JPH0129835B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a liquid crystal composition containing a dye. [Prior Art] In general, display devices using liquid crystals include those that utilize the electro-optical effect of the liquid crystal substance itself, and those that utilize the electro-optical effect that occurs as a result of interaction with other contaminants. A typical example of the latter is a host liquid crystal such as a nematic liquid crystal, a cholesteric liquid crystal, or a smectic liquid crystal in which a dye called a pleochroic dye is dissolved as a guest.
There are roughly two types of pleochroic pigments. First, the direction of the absorption transition moment of visible light is almost parallel to the long axis direction of the molecules, and when dissolved in the liquid crystal as a guest molecule, the long axis of the dye molecules is well aligned in the same direction as the liquid crystal molecular axis. It is a pigment. Such dyes are called pleochroic dyes having parallel dichroism. The second is that the direction of the visible light absorption transition moment is almost perpendicular to the long axis direction of the molecule, and when dissolved in the liquid crystal as a guest molecule, the long axis of the dye molecule is in the same direction as the liquid crystal molecular axis. It is a well-aligned dye. Such dyes are called pleochroic dyes with vertical dichroism. The present invention relates to the first of these, namely, a liquid crystal composition containing a pleochroic dye having parallel dichroism. The quality of the arrangement of the pleochroic dye molecules dissolved in such a liquid crystal substance can be quantitatively expressed by the order parameter S described below. If a nematic liquid crystal or cholesteric liquid crystal containing such a pleochroic dye is interposed between two opposing electrode plates and a voltage is applied, the liquid crystal molecules will undergo disturbance motion based on the dielectric and flow characteristics of the liquid crystal. or arrange molecules aligned in the direction of the electric field. At this time, the pleochroic dye molecules also move cooperatively with the liquid crystal molecules, causing a change in the relative direction of the absorption transition moment of the pleochroic dye molecules and the incident light, resulting in a liquid crystal display device. This will result in a change in the light absorption properties of. Such a phenomenon is widely known as the "guest-host effect," and by utilizing this effect, an electrically controlled color display device can be constructed. [Problems to be solved by the invention] In order to obtain excellent contrast between the on state and the off state in a liquid crystal display device that utilizes such a guest-host effect, it is necessary to use a guest pleochroic dye. It must have the property of exhibiting strong coloring in one state and an uncolored state close to colorless and transparent in the other state. That is, in order to provide strong coloring, the absorption transition moment of the pleochroic dye must be parallel to the electric vector of the incident white light,
That is, it must be aligned perpendicular to the direction of light propagation, and on the other hand, in order to provide a near-transparent, non-colored state, the absorption transition moment of the pleochroic dye molecule must be aligned perpendicular to the electric vector of the incident white light, i.e. They must be aligned parallel to the direction of light propagation. However, liquid crystal molecules and dye molecules undergo random thermal fluctuations with respect to alignment, and the absorption transition moment cannot always be perpendicular or parallel to the direction of propagation of light. Therefore, the orderliness of the arrangement of dye molecules in a particular direction in the liquid crystal has a great effect on the contrast of the device. The degree of arrangement of dye molecules in a liquid crystal medium is usually expressed by a value called an order parameter. The order parameter S represents the degree of parallelism of the absorption transition moment of the dye molecule to the orientation direction of the liquid crystal molecules (usually expressed as a vector called a director), and is defined as follows. S = 1/2 (3 ² -1) In the formula, the term cos ² θ is time averaged, and θ is the angle between the absorption transition moment of the pleochroic dye and the orientation direction (director) of the liquid crystal. be. The order parameter S of the pleochroic dye dissolved in the liquid crystal can be determined using the following equation. S=A-A⊥/2A⊥+A In the formula, A and A⊥ represent the absorbance of the dye molecule with respect to light polarized parallel and perpendicular to the orientation direction (director) of the host liquid crystal, respectively.
Therefore, by measuring the absorption spectrum, A, A⊥
By determining the order parameter S of the dye in the host liquid crystal, it is possible to evaluate the orientation of the dye (the method for measuring the order parameter of a pleochroic dye is
Junior S Aftergout, Journal
of Chemical Physics, HSCole, Jr.
S. Aftergut, Journal of Chemical Physics,
(1978, Vol. 68, p. 896). Theoretically, the value of the order parameter S of the pleochroic dye dissolved in the host liquid crystal ranges from −0.5 to 1.
It can take values between . In the case of a pleochroic dye having positive dichroism, the closer the value of the order parameter is to 1, the greater the degree of order of arrangement of the dye in the liquid crystal, and the contrast of the device can be improved. For these pleochroic dyes, in order to obtain a large contrast between the colored state and the non-colored state, the order parameter S in the host liquid crystal is
In order to achieve clear colors with a small amount of addition to the host liquid crystal material, the molecules must have a large extinction coefficient, have excellent stability against light, heat, water, oxygen, etc., and have high solubility in liquid crystals. It must have properties that satisfy conditions such as having a large concentration, being able to obtain an arbitrary concentration within the required range, and not having a negative effect on the electrical characteristics of the device due to ionic dissociation or the like. In the case of pleochroic dyes with parallel dichroism, the value of the order parameter S is usually around room temperature.
It is desirable that it is 0.65 or more. This order
Even if the dye is the same, the value of the parameter S usually varies somewhat if conditions such as the type of host liquid crystal, dye concentration, temperature, etc. change. Further, it is desirable that the solubility of the dye is sufficient to ensure the required dye concentration. The concentration of the dye is selected depending on the thickness of the liquid crystal layer of the liquid crystal device and the extinction coefficient of the dye molecules, but is usually used in the range of about 0.5 weight percent to about 3 weight percent. Therefore, in practice, the solubility of the pleochroic dye in the host liquid crystal is often required to be at least 0.5 weight percent or more at around room temperature. Among known dyes, there are very few that can satisfy the above conditions. For example, merocyanine-based, azo-based, azomethine-based, and anthraquinone-based dyes are known, but it is thought that none of these dyes satisfy all of the above conditions. In addition, in terms of hue, there are very few pigments that exhibit a cyan color, with the exception of some merocyanine pigments. Cyan is an essential hue for preparing border colors through subtractive color mixing with yellow.
Cyan color is a hue that belongs to blue in a broad sense, but a good edge color cannot be obtained by mixing so-called blue color, which also belongs to blue in a broad sense, and yellow. An object of the present invention is to provide a liquid crystal composition that satisfies the above-mentioned conditions and contains a dye that exhibits a cyan hue. [Means for solving the problem] Pleochroic pigments with good order parameters, extinction coefficients, stability, and solubility are blue and violet pigments. Anthraquinone pigments are known, among which [ ] is a blue pigment with a maximum absorption wavelength of 594 nm, and [ ] is a purple pigment with a maximum absorption wavelength of 556 nm. In general, the hue of anthraquinone dyes is closely related to the position and type of substituents on the basic skeleton. With its structure, it is difficult to achieve hues other than blue. Furthermore, it is difficult to realize a hue other than purple with a structure in which allyl amino groups are attached at both the 1 and 5 positions like [ ]. Therefore, in order to achieve the cyan color that is absolutely necessary for producing green color using anthraquinone dyes, the positions and types of substituents must be significantly changed. However, with such a change in substituents, properties other than hue, such as order parameters, extinction coefficient, solubility, stability, etc., also change significantly. Therefore, when changing the hue, it is necessary to carefully select a molecular structure that does not adversely affect other properties. In view of such prior art, the present inventors have conducted intensive studies to realize cyan pleochroic dyes using anthraquinone dyes, and have found that We were able to complete the present invention by obtaining an excellent cyan-colored pleochroic anthraquinone dye. The feature of the present invention is that the liquid crystal has a general formula [Wherein, X is an oxygen atom, a sulfur atom, -NR-
(R is a hydrogen atom or a lower alkyl group) and Ar is a straight-chain alkyl group. The pleochroic anthraquinone dye represented by the general formula [] is, for example, the following general formula: It can be produced by reducing a compound represented by the formula [wherein X and Ar are the same groups as in the above formula []] with sodium sulfide, hydrazine hydrate, etc. The purity of the dye produced in this manner can be increased using purification means such as column chromatography, recrystallization, and sublimation. The nematic liquid crystal used in the present invention may be one that exhibits a nematic state within the operating temperature range.
You can choose from a fairly wide range. Further, by adding an optically active substance to be described later to such a nematic liquid crystal, it can be made to take a cholesteric state. The first example of a nematic liquid crystal is
Examples include the substances shown in the table or their derivatives.

