| CORP. SALE |
Benzene-1,3-di-F-2-CH2X-5-[O-CO-C6H10-OCH2-C6H10- Me] |
| PATENT ASSIGNEE'S COUNTRY | Japan |
| UPDATE | 11.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 21.11.00 |
| PATENT TITLE |
Carboxylate derivatives comprising an ether group and liquid crystal composition comprising the same |
| PATENT ABSTRACT |
A compound represented by the following general formula (I), a liquid crystal composition comprising the same, and a liquid crystal element using this liquid crystal composition. ##STR1## (wherein B.sub.1 and B.sub.2 represent independently a trans-1,4-cyclohexylene group or a 1,4-phenylene group wherein at least one hydrogen atom on the six-membered ring is optionally substituted by a halogen atom, Y represents a halogen-substituted alkyl group having 1 to 3 carbon atoms, a halogen-substituted alkoxy group having 1 to 3 carbon atoms, a cyano group, a fluorine atom or a chlorine atom, X represents a fluorine atom, a chlorine atom or a hydrogen atom, R.sub.1 represents an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, n and m represent independently 1 or 2 and p represents 0 or 1.) The compound of the present invention exhibits a large dielectric anisotropy, low threshold voltage, and favorable temperature-dependency of threshold voltage, as well as a favorable miscibility with a known liquid crystal compound, and therefore a liquid crystal composition comprising the compound can provide low voltage-operable liquid crystal display elements. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 04.08.98 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A compound represented by the following formula (I): ##STR42## wherein B.sub.1 and B.sub.2 represent independently trans-1,4-cyclohexylene group or 1,4-phenylene group, wherein the six-membered ring is optionally substituted by one or more halogen atom, Y represents a halogen-substituted alkyl group having 1 to 3 carbon atoms, a cyano group, a fluorine atom or chlorine atom, X represents a fluorine atom, chlorine atom or a hydrogen atom, R.sub.1 represents an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, n and m represent independently 1 or 2 and p represents 0 or 1, provided that, when n and m represent 1, p represents 0, B.sub.1 represents a 1,4-phenylene group and Y represents a fluorine atom or a cyano group, X is F or Cl. 2. The compound according to claim 1 wherein m represents 1. 3. The compound according to claim 2 characterized in that B.sub.1 represents a 1,4-phenylene group wherein at least one hydrogen atom on the six-membered ring is optionally substituted by a halogen atom. 4. The compound according to claim 3 characterized in that B.sub.1 represents a 1,4-phenylene group wherein at least one hydrogen atom on the six-membered ring is substituted by a fluorine atom. 5. The compound according to claim 2 wherein B.sub.1 represents a trans-1,4-cyclohexylene group. 6. The compound according to claim 1 wherein m represents 2. 7. A liquid crystal composition comprising at least one compound according to claim 1. 8. A liquid crystal composition comprising at least one compound according to claim 1 as a first component, and as a second component at least one compound selected from the group consisting of the compounds of the formula (II), (III) or (IV): ##STR43## wherein R.sub.2 represents an alkyl group having 1 to 10 carbon atoms, V represents F, Cl, CF.sub.3, OCF.sub.3, OCF.sub.2 H or an alkyl group having 1 to 10 carbon atoms, L.sub.1, L.sub.2, L.sub.3 and L.sub.4 represent independently H or F, a represents 1 or 2, b represents 0 or 1, Z.sub.1 and Z.sub.2 represent independently --CH.sub.2 CH.sub.2 --, --CH.dbd.CH-- or a covalent bond, and ring G.sub.1 represents a trans-1,4-cyclohexylene group or a 1,4-phenylene group. 