JPH11162648A - Electric charge conveying material of liquid crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge the photo-sensitive region to the long wave side and exert an excellent photo-conductiveness and electric charge conveying characteristics by including a certain amount of Fullerence C70 having a sensitivity intensifying effect in a liquid crystal compound exhibiting a smectic phase having self- orienting property, and thereby making it possible to excite visible rays. SOLUTION: A liquid crystalline electric charge conveying material contains a liquid crystal compound exhibiting smectic phase having liquid crystalline property and Fullerence C70, wherein 0.0001-5 pts.wt. Fullerence C70 is contained relative to 100 parts by wt. liquid crystal compound. The liquid crystal compound should preferably have an electron mobility of 1×10<-5> cm<2> /vs or more and a degree of hole mobility of 1×10<-5> cm<2> /vs or more. Also the liquid crystal compound should preferably have (6 πelectron type aromatic ring)l , (10 π electron type aromatic ring)m , or (14 π aromatic ring)n under the condition that l+m+n=1 thru 4, where (l), (m), (n) are each integer between 0 and 4, in at least part of the core, and further it is preferable that these aromatic rings are in C=C or C≡C coupling in the same or different combination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal charge transporting material which exhibits charge transporting properties in response to light in the visible region.

[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 transport material, in the case of a dispersion type charge transport material, the charge transport molecule has high solubility in a polymer as a matrix to improve the charge transport 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, the proportion of the pendant having the charge-transporting property is high, but the mechanical strength, environmental stability, durability and film formability of the formed film are high. There are many practical problems. In addition, since this kind of charge transporting material has a locally close arrangement of the charge transporting pendant, such a locally adjacent portion becomes a stable site when hopping charges, and acts as a kind of trap. There is a problem of lowering the mobility of charges. Further, in any of the above materials, the characteristic of the above-described amorphous material in terms of the electrical characteristics is different from the crystalline material in that the hopping site has a fluctuation not only in space but also in energy. I do. Therefore, the mobility largely depends on the concentration of the charge transport site, and the mobility is generally 1 unit.
About 0 ^-6 to 10 ^-5 cm ² / vs.
Remarkably smaller than １1 cm ² / vs. 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 charge-transporting film can be formed uniformly over a large area. The material is essentially a non-uniform material microscopically, and has problems such as a need to suppress defects formed at the particle 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 high quality charge transporting property, thin layer forming property and various durability has been proposed (see Japanese Patent Application No. 9-55450). The liquid crystal compound having the charge transporting property proposed by the present inventors generates a photocurrent by irradiating light of a specific wavelength, and the wavelength at which the photocurrent is generated is determined by the structure of the liquid crystal compound. Most of these compounds have absorption in the short wavelength region (ultraviolet region), and therefore, light sources are restricted in order to develop good photoconductivity, and it is difficult to apply them to optical sensors and the like. The problem remained. Such a problem can be considered in the related art by mixing various sensitizers in the liquid crystal for the purpose of generating a photocurrent in visible light, but when a conventionally known sensitizer is added, The affinity at the interface between the liquid crystal compound and the sensitizer is poor, and efficient transfer of generated electrons and holes cannot be obtained. Further, even if a large amount of a sensitizer is mixed in the liquid crystal compound for improving the sensitivity, another problem occurs in that the charge transporting property and the liquid crystal property are reduced. Accordingly, an object of the present invention is to provide a liquid crystal charge transport material having a photosensitive region on the longer wavelength side and exhibiting excellent photoconductivity and charge transportability.

[0005]

The above object is achieved by the present invention described below. That is, the present invention has a liquid crystal property,
Liquid crystalline compound showing smectic phase and fullerene C70
And a liquid crystalline charge transporting material.
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 liquid crystals are realized. For this reason, an extremely large mobility can be realized as compared with the conventional molecular dispersion material, and furthermore, there is a feature that its electric field dependence is not observed. Further, fullerene C7 is added to such a liquid crystalline compound.
By adding 0, the selection range of the wavelength for generating the photocurrent of the liquid crystalline compound can be greatly expanded, that is, in the ultraviolet to visible range. In particular, a photocurrent in the visible region can be generated by the sensitizing action of fullerene C70 without depending on the structure of the liquid crystalline compound. In general, visible light excitation has a greater penetration depth of light rays than ultraviolet light excitation, and thus is less susceptible to the localized level at the interface. However, in the present invention, fullerene C7
Visible light excitation of the liquid crystal compound becomes possible by adding 0, and the above advantage is obtained. Further, since fullerene C70 used as a sensitizer has high solubility (fine dispersion) in a liquid crystal compound, the absorption coefficient, carrier generation efficiency, charge transportability, and liquid crystallinity of the liquid crystal compound are not reduced. The above effect can be sufficiently obtained with the addition amount of.

[0006]

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. Fullerene C70 used in the present invention has a carbon number of 70, and is a substance in which a six-membered carbon ring and a five-membered carbon ring are bonded to form a hollow sphere (soccer ball shape). A very small amount can be separated from the soot generated at that time. The fullerene C70 has, for example, a structure schematically shown in FIG. 13, and can be obtained, for example, from Lancaster under the name of fullerene 70.

