JPH11199871A - Liquid crystal charge transfer material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject material capable of being used in a wide temperature range by including a mixture containing a smectic liquid crystal compound. SOLUTION: This liquid crystal charge transfer material comprises a mixture containing at least one smectic liquid crystal compound, preferably a compound of formula I (R1 and R2 are each a 1-22C hydrocarbon; R3 is H, cyano or the like; X1 and X2 are each O, S or the like) and preferably further a compound of formula II, and can change its employment temperature range without relating to the characteristic liquid crystallization temperature of the liquid crystal compound having a charge transfer property. The compound preferably has an electron or hall mobility of >=1×10<-5> cm<2> /vs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystalline charge transporting material comprising a mixture containing at least one kind of smectic liquid crystalline compound.

[0002]

2. Description of the Related Art Conventionally, as a charge transporting material, a material in which a charge transporting molecule serving as a site for transporting a charge is dissolved or dispersed in a matrix material such as a polycarbonate resin, or a polymer main chain such as polyvinyl carbazole is used. There is known a material in which a charge transporting molecular structure is pendant. These materials are widely used as materials for photoconductors such as copiers and printers.

[0003]

In the above-mentioned conventional charge transporting material, in the case of a dispersion type charge transporting material, the charge transporting molecule has high solubility in a polymer as a matrix to improve the charge transporting performance. However, in practice, when the concentration of the charge transport molecules in the matrix is increased, the charge transport molecules crystallize in the matrix, and the concentration of the charge transport molecules varies depending on the type. % Concentration is the limit.
As a result, 50% by weight or more of the entire matrix is occupied by the matrix having no charge transporting property, and there is a problem in that a sufficient charge transporting property and a sufficient response speed when the film is formed are limited by the matrix.

On the other hand, in the case of the pendant type charge transporting polymer, although the proportion of the pendant having the charge transporting property is high, the mechanical strength, environmental safety, durability and film forming property of the formed film are high. There are many practical problems in this respect. or,
This kind of charge transporting material is such that the locally close proximity of the charge transporting pendant becomes a stable site when the locally approaching portion hops the charge, and acts as a kind of trap. There is a problem of lowering the mobility.

[0005] In any of the above materials, the characteristic of the above-mentioned amorphous material in terms of electric characteristics is that, unlike the crystalline material, the hopping site has fluctuations not only in space but also in energy. The problem exists. Therefore, the mobility largely depends on the concentration of the charge transport site, and the mobility is generally 10 ⁻⁶ to 10 ⁻⁵ cm ² / v ·
s, which is remarkably smaller than 0.1 to ¹ cm ² / v · s of the molecular crystal. Further, there is a problem that the charge transport characteristics have strong temperature dependence and electric field intensity dependence. This point is significantly different from a crystalline charge transport material. In applications where a large-area charge-transporting layer is required, a polycrystalline charge-transporting material is expected in that a uniform charge-transporting film can be uniformly formed over a large area, A polycrystalline material is a material that is essentially non-uniform microscopically, and has problems such as the need to control defects formed at the grain interface.

The present inventors have solved the above-mentioned problems of the prior art, and have at the same time the advantage of an amorphous material having structural flexibility and uniformity over a large area, and the advantage of a crystalline material having molecular orientation. A novel charge transporting material having excellent charge transporting properties, thin film forming properties and various durability has been proposed (see Japanese Patent Application No. 9-55450). However, the liquid crystal material having the charge transporting property proposed by the present inventors has a problem that the use of a single material is limited to a liquid crystalization temperature specific to the liquid crystal compound. Accordingly, an object of the present invention is to widen the usable temperature range of the liquid crystalline charge transporting material proposed by the present inventors so that the material can be suitably used for various applications.

[0007]

