4-Fluorophenylbenzoates and liquid crystal compositions containing them

Abstract: An ester derivative represented by the following formula (I). In the formula, V, W, X, Y and Z represent hydrogen atom or a halogen atom, respectively, and a liquid crystal composition containing it. The ester derivative can optimize n value, can lower viscosity and can reduce threshold voltage Vth of the liquid crystal composition.

Description: This invention relates to an ester derivative useful as a liquid crystal material and a liquid crystal composition containing the ester derivative. Liquid crystal displays are widely utilized for watches, electronic calculators, word processors, televisions and the like. Among various liquid crystal displays, a common one is the liquid crystal display in TN type (twisted nematic type) which utilizes optical anisotropy and dielectric anisotropy of a liquid crystal material. The liquid crystal materials which are presently used for liquid crystal displays such as in the TN type are required to have a wide liquid crystal temperature range, a rapid electro-optical response, a wide visual angle range, a low driving electric voltage, a chemical stability, an optical stability, and the like. In order to obtain a wide visual angle range and a high contrast, it is necessary to optimize the retardation of the liquid crystal layer, i.e. Δn·d ( Δn : birefringence of liquid crystal material, d : thickness of liquid crystal layer). In the liquid crystal displays to be put to practical use, the thickness of the liquid crystal layer is set in a restricted range, and accordingly, the optimization of Δn of the liquid crystal material is necessary. The liquid crystal material is also desired to have a low viscosity for speeding up of the response. The relation between the rise time τ on at the time of impressing electric voltage and the decay time τ off at the time of breaking electric voltage is represented by the following formulas : τ on = η ii d 2 (ε 0 Δε v 2 -Kπ 2 ) -1 τ off = η ii d 2 / π 2 K In the formulas, η ii is a parameter of viscosity, d is the thickness of the liquid crystal layer, ε 0 is the dielectric constant in vacuum, Δε is the anisotropy of dielectric constant, V is the impressed electric voltage, K = K 11 + (K 33 - 2K 22 )/4(K 11 : spraying elastic modulus, K 22 : twisting elastic modulus, K 33 : bending elastic modulus) . Accordingly, in order to raise the response speed, it is essential that the liquid crystal material has a low viscosity, i.e. a low viscosity liquid crystal compound is essential. Moreover, the driving electric voltage depends upon threshold voltage Vth, and a liquid crystal display can be driven by a lower electric voltage by reducing the threshold voltage Vth. Accordingly, a liquid crystal material capable of reducing the threshold electric voltage Vth is required It has been not found a liquid crystal compound which satisfies all of the above required properties by a single material. Accordingly, in order to comply with the requirement, several kinds of liquied crystal compounds having various properties were mixed or a non-liquid crystal compound was mixed, to put to practical use. GB-A-2 070 593 relates to halogenated ester derivatives for use in liquid crystal compositions expressed by the general formula wherein X is R is 1-15C alkyl or alkoxy; and Y is oxycarbonyl or carbonyloxy. SUMMARY OF THE INVENTION An object of the invention is to provide an ester derivative capable of optimizing Δn value, lowering viscosity and reducing threshold voltage Vth of a liquid crystal composition by blending therewith. The present provides an ester derivative which has achieved the above object, which is represented by the following formula (I) : wherein V, W, X, Y and Z represent hydrogen atom or a halogen atom, respectively, with the proviso that the following compounds are excluded: BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 through 9 are graphs illustrating infrared spectra of examples of the ester derivative of the invention. DETAILED DESCRIPTION OF THE INVENTION The halogen atom includes fluorine, chlorine and bromine, and fluorine is preferred. Preferable ester derivatives are those of Examples 2, 3, 5, 6, 7, 9 described later, and those of Examples 2 and 6 are particularly preferred. Two or more of the ester derivatives may be combined. The ester derivative of the invention can be prepared according to various known esterification methods, and a typical method is to react between a halogenated benzoyl halide and a halogenated phenol. The