JPH04290875A - New ester compound, liquid crystal composition containing the same and optical switching element - Google Patents

Abstract

PURPOSE:To provide a new compound useful as a liquid crystal composition for a liquid crystal display element having high response speed. CONSTITUTION:The compound of formula I (R and R' are 2-18C alkyl), e.g. 2-(2-fluoro-4-hexyloxyphenyl)-5-(4-(2-fluoro-2-methylheptanoyloxy)-phe nyl)pyridine. The compound can be produced by esterifying a phenolic compound of formula II with a carboxylic acid of formula III. An optically active ester compound of formula I is obtained by using an optically active isomer as the carboxylic acid of formula III. The reaction may be carried out in the presence of a dehydrative condensation agent such as dicyclohexylcarbodiimide.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention can take a stable thermotropic liquid crystal state, and can be used, for example, in displays such as liquid crystal televisions, optical printer heads, optical Fourier transform elements, etc.
The present invention relates to a novel optically active ester compound that can be used as a liquid crystal material that is useful as a material for optoelectronic-related elements that utilize liquid crystals or electrochemometry, such as light valves, as well as liquid crystal compositions and optical switching devices that contain this compound.

0002

BACKGROUND OF THE INVENTION At present, liquid crystal compounds are used as display materials in various devices, and have been put to practical use in watches, calculators, small televisions, and the like. These devices use a cell mainly composed of a nematic liquid crystal material, and employ a display system called a TN type or STN type. The cell in this case operates based on the weak interaction (ΔεE2/2) between the dielectric anisotropy Δε of the liquid crystal compound and the electric field E, and the disadvantage is that the response speed to the electric field is slow at several msec. There is. For this reason, when used in televisions, an active matrix drive system in which a switching element is arranged and added to each pixel is mainly used as a drive system, which is one of the obstacles to achieving a larger screen. However, 19
1975 R. B. 4 synthesized by Meyer et al.
-(4-n-decyloxybenzylideneamino) cinnamic acid-2-methylbutyl ester (DOBAMBC)
The emergence of ferroelectric liquid crystals, with ferroelectric liquid crystals as a representative example, and the use of
．． A. A new display method proposed by Clark et al. (Ap
plied Phys. Lett. 1980, 36
, 899), it has become possible to create a liquid crystal cell that has a high-speed response on the μ sec order and a property that the orientation of liquid crystal molecules does not change even when the electric field is turned off (memory property). By using display elements made of these materials, it becomes possible to create liquid crystal televisions using a simple matrix method using multiplex drive without using switching elements, resulting in improved productivity, cost, reliability, and larger screens compared to active matrix devices. It will be much more advantageous in this respect.

For this reason, many ferroelectric liquid crystal materials have been synthesized and proposed up to now. In order for these ferroelectric liquid crystal materials to be used as display materials, several physical properties are required, among which the basic ones are that they exhibit a smectic C phase in a wide temperature range near room temperature;
It has a large spontaneous polarization and is chemically stable. However, early ferroelectric liquid crystals had a small spontaneous polarization of 10 nC/cm2 or less, and many had Schiff bases in their molecules, so they were chemically unstable.

[0004] Recently, it has been reported that chemically stable ester compounds exhibit large spontaneous polarization. For example, the following formula

The compound of [Image Omitted] exhibits a chiral smectic C phase in the temperature range of 78.7 to 103.3°C, and also a chiral smectic C phase in the temperature range of 103.3 to 120°C.
It becomes a cholesteric phase liquid crystal in the temperature range of 8 °C, but
The spontaneous polarization of this liquid crystal at 83°C is 89 nC/c
m2 (Japanese Unexamined Patent Publication No. 1988-43).

On the other hand, two-ring compounds have been synthesized in order to lower the temperature at which chiral smectic C phase is exhibited.
For example, the following formula

The biphenyl compound of [Chemical formula 3] exhibits a chiral smectic C phase from 44°C upon cooling (Japanese Patent Application Laid-Open No. 118744/1983).
.

Furthermore, phenylpyrimidine compounds that stably exhibit a chiral smectic C phase near room temperature have been reported. For example, the following formula

The compound of formula 4 becomes a liquid crystal in a chiral smectic C phase at 40.7 to 82.8°C and a smectic A phase at 82.8 to 89.1°C (Japanese Patent Laid-Open No. 61-200973).

[0007]

[Problems to Solve the Problems] However, the above-mentioned ester compounds have the disadvantage that the temperature range of the chiral smectic C phase is narrow. Further, although the above-mentioned biphenyl compound exhibits a chiral smectic C phase at a temperature close to room temperature, the temperature range is about 10°C, which is not sufficiently wide. Moreover, the response time of the above phenylpyrimidine compound is 43
It is estimated that the spontaneous polarization is as slow as 1500 μs at ℃ and is quite small.