The above objects are achieved by the present invention described below. That is, the present invention is a liquid crystalline charge transport material comprising a mixture containing at least one type of smectic liquid crystalline compound. Since liquid crystal molecules have self-orientation due to their molecular structure, the charge transport using this as a hopping site is different from the above-described molecular dispersion material, and the spatial and energy dispersion of the hopping site is suppressed, The band-like transport characteristics found in molecular crystals are realized. For this reason, an extremely large mobility can be realized as compared with a conventional molecular dispersion material, and furthermore, there is a characteristic that its electric field dependence is not observed. Further, in the conventional amorphous material, the mobility tends to decrease by about 2 to 4 digits depending on the concentration of the charge transporting material. However, in the liquid crystal charge transporting material, the dependency of the concentration is small, and the decrease in the mobility is reduced. There is a great feature that can be suppressed to about 1 to 2 digits. Further, by mixing at least one other compound with such a liquid crystal compound having a charge transporting property, the use temperature range is changed without being limited to the liquid crystalization temperature inherent to the liquid crystal compound having a charge transporting property. It is possible.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in more detail with reference to preferred embodiments of the invention. The liquid crystal compounds having a charge transporting property and exhibiting a smectic phase used in the present invention are listed below. Among the charge transport materials exemplified below, preferred materials are liquid crystal compounds having an electron or hole mobility of 1 × 10 ⁻⁵ cm ² / vs or more, and (6π-electron aromatic ring) _l , (10π-electron aromatic ring) _m or (14π-electron aromatic ring) _n (l + m + n = 1)
-4, l, m, and n each represent an integer of 0 to 4) in at least a part of the core, and a 6π-electron aromatic ring, a 10π-electron aromatic ring or 14
A charge transport material in which π-electron aromatic rings are connected to each other in the same or different combinations by a linking group having a carbon-carbon double bond or a carbon-carbon triple bond.
The number of aromatic rings connected is limited from the viewpoint of mobility.

The 6π-electron aromatic ring includes, for example, benzene ring, pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, tropolone ring, and the 10π-electron aromatic ring includes, for example, naphthalene ring, azulene ring, benzofuran ring, Examples of the indole ring, indazole ring, benzothiazole ring, benzoxazole ring, benzimidazole ring, quinoline ring, isoquinoline ring, quinazoline ring, quinoxaline ring, and 14π electron aromatic ring include a phenanthrene ring and an anthracene ring.

[0010]

[Table 1]

[0011]

[Table 2]

[0012]

[Table 3]

[0013]

[Table 4]

[0014]

[Table 5]

[0015]

[Table 6]

[0016]

[Table 7]

[0017]

[Table 8]

[0018]

[Table 9]

[0019]

[Table 10]

[0020]

[Table 11]

[0021]

[Table 12]

[0022]

[Table 13]

[0023]

[Table 14]

[0024]

[Table 15]

[0025]

[Table 16]

[0026]

[Table 17]

[0027]

[Table 18]

[0028]

[Table 19]

[0029]

[Table 20]

[0030]

[Table 21]

[0031]

[Table 22]

[0032]

[Table 23]

[0033]

[Table 24]

[0034]

[Table 25]

[0035]

[Table 26]

[0036]

[Table 27]

[0037]

[Table 28]

[0038]

[Table 29]

[0039]

[Table 30]

[0040]

[Table 31]

[0041]

[Table 32]

[0042]

[Table 33]

[0043]

[Table 34]

[0044]

[Table 35]

[0045]

[Table 36]

[0046]

[Table 37]

[0047]

[Table 38]

[0048]

[Table 39]

[0049]

[Table 40]

[0050]

[Table 41]

[0051]

[Table 42]

[0052]

[Table 43]

[0053]

[Table 44]

[0054]

[Table 45]

[0055]

[Table 46]

[0056]

[Table 47]

[0057]

[Table 48]

[0058]

[Table 49]

[0059]

[Table 50]

[0060]

[Table 51]

[0061]

[Table 52]

[0062]

[Table 53]

[0063]

[Table 54]

The present invention is characterized in that at least one kind of the above-described charge transporting liquid crystal compounds is mixed to change the melting point of a single charge transporting liquid crystal compound (mainly at a lower temperature). I have. When mixing two or more compounds, at least one type of liquid crystal compound has a π-electron conjugated system of a core portion composed of only carbon atoms, and
A liquid crystal compound (a) having a 0π-electron aromatic ring or a 14π-electron aromatic ring, and a compound (b) mixed therewith
Is preferably a compound having a smaller π-electron conjugate system in the core part than the compound (a), for example, a compound having a 6π-electron conjugate system.

As the compound to be mixed with the charge transporting liquid crystalline compound, any of the conventionally known compounds can be used, and one example of a preferable compound is the following compound (B). A preferred example of the charge transporting liquid crystal compound suitable for mixing with the compound (B) includes the following liquid crystal compound (A). (However, R ₁ and R ₂ in the above formula are each independently a saturated or unsaturated hydrocarbon group having a linear, branched or cyclic structure having 1 to 22 carbon atoms, and R ₁ and R ₂ are X ₁ or optionally .R ₃ be bonded directly without passing through the X ₂ is a hydrogen atom, a cyano group, a nitro group, a fluorine atom or a methyl group, X ₁
And X ₂ are each independently an oxygen atom, a sulfur atom, -CO
— Group, —OCO— group, —COO— group, —N ＝ CH— group,
-CONH- group, -NH- group, -NHCO- group or -C
An H ₂ — group. )