【table】

【table】

[Effect]

The anthraquinone dye of the present invention can be used as a guest dye for liquid crystals, including order parameter S.
The reason why each of the above characteristics is excellent when blended into a liquid crystal is not clear, but the mother nucleus of the dye has a diaminoanthraquinone structure at the 1,4-position, and -COO-, COS-, −CONH−, −CONR−
This is thought to be because it has a structure in which a phenyl group having a nonionic substituent is bonded via a specific linking group selected from (R is a lower alkyl group). [Examples] Example 1 First, examples of pleochroic anthraquinone dyes used in the present invention are shown in Table 2 along with their maximum absorption wavelengths and order parameters.

【table】

【table】

〔Effect of the invention〕

Since the liquid crystal composition containing the anthraquinone dye of the present invention as a guest dye has a high value of the order parameter S of the dye, a color liquid crystal display device with excellent contrast can be obtained by using the liquid crystal composition. be able to.

[Brief explanation of drawings]

FIGS. 1 and 4 are schematic cross-sectional views of a guest-host type liquid crystal display device, and FIGS. 2, 5, and 6 show the spectral characteristics of the device filled with the liquid crystal composition of the present invention. FIG. 3 is a curve diagram showing the results of an accelerated deterioration test using a weather meter regarding the practical stability of the guest dye of this example. 1...Substrate, 2...Guest dye, 3...Host liquid crystal,
4...Transparent electrode, 5...Light, 6...Observer, 17...Horizontal axis.

Claims (1)

[Claims] 1. General formula A liquid crystal composition characterized in that X is an oxygen atom, a sulfur atom, a -NR- group (R is a hydrogen atom or a lower alkyl group), and Ar is a straight-chain alkyl group. thing. 2. The liquid crystal composition according to claim 1, wherein in the general formula (1), Ar is an n-butyl group. 3. The liquid crystal composition according to claim 1 or 2, wherein the content of the dye is 0.1 to 10% by weight. 4. The liquid crystal composition according to claim 1, 2, or 3, wherein the host liquid crystal is a nematic liquid crystal.