In other words, liquid crystal materials for display devices and the like that require high-speed response must have large spontaneous polarization.
Physical properties such as low viscosity and exhibiting a chiral smectic C phase over a wide temperature range including around room temperature are required, but the reality is that to date there are no materials that fully satisfy these physical properties. there were.

[0009] In contrast, the applicant of the present invention first proposed the following formula having a fluorine atom and a methyl group on the asymmetric carbon:

It was reported that the compound [Chemical formula 5] shows large spontaneous polarization and is useful as a material for compositions capable of high-speed response (Patent application No.
-287994).

This compound alone exhibited a stable chiral smectic C phase and exhibited very large spontaneous polarization. Furthermore, a high-speed response was exhibited even when only a small amount was added to the base liquid crystal composition. However, when this compound is added to a pyrimidine-based liquid crystal composition, it no longer exhibits a cholesteric phase, resulting in the problem that good alignment is difficult to obtain.

[0011] The present inventors have made extensive studies to improve the liquid crystal properties of such a compound, and have found that the compound has a thermotropically stable liquid crystal structure by using a diphenylpyrimidine skeleton having a fluorine substituent in the core. We have discovered that this compound has properties that make it difficult to eliminate the cholesteric phase when mixed with a base liquid crystal, and that it has properties that broaden the temperature range of the chiral smectic C phase.

The present invention has been made based on this knowledge, and an object of the present invention is to provide a novel ester compound useful as a liquid crystal composition, an optically active substance thereof, and a liquid crystal composition containing the same. There is a particular thing. Further, the present invention aims to provide a liquid crystal display element having high-speed response using a liquid crystal composition containing such a novel optically active ester compound.

[0013]

[Means for Solving the Problems] The present invention is based on the following general formula:

In the novel ester compound represented by [Formula 6] (wherein R and R' represent an alkyl group having 2 to 18 carbon atoms) and the compound, on the methine carbon to which fluorine and methyl group are bonded, The present invention relates to an optically active ester compound having an asymmetric center, and a liquid crystal composition and an optical switching element containing the optically active ester compound.

Examples of representative compounds of the above formula 6 and their physical and chemical properties are as follows. 2-(2-fluoro-4-hexyloxyphenyl)-
5-(4-(2-fluoro-2-methylheptanoyloxy)phenyl)pyrimidine ■ 1H-NMR (270 MHz, TMS standard,
δ value) δ 0.91 6H
mδ 1.2 ~ 2.2 16H
mδ 1.77 3H
d(J=22Hz)δ 4.01
2H t(J=7Hz)δ 6.80
2H mδ 7.26
2H d(J=9Hz)δ
7.68 2H d(
J=9Hz) δ 8.16 1
H t (J=9Hz) δ 9.02
2H s■ IR (KBr method, c
m-1) 2910, 2840, 1750, 1600, 1500
The compound of chemical formula 6 above has the following reaction formula

[Image Omitted] That is, phenol (1
) with carboxylic acid (2). In this case, if an optically active substance is used as the carboxylic acid (2), the optically active ester compound of the present invention can be obtained. As a method for esterification, for example, a dehydration condensation agent such as dicyclohexylcarbodiimide can be used. Alternatively, carboxylic acid (2) can be made into an acid halide using a halogenating agent such as thionyl chloride, and then reacted with phenol (1) in the presence of a base.

[0015] The phenol (1) used here was manufactured by Jouur Practical Chemi.
rnal fuel Praktische Chem
ie) 323 (2) Referring to the method shown in 119, the following reaction formula

It can be obtained as follows. In addition, the carboxylic acid (2) used here has the following reaction formula:

It can be obtained as follows. That is, first, 2-
Methyl-1,2-epoxyalkane is reacted with an amine-hydrogen fluoride complex or silicon tetrafluoride to produce 2-fluoro-2-methyl-1-alkanol (Unexamined Japanese Patent Application Publication No. 2003-100000).
235828). By oxidizing this using an oxidizing agent such as potassium permanganate, carbonic acid (2
) can be obtained (Japanese Patent Application No. 1-278471).

It should be noted that R in the compound shown in the above general formula 6
, R' has an influence on the physical properties such as the temperature range in which the compound can take a liquid crystal state, and can be appropriately selected depending on the purpose.

