JPH1187061A - Synthesizing method of charge transfer material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method synthesizing a charge transfer material able to improve the reaction rate and yield, in the case of synthesizing tetraphenyldiamine by uruman condensation reaction of diphenyl amine and allyl halide. SOLUTION: In this method, in the case that tetraphenyldiamine used as a charge transfer material formed of a charge transfer layer of EL element is synthesized in a solution containing diphenyl amine and allyl halide by Ullmann condensation using copper as a catalyst, in order to perform the uruman condensation reaction in the basic solution, KOH, NaOH or K2 CO3 and crown ether are added in the solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a charge transport material, and more particularly, to tetraphenyldiamine used as a charge transport material for forming a charge transport layer of an EL (electroluminescent) device, comprising diphenylamine and allyl halide. The present invention relates to a method for synthesizing a charge transport material synthesized by an Ullmann condensation reaction using copper as a catalyst in a solution containing

[0002]

2. Description of the Related Art As an EL element using a light emitting material which emits electroluminescence by applying a voltage, Japanese Patent Application Laid-Open No.
In JP-A-133281 and JP-A-7-133483, the EL device shown in FIG. 1 is proposed. FIG.
EL element 10 shown in FIG. 1 is formed on an ITO transparent electrode 14 (an alloy of indium and tin) formed on a transparent glass plate 12.
The charge transport layer 16, the light emitting layer 18, and the upper electrode 20 made of a metal such as aluminum are sequentially formed.
According to the EL element 10, when a direct current or a pulse current is applied from a power source using the ITO transparent electrode 14 as an anode and the upper electrode 20 as a cathode, the light emitting material of the light emitting layer 18 is excited to emit light.

As a charge transport material for forming the charge transport layer 16 used in the EL device 10, tetraphenyldiamine [N, N'-diphenyl-bis (3-methylphenyl)-(1 1,1'-biphenyl)
-4, 4'-diamine; hereinafter may be referred to as TPD].

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This TPD can be synthesized by an Ullmann condensation reaction using copper as a catalyst in a solution containing diphenylamine and allyl halide. An example of performing such a reaction using N, N′-diphenylbenzidine as diphenylamine and m-iodotoluene as allyl halide is shown in [Chemical Formula 2].

Embedded image This reaction uses copper powder [Cu (II)] as a catalyst,
In order to improve the basicity of the solution, anhydrous potassium carbonate (K
₂ CO ₃ ) was added and the reaction was carried out at a temperature of 167 ° C.

[0005]

As described above, TPD can be obtained by subjecting diphenylamine and allyl halide to an Ullmann condensation reaction. However, since the Ullmann condensation reaction shown in [Chemical Formula 2] has a low reaction rate and a low yield, the production cost of TPD is high, and the production cost of an EL device as a final product is also high. Therefore, an object of the present invention is to provide a method for synthesizing a charge transport material capable of improving the reaction rate and yield when synthesizing tetraphenyldiamine by Ullmann condensation reaction of diphenylamine and allyl halide. .

[0006]

The present inventor has solved the above-mentioned problems.
After repeated investigations to solve the problem, the basicity in the reaction system was
By making it higher than before, the Ullmann condensation reaction
It has been found that the reaction rate and yield can be improved. Furthermore, K
_TwoCO_ThreeAnd crown ether
And K_TwoCO_ThreeCompared to the case where
Knowing that the basicity in the system can be easily increased, the present invention
Reached. That is, the present invention relates to the charge transport of an EL element.
Tetraphe used as a charge transport material to form a layer
Nyldiamine, with diphenylamine and allyl halide
Condensation reaction using copper as a catalyst in a solution containing sulfur
When synthesizing by the Ullmann condensation reaction
KOH, NaOH, or K_TwoCO _Three
And crown ether are added to the solution.
A feature is a method for synthesizing a charge transport material.

In the present invention, it is preferable to use N, N'-diphenylbenzidine as diphenylamine and m-halogenated toluene as allyl halide. Also, as a crown ether,
By using 18-crown-6, the basicity in the reaction system can be easily increased.

In the present invention, the Ullmann condensation reaction can be carried out in a solution exhibiting a high basicity, and the abstraction of the hydrogen atom linked to the nitrogen atom of diphenylamine can be carried out easily. Therefore, it is presumed that the reaction rate and the yield of the Ullmann condensation reaction between diphenylamine and allyl halide can be improved.

