JPH0613702B2 - Chiral smectic liquid crystal composition - Google Patents

Description

The present invention relates to a chiral smectic liquid crystal composition. More specifically, by mixing a chiral smectic compound in which the twist direction of the spiral axis is clockwise with a chiral smectic compound in which the twist direction of the spiral axis is counterclockwise, the helical pitch is long and the spontaneous polarization The present invention relates to a ferroelectric liquid crystal material having a large size and excellent responsiveness.

(Prior Art) Currently, liquid crystals are widely used as display materials, but most of such liquid crystal display devices are TN (Twisted Nemati).
The c) type display system uses liquid crystal belonging to a nematic phase as a liquid crystal material. Since this TN type display system is a light receiving type, it has features that eyes are not tired and power consumption is extremely small, but it has a drawback that the response is slow and the display cannot be seen depending on the viewing angle. Nowadays,
Particularly, high-speed response is required for the display device, and improvement of the liquid crystal material has been attempted to meet such demand. However, as compared with other light emitting type displays (EL (electroluminescence) display, plasma display, etc.), there is still a large difference in response time. Taking advantage of the characteristics of light receiving type, low power consumption and liquid crystal,
Furthermore, in order to secure a response comparable to that of the light emitting display, it is indispensable to develop a new liquid crystal display system to replace the TN type display system. One of such attempts is a display device (NA Clark, ST Lagerwall; Appl. Phys, 3) that utilizes the optical switching phenomenon of a strongly induced liquid crystal.
6 , 899 (1980)). Ferroelectric liquid crystal was introduced in 1975 by R.M. B. Its existence was first announced by Meyer et al. (RB Meyer et al; J. Physiq
ue 36, L-69 (1975 ) see, chiral smelling lipped poke C phase from the liquid crystal classification, I phase, F phase, G phase or H phase (S _C ^* phase, S _I ^* phase, S _F ^* phase, S ⁽ Abbreviated as _G ^* phase and S _H ^* phase)
Belong to.

When the light switching effect of the S _C ^* phase is applied as a display element, it has three excellent characteristics as compared with the TN display method.
The first feature is that it responds very quickly, and its response time is 1/100 or less as compared with an element of a normal TN display system. The second feature is that it has a memory effect, and time sharing drive is easy in combination with the above-mentioned high-speed response. The third characteristic is that gray scales can be easily obtained. T
To take shades of gray in the N display system, for performing by adjusting the applied voltage, as compared to have challenges such as a voltage dependent temperature-dependent and the response speed of the threshold voltage, S _C ^{* When} applying the phase optical switching effect, gradation can be easily obtained by adjusting the polarity inversion time.
It is very suitable for displaying Kraftick.

There are two possible display methods. One is a birefringence type using two polarizers, and the other is a guest-host type using a dichroic dye.
Since the S _C ^* phase has spontaneous polarization, reversing the polarity of the applied voltage causes the molecule to invert with the helical axis as the axis of rotation.
A liquid crystal composition having a S _C ^* phase is injected into a liquid crystal display cell that has been subjected to an alignment treatment so that liquid crystal molecules are aligned parallel to the electrode surface,
The liquid crystal cell is sandwiched between a director of liquid crystal molecules and two polarizers arranged so that one polarization plane is parallel to each other.
A bright field and a dark field (determined by the facing angle of the polarizer) are obtained by applying a voltage and reversing the polarity. On the other hand, when operating as a guest-host type, a bright field and a dark field (determined by the arrangement of polarizing plates) can be obtained by reversing the polarity of the applied voltage.

The S _C ^* phase has spontaneous polarization, and due to the reversal of the polarity of the applied voltage, two stable states (bistable) are formed on the electrode surface.
It is required to be possible. In order to obtain a liquid crystal display device with this bistable state and high-speed response, as suggested by Clark et al., The cell gear d is held in a spiral pitch P.
Smaller than , It is necessary to unwind the spiral (NA Clark, STLage
rwall; Apppl. Phys. Lett., 36 , 899 (1980)).

In general, many of the current ferroelectric liquid crystal compounds have short helical pitches (1 to 3 μm), and it is necessary to set the cell gap to about 1 to 2 μm to unwind the helix of these compounds. Considering it, there are difficult problems in terms of cost and yield. Development TN
Approximately 5 to 5 cell gears used in the model display method
Since it is about 10 μm, in order to put the ferroelectric liquid phase into practical use, it is desired that the helical pitch be 5 μm or more.

