WO2003018712A1

WO2003018712A1 - Organic luminescent compound and organic light-emitting device using the same

Info

Publication number: WO2003018712A1
Application number: PCT/KR2002/001633
Authority: WO
Inventors: Jai-Han Seok
Original assignee: Neoview Co., Ltd.
Priority date: 2001-08-31
Filing date: 2002-08-30
Publication date: 2003-03-06
Also published as: KR20030018865A; KR100407250B1

Abstract

An organic luminescent compound having high heat resistance and emitting blue light of good quality, and the organic light-emitting device using the compound are disclosed. The organic light-emitting device comprises the first electrode having a high work function; the second electrode having a low work function; and at least one organic layer which includes an organic luminescent compound of the following chemical formula, and is formed between the first electrode and the second electrode. wherein, M is Li, Na or K; X is N, O or S; and R1 to R8 are independently hydrogen, or substituted or non-substituted alkyl, aryl, heteroaryl or fused ring contain from 1 to 10 carbon atoms.

Description

ORGANIC LUMINESCENT COMPOUND AND ORGANIC LIGHT-EMITTING DEVICE USING THE SAME

FIELD OF THE INVENTION The present invention relates to novel organic luminescent compounds, and more particularly, to organic luminescent compounds for forming a light- emitting layer and/or an electron transporting layer of an organic light-emitting device(OLED).

BACKGROUNDS OF THE INVENTION

The OLED is one of the representative flat-panel displays along with Liquid Crystal Display(LCD), Plasma Display Panel(PDP), and Field Emission Display(FED). The OLED has not only a fast response speed but also an excellent brightness and wide viewing angle. Also, the OLED have advantages that the OLED can be operated with a low driving voltage, full colors in a visible region can be displayed and it does not need a backlight for light-emitting due to its self-light emitting property. In addition, the OLED can be manufactured into a thin film and flexible type device and can be mass-produced by well-known film ^ fabrication techniques.

In OLED, an organic light-emitting layer is interposed between two electrodes having a high work function and a low work function, respectively. The holes and electrons generated in the electrodes are moved into the organic light- emitting layer and visible rays are radiated from the light-emitting layer through the recombination of electrons and holes.

The organic light-emitting layer can be made of conducting, nonconducting or semi-conducting small organic luminescent compounds, oligomers or polymers. Typically, conjugated organic host material or combination system of host materials and conjugated organic activating materials which have fused benzene ring are used as the organic luminescent compounds. Examples of the organic host material include naphthalene, anthracene, phenanthrene, pyrene, benzopyrene, chrisene, picene, carbazole, fluorene, biphenyl, terphenyl, qurterphenyl, triphenylene oxide, dihalobiphenyl, transstilbene, 1 ,4-diphenyl butadiene etc., and examples of the activator include anthracene, tetracene, pentacene etc. However, because of its thickness of more than 1μm, the light- emitting layer made of the conventional small organic compound have disadvantages of high resistance and high driving voltages. Thus, the OLED made of the conventional organic compound requires high driving voltage for its operation.

Therefore, various organic compounds were developed to reduce the thickness and resistance of the light-emitting layer, and thereby the driving voltage of the OLED. Representatively, aluminaquinone (aluminum-tris(8- hydroxyquinolinate); Alq3), BeBq2 (10-benzo[h]quinolinol-beryllium complex), and

Almp (tris(4-methyl-8-quinolinolate)aluminum) were developed as compounds for emitting a green light (550nm). Metal complex such as Balq (Bis(2-methyl-8- quinolinolato)(para-phenyl-phenolato)aluminum), styrylarylene derivatives such as DPVBi (1 ,4-bis(2,2'-diphenyl-vinyl)biphenyl), oxadiazole derivatives and BczVBi (4,4'-bis((2-carbazole)vinylene)biphenyl) were developed as compounds for emitting blue light (460nm). 4-dicyanomethylene-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran(DCM) was developed as a compound for emitting red light(590nm). In addition, various guest-host systems produced by doping the dopants having various colors into a host material having sufficient luminescent property were developed to enhance the luminescent efficiency and life-time of the light-emitting layer. Among the luminescent compounds, DPVBi derivative having the following chemical formula 1 is representatively used as a blue light emitting material (See U.S. Patent Nos. 5,503,910 and 5,536,949). [Chemical formula 1]

However, DPVBi derivatives are easily degraded due to its low heat resistance and which results in the decrease of the lifetime of the OLED.

