JPH0416454B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel liquid crystal substance and a liquid crystal composition containing the liquid crystal, particularly a liquid crystal composition exhibiting a chiral smectic C phase. In this specification, the term "liquid crystalline substance" refers to a substance that exhibits a liquid crystal phase by itself, and a substance that is useful as a component of a liquid crystal composition even if it is not detected to exhibit a liquid crystal phase by itself. Currently, liquid crystals are becoming widely used as display materials, and most of the liquid crystal display elements using them are TN (Twist Nematic) type display systems (for example, see Japanese Patent Application Laid-Open No. 11737-1983). was adopted. The TN display system is light-receiving and does not strain the eyes. Although it has excellent features such as extremely low power consumption, it has drawbacks such as slow response and the display cannot be seen depending on the viewing angle. Recent demands for display devices include particularly high-speed response, and in order to meet these demands, various improvements have been made in the field of liquid crystal materials. However, there is still a large difference in response time compared to other light-emitting display elements (EL (electroluminescent) displays, plasma displays, etc.). In order to take advantage of the light-receiving low power consumption feature of liquid crystal display elements and still ensure responsiveness comparable to light-emitting displays, it is essential to develop a new liquid crystal display method to replace the TN display method. One such attempt is a display device that utilizes the optical switching phenomenon of ferroelectric liquid crystals (for example, Japanese Patent Application Laid-Open No. 107216/1983).
No., NAClark, STLagerwall; Appl.Phys.
Lett., 36 , 899 (1980)). The existence of ferroelectric liquid crystals was first announced in 1975 by RBMeyer et al.
et al.; J. Physique, 36 , L-69 (1975)), and from the crystal structure, chiral smectic C phase (hereinafter referred to as
It is said to belong to the chiral smectic H phase (hereinafter abbreviated as ^{SmH* phase} ). Currently, the compounds shown in Table 1 are known as ferroelectric liquid crystal compounds (Ph.Martinot
- Lagarde; see J. Physique, 37 , C3-129 (1976)).

