Halogen-containing, optically active liquid crystal compound and liquid crystal composition containing same

Abstract: A novel optically active liquid crystal compound and a liquid crystal composition containing the same are provided, which compound is expressed by the formula wherein R₁ is alkyl or alkoxy of 4 - 18 C; R₂ is alkyl, alkoxy, acyl or alkoxymethyl of 4 - 18C; but either one of R₁ or R₂ is an optically active group; either one of X₁ or X₂ is halogen atom and the other is H; m and n each are 0 or 1 and m+n is 0 or 1.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a novel liquid crystal substance and a liquid crystal composition containing the same, and more particularly it relates to a chiral liquid crystal substance having an optically active group and a chiral liquid crystal composition containing the same. Description of the Prior Art As to liquid crystal display elements, TN type display mode has now been most widely employed, but TN type display elements are inferior in response speed to emissive display elements (such as electroluminescence, plasma display, etc.); hence various improvements therein have been attempted and nevertheless it does not appear that a large extent of improvement has been left behind. Thus, various liquid crystal display devices based on a different principle, in place of TN type display elements have been attempted, and among them there is a display mode utilizing a ferroelectric liquid crystal (N.A. Clerk et al, Applied Phys. lett., 36 , 899 (1980)). This mode utilizes the chiral smectic C phase (hereinafter abbreviated to S c * phase) or the chiral smectic H phase (hereinafter abbreviated to S H * phase), and it is preferred that such phases be present in the vicinity of room temperature. Certain compounds used for such applications have already been known. The present inventors, too have filed patent applications directed thereto. For example, EP-A-110299 discloses a compound expressed by the formula wherein R₁₁ represents an alkyl group or an alkoxy group; R * represents an optically active group; and m and n each represent 0 or 1. EP-A-115693 discloses a compound expressed by the formula wherein R₁₁, R * , m and n are as defined above. EP-A-164814 discloses a compound expressed by the formula wherein R * , R₁₁, m and n are nearly as defined above. The present inventors have further made research on a liquid crystal substance suitable for utilizing the chiral smectic phase of these ferroelectric liquid crystals, and as a result have found that certain above compounds of (A), (B) or (C) but whose benzene ring is substituted by a halogen atom, particularly fluorine atom as a lateral substituent have superior characteristics to those of (A), (B) or (C). Similar such halogenated compounds are disclosed in "Molecular Crystals and Liquid Crystals", 114 , pp 237-247 and 110 , pp 175-203; EP-A-0153826 ; EP-A-0188222 ; and WO-A-8604327 . The present invention resides in an optically active liquid crystal compound expressed by the formula: wherein R₁ represents an optically active 1-methyl-heptyloxy group; R₂ represents a non-optically active group which is an alkyl group, an alkoxy group, an acyl group or an alkoxycarbonyl group each of 4 to 18 carbon atoms; X₁ represents a halogen atom; m and n each represent 0 or 1 and m + n is 1, and a liquid crystal composition containing the same. DESCRIPTION OF PREFERRED EMBODIMENTS The above compounds expressed by the following formulae (Ia) and (Ib): wherein-OR₃ * represents an optically active 1-methyl-heptyloxy group; R₄ which is non optically active represents an alkyl group, an alkoxy group, an acyl group or an alkoxycarbonyl group each of 4 to 18 carbon atoms; X₁ represents a halogen atom; wherein R₃ * , R₄ and X₁ are as defined above. Representative examples of the respective compounds have the following values of physical properties (phase transition points) shown in Tables 1 ∼ 7. Compounds of the formula (I) which have three benzene rings have higher upper limit temperatures of Sc* phase, and among these compounds, those having no unfavorably high melting points are useful as a main component for constituting liquid crystal compositions. Next, the effectiveness of having a halogen atom as a lateral substituent on the benzene ring will be described. Table 3 shown below illustrates the phase transition points and the spontaneous polarization values (Ps) of halogen-substituted compounds and halogen-unsubstituted compounds (parent compounds). Such a halogen introduction reduces the melting points of the parent compounds in most cases, but raises them in some cases. As to the compounds of the types shown in Table 3, when the halogen is F or Cℓ, a preferred rise in the upper limit temperature of Sc* phase is observed. Whereas when the halogen is Br, the upper limit temperature