9. A liquid crystal composition comprising at least one compound according to claim 1 as a first component, and as a second component and at least one compound selected from the group consisting of the compounds of the formula (V), (VI), (VII), (VIII) or (IX): ##STR44## wherein R.sub.3 represents F, an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, any methylene group (--CH.sub.2 --) in said alkyl or alkenyl group may be replaced by one or more oxygen atoms (--O--), provided that two or more successive methylene groups are not replaced by oxygen atoms, Z.sub.3 represents --CH.sub.2 CH.sub.2 --, --CO--O-- or a covalent bond, L.sub.5 and L.sub.6 represent independently H or F, D.sub.1 represents a trans-1,4-cyclohexylene, 1,4-phenylene or trans 1,3-dioxane-2,5-diyl group, ring G.sub.2 represents a trans-1,4-cyclohexylene, or 1,4-phenylene group, and c and d represent independently 0 or 1, ##STR45## wherein R.sub.4 represents an alkyl group having 1 to 10 carbon atoms, L.sub.7 represents H or F, and e represents 0 or 1, ##STR46## wherein R.sub.5 represents an alkyl group having 1 to 10 carbon atoms, M represents a trans-1,4-cyclohexylene or 1,4-phenyelne group, L.sub.8 and L.sub.9 represent independently H or F, Z.sub.4 represents --CO--O-- or a covalent bond, Z.sub.5 represents --CO--O-- or --C.tbd.C--, and f and g represent independently 0 or 1, R.sub.6 --W--Z.sub.6 Q--R.sub.7 (VIII) wherein R.sub.6 and R.sub.7 represent independently an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms or an alkoxymethyl group having 1 to 10 carbon atoms, W represents a trans-1,4-cyclohexylene, 1,4-phenylene or 1,3-pyrimidine-2,5-diyl group, Q represents a trans-1,4-cyclohexylene or 1,4-phenylene, and Z.sub.6 represents --C.tbd.C--, --CO--O--, --CH.sub.2 CH.sub.2 -- or a covalent bond, ##STR47## wherein R.sub.8 represents an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, R.sub.9 represents an alkyl group having 1 to 10 carbon atoms, any methylene group (--CH.sub.2 --) in R.sub.9 may be replaced by an oxygen atom (--O--), provided that two or more successive methylene groups are not replaced by oxygen atoms, T represents a trans-1,4-cyclohexylene group or 1,3-pyrimidine-2,5-diyl group, ring G.sub.3 and U represent independently a trans-1,4-cyclohexylene group or a 1,4-phenylene group, Z.sub.7 represents --CH.sub.2 CH.sub.2 --, --CH.dbd.CH--, --CO--O-- or a covalent bond, Z.sub.8 represents --C.tbd.C--, --CO--O-- or a covalent bond, h represents 0 or 1, and L.sub.10 represents H or F. 10. A liquid crystal display element wherein the liquid crystal composition according to claim 7 is used. 11. A liquid crystal composition comprising a first component, a second component and a third component, wherein the first component is at least one compound according to claim 1; the second component is at least one compound selected from the group consisting of compounds of formulae (II), (III) and (IV): ##STR48## wherein R.sub.2 represents an alkyl group having 1 to 10 carbon atoms, V represents F, Cl, CF.sub.3, OCF.sub.3, OCF.sub.2 H, or an alkyl group having 1 to 10 carbon atoms, L.sub.1, L.sub.2, L.sub.3, and L.sub.4 represent independently H or F, "a" represents 1 or 2, b represents 0 or 1, Z.sub.1 and Z.sub.2 represent independently --CH.sub.2 CH.sub.2 --, --CH.dbd.CH--, or a covalent bond, and ring G.sub.1 represents a trans-1,4-cyclohexylene group or a 1,4-phenylene group; and the third component is at least one compound selected from the group consisting of compounds of formulae (V), (VI), (VII), (VIII) and (XI): ##STR49## wherein R.sub.3 represents F, an alkyl group having 1 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms, any methylene (--CH.sub.2 --) group in said alkyl or alkenyl group may be replaced by one or more oxygen atoms (--O--), provided that two or more successive methylene groups are not replaced by oxygen atoms, Z.sub.3 represents --CH.sub.2 CH.sub.2 --, --CO--O--, or a covalent bond, L.sub.5 and L.sub.6 represent independently H or F, D.sub.1 represents a trans-1,4-cyclohexylene, 1,4-phenylene or trans-1,3-dioxane-2,5-diyl group, ring G.sub.2 represents a trans-1,4-cyclohexylene, or 1,4-phenylene group, and c and d represent independently 0 or 1; ##STR50## wherein R.sub.4 represents an alkyl group having 1 to 10 carbon atoms, L.sub.7 represents H or F, and e represents 0 or 1; ##STR51## wherein R.sub.5 represents an alkyl group having 1 to 10 carbon antoms, M represents a trans-1,4-cyclohexylene or 1,4-phenylene group, L.sub.8 and L.sub.9 represent independently H or F, Z.sub.4 