【table】

[Table] However, as can be seen from Table 1, the temperature range (SmC ^* phase or
In many cases, the SmH ^* phase (temperature range showing phase) is higher than room temperature, and in all compounds, the carbon-carbon double bond attached to the benzene ring easily undergoes isomerization in a short time when exposed to light, resulting in the cis form. As a result, it is unstable in that it no longer exhibits a liquid crystal phase, and is not suitable for use in display devices. Therefore, as a result of earnestly pursuing a molecular structure that eliminates such unstable factors and exhibits ferroelectricity in the temperature range near room temperature, we have arrived at the compound of the present invention and a liquid crystal composition containing it as a compounding ingredient. did. That is, the present invention is based on the general formula (In the above formula, R represents an alkyl group having 7 to 12 carbon atoms, and * represents an asymmetric carbon atom).
-Alkyloxy-4'-biphenylcarboxylic acid ester and a ferroelectric liquid crystal composition containing this compound as a constituent component. Comparing the compound of formula () of the present invention with the existing ferroelectric liquid crystal compounds shown in Table 1, it is found that the carbon-carbon double bond, which is a factor of instability against light, is eliminated;
Furthermore, the azomethine bond, which is a factor that makes it unstable with respect to water, is eliminated, making it an extremely stable substance. Furthermore, although this compound exhibits ferroelectricity in a preferable temperature range around room temperature, such a fact cannot be easily deduced from known experimental facts. As a compound related to the compound of the present invention, GWGray et al. (Mol.Cryst.Liq.Cryst., 37 ,
157 (1976)) reported the following three series of compounds and indicated their liquid crystal phase transition temperatures. (In the above formula, CnH2n ₊₁ represents a linear alkyl group.) On the other hand, in the compound () of the present invention, all the corresponding groups have a branched alkyl group, and it is an optically active substance, and its SmC ^* phase is It was previously unknown that it exhibited ferroelectricity. Furthermore, a compound of the following formula having a chemical structure similar to that of the compound of the present invention is disclosed in JP-A-57-11944. (R represents an alkyl group having 1 to 10 carbon atoms) However, these do not show any smectic phase, but only show a cholesteric phase at low temperatures. The chemical structure of the liquid crystalline compound of the present invention is characterized by having a biphenyl skeleton as is clear from the formula ().
an alkyloxy group at the 4-position, and an alkyloxy group at the 4'-position.
It lies in having COOR ^* . The alkyloxy group at the 4-position is an alkyloxy group having 7 to 12 carbon atoms. In the COOR ^* group at the 4'-position, R ^* is an optically active group having the structure shown by the following formula. By the way, as mentioned earlier, ferroelectric liquid crystals
It belongs to SmC ^* phase or SmH ^* , but the characteristics of these two liquid crystal phases are that the molecules are distributed and arranged in a layered manner, and on the plane of the layer, the molecules are arranged tilted in a certain direction. Moreover, the direction of the inclination is slightly shifted from layer to layer, resulting in a liquid crystal structure with a spiral structure as a whole (RB
Meyer; Mol.Cryst.Liq.Cryst., 40 , 33 (1977)). Spontaneous polarization is oriented in a direction perpendicular to this helical axis (perpendicular to the layer plane) and the alignment direction of the liquid crystal molecules. Now, in order to induce such a liquid crystal structure and spontaneous polarization, it is thought that the following two elements are necessary in the molecular structure. That is, in order to induce a helical structure, the terminal group must have an asymmetric structure, and in order to induce spontaneous polarization, the terminal group must have a permanent dipole in a direction approximately perpendicular to the long axis direction of the liquid crystal molecules. It is to have. The compound of formula () satisfies these two conditions and has photochemical stability and chemical stability not found in existing ferroelectric liquid crystal compounds. Furthermore, as shown in the Examples described below, by blending other liquid crystal compounds, the effect of lowering the temperature range in which the liquid crystal composition exhibits ferroelectricity to around room temperature is also shown. Compound () is produced by reacting 4-alkyloxy-4'-biphenylcarboxylic acid with a halogenating agent such as thionyl chloride or phosphorus pentachloride to form an acid halide, which is then converted to an optically active alcohol in a basic solvent such as pyridine. Although it is most preferably synthesized by reacting esters, other commonly known esterification methods may also be used. Next, Table 2 shows the phase transition temperature of the compound () obtained as described above. (All optically active groups R ^* are 2-methylbutyl groups)

[Production of 4 _- octyloxy-4'-biphenylcarboxylic acid-2-methylbutyl ester (in the formula (), R is _C8H17 )]