of Sc* phase is notably reduced to make impossible its observation. The effectiveness of these halogens cannot be naturally anticipated, but it can be said that F and Cℓ have a particularly preferred effectiveness. As to the Ps value, it has been found that those of halogen-substituted compounds increase to about twice those of halogen-unsubstituted compounds. Table 4 shows other comparison examples of halogen-substituted compounds and halogen-unsubstituted ones. As to the compounds of these types, too, the presence of halogen atom reduces the melting points of the parent compounds in most cases, and raises the upper limit temperatures of Sc*. The clearing point (Ch-I point) generally lowers, but only this fact is a fact anticipated from the so far known rule. The Ps value is also raised, but the effectiveness in this case is not so notable as that in the case of the compounds of the types shown in Table 3. The compound of the formula (I) may be prepared through the following passageways: Namely, it may be prepared by reacting an acid halide of substituted benzoic acids or substituted biphenylcarboxylic acids as expressed by the formula (II) with a substituted phenol or substituted phenyl-phenol as expressed by the formula (III), in a basic solvent such as pyridine. Among the acid halides of carboxylic acids (II) as one of the raw materials, those wherein X₁ = 3-halogen and R₁ = alkyloxy group as defined in claim 1 may be prepared using a known carboxylic acid (I) wherein X₁ =H as raw material, according to the following steps: Namely, a p-alkoxy-substituted-benzoic acid or a p-alkoxy-substituted-biphenylcarboxylic acid (I) is reacted with a halogenating agent such as bromine, chlorine, N,N-dichloro-p-toluenesulfonamide. for introducing a halogen atom to prepare a compound (2). However, among compounds (II), those wherein X₁ = 3-F are preferred to prepare according to the following steps: In case of m=0, In case of m = 1, Among compounds of (II), those wherein X₁ = 2-halogen and R₁ = alkyloxy group as defined in claim 1 may be prepared from (known compound) in the same manner as above. The substituted benzoic acids and substituted biphenylcarboxylic acids expressed by the formula (II) include the following compounds: Further, the substituted phenols or substituted phenylphenols expressed by the formula (III) as another of the raw materials include the following compounds: In the above formulas, R represents an alkyl group of 4 to 18C; R*, an optically active 1-methyl-heptyl group atoms; X₂, a halogen atom or hydrogen atom; and n, 0 or 1. In the above formulas, preparation of compounds wherein X₂ = H is known. The optically active ester liquid crystal compound of the present invention will be described in more detail by way of Examples. In the succeeding Examples are described only those using S-type compounds as the optically active alcohol for the raw material, but even when R-type optically active alcohols are used as the raw material, products having the same phase transition points as those in the S-type case are obtained. This is also theoretically natural. However, the angle of rotation, the helical twist direction and the direction of the spontaneous polarization in the R-type case are reverse to those in the S-type case. Example 1 Preparation of optically active 3-fluoro-4-(1-methyl-heptyloxy)-benzoic acid 4'-octyloxy-4-biphenyl ester (a compound of the formula (I a ) wherein n=1, R₄ =-OC₈H₁₇; sample No. 14) (i) S(+)-2-octanol (200 g, 1.536 mol) was dissolved in dry pyridine (600 mℓ), followed by dropwise adding to the solution, a solution of p-toluenesulfonyl chloride (292.8 g, 1.536 mol) dissolved in dry toluene (440 mℓ) while keeping the temperature of the system at 10°C or lower, agitating the mixture at room temperature for one hour, raising the temperature of the system up to 50°C, keeping the material,as it was, for 2 hours, thereafter cooling, further adding water (1 ℓ) and toluene (500 mℓ) with stirring, washing the separated toluene layer with 6N-HCℓ, then with 2N-NaOH aqueous solution and further with water till the washing liquid became neutral, and distilling off toluene to obtain as a residue, optically active p-toluenesulfonic acid 1-methyl-heptyl ester (321.0 g). (ii) On the other hand, o-fluorophenol (500 g, 4.46 mols) was added to a solution of NaOH (1,250 g, 31.26 mols) dissolved in water (2 ℓ), followed by dropwise adding chloroform (1,230 g), agitating the mixture at about 60°C for 2 hours, acidifying it with sulfuric acid, filtering off the residue on heating, and recrystallizing the deposited crystals from a mixed solvent of water-methanol to obtain 3-fluoro-4-hydroxybenzaldehyde (35.3 g) having a m.p. of 119.5 ∼ 123.5°C. This product (30 g, 0.21 mol) was dissolved in methanol (300 mℓ) , followed by adding and dissolving KOH (12 