represents --CO--O-- or a covalent bond, Z.sub.5 represents --CO--O-- or --C.tbd.C--, and f and g represent independently 0 or 1; R.sub.6 --W--Z.sub.6 --Q--R.sub.7 (VIII) wherein R.sub.6 and R.sub.7 represent independently an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms or an alkoxymethyl group having 1 to 10 carbon atoms, W represents a trans-1,4-cyclohexylene, a 1,4-phenylene, or -a 1,3-pyrimidine-2,5-diyl group, Q represents a trans-1,4-cyclohexylene or a 1,4-phenylene group, and Z.sub.6 represents --C.tbd.C--, --CO--O--, --CH.sub.2 CH.sub.2 --, or a covalent bond; ##STR52## wherein R.sub.8 represents an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, R.sub.9 represents an alkyl group having 1 to 10 carbon atoms, any methylene group (--CH.sub.2 --) in R.sub.9 may be replaced by an oxygen atom (--O--), provided that two or more successive methylene groups are not replaced by oxygen atoms, T represents a trans-1,4-cyclohexylene or a 1,3-pyrimidinyl-2,5-diyl group, rings G.sub.3 and U represent independently a trans-1,4-cyclohexylene group or a 1,4-phenylene group, Z.sub.7 represents --CH.sub.2 CH.sub.2 --, --C.tbd.C--, --CO--O--, or a covalent bond, Z.sub.8 represents --C.tbd.C--, --CO--O--, or a covalent bond, h represents 0 or 1 and L.sub.10 represents H or F. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION This invention relates to a liquid crystal compound, and more specifically a carboxylate derivative containing an ether group, a liquid crystal composition comprising the compound and a liquid crystal element using the liquid crystal composition. BACKGROUND OF THE INVENTION Liquid crystal display elements are used widely in watches, electronic calculators, electronic notebooks, word processors, note book type-personal computers, video cameras equipped with a monitor, car-navigation systems, etc. These liquid crystal display elements utilize optical anisotropy (.DELTA.n) and dielectric anisotropy (.DELTA..epsilon.) of liquid crystal materials. Display systems of the liquid crystal display elements include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a dynamic scattering (DS) mode, a guest-host mode, DAP (Deformation of Aligned Phases) mode and the like, according to electro-optical effects which are applied to the liquid crystal display element. In any system, it is desirable that a liquid crystal compound shows a liquid crystal phase at a temperature ranging as broad as possible, and it is necessary that a liquid crystal compound is stable against water, heat, air or the like. It is also necessary that a liquid crystal compound shows high miscibility with other liquid crystal compounds. Although a number of liquid crystal compounds have been already known, there is no liquid crystal compounds which satisfy all the above-mentioned conditions at present, and in practice several liquid crystal compounds are used in admixture with non-liquid crystalline compounds. Recently, there is an increasing need for a low-voltage operation in association with a decreased electric power consumption and miniaturization of a display element, and thus there is in need of a liquid crystal compound having low threshold voltage (Vth). In order to decrease the threshold voltage, it is necessary to increase dielectric anisotropy (.DELTA..epsilon.). Examples of a liquid crystal compound having large dielectric anisotropy include an ester derivative represented by the following general formula 1) disclosed in WO89/08102. ##STR2## wherein R represents R.sub.1, R.sub.1 O or R.sub.1 COO, R.sub.1 represents an alkyl group having 1 to 12 carbon atoms, n and m individually represent 0 or 1, (n+m) also represents 0 or 1, a, b, c and d independently represent 0 or 1, and (a+b+c+d) does not represent 0, excluding a case wherein a and b individually represent 0, m represents 0, and one of c and d represents 0, provided that these symbols are different from those used in the present invention and are applied to merely the general formula 1). However, there is a need for a liquid crystal material which has improved miscibility with known liquid crystal compounds at a low temperature over the compound represented