Novel Liquid Crystal Compound

This invention relates to a novel liquid crystal compound and a liquid crystal composition containing the same.

Liquid crystal display elements utilize the optical anisotropy and the dielectric anisotropy of liquid crystal substances, and are classified into various modes such as those of TN type (twisted nematic type), DS type (dynamic scattering type), guest-host type, DAP type, etc., depending on the display mode of the elements; thus the properties of liquid crystal substances may be varied to render them suitable to their respective uses. However, many of liquid crystal substances have been required in common to be stable to moisture, air, heat, light, etc. and also those which exhibit liquid crystal phases in a temperature range as broad as possible around room temperature have been desired. At present, however, there is no single substance which satisfies such conditions; hence liquid crystal compositions obtained by blending several kinds of liquid crystal compounds or mixtures thereof with non-crystal compounds have been used.

The object of the present invention is to provide a novel liquid crystal compound which, when added to liquid crystal substance(s), can improve some characteristics required for the above liquid crystal compositions.

The present invention is a first aspect resides in (1) A novel liquid crystal compound expressed by the formula (I) ##STR2## wherein R represents an alkyl group or an alkoxy group each of 1 to 10 carbon atoms; Y represents F, Cl or H; and Z represents F, Cl, cyano group or an alkyl group or an alkoxy group each of 1 to 10 carbon atoms.

The above present invention in a first aspect has the following embodiments (2) to (5) shown below:

(2) A 2-(.beta.-substituted ethyl)-5-substituted pyridine according to the above paragraph (1) wherein R represents an alkyl group or an alkoxy group each of 1 to 10 carbon atoms; Y represents H; and Z represents F, Cl or cyano group, in said formula (I).

(3) A 2-(.beta.-substituted ethyl)-5-substituted pyridine according to the above paragraph (1) wherein R represents an alkyl group or an alkoxy group each of 1 to 10 carbon atoms; Y represents F or Cl; and Z represents, F, Cl or cyano group, in said formula (I).

(4) A 2-(.beta.-substituted ethyl)-5-substituted pyridine according to the above paragraph (1) wherein R represents an alkyl group or an alkoxy group each of 1 to 10 carbon atoms; Y represents F, Cl or H; and Z represents an alkyl group of 1 to 10 carbon atoms, in said formula (I).

(5) A 2-(.beta.-substituted ethyl)-5-substituted pyridine according to the above paragraph (1) wherein R represents an alkyl group or an alkoxy group each of 1 to 10 carbon atoms; Y represents F, Cl or H; and Z represents an alkoxy group of 1 to 10 carbon atoms, in said formula (I).

The present invention in a second aspect resides in a liquid crystal composition having at least two components at least one of which is a liquid crystal compound expressed by the formula (I) as set forth in the above paragraph (I).

The compounds of the present invention expressed by the formula (I) may be prepared according to a known method expressed by the following reaction scheme: ##STR3##

Namely, 3-cyano-6-methylpyridine (II) is reacted with hydrogen chloride in the presence of an alcohol solvent to obtain an imide ether hydrochloride derivative (III), followed by reacting this compound (III) with ammonia in an alcohol solvent to obtain an amidine hydrochloride derivative (IV), thereafter subjecting this compound (IV) and an acrolein derivative having a suitable substituent R (V) to condensation-cyclization reaction in the presence of a suitable basic catalyst such as an alkali alcoholate or pyridine and triethylamine, etc. to obtain a pyrimidylpyridine derivative (VI), subjecting this compound (VI) and a substituted benzaldehyde (VII) to dehydration-condensation reaction in the presence of acetic anhydride to obtain a 2-[.beta.-(substituted phenyl)vinyl]-5-(5'-substituted pyrimidinyl-2')pyridine (VIII), and reducing this compound (VIII) to obtain the objective a 2-[.beta.-(substituted phenyl)ethyl]-5-(5'-substituted pyrimidinyl-2')pyridine (I).

