JPH08253766A - Liquid crystal phosphonium salt - Google Patents

Abstract

PURPOSE: To obtain a liquid crystal phosphonium salt excellent in the capability of homeotropic alignment and improved in stability in the form of a smectic liquid crystal in a wide temperature range by reacting an alkylphosphine compound with an alkyl halide. CONSTITUTION: A dialkylphosphine or a trialkylphosphine is reacted with an alkyl halide to obtain a liquid crystal phosphonium salt of the formula (wherein R<1> and R<2> are each 1-4C alkyl; R<3> and R<4> are each 8-24C alkyl; and X<-> is an anion).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display material such as a liquid crystal element utilizing thermo-electro-optical effect, an optical recording material, a homeotropic alignment treatment agent (liquid crystal molecules in a direction perpendicular to a substrate). The present invention relates to a novel phosphonium salt-based liquid crystalline compound useful as a surface treatment agent for orientation.

[0002]

2. Description of the Related Art Liquid crystals are classified into thermotropic liquid crystals and lyotropic liquid crystals on the basis of means for giving a phase transition. Thermotropic liquid crystals exhibit a liquid crystal phase by heating or cooling, and are widely used for optical display materials or optical recording materials by utilizing their various electro-optical effects. Lyotropic liquid crystals exhibit a liquid crystal phase when coexisting with a solvent, and are of interest in fields such as biophysics and biotechnology.

Thermotropic liquid crystals include a nematic liquid crystal and a smectic liquid crystal, but most of the thermotropic liquid crystals currently in practical use are nematic liquid crystals. However, since nematic liquid crystals generally have high viscosity and low fluidity, they have been unsuitable for application fields such as displays requiring high-speed response. On the other hand, since smectic liquid crystals form a layer of liquid crystal molecules, and the order of molecular arrangement is higher than nematic liquid crystals, and it has properties closer to those of crystals. The application to the and projection type displays has been pioneered, and the application development is being energetically carried out as the next-generation liquid crystal technology.

In the development of liquid crystal displays, the expansion of the liquid crystal temperature range is strongly required from the viewpoint of the operating temperature of liquid crystal display elements regardless of nematic liquid crystal or smectic liquid crystal. A known liquid crystal compound has a narrow liquid crystal temperature range by itself, and a multi-component mixed liquid crystal is used in a liquid crystal display that has been commercialized. Therefore, a novel liquid crystalline compound showing liquid crystallinity in a wide temperature range from low temperature to high temperature is desired.

Further, when a liquid crystal display panel is manufactured, the substrate is subjected to a surface treatment for orienting liquid crystal molecules in a cell in a certain direction in order to prevent alignment defects of the liquid crystal molecules. In particular, when aligning liquid crystal molecules in a direction perpendicular to the substrate (homeotropic alignment), a substrate such as lecithin or a quaternary ammonium salt is applied to the substrate, or these aligning agents are added to the liquid crystal. It involved complicated operations such as addition, and its effect was not sufficient. Therefore, there is a demand for a liquid crystal having homeotropic alignment having no defects without pretreatment. It is known that an amphipathic substance having a hydrophilic group and a flexible long-chain alkyl group (hydrophobic group) exhibits a liquid crystal state (lyotropic liquid crystal) at a certain temperature when coexisting with water or an organic solvent. However, it is only known that lecithin and some quaternary ammonium salts can become smectic liquid crystals in the liquid crystal transition of anhydrous amphiphiles caused by temperature changes. In other words, the current situation is that amphiphilic substances have not been applied as thermotropic liquid crystals.

The phosphonium salt represented by the general formula (1) according to the present invention is a compound already known as a biocide (JP-A-51-43722). However,
Up to now, the liquid crystallinity of phosphonium salts has not been known at all, regardless of whether they are lyotropic liquid crystals or thermotropic liquid crystals.

[0007]

DISCLOSURE OF THE INVENTION As a result of intensive studies conducted by the present inventors in view of the above facts, the phosphonium salt represented by the general formula (1) has an excellent homeotropic alignment ability as a thermotropic liquid crystal. They have found that they have a smectic liquid crystal phase which has a stable temperature range over a wide temperature range, and completed the present invention.

[0008]

That is, the present invention provides a liquid crystalline phosphonium salt represented by the following general formula (1).

[0009]

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(In the formula, R ¹ and R ² are the same or different alkyl groups having 1 to 4 carbon atoms, and R ³ and R ⁴ are the same or different alkyl groups having 8 to 20 carbon atoms. X ⁻ is Indicates an anion.)

The liquid crystal compound represented by the general formula (1) of the present invention is characterized in that it has a stable liquid crystal state in a wide temperature range and the phase transfer temperature is almost the same during heating and during cooling. And has excellent homeotropic alignment ability. Moreover, since this compound has a P—C bond, it has excellent chemical and thermal stability.

