JPH093342A - Pyrazinoquinoxaline derivative, its production, and organic electroluminescent element - Google Patents

Abstract

PURPOSE: To obtain a pyrazinoquinoxaline deriv. having high m.p. and glass transition point and improved in stability, thermal stability, durability, and luminescent efficiency in a thin-film state by reacting 1,2,4,5-tetraaminobenzene with a specific diketone. CONSTITUTION: 1,2,4,5-Tetraaminobenzene is reacted with a diketone of the formula I [R1 and R2 are each H, a halogen, a 1-6C alkyl, a perfluoroalkyl, or an optionally substd. aryl provided they may combine with each other to form condensed arom. rings] in an inert solvent at room temp. or higher, if necessary in the presence of an org. acid (e.g. p-toluenesulfonic or camphorsulfonic acid) or a dehydrating agent (e.g. thionyl chloride) as the catalyst, to give a pyrazinoquinoxaline deriv. represented by the formula II [R1 to R4 are each H, a halogen, a 1-6C alkyl, a perfluorolalkyl, or an optionally substd. aryl provided they may combine with each other to form condensed arom. rings].

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pyrazinoquinoxaline derivative and an electroluminescence (EL) device using the same.

[0002]

2. Description of the Related Art In recent years, an organic EL element has attracted attention as a candidate for an unprecedented high-intensity flat display, and research and development thereof have been activated. The organic EL element has a structure in which an organic light emitting layer is sandwiched between two electrodes, and holes injected from the anode and electrons injected from the cathode are recombined in the light emitting layer to emit light. There are low molecular weight materials and high molecular weight materials as the organic materials used, and it has been shown that EL elements with high brightness can be formed. There are two types of such organic EL devices. One is the addition of a fluorescent dye, which was published by CWTang et al., To the charge transport layer (Journal of the Applied Physics (J. Appl. Ph.
ys.), 65, 3610 (1989)), and the other one using a fluorescent dye alone (for example, Japanese Journal of the Applied Physics (Jpn.J.Appl.Phys.), 27, L2).
69 (1988)). In the latter device, the luminous efficiency is improved when the fluorescent dye is laminated with a hole transport layer that transports only holes, which is one of the charges, and / or an electron transport layer that transports only electrons. It is shown.

However, none of them has sufficient conditions for practical use. For example, in the former case, the hole transport material has poor physical durability in a thin film state, and the electron transporting host material itself used for adding the fluorescent dye emits green light, so that it emits blue light. It is difficult to obtain the latter, and in the latter case, the electron transport material used has low durability and low charge transport ability, and there is a problem that sufficient performance cannot be obtained in practical use. 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4 as one of electron transport materials
-Oxadiazole (PBD) is known. This P
As an example of using BD as an electron transport layer, the above-mentioned organic EL
There is a device (Jpn.J.Appl.Phys., 27, L269 (1988)). However, it was pointed out that the stability of the thin film was poor, such as crystallization was likely to occur, and a compound having a plurality of oxadiazole rings was developed (Journal of the Chemical Society of Japan, 11, 1540 (1991), JP-A-6).
-14658, JP-A-6-92947, 5-1
52072, JP-A-5-2011, JP-A-6-13
6359 etc.). However, these also did not have sufficient properties for practical use. As another compound system, a quinoxaline derivative has been reported (JP-A-6-207169). The dimerization increased the molecular weight and improved the stability of the thin film, but it was not sufficient for practical use. It is considered that this is because the bond connecting the two quinoxaline rings was rotated, so that the interaction between the molecules was weakened, and as a result, the stability in the thin film state was not sufficiently improved.

On the other hand, an element using a polymer medium such as a hole transporting polymer has been reported as an element having improved thin film stability (Japanese Patent Laid-Open No. 4-212286). However, although the driving voltage was high and the stability of the thin film was improved, the durability of the device was not improved. An EL device using a quinoxaline-based polymer has also been reported, but the brightness is very low and not practical (Jpn.J.
Appl. Phys., 33 (2B), L250, 1994). The characteristics of the electron transport material used for the organic EL device are that it is required to have excellent electron transport ability and high physical and chemical stability in a thin film state. Many of the thin films used for the charge transport layer or the light emitting layer of the organic EL element are in an amorphous state, and when the Tg of this thin film is low, crystallization gradually progresses from the amorphous state and it becomes impossible to maintain a uniform state. As a result, it becomes difficult for current to flow, and eventually dielectric breakdown occurs, causing the device to collapse. On the other hand, an element using a phenazine derivative as a light emitting material has been reported, but it is difficult to form a thin film having a small molecular weight and having sufficient stability by itself (JP-A-7-102250). Therefore, as a result of intensive studies to solve these problems and to find an organic EL element having high durability and high light emission efficiency, it was found that an organic EL element using a quinoxaline derivative solves the above problems, and the present invention Was completed.