In mixing the liquid crystal compounds as described above, the temperature at which the mixture exhibits liquid crystallinity is, for example, about -60 to
It is preferable to mix so as to be in the range of 100 ° C.
For example, in the case of mixing the charge-transporting liquid crystal compounds, the liquid crystalization temperature of the mixture can be adjusted to the above range by mixing about 2 to 10 different liquid crystal compounds at an appropriate ratio. it can. As described above, the liquid crystalline charge transporting material of the present invention has smectic liquid crystallinity, has an electron transporting speed of 10 ⁻⁵ cm ² / v · s or more, and has a hole transporting speed of 10 ⁻⁵ cm ² / s. It is preferably at least v · s.

As the compounds to be mixed as described above, it is desirable to select compounds that do not hinder the charge transport ability of the resulting mixture as much as possible, and the selection criteria are determined by the values of the ionization potential and electron affinity of each other.
In order not to disturb the charge transport properties of both electrons and holes, it is necessary that the ionization potential of the charge transportable liquid crystalline compound is lower than that of the mixed compound, and that the electron affinity is higher than that of the mixed compound. preferable. In the case where the π-electron conjugated system of the liquid crystal compound is a charge-transporting liquid-crystalline compound composed only of carbon, if the spread of the π-electron conjugated system composed of only carbon is narrower, the values of the ionization potential and the electron affinity are reduced The above conditions can be satisfied.

The liquid crystalline charge transporting material of the present invention as described above is useful for various uses such as an optical sensor, an electroluminescence element, a photoconductor, a spatial modulation element, and a thin film transistor. Since the liquid crystal charge transporting material of the present invention suppresses the formation of high-speed mobility and structural traps,
A first application is a high-speed response optical sensor. Next, since it has excellent charge transport performance, it can be used as a charge transport layer of an electroluminescence device.If a charge transport material that does not form a new bond is included, electric field orientation and photoconductivity can be improved. Since switching can be performed at the same time, it can be used for an image display element. Similarly, the liquid crystalline charge transporting material of the present invention has liquid crystallinity, each phase exhibits different charge mobility depending on temperature, and has different photoconductivity, so that it can be simultaneously switched by temperature and light. It can be used as a member of different temperature sensors.

FIGS. 1 to 3 are diagrams for explaining application to an optical sensor as a typical example. As the configuration conditions of the optical sensor,
It comprises electrodes 13, 13 'and a film 14 made of the liquid crystalline charge transporting material of the present invention. As a property that can be used as an optical sensor, a change in current value due to light irradiation can be used.

FIG. 4 is a diagram for explaining an application to an image display device. In the image display device, a transparent substrate such as glass, a transparent electrode such as ITO (indium titanium oxide), a charge generation layer that generates carriers in response to exposure, a film made of the liquid crystalline charge transport material of the present invention, a counter electrode ( When an image is exposed (input image) from the bottom of the schematic diagram to a device in which gold electrodes and the like are sequentially laminated, the liquid crystal compound in the film is oriented according to the exposure, and carriers flow to the counter electrode (gold electrode). An input image can be reproduced by optically reading the orientation of the liquid crystal compound. If the smecticity of the liquid crystal compound is large, the orientation of the liquid crystal compound is stored for a long time, and the input information is stored for a long time.

FIG. 5 is a view for explaining an example in which a film made of the liquid crystalline charge transport material of the present invention is applied to the charge transport layer of the image recording apparatus. The method of use will be described in more detail.
As shown in (1), pattern exposure is performed from the upper part of the drawing while applying a voltage to the upper and lower electrodes 13 and 13 '. At 14 ′, carriers are generated in a pattern, and the charges transported by the charge transport layer 14 are discharged in the space 19 and reach the surface of the information recording layer 11.

FIG. 6 performs voltage application exposure similarly to the case of FIG. The generated charges (images) are accumulated on the upper surface of the dielectric layer 20, and the liquid crystal compound is aligned and accumulated in a pattern by an electric field due to the accumulated charges as in FIG. 5, so that optical reading can be performed. .

FIGS. 7 to 10 are diagrams illustrating the application of a film made of the liquid crystal charge transporting material of the present invention to an electroluminescent device as a typical example. The simplest structure of the device has a light emitting layer sandwiched between a cathode and an anode as shown in FIG. In order to obtain strong light emission, it is preferable to select a cathode material that plays a role of electron injection with a small work function, and conversely, an anode material with a work function value equal to or larger than that of the cathode.

