteric phase, the helical pitch is 4μ
5. The ferroelectric liquid crystal composition according to claim 4, wherein the ferroelectric liquid crystal composition is at least m.