JPS621636B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid crystal composition, and in particular to an electro-optic system in which a liquid crystal composition containing a specific dye is interposed between two opposing electrode plates, and which utilizes the guest-host effect of the liquid crystal to enable good color display. The present invention relates to a liquid crystal composition used in an element. 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 one in which a dye called a pleochroic dye is dissolved in a liquid crystal such as a nematic liquid crystal, a cholesteric liquid crystal, or a smectic liquid crystal. There are roughly two types of pigments called pleochroic pigments. In the first type, the direction of absorption transition moment of visible light is almost parallel 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 preferably aligned in the same direction as the liquid crystal molecular axis. It is a pigment that has the property of arranging in Such dyes are called pleochroic dyes having parallel dichroism. Second
In this type, the direction of absorption transition moment of visible light is almost perpendicular to the long axis direction of the molecule, and when dissolved in the above liquid crystal as a guest molecule, the long axis of the dye molecule is well aligned in the same direction as the liquid crystal molecular axis. It is a pigment that has the property of arranging. Such dyes are called pleochroic dyes having vertical dichroism. The present invention relates to the first of these two types, namely a liquid crystal composition containing a pleochroic dye having parallel dichroism. The quality of the alignment of the pleochroic dye molecules dissolved in such a liquid crystal substance can be quantitatively expressed by a quantity called an order parameter S, which will be described later. 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 This will cause a change in the light absorption characteristics of the liquid crystal display device. This phenomenon is called the “guest-host effect.”
It is widely known as, and using this effect,
An electrically controlled color display device can be constructed. (“Guest−Host Interaction in Nematic Liguid
Crystals: A New Electro-Optic Effects”
GH Heilmeier and LAZanoni, Applied
See Physics Letters, vol. 13, p. 91 (published in 1968). ) For example, a nematic liquid crystal containing a pleochroic dye having parallel dichroism and having positive dielectric anisotropy is interposed between two transparent electrode plates facing in parallel and subjected to homogeneous alignment treatment. The liquid crystal molecules form a homogeneous alignment in which their long axes are aligned in the same direction and parallel to the electrode plane. At this time, the molecules of the pleochroic dye dissolved in the liquid crystal also align their long axes parallel to the electrode plane. When white light traveling in a direction perpendicular to the electrode surface propagates through the guest-host material arranged in this manner, the long axis of the pleochroic dye molecules becomes parallel to the electric vector of the incident white light. Therefore, a specific wavelength region of the incident light is strongly absorbed by the pleochroic dye that is the guest material, and as a result, the guest-host material assumes a colored state. (See Figure 1.) Next, when an electric field is applied to a liquid crystal substance with such an arrangement, the host liquid crystal molecules and the guest pleochroic dye molecules will change due to the positive dielectric anisotropy of the host liquid crystal. It adopts a homeotropic orientation with its long axis aligned perpendicular to the electrode plane. (See Figure 2.) At this time, the long axis of the pleochroic dye molecule is perpendicular to the electric vector of the incident white light, so the incident light is hardly absorbed by the pleochroic dye molecule, and the guest-host substance appears transparent. In this way, display can be performed using the difference between the colored state and the transparent state. In addition, by adding optically active substances, nematic liquid crystals that have a helical structure or cholesteric liquid crystals that originally have a helical structure are used as host substances, and pleochroic dyes that have parallel dichroism are dissolved therein. In this case, the molecules of the pleochroic dye are arranged in a helical structure, similar to these host substances. (See Figure 3.) When light propagates parallel to the helical axis of such a guest-host material, the guest-host material propagates the white incident light in two reference modes, which are clockwise and counterclockwise, respectively. becomes elliptically polarized light. The direction of the electric vector of the light that displays these modes is closely related to the long axis of the guest molecule, and a specific wavelength region of the incident light is absorbed by the guest material, resulting in the guest-host material being colored. take a state. Next, when an electric field is applied in a direction parallel to the helical axis of such a guest-host material, if the dielectric anisotropy of the host liquid crystal is positive, the helical structure of the guest-host material will be unwound. As a result, a nematic state is created in which the long axes of liquid crystal molecules and dye molecules are aligned in the direction of the electric field. (See Figure 4.) In this arrangement, the direction of the absorption transition moment of the pleochroic dye molecules is perpendicular to the electric vector of the incident white light, so the incident light is hardly absorbed by the guest molecules, and the guest molecules The host material appears transparent. (Such a color display method is described in detail in, for example, Japanese Patent Application Laid-Open No. 49-127645.) Even when a smectic liquid crystal is used as the host liquid crystal, if an appropriate element configuration and driving method are used,
Similar to the case of nematic liquid crystal and cholesteric liquid crystal, display is possible by utilizing the difference between the colored state and the transparent state. (For example, “New electrothermo-optic