halogenated benzoyl halide can be prepared from a halogenated benzoic acid by reacting with a halogenating agent, such as thionyl chloride and phosphorus pentoxide. Then, the halogenated benzoyl halide is reacted with a halogenated phenol to produce the object ester derivative. Purification of the ester derivative from the reaction mixture may be conducted by a common method, such as recrystallization, fractional distillation and washing with water. The ester derivative does not exhibit liquid crystal properties as itself, and used by blending with liquid crystal compound(s) to form a liquid crystal composition. As the liquid crystal compound blendable with the ester derivative of the invention, there are various ester compounds, cyclohexyl phenyl compounds, biphenyl compounds, pyrimidine compounds, dioxane compound, tolan (diphenylacetylene) compounds, and the like capable of exhibiting liquid crystalizability. Preferable liquid crystal compounds are ester compounds and cyclohexylphenyl compounds, and include 4-alkylcyclohexane carboxylic acid-(4-cyanophenyl) ester, 4-alkylcyclohexane carboxylic acid-(4-alkoxyphenyl) ester, 4-alkyl-(4-cyanophenyl) cyclohexane and the like. The liquid crystal composition, consists essentially of the ester derivative and a liquid crystal compound, and may contain a chiral material as a third component. A suitable blending amount of the ester derivative in the liquid crystal composition is 0.1 to 20 wt. %, preferably 3 to 10 wt. %, particularly preferably 4 to 8 wt. %. The content of the third component is less than 3 wt. %, usually less than 1 wt. %. The blending is conducted according to a known method, such as mixing with heating to obtain a liquid state. The ester derivative of the invention can optimize Δn, can lower threshold voltage Vth and can reduce viscosity of liquid crystal composition by blending it. Thereupon, the liquid crystal composition containing the ester derivative of the invention has excellent properties as a liquid crystal material, and liquid crystal displays loaded with the liquid crystal composition have good displaying properties. Futhermore, the ester derivative of the invention has a great mutual solubility with various compounds, and can be combined as a constituent of a liquid crystal composition with many liquid crystal materials to improve properties of the liquid crystal composition. EXAMPLES Example 1 (Reference) To 12.2 g of benzoic acid, 24 g of thionyl chloride was added, and allowed to react under reflux for 2 hours. After the termination of the reaction, thionyl chloride was evaporated under reduced prossure, and then distilled under reduced pressure at 20 mmHg to obtain 10 g of benzoic acid chloride at a distillation temparature of 105 °C. The benzoic acid chloride was dissolved in 50 ml of toluene, and added with 8 g of 4-fluorophenol and 8 g of pyridine to react at 40 °C for 3 hours. After the termiration of the reaction, 100 ml of water was added, and the organic layer was separated. The organic layer was washed with dilute hydrochloric acid, dilute alkali aqueous solution and saturated sodium chloride solution successively, and then, dried by adding anhydrous sodium sulfate. Subsequently, the organic layer was filtered, and solvent was evaporated from the filtrate under reduced pressure. The reaction product was recrystallized from hexane, and then distilled under reduced pressure at 1 mmHg to collect the fractions at a distillation temperature of 160 °C. Thus, 9 g of benzoic acid (4-fluorophenyl) ester represented by the following formula was oblained. The melting point of the ester was 58.0 °C. Infrared absorption spectrum of the ester is shown in Figure 1. This ester is not a compound according to the invention. Example 2 10 g of 2-fluorobenzoic acid-(4-fluorophenyl) ester represented by the following formula was prepared similar to Example 1, except that 14.6 g of 2-fluorobenzoic acid was used instead of 12.2 g of benzoic acid. The ester had a melting point of 40.8 °C, a boiling point of 150 °C at 1 mmHg and infrared absorption sprectrum shown in Figure 2. Example 3 11 g of 2,6-difluorobenzoic acid-(4-fluorophenyl) ester represented by the following formula was prepared similar to Example 1, except that 16.2 g of 2,6-difluorobenzoic acid was used instead of 12.2 g of benzoic acid. The ester had a melting point of 60.0 °C and infrared absorption spectrum shown in Figure 3. Example 4 12 g of 2,6-dichlorobenzoic acid-(4-fluorophenyl) ester represented by the following formula was prepared similar to Example 1, except that 