Between the threshold voltage Ec required for molecule inversion, the helical pitch P, and the spontaneous polarization magnitude Ps when the display element using the ferroelectric liquid crystal is brought into the two stable states described above. Is generally (B.Meyer; Mol.Cryst. & Lig.Cryst., 40 , 38
(1977)). In the formula (I), K is an elastic constant when the molecule rotates and deforms. As is clear from the formula (I), in order to reduce the threshold voltage, it is necessary that the helical pitch is long and the spontaneous polarization is large. But,
There is no compound having a long helical pitch and a large spontaneous polarization among the present ferroelectric liquid crystal compounds, and almost all the compounds have a short helical pitch. Therefore, by mixing several kinds of ferroelectric liquid crystal compounds, a ferroelectric liquid crystal composition having a long helical pitch and a large spontaneous polarization must be prepared.

(Problems to be Solved by the Invention) An object of the present invention is to realize a high-speed response display by using a cell with a cell gear which is almost the same as a cell currently widely used in the TN type display system, and has a long spiral pitch. Another object of the present invention is to provide a ferroelectric liquid crystal composition having a large spontaneous polarization.

Another object of the present invention is to provide a light-switching device with extremely fast response.

(Means for Solving Problems) Generally, a method of increasing the helical pitch of a chiral smectic liquid crystal composition is to add a smectic C (abbreviated as SC) compound having no helical structure to a ferroelectric liquid crystal compound. And a compound in which the helical twist of the present invention has a clockwise twist and a counterclockwise twist are mixed to cancel the helical twisting direction to lengthen the helical pitch.

Generally, the twisting of the helical axis is divided into clockwise and counterclockwise depending on the position of the asymmetric carbon atom in the side chain of the compound relative to the carbon atom of the benzene ring. It is interpreted that this is because the direction in which the methyl group (-CH ₃ ) attached to the asymmetric carbon atom (C ^* ) is different depending on the position of the asymmetric carbon atom due to the odd-even property of the arrangement of atoms. (M, Ts
ukamoto, T.Ohtsuka, K.Morimoto, Y.Murakami; Japan J.Ap
pl. Phys., 14 , 1307 (1975)). That is, depending on whether the position of the side chain asymmetric carbon atom is an even number or an odd number counted from the carbon atom of the benzene ring, it is classified into clockwise and counterclockwise. In the following, regarding the position of the asymmetric carbon atom of the side chain, the carbon atom of the benzene ring to which the side chain is bonded is defined as the 0th position, and the carbon atom of the side chain bonded to this is counted as the 1st position, and the odd rules are discussed.

Also, as is well known, the absolute configuration of the optically active substance is S-type (Si
There are two types, a nister type) and an R type (Rectus type), and it is conceivable that two types of compounds having the same structural formula are in mirror symmetry with each other. For example, for 2-methylalkan-1-ol, the following two types The following two types are available for 1-methylalkan-1-ol. It is possible that there is an absolute arrangement of. When a chiral smectic liquid phase compound is synthesized using these optically active substances as raw materials, the absolute configuration of the product is considered as follows.

When 2-methylalkan-1-ol is used as the starting material, the absolute configuration before and after the reaction does not change because the asymmetric carbon atom is not the reaction point in the synthetic process. That is, the absolute configuration of the product is the same as that of the starting compound. On the other hand, when 1-methylalkan-1-ol is used as the starting material, the asymmetric carbon atom may serve as the reaction point, so the absolute configuration before and after the reaction is reversed depending on the synthesis method, so-called Walden inversion. May be placed. In fact, Y in the formula (I) of the present invention prepared by including Walden inversion in the synthetic process is In the chiral smectic liquid crystal compound, the absolute configuration of the asymmetric carbon atom is opposite to that of the starting material, 1-methylheptan-1-ol. That is, the R-type product is obtained from the S-type 1-methylheptan-1-ol.

Further, regarding the compound of the formula (I) used in the present invention, in the compound of which the absolute configuration of the optically active substance is S type, the side chain Y is
When the position of the asymmetric carbon atom of is an even number from the carbon atom of the benzene ring, the twisting of the helix is clockwise,
In the case of an odd number position, it is counterclockwise, and when the absolute configuration of the optically active substance is the R type compound, it is the reverse of the S type compound,
It is known that when the position of the asymmetric carbon atom of the side chain Y is an even number from the carbon atom of the benzene ring, the twisting of the helix is counterclockwise, and when the position is an odd number, it is counterclockwise.