effect in a certain smectic liquid crystal
with a pleochroic dye added”C.Tani and
T. Ueno, Applied Physics Letters, Volume 33,
See page 275 (published in 1978). ) In order to obtain excellent contrast between the on-state and off-state in a liquid crystal display device that utilizes the guest-host effect as described above, the pleochroic dye that is the guest must exhibit strong coloring in one state. , the other state must have a property that it becomes an uncolored state that is close to transparent. That is, in order to give strong coloring, the absorption transition moments of pleochroic dyes need to be aligned parallel to the electric vector of the incident white light, i.e. perpendicular to the direction of light propagation, while on the other hand, non-colored, close to transparent In order to provide this state, the absorption transition moments of the pleochroic dye molecules need to be aligned perpendicular to the electric vector of the incident white light, that is, 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 numerical value called an order parameter. Order parameter S
represents the parallelism of the absorption transition moment of the dye molecule to the alignment direction of the liquid crystal molecules (usually expressed as a vector called 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 this, the order parameter S of the dye in the host liquid crystal can be obtained, and the orientation of the dye can be evaluated. (For a paper on the method for measuring the order parameters of pleochroic dyes dissolved as guests in liquid crystals, see “Absorption and
Pitch Relationships in Dichroic Guest−Host
Liquid Crystal System.”HSCole, Jr., S.
Aftergut, Journal of Chemical Physics, 1978
See Vol. 68, p. 896. ) The value of the order parameter S of the pleochroic dye dissolved in the host liquid crystal is theoretically -0.5 to 1.
It can take values between . In the case of a pleochroic dye having parallel 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. Therefore, in a display element using a pleochroic dye having parallel dichroism, the contrast of the element can be improved by applying a dye whose order parameter value is as close to 1 as possible. In general, in an electro-optical device of the type in which a liquid crystal in which a pleochroic dye is dissolved is interposed between two opposing electrode plates to perform color display based on the guest-host effect, the pleochroic dye is colored In order to obtain a large contrast between the state and the uncolored state, the order parameter S in the host liquid crystal should be large, and the extinction coefficient of the molecule should be It has high stability against light, heat, water, oxygen, etc., has high solubility in liquid crystals and can be used at any concentration within the required range, and has negative effects on the electrical properties of the device due to ionic dissociation, etc. It must have properties that satisfy conditions such as having no influence. Of these, the value of the order parameter S usually varies somewhat even for the same dye if conditions such as the type of host liquid crystal, dye concentration, temperature, etc. change. Also,
It is desirable that the solubility of the dye be 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 it is usually used in the range of about 0.5 weight percent to about 3 weight percent. Therefore, in practice, the solubility of pleochroic dyes in host liquid crystals is at least around room temperature.
Values of 0.5 weight percent or more are often required. Among the known dyes, very few have been found that satisfy all of the above conditions and can be used for guest-host type liquid crystal displays. For example, merocyanine, azo,
Dyes such as azomethine and anthraquinone are used as pleochroic dyes for guest-host liquid crystal displays.
JP-A-50-56386, JP-A-52-2885, JP-A-53-
126033, JP 54-71088, U.S. Patent 4122027, U.S. Patent 4128496, U.S. Patent 4128497, U.S. Patent
4137193, British Patent No. 1459046, etc., but it is thought that these dyes only partially satisfy the above conditions. Yellow pigments are used not only for yellow color, but also for
It is an indispensable component for blending colors such as orange, green, and black, and as a result of extensive study by the present inventors, it has been found that it is excellent in all of the above order parameters, extinction coefficient, stability, and solubility. The present invention was completed by obtaining a yellow pleochroic quinophthalone dye. The yellow pleochroic dye contained in the liquid crystal composition of the present invention has the following general formula [] (In the formula, X represents a hydrogen atom, a chlorine atom, or a bromine atom, and R ¹ and R ² are a hydrogen atom, an alkyl group,
hydroxyalkyl group, alkoxyalkyl group,
It represents a cycloalkyl group, a phenyl group, a p-alkylphenyl group, a p-hydroxyphenyl group, a p-alkoxyphenyl group, or an aralkyl group, or 〓〓〓〓〓 represents a saturated heterocyclic residue. )
It is a quinophthalone dye represented by More specifically, in the above general formula [], specific examples of the alkyl group represented by R ¹ and R ² include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, octyl group, nonyl group, Examples include alkyl groups having 1 to 18 carbon atoms such as a decyl group, a dodecyl group, a hexadecyl group, and a stearyl group. Examples of the alkoxyalkyl group include lower alkoxy lower alkyl groups such as methoxyethyl group, ethoxyethyl group, γ-methoxypropyl group, and γ-isoproboxypropyl group. As a cycloalkyl group, a cyclopentyl group,
Examples include cyclohexyl group. Examples of the p-alkylphenyl group include p-tolyl group, p-ethylphenyl group, p-propylphenyl group, p-butylphenyl group, p-pentylphenyl group, p-hexylphenyl group, p-octylphenyl group, p- Examples thereof include p-alkyl (C ₁ -C ₁₂ ) phenyl groups such as -decylphenyl group and p-dodecylphenyl group. Examples of the p-alkoxyphenyl group include p-methoxyphenyl group, p-ethoxyphenyl group, p-propoxyphenyl group, p-butoxyphenyl group,
p-alkoxy (C ₁ to C ₁₈ ) phenyl group. Examples of the aralkyl group include benzyl group and phenethyl group.