by the general formula 1). Furthermore, examples of a liquid crystal compound having large dielectric anisotropy include an ester derivative represented by the following general formula 2) disclosed in J.P. KOKAI No. Hei 4-300861. ##STR3## wherein A.sub.1 and A.sub.2 represent a 1,4-phenylene group or the like, R represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, X represents --O--, --CO--O--, --O--CO-- or a covalent bond, Y represents --O--, --CO--O--, --O--CO--, a covalent bond or the like, m and n represent 0 to 4, and q represents 0 or 1, provided that these symbols are different from those used in the present invention and are applied to merely the general formula 2). However the compound represented by the general formula 2) has an unsaturated bond at the one terminal of the molecule and thus it does not have enough heat stability. Accordingly, there is a need for a liquid crystal material which has an improved heat stability. DISCLOSURE OF THE INVENTION Thus, an object of the invention is to solve the above-mentioned problems in the prior art, and to provide a liquid crystal compound having a large dielectric anisotropy, which is chemically stable and has good heat stability, low threshold voltage and favorable temperature-dependency of the threshold voltage as well as good miscibility with other liquid crystal compounds known in the art. Another object of the invention is to provide a liquid crystal composition comprising said liquid crystal compound and a liquid crystal display element using the liquid crystal composition. The present invention provides a compound of the following general formula (I): ##STR4## wherein B.sub.1 and B.sub.2 represent independently a trans-1,4-cyclohexylene group or a 1,4-phenylene group wherein one or more hydrogen atoms on the six-membered ring are optionally substituted by halogen atoms, Y represents a halogen-substituted alkyl group having 1 to 3 carbon atoms, a halogen-substituted alkoxy group having 1 to 3 carbon atoms, a cyano group, a fluorine atom or a chlorine atom, X represents a fluorine atom, a chlorine atom or a hydrogen atom, R.sub.1 represents an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, n and m represent independently 1 or 2, and p represents 0 or 1. Preferred compounds according to the present invention are given below. 1 A compound of the general formula (I) wherein m represents 1. 2 A compound of the general formula (I) wherein B.sub.1 represents 1,4-phenylene group wherein one or more hydrogen atoms on the six-membered ring are optionally substituted by halogen atoms, and m represents 1. 3 A compound of the general formula (I) wherein B.sub.1 represents 1,4-phenylene group wherein one or more hydrogen atoms on the six-membered ring are substituted by fluorine atoms, and m represents 1. 4 A compound of the general formula (I) wherein B.sub.1 represents a trans-1,4-cyclohexylene group, and m represents 1. 5 A compound of the general formula (I) wherein m represents 2. The present invention also provides a liquid crystal composition which comprises at least one compound represented by the general formula (I). The present invention further provides a liquid crystal composition which comprises at least one compound of the formula (I) and at least one compound selected from the group consisting of the compounds of following formulas (II), (III) and (IV). ##STR5## wherein R.sub.2 represents an alkyl group having 1 to 10 carbon atoms, V represents F, Cl, CF.sub.3, OCF.sub.3, OCF.sub.2 H or an alkyl group having 1 to 10 carbon atoms, L.sub.1, L.sub.2, L.sub.3 and L.sub.4 represent independently H or F, a represents 1 or 2, b represents 0 or 1, Z.sub.1 and Z.sub.2 represent independently --CH.sub.2 CH.sub.2 --, --CH.dbd.CH-- or a covalent bond, and ring G.sub.1 represents a trans-1,4-cyclohexylene group or 1,4-phenylene group. The present invention also provides a liquid crystal composition which comprises at least one compound of the formula (I) and at least one compound selected from the group consisting of the compounds of following formulas (V), (VI), (VII), (VIII) and (IX). ##STR6## In the formula (V), R.sub.3 represents