As the anode material, generally, for example, I
TO, indium oxide, tin oxide (doped with antimony, arsenic, or fluorine), Cd ₂ SnO ₄ , zinc oxide, copper iodide,
Or sodium, potassium, magnesium, lithium, sodium-potassium alloy, magnesium-indium alloy, based on alkali metal or alkaline earth metal,
Magnesium-silver alloys, aluminum, gold, silver, gallium, indium, copper, etc., and the same materials as those used for the anode can also be used.

The material used for the light emitting layer is composed of the film made of the liquid crystalline charge transporting material of the present invention and the light emitting material. The liquid crystal compound contained in the film composed of the liquid crystal charge transport material is preferably a mixture of an electron and hole transport material or a mixture of both transport materials, or a mixture of an electron transport material and a hole transport material. When light emission at the interface is used, only one of the transporting materials may be used. When the liquid crystal compound itself has fluorescence, a light emitting material is not particularly required, but may be used in combination. Many cases where the core of the liquid crystal compound is composed of organic dyes that emit strong fluorescence in a solid state correspond to the above conditions.

As the light emitting material, a dye material having a high fluorescence quantum yield is used. For example, diphenylethylene derivative, triphenylamine derivative, diaminocarbazole derivative, bisstyryl derivative, benzothiazole derivative, benzoxazole derivative, aromatic diamine derivative,
Examples include quinacridone-based compounds, perylene-based compounds, oxadiazole derivatives, coumarin-based compounds, anthraquinone derivatives, and laser oscillation dyes such as DCM-1. These dyes are preferably used to such an extent that the liquid crystallinity of the film composed of the liquid crystalline charge transport material of the present invention is not destroyed.
It is added in an amount of about 0.01 to 30% by weight based on parts by weight.

In the case of the layer structure shown in FIGS. 9 and 10, the thickness of the light-emitting layer (light-emitting material) is set so as not to hinder the movement of electrons or holes. The thickness of the light emitting layer is preferably 0.2 to 15 μm, and the thickness can be adjusted by dispersing spacer particles in the material or by using a sealant provided around the cell.

Further, the film made of the liquid crystalline charge transporting material of the present invention can be used for a spatial light modulator as schematically shown in FIG. Further, the film made of the liquid crystalline charge transporting material of the present invention can be used as an active layer of a thin film transistor. For example, as shown in FIG. 12, a film made of the above liquid crystalline charge transport material can be used on a substrate on which source, drain, and gate electrodes are provided.

[0079]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples. Example 1 A naphthalene-based liquid crystal (2- (4'-oc) recrystallized with a degassed solvent
tylphenyl) -6-dodecyloxynaphthalene, Crystal-79 ℃ -Sm
B-101 ° C-SmA-121 ° C-Iso.) (8-PNP-O12) and biphenyl liquid crystal (4- (hexyloxy) -4'-octylbipheny, Cryst
al-30 ℃ -SmE-48 ℃ -SmB-84 ℃ -Iso.) (6O-BP-8)
Were mixed at a molar ratio of 1: 1 and sealed in a cell (interelectrode distance: 15 μm, electrode area: 0.16 cm ² ) consisting of two rubbed ITO electrodes to obtain a sample. The liquid crystal phase was homogeneously aligned in the cell, and no change in molecular orientation was observed even when an electric field was applied. The charge mobility of the liquid crystal phase was determined by the TOF method. The excitation light for the liquid crystal layer is a nitrogen laser (Laser Phtonics LN2033, λ = 33).
7 nm, pulse width = 600 ps). The obtained current signal is converted to a current amplifier (Princeton Applied Research
115) and amplify it with a digital oscilloscope (Nicolet
Pro92) and analyzed. The sample was placed on a hot stage and the temperature was controlled with an accuracy of ± 0.1 ° C.
C. to 125.degree. FIG. 13 shows a change in the charge mobility of the liquid crystal layer due to a temperature change. From FIG. 13, it was found that the charge mobility was 10 ⁻⁵ cm ² / vs or more at all temperatures.

Example 2 8-PNP-O12 and 6O-BP-8 in Example 1
The charge mobilities in the Sm1 phase and the Sm2 phase of the liquid crystal layer were measured in the same manner as in Example 1 except that the mixing ratio was changed. From the observation of the liquid crystal phase with a polarizing microscope, both were uniformly mixed at any ratio, and no phase separation was observed. The result is shown in FIG. As shown in FIG. 14, the charge mobility of the mixture decreases as the amount of the biphenyl-based liquid crystal increases, but the charge mobility of the mixture is 1.1 × 10 ⁻⁴ cm even at a mixing ratio of 5: 5. ² / vs and functions as a charge transporting material. It was found that the temperature range of the smectic phase at this time had dropped to around room temperature (about 40 ° C.).

