Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2002-02-11
2003-11-11
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S428000, C564S426000, C257SE51018, C257SE51051, C427S066000, C428S690000
Reexamination Certificate
active
06646164
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel triphenylamine derivative which can be preferably used as a hole-transporting material, e.g., for organic electroluminescence device and an organic electroluminescence device comprising the same.
BACKGROUND OF THE INVENTION
As an organic electroluminescence device comprising an organic layer mainly comprising an organic compound provided interposed between a pair of electrodes, i.e., cathode and anode there had been generally used one comprising a single organic layer. In recent years, however, various organic electroluminescence devices comprising a plurality of organic layers each independently having a function such as emission of light and transportation of carrier (e.g., hole, electron) (as disclosed in C. W. Tang and S. A. VanSlyke, “Appl. Phys. Lett.”, 51, 913 (1987), C. Adachi, T. Tsutsui and S. Saito, “Appl. Phys. Lett.”, 55, 1489 (1989), J. Kido, M. Kimura, and K. Nagai, “Science”, Vol. 267, 1332 (1995)).
Such an organic electroluminescence device has the following advantages:
(1) It can emit light with a high luminance at a low voltage as compared with the conventional devices mainly comprising inorganic material;
(2) Since the formation of the various layers can be accomplished not only by vacuum evaporation method but also by solution coating method and any method can be selected taking into account the structure of each of the various layers, the degree of freedom of device design is enhanced, making it possible to enlarge the surface of device; and
(3) A multi-color system can be provided by designing the organic molecules.
Examples of the various layers constituting the organic layer comprising a plurality of layers include light-emitting layer, hole-transporting layer capable of transporting hole, and electron-transporting layer capable of electron. These layers are each formed by the foregoing organic compounds having excellent various properties or by dispersing those organic compounds in an appropriate polymer binder.
However, the conventional organic electroluminescence devices are disadvantageous in that they exhibit insufficient stability and durability mainly attributed to (1) deterioration of organic compound itself due to Joule's heat developed when the device is energized or (2) deterioration in the carrier injection efficiency between various layers due to the reduction in smoothness of interface caused by the crystallization of organic compound by Joule's heat thus developed, and hence exhibit a drastically reduced luminance during a repeated use.
The foregoing problem is remarkable particularly with a hole-transporting material having a low heat resistance constituting a hole-transporting layer among the organic compounds constituting the foregoing various layers. It is not too much to say that the heat resistance of organic electroluminescence devices is determined by the heat resistance