Examples of the saturated heterocyclic residue represented by the formula include piperidine residues, morpholine residues, piperazine residues, and the like. 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】

[Table] In the above table, R' represents an alkyl group or an alkoxy group, and X represents a nitro group, a cyano group, or a halogen atom. All of the liquid crystals listed in Table 1 have positive dielectric anisotropy. LCD also
By mixing it with a liquid crystal whose dielectric anisotropy is positive, the dielectric anisotropy can be made positive as a whole. Furthermore, it goes without saying that even a liquid crystal with negative dielectric anisotropy can be used as is if an appropriate element configuration and driving method are used. The host liquid crystal substance used in the present invention may be any of the liquid crystal compounds shown in Table 1 or a mixture thereof, but the following four types of liquid crystal compounds may be used. A liquid crystal material sold under the trade name ZLI-1132 by Merck & Co. has been found to be particularly useful in the present invention. As the optically active substance used in the present invention, chiral nematic compounds such as 2-methylbutyl group,
3-methylbutoxy group, 3-methylpentyl group,
There are compounds in which optically active groups such as 3-methylpentoxy, 4-methylhexyl, and 4-methylhexyl groups are introduced into nematic liquid crystal compounds.
Also, l-menthol shown in Japanese Patent Application Laid-open No. 51-45546,
Alcohol derivatives such as d-bornel, ketone derivatives such as d-citronyl and 3-methylcyclohexane, carboxylic acid derivatives such as d-citronellaic acid and l-cyclohexane, aldehyde derivatives such as d-citronellal, and alkenes such as d-linonene. Of course, optically active substances such as derivatives and other amine, amide, and nitrile derivatives can be used. As the element used in the present invention, a known liquid crystal display element can be used. That is, generally, transparent electrodes in an arbitrary pattern are provided on two glass substrates, at least one of which is transparent, and the two glass substrates are placed parallel to each other with an appropriate spacer interposed so that the electrode surfaces face each other. A configuration of elements is used. In this case, the gap of the element is determined by the spacer. The element gap is preferably 3 to 100 .mu.m, particularly 5 to 50 .mu.m from a practical standpoint. The yellow pleochroic quinophthalone dye used in the present invention can be produced, for example, by heating and condensing 2-methyl-3-hydroxyquinoline-4-carboxylic acids and trimellitic anhydride using a known method. A quinophthalone carboxylic acid represented by the following formula is obtained, which is reacted with a halogenating agent such as thionyl chloride or phosphorus oxychloride in an inert organic solvent to derive an acid halide, and then the formula [] (In the formula, R ¹ and R ² are the same as defined above.)
When introducing chlorine or bromine at the - position, it can be produced by halogenation using a conventional method. The purity of the dye thus produced can be increased using purification methods such as column chromatography, recrystallization, and sublimation. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 Table 1 shows examples of pleochroic quinophthalone dyes contained in the liquid crystal composition of the present invention, maximum absorption wavelengths, and order parameters.