The inventors of the present invention have already disclosed a ferroelectric liquid crystal composition comprising a chiral smectic liquid crystal compound having a right-handed helical twist and a chiral smectic liquid crystal compound having a left-handed helical twist. It has been found that the same object can be achieved (see Japanese Patent Laid-Open No. 60-90290), but the same object is achieved when a chiral smectic liquid crystal compound having an R-type absolute configuration of an optically active substance is used as a component. The inventors have found out what can be done and have completed the present invention. That is,
The first aspect of the present invention is (1) a ferroelectric containing at least one chiral smectic liquid crystal compound having a right-handed helical twist and at least one chiral smectic liquid-crystal compound having a left-handed helical twist. In a chiral smectic liquid crystal composition, a compound having the general formula as a chiral smectic liquid crystal compound in which the twist of the helix is clockwise (In the formula (I), m or n represents an integer of 1 or 2, (m + n) is 2 or 3, and X is Or -OCH ₂ - indicates, R represents an alkyl group or alkyloxy group having 1 to 18 carbon atoms, Y represents an alkyl group, an alkyloxy group or an alkoxycarbonyl group having an asymmetric carbon atom. ), A compound having an asymmetric carbon atom of the side chain Y at an odd number position from the carbon atom to which the Y of the benzene ring is bonded is the 0th position, and the absolute configuration at the asymmetric carbon atom is R type. One or more, or
As a compound in which the twisting of the helix is counterclockwise, the asymmetric carbon atom of the side chain Y in the general formula is an even number counted from the carbon atom with the carbon bonded to Y of the benzene ring being the 0th position, A ferroelectric chiral smectic liquid crystal composition comprising at least one compound whose absolute configuration at a chiral carbon atom is R-type, which embodiment is (2) above (1). In the formula (1), the side chain Y is a chiral smectic liquid crystal compound in which the helical twist is clockwise. Ferroelectric chiral smectic liquid crystal composition cormorant which is an optically active compound, and (3) in the above item (1) or (2), the helical twisting direction is a counterclockwise chiral smectic liquid crystal. The compound is
In the formula (1), the side chain Y is Is a ferroelectric chiral smectic liquid crystal composition which is an optically active compound.

A second aspect of the present invention is (4) an optical switching element characterized by using the ferroelectric chiral smectic liquid crystal composition according to the above (1).

In the above formula (I), m = 1, n as a chiral smectic liquid crystal compound in which the helical twist is counterclockwise.
= 2, R = C ₇ H ₁₅ O-, And the absolute configuration of the optically active substance is R type. As a compound in which the twist of the helix is clockwise,
In the formula (I), m = 1, n = 2, R = C ₈ H ₁₇ O-, And the absolute configuration is S-shaped 1 and 2 show the relationship between the spontaneous polarization magnitude (Ps) and the reciprocal number (1 / P) of the helical pitch and the composition of the binary mixture system including the above. That is, FIG. 1 shows the magnitude of spontaneous polarization at a temperature (T) lower by 10 ° C. and 20 ° C. than the S _C ^* -S _A phase transition temperature (T _C ) of the binary system, which is plotted as a composition. , Figure 2 shows 20 ° _C from T _C
FIG. 3 is a diagram showing the reciprocal of a binary pitch of a binary system at a low temperature. In FIG. 2, R and L respectively indicate that the twist of the spiral of the mixed system is in the right-handed and left-handed regions. As can be seen from FIG. 1, in this binary mixture system, additivity holds for the magnitude of spontaneous polarization. Further, from FIG. 2, the helical pitch of the mixed system becomes infinite when the concentration of compound B is about 32% by weight, and the magnitude of spontaneous polarization at this time is 28 to 36 nC / cm ³ from FIG. Figure 1
And FIG. 2 suggests that a ferroelectric chiral smectic liquid crystal composition having arbitrary helical pitch and large spontaneous polarization can be prepared. The above additivity of the magnitude of spontaneous polarization can be interpreted as follows.

Ferroelectric liquid crystal, when no electric field is applied, twists the helical axis clockwise or counterclockwise, and the dipole moment of the molecule points in a random direction, but an electric field is applied. The molecules are aligned in a certain direction because the dipole moment of the untwisted molecule is aligned with the electric field direction. That is, when a compound in which the helical axis twists in a clockwise direction is mixed with a compound in a counterclockwise direction, an electric field is applied to untwist the helix, regardless of whether the helix twists clockwise or counterclockwise. Since the dipole moments are aligned in the electric field direction, they are arranged in a fixed direction, and the molecules are inverted in response to the reversal of the polarity of the applied voltage. Therefore, regardless of whether the spiral axis is twisted clockwise or counterclockwise, the magnitude of the spontaneous polarization does not matter in the twisting direction of the helix, and appears as a large sum of the spontaneous polarizations of the individual component compounds. Yotsutte
It is considered that the magnitude of the spontaneous polarization is additive regardless of the twisting direction of the spiral axis.

