Organic electroluminescent device

Details Organic electroluminescent device Organic electroluminescent device

2001-11-05

2004-06-08

Kelly, Cynthia H. (Department: 1774)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S917000, C313S504000, C313S503000, C252S301160, C548S108000

Reexamination Certificate

active

06746784

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescent device having an excellent light-emitting property such as high luminance efficiency.
An organic electroluminescent device (which will hereinafter be called “organic EL device”) is a light-emitting device which makes use of the principle that when an electric field is applied, a fluorescent material emits light in response to the charge recombination of holes injected from an anode and electrons injected from a cathode. After C. W. Tang et al. of Eastman Kodak Company reported a low-voltage-driven organic EL device using a double layered structure (C. W. Tang, S. A. Vanslyke, Applied Physics Letters, Vol. 51, 913 (1987) and the like), studies on an organic EL device and materials have been briskly carried out. Tang et al. reported a multi-layered organic EL device using tris (8-hydroxyquinolinol aluminum) in a light-emitting layer and a triphenyldiamine derivative in a hole-transporting layer. This stacked structure gives such advantages as an improvement in the injection efficiency of holes into the light-emitting layer; blocking of electrons injected from a cathode; and confinement of the excitons into the light-emitting layer.
A double layered structure composed of a hole-injecting and transporting layer and an electron-transporting and light-emitting layer or a triple layered structure composed of a hole-injecting and transporting layer, a light-emitting layer and an electron-injecting and transporting layer is well known as an organic EL device. In order to increase the recombination efficiency of injected holes and electrons, various improvements in the device structure or fabrication process have been introduced to such multi-layered devices.
As a hole transporting material, triphenyl amine derivatives and aromatic diamine derivatives such as 4′,4′,4″-tris(3-methylphenylphenylamino)-triphenyl amine which is a star burst molecule and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine are well known (for example, Patent Publications JP-A-8-20771, JP-A-8-40995, JP-A-8-40997, JP-A-8-53397, and JP-A-8-87122). As an electron transporting material, oxadiazole derivatives, triazole derivatives and the like are well known.
Chelate complexes such as tris(8-quinolinolate)aluminum complex, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives, oxadiazole derivatives and the like are known as light emitting materials. Since various color lights in a visible region from blue to red are obtained from these light emitting materials, there is increased expectation for industrialization of a full color organic EL device (refer to, e.g., JP-A-8-239655, JP-A-7-138561, and JP-A-3-200889).
Besides, various materials for the electroluminescent devices have been reported. However, in the case of some compounds, we can not use most method for film fabrication due to excessively strong intermolecular interactions. In addition, for such compounds having a strong intermolecular interaction, concentration quenching is observed when they are used as a light emitting material, which has decreased the luminance and luminous efficiency of the device.
Moreover, the materials used for the organic EL devices are required to have good charge transporting injecting properties. In recent days, organic EL devices with high brightness and long lifetime have been disclosed or reported, but any of them are not enough in these properties. It has been, therefore, desired to develop materials having a high performance.
SUMMARY OF THE INVENTION
In view of the above problems, an objective of this invention is to provide an organic EL device with an improved luminance luminous efficiencies and little limitation on to film fabrication method.
Another object of the present invention is to provide an organic electroluminescent device with improved luminance by using a compound having improved charge injecting properties.
The present inventors have repeated experiments to solve above problem, and found that an organic EL device having superior emission properties is obtained by using a compound having at least one substituted or unsubstituted cyclohexylidenemethine group. The compounds have the intermolecular interactions reduced by the steric hindrance of the cyclohexylidenemethine group. Thus, the concentration quenching is decreased when the compounds are used as a light emitting material, and the film comprising the compounds can be fabricated with ordinary method.
Some conventional compounds with aryl amine moety or styryl moety don't have enough hole injection properties because their energy level of their highest occupied molecular orbital (HOMO) is too low. It has been known that some substituents shift the HOMO level slightly, but it is not enough to improve their hole injection properties. Then, there has been no method to shift the HOMO of such compounds to higher without effects on energy gap between HOMO and lowest unoccupied molecular orbital (LUMO), light emitting properties and carrier transpoting properties. The present inventors also found that the cyclohexylidenemethine group shifts the energy level of HOMO of the compounds to higher, which improves the hole injecting properties, without effect on the energy gap between HOMO and LUMO. Thus, the present invention was achieved.
An organic electroluminescent device according to the present invention comprises an anode, a cathode, and one or more organic thin film layers between the said anode and the said cathode, the organic thin film layer(s) including a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds having a cyclohexylidenemethine group, either singly or as a mixture.
The present inventors have found that an organic EL device using bis(diarylamino)arylene compound having a cyclohexylidenemethine group has improved light-emitting properties.
An organic electroluminescent device according to a first aspect of the present invention comprises an anode, a cathode, and one or more organic thin film layers placed between said anode and said cathode, the organic thin film layer(s) having a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds represented by the following general formula [A], either singly or as a mixture:
wherein
Ar
1
represents a substituted or unsubstituted aromatic hydrocarbon group having 5 to 42 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 4 to 42 carbon atoms;
each of Ar
2
to Ar
5
independently represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 6 to 20 carbon atoms;
each of X
1
and X
2
independently represents a divalent linking group; and
each of R
1
to R
20
independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted amino group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryloxy group, or a substituted or unsubstituted alkoxycarbonyl group, provided that two of R
1
to R
1
or R
1
to R may form a ring and that Ar
2
and Ar
3
or Ar
4
and Ar
5
may be bonded to each other to form a ring.
In the general formula [A], it is preferable that at least one of the linking groups represented by X
1
and X
2
is a substituted or unsubstituted styryl group.
An organic electroluminescent device according to a second aspect of the present invention comprises an anode, a cathode, and one or more organic thin film layers placed between said anode and said cathode, the organic thin film layer(s) having a light-e

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