JPH083093B2 - Ferroelectric smectic liquid crystal composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ferroelectric smectic liquid crystal composition used in a display device or an electro-optical device.

[Prior Art] A liquid crystal display element using a nematic liquid phase, which has been conventionally used for a display unit of a timepiece calculator or the like, has a response speed which is much slower than that of another display element, for example, an emitting diode. However, applications to liquid crystal display devices in fields such as optical communication and printer heads where the response of (1) has been required have been limited.

Recently, a liquid crystal display device using a smectic liquid crystal exhibiting ferroelectricity has been reported as a liquid crystal display device exhibiting high-speed response (for example, NAClark, STLagerwall, Appl.Phy.
s. Lett. 36 , 899 (1980)) is attracting attention.

Smectic liquid crystals exhibiting ferroelectricity include a chiral smectic C phase and a chiral smectic H phase, which have a layered structure in which liquid crystal molecules are inclined not perpendicular to the stacking direction of layers. The liquid crystal molecules are arranged so that this tilting direction spirals with respect to the stacking direction of the layers, and spontaneous polarization occurs in a direction parallel to this layer and perpendicular to the liquid crystal molecules, and the ferroelectricity is improved. Show. This helical structure is considered to be the cause of the ferroelectricity. A material exhibiting ferroelectricity exhibits responsiveness as a ferroelectric substance to an electric field, and reorients spontaneous polarization by reversing the direction according to the direction of the electric field.

At this time, it is known that the responsiveness has a large spontaneous polarization, and the lower the viscosity is, the faster the response is for the same electric field strength. In addition, an element using a ferroelectric smectic liquid crystal has a memory property, and researches using this memory property for high-density display are being actively conducted.

[Problems to be Solved by the Invention] As a ferroelectric smectic liquid crystal, conventionally, a lot of compounds having a Schiff base type as shown below have been studied.

p-decyloxybenzylidene-p'-amino-2-
Methyl butyl-cinnamic acid ester (DBAMBC) However, since such a Schiff base type compound is easily hydrolyzed, there is a problem that it is easily decomposed by water.

Further, as an ester type compound exhibiting a chiral smectic C phase, a compound represented by the following general formula (II) has been known.

(GW Gray etc.Mol.Cryst.Liq.Cryst, 1976, 37 189-21
1) (R is a straight-chain alkyl group having 5 to 10 carbon atoms) However, this ester compound has a problem that its spontaneous polarization value is small although it withstands moisture.

More recently, as a compound with large spontaneous polarization, DOBA-
The compound of the following structure, abbreviated as 1-MBC, is
OSHINO et al., JJAP, 1984, 23 L 175-177).

However, since this compound is also a Schiff base type, it has a drawback that it is easily decomposed by water.

[Means for Solving the Problem] The present invention has been made to solve the above-mentioned problems, and at least one compound represented by the general formula (I) is used.
A ferroelectric smectic liquid crystal composition containing a seed is provided.

(In the formula, R represents an alkyl group or an alkoxy group having 1 to 12 carbon atoms, and ring A and ring B each independently represent 1,4-di-substituted phenylene or trans-1,4-di-substituted cyclohexylene, and X And X'are independently a single bond, -COO
-, - OCO -, - CH 2 -CH 2 -, - CH 2 -O- or -O-
CH ₂ -representation, n represents 0 or 1, and * represents an optically active center).
A ferroelectric smectic liquid crystal composition containing a seed.

In the compound of the general formula (I), R is an alkyl group or an alkoxy group, and when the number of carbon atoms is small, the melting point is high, and when it is too large, the viscosity is high, so that it is 1 to 12, but preferably 2-8 is good. R may be linear or branched, but linear ones are generally preferable because the liquidus upper limit temperature showing the smectic C phase when mixed with another compound exhibiting liquid crystallinity is high.

Ring A is 1,4-di-substituted phenylene or trans-1,4-di-substituted cyclohexylene, and Ring A is
In the case of 1,4-disubstituted phenylene, the range showing the smectic C phase is wide, and in the case where ring A is a trans-1,4-substituted cyclohexane ring, its viscosity is low.