The amount of the fullerene C70 added to the liquid crystal compound is 0.1 to 100 parts by weight of the liquid crystal compound.
The effect of the present invention can be obtained in the range of 0001 to 5 parts by weight, but a more preferable addition amount is in the range of 0.01 to 1.0 part by weight based on 100 parts by weight of the liquid crystal compound. In this preferred range, trapping of electrons and holes, inhibition of liquid crystallinity, and the like are not particularly observed. When the addition amount of fullerene C70 is 0.0
If the amount is less than 001 parts by weight, the effects of the present invention cannot be obtained.
If the added amount exceeds 5% by weight, precipitation is observed, which is not preferable in terms of trapping of electrons and holes and inhibition of liquid crystallinity.

The liquid crystalline 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 a liquid crystal compound having an electron mobility of 1 × 10 ⁻⁵ cm ² / vs or more, and a hole mobility of 1 × 10 ⁻⁵ cm ^2.
/ Vs or more and (6π electron aromatic ring) _l , (10π electron aromatic ring) _m , or (14π
An electronic 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, and each of the above aromatic rings is the same or different In combination, a charge transport material linked by a linking group having a carbon-carbon double bond or a carbon-carbon triple bond may be mentioned. The number of aromatic rings connected is limited from the viewpoint of mobility. As 6π-electron aromatic rings, for example, benzene ring, pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, tropolone ring, and as 10π-electron aromatic ring, for example, naphthalene ring, azulene ring, benzofuran ring, indole ring, Indazole ring, benzothiazole ring, benzoxazole ring, benzimidazole ring, quinoline ring, isoquinoline ring, quinazoline ring, quinoxaline ring,
Examples of the 14π-electron aromatic ring include a phenanthrene ring and an anthracene ring.

When these liquid crystalline compounds are unipolar, the charge which is not transported forms a space charge, or in a fluid, the response speed is reduced due to ionic conduction. In applications such as these, compounds having ambipolar charge transport properties are preferred. As a method of blending the fullerene C70 with such a liquid crystal compound, the liquid crystal compound and the fullerene C70 are dissolved together in an organic solvent that dissolves or finely disperses the fullerene C70. Or finely dispersed, remove insolubles after mixing well, in a state in which the solvent is sufficiently removed by heating under reduced pressure and in an inert atmosphere, for example, it is preferable to encapsulate the liquid crystal cell in an argon atmosphere, By doing so, fullerene C70 can be uniformly dissolved or finely dispersed in the liquid crystal compound. Preferred solvents are benzene,
And aromatic solvents such as toluene and xylene.

[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 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 and exhibits fluorescence itself, it can be used as a charge transport layer of an electroluminescent device that can be prepared while maintaining high mobility, and has an electric field orientation property and a photoconductive property. Can be simultaneously switched, so that it can be used for an image display device.

FIG. 1 to FIG. 3 are diagrams illustrating application to an optical sensor as a representative example. As the configuration conditions of the optical sensor,
It is composed of the electrodes 13, 13 'and the liquid crystalline charge transporting material 14 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 illustrating application to an image display device as a representative example. In an 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 liquid crystal charge transport material of the present invention, a counter electrode (such as a gold electrode) ) Is sequentially image-exposed (input image) from the lower part of the schematic diagram under voltage application, carriers flow through the liquid crystal charge transporting material to the counter electrode (gold electrode) according to the exposure. By electrically reading the carrier, an input image can be reproduced by EL, electrochromy, or the like. If the smecticity of the liquid crystal is large, the orientation of the liquid crystal 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 the liquid crystal charge transport material of the present invention is applied to a charge transport layer of an image recording apparatus. As shown in FIG. 5, pattern exposure is performed from the upper part of the drawing while applying a voltage to the upper and lower electrodes 13 and 13 '. 1
At 4 ', 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. The information recording layer is, for example, a liquid crystal polymer composite layer composed of a composite of a smectic liquid crystal and a polymer, and the liquid crystal is oriented in a pattern by an electric field due to the stored electric charges, is stored, and performs optical reading. Can be. FIG. 6 performs voltage application exposure in the same manner as in FIG. The generated charge (image) is stored in the dielectric layer 20.
Accumulates on the upper surface of the device for optical reading.