【table】

【table】

【table】

【table】

[Table] The maximum absorption wavelength and order parameters of each dye listed in Table 1 were measured as follows.
That is, ZLI-1132 (nematic liquid crystal temperature range -6 to 70°C), which is a phenylcyclohexane mixed liquid crystal manufactured by Merck & Co., was added as an optically active substance.
Approximately 7% by weight of 4-(2-methylbutyl)-4'-cyanobiphenyl manufactured by BDH was added, and any of the pigments shown in Table 1 was added as a pleochroic pigment,
The dye was dissolved by repeating the process of heating to 70°C or higher, stirring well in an isotropic liquid state, and then leaving to cool. The above-mentioned liquid crystal composition prepared in this way was sealed in an element having a gap of 10 μm and consisting of two glass substrates, an upper and lower glass substrate, each having a transparent electrode and whose surfaces in contact with the liquid crystal had been coated with a polyamide resin, hardened and rubbed. When no voltage is applied within the element subjected to the alignment treatment, the liquid crystal composition assumes a cholesteric state called Grangian alignment, in which the helical axis is perpendicular to the substrate surface, and the dye molecules follow the host liquid crystal in a similar alignment. Take. As a result, the device appears strongly colored.
FIG. 3 shows a sectional view of the above element when no voltage is applied. When an AC voltage of 30 V and 50 Hz is applied to the above element, the liquid crystal composition assumes a homeotropic alignment in which the alignment direction is perpendicular to the substrate surface, and the dye molecules also follow the host liquid crystal and take a similar alignment, leaving the element in an uncolored state. exhibits. FIG. 4 shows a sectional view of the above element when this voltage is applied. Furthermore, when a copper block with a heating wire passed through it is brought into close contact with the element and heated to 70°C or higher, the liquid crystal composition assumes an isotropic liquid state, and both the liquid crystal molecules and the dye molecules become in a random state. The visible absorption spectrum of the guest-host element was measured in each of the Grangian state, homeotropic state, and isotropic liquid state, and the absorbance and maximum absorption wavelength of the dye in each of the above states were determined. In determining the absorbance of the dye, corrections were made for absorption by the host liquid crystal and reflection loss of the device. Using the absorbance values of the dye in each of the above states obtained in this way, the above-mentioned “Absorption and Pitch Relationships in
Dichroic Guest−Host Liquid Crystal System.
“HSCole, Jr., S. Aftergut, Journal of
The values of the order parameters were calculated according to the method described in Chemical Physics, 1978, Vol. 68, p. 896. The amount of dye added to the host liquid crystal when determining the order parameters shown in Table 1 varies depending on the dye, but is generally in the range of 0.3 to 3% by weight. Since the value of the order parameter is partially dependent on the type of host liquid crystal and the concentration of the pleochroic dye, it may vary somewhat when changing the type of host liquid crystal or the concentration of the dye. In addition, each dye in Table 1 was used with ZLI-1132 manufactured by Merck & Co.
The solution was sealed in a liquid crystal display device consisting of two transparent glass substrates with a thickness of 3 mm, and an accelerated deterioration test was conducted using a sunshine weather meter. As a result, after 100 hours of accelerated deterioration, the absorbance of all dyes decreased by 10% or less, indicating that the photostability of the dyes used in the present invention is extremely high. Example 2 A liquid crystal exactly the same as that used in Example 1 (added with 7% by weight of an optically active substance) was used as a pleochroic dye.
1No.17 dye A liquid crystal composition saturated with was encapsulated in a device exactly the same as in Example 1, and absorption spectra were measured with no voltage applied and with voltage applied (30 V, 50 Hz). Figure 5 shows the spectrum. The maximum absorption wavelength of the dye of this example in the liquid crystal was 449 nm, and the order parameter was 0.54. Furthermore, an accelerated deterioration test was conducted to obtain knowledge regarding the practical stability of the guest dye of this example. That is, the above-mentioned liquid crystal in which the above-mentioned dye had been dissolved was sealed in the above-mentioned device and left in a sunshine weather meter for 100 hours, and the rate of decrease in absorbance was monitored. For comparison, a typical conventional dye was similarly fabricated into a device and an accelerated deterioration test was conducted. The sunshine weather meter used in this example uses a carbon arc to continuously irradiate a sample with intense, nearly white light. In addition, water is sprayed directly onto the sample for 18 minutes in 120 minutes. The sample chamber of the weather meter is at atmospheric pressure, the temperature is 35-60℃, and the humidity is 30-60℃.
Each is retained at 70%. The results of the accelerated deterioration test using the weather meter are shown in FIG. In the graph of Figure 6, the vertical axis is the absorbance A at each time point relative to the initial absorbance Ai.
The horizontal axis shows the accelerated deterioration time. In the figure, curve 9 represents the dye of this example, and curve 10 represents the merocyanine dye (hereinafter referred to as dye A). , curve 11 is an azo dye (hereinafter referred to as dye B) , curve 12 is azomethine dye (hereinafter referred to as dye C) It shows the change in absorbance of elements containing respectively. From FIG. 6, the dyes of the present invention are dyes A, B and C.
It is clear that this dye is more stable than the conventional dye represented by. That is, the value of A/Ai of the quinophthalone dye of this example at 100 hours of accelerated deterioration was 0.93. Note that the transparent glass substrate used in this example had almost zero transmittance at wavelengths of 300 nm or less. Example 3 The same liquid crystal as that used in Example 2 (7% by weight of optically active substance added) was used as a pleochroic dye as shown in Table 1.
NO.6 dye A liquid crystal composition to which 1.0% by weight of was added was sealed in a device exactly the same as in Example 2, and the absorption spectra were measured with no voltage applied and with voltage applied (30 V, 50 Hz). Figure 7 shows the spectrum. The maximum absorption wavelength of the dye of this example in the liquid crystal was 449 nm, and the order parameter was 0.54. Further, it was found that the solubility of the dye of this example in the host liquid crystal ZLI-1132 was 2% by weight or more at room temperature. Furthermore, when a 100-hour accelerated deterioration test was conducted in the same manner as in Example 2, the rate of decrease in absorbance was
It was found to be less than 10%, indicating extremely excellent stability.