F, an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms. Any methylene group (--CH.sub.2 --) in said alkyl or alkenyl group may be replaced by one or more oxygen atoms (--O--), provided that two or more successive methylene groups are not replaced by oxygen atoms. Z.sub.3 represents --CH.sub.2 CH.sub.2 --, --CO--O-- or a covalent bond, L.sub.5 and L.sub.6 represent independently H or F, D.sub.1 represents a trans-1,4-cyclohexylene, 1,4-phenylene or trans 1,3-dioxane-2,5-diyl group, ring G.sub.2 represents a trans-1,4-cyclohexylene, or 1,4-phenylene group, and c and d represent independently 0 or 1. ##STR7## In the formula (VI), R.sub.4 represents an alkyl group having 1 to 10 carbon atoms, L.sub.7 represents H or F, and e represents 0 or 1. ##STR8## In the formula (VII), R.sub.5 represents an alkyl group having 1 to 10 carbon atoms, M represents trans-1,4-cyclohexylene or 1,4-phenyelne group, L.sub.8 and L.sub.9 represent independently H or F, Z.sub.4 represents --CO--O-- or a covalent bond, Z.sub.5 represents --CO--O-- or --C.tbd.C--, and f and g represent independently 0 or 1. R.sub.6 --W--Z.sub.6 --Q--R.sub.7 (VIII) In the formula (VIII), R.sub.6 and R.sub.7 represent independently an alkyl groups having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms or an alkoxymethyl group having 1 to 10 carbon atoms, W represents a trans-1,4-cyclohexylene, 1,4-phenylene or 1,3-pyrimidine-2,5-diyl group, Q represents a trans-1,4-cyclohexylene or 1,4-phenylene, and Z.sub.6 represents --C.tbd.C--, --CO--O--, --CH.sub.2 CH.sub.2 -- or a covalent bond. ##STR9## In the formula (IX), R.sub.8 represents an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms. R.sub.9 represents an alkyl group having 1 to 10 carbon atoms. Any methylene group (--CH.sub.2 --) in R.sub.9 may be replaced by one or more oxygen atoms (--O--), provided that two or more successive methylene groups are not replaced by oxygen atoms. T represents a trans-1,4-cyclohexylene group or 1,3-pyrimidine-2,5-diyl group, ring G.sub.3 and U represent independently a trans-1,4-cyclohexylene group or a 1,4-phenylene group, Z.sub.7 represents --CH.sub.2 CH.sub.2 --, --CH.tbd.CH--, --CO--O-- or a covalent bond, Z.sub.8 represents --C.tbd.C--, --CO--O--, or a covalent bond, h represents 0 or 1, and L.sub.10 represents H or F. The present invention further provides a liquid crystal composition which comprises at least one compound of the formula (I), at least one compound selected from the group consisting of the compounds of the formulas (II), (III) and (IV), and at least one compound selected from the group consisting of the compounds of the formulas (V), (VI), (VII), (VIII) and (IX). The present invention further provides a liquid crystal display element comprising the liquid crystal composition mentioned above. BEST MODE FOR CARRYING OUT THE INVENTION The compounds of the formula (I) of the present invention are carboxylate derivatives characterized in that they exhibit large dielectric anisotropy because they have halogen-substituted alkyl groups, halogen-substituted alkoxy groups, cyano groups or halogen atoms on the phenyl group at the one terminal of molecule thereof, they show excellent heat-stability, they exhibit low threshold voltage when used as a display element, and further they have favorable temperature-dependency of threshold voltage. Furthermore, the compounds of the present invention have high miscibility with other known liquid crystal compounds at low temperature and they are physically and chemically stable under the conditions which are usually employed. Accordingly, when the compound of the present invention is used as a component of a liquid crystal composition, a novel liquid crystal composition having favorable properties can be provided. The compounds represented by formula (I) according to the present invention fall into the following formulas (I-1) to (I-8). ##STR10## wherein R.sub.1, B.sub.1, m, n, X, Y are defined as above, and E.sub.1 and E.sub.2 represent independently a halogen atom or a hydrogen atom. Among these compounds, particularly preferred are the compounds represented by the formulas (I-1) and (I-2) in attaining the