20 g of 4-octyloxy-4'-biphenylcarboxylic acid and 50 ml of thionyl chloride were heated under reflux for 2 hours, excess thionyl chloride was distilled off, and 4-octyloxy-4'-biphenylcarboxylic acid chloride was obtained. obtain. This product is not particularly purified and is used as a toluene solution in the next step. On the other hand, 16 g of (-)2-methyl-1-butanol (manufactured by Eastman Kodak) dissolved in 50 g of pyridine was cooled in water, and a toluene solution of the above acid chloride was added thereto for about 30 minutes with stirring. Add with
Further stir for 30 minutes on a 90°C water bath. After cooling, add 6N hydrochloric acid and ice to make it acidic, separate the layers, take the organic layer, wash with water, wash with 2N sodium hydroxide solution,
After washing with water, toluene is distilled off to obtain the target product (crude product). This was dissolved in about 70 ml of heptane, passed through an alumina/heptane chromatography column, and recrystallized twice from ethanol to obtain 18.0 g of colorless needle-shaped crystals. Its NMR
The spectra and elemental analyzes were consistent with the desired compound, 4-octyloxy-4'-biphenylcarboxylic acid-2-methylbutyl ester. In addition, the degree of light application [α] ²⁴ _D in a chloroform solution was +3.5°C. The phase transition temperatures are shown in Table 2 above along with those of other compounds of formula (). The raw material 4-octyloxy-4'-biphenylcarboxylic acid is commercially available 4-octyloxy-4'-
It is a known substance obtained by alkaline hydrolysis of cyanobiphenyl (M-24 manufactured by BDH). Example 2 4-heptyloxy-4'-biphenylcarboxylic acid-2-methylbutyl ester and 4-octyloxy-4'-biphenylcarboxylic acid-2-methylbutyl ester (both formulas ( ) shown in Table 2) The melting point (C-SmC ^* point) of an equimolar mixture of
33℃, SmC ^* −SmA point is 42.2℃, SmA−I point is
The temperature reached 65°C, indicating that the compound has properties more suitable for display elements than a single compound. Example 3 In the formula (), R is respectively C ₇ H ₁₅ , C ₈ H ₁₇ , C ₉ H ₁₉ ,
Compounds of C ₁₀ H ₂₁ and C ₁₂ H ₂₅ (both listed in Table 2)
A 14:11:6:10:9 mixture (weight ratio) of SmC ^*
-SmA point is 34.6°C and SmA-I point is 63.2°C, which has characteristics suitable for use in display devices. Example 4 4-octyloxy-4'-biphenylcarboxylic acid-2-methylbutyl ester (listed in Table 2),
The equimolar mixture of p-octyloxybenzylidene-p-(2-methylbutyloxycarbonyl)aniline, which is one of the ferroelectric liquid crystal compounds discovered and patented by the present inventors, is C
-SmC ^* point 20~21℃, SmC ^* -SmA point 33,6℃,
The SmA-I point has a phase transition point of 62°C, and the value of the spontaneous polarization of this mixture is shown in Fig. 1 by 〓. Example 5 A liquid crystal display element having the liquid crystal composition of Example 4 as a liquid crystal phase was manufactured, and its response characteristics were evaluated. A liquid crystal display element consists of a polyimide polymer film placed on a glass substrate with an indium oxide transparent electrode.
After rubbing in a certain direction using gauze, a liquid crystal cell was assembled using a glass fiber as a spacer so that the rubbing directions of the two substrates were parallel to each other, and the liquid crystal composition of Example 5 was vacuum-sealed into this cell. It is something. The cell spacing is 5.4 μm.
This liquid crystal display element was placed between two orthogonal polarizers, and changes in the intensity of transmitted light when an electric field was applied were measured. The response waveform measured at 24°C is shown in Figure 2, and as is clear from it, the response time of this liquid crystal display element is extremely short, approximately 1 millisecond, indicating that this liquid crystal display element has excellent high-speed response. It shows that

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the spontaneous polarization value of liquid crystal and temperature. In the figure, A (●) is the value of B (○ ) is 4-heptyloxy-
C (〓) of 4'-biphenylcarboxylic acid-2-methylbutyl ester indicates the measured value of the liquid crystal mixture of Example 4. FIG. 2 is a graph showing the response characteristics of the liquid crystal display element of Example 5.

Claims (1)

[Scope of Claims] 1. A liquid crystalline 4-alkyloxy-4'-biphenylcarboxylic acid ester exhibiting a chiral smectic C phase with a molecular structure represented by the general formula (). (In the above formula, R represents an alkyl group having 7 to 12 carbon atoms, * represents an asymmetric carbon atom) 2 Liquid crystallinity 4 exhibiting a chiral smectic C phase with a molecular structure represented by the general formula () -A ferroelectric liquid crystal composition containing at least one alkyloxy-4'-biphenylcarboxylic acid ester as a compounding component. (In the above formula, R represents an alkyl group having 7 to 12 carbon atoms, * represents an asymmetric carbon atom) 3 Liquid crystalline compound of formula () and p-alkyloxybenzylidene-p'-(2-methyl 3. The ferroelectric liquid crystal composition according to claim 2, which comprises p-alkyloxybenzylidene-p'-amino-2-methylbutylcinnamates and/or p-alkyloxybenzylidene-p'-amino-2-methylbutylcinnamates.