Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-12-16
2002-04-23
Yamnitzky, Marie (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S704000, C428S917000, C313S504000, C313S506000, C564S429000
Reexamination Certificate
active
06376106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diaminonaphthalene derivative and to an electroluminescent material, particularly an organic electroluminescent material, using the same, as well as to an organic electroluminescent device (hereinafter abbreviated as an organic EL device).
2. Related Art
In recent years, organic EL devices have become of interest as candidates for flat displays of high brightness. In accordance with this trend, much research and development therefor has been actively performed. An organic EL device has a structure in which a luminescence layer is sandwiched by two electrodes. Holes injected from an anode and electrons injected from a cathode are united within the luminescence layer to thereby emit light. High- and low-molecular-weight materials may both be used for fabrication of organic EL devices, and both have been proven to provide organic EL devices of high brightness.
Organic EL devices are categorized into two types. One type utilizes a fluorescent-dye-added charge transportation material to form a luminescence layer (C. W. Tang, Journal of the Applied Physics, 65, 3610, 1989), and the other type employs a fluorescent dye per se to serve as the luminescence layer (see, for example, Japanese Journal of the Applied Physics, 27, L269, 1988).
Organic EL devices using a fluorescent dye per se for the luminescence layer are further grouped into the following three types. A first type is drawn to three-layered devices in which a luminescence layer is sandwiched by a hole-transportation layer and an electron-transportation layer; a second type is drawn to two-layered devices in which a hole-transportation layer and a luminescence layer are superposed one on the other; and a third type is drawn to two-layered devices in which an electron transportation layer and a luminescence layer are superposed one on the other. Thus, organic EL devices are known to have improved luminous efficacy when they have a two- or three-layered structure.
In the above-mentioned organic EL devices, the electron transportation layer contains an electron-transfer compound and has a function of transferring electrons injected from a cathode into the luminescence layer. The hole-injection layer and the hole-transportation layer both contain a hole-transfer compound and have a function of transferring holes injected from an anode into the luminescence layer. When the hole-injection layer is interposed between the anode and the luminescence layer, organic EL devices having excellent luminous performance can be realized, because an increased number of holes can be injected into the luminescence layer at a lower electric field, and in addition, electrons injected from the cathode or electron-injection layer can be confined within the luminescence layer, to thereby enhance the luminous efficacy.
However, the aforementioned conventional organic EL devices do not necessarily exhibit sufficient performance in practical application. One major reason for this may be attributed to lack of durability of the material of the devices; particularly, hole-transportation material. It has been accepted that if an irregular portion such as a grain boundary exists in the organic layer of an organic EL device, the electric field concentrates to such a portion to thereby lead to degradation and breakage of the device. Therefore, the organic layer is usually used in its amorphous state. Moreover, since an organic EL device is a current-injection-type device, if the material used has a low glass transition point, heat generated during use causes degradation of the organic EL device. From this viewpoint, materials having a high glass transition temperature (Tg) are desired.
Furthermore, hole-transportation materials used for conventional devices have insufficient hole transportability and therefore the luminous efficacy of the devices has not been satisfactory in practice.
A variety of materials centering on triphenylamine derivatives have been known as hole-transportation materials used for such organic EL devices, yet very few materials are suitable for practical use.
For example, there has been known N,N′-diphenyl-N,N′-di(3-methylphenyl)-4,4′-diaminobiphenyl (hereafter abbreviated as TPD) (Applied Physics Letter, Vol. 57, No. 6, page 531, 1990). This compound is thermally unstable, and has disadvantages in service life of the resultant device. Many other triphenylamine derivatives are disclosed in, for example, U.S. Pat. Nos. 5,047,687, 4,047,948, and 4,536,457; Japanese Patent Publication (kokoku) No. 6-32307; and Japanese Patent Application Laid-Open (kokoku) Nos. 5-234681, 5-239455, 8-87122, and 8-259940. However, none of these triphenylamine derivatives are satisfactory in terms of their characteristics.
Star-burst amine derivatives disclosed in Japanese Patent Application Laid-Open (kokai) No. 4-308688 or 6-1972, or “Advanced Material” Vol. 6, page 677 (1994) do not meet essential requirements for organic EL devices in practice, i.e., high luminous efficacy and long service life; and neither do respective compounds disclosed in Japanese Patent Application Laid-Open (kokai) Nos. 7-126226, 7-126615, 7-331238, 7-97355, 8-48656, and 8-100172, and “Journal of the Chemical Society Chemical Communication” page 2175 (1996).
Japanese Patent Application Laid-Open (kokai) No. 9-194441 discloses examples in which naphthylamine derivatives are used, and these derivatives are described as having improved characteristics as compared with TPD. However, these derivatives require improvements regarding hole transportability and heat resistance.
As described above, hole-transportation materials used in conventional organic EL devices still require improved performance, and thus there is need for an excellent material that can enhance the luminous efficacy and service life of organic EL devices.
In most cases, emission of light from organic EL devices is obtained from a luminescence layer or an electron-transportation layer which is provided independently of an electron-transportation layer; in very few cases is emission of light obtained from a hole-transportation layer. The reason for this may be partially attributed to the compatibility with the co-used electron-transportation layer; but it is also considered that the color and intensity of the luminescent light from the hole-transportation layer itself may be a critical factor. If luminescent light can be procured from a hole-transportation layer, such a technique would add value in practice. However, there are known only a few materials which serve such a purpose, and in many cases, materials which serve this purpose emit light having a long wavelength and have a disadvantage in that luminescent light having a short wavelength cannot be obtained.
SUMMARY OF THE INVENTION
In view of the foregoing, the inventors of the present invention have conducted extensive studies in an attempt to solve the aforementioned problems involved in conventional organic EL devices, and have found that when a specific type of diaminonaphthalene derivative is used, organic EL devices having a high luminous efficacy and a longer service life can be obtained, leading to completion of the present invention.
Accordingly, an object of the present invention is to provide an organic EL device having high luminous efficacy and a prolonged service life.
Another object of the present invention is to provide a novel compound which is used for the organic EL device.
A further object of the present invention is to provide a hole-transportation material which is used for the organic EL device.
A still further object of the present invention is to provide a novel organic electroluminescent material used for the device.
In a first aspect of the present invention, there is provided a diaminonaphthalene derivative of formula (1):
wherein R
21
to R
30
independently and individually represent a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, a substituted or unsubstituted amino group, a substituted or unsubstitut
Furukawa Kenji
Izumizawa Takenori
Koike Toshihiro
Uchida Manabu
Chisso Corporation
Yamnitzky Marie
LandOfFree
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