The present invention will be described in detail below. R ¹ and R ² represented by the general formula (1) are alkyl groups having 1 to 4 carbon atoms, and examples thereof include a lower alkyl group such as a methyl group, an ethyl group, a propyl group and a butyl group, preferably a methyl group. , An ethyl group. R ³ and R ⁴ are not particularly limited as long as they are hydrophobic alkyl groups, for example, octyl group,
8 to 20 carbon atoms such as decyl group, dodecyl group, tetradecyl group, hexadecyl group, octadecyl group, eicosyl group
The straight-chain alkyl group or the branched alkyl group may be mentioned, and the straight-chain alkyl group is preferable.

X ⁻ is not particularly limited as long as it is an anion atom and an atomic group. For example, halogen ion such as fluorine, chlorine, bromine or iodine, carboxyl ion such as formic acid, acetic acid and oxalic acid, sulfate ion and phosphate ion. , Phosphate ions such as methyl or dimethyl phosphate ion, ethyl or diethyl phosphate ion, antimony fluoride ion, phosphorus fluoride ion, arsenic fluoride ion, boron fluoride ion, perchlorate ion and the like, and preferably It is a halogen ion.

As the preferred compound represented by the general formula (1) according to the present invention, a linear alkyl group in which R ¹ and R ² and R ³ and R ⁴ are the same is desirable, for example, dioctyldimethylphosphonium bromide and dioctyl. Diethylphosphonium chloride, dioctyldimethylphosphonium chloride, dioctyldiethylphosphonium chloride, dioctyldimethylphosphonium iodide,
Dioctyldiethylphosphonium iodide, Dioctyldimethylphosphonium iodide, Dioctyldiethylphosphonium iodide, Didecyldimethylphosphonium bromide, Didecyldiethylphosphonium bromide, Didecyldimethylphosphonium chloride, Didecyldiethylphosphonium chloride, Didecyldimethylphosphonium iodide, Di Decyldiethylphosphonium iodide, didecyldimethylphosphonium iodide, didecyldiethylphosphonium iodide, ditetradecyldimethylphosphonium bromide, ditetradecyldiethylphosphonium bromide, ditetradecyldimethylphosphonium chloride,
Ditetradecyldiethylphosphonium chloride, ditetradecyldimethylphosphonium iodide, ditetradecyldiethylphosphonium iodide, ditetradecyldimethylphosphonium iodide, ditetradecyldiethylphosphonium iodide, dioctadecyldimethylphosphonium bromide, dioctadecyldiethylphosphonium bromide , Dioctadecyldimethylphosphonium chloride, dioctadecyldiethylphosphonium chloride, dioctadecyldimethylphosphonium iodide, dioctadecyldiethylphosphonium iodide, dioctadecyldimethylphosphonium iodide, dioctadecyldiethylphosphonium iodide, phosphonium salts such as This is the compound of the invention The present invention is not limited.

The liquid crystalline compound of the present invention may be produced by any method. For example, the liquid crystalline compound of the present invention can be easily obtained by reacting a dialkylphosphine or trialkylphosphine with an alkyl halide. The liquid crystal compound represented by the general formula (1) of the present invention can be used alone or as a mixture of two or more kinds, and is also useful, for example, as a composition for further expanding the liquid crystal temperature range of other liquid crystal compounds. Further, by utilizing the excellent homeotropic alignment ability of the compound of the present invention, other known liquid crystal compounds can be used as an aligning agent for homeotropic alignment. When the present invention is used as an aligning agent for giving homeotropic alignment to another liquid crystal, the type of the other liquid crystal is not particularly limited, and examples thereof include Schiff base type, azo type, azoxy type, benzoic acid ester type, and biphenyl type. Examples thereof include nematic liquid crystals such as a system, a terphenyl system, a pyrimidine system, and a dioxane system. The amount added is usually about 0.0001 to 5% by weight, preferably 0.25 to 2.
It is 5% by weight.

[0016]

The structural characteristic of the liquid crystalline compound represented by the general formula (1) of the present invention is that it has a positively charged phosphorus atom as a polar part and two long-chain alkyl groups as a non-polar part. It is that you are. Basically, it resembles a biological lipid having a bilayer formation property, in which two long alkyl chains are aligned and packed in a straight line, and when heated or cooled, they spontaneously generate an ordered structure. The state is guided. The action of this compound as an aligning agent for homeotropically aligning other liquid crystals is based on the hydrophobicity of the glass substrate surface. That is, the positively charged phosphorus atom, which is a hydrophilic group, electrostatically interacts with or adheres to the glass surface, so that the long alkyl chain, which is a hydrophobic group, stands upright on the glass substrate.

[0017]

The present invention will be described in detail below with reference to examples. Example 1 To a 100 ml four-necked flask which had been sufficiently replaced with nitrogen, 11.7 g (0.058 mol) of decyldimethylphosphine and 15.3 g (0.087 mol) of decyl chloride were placed and heated to 140 ° C. with stirring. The reaction was carried out without solvent for 24 hours. The solidified product was dissolved in acetonitrile, washed thoroughly with n-hexane, and then the organic phase was concentrated under reduced pressure. The obtained white crystals were recrystallized from ethyl acetate to obtain 17.7 g (yield 81%) of didecyldimethylphosphonium chloride.