Furthermore, DPVBi has a disadvantage that the blue light emitted from the compound does not have the desired quality of real blue on the chromaticity diagram.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide stable organic luminescent compounds having a high heat resistance.

It is other object of the present invention to provide the organic luminescent compounds which emit the good quality of blue light and the organic light-emitting device using the same.

It is another object of the present invention to provide the organic luminescent compounds which can be used as a host material or a blue dopant in organic light-emitting layer and also can be used to form an electron-transporting layer.

In order to achieve these objects, the present invention provides organic luminescent compounds of the following chemical formula. The present invention also provides an organic light-emitting device comprising: a first electrode having a high work function; a second electrode having a low work function; and at least one organic layer formed between the first electrode and the second electrode, and includes the organic luminescent compound of the following chemical formula,

wherein, M is Li, Na or K;

X is N, O or S; and Ri to R₈ are independently hydrogen or substituted or non- substituted alkyl, aryl, heteroaryl or fused ring contain from 1 to 10 carbon atoms. BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendant advantages thereof, can be better appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein:

Fig. 1 is a cross sectional views of the OLED according to an embodiment of the present invention; and

Fig. 2 is a cross sectional views of the OLED according to other embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The organic luminescent compound according to the present invention is a boron complex which has the following chemical formula 2: [Chemical formula 2]

wherein, M is Li, Na or K; X is N, O or S; and Ri to R₈ are independently hydrogen, or substituted or non-substituted alkyl, aryl, heteroaryl or fused ring contain from 1 to 10 carbon atoms.

Preferably, M is Li and X is O. The fused ring means a functional group produced by fusing ring compounds, and the non-limiting examples of the fused rings includes functional groups having one or more fused benzene rings, such as

wherein R' is hydrogen or alkyl group contain from 1 to 4 carbon atoms.

In addition, Ri and R₂, R₂ and R₃, R₃ and R₄, Rsand Re, Re and R , and/or R₇ and Re can be connected to form a fused ring, and the fused ring can be a hetero-ring compound.

The organic luminescent compounds according to the present invention emits blue light by absorbing the energy generated by the electron-hole recombination, and the preferable example of the organic luminescent compounds includes a compound of the following chemical formula 3. [Chemical formula 3]

The organic luminescent compounds according to the present invention can be produced by conventional methods. For example, the compound of the chemical formula 3 can be produced by a method comprising the steps of; (1) mixing excess 2-(2-hydroxyphenyl)benzoxazole with metal boron compound such as LiBH₄, NaBH₄, and KBH₄ in alcoholic solvent such as methanol, ethanol and isopropylalcohoi; (2) producing a solid product by stirring at room temperature or refluxing the reactants for 30 or 60 hours; and (3) obtaining a relatively pure boron complex by washing the solid product with alcohol and drying the same in vacuum. In addition, by further purifying the obtained boron complex using the conventional sublimation techniques under vacuum and high temperature, the remaining impurities in the boron complex can be removed, and the boron complex of high purity can be obtained.

Fig.1 is a cross sectional views of an OLED according to an embodiment of the present invention. As shown in Fig.1 , the first electrode 12 having a high work function is formed on a substrate 10 as a hole injection electrode (anode), and at least one light-emitting layer 14 including the organic luminescent compound according to the present invention is formed on the first electrode 12.