[0005]

The present invention provides the following (1):
Each of the configurations (2), (3), (4) to (5) is provided. (1) A pyrazinoquinoxaline derivative represented by the general formula (1).

Embedded image [In the general formula (1), R _{1 to} R ₄ each independently represent hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group, a substituted or unsubstituted aryl group, or an adjacent group. In this case, the aromatic ring may be condensed. ] (2) 1,2,4,5-Tetraaminobenzene and the general formula (2)

Embedded image A method for producing a pyrazinoquinoxaline derivative represented by the general formula (1), which comprises reacting a diketone represented by: [In the general formula (2), R ₁ and R ₂ each independently represent hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group, a substituted or unsubstituted aryl group, or In this case, the aromatic ring may be condensed. (3) An electroluminescent device using a pyrazinoquinoxaline derivative represented by the general formula (1). (4) An electroluminescent device using a pyrazinoquinoxaline derivative represented by the general formula (1) as a charge transport material. (5) The structure of the electroluminescent element is anode / pyrazinoquinoxaline derivative layer / cathode, anode / hole transport layer / pyrazinoquinoxaline derivative layer / cathode, anode / hole transport layer / light emitting layer / pyrazinoquinoxaline derivative layer / The electroluminescent element, which is any one of a cathode, an anode / a hole transporting material + a light emitting material + a pyrazinoquinoxaline derivative layer / a cathode.

The structure and effects of the present invention will be described in detail below. The pyrazinoquinoxaline derivative used in the present invention described above can be produced, for example, as follows. First, it is obtained by reacting 1,2,4,5-tetraaminobenzene with a diketone represented by the general formula (2). The solvent at this time is not particularly limited as long as it is an inert solvent. Preferred are toluene,
Examples include aromatics such as xylene. The reaction temperature is preferably room temperature or higher, and particularly preferably 80 ° C. or higher. Further, when an organic acid such as paratoluene sulfonic acid or camphor sulfonic acid or a dehydrating agent such as thionyl chloride is used as a catalyst, the reaction rate is increased.

Specific examples of the pyrazinoquinoxaline derivative of the present invention include compounds represented by the formulas (3), (4) and (5).

Embedded image

[Chemical 6]

[Chemical 7] Or expression

Embedded image

Embedded image

Embedded image The compound shown by these can be mentioned.

These pyrazinoquinoxaline derivatives are
It was found to be useful as an electron transport material for EL devices. In particular, it was found that the stability in the thin film state is higher than that of the existing electron transport material, and that a stable electron transport layer can be formed by itself. This is because the glass transition point (Tg) increased due to the influence of the pyrazinoquinoxaline ring. Further, since it has two pyrazine rings in the molecule, it has an excellent electron-transporting ability as compared with a quinoxaline derivative having only one pyrazine ring.

The EL element of the present invention may have various configurations, but basically, the pyrazinoquinoxaline derivative is sandwiched between a pair of electrodes (anode and cathode), and if necessary, Then, a hole-transporting material, a light-emitting material, and an electron-transporting material may be added or they may be stacked as separate layers. As a specific example, an anode / pyrazinoquinoxaline derivative layer /
Cathode, anode / hole transport layer / pyrazinoquinoxaline derivative layer / cathode, anode / hole transport layer / light emitting layer / pyrazinoquinoxaline derivative layer / cathode, anode / hole transport material + light emitting material + pyrazinoquinoxaline derivative layer / A cathode etc. are mentioned. Further, it is preferable that all of the elements of the present invention are supported by a substrate, and there is no particular limitation on the substrate, and those conventionally used for EL elements such as glass, transparent plastic, and highly conductive material are conventionally used. Those made of molecules or quartz can be used.

