KR20020096025A - Light-emitting compound and display device adopting light-emitting compound as color-developing substance - Google Patents

Abstract

PURPOSE: A biphenyl derivative having aldehyde and hydroxyquinoline and an organic electroluminescence device employing the derivative as a chromophoric material are provided, which derivative is improved in the luminescence efficiency and emits the red light. CONSTITUTION: The biphenyl derivative is represented by the formula 1, wherein R1 is an aldehyde; and R2 is represented by the formula 2; and R3 is H, an alkyl group of C1-C20, an aryl group of C6-C20 containing an alkyl group of C1-C20, or an aryl group of C6-C20 containing an alkoxy group of C1-C20.

Description

Light-emitting compound and display device adopting light-emitting compound as color-developing substance

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to biphenyl derivatives having aldehydes and hydroxyquinolines of luminescent properties, and a display device employing the same as a coloring material.

An electroluminescence device (EL device) is a self-luminous display device having advantages of wide viewing angle, excellent contrast and fast response time.

EL elements are classified into inorganic EL elements and organic EL elements according to materials for forming an emitter layer. Herein, the organic EL device has an advantage of excellent luminance, driving voltage, and response speed, and multicoloring, compared to the inorganic EL device.

A typical organic EL device has a structure in which an anode is formed on a substrate, and a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are sequentially formed on the anode. Here, the hole transport layer, the light emitting layer and the electron transport layer are organic thin films made of an organic compound.

The driving principle of the organic EL element having the above structure is as follows.

When a voltage is applied between the anode and the cathode, holes injected from the anode are moved to the light emitting layer via the hole transport layer. On the other hand, electrons are injected from the cathode into the light emitting layer via the electron transport layer, and carriers recombine in the light emitting layer region to generate excitons. This exciton is changed from an excited state to a ground state, whereby an image is formed by the fluorescent molecules of the light emitting layer emitting light.

In 1987, Eastman Kodak, for the first time, developed an organic electroluminescent device using a low molecular weight aromatic diamine and an aluminum complex as a material for forming a light emitting layer (Appl. Phys. Lett. 51 , 913, 1987). On the other hand, red light emitting materials include 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM), DCJT, DCJTB and Eu (III) complexes (Chem. Lett. 1267, 1991). The compound of was developed.

In the fabrication of red light emitting devices, these compounds are used as a dopant in small amounts in host materials such as AlQ ₃ . When the concentration of the red light emitting dopant such as DCM is low, the spectrum of the orange region is obtained, and when the concentration is increased, the light is emitted in the red region, but there is a problem that the luminous efficiency is lowered by selfquenching. Therefore, in order to develop a full-color light emitting device for the practical use of the electroluminescent device, the development of a new red light emitting compound is an urgent problem.

The technical problem to be achieved by the present invention is to provide a biphenyl derivative having aldehyde and hydroxyquinoline improved luminous efficiency characteristics.

Another technical problem of the present invention is to provide a display device employing the compound having aldehyde and hydroxyquinoline as a coloring material.

1 is a cross-sectional view illustrating a structure of a general organic electroluminescent device manufactured from a substrate / anode / hole transport layer / light emitting layer / electron transport layer / cathode.

FIG. 2 is a diagram illustrating UV absorption and PL (Photoluminescence) spectra in a solution state of the electroluminescent compound represented by Chemical Formula 2 of the present invention and a PL spectrum in a film state.

* Description of the symbols for the main parts of the drawings *

11: substrate

12: anode

13: hole transport layer

14 light emitting layer

15: electron transport layer 16: cathode

In order to achieve the first technical problem, the present invention provides a biphenyl derivative having a new aldehyde and hydroxyquinoline represented by the formula (1).

R ₃ has 6 to 20 carbon atoms while having 1 to 20 carbon atoms, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and an aryl having 6 to 20 carbon atoms. It is selected from the group consisting of groups.

A second object of the present invention is achieved by a display element, wherein the light-emitting compound having benzooxazole is employed as a coloring material. As a preferable aspect of this invention, the organic electroluminescent element which employ | adopts the light emitting compound which has the said benzooxazole as a coloring material is mentioned.

That is, the second object of the present invention is also an organic electroluminescent device comprising an organic film provided between a pair of electrodes,

The organic film is made by an organic electroluminescent device characterized in that it comprises a compound of the formula (1).

R ₃ has 6 to 20 carbon atoms while having 1 to 20 carbon atoms, such as hydrogen, methyl and tertbutyl, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an alkoxy group having 1 to 20 carbon atoms. It is selected from the group consisting of an aryl group.