[Brief explanation of the drawing]

FIG. 1 Schematic cross-sectional view of the display element of the present invention in a state where no voltage is applied 1... Transparent glass substrate, 2... Pleochroic dye molecules, 3... Host liquid crystal molecules, 4... Transparent electrode, 5
...Incoming light, 6...Observer. FIG. 2 Schematic cross-sectional view of the voltage applied state of the display element of the present invention 1...Transparent glass substrate, 2...Pleochroic dye molecules, 3...Host liquid crystal molecules, 4...Transparent electrode, 5
...Incoming light, 6...Observer. FIG. 3 Schematic cross-sectional view of the display element of the present invention in a state where no voltage is applied 1... Transparent glass substrate, 2... Pleochroic dye molecules, 3... Host liquid crystal molecules, 4... Transparent electrode, 5
...Incoming light, 6...Observer. FIG. 4 Schematic cross-sectional view of the voltage applied state of the display element of the present invention 1...Transparent glass substrate, 2...Pleochroic dye molecules, 3...Host liquid crystal molecules, 4...Transparent electrode, 5
...Incoming light, 6...Observer. FIG. 5 Spectral characteristics of the display element of Example 2 of the present invention when no voltage is applied and when voltage is applied. The horizontal axis shows wavelength, and the vertical axis shows absorbance. 7...Spectral characteristics when no voltage is applied. 8...
Spectral characteristics when voltage is applied. FIG. 6 shows changes over time in absorbance of an element containing the quinophthalone dye of Example 2 of the present invention and an element containing a typical conventional dichroic dye. The horizontal axis shows the accelerated deterioration time measured by the sunshine weather meter, and the vertical axis shows the ratio A/Ai of the absorbance A at each time point to the initial absorbance Ai. 9... Change in absorbance over time of the quinophthalone dye of Example 2, 10... Change in absorbance over time of conventional pleochroic merocyanine dye (dye A), 11...
Time-dependent change in absorbance of a conventional pleochroic azo dye (dye B), 12... Time-dependent change in absorbance of a conventional pleochroic azomethine dye (dye C). FIG. 7 shows the spectral characteristics of the display element of Example 3 of the present invention when no voltage is applied and when a voltage is applied. The horizontal axis shows wavelength, and the vertical axis shows absorbance. 13... Spectral characteristics when no voltage is applied. 14
...Spectral characteristics when voltage is applied.

Claims (1)

[Claims] 1. General formula (In the formula, X represents a hydrogen atom, a chlorine atom, or a bromine atom, and R ¹ and R ² are a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkoxyalkyl group, a cycloalkyl group, a phenyl group, a p-alkylphenyl group) , p-hydroxyphenyl group, p-
It represents an alkoxyphenyl group or an aralkyl group, or [Formula] represents a saturated heterocyclic residue. ) A liquid crystal composition containing at least one type of quinophthalone dye.