Each layer used in the present invention can be formed into a thin film by a known method such as a vapor deposition method or a coating method. The layer using the pyrazinoquinoxaline derivative does not require a binder such as a resin because it has a high stability in a thin film state, and can be formed into a thin film by a vapor deposition method or the like, which is industrially advantageous. . The thickness of the thin film of each layer thus formed is not particularly limited and can be appropriately selected depending on the situation, but is usually selected in the range of 2 nm to 5000 nm. As the anode in the EL device of the present invention, those having an electrode substance of a metal, an alloy, an electrically conductive compound having a large work function (4 eV or more) and a mixture thereof are preferably used. Specific examples of such an electrode material include a metal such as Au and a dielectric transparent material such as CuI, ITO, SnO ₂ and ZnO. The anode can be prepared by forming a thin film of these electrode substances by a method such as vapor deposition or sputtering. When light is extracted from this electrode, the transmittance is desirably greater than 10%, and the sheet resistance of the electrode is several hundred Ω.
/ Square or less is preferable. Further, the film thickness depends on the material, but is usually 10 nm to 1 μm, preferably 10 to 20.
It is selected in the range of 0 nm.

On the other hand, as the cathode, a material having a low work function (4.3 eV or less), an alloy, an electrically conductive compound and a mixture thereof as an electrode material is used. Specific examples of such electrode materials include calcium, magnesium, lithium, aluminum, magnesium alloys, lithium alloys, aluminum alloys, and aluminum /
Examples include lithium mixtures, magnesium / silver mixtures, indium and the like. The cathode can be produced by forming a thin film of these electrode substances by a method such as vapor deposition or sputtering. The sheet resistance as an electrode is preferably several hundreds Ω / square or less, and the film thickness is usually 10 nm to 1 μm, preferably 50 to 200 n.
m.

The EL device of the present invention has various configurations as described above, but the provision of the hole transport layer improves the luminous efficiency. The hole transport material used for the hole transport layer is arranged between two electrodes to which an electric field is applied, and when holes are injected from the anode, the holes can be appropriately transferred to the light emitting layer. A compound, for example, 10 ⁴ to 10 ⁶ V / c
Those having a hole mobility of at least 10 ⁻⁶ cm ² / V · sec or more when an electric field of m is applied are preferable. Such hole transport material is not particularly limited as long as it has the above-mentioned preferable properties, and conventionally, in the photoconductive material,
Any material can be selected and used from the materials commonly used as the hole charge transport material and the known materials used for the hole transport layer of EL elements.

Examples of the hole transport material include carbazole derivatives (N-phenylcarbazole, polyvinylcarbazole, etc.), triarylamine derivatives (N,
N'-diphenyl-N, N'-di (3-methylphenyl) -4,4'-diaminobiphenyl (TPD), a polymer having an aromatic tertiary amine in its main chain or side chain,
1,1-bis (4-di-p-tolylaminophenyl) cyclohexane, N, N'-diphenyl-N, N'-dinaphthyl-4,4'-diaminobiphenyl, etc., phthalocyanine derivative (metal-free, copper phthalocyanine) Etc.) and polysilane.

When a plurality of electron-transporting materials are used in the electron-transporting layer in the EL device of the present invention, not only the pyrazinoquinoxaline derivative but also other electron-transporting materials may be used. There is no particular limitation on such an electron transporting material, and any one of conventionally known compounds can be selected and used. Preferred examples of the electron transport material include:

Embedded image Derivatives of diphenylquinone (Journal of the Electrophotographic Society, 30, 3
(1991, etc.), or

[Chemical 12]

Embedded image

Compounds such as (J. Apply. Phys., 27, 269 (198
8) and the like, and oxadiazole derivatives (the above-mentioned document, Jpn.J.Appl.Phys., 27, L713 (1988), Applied Physics Letter (Appl.Phys.Lett.), 55,1489 ( (1989)
Etc.) and thiophene derivatives (JP-A 4-2)
12286, etc.), triazole derivatives (described in Jpn.J.Appl.Phys., 32, L917 (1993), etc.), thiadiazole derivatives (43rd Annual Meeting of the Polymer Society of Japan, 〓P1a007 etc. ), Metal complexes of oxine derivatives (Technical Report of IEICE, 92 (31)
1), 43 (1992), etc.), quinoxaline derivative polymers (described in Jpn. J. Appl. Phys., 33, L250 (1994) etc.), phenanthroline derivatives (43rd Polymer Discussion) Meeting proceedings, those described in 14J07, etc.) and the like.