FIGS. 7 to 10 are diagrams illustrating the application of the 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 and a charge transport layer sandwiched between a cathode and an anode as shown in FIG. 7, and has a charge transport property such as the liquid crystal charge transport material of the present invention. Only in the case of having both the fluorescent property and the like, it is possible to manufacture an electroluminescent element with this layer configuration. At this time, in order to obtain strong light emission, it is preferable that the cathode material that plays the role of electron injection has a small work function, and that the anode material has the same or larger work function value as 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 materials used for the light emitting layer and the charge transport layer consist of a charge transport material and a light emitting material. The charge transporting material is preferably an electron and hole transporting material or a mixture of both transporting materials, or a mixture of an electron transporting material and a hole transporting material. May be used alone. In the present invention, since the charge transport material of the present invention itself has fluorescence, a light emitting material is not particularly required, but may be used in combination. In the case of the layer configuration 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 liquid crystalline charge transporting material of the present invention is shown in FIG.
As described schematically in FIG. 1, it can be used for a spatial light modulator. Further, the liquid crystalline charge transport material of the present invention,
It can also be used as an active layer of a thin film transistor. For example, as shown in FIG.
The liquid crystal material can be used by arranging it on a substrate on which the gate electrodes are arranged.

[0072]

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 An ITO electrode (surface resistance: 100 to 200) was formed by vacuum film formation.
A glass substrate provided with Ω / □ was provided with a gap by spacer particles so that the ITO electrode was opposed to the glass substrate, and a cell was prepared. Naphthalene liquid crystal (2- (4'-octy
lphenyl) -6-dodecyloxynaphthalene, Crystal-80 ℃ -SmB-
100 ° C-SmA-121 ° C-Iso.), 0 (comparative example),
The mixture obtained by adding 0.5, 1.0, 2.0 and 6% by weight (comparative example) of fullerene C70 was homogenized and sealed in the above cell at 125 ° C.

When a time-of-flight was performed using a dye laser having a wavelength of 590 nm as a light source, clear non-dispersive waveforms were obtained for both holes and electrons, and the generation of photocurrent was confirmed. Was completed. At this time, the mobility of both holes and electrons is 1.5 × 10 ⁻³ cm ² / vs.
Met. The generation state of the photocurrent due to the addition of fullerene C70 was as follows.

Example 2 In the same cell as used in Example 1, a benzothiazole liquid crystal (2- (4'-heptyloxyphenyl) -6-dodecyl-benzothiazole,
Crystal-90 ° C.-SmA-100 ° C.-Iso.) Was added with 0.5% by weight of fullerene C70, and the mixture was homogenized and sealed in the same manner as in Example 1. When time of flight was performed using a dye laser having a wavelength of 590 nm as a light source, a waveform was obtained with holes, and generation of a photocurrent could be confirmed.
At this time, the mobility of holes was 5 × 10 ⁻³ cm ² / vs.

[0075]

According to the present invention as described above, a novel liquid crystal charge transport material having liquid crystal properties and exhibiting charge transport properties in response to light in the visible region is provided. The liquid crystalline charge transporting material is, in addition to the use as a conventional liquid crystal, an optical sensor utilizing charge transporting properties, an electroluminescent element, a photoconductor, a spatial modulation element, a thin film transistor,
It is useful as a material for photorefractive elements and other sensors. In particular, the liquid crystalline charge transporting material of the present invention has excellent sensitivity in the visible region, and thus is useful as a material for an optical sensor.

[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 diagram of an image recording apparatus.

FIG. 6 is a schematic diagram of an image recording apparatus.

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

FIG. 8 is a schematic diagram of an electroluminescent element (an example of an electrode pattern).

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 schematic view of a thin film transistor.

FIG. 14 is a schematic diagram of fullerene C70.

[Description of Signs] 11: Information recording layer 13: Transparent electrode 13 ': Electrode (counter electrode) 14: Liquid crystal charge transport material 14': Charge generation layer 15: Transparent substrate 15 ': Substrate 19: Space 20: Dielectric layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C09K 11/06 620 C09K 11/06 620 635 635 645 645 650 650 650 655 655 680 680

Claims (14)

[Claims] 1. A liquid crystal charge transport material comprising a liquid crystal compound having a liquid crystal property and exhibiting a smectic phase and fullerene C70. 2. Fullerene C70 is a liquid crystal compound 10
The liquid crystalline charge transport material according to claim 1, wherein the amount is in the range of 0.0001 to 5 parts by weight per 0 parts by weight. 3. The liquid crystal compound has an electron mobility of 1 × 10
The liquid crystalline charge transport material according to claim 1, wherein the charge transportability is ⁻⁵ cm ² / vs or more. 4. The liquid crystal compound has a hole mobility of 1 × 10
^{4. The method according to} claim 1, wherein the pressure is not less than ^-5 cm ² / vs.
Item 10. The liquid crystalline charge transport material according to item 8. 5. The liquid crystalline compound is (6π-electron aromatic ring) ₁ , (10π-electron aromatic ring) _m or (14π-electron aromatic ring) _n (1 + m + n = 1 to 4, 1, m and n are each 0)
The liquid crystalline charge transport material according to any one of claims 1 to 4, wherein the liquid crystal charge transport material has an integer of 1 to 4) at least in a part of the core. 6. A 6π-electron aromatic ring, a 10π-electron aromatic ring, and a 14π-electron aromatic ring are connected to each other in the same or different combination by a linking group having a carbon-carbon double bond or a carbon-carbon triple bond. The liquid crystal charge transport material according to claim 5, wherein 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 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.