Preferably, R ₃ of the red light-emitting compound of Formula 1 according to the present invention is a compound of Formula 2 wherein hexyloxy.

It has a long alkoxy group hexyloxy in the 2-position of biphenyl of the formula (2) having the structure as described above. Wherein the hexyloxy group is -Prevents stacking. like this If the stacking is interrupted, the excitons will not be able to interact. As a result, the resulting luminous efficiency can be prevented.

In addition, the benzooxazole group at the terminal can improve red light emission efficiency as an electron donor material.

Hereinafter, a method of manufacturing an organic electroluminescent device according to the present invention will be described.

First, an anode electrode material is coated on the substrate. Here, a substrate used in a conventional organic EL device is used, and a glass substrate or a transparent plastic substrate excellent in transparency, surface smoothness, ease of handling, and waterproofness is preferable. In addition, transparent and conductive indium tin oxide (ITO), tin oxide (SnO ₂ ), and zinc oxide (ZnO) are used as the anode electrode material.

The hole transport layer is formed by vacuum deposition or spin coating a material for forming a hole transport layer on the anode electrode.

The hole transport layer material is not particularly limited, and N, N'-bis (3-methylphenyl) -N, N'-diphenyl- [1,1'-biphenyl] -4,4'-diamine (TPD) , N, N'-di (naphthalen-1-yl) -N, N'-diphenyl-benzidine {N, N'-di (naphthalene-1-yl) -N, N'-diphenyl-benzidine: -NPD} and the like.

Subsequently, a light emitting layer is formed by vacuum depositing a light emitting material including a light emitting compound of Formula 1 on the hole transport layer.

Thereafter, an organic EL device is completed by forming a cathode by vacuum depositing a metal for forming a cathode on the light emitting layer. The metal for forming the cathode may be lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver ( Mg-Ag) and the like.

The electron transport layer may be formed on the emission layer before forming the cathode. This electron transport layer uses a conventional material for forming an electron transport layer.

The organic electroluminescent device of the present invention can further form an intermediate layer for improving properties between two layers selected from an anode, a hole transport layer, a light emitting layer, an electron transport layer and a cathode. For example, a hole injection layer (HIL) may be further formed between the anode and the hole transport layer. If the hole injection layer is formed in this way, the hole transport layer (for example, It improves the adhesion between NPD) and the anode (ITO) and at the same time helps to inject holes from the anode into the hole transport layer.

The hole injection layer forming material is not particularly limited, but CuPc, m-MTDATA, I-TNATA, etc. of the following structural formulas are used.

The organic electroluminescent device may be manufactured in the order described above, that is, in the order of anode / hole transport layer / light emitting layer / electron transport layer / cathode, or in the reverse order, namely cathode / electron transport layer / light emitting layer / hole transport layer / anode. You may manufacture.

Hereinafter, the present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples.

Example 1

An ITO electrode was formed on the glass substrate, and then N, N'-bis (3-methylphenyl) -N, N'-diphenyl- [1,1'-biphenyl] -4,4'-diamine on top of this. (TPD) was vacuum deposited to form a hole transport layer with a thickness of 500 mm3.

Subsequently, the compound of Formula 2 was vacuum deposited on the hole transport layer to form a light emitting layer having a thickness of 280 Å.

Thereafter, the compound of Formula 3 was vacuum-deposited on the emission layer to form an electron transport layer having a thickness of 35OÅ. An organic electroluminescent device was manufactured by vacuum depositing an Al: Li alloy on the electron transport layer to form an aluminum lithium electrode having a thickness of 1500 mW.

Example 2

Characterization of Organic Electroluminescent Compounds

The light emitting diode I-V characteristics were measured by applying an electric field to the electroluminescent device manufactured as described above. When the red light emitting compound manufactured according to the example was used, the turn-on voltage was 5.5V. In addition, the efficiency was 2.5 cd / A.

The compound of formula 1 according to the present invention is biphenyl derivative having an aldehyde and hydroxyquinoline is excellent in luminous efficiency, it is useful as a coloring material of the display device.

In addition, the compound of formula 1 according to the present invention is a red light emitting material, it is useful as a coloring material of the display device. In addition, the organic electroluminescent device according to the present invention forms an organic film such as a light emitting layer using the compound of Formula 1, and emits red light.

Claims (2)

Biphenyl derivatives including aldehydes and hydroxyquinoline have the structure of Formula 1 below. R ₃ has 6 to 20 carbon atoms while having 1 to 20 carbon atoms, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, and an aryl having 6 to 20 carbon atoms. It is selected from the group consisting of groups. The organic electroluminescent device according to claim 1, wherein the light emitting compound is employed as a color generating material.