As concrete examples of other liquid crystal compounds constituting liquid crystal compositions together with the compound of the formula (I), a group of known compounds expressed by the following formulas (i)-(xxxiii) may be enumerated wherein X represents ##STR4## W represents --CN, halogen, R" or OR"; and R' and R" each represent an alkyl group: ##STR5##

The content of the compound of the present invention in the composition of the present invention varies depending on the kind of other components to be blended therewith. It is usually in the range of 1 to 30% by weight, preferably 5 to 15% by weight. A concrete example of composition is as follows:

one kind or mixtures of several kinds of trans-4-alkyl-(4-cyanophenyl)cyclohexanes (70 to 99% by weight, preferably 85 to 95% by weight) and the novel liquid crystal compound of the present invention (1 to 30% by weight, preferably 5 to 15% by weight).

Another example of composition is as follows:

one kind or mixtures of several kinds of trans-4-alkyl-(4-cyanophenyl)cyclohexanes (60 to 84% by weight, preferably 72 to 81% by weight), one kind or mixtures of several kinds of 4-(trans-4-alkylcyclohexyl)-4'-cyanobiphenyls (10 to 15% by weight, preferably 12 to 15% by weight) and the novel liquid crystal compound of the present invention (1 to 30% by weight, preferably 5 to 15% by weight).

A prior art which the present inventors consider as most relevant to the present invention is EP 97033A. One of the claims of this European Patent discloses the compounds expressed by ##STR6## (wherein R.sub.1 represents an alkyl group; R.sub.2 represents F, cyano group or an alkyl group or an alkoxy group; Q represents 1,4-disubstituted benzene containing F, Cl or methyl group).

The compound of the present invention has much superior properties in that it has a relatively low viscosity and nevertheless has a large dielectric anisotropy value (hereinafter abbreviatd to .DELTA..epsilon.) and optical anisotropy value (hereinafter abbreviated to .DELTA.n), and yet, when added to a liquid crystal composition, raises the clearing point of the composition, as shown in Table 1. As to the improvement in these characteristics, it is evident that the nitrogen atoms of the pyrimidine ring and the pyridine ring constituting the compound of the present invention are contributing to increase in .DELTA..epsilon. and .DELTA.n.

In the Table, .eta..sub.20 (cp) means a viscosity at 20.degree. C.

In the case of a compound expressed by the formula ##STR9## (crystalline-nematic point: 141.degree. C., nematic-clearing point: 184.degree. C.) having a covalent bond in place of a bond of ethylene group, when it is added in a quantity of 10% by weight or more to the composition (A), the resulting composition crystallizes at room temperature, whereas even when the compound of the present invention expressed by the formula (I) ##STR10## is added in a quantity of 15% by weight to the composition (A), the resulting composition does not crystallize. Thus, it is evident that the presence of an ethylene bond in the molecule improves the compatibility of the compound with other compounds in a liquid crystal composition.

As described above, the compound of the present invention is superior in compatibility with other liquid crystal compounds or liquid crystal compositions; it is chemically stable; and when added to liquid crystal compositions, it can raise the clearing point of the compositions almost without increasing their viscosity and enhance their .DELTA..epsilon. and .DELTA.n.

The present invention will be described in more detail by way of Examples, but it should not be construed to be limited thereto.

Preparation of 2-[.beta.-(4-fluorophenyl)ethyl]-5-(5'-pentylpyrimidinyl-2')pyridine

Into a solution of sodium methylate (12.6 g) dissolved in anhydrous methanol (150 ml) were added 6-methyl-3-pyridylcarboxamidine hydrochloride (20 g) corresponding to the formula (IV) and .alpha.-pentyl-.beta.-dimethylaminoacrolein (20 g) corresponding to the formula (V), followed by heating the mixture under reflux with stirring for 2 hours, distilling off methyl alcohol, adding toluene (200 ml) to the reaction residue to extract the product, washing the liquid extract with water, drying over anhydrous sodium sulfate, distilling off toluene, and three times repeating recrystallization from methanol to obtain 2-methyl-5-(5'-pentylpyrimidinyl-2')pyridine (m.p. 75.3.degree.-75.8.degree. C.) (15.6 g) corresponding to the formula (VI).