19.5 g of 2,6-dichlorobenzoic acid was used instead of 12.2 g of benzoic acid. The ester had a melting point of 86.0 °C and infrared absorption spectrum shown in Figure 4. Example 5 9 g of benzoic acid-(3,4-difluorophenyl) ester represented by the following formula was prepared similar to Example 1, except that 9.5 g of 3,4-difluorophenol was used instead of 8 g of 4-fluorophenol. The ester had a melting point of 74.0 °C and infrared absorption spectrum shown in Figure 5. Example 6 10 g of 2-fluorobenzoic acid-(3,4-difluoropheyl) ester represented by the following formula was prepared similar to Example 1, except that 14.6 g of 2-fluorobenzoic acid and 9.5 g of 3,4-difluorophenol were used instead of 12.2 g of benzoic acid and 8 g of 4-fluorophenol, respectively. The ester had a melting point of 65.1 °C and infrared absorption spectrum shown in Figure 6. Example 7 11 g of 2,6-difluorobenzoic acid-(3,4-difluorophenyl) ester represented by the following formula was prepared similar to Example 1, except that 16.2 g of 2,6-difluorobenzoic acid and 9.5 g of 3,4-difluorophenol were used instead of 12.2 g of benzoic acid and 8 g of 4-fluorophenol, respectively. The ester had a melting point of 78.0 °C and infrared absorption spectrum shown in Figure 7. Example 8 12 g of 2,6-dichlorobenzoic acid-(3,4-difluorophenyl) ester represented by the following formula was prepared similar to Example 1, except that 19.5 g of 2,6-dichlorobenzoic acid and 9.5 g of 3,4-difluorophenol were used instead of 12.2 g of benzoic acid and 8 g of 4-fluorophenol, respectively. The ester had a melting point of 86.0 °C and infrared absorption spectrum shown in Figure 8. Example 9 11 g of 2-fluorobenzoic acid-(2,3,4,-trifluorophenyl) ester represented by the following formula was prepared similar to Example 1, except that 14.6 g of 2-fluorobenzoic acid and 10.5 g of 2,3,4-trifluorophenol were used instead of 12.2 g of benzoic acid and 8 g of 4-fluorophenol, respectively. The ester had a melting point of 50.3 °C and infrared absorption spectrum shown in Figure 9. Example 10 A liquid crystal composition was prepared by mixing with heating 10 parts by weight of the ester prepared in Example 1 with 90 parts by weight of a liquid crystal mixture composed of the following four compounds in a mixing ratio of A : B : C : D by weight of 24 : 36 : 25 : 15. Properties of the liquid crystal composition were measured and shown in Table 1. In the table, the threshold voltage Vth was measured by loading the liquid crystal composition in a TN type liquid crystal display having a cell thickness of 9 um. The above liquid crystal mixture composed of the four compounds A, B, C, D alone had a N-I point of 72 C, a n of 0.138, a viscosity of 27.9 cp and a Vth of 1.68 V. Examples 11-16 Liquid crystal compositions were prepared by mixing 10 parts by weight of the ester prepared in Example 2, 3, 5, 6, 7 or 9 with 90 parts by weight of the same liquid crystal mixture used in Example 10, and their properties were measured and shown in Table 1. As can be seen from Table 1, by blending the ester dervative of the invention, The n of a conventional liquied crystal composition can be optimized, and the threshold voltage Vth can be lowered. In most cases, the viscosity can be reduced.

Claims: An ester derivative represented by the following formula (I). wherein V, W, X, Y and Z represent hydrogen atom or a halogen atom, respectively, with the proviso that the following compounds are excluded: The ester derivative of claim 1 having the formula: The ester derivative of claim 1 having the formula: A liquid crystal composition consisting essentially of an ester derivative represented by the following formula (I) wherein V, W, X, Y and Z represent hydrogen or halogen, and a liquid crystal compound The liquid crystal composition of claim 4 wherein the liquid crystal compound is a member selected from the group consisting of ester compounds, cyclohexyl phenyl compounds, biphenyl compounds, pyrimidine compounds, dioxane compounds and tolan (diphenylacetylene) compounds, capable of exhibiting liquid crystallinity. The liquid crystal composition of claim 4 wherein the liquid crystal compound is a member selected from the group consisting of ester compounds and cyclohexylphenyl compounds, capable of exhibiting liquid crystallinity.

Inventors: NAITO TOMIJIRO, SAKAMAKI YUMIKO, YUKINARI TOSHIRO, NAITO, TOMIJIRO, SAKAMAKI, YUMIKO, YUKINARI, TOSHIRO
Applicants: CITIZEN WATCH CO LTD, CITIZEN WATCH CO., LTD.
Application year: 1993
Main classification: C07C69
IPC codes: C09K19, C07C69