g, 0.21 mol), dropwise adding optically active p-toluenesulfonic acid 1-methyl-heptyl ester (65 g, 0.23 mol) prepared above, keeping the mixture under reflux for 4 hours, cooling, adding toluene (200 mℓ) and 6N-HCℓ (100 mℓ), washing the resulting toluene layer with 2N-NaOH aqueous solution, further washing with water till the washing layer became neutral, and distilling off toluene to obtain as residue, optically active 3-fluoro-4-(1-methyl-heptyloxy)-benzaldehyde (14.7 g). This product (10 g, 0.04 mol) was dissolved in acetic acid (200 mℓ), followed by dropwise adding a solution of chromic anhydride (4 g, 0.04 mol) dissolved in acetic acid (50 mℓ) and water (40 mℓ), agitating the mixture at 40 ∼ 50°C for about 6 hours, pouring the resulting reaction material in ice water and filtering off the deposited crystals to obtain optically active 3-fluoro-4-(1-methyl-heptyloxy)-benzoic acid (6.1 g) having a m.p. of 57.2 ∼ 59.2°C, adding thionyl chloride (4.2 g, 0.035 mol) to the above product (6 g, 0.022 mol), heating the mixture under reflux with stirring for one hour, and distilling off excess thionyl chloride to obtain optically active 3-fluoro-4-(1-methyl-heptyloxy)-benzoic acid chloride (6.1 g). (iii) Further, 4-(4'-octyloxyphenyl)phenol (11.2 g, 0.039 mol) was dissolved in pyridine (10 mℓ) , followed by adding to the solution, optically active 3-fluoro-4-(1-methyl-heptyloxy)-benzoic acid chloride (10 g, 0.035 mol) prepared above, agitating the mixture at 50 ∼ 60°C for about 2 hours, allowing it to stand overnight, adding toluene (300 mℓ) and water (200 mℓ), washing the toluene layer with 6N-HCℓ, then with 2N-NaOH aqueous solution and further with water till the washing water became neutral, distilling off toluene and recrystallizing the residue from ethanol to obtain the objective optically active 3-fluoro-4-(1-methyl-heptyloxy)-benzoic acid 4'-octyloxy-4-biphenyl ester (2.3 g). The phase transition points of this product were as follows: C-S c * point 64.5°C, S c *-I point 99.8°C. Further, the values of elemental analysis of this compound accorded well with the calculated values as follows: Observed values Calculated values in terms of C₃₅H₄₅O₄F C 76.10% 76.41% H 8.00% 8.27% F 3.20% 3.46% Example 2 (Use example 1) A liquid crystal composition consisting of the following liquid crystal compounds of the formula (I) of the present invention was prepared: This liquid crystal composition was sealed in a cell of 2 µm thick provided with transparent electrodes coated with polyvinyl alcohol and subjected to parallel alignment by rubbing the surface, and the resulting liquid crystal element was placed between two crossed polarizers and an electric field of 15 V was impressed to observe change in the intensity of transmitted light. Response time was sought from the change in the intensity of transmitted light at that time to give about 180 µsec at 25°C. The above liquid crystal composition had an upper limit temperature of S c * of 99°C, and no crystallization could be observed. Further, observation was carried out down to -50°C, but smectic phase other than S c * phase did not appear. In addition, the spontaneous polarization value was 150 nC/cm² at 25°C and the tilt angle was 34°.

Claims: An optically active liquid crystal compound expressed by the formula wherein R₁ represents an optically active 1-methyl-heptyloxy group; R₂ represents a non-optically active group which is an alkyl group, an alkoxy group, an acyl group, or an alkoxy carboxyl group; each of 4 to 18 carbon atoms; X₁ represents a halogen atom; m and n each represent 0 or 1 and m+n is 1. An optically active liquid crystal compound according to claim 1 expressed by the formula (I a ) wherein R₃*0- has the meaning defined for R₁ in claim 1; R₄ represents a non-optically active group which is an alkyl group, an alkoxy group, an acyl group or an alkoxycarbonyl group each of 4 to 18 carbon atoms; and X₁ represents a halogen atom. An optically active liquid crystal compound according to claim 1, expressed by the formula (I b ) wherein R₃*, R₄ and X₁ are as in claim 2. A liquid crystal composition having at least two components at least one of which is an optically active compound expressed by the formula (I) as set forth in claim 1. A chiral smectic liquid crystal composition having at least two components at least one of which is an optically active liquid crystal compound expressed by the formula (I) as set forth in claim 1.

Inventors: ICHIHASHI MITSUYOSHI, INOUE HIROMICHI, INUKAI TAKASHI, MIYAZAWA KAZUTOSHI, SAITO SHINICHI, TERASHIMA KANETSUGU NOKENDO-KO, ICHIHASHI, MITSUYOSHI, INOUE, HIROMICHI, INUKAI, TAKASHI, MIYAZAWA, KAZUTOSHI, SAITO, SHINICHI, TERASHIMA, KANETSUGU NOKENDO-KOPO
Applicants: CHISSO CORP, CHISSO CORPORATION
Application year: 1986
Main classification: C09K19
IPC codes: C07C69, C09K19, G02F1