The light-emitting material used in the present invention is a polymer functional material series "Optical functional material" edited by The Society of Polymer Science, Kyoritsu Shuppan
(1991), known light-emitting materials such as daylight fluorescent materials, fluorescent brighteners, laser dyes, organic scintillators, and various fluorescent analysis reagents as described in P236 can be used. Polycyclic condensed compounds such as anthracene, anthracene, phenanthrene, pyrene, chrysene, perylene, coronene, rubrene, and quinacridone; oligophenylene-based compounds such as quarterphenyl; 1,4-bis (2-methylstyryl) benzene; 1,4-bis (4-methylstyryl) benzene, 1,4-bis (4-methyl-5-phenyl-2-oxazolyl) benzene, 1,4-bis (5
-Phenyl-2-oxazolyl) benzene, 2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene, 1,4-diphenyl-1,3-butadiene, 1,6-diphenyl-1, Liquid scintillators such as 3,5-hexatriene and 1,1,4,4-tetraphenyl-1,3, -butadiene; metal complexes of oxine derivatives described in JP-A-63-264692; coumarin dyes; Dicyanomethylenepyran dye, dicyanomethylenethiopyran dye, polymethine dye, oxobenzanthracene dye, xanthene dye, carbostyril dye and perylene dye, oxazine compounds described in German Patent 2534713, the 40th Joint Lecture on Applied Physics Stilbene derivatives described in Proceedings of the Conference, 1146 (1993) and JP-A-4-363891 Preferably the oxadiazole compound.

An example of a suitable method for producing the EL device of the present invention will be described for the device having the following constitution. A method of manufacturing an EL element composed of an anode / the pyrazinoquinoxaline derivative layer / cathode will be described. First, a thin film made of a desired electrode material, for example, a material for an anode, is formed on a suitable substrate at 1 μm or less, preferably 10 to 200 nm. After forming the anode by a method such as vapor deposition or sputtering so as to have a film thickness in the range, a pyrazinoquinoxaline derivative thin film is formed thereon. As a thinning method,
For example, dip coating method, spin coating method, casting method,
Although there are vapor deposition methods and the like, the vapor deposition method is preferred because a uniform film is easily obtained, impurities are not easily mixed, and pinholes are not easily generated.

Next, after the formation of this pyrazinoquinoxaline derivative layer, a thin film of a cathode material is formed thereon to a thickness of 1 μm.
Hereinafter, a desired EL element can be obtained by forming it by a method such as vapor deposition or sputtering and providing a cathode. In the production of this EL device, the production order was reversed and the cathode, the pyrazinoquinoxaline derivative layer,
It is also possible to fabricate in the order of the anode. When a DC voltage is applied to the EL device thus obtained, a voltage of about 3 to 40 V is applied, and light emission can be observed from the transparent or semitransparent electrode side. Furthermore, light is emitted by applying an AC voltage. The waveform of the applied alternating current may be arbitrary.

EXAMPLES Next, the present invention will be described in more detail based on examples. Example 1 Compound represented by Formula (3) (TPPQ)
Synthesis of 1,2,4,5-tetraaminobenzene hydrochloride 400m
g, benzyl 592 mg, tetramethylethylenediamine 320 mg and ethanol 50 ml are mixed, and 30
Reflux for hours. After cooling, the precipitated solid was collected by filtration, washed with water and methanol, and dried. The yield was 290 mg. This was purified by sublimation to obtain the target compound. It was solid and emitted yellow-green fluorescence. ¹ H-NMR δ
7.40 (m, 12H), 7.62 (m, 8H), 9.03 (s, 2H).

Example 2 Synthesis of Compound (TBQP) Represented by Formula (5) 1,2,4,5-Tetraaminobenzene Hydrochloride 500 m
g, 9,10-phenanthrenequinone 733 mg, tetramethylethylenediamine 400 mg and ethanol 50 ml were mixed and refluxed for 30 hours. After cooling, the precipitated solid was collected by filtration, washed with water and methanol, and dried.
The yield was 680 mg. This was purified by sublimation to obtain the target compound.

Example 3 Synthesis of Compound (TTPQ) Represented by Formula (4) The procedure was performed except that 9,10-phenanthrenequinone used in Example 2 was replaced with 4,4′-dimethylbenzyl. It was synthesized by the method according to Example 2.