As is clear from the fact that the magnitude of spontaneous polarization of the mixed system is additive, the chiral smectic liquid phase compound as a component of the composition of the present invention has a larger spontaneous polarization of itself. Is desirable.

As a component of the liquid crystal composition of the present invention, in the formula (I), the asymmetric carbon atom of the side chain Y is at an odd number from the carbon bonded to Y of the benzene ring, and the twist of the helix is clockwise clockwise. A smectic liquid crystal compound or a compound in which the asymmetric carbon atom of the side chain Y is in an even number position from the carbon to which Y of the benzene ring is bonded and the twist of the helix is counterclockwise is used. These chiral smectic liquid crystal compounds are compounds in which the absolute configuration of the optically active substance is R type. The chiral smectic liquid crystal compound having an opposite spiral twist added to the compound having the R-type S _C ^* phase has an absolute configuration of R-type or S-type as an optically active substance. Good.

As a ferroelectric liquid crystal material, the S _C ^* phase temperature range is desired to be as wide as possible including a practical temperature, and this is satisfied as follows. The maximum temperature of the S _C ^* phase can be controlled by adjusting the molecular chain lengths of the component S _C ^* compounds, that is, by reducing the difference between the molecular chain lengths, to suppress a sudden drop due to mixing. See JP-A-61-190585. ).

The lower limit temperature of the S _C ^* phase is often the melting point, but the melting point of the mixed system is effectively lowered by increasing the number of components and by mixing S _C ^* compounds that are not homologs (special characteristics). (See Kai 61-190585).

Although the melting point of the mixed system can be lowered by adding a compound having a nematic phase (see Japanese Patent Laid-Open No. 61-97382), it is necessary to take into consideration the decrease in the magnitude of spontaneous polarization due to the addition of the nematic liquid crystal compound. I won't.

In the present invention, since S _C ^* compounds having different Ys in the formula (I) are always included, the composition of the present invention can expand the S _C ^* phase to a low temperature side as compared with a mixed system consisting of homologues. There is.

(Effect of the Invention) According to the present invention, a ferroelectric chiral smectic liquid crystal compound having a short helical pitch is used as a component, and the ferroelectric chiral smectic has a sufficiently long helical pitch and a considerably large spontaneous polarization. A click liquid crystal composition is obtained. Since the composition of the present invention has a long helical pitch, it can form a liquid crystal display device having a sufficiently good orientation even if it is enclosed in a cell having an interelectrode distance of about 5 μm. Very fast as shown.

(Examples) The present invention is described in detail below with reference to examples, but the present invention is not limited to these examples. The magnitude of the spontaneous polarization is measured by the Sawyer-Tower method, and the spiral pitch is measured by using a cell whose spiral axis is parallel to the substrate and polarizing the stripe pattern corresponding to full pitch. It was measured directly by a microscope.

Example 1 Compound in which the helical twist is clockwise 10% by weight 25% by weight and a compound in which the twist of the helix is counterclockwise 30% by weight 25% by weight and nematic liquid crystal compound A composition consisting of 10% by weight was prepared. Of the four component compounds having the S _C ^* phase, the first compound has the absolute configuration of the optically active substance R
The latter three are compounds having an absolute configuration of S type.

This liquid crystal composition exhibits an SC ^* phase in the temperature range of 0 ° C. to 65 ° C., at which temperature side indicates the S _A phase, becomes such an isotropic liquid at 80 ° C.. The helical pitch of this composition is 6 μm at 25 ° C.
And the magnitude of spontaneous polarization is as large as 33 nC / cm ^2, and the ferroelectric chiral smectic liquid crystal composition has a large magnitude of spontaneous polarization despite the long helical pitch. The thing was obtained.

Example 2 Compound in which the helical twist is clockwise 10% by weight 20% by weight and compound in which the twist of the helix is counterclockwise 40% by weight A liquid crystal composition containing 30% by weight was prepared. In this component compound,
The compound described first is an optically active substance having an absolute value of R type, and the latter three compounds have an absolute configuration of S type.