[0081]

According to the present invention as described above, by mixing at least one of the other compounds with a liquid crystal compound having a charge transport property, the liquid crystalization temperature inherent to the liquid crystal compound having a charge transport property can be reduced. Without being limited, it is possible to change the operating temperature range.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical sensor.

FIG. 2 is a schematic diagram of an optical sensor.

FIG. 3 is a schematic diagram of an optical sensor.

FIG. 4 is a schematic diagram of an image display device.

FIG. 5 is a schematic view of an image display device.

FIG. 6 is a schematic diagram of an image display device.

FIG. 7 is a schematic diagram of an electroluminescent element.

FIG. 8 is a schematic diagram of an electroluminescence element.

FIG. 9 is a schematic diagram of an electroluminescence element.

FIG. 10 is a schematic diagram of an electroluminescent element.

FIG. 11 is a schematic view of a spatial modulation element.

FIG. 12 is a schematic view of a thin film transistor.

FIG. 13 is a diagram showing the results of Example 1.

FIG. 14 is a diagram showing the results of Example 1.

[Explanation of symbols]

 11: Information recording layer 13: Transparent electrode 13 ': Electrode (counter electrode) 14: Film made of liquid crystalline charge transport material 14': Charge generation layer 15: Transparent substrate 15 ': Substrate 19: Space 20: Dielectric layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoo Takeuchi 1-11-22-201 Higashi Tamagawa, Setagaya-ku, Tokyo (72) Kyoko Kogo 1-1-1, Ichigaya-Kaga-cho, Shinjuku-ku, Tokyo Dainippon (72) Inventor Masahiro Funahashi 1-13-6-301 Fuchinobe, Sagamihara City, Kanagawa Prefecture

Claims (14)

[Claims] 1. A liquid crystal charge transporting material comprising a mixture containing at least one kind of smectic liquid crystal compound. 2. The liquid crystal charge transport material according to claim 1, wherein at least one kind of the mixture is a liquid crystal compound having a hole and / or electron charge transport property. 3. The method according to claim 1, wherein the at least one liquid crystalline compound is (6)
π-electron aromatic ring) _l , (10π-electron aromatic ring) _m , or (14π-electron aromatic ring) _n (l + m + n = 1 to 4, l,
m and n each represent an integer of 0 to 4) in at least a part of the core.
Or the liquid crystalline charge transport material according to 2. 4. The liquid crystalline charge according to claim 1, wherein the smectic liquid crystalline compound is a compound represented by the following general formula (A), and the other compound is a compound represented by the following general formula (B). Transport materials. (However, R ₁ and R ₂ in the above formula are each independently a saturated or unsaturated hydrocarbon group having a linear, branched or cyclic structure having 1 to 22 carbon atoms, and R ₁ and R ₂ are X ₁ or optionally .R ₃ be bonded directly without passing through the X ₂ is a hydrogen atom, a cyano group, a nitro group, a fluorine atom or a methyl group, X ₁
And X ₂ are each independently an oxygen atom, a sulfur atom, -CO
— Group, —OCO— group, —COO— group, —N ＝ CH— group,
-CONH- group, -NH- group, -NHCO- group or -C
An H ₂ — group. ) 5. The composition according to claim 1, which has a smectic liquid crystal property and an electron transport speed of 10 ⁻⁵ cm ² / v · s or more.
The liquid crystal charge transport material according to any one of the above. 6. The composition according to claim 1, which has a smectic liquid crystal property and a hole transport rate of 10 ⁻⁵ cm ² / v · s or more.
The liquid crystal charge transport material according to any one of the above. 7. An optical sensor comprising at least one kind of the material according to claim 1 in a drive path. 8. A photoconductor comprising at least one kind of the material according to claim 1 in a drive path. 9. An image display device comprising at least one kind of the material according to claim 1 in a drive path. 10. An electroluminescence device comprising at least one of the materials according to claim 1 in a drive path. 11. A spatial modulation device comprising at least one of the materials according to claim 1 in a drive path. 12. A thin film transistor having at least one kind of the material according to claim 1 in a driving path. 13. A temperature sensor comprising at least one of the materials according to claim 1 in a drive path. 14. A photorefractive element comprising at least one kind of the material according to claim 1 in a drive path.