Metal coordination compound and electroluminescence device

Details Metal coordination compound and electroluminescence device Metal coordination compound and electroluminescence device

2002-07-17

2004-11-30

Yamnitzky, Marie (Department: 1774)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S917000, C313S504000, C257S102000, C257S103000, C544S225000, C546S004000, C546S010000

Reexamination Certificate

active

06824894

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an electroluminescence device using an organic compound, more particularly to an organic electroluminescence device (hereinafter, referred to as an “organic EL device”) using a metal coordination compound as a luminescent material.
BACKGROUND ART
An applied study on an organic EL device as a luminescence device of a high-speed responsiveness and a high efficiency has been energetically conducted. Basic structures thereof are shown in FIGS.
1
(
a
) and (
b
) (e.g., Macromol. Symp. 125, 1-48 (1997)).
As shown in
FIG. 1
, 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.
1
(
a
), 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 layers. These electrodes have a thickness of 50-200 nm.
For the luminescence layer
12
, aluminum quinolinol 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.
1
(
b
), 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, efficient luminescence can be performed. For the electron-transporting layer
16
, an electron-transporting material, such as an oxadiazole derivative, can be used.
Luminescence used heretofore in organic EL devices generally includes two types including fluorescence and phosphorescence. In a fluorescence device, fluorescence at the time of transition of luminescence material molecule from a singlet exciton state to the ground state is produced. On the other hand, in a phosphorescence device, luminescence via a triplet exciton state is utilized.
In recent years, the phosphorescence device providing a higher luminescence yield than the fluorescence device has 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 as shown in FIG.
1
(
c
) 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. Abbreviations of the respective materials are as follows.
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-phenylpyridine complex
However, the organic EL device utilizing phosphorescence described above is accompanied with a problem regarding a deterioration in luminescence particularly in an energization state. The reason of the deterioration has not been clarified, but is conceived as follows. Generally, a life of the triplet excitons is longer by three or more digits than the life of a singlet exciton, so that excited molecules are held in a high-energy state for a longer period. As a result, it may be considered that reaction with surrounding materials such as polymer formation among the excitons, a change in minute molecular structure and a change in structure of the surrounding material are caused.
Anyway, the phosphorescence device is expected to have a high luminescence efficiency but on the other hand, the device is problematic in terms of deterioration in energized state. As a result, the luminescent material used in the phosphorescence device is desired to be a compound providing a high-efficiency luminescence and a high stability.
DISCLOSURE OF INVENTION
Accordingly, an object of the present invention is to provide a luminescence device allowing high-efficiency luminescence, retaining a high luminance or brightness for a long period and exhibiting a stability. The present invention provides a particular metal coordination compound as a novel luminescent material therefor.
A metal coordination compound according to the present invention is represented by the following formula (1):
ML
m
L′
n
  (1),
wherein M is a metal atom of Ir, Pt, Rh or Pd; L and L′ are mutually different bidentate ligands; m is 1, 2 or 3; n is 0, 1 or 2 with the proviso that m+n is 2 or 3; a partial structure ML
m
is represented by formula (2) shown below and a partial structure ML′
n
is represented by formula (3), (4) or (5) shown below:
wherein N and C are nitrogen and carbon atoms, respectively; A, A′ and A″ are respectively a cyclic group capable of having a substituent and connected to the metal atom M via the nitrogen atom; B, B′ and B″ are respectively a cyclic group capable of having a substituent and connected to the metal atom M via the carbon atom;
{wherein the substituent denotes a halogen atom, a cyano group, a nitro group, a trialkylsilyl group (of which the alkyl groups are independently a linear or branched alkyl group having 1 to 8 carbon atoms), a linear or branched alkyl group having 1 to 20 carbon atoms (of which the alkyl group can include one or non-neighboring two or more methylene groups that can be replaced with —O—, —S—, —CO—, —CO—O—, —O—CO—, —CH═CH— or —C≡C— and the alkyl group can include a hydrogen atom that can be replaced with a fluorine atom), or an aromatic cyclic group capable of having a substituent (of which the substituent denotes a halogen atom, a cyano group, a nitro group, a linear or branched alkyl group having 1 to 20 carbon atoms (of which the alkyl group can include one or non-neighboring two or more methylene groups that can be replaced with —O—, —S—, —CO—, —CO—O—, —O—CO—, —CH═CH— or —C≡C— and the alkyl group can include a hydrogen atom that can be replaced with a fluorine atom)};
A and B, A′ and B′, and A″ and B″ are respectively bonded to each other via a covalent bond; and
A and B, and A′ and B′ are bonded to each other via X and X′, respectively, in which X and X′ are respectively a linear or branched alkylene group having 2-10 car

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