Organic electro-luminescence device

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Reexamination Certificate

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C428S917000, C313S504000, C313S506000

Reexamination Certificate

active

06821650

ABSTRACT:

TECHNICAL FIELD
The present invention relates to organic electroluminescent devices, and more particularly, to an organic electroluminescent device capable of emitting a high-luminance, high-color purity red light.
BACKGROUND ART
Rapid changing to information oriented society needs high-definition, high-efficiency, light-weight displays for personal computers or televisions. Cathode ray tubes (CRTs), the most widely used display devices, have an advantage of high-picture quality but with drawbacks of large volume and heavy weight. Thin-film type liquid crystal displays (LCDs) have been used in notebook computers. However, these LCDs are non-self-luminous types, so they have poor luminance, narrow viewing angle and poor picture quality, compared to CRTs. LCDs also have a slow response time and cannot be applied in the manufacture of large-screen displays.
Recently, organic electroluminescent (EL) devices are receiving a lot of attention for the ability to give high picture quality and to be manufactured as a thin film like for LCDs. The organic EL device includes a thin organic layer between two electrodes as a single layer or a stack of multiple layers, wherein one of the electrodes is transparent. When a voltage is applied between the electrodes, the cathode injects electrons into the lowest unoccupied molecular orbital (LUMO) of the organic layer, while the anode injects holes into the highest occupied molecular orbital (HOMO) of the organic layer, and excitons are formed by the recombination of the electrons and holes injected into the organic layer. As these excitons lose their activity by radiation, light is emitted and propagates externally through the transparent electrode.
C. W. Tang et al. reported first in 1987 the performance of organic EL devices for practical use (Applied Physics Letters, No. 51(12), pp. 913-915). They suggested a stacked structure of organic layers including a thin film (hole transporting layer) formed of diamine derivative and a thin film (electron transporting emissive layer) formed of tri(8-quinolinolato)aluminum (hereinafter, “Alq
3
”). By employing the stack structure of organic layers, electron and hole injection barriers from electrodes to the organic layers are lowered and probability of electron-hole recombination in the organic layers is increased.
C. Adachi et al. disclosed a three-layered organic EL device including a hole transporting layer, an emissive layer and an electron transporting layer (Japanese Journal of Applied Physics, No. 27(2), pp, L269-L271, 1988) and a two-layered organic EL device including a hole transporting emissive layer and an electron transporting layer (Applied Physics Letter, No. 55(15), pp. 1489-1491, 1989). Also, it was taught that formation of a variety of appropriate multi-layer structures in the consideration of material compositions could optimize device characteristics.
C. W. Tang et al. developed a device structure having a Alq
3
electron transporting emissive layer doped with a light-emitting material such as cumalin derivatives, 4-dicyanomethylene-6-(p-dimethylaminostyryl)-2-methyl-4H-pyrane (hereinafter, “DCM”) and the like (Journal of Applied Physics, No. (65(9), pp. 3610-3616, 1989). This structure effectively increases the use of the light-emitting material that exhibits poor film formability and undergoes concentration quenching when used alone.
For a full-color display, organic EL devices of three primary colors, red, green, and blue, are required. Of these devices, the red-emitting device needs the most improvement, and its luminance and color purity are insufficient. As an example, the emission spectrum of DCM used as a red-emitting material has a peak wavelength of about 600 nm and a wide half band width of about 100 nm. Thus, red color purity in the emission is too low to achieve a full color display.
Europium, embedded into an organometallic complex as a metal core, has been identified as a high-color purity red-emitting material. However, europium-based organic EL devices have very low maximum luminance.
Japanese Patent Laid-open Publication No. hei 11-329731 discloses a high-luminance, red-emitting, organic EL device manufactured using a specific distyryl compound. However, the emission spectrum of the EL device shows a large half band width of 100 nm or greater and it is undesirable in terms of color purity.
Therefore, there is a need to implement a high-luminance, high-color purity, red-emitting organic EL device with a narrow half band width in its emission spectrum.
DISCLOSURE OF THE INVENTION
It is an objective of the present invention to provide a high-luminance, high-color purity, red-emitting, organic electroluminescent (EL) device.
In approaching to the objective of the present invention, the present inventors have found that light-emitting materials having formula (1) and (2) below is have narrow half band widths in their emission spectra:
where A
1
is a functional group having electron acceptor activity, D
1
and D
2
are the same or different functional groups having electron donor activity, D
3
is a functional group having electron acceptor activity, A
2
and A
3
are the same or different functional groups having electron donor activity.
The present inventors have also found that a high-luminance, high-color purity red-emitting organic EL device according to the present invention can be implemented with a particular one of formula (1) above.
The present invention provides an organic EL device with an organic layer including an emissive layer between an anode and a cathode, the organic layer comprising at least one compound having formula (3) below as a light-emitting material that is responsive to current injection:
where the substituent groups of ethylene groups are in a cis or trans form; R
1
and R
2
are the same or different groups and are benzo 5-membered heterocyclic groups having 0 to 4 methyl groups, benzo 6-membered heterocyclic groups having 0 to 4 methyl groups, phenyl groups having 0 to 3 substituent groups selected from Table 1 below, naphthyl groups having 0 to 3 substituent groups selected from Table 1 below, 5-membered heterocyclic groups having 0 to 3 substituent groups selected from Table 1 below, or 6-membered heterocyclic groups having 0 to 3 substituent groups selected from Table 1 below:
TABLE 1
—NO
2

—R
3

—CN —R
4
—O—R
4



—CF
3
—R
4
—R
10
—OH

—S—R
11

—R
6
—CH
3
where R
3
is a halogen atom, R
4
is an alkyl group having 1 to 4 carbon atoms; R
5
is an alkylene group having 1 to 4 carbon atoms; R
6
is an alkylene group having 2 to 4 carbon atoms; R
7
is a substituent selected from Table 2 below, a phenyl group having 0 to 2 substituent groups selected from Table 4 below, or a naphthyl group having 0 to 4 substituent groups selected from Table 4 below; R
8
is a substituent group selected from Table 3 below, a phenyl group having 0 to 2 substituent groups selected from Table 4 below, or a naphthyl group having 0 to 4 substituent groups selected from Table 4 below; R
9
is an alkyl group having 1 to 4 carbon atoms or a phenyl group having 0 to 2 substituent groups selected from Table 4 below; R
10
is an halogen atom, an alkoxy group having 1 to 4 carbon atoms, or a phenyl group having 0 to 2 substituent groups selected from Table 4 below; R
11
is a cycloalkyl group having 5 to 6 carbon atoms, an alkyl group having 1 to 4 carbon atoms, 2-hydroxyethyl group, or a phenyl group having 0 to 2 substituent groups selected from Table 4:
TABLE 2
—R
12
—R
13
—CN
—R
13
—R
14
—R
13
—OH


—R
13
—O—R
12





TABLE 3
—R
12
—R
13
—CN —R
13
—R
14
—R
13
—OH





TABLE 4
—O—R
12
—R
14
—NO
2
—CN —R
12
where R
12
is an alkyl group having 1 to 4 carbon atoms; R
13
is an alkylene group having 2 to 4 carbon atoms; R
14
is an halogen atom; R
15
is an alkylene group having 1 to 4 carbon atoms; R
16
is an alkyl group having 1 to 4 carbon atoms or a phenyl group having 0 to 2 substituent groups selected from Table 4 below; and R
17
and R
18
are the same or different and are alkyl groups having 1 to 4 carbon atoms or hydrogen atom.
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