This compound (7.2 g) and 4-fluorobenzaldehyde (3.7 g) corresponding to the formula (VII) were heated under reflux in the coexistence of acetic anhydride (4 ml) for 30 hours, cooling the reaction fluid, and washing the resulting solid product with methanol to obtain 2-[.beta.-(4-fluorophenyl)vinyl]-5-(5'-pentylpyrimidinyl-2')-pyridine (6.0 g) corresponding to the formula (VIII), dissolving this compound (6.0 g) corresponding to the formula (VIII) in toluene (200 ml), adding palladiumcarbon (1.0 g), carrying out catalytic reduction at normal temperature and normal pressure for 2 hours, filtering off the catalyst from the reaction fluid, distilling off toluene and recrystallizing the remaining solids from ethanol to obtain the objective 2-[.beta.-(4-fluorophenyl)ethyl]-5-(5'-pentylpyrimidinyl-2')pyridine (4.7 g), which had the following phase transition points:

Crystalline-nematic point (C-N point) 90.8.degree.-91.4.degree. C.

Smectic-nematic point (S-N point) (80.1.degree.-80.3.degree. C.)

Nematic-clearing point (N-I point) 100.1.degree.-100.5.degree. C.

The above numerical values in the parenthese indicate that the phase is monotropic.

The following liquid crystal compounds corresponding to the formula (I) were obtained using the following compounds corresponding to the formulas (VI) and (VII) in the same manner as in Example 1:

(VI): 2-methyl-5-(5'-propylpyrimidinyl-2')pyridine

(VII): 4-ethylbenzaldehyde

(I): 2-[.beta.-(4-ethylphenyl)ethyl]-5-(5'-propylpyrimidinyl-2')pyridine

C-N point 68.5.degree.-69.5.degree. C.

N-I point 101.3.degree.-101.5.degree. C.

(VI): 2-methyl-5-(5'-pentylpyrimidinyl-2')pyridine

(VII): 4-cyanobenzaldehyde

(I): 2-[.beta.-(4-cyanophenyl)ethyl]-5-(5'-pentylpyrimidinyl-2')pyridine

C-S point 101.8.degree.-102.6.degree. C.

S-N point 113.3.degree.-113.5.degree. C.

N-I point 161.1.degree.-161.5.degree. C.

(VI): 2-methyl-5-(5'-propylpyrimidinyl-2')pyridine

(VII): 4-anisaldehyde

(I): 2-[.beta.-(4-methoxyphenyl)ethyl]-5-(5'-propylpyrimidinyl-2')pyridine

C-N point 76.2.degree.-77.0.degree. C.

N-I point 125.6.degree.-125.9.degree. C.

(VI): 2-methyl-5-(5'-propylpyrimidinyl-2')pyridine

(VII): 3,4-difluorobenzaldehyde

(I): 2-[.beta.-(3,4-difluorophenyl)ethyl]-5-(5'-propylpyrimidinyl-2')pyridine

C-N point 75.1.degree.-76.0.degree. C.

S-N point (59.2.degree.-60.0.degree. C.)

N-I point 81.5.degree.-82.3.degree. C.

A liquid crystal composition (A) consisting of ##STR11## has a N-I point of 52.1.degree. C., a viscosity at 20.degree. C. of 23.4 cp, a dielectric anisotropy value (.DELTA..epsilon.) of 11.2 and an optical anisotropy value (.DELTA.n) of 0.119. This liquid crystal composition (A) was sealed in a TN cell of 10 .mu.m thick provided with opposed, transparent electrodes. The resulting liquid crystal cell had a threshold voltage driven at 20.degree. C. of 1.54 V and a saturation voltage of 2.13 V.

A liquid crystal composition (B) consisting of the above liquid crystal composition (A) (85% by weight) and 2-[.beta.-(4-fluorophenyl)ethyl]-5-(5'-pentylpyrimidinyl-2')-pyridine (15% by weight) had a N-I point of 55.4.degree. C., a viscosity at 20.degree. C. of 24.7 cp, a .DELTA..epsilon. of +13.7 and a .DELTA.n of 0.127. When this composition (B) was sealed in the above T-N cell, the resulting liquid crystal cell had a driven threshold voltage of 1.48 V and a saturation voltage of 2.12 V.