Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-08-27
2004-02-24
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S504000, C252S301160, C546S256000
Reexamination Certificate
active
06696182
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an organic electroluminescent device (hereunder abbreviated to organic EL device). More specifically, it relates to an organic EL device comprising a dipyridylthiophene derivative.
BACKGROUND ART
Recent years have seen greater attention focused on organic EL devices as next-generation full color flat panel displays, and this has led to their active research and development. Organic EL devices are injection-type EL devices which comprise a luminescent layer sandwiched between two electrodes, wherein injection of electrons and holes in the organic luminescent layer results in their recombining and consequent light emission. The materials used include low molecular materials and polymer materials, which are known to give organic EL devices with high luminance.
Two types of such organic EL devices exist. One is obtained by doping a fluorescent dye to a charge transport layer, as published by C. W. Tang et al. (J. Appl. Phys., 65, 3610(1989)), and the other employs the fluorescent dye itself alone (for example, the device described in Jpn. J. Appl. Phys. 27, L269(1988)).
The devices using fluorescent dyes as luminescent layers are largely classified into three types. The first type has three layers with a luminescent layer sandwiched between an electron transport layer and a hole transport layer, the second type has two layers with a hole transport layer and a luminescent layer laminated together, and the third type has two layers with an electron transport layer and a luminescent layer laminated together. Such multilayer structures are known to enhance the luminous efficiency of organic EL devices.
The known hole transport materials used in organic EL devices include many and various materials which are primarily triphenylamine derivatives, but few materials are known to be usable as electron transport materials. Furthermore, the existing electron transport materials have low charge transport capacity compared to known hole transport materials such as N,N′-di(1-naphthyl)-N,N′-diphenyl-4,4′-diaminobiphenyl, and when used in organic EL devices, they restrict the performance of EL devices, such that it has not been possible to achieve satisfactory device characteristics.
As specific examples of such electron transport materials there are known metal complexes of oxine derivatives (described in JP-A 59-194393 and elsewhere), 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), and the like. The former allows driving of organic EL devices at relatively low voltage, but this is still inadequate, and because the luminescence itself is green it is difficult to achieve emission of blue light. The above-mentioned organic EL device (Jpn. J. Appl. Phys. 27, L269(1988)) is an example of using the latter as an electron transport layer. However, instability of thin films, including a tendency toward crystallization, has been indicated as a problem, and therefore compounds with multiple oxadiazole rings have been developed (Journal of the Chemical Society of Japan, 11, 1540(1991), JP-A 6-145658, JP-A 6-92947, JP-A 5-152027, JP-A 5-202011, JP-A 6-136359, etc.). Nevertheless, these compounds have also exhibited properties unsuitable for practical use, such as high driving voltage. Quinoxaline derivatives have been reported as additional compounds (JP-A 6-207169). Dimerization increases molecular weight and thus enhances the stability of thin films, but still a high driving voltage has been required, and such dimers have thus been inadequate for practical use. Silacyclopentadiene derivatives have been reported as well (described in JP-A 9-87616 and elsewhere). These have been capable of driving organic EL devices at relatively low voltage, but have also been insufficient for practical use. Dibenzoxazolyl-thiophene derivatives have been reported as thiophene ring-containing compounds (JP-A 5-343184, JP-A 11-345686 and elsewhere). However, while thin-film stability is improved by introduction of substituents, the driving voltage has been too high to be adequate for practical use.
As mentioned above, the electron transport materials used in conventional organic EL devices do not meet the current demands for high performance by full color flat panel displays, and therefore superior materials have been desired in order to achieve lower voltage and higher efficiency for organic EL devices.
The present invention has been accomplished in light of these problems of the prior art, and its object is to provide a low-voltage, high-efficiency organic EL device.
As a result of diligent research directed toward solving the aforementioned problems associated with conventional organic EL devices, the present inventors have found that certain dipyridylthiophene derivatives are high performance electron transport materials which when employed can give low-voltage, high-efficiency organic EL devices, and the present invention has thus been completed.
DISCLOSURE OF THE INVENTION
In other words, the present invention has the following construction.
A first aspect of the invention is an organic electroluminescent device characterized by comprising a dipyridylthiophene derivative represented by the following general formula (1):
where X is S or SO
2
, R
5
and R
6
each independently represent a hydrogen atom, an alkyl group of 1-6 carbons, an alkenyl group of 2-6 carbons, an alkoxy group of 1-6 carbons, an aryloxy group, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group, with the proviso that when R
5
and R
6
each independently represent an alkenyl, alkoxy, aryl or heterocyclic group they may be bonded together but not into a benzo condensed ring, and A
1
and A
2
are independently represented by the following formula (2) or (3):
where R
1
-R
4
and R
7
-R
10
each independently represent a hydrogen atom, an alkyl group of 1-6 carbons, an alkenyl group of 2-6 carbons, an alkoxy group of 1-6 carbons, an aryloxy group, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group, with the proviso that when they are each independently an alkenyl, alkoxy, aryl or heterocyclic group and are adjacent, they may be bonded together.
According to a preferred mode of the invention, both A
1
and A
2
in general formula (1) are groups represented by general formula (2).
According to another preferred mode of the invention, both A
1
and A
2
in general formula (1) are groups represented by general formula (3).
According to still another preferred mode of the invention, A
1
in general formula (1) is a group represented by general formula (2) and A
2
is a group represented by general formula (3).
Still another preferred mode of the invention is an organic electroluminescent device wherein the dipyridylthiophene derivative represented by general formula (1) is contained in an electron transport layer.
Still another preferred mode of the invention is an organic electroluminescent device wherein the dipyridylthiophene derivative represented by general formula (1) is contained in a luminescent layer.
A second aspect of the invention is an electron transport material comprising a dipyridylthiophene derivative represented by general formula (1).
A third aspect of the invention is a luminescent material comprising a dipyridylthiophene derivative represented by general formula (1).
PREFERRED MODES OF THE INVENTION
The present invention will now be explained in further detail. In general formulas (1), (2) and (3), X is S or SO
2
, and R
1
to R
10
each independently represent a hydrogen atom, an alkyl group of 1-6 carbons, an alkenyl group of 2-6 carbons, an alkoxy group of 1-6 carbons, an aryloxy group, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group.
As examples of the alkyl groups there may be mentioned methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. As examples of the alkenyl groups there may be mentioned vinyl, allyl, 1-propenyl, 1,3-butadi
Furukawa Kenji
Nakano Takaharu
Uchida Manabu
Yamada Hiroshi
Chisso Corporation
Garrett Dawn
Kelly Cynthia H.
Wenderoth , Lind & Ponack, L.L.P.
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