Ring B has a low viscosity in the case of a trans-1,4-substituted cyclohexane ring, and has a wide range showing a smectic C phase in the case of a 1,4-disubstituted phenylene.

X and X'are each independently a single bond or -COO- or -OCO.
_{-, - CH 2 -CH 2 -} , - CH 2 -O- or -OCH ₂ - are illustrated, inter alia because their low viscosity in the case of single bond preferred. In the general formula (I), The compound represented by is preferable because it has a low viscosity and a wide temperature range in which the smectic C phase is exhibited. The optical rotatory power of the compound represented by formula (I) may be right or left.

The compound represented by the general formula (I) is used for a ferroelectric smectic liquid crystal display device or an electro-optical device,
It is used as a ferroelectric smectic liquid crystal composition by appropriately mixing it with another ferroelectric smectic liquid crystal or smectic liquid crystal or an optically active substance so as to have a chiral smectic C phase in a desired temperature range. Further, nematic liquid crystal, non-liquid crystal, dichroic dye or the like may be added for adjusting the spiral pitch or for displaying color. When the content of the compound represented by the general formula (I) in the ferroelectric smectic liquid crystal composition of the present invention is too high, the ferroelectric smectic maximum temperature tends to be lowered, and when it is too low, Since the effect of increasing the spontaneous polarization is small, 1% by weight or more and 90% by weight or less, preferably 2%
It is preferable that the content is 50% by weight or more and 50% by weight or less.

Examples of the counterpart compound used as a ferroelectric smectic liquid crystal composition by mixing with the compound of the general formula (I) of the present invention include the following.

In the following examples, R ^* represents an optically active alkyl group or an alkoxy group, R represents a linear or branched alkyl group or an alkoxy group regardless of R of the present invention, and the same R in one compound is used. ^{Even if *} and R are shown, they are not necessarily the same group.

In addition to these, various known liquid crystal or non-liquid crystal liquid crystal additives can be used in combination.

And compounds in which a part of hydrogen atoms of these benzene ring and cyclohexane ring are substituted with halogen, cyano group, methyl group and the like.

Examples of the dichroic dye include dyes used in so-called guest-host type liquid crystal display devices such as trisazo type and anthraquinone type.

The ferroelectric liquid crystal display element or the electro-optical element is arranged so as to sandwich the liquid crystal layer, and at least one transparent substrate having a plurality of electrodes having electrodes on the whole surface or a part thereof is surrounded by the liquid layer. And a seal member formed between the electrode substrates. In the liquid crystal display element, the thickness between the substrates is
0.5 to 20 μm is preferable. Further, the substrates may be subjected to alignment control processing parallel to each of them. As a means for controlling the orientation, an orientation control film may be applied partially or entirely on the electrode substrate. As the orientation control film, a polymer material such as polyimide having a refractive index of 1.5 or more is preferable. Furthermore, at least one polarizer is preferably attached to the liquid crystal element. At least two electrode substrates are required, but a larger number of electrode substrates may be stacked and used.

The compound of the present invention can be synthesized, for example, by the route shown below.

That is, a benzoic acid derivative (II) is treated with a chlorinating agent such as thionyl chloride or phosphorus oxychloride to form an acid chloride (II
I) and then the optically active phenethyl alcohol (I
Pure (I) can be synthesized by reacting V) with a basic substance such as pyridine and performing a series of purification treatments such as extraction, recrystallization and column chromatography.

[Examples] Next, the present invention will be specifically described with reference to Examples.