object of the present invention. Further, the formula (I-1) falls into the following formulas (I-1a) to (I-1i) and the formula (I-2) falls into the following formulas (I-2a) to (I-2c). ##STR11## wherein R.sub.1 and n are defined as above. In the compound of the present invention, when Y represents a halogen-substituted alkyl group having 1 to 3 carbon atoms or a halogen-substituted alkoxy group having 1 to 3 carbon atoms, a preferred halogen is fluorine or chlorine, and fluorine is particularly preferred. The most preferred groups include specifically CF.sub.3, CH.sub.2 CF.sub.3, C.sub.2 F.sub.5, OCF.sub.3, OCF.sub.2 H, OCF.sub.2 CF.sub.2 H, OCF.sub.2 CF.sub.3, OCFHCF.sub.3, OCH.sub.2 CF.sub.3, OCF.sub.2 CH.sub.3, OCH.sub.2 CF.sub.2 H, OCF.sub.2 CFHCF.sub.3 and the like. The compound represented by the general formula (I) according to the present invention may be prepared, for example, by the following steps. ##STR12## wherein R.sub.1, n, m, p, B.sub.1, B.sub.2, X and Y are defined as above. A carboxylic acid derivative (I-9) is chlorinated with thionyl chloride, and an acid chloride derivative (I-10) is synthesized. Further, the acid chloride derivative (I-10) is reacted with phenol derivative (I-11) in the presence of pyridine to give the liquid crystal compound represented by the general formula (I). Incidentally, the starting materials, a carboxylic acid derivative represented by the formula (I-9) and a phenol derivative represented by the formula (I-11) may be prepared, for example, by the following method. ##STR13## wherein R.sub.1, B.sub.1, n, m, p, X are defined as above, B' represents 1,4-phenylene group wherein one or more hydrogen atoms on six-membered ring may be substituted by halogen atoms. A cyclohexylmethylbromide derivative (I-12) is reacted with a phenol derivative to give an ether derivative (I-13), and then the ether derivative (I-13) is hydrolyzed in the presence of an alkali to give a carboxylic acid derivative (I-14). The formula (I-14) is encompassed by a carboxylic acid derivative represented by the formula (I-9). An anisol derivative (I-16) is synthesized from a phenol derivative (I-15), and then via a phenyl lithium derivative (I-17), a carboxylic acid derivative (I-18) is obtained. Then, via an acid chloride derivative (I-19) and an acid amide derivative (I-20), benzonitrile derivative (I-21) is synthesized, and further a cyanophenol derivative (I-22) is obtained. The formula (I-22) is encompassed by a phenol derivative represented by formula (I-11). The liquid crystal composition of the present invention may be the one which comprises at least one of the compound represented by the general formula (I) (hereinafter also referred to as "a first component") and more preferred is the one which comprises additionally as a second component at least one compound selected from the group consisting of the compounds of the formulas (II), (III) and (IV) (hereinafter also referred to as "a second component A") and/or at least one compound selected from the group consisting of the compounds of the formulas (V), (VI), (VII), (VIII) and (IX) (hereinafter also referred to as "a second component B"). Further, the composition may contain one or more known compounds, as a third component, to adjust threshold voltage, liquid crystal phase temperature range, optical anisotropy, dielectric anisotropy, and viscosity. Among the second component A, preferred examples of the formula (II) are the following (II-1) to (II-15), preferred examples of the formula (III) are the following (III-1) to (III-48), and preferred examples of the formula (IV) are (IV-1) to (IV-39). ##STR14## The compounds represented by the formulas (II) to (IV) show positive dielectric anisotropy and have very good heat stability. Thus these compounds are essential to prepare a liquid crystal composition suitable for AM-LCD (TFT) which requires a large voltage holding ratio and high reliability. The amount of the compounds of the formulas (II) to (IV) is suitably 1 to 99% by weight, preferably 10 to 97% by weight, and more preferably 40 to 95% by weight based on the total weight of the liquid crystal composition. Among the second component