This composition exhibited an S _C ^* phase at 17 ° C to 49 ° _C , an S _A phase at higher temperatures, and an isotropic liquid phase at 75 ° C. The helical pitch of this composition was as long as 15 μm at 20 ° C., and the spontaneous polarization showed a very large value of 19 nC / cm ² and the spontaneous polarization was large despite the long helical pitch. A ferroelectric chiral smectic liquid crystal composition having a large value was obtained.

Example 3 The liquid crystal composition prepared in Example 1 was coated with polyvinyl alcohol (PVA) as an alignment agent, and the surface was rubbed to perform parallel alignment treatment. I made a cell. This liquid crystal cell was sandwiched between two polarizers arranged in a crossed Nicols state, and when a low-frequency alternating current of 0.5 Hz and 15 V was applied, a clear switching operation with very good contrast was observed, and the reaction time A liquid crystal display device having a very fast response of 0.6 msec at 25 ° C. was obtained.

Example 4 The liquid crystal composition prepared in Example 2 had the chemical formula 3% by weight of anthraquinone dye 16 represented by BDH (manufactured by BDH) is added to the composition as a guest-host type, PVA is applied as an alignment treatment agent, and the surface is rubbed for parallel alignment treatment. did. The cell gap was injected into a cell having a transparent electrode of 5 μm to prepare a color liquid crystal display cell. This liquid crystal cell was arranged with one polarizer so that the plane of polarization was parallel to the molecular axis, and when an alternating current of low frequency of 0.5 Hz and 15 V was applied, a very good contrast and clear switching operation were obtained. Observed, response speed is 2
A color liquid crystal display device having a very fast value of 1 mesec at 0 ° C. was obtained.

[Brief description of drawings]

FIG. 1 and FIG. 2 are diagrams showing the magnitude of spontaneous polarization and the reciprocal of the helical pitch, respectively, in a binary mixed system of compound A and compound B.

Claims (4)

[Claims] 1. A ferroelectric chiral smectic liquid crystal composition containing at least one chiral smectic liquid crystal compound having a right-handed helical twist and at least one kylme smectic liquid crystal compound having a left-handed helical twist. As a chiral smectic liquid crystal compound that twists clockwise, (In the formula (I), m or n is an integer of 1 or 2, (m + n) is 2 or 3, and X is Or -OCH 2 _- indicates, R represents an alkyl group or alkyloxy group having 1 to 18 carbon atoms, Y represents an alkyl group, an alkyloxy group or an alkoxycarbonyl group having an asymmetric carbon atom. 1) is a compound in which the asymmetric carbon atom of the side chain Y is at an odd number position from the carbon atom to which the Y of the benzene ring is bonded is the 0th position, and the absolute configuration at the asymmetric carbon is R type. One or more, or as a compound in which the twist of the helix is counterclockwise, the asymmetric carbon atom of the side chain Y in the general formula is counted from the carbon atom to which the Y-bonding carbon of the benzene ring is attached as the 0th position. A ferroelectric chiral smectic liquid crystal composition comprising one or more compounds in even positions and having an R-type absolute configuration at the asymmetric carbon. 2. A chiral smectic liquid crystal compound according to claim (1), wherein the helical twist is clockwise, and the side chain Y in formula (I) is A ferroelectric chiral smectic liquid crystal composition which is an optically active compound. 3. Claims (1) or (2)
In the item, the chiral smectic liquid crystal compound in which the twist of the helix is counterclockwise has a side chain Y in the formula (I). A ferroelectric chiral smectic liquid crystal composition which is an optically active compound. 4. A ferroelectric chiral smectic liquid crystal composition containing at least one chiral smectic liquid crystal compound having a right-handed helical twist and at least one kylme smectic liquid crystal compound having a left-handed helical twist. As a chiral smectic liquid crystal compound that twists clockwise, (In the formula (I), m or n is an integer of 1 or 2, (m + n) is 2 or 3, and X is Or -OCH ₂ - indicates, R represents an alkyl group or alkyloxy group having 1 to 18 carbon atoms, Y represents an alkyl group, an alkyloxy group or an alkoxycarbonyl group having an asymmetric carbon atom. ), A compound having an asymmetric carbon atom of the side chain Y at an odd number position from the carbon atom to which the Y of the benzene ring is bonded is the 0th position, and the absolute configuration at the asymmetric carbon atom is R type. As a compound containing one or more or a helical twist in the left-hand direction, the asymmetric carbon atom of the side chain Y in the general formula is counted from the carbon atom to which the Y-bonding carbon of the benzene ring is bonded as the 0th position. An optical switching device comprising a ferroelectric chiral smectic liquid crystal composition containing at least one compound having an R-type absolute configuration at the asymmetric carbon atom.