The second electrode 16 having a low work function is formed on the light-emitting layer 14 with facing the first electrode 12 as an electron injection electrode (cathode). When a voltage is applied between the first electrode 12 and the second electrode 16, the holes and the electrons produced in the two electrodes 12, 16 are injected into the light-emitting layer 14. Thereafter the injected holes and the electrons are recombined in the layer 14 and which activates the organic luminescent compound in the layer 14 to radiate light through the first electrode 12 and the transparent substrate 10. The substrate 10 is made of electrically insulating materials and if the OLED radiates light through the first electrode 12, the substrate 10 must be made of transparent material, preferably glass or transparent plastic film. The first electrode 12 works as a hole injection electrode (anode), and for example, Indium Tin Oxide (ITO), polyaniline or Ag can be used to form the first electrode 12. The second electrode 16 works as an electron injection electrode (cathode), and for example, Al, Mg, Ca or alloy of Li-Al or Mg-Ag can be used to form the second electrode 16.

Fig.2 is a cross sectional views of an OLED according to other embodiment of the present invention. The OLED in Fig.2 includes a hole injection layer 21 and a hole transporting layer 22 between the first electrode 12 and the light-emitting layer 14 to facilitate the injection and transportation of holes from the first electrode 12 into the light-emitting layer 14. The OLED further includes an electron injection layer 25 and an electron transporting layer 26 between the second electrode 16 and the light-emitting layer 14 to facilitate the injection and transportation of electrons.

As the materials for forming the hole injection layer 21 , for example, porphyrinic compound such as copper phthalocyanine (CuPc, for example, see U.S. Pat. No. 4,356,429) and MTDATA ((4,4\4^"-tris(N-3-methylphenyl-N-phenyl- amino)-triphenylamine) can be used. As the materials for forming the hole transporting layer 22, for example, tri(phenyldiamine) derivatives, styrylamine derivatives, and amine derivatives such as N,N'-bis-(1-naphthyl)-N,N'- diphenylbenzidine can be used. The non-limiting examples of the materials for forming the electron injection layer 25 and the electron transporting layer 26 include (3-(4-Biphenyl)-4-phenyl-5-tert-butylphenyl)-1 ,2,4-triazole) and quinoline derivatives such as tris(8-qunolinolate)aluminum (aluminaquinone, Alq₃). These layers improve the luminescent efficiency of the OLED by increasing the amounts of the holes and the electrons injected into the organic luminescent layer 14, by constraining the holes and the electrons in the light-emitting layer 14, and by accelerating the hole-electron recombination. The thickness of the light-emitting layer 14, the hole injection layer 21 , the hole transporting layer 22, the electron injection layer 25 and the electron transporting layer 26 can be varied according to the usage of OLED, materials for forming the layers, and manufacturing method.

The thickness is not limited but is generally 5-500 nm.

The organic layers can be formed by conventional film fabrication processes such as vacuum deposition and spin coating. The organic compound according to the present invention can be used for producing not only the OLED structures of Fig. 1 or Fig. 2 but also for producing various OLED having other structures. In addition, the organic compound according to the present invention can be included in the organic luminescent layer 14 as a blue-emitting dopant or a host material, or can be used for forming the electron transporting layer.

Hereinafter, a non-limiting example is provided for better understanding of the present invention.

[Synthetic Example 1] 30g (0.142mol) of 2-(2-Hydroxyphenyl)benzoxazole was added to 450ml of isopropylalcohoi, and 0.773g (0.0355mol) of LiBH₄ was added thereto, and then stirred for 48 hours at room temperature. By filtering the reaction products, a solid product was obtained. The solid product was added into 450ml of isopropylalcohoi, and then stirred, filtered and dried in vacuum to obtain 21.43g of relatively pure boron complex (yield 70%). 1g of the obtained boron complex was purified by conventional sublimation process to remove the remaining impurities. The sublimation was carried out under vacuum (4.2 x 10^"3 torr) while rising the temperature by 2^°C/min until 370 ^°C. The yield of the sublimation process was 0.3g (30%).

