Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-08-03
2003-09-09
Yamnitzky, Marie (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S504000, C313S506000
Reexamination Certificate
active
06617053
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an organic electroluminescent device (hereinafter abbreviated as an organic EL device). More specifically, it relates to an organic electroluminescent device containing a dithiafulvene derivative.
BACKGROUND OF THE INVENTION
In recent years, an organic EL device has been the focus of interest as a next-generation full color flat panel display, and actively researched and developed. The organic EL device is an injection type luminescent device wherein a luminescent layer is sandwiched between two electrodes, and the device emits light by injecting an electron and a hole into an organic luminescent layer and recombining them. The materials used include a low molecular material and a high molecular material, and it is known that both provide organic EL devices having a high luminance.
Such organic EL devices include two types. One is a device in which an electron-transporting material containing a fluorescent dye is used as a luminescent layer, reported by C. W. Tang, et al. (J. Appl. Phys., 65, 3610 (1989)), and the other is a device in which a fluorescent dye itself is used as a luminescent layer (e.g., a device described in Jpn. J. Appl. Phys., 27, L269 (1988)).
The device using a fluorescent dye as a luminescent layer is further divided roughly into three types. The first one is a device having a three-layer structure in which a luminescent layer is sandwiched between an electron-transporting layer and a hole-transporting layer. The second one is a device having a two-layer structure in which a hole-transporting layer and a luminescent layer are laminated. The third one is a device having a two-layer structure in which an electron-transporting layer and a luminescent layer are laminated. It is known that an organic EL device is improved in luminous efficiency by employing such multilayer structures.
An electron-transporting layer in the organic EL devices of the respective structures described above contains an electron-transferring compound and has a function to transfer an electron injected from a cathode to a luminescent layer. A hole-transporting layer and a hole-injecting layer are layers containing hole-transferring compounds and carry out a function to transfer a hole injected from an anode to a luminescent layer. The intervention of a hole-injecting layer between an anode and a luminescent layer makes it possible to transfer many holes from the anode to the luminescent layer by a lower electric field and to confine electrons injected from an electron-transporting layer or an electron-injecting layer in the luminescent layer. Thus, an organic EL device having an excellent luminescent performance such as an improved luminous efficiency can be obtained.
However, these organic EL devices do not show a sufficiently high performance for practical use. This is mainly due to poor durability of the materials used, and particularly poor durability of a hole-transporting material. It is considered that if a heterogeneous part such as a grain boundary is present in an organic layer of an organic EL device, an electric field is concentrated into the part, which results in deteriorating and breaking the device. Accordingly, the organic layer is used in an amorphous state in many cases. An organic EL device is an electron-injecting type device, which requires a material having a high glass transition temperature (hereinafter abbreviated as Tg), because use of a material having a low glass transition point results in deteriorating the organic EL device due to heat generated during driving. Further, the hole-transporting materials used do not have a satisfactory hole-transporting property, and the device does not have a sufficiently high luminous efficiency for practical use.
A wide variety of materials including amino compounds are known as hole-transporting materials used for such organic EL devices, but only a few materials are suitable for practical use. For example, N,N′-diphenyl-N,N′-di(3-methylphenyl)-4,4′-diaminobiphenyl (hereinafter abbreviated as TPD) has been reported (Appl. Phys. Lett., 57, 6, 531 (1990)), but this compound has a poor heat stability and also has problems with the life of the device, etc. Many triphenylamine derivatives have been described in U.S. Pat. Nos. 5,047,687, 4,047,948, 4,536,457, JP-B 6-32307, JP-A 5-234681, JP-A 5-239455, JP-A 8-87122 and JP-A 8-259940, but they do not have satisfactory characteristics.
Star-burst amine derivatives described in JP-A 4-308688, JP-A 6-1972 and Adv. Mater., 6, 677 (1994), and compounds described in JP-A 7-126226, JP-A 7-126615, JP-A 7-331238, JP-A 7-97355, JP-A 8-48656, JP-A 8-100172 and J. Chem. Soc. Chem. Comm., 2175, (1996) do not have both a high luminous efficiency and a long life which are the essential characteristics for practical use. Further, JP-A 9-194441 has reported examples wherein naphthylamine derivatives are used, and described that the properties thereof are more improved than those of TPD. These compounds, however, do not have any satisfactory hole-transporting property or durability.
As described above, conventional amine-based hole-transporting materials used for organic EL devices do not meet high performance requirements of recent full color flat panel displays, and excellent materials have been desired to provide an organic EL device having a higher efficiency and a longer life.
SUMMARY OF THE INVENTION
The present invention has been achieved in light of the problems of such conventional techniques as described above. An object thereof is to provide a material comprising a hole-transferring compound other than amino compounds conventionally used, and an organic EL device having a high luminous efficiency and a long life which contains the above compound.
The present inventors have made intensive investigations in order to solve the preceding problems involved in conventional organic EL devices and, as a result, found that specific dithiafulvene derivatives are high-performance hole-injecting and hole-transporting materials and that use of this derivative provides an organic EL device having a high luminous efficiency and a long life. Thus, they have completed the present invention.
The present invention is described as follows.
(1) An organic electroluminescent device comprising a dithiafulvene derivative represented by Formula (1):
wherein R
1
and R
2
each independently represent an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group; R
3
to R
6
each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkylthio group having 1 to 6 carbon atoms, a substituted or unsubstituted arylthio group, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group; when R
3
to R
6
are an aryl group or a heterocyclic group adjacent to each other, they may be condensed to each other; and when R
3
to R
6
are an alkenyl group or an alkylthio group adjacent to each other, they may be bonded to each other.
(2) The organic electroluminescent device as described in the above item (1), wherein the dithiafulvene derivative represented by Formula (1) is contained in a hole-injecting layer.
(3) The organic electroluminescent device as described in the above item (1), wherein the dithiafulvene derivative represented by Formula (1) is contained in a hole-transporting layer.
(4) A hole-injecting material comprising the dithiafulvene derivative represented by Formula (1).
(5) A hole-transporting material comprising the dithiafulvene derivative represented by Formula (1).
DETAILED DESCRIPTION OF THE INVENTION
The present invention shall be explained below in details.
When R
1
, R
2
, R
3
, R
4
, R
5
or R
6
is an alkyl group in Formula (1), it preferably has 1 to 6 carbon atoms. Examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. Exam
Fujishita Yuichi
Furukawa Kenji
Nakano Takaharu
Uchida Manabu
Chisso Corporation
Wenderoth , Lind & Ponack, L.L.P.
Yamnitzky Marie
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