B, preferred examples of the compounds of the formulas (V), (VI) and (VII) are (V-1) to (V-27), (VI-1) to (VI-3) and (VII-1) to (VII-13), respectively. In the formulas, R' represents an alkylene group. ##STR15## The compounds represented by the formulas (V) to (VII) have large and positive value of dielectric anisotropy and are used especially for decreasing threshold voltage of the composition. They are also used for adjusting viscosity and optical anisotropy (.DELTA.n) and broadening nematic phase temperature range such as heightening a clearing point, as well as for improving steepness. Among the second component B, preferred examples of the compounds represented by the formulas (VIII) and (IX) are (VIII-1) to (VIII-15) and (IX-1) to (IX-14), respectively. ##STR16## The compounds represented by the formulas (VIII) and (IX) have negative or weakly positive dielectric anisotropy. The compounds of the formula (VIII) are used for lowering viscosity or adjusting optical anisotropy (.DELTA.n), and the compounds of the formula (IX) are used for broadening temperature range of nematic phase such as heightening a clearing point and for adjusting optical anisotropy (.DELTA.n) in the composition. The compounds of the formulas (V) to (IX) are essential for preparing a liquid crystal composition for STN display mode or TN display mode. The amount of the compounds used for the preparation of a liquid crystal composition for STN display mode or TN display mode is suitably 1 to 99% by weight, preferably 10 to 97% by weight, more preferably 40 to 95% by weight based on the total weight of the liquid crystal composition. As mentioned above, a liquid crystal composition for TFT may be prepared from the first component and the second component A, and may also contain additionally the second component B. A liquid crystal composition for STN display mode or TN display mode may be prepared from the first component and the second component B, and may also contain additionally the second component A. The liquid crystal composition of the present invention preferably includes at least one compound of the formula (I) in the amount of 0.1 to 99% by weight to exhibit excellent characteristics. The liquid crystal composition of the present invention can be prepared by conventional methods. Generally, they may be prepared by dissolving various components at an elevated temperature. Further, the liquid crystal composition of the present invention may be improved and optimized by the addition of an additive suitable for an intended purpose. Such additives are well known by a person skilled in the art and described in detail in literature. Typically, a chiral dopant is added to induce spiral structure of the liquid crystal so as to adjust a desired degree of twist angle and to avoid reverse twist. The liquid crystal composition of the present invention can be used for guest-host (GH) mode if a dichroic dye such as merocyanine, styryl, azo, azomethine, azoxy, quinophthalone, anthraquinone and tetrazine dyes is added thereto. Further, the composition of the present invention can be used as a liquid crystal composition for polymer dispersed type liquid crystal display element (PDLCD) represented by NCAP (Nematic Curvilinear Aligned Phases) which is obtained by microencapsulating nematic liquid crystals, and for polymer network liquid crystal display element (PNLCD) which is obtained by forming a three dimensional polymer network in liquid crystals. In addition, the composition of the present invention can also be used as a liquid crystal composition for electrically controlled birefringence (ECB) mode and dynamic scattering (DS) mode. EXAMPLES The following examples explain in detail the present invention and the examples are not intended to limit the scope of the present invention. In the examples, CN means a transition temperature (.degree. C.) between a crystal phase and a nematic phase, NI means a transition temperature (.degree. C.) between a nematic phase and an isotropic phase, and CI means a transition temperature (.degree. C.) between a crystal phase and an isotropic phase. |
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