[Synthetic Example 2]

45.6g of 4-methyl salicylic acid and 36g of 2-aminophenol were added to a 1 L 2-neck flask, and 800g of polyphosphoric acid (PPA) was added thereto. The temperature of the reactants was raised to 150°C. After reacting the reactants for

14 hours at 150°C, the reaction product was poured into 2L ice water, and stirred well to obtain a solid product. After filtering the solid product, the solid product was added to 10% sodium bicarbonate solution (NaHCO₃ solution), stirred well, and extracted with chloroform solution. Then, chloroform was removed from the extracted solution with a rotary evaporator to give 35.2g of 2-(2-hydroxy-4- methylphenyl) benzoxazole (Yield: 48.2%).

In place of 2-(2-hydroxyphenly)benzoxazole of synthetic example 1 , the produced 2-(2-hydroxy-4-methylphenyl)benzoxazole was used to produce a boron complex according to the same method of synthetic example 1. The yield of the boron complex was 64%, and the yield of the boron complex after purification by sublimation was 32%.

[Synthetic Example 3] In place of 4-methyl salicylic acid of synthetic example 2, 5-methyl salicylic acid was used to produce 2-(2-hydroxy-5-methylphenyl)benzoxazole with the yield of 67% according to the same method of synthetic example 2. The produced 2- (2-hydroxy-5-methylphenyl)benzoxazole was used to produce a boron complex according to the same method of synthetic example 1. The yield of the boron complex was 58%, and the yield of the boron complex after purification by sublimation was 29%.

[Device manufacturing Example]

An Indium Tin oxide (ITO) coated glass substrate was ultrasonically washed and then washed with deionized water. The grease on the washed substrate was removed with gas phase toluene. A hole injection layer of thickness of 300 A was formed by vacuum depositing MTDATA

methylphenyl-N-phenyl-amino)-triphenylamine) on the ITO layer, and a hole transporting layer of thickness of 300A was formed by vacuum depositing N,N'- bis-(1-naphthyl)-N,N'-diphenylbenzidine on the hole injection layer.

The organic luminescent compounds of synthetic examples 1-3 were deposited to a thickness of 500 A to form organic luminescent layers on the hole transporting layer, respectively. Then, TAZ(3-(4-Biphenyl)-4-phenyl-5-tert- butylphenyl)-1 ,2,4-triazole) was vacuum deposited to a thickness of 50 A to form an electron transporting layer on the organic luminescent layer, and LiF of thickness of 20 A and Al of thickness of 2000 A were subsequently deposited on the electron transporting layer to form a cathode.

The physical properties of the produced organic light-emitting devices were measured, and shown in the following table 1.

[Table 1 : Physical properties of organic light-emitting devices]

As shown in Table 1 , the organic light-emitting devices produced with the compound of the present invention have superior brightness and luminescent efficiency, and radiates blue color of good quality.

In this disclosure, there are shown and described only the preferred examples of the invention, but, as aforementioned, it is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concepts as expressed herein.

Claims

1. An organic luminescent compound of the following chemical formula which emits light by absorbing the energy generated by electron-hole recombination:

wherein, M is Li, Na or K; X is N, O or S; and Ri to Rs are independently hydrogen, or substituted or non-substituted alkyl, aryl, heteroaryl or fused ring contain from 1 to 10 carbon atoms.

2. The organic luminescent compound according to claim 1 , wherein the organic luminescent compound is a compound of the following chemical formula.

3. The organic luminescent compound according to claim 1 , wherein M is Li;

X is O; R₃ is methyl; and Ri, R₂, R₄, R₅, Re, R₇ and Re are hydrogen.

4. An organic light-emitting device comprising: a first electrode having a high work function; a second electrode having a low work function; and at least one organic layer which includes an organic luminescent compound of the following chemical formula, and is formed between the first electrode and the second electrode,

5. The organic light-emitting device according to claim 4, wherein the organic luminescent compound forms an electron transporting layer between the second electrode and an organic luminescent layer.