(Embodiment 4) 25 mm × 75 mm × 1.1
A transparent support substrate was prepared by depositing ITO with a thickness of 50 nm on a glass substrate having a thickness of 50 mm (manufactured by Tokyo Sanyo Vacuum Co., Ltd.). This transparent support substrate was fixed to a substrate holder of a commercially available vapor deposition apparatus (manufactured by Vacuum Kiko Co., Ltd.), a TPD was placed in a quartz crucible, and 1,3-di (9-anthryl) -2- was placed in another crucible. (9-Carbazolylmethyl) -propane (AnCz) was added, TPPQ was placed in the other crucible, and the pressure in the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa. The crucible containing TPD was heated and vapor-deposited so as to have a film thickness of 50 nm. Next, heat the crucible containing AnCz on this,
It was vapor-deposited so as to have a film thickness of 50 nm. Finally, TPPQ
The crucible containing was heated to vapor-deposit it to a film thickness of 50 nm. The deposition rate was 0.1-0.2 nm / sec.
After that, the pressure in the vacuum chamber was reduced to 2 × 10 ⁻⁴ Pa, and then 1.2 to 2. Magnesium was added from the graphite crucible.
Silver was evaporated from the other crucible at a deposition rate of 4 nm / sec and simultaneously from the other crucible at a deposition rate of 0.1 to 0.2 nm / sec. Under the above conditions, a mixed metal electrode of magnesium and silver was laminated and vapor-deposited to a thickness of 200 nm on the light emitting layer to form a counter electrode, thereby forming an element. When an ITO electrode was used as an anode and a mixed electrode of magnesium and silver was used as a cathode, a DC voltage of 8 V was applied to the device thus obtained, and a current of 60 mA / cm ² flowed to obtain green light emission of 1900 cd / m ² . This device stably emitted light even after being driven for 5 hours.

Comparative Example 1 A device was prepared in the same manner except that the quinoxaline derivative used in Example 4 was replaced with PBD. When a DC voltage of 13 V was applied to the obtained device, a current of 70 mA / cm ² flowed and a green light emission of 1300 cd / m ² was obtained. In this device, a non-light emitting portion was generated after driving for 5 minutes, and the light emission luminance was reduced to about 1/3.

(Example 5) A device was prepared in the same manner as in Example 4, except that the AnCz used in Example 4 was replaced with 4,4'-bis (2,2-diphenylvinyl) biphenyl. When a DC voltage of 9 V is applied to the obtained device, 50 mA / cm ²
Current flowed and blue emission of 1500 cd / m ² was obtained. This device stably emitted light even after being driven for 5 hours.

(Example 6) An element was prepared in the same manner except that TBQP was used instead of TPPQ used in Example 4.
Approximately 60 m when a DC voltage of 11 V is applied to the obtained device
A current of A / cm ² flowed and green light emission of 1800 cd / m ² was obtained. This device stably emitted light even after being driven for 5 hours.

(Example 7) An element was prepared in the same manner except that the TPPQ used in Example 4 was replaced with TTPQ.
Approximately 70 m when a DC voltage of 11 V is applied to the obtained device
A current of A / cm ² flowed, and green light emission of 1900 cd / m ² was obtained. This device stably emitted light even after being driven for 5 hours.

[0027]

The pyrazinoquinoxaline derivative of the present invention has a high melting point and glass transition point due to its polycyclic structure, is excellent in thermal stability, and is excellent in stability in a thin film state. The EL element has a long life and high practical value. By using these, a highly efficient light emitting device such as a full color display can be produced.

Claims (5)

[Claims] 1. A compound represented by the general formula (1): A pyrazinoquinoxaline derivative represented by. [In the general formula (1), R _{1 to} R ₄ each independently represent hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group, a substituted or unsubstituted aryl group, or an adjacent group. In this case, the aromatic ring may be condensed. ] 2. 1,2,4,5-Tetraaminobenzene and the general formula (2): A method for producing a pyrazinoquinoxaline derivative represented by the general formula (1), which comprises reacting a diketone represented by: [In the general formula (2), R ₁ and R ₂ each independently represent hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group, a substituted or unsubstituted aryl group, or In this case, the aromatic ring may be condensed. ] 3. An electroluminescent device using a pyrazinoquinoxaline derivative represented by the general formula (1). 4. An electroluminescent device comprising a pyrazinoquinoxaline derivative represented by the general formula (1) as a charge transport material. 5. The electroluminescent device has a structure of anode / pyrazinoquinoxaline derivative layer / cathode, anode / hole transport layer / pyrazinoquinoxaline derivative layer / cathode, anode / hole transport layer / light emitting layer / pyrazinoquinoxaline derivative. The electroluminescent device according to any one of layer / cathode, anode / hole transport material + light emitting material + pyrazinoquinoxaline derivative layer / cathode.