Example 2 In the same manner as in Example 1, 9.4 g (0.036 mol) of tetradecyldimethylphosphine and 12.7 g (0.055 mol) of tetradecyl chloride were reacted at 140 ° C. for 24 hours. By recrystallizing the obtained white crystal, ditetradecyldimethylphosphonium chloride 1
0.4 g (yield 58%) was obtained.

Example 3 In the same manner as in Example 1, 17.3 g (0.055 mol) of octadecyldimethylphosphine and 20.0 g (0.069 g) of octadecyl chloride were reacted at 140 ° C. for 24 hours to obtain the product. The white crystals were recrystallized to obtain 4.0 g of dioctadecyldimethylphosphonium chloride (yield 12%).

Comparative Examples 1 to 3 For comparison, didecyldimethylammonium chloride, which is a commercially available quaternary ammonium salt which is the same amphiphile as the present invention and which corresponds to the phosphonium salts of Examples 1 to 3, Ditetradecyldimethylammonium chloride and dioctadecyldimethylammonium chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) were prepared.

(Measurement of Phase Transition Temperature) The thermal physical properties of the compounds obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were measured by a scanning differential calorimeter (DSC: SEIKO I & E SSC-52).
00 DSC 220C). The heating / cooling was repeated three times at 1 ° C./min. After confirming the reproducibility of the measurement, the phase transfer temperature was determined from the thermal analysis curve during the second heating / cooling. The results of the thermal analysis obtained are shown in Table 1. In addition, T
cs indicates the phase transfer temperature between the crystal and the liquid crystal phase, and T _SI indicates the phase transfer temperature between the liquid crystal phase and the isotropic liquid.

[0022]

[Table 1]

From the above results, the phosphonium salt of the present invention has a wider liquid crystal temperature range than the quaternary ammonium salt, and T _SI is almost the same during heating and during cooling. It has been found that can be efficiently induced, and that coloring due to decomposition is not observed.

(Evaluation of homeotropic alignment ability) Next,
Each of the compounds obtained in Examples 1 to 3 was sandwiched between two glass plates, heated to a liquid crystal phase-isotropic liquid transition temperature or higher, cooled to a liquid crystal temperature region, and the transmitted light thereof was analyzed by a polarizing microscope. I observed. As a result, all compounds showed an extinction state irrespective of the polarization direction.However, when the glass plate was shifted from the top to the parallel direction while applying pressure, the birefringent optical pattern peculiar to the liquid crystal phase was clearly seen. Was given. Therefore, it was confirmed that these compounds have homeotropic alignment ability.

Example 4 The following six types of nematic liquid crystals: p-butylethoxyphenyl terephthalate p-hexanoyloxyphenylazophenylethane p-methoxybenzylidene-p-butylaniline p-azoxyanisole p-methoxybenzylidene-p- A liquid crystal composition was prepared by adding 0.25% by weight of didecyldimethylphosphonium chloride to aminophenyl acetate butyl-p- (p-ethoxyphenoxycarbonylphenyl carbonate). Each composition was heated to a temperature above the phase transition temperature between the nematic and isotropic liquids, cooled to room temperature, and filled in a gap between two glass plates sandwiching a spacer of a polyester film having a thickness of 25 μm. A cell was prepared.

Example 5 To the above nematic liquid crystal, 1% by weight of ditetradecyldimethylphosphonium chloride was added, and Example 4 was added.
A liquid crystal cell was prepared by the same operation as in.

Example 6 A liquid crystal cell was prepared in the same manner as in Example 4, except that 2.5% by weight of dioctadecyldimethylphosphonium chloride was added to each of the above nematic liquid crystals.

Example 7 A liquid crystal cell was prepared in the same manner as in Example 4, except that 0.25% by weight of decyltrimethylphosphonium chloride was added to each of the above nematic liquid crystals.

(Evaluation of Homeotropic Alignment Ability of Liquid Crystal Compositions) As a result of observing the transmitted light of each of the 24 liquid crystal cells prepared in Examples 4 to 7 with a polarization microscope, all of them were in the extinction state regardless of the polarization direction. However, when the glass plate was displaced in the parallel direction while applying pressure from above, a birefringent optical pattern peculiar to the liquid crystal phase was clearly seen. Therefore, it was confirmed that these liquid crystal compositions have homeotropic alignment ability.

[0030]

The compound represented by the general formula (1) of the present invention has excellent homeotropic alignment ability as a thermotropic liquid crystal and shows a stable smectic liquid crystal phase in a wide temperature range. It can be used as a display material, an optical recording material and a homeotropic alignment treatment agent.

Claims (1)

[Claims] 1. A compound represented by the general formula (1): (In the formula, R ¹ and R ² are the same or different alkyl groups having 1 to 4 carbon atoms, and R ³ and R ⁴ are the same or different carbon numbers 8 to 20.
Is an alkyl group. X ⁻ represents an anion. ) A liquid crystalline phosphonium salt represented by.