[0009]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the Ullmann condensation reaction between diphenylamine and allyl halide is carried out by KO.
It is important to use at least one compound from the compound group consisting of H, NaOH, and K ₂ CO ₃ as a base and in the presence of a crown ether. Here, an example of an Ullmann condensation reaction using N, N′-diphenylbenzidine as diphenylamine, m-iodotoluene as allyl halide, and K ₂ CO ₃ as a base and copper powder as a catalyst is used. It is shown in [Formula 3].

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The crown ether used in this [Chemical formula 3] is a cyclic polyether, and the whole ring becomes a polydentate ligand by electron donating oxygen, and metal ions or organic cations are converted into vacancies in the ring. It has the function of taking in. In particular, an 18-membered ring containing six ether oxygens
Crown-6 can be suitably used. This 18-
Crown-6 is shown in [Formula 4].

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Incidentally, in the above [Chemical Formula 3], K ₂ CO ₃ used as a base is dissociated in two stages while maintaining an equilibrium state as shown in [Chemical Formula 5] unless a crown ether is present. .

Embedded image In this regard, when 18-crown-6 shown in [Formula 4] is added, 18-crown-6 becomes K _{2 as} shown in [Formula 6].
The K ⁺ generated in the first stage dissociation of CO ₃ is incorporated into the vacancies.

Embedded image Therefore, in the case where 18-crown-6 is present, chemical dissociation of the second stage of K ₂ CO ₃ is unlikely to occur.
The basicity can be improved as compared with the case of [Formula 5]. For this reason, the concentration of KCO ₃ ⁻ becomes higher than that in the case of [Chemical Formula 5], and hydrogen atoms connected to nitrogen atoms of diphenylamine can be easily extracted. As a result, the reaction rate of the Ullmann condensation reaction between diphenylamine and allyl halide can be improved, and the yield of TPD can be improved.

In the above-mentioned Chemical Formulas 3 to 6, K ₂ CO ₃ was used as a base.
Alternatively, NaOH can be used as the base. The detailed reason why KOH or NaOH can be used as the base in the Ullmann condensation reaction of the present invention is not clear, but is presumed as follows. That is, KOH or NaOH is completely dissociated in the presence of sufficient water to exhibit a strong base, but cannot be completely dissociated under the Ullmann condensation reaction conditions of the present invention because there is not enough water. In this regard, in the present invention, KOH or NaO
By taking K ⁺ or Na ⁺ generated by dissociation of a part of H into pores of the crown ether, the basicity can be improved and the Ullmann condensation reaction can proceed. Further, copper powder (II) was used as a catalyst, but copper (I) iodide may be used.
Although iodotoluene was used, any m-halogenated toluene shown in Chemical Formula 7 can be used.

Embedded image In the m-halogenated toluene shown in this [Formula 7],
X represents a halogen atom, and is preferably I, Br, or Cl.

Using the TPD obtained by the Ullmann condensation reaction described above, the EL device shown in FIG. 1 is manufactured. At this time, the obtained T was placed on the ITO transparent electrode 14 (an alloy of indium and tin) formed on the transparent glass plate 12.
The charge transport layer 16 is formed using PD, and the light emitting layer 18 is further formed.
And upper electrodes 20 made of a metal such as aluminum. Here, the charge transport layer 16 and the light emitting layer 1
8 and the upper electrode 20 are formed by a vacuum deposition method. In particular, the charge transport layer 16 and the light emitting layer 18
^It is formed by continuous evaporation under a high vacuum of about ^-6 Torr without breaking a vacuum state. Therefore, the surface areas of the charge transport layer 16 and the light emitting layer 18 are the same. This light emitting layer 1
As a light emitting material for forming No. 8, the following [Chem. 8] to [Chem.
0] can be used.

