Metal coordination compound and organic luminescence device

Details Metal coordination compound and organic luminescence device Metal coordination compound and organic luminescence device

2002-06-13

2004-08-31

Yamnitzky, Marie (Department: 1774)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S917000, C313S504000, C252S301160, C257S103000, C544S225000, C546S002000, C546S004000, C548S101000, C548S108000

Reexamination Certificate

active

06783873

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a metal coordination compound having a binuclear molecular structure and an organic luminescence device using the metal coordination compound, more particularly to an organic luminescence device exhibiting a long life and a high luminescence efficiency by using the metal coordination compound as a luminescence material.
An extensive study on an organic electroluminescence (EL) device for device formation as a luminescence device of a high-speed responsiveness and a high efficiency, has been conducted.
As described in detail in, e.g., Macromol. Symp. 125, 1-48 (1997), an organic EL device generally has a structure comprising upper and lower two electrodes and a plurality of organic film layers between the electrodes formed on a transparent substrate. Basic structures thereof are shown in
FIGS. 1A-1D
.
As shown in these figures, an organic EL device generally has a structure comprising a transparent electrode
14
, a metal electrode
11
, and a plurality of organic film layers therebetween on a transparent substrate
15
.
In the device of
FIG. 1A
, the organic layers comprise a luminescence layer
12
and a hole-transporting layer
13
. For the transparent electrode
14
, ITO, etc., having a large work function are used, for providing a good hole-injection characteristic from the transparent electrode
14
to the hole-transporting layer
13
. For the metal electrode
11
, a metal, such as aluminum, magnesium or an alloy of these, having a small work function is used for providing a good electron-injection characteristic to the organic film layers. These electrodes have a thickness of 50-200 nm.
For the luminescence layer
12
, aluminum quinolynol complexes (a representative example thereof is Alq3 shown hereinafter), etc., having an electron-transporting characteristic and luminescence characteristic are used. For the hole-transporting layer
13
, biphenyldiamine derivatives (a representative example thereof is &agr;-NPD shown hereinafter), etc., having an electron-donative characteristic are used.
The above-structured device has a rectifying characteristic, and when an electric field is applied between the metal electrode
11
as a cathode and the transparent electrode
14
as an anode, electrons are injected from the metal electrode
11
into the luminescence layer
12
and holes are injected from the transparent electrode
15
. The injected holes and electrons are recombined within the luminescence layer
12
to form excitons and cause luminescence. At this time, the hole-transporting layer
13
functions as an electron-blocking layer to increase the recombination efficiency at a boundary between the luminescence layer
12
and hole-transporting layer
13
, thereby increasing the luminescence efficiency.
Further, in the structure of
FIG. 1B
, an electron-transporting layer
16
is disposed between the metal electrode
11
and the luminescence layer
12
. By separating the luminescence and the electron and hole-transportation to provide a more effective carrier blocking structure, effective luminescence can be performed. For the electron-transporting layer
16
, an electron-transporting material, such as an oxidiazole derivative, is used.
Further, in the structure of
FIG. 1D
, a luminescence layer
12
as a single organic layer is disposed between the metal electrode
12
and the transparent electrode
14
. This structure is advantageous in view of productivity of the resultant device, and applicable to production processes using vapor deposition and wet coating. The luminescence layer
12
used in this structure is required to exhibit electron and hole transfer performances in addition to a luminescence performance.
Known luminescence processes used heretofore in organic EL devices include one utilizing an excited singlet state and one utilizing an excited triplet state, and the transition from the former state to the ground state is called “fluorescence” and the transition from the latter state to the ground state is called “phosphorescence”. And the substances in these excited states are called a singlet exciton and a triplet exciton, respectively.
In most of the organic luminescence devices studied heretofore, fluorescence caused by the transition from the excited singlet state to the ground state, has been utilized. On the other hand, in recent years, devices utilizing phosphorescence via triplet excitons have been studied.
Representative published literature may include:
Article 1: Improved energy transfer in electrophosphorescent device (D. F. O'Brien, et al., Applied Physics Letters, Vol. 74, No. 3, p. 422-(1999)); and
Article 2: Very high-efficiency green organic light-emitting devices based on electrophosphorescence (M. A. Baldo, et al., Applied Physics Letters, Vol. 75, No. 1, p. 4-(1999)).
In these articles, a structure including 4 organic layers devices as shown in
FIG. 1C
has been principally used, including, from the anode side, a hole-transporting layer
13
, a luminescence layer
12
, an exciton diffusion-prevention layer
17
and an electron-transporting layer
16
. Materials used therein include carrier-transporting materials and phosphorescent materials, of which the names and structures are shown below together with their abbreviations.
Alq3: aluminum quinolinol complex
&agr;-NPD: N4,N4′-di-naphthalene-1-yl-N4,N4′-diphenyl-biphenyl-4,4′-diamine
CBP: 4,4′-N,N′-dicarbazole-biphenyl
BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline
PtOEP: platinum-octaethylporphyrin complex
Ir(ppy)
3
: iridium-phenylpyrimidine complex
Such a phosphorescent material is particularly noted at present because it is expected to provide a luminescence efficiency of 100% in principle being four times that of a fluorescent material.
However, such an organic luminescence device utilizing phosphorescence is generally required to be further improved regarding the deterioration of luminescence efficiency and device stability.
The reason of the deterioration has not been fully clarified, but the present inventors consider as follows based on the mechanism of phosphorescence.
Generally, in a phosphorescent material, a life of the triplet excitons is longer by three or more digits than the life of a-singlet exciton. More specifically, molecules are held in a high-energy excited state for a longer period to cause reaction with surrounding materials, polymer formation among the excitons, a change in fine molecular structure, and a change in structure of the surrounding materials.
For this reason, a luminescence center material for use in the phosphorescent-type luminescence device is desired to exhibit a high-efficiency luminescence and a high stability. Further, a phosphorescent material providing a high phosphorescence yield and allowing control of emission wavelength has not been proposed heretofore. Accordingly, such a phosphorescent material is desired to be provided.
SUMMARY OF THE INVENTION
In view of the above-mentioned circumstances, an object of the present invention is to provide a phosphorescent material allowing a high phosphorescence yield and control of emission wavelength.
Another object of the present invention is to provide an organic luminescence device using the phosphorescent material capable of producing high-efficiency luminescence and holding a high luminescence for a long period.
According to the present invention, there is provided a metal coordination compound represented by the following formula (1):
wherein M1 and M2 independently denotes a metal atom selected from the group consisting of Ir, Pt, Rh, Pd, Ru and Os; P is a quadridentate ligand connected to M1 and M1; Q1 is a bidentate ligand connected to M1; Q2 is a bidentate ligand connected to M2; and n is 1 or 2.
In a preferred embodiment, the bidentate ligand Q1 is represented by formula (2) shown below and the bidentate ligand Q2 is represented by formula (3) shown below:
wherein CyN1 and CyN2 are each cyclic group capable of having a substituent, including a nitrogen atom and bonded to the met

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