Compound Production Example A mixture of 1.75 g (5.1 mmol) of 4 '-(4 "-n-pentylcyclohexyl) biphenyl-4-carboxylic acid, 2.4 g (20 mmol) of thionyl chloride and 20 ml of carbon tetrachloride was heated under reflux for 6 hours. The solvent and excess thionyl chloride were distilled off to obtain an acid chloride, which was dissolved in 10 ml of toluene, and 0.5 g (4.1 mmol) of L-(-)-α-phenylethyl alcohol and pyridine were added to the solution. After adding 1 ml and stirring overnight, the precipitated pyridine hydrochloride was separated, the solution was washed with dilute aqueous solution of hydrochloric acid NaOH and water in this order, the organic layer was dried over anhydrous magnesium sulfate, and the solvent was distilled off. Was recrystallized from ethanol and toluene and further subjected to triene-activated alumina column chromatography, Was obtained. Melting point 91.0 ° C, yield 1.2 g, yield 64,5%.
The infrared spectrum of this compound is shown in FIG. 1, and the NMR spectrum (CDCl ₃ solvent, TMS internal standard) is shown in FIG.

Example 1 The phase transition temperature and the spontaneous polarization (Ps) of the liquid crystal composition obtained by mixing 5 to 15 wt% of the following four types of compounds based on the compound shown in were measured. The results are shown in Table 1.

The spontaneous polarization was measured by enclosing the sample in a cell with a spacer of 3 μm and having an electrode area of 1 cm ^{2, and} at a maximum temperature of the chiral smectic C phase of −10 ° C., 20 Hz, 10 V.
Was applied according to the method of Miyasato et al.
(K. Miyasato et al., Japan.j.Appl.Phys., 22 L661, (198
3)) Moreover, the phase transition temperature was determined by observation under a polarizing microscope with a hot stage.

As can be seen from Table 1, these compositions exhibit a practically sufficiently high chiral smectic C phase maximum temperature. Also, the spontaneous polarization is It was found that the spontaneous polarization of (DOBAMBC) alone was 3.7 nC / cm ² , while it showed the same or higher value.

Example 2 Composition 1 using the liquid crystal composition obtained by mixing 5 wt% of compound 1 of Example 1 and DOBAMBC were put in a sample tube and left in an atmosphere of temperature 80 ° C. and humidity 90% for 20 hours, The change in Tc was examined before and after that.

Since DOBAMBC is a Schiff base type compound, it is easily hydrolyzed, and the maximum temperature of the chiral smectic C phase is decreased from 93.0 ° C to 76.1 ° C by 16.9 ° C, while the composition 1 of the present invention is from 65.1 ° C. It was found that there was no problem in practical use, as it decreased to 64.8 ° C by only 0.3 ° C.

In the same manner as in Example 1, 5% by weight of the following compound was added. A ferroelectric chiral smectic C liquid crystal composition can be obtained by mixing with 95% by weight.

[Effects of the Invention] The present invention provides a ferroelectric smectic liquid crystal composition containing at least one compound represented by the general formula (I), which has large spontaneous polarization and is chemically stable. It has an excellent effect of forming a display element or an electro-optical element having excellent properties and capable of high-speed response.

[Brief description of drawings]

1 and 2 are an infrared spectrum diagram and an NMR spectrum diagram (CDCl ₃ solvent, TMS internal standard) of the compound of the compound production example.

Claims (7)

[Claims] 1. A general formula (In the formula, R represents an alkyl group or an alkoxy group having 1 to 12 carbon atoms, ring A and ring B each independently represent 1,4-di-substituted phenylene or trans-1,4-di-substituted cyclohexylene, and X And X'are independently a single bond, -COO
-, - OCO -, - CH 2 -CH 2 -, - CH 2 O- or -O-CH ₂
Represents-, n represents 0 or 1, and * represents an optically active center). A ferroelectric smectic liquid crystal composition containing at least one compound represented by the formula. 2. The liquid crystal composition according to claim 1, wherein both X and X'in the general formula (I) represent a single bond. 3. The liquid crystal composition according to claim 2, wherein in the general formula (I), n is 0. 4. In the general formula (I), n is 1 and ring B is 1,4-disubstituted phenylene.
Item. 5. In the general formula (I), ring A is trans-
The liquid crystal composition according to claim 2, which is 1,4-di-substituted cyclohexylene. 6. The liquid crystal composition according to claim 2, wherein ring A in the general formula (I) is 1,4-disubstituted phenylene. 7. The liquid crystal composition according to any one of claims 1 to 6, wherein R in the general formula (I) is linear.