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Among these compounds, the compound represented by the general formula [Formula 8] is a metal complex of 2- (O-hydroxyphenyl) benzoxazole, and can form the light-emitting layer 18 that emits blue light with high luminance. M in the general formula of [Formula 8]
Represents a divalent metal, and is preferably zinc or copper. Further, the compound represented by the general formula of [Formula 9] is 10-
It is a hydroxybenzo [h] quinoline metal complex, and can form the light-emitting layer 18 that emits yellowish green to yellow at high luminance. R ₁ , R ₂ and R _{3 in} the general formula [Chemical Formula 9] represent a hydrogen atom or a lower alkyl group, and M represents a divalent metal. Among the compounds represented by the general formula of [Formula 9],
A compound in which R ₁ , R ₂ , and R ₃ are hydrogen atoms and M is zinc or copper is preferable because it can develop a high-luminance color.
The compound represented by the general formula [Chemical Formula 10] is 2- (O
-Hydroxyphenyl) benzothiazole zinc complex, and can form the light-emitting layer 18 that emits blue-green light with high luminance.
Note that an electron transport layer may be provided between the upper electrode 20 and the light emitting layer 18, and this electron transport layer may be, for example, 2- (4-biphenylyl) -5- (4-t-butylphenyl)-
An organic layer composed of 1,3,4-oxadiazole or the like can be employed.

In the EL device 10 shown in FIG. 1, the charge transport layer 16 using TPD and the light emitting layer 18 are separately formed. However, like the EL device 40 shown in FIG. The light emitting layer 30 may be formed by dispersing a material and a light emitting material in a polymer such as polymethyl methacrylate. The light emitting layer 30 is formed by dispersing a charge transporting material such as TPD and a light emitting material in a polymer such as polymethyl methacrylate, and then dissolving the solution with an organic solvent to obtain an ITO by dip coating or spin coating. It can be formed by forming a film on the transparent electrode 14. Of these, the dip coating method
The obtained solution was added to the ITO transparent electrode 1 on the transparent glass plate 12.
4 is a method of forming a thin film by dipping the surface on which the ITO transparent electrode 14 is formed on the transparent glass plate 12 which is rotating at a high speed. And forming a thin film by centrifugal force. In this method, the mixing molar ratio of the charge transporting material and the light emitting material is preferably about 4: 6, and the mixing ratio of the polymer, the charge transporting material and the light emitting material is preferably about 1: 1. Further, it is preferable to use a transparent polymer as the polymer, and it is particularly preferable to use polymethyl methacrylate having a molecular weight of about 100,000.
Further, as the light emitting material for forming the light emitting layer 30, the compounds represented by the aforementioned general formulas [Chemical Formula 8] to [Chemical Formula 10] can be used. Further, as the charge transporting material, in addition to TPD, T
Derivatives of PD, polyvinyl carbazole, or polycarbonate can be used, but TPD is most preferred. The polymer includes the above-described electron transporting material, for example, 2
-(4-Biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole may be mixed.

[0016]

The present invention will be described in more detail by way of examples. Example 1 In a 20 ml eggplant-shaped flask purged with nitrogen, N, N'-
546 mg of diphenylbenzidine (1.62 mmol
l), 5 ml of m-iodotoluene (38.94 mmol)
l), 995 mg of K ₂ CO ₃ as a base (7.20 m
mol) and 276 mg (4.34) of copper powder as a catalyst.
mmol) and add 18-crown-6 to 152 m
g (0.58 mg) was added. Then, while the reaction was carried out while stirring under a nitrogen atmosphere and maintaining the temperature at 157 to 171 ° C., the time-dependent change of the reaction was followed by thin-layer chromatography. Eight hours after the start of the reaction, the starting materials N and N '
After confirming that diphenylbenzidine had disappeared, the eggplant-shaped flask was allowed to cool. Thereafter, the liquid in the eggplant-shaped flask cooled to room temperature was added with toluene and filtered, and the obtained filtrate was concentrated to obtain a pale yellow liquid. After separating the target substance from the pale yellow liquid by column chromatography, hexane was added for crystallization, followed by filtration and drying.
After drying, 743 mg of a white powder was obtained, and the yield was 88.6%.
Met. Further, when the obtained white powder was subjected to elemental analysis, it was found to be 88.0% of C, 6.30% of H, and 5.30% of N. The theoretical element composition of TPD was 88.3% of C, 86.3% of H6.
60% and N 5.40%. For this reason, the elemental constitutions of both are very well in agreement, and the obtained white powder is TP
D was confirmed.