[0017]

[Examples] Next, the present invention will be specifically explained using the following examples and comparative examples. Example 1 2-(2-fluoro-4-hexyloxyphenyl)-5
-(4-(2-fluoro-2-methylheptanoyloxy)phenyl)pyrimidine synthesis method 2-(2-fluoro-4-hexyloxyphenyl)-
5-(4-hydroxyphenyl)pyrimidine 2.08g
(5.68 mmol), 2-fluoro-2-methylheptanoic acid 1.01 g (6.23 mmol), dicyclohexylcarbodiimide 1.42 g (6.89 mmol)
l), 4-dimethylaminopyridine 0.08g (0.6
6 mmol) and 20 ml of dry dichloromethane were placed in a flask and stirred at room temperature for 2.5 hours. The resulting solid was removed by filtration, the solvent was distilled off, and the resulting crude crystals were purified by silica gel column chromatography and recrystallization from ethanol to obtain 2-(2-fluoro- 4-hexyloxyphenyl)
-5-(4-(2-fluoro-2-methylheptanoyloxy)phenyl)pyrimidine 1.79 g (yield 62%)
) was obtained.

Evaluation of liquid crystallinity The compound obtained as described above was injected into a 3 μm thick cell made of a glass plate with a transparent electrode coated with polyimide and subjected to a rubbing treatment, and heated at a rate of -2° C./min. When observed with a crossed Nicol polarizing microscope while the temperature was decreasing, the temperature was 90.
It changed from an isotropic liquid to a chiral smectic C phase at 4°C, and crystallized at 63.5°C. Also, 30V at 85.4℃
When we applied a pp triangular wave and measured the spontaneous polarization, we found that 2
It was extremely large at 39.6 nC/cm2.

Example 2 Preparation of liquid crystal composition and optical switching device The following chemical formula 1
Non-optically active liquid crystal compounds shown in 0 (3), (4),
A base liquid crystal mixture A was prepared by mixing (5), (6), (7), (8), (9) and (10) in the same proportions shown in Chemical Formula 10 below.

embedded image This liquid crystal composition A exhibited the following phase transition behavior. (Cr indicates a crystalline phase, Sc indicates a smectic C phase, SA indicates a smectic A phase, N indicates a nematic phase, and I indicates an isotropic phase.)

Since this liquid crystal composition A does not contain a compound having an asymmetric carbon, it does not exhibit ferroelectric behavior. Liquid crystal composition B was prepared by mixing this liquid crystal composition A and the compound of Example 1 in the ratio shown in Chemical formula 11 below.

embedded image This liquid crystal composition B exhibited the following phase transition behavior. (Sc* indicates chiral smectic C phase, Ch indicates cholesteric phase.)

[0021] Further, this liquid crystal composition was injected into a 2 μm thick cell made of a glass plate with a transparent electrode coated with polyimide and subjected to a rubbing treatment, and from the state of an isotropic liquid,
The temperature was gradually lowered to orient the cholesteric phase. When the temperature was further lowered to change the state from the smectic A phase to the chiral smectic C phase, well-oriented cells were easily obtained. When an electric field was applied to the cell while observing it with a crossed Nicol polarizing microscope, clear switching behavior was observed.

Furthermore, when a 20 Vpp rectangular wave was applied to this cell at 25° C. and the amount of transmitted light was measured with a photodiode to detect optical switching operation, it was found that the amount of transmitted light changed from 10% to 90%. The time required is 4
It was extremely fast at 6 μs.

Comparative Example The liquid crystal composition A used in Example 2 and the compound described in Japanese Patent Application No. 1-287994 shown in the following chemical formula 12 were mixed in the same proportion as shown in the following chemical formula 12 to form a liquid crystal composition. Composition C was created.

embedded image This liquid crystal composition C exhibited the following phase transition behavior. As described above, since this liquid crystal composition C does not have a cholesteric phase, it is difficult to obtain good alignment. Also,
The temperature range of the chiral smectic C phase was also narrower compared to liquid crystal composition B.

[0024]

Effects of the Invention The compound of the present invention can take a stable thermotropic liquid crystal state, and the optically active compound of the present invention can be added to a non-chiral liquid crystal to form a ferroelectric material with large spontaneous polarization and a fast response speed. It has extremely excellent effects as a material for optoelectronics-related elements, such as forming a liquid crystal composition.

Therefore, the present invention provides a liquid crystal material that is useful as a material for optoelectronics-related elements that utilize liquid crystals and electrochemometry, such as displays such as liquid crystal televisions, optical printer heads, optical Fourier transform elements, and light valves. It can be said.

Claims (4)

[Claims] 1. A novel ester compound represented by the following general formula: [Formula 1] (wherein R and R' represent an alkyl group having 2 to 18 carbon atoms). 2. A novel ester compound represented by the general formula 1 according to claim 1, which is an optically active ester compound having an asymmetric center on the methine carbon to which fluorine and a methyl group are bonded. 3. A liquid crystal composition containing at least one optically active ester compound according to claim 2. 4. An optical switching element comprising at least one optically active ester compound according to claim 2 as a constituent element.