Example 2 and Comparative Example In a 20 ml eggplant-shaped flask purged with nitrogen, N, N'-
Diphenyl benzidine, m- iodotoluene, copper powder as K ₂ CO ₃ and a catalyst as base with added amounts shown in Table 1, the 18-crown-6 was added in an amount shown in Table 1. Next, the reaction was carried out at a temperature shown in Table 1 for 8 hours while stirring under a nitrogen atmosphere, and then the eggplant-shaped flask was allowed to cool, and TPD was isolated in the same manner as in Example 1. Table 1 also shows the yield of TPD.

[Table 1] As is apparent from Table 1, the yield of the example of the present invention was higher than that of the comparative example in which 18-crown-6 was not added.

Example 3 Synthesis of zinc 10-hydroxybenzo [h] quinoline complex In a methanol solution in which 976 mg of 10-hydroxybenzo [h] quinoline was dissolved, 565 mg of zinc acetate was slowly added at room temperature. Next, the mixture was stirred at room temperature for 2 hours and then boiled for 4 hours. After allowing to cool, the precipitate was collected by filtration. The precipitate collected by filtration was dispersed in methanol and boiled for 1 hour to remove insolubles by filtration, washed with hexane, and dried in vacuo. The yield was 260 mg. In addition, according to the measurement of the mass spectrum, a main peak was observed near a mass number of 453, which is a unique spectrum of the 10-hydroxybenzo [h] quinoline zinc complex. Manufacture of EL element On the ITO transparent electrode 14 (an alloy of indium and tin) formed on the transparent glass plate 12, the TP obtained in Example 1 was formed.
D, a light-emitting layer 18 composed of the 10-hydroxybenzo [h] quinoline zinc complex synthesized above, and an upper electrode 20 composed of a metal such as aluminum.
Were sequentially formed to form the EL device shown in FIG.
The charge transport layer 16, the light emitting layer 18, and the upper electrode 20
Were formed by vacuum evaporation. Among them, the charge transport layer 16 and the light emitting layer 18 were formed by continuous vapor deposition under a high vacuum of about 10 ^-6 Torr without breaking the vacuum state. Light Emission Test When a DC or pulse voltage of 18 V was applied from a power supply using the ITO transparent electrode 14 of the EL element 10 shown in FIG.
Yellow light having a luminance exceeding 00 cd / m ² was emitted. Further, when a continuous light emission experiment was performed, the emission of yellow light stably continued for several hundred hours or more.

Example 4 Synthesis of zinc complex of 2- (O-hydroxyphenyl) benzoxazole 2.147 g collected in a 300 ml eggplant type flask
(10.16 mmol) of 2- (O-hydroxyphenyl) benzoxazole was completely dissolved by adding 200 ml of methanol and stirring while heating to 50 ° C. 1.108 collected in a 100 ml eggplant-shaped flask was used.
g (5.05 mmol) of zinc acetate dihydrate in 50 m
One liter of methanol was added and stirred at room temperature to completely dissolve. Next, a methanol solution of zinc acetate was slowly added to a methanol solution of 2- (O-hydroxyphenyl) benzoxazole. Immediately, a white precipitate was deposited. After stirring for 3 hours while heating at 50 ° C. in a state where the white precipitate was deposited, the deposited white precipitate was filtered. The white precipitate obtained by filtration was washed with water and a saturated aqueous solution of sodium hydrogencarbonate, and then washed with warm water of 80 ° C. for 1 hour.
After stirring for an hour, the mixture was filtered. Furthermore, the resulting precipitate is
Washing was performed by changing the washing solution in the order of a saturated aqueous solution of sodium hydrogencarbonate, water, methanol and hexane, followed by drying under reduced pressure to obtain 2.152 g of a white powder. Elemental analysis of the finally obtained white powder showed C64.32%,
H was 3.21% and N was 5.43%. On the other hand, 2- (O
-Hydroxyphenyl) benzoxazole zinc complex has the following theoretical values: C 64.28%, H 3.32%, N 5.77.
%, And the two showed good agreement, so it was determined that the obtained white powder was a zinc complex of 2- (O-hydroxyphenyl) benzoxazole. Manufacture of EL element On the ITO transparent electrode 14 (an alloy of indium and tin) formed on the transparent glass plate 12, the TP obtained in Example 1 was formed.
D and 2- (O-hydroxyphenyl) obtained above
A solution obtained by adding a polymethyl methacrylate having a molecular weight of about 100,000 to a mixture obtained by mixing a benzoxazole zinc complex at a molar ratio of 4: 6, further adding dichloromethane as a solvent and dissolving the resulting mixture, is added. The light emitting layer 30 shown in FIG. 2 was formed by dip coating. This dip coating method is a method in which a thin film is formed by dipping the surface of the transparent glass plate 12 on which the ITO transparent electrode 14 is formed into the obtained solution. The amount was the same as the mixture with the (O-hydroxyphenyl) benzoxazole zinc complex. Further, the upper electrode 20 made of a metal such as aluminum was formed on the formed light emitting layer 30, and the EL element 40 shown in FIG. 2 was formed. Luminescence test The obtained ITO transparent electrode 14 of the EL element 40 shown in FIG.
Is used as an anode, and the upper electrode 20 is used as a cathode.
When a DC voltage of V was applied, blue light was emitted from the light-emitting layer 30 in a dark place with a luminance that could be confirmed with the naked eye.

Example 5 In Example 4, 2- (O-
2 in the same manner as in Example 4 except that a 2- (O-hydroxyphenyl) benzothiazole zinc complex was used instead of the (hydroxyphenyl) benzoxazole zinc complex.
Was manufactured and a light emission test was performed. As a result, the light-emitting layer 30 emitted blue-green light having a luminance that could be visually confirmed in a dark place. The 2- (O-hydroxyphenyl) benzothiazole zinc complex used in this example was synthesized by the following method. 484 mg (2.13 mmol) of 2- (O-hydroxyphenyl) benzothiazole collected in a 100 ml eggplant-shaped flask were completely dissolved by adding 40 ml of methanol and stirring while heating to 50 ° C. In addition, 2 collected in a 50 ml eggplant-shaped flask
26 mg (1.03 mmol) of zinc acetate dihydrate
20 ml of methanol was added, and the mixture was stirred and dissolved completely while heating to 50 ° C. Next, a methanol solution of zinc acetate was slowly added to a methanol solution of 2- (O-hydroxyphenyl) benzothiazole. Immediately, a yellow-green precipitate was deposited. After stirring at 50 ° C. for 1 hour and 45 minutes while the precipitate was deposited, the deposited precipitate was filtered. The precipitate obtained by filtration was washed by changing the washing solution in the order of water, a saturated aqueous solution of sodium hydrogen carbonate, water, methanol and hexane, and then dried under reduced pressure to obtain 316 mg of a yellow-green powder. Elemental analysis of the finally obtained yellow-green powder showed C59.40.
%, H 3.40%, and N 5.20%. On the other hand, 2-
The theoretical values of the (O-hydroxyphenyl) benzothiazole zinc complex are as follows: C 60.30%, H 3.11%, N 5.4
Since it was 1%, and both showed good agreement, it was determined that the obtained yellow-green powder was a 2- (O-hydroxyphenyl) benzothiazole zinc complex.

According to the present invention, the charge transporting material T
PD can be synthesized easily and with high yield, which can contribute to a reduction in the manufacturing cost and the like of the EL element.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an example of an EL device using a charge transport material manufactured according to the present invention.

FIG. 2 is an explanatory diagram for explaining another example of an EL device using a charge transporting material manufactured according to the present invention.

[Explanation of symbols]

 10, 40 EL element 12 transparent glass plate 14 ITO transparent electrode 16 charge transport layer 18, 30 light emitting layer 20 upper electrode

Claims (4)

[Claims] 1. A charge transport layer for forming a charge transport layer of an EL device.
The tetraphenyldiamine used as the feed material is
Catalyst in solution containing phenylamine and allyl halide
Synthesis by Ullmann condensation reaction using copper as
In order to carry out the Ullmann condensation reaction in a basic solution,
H, NaOH, or K _TwoCO_ThreeAnd the crown ether
Is added into the solution,
How to combine the ingredients. 2. The method according to claim 1, wherein N, N′-diphenylbenzidine is used as diphenylamine. 3. The method according to claim 1, wherein m-halogenated toluene is used as the allyl halide. 4. The method for synthesizing a charge transport material according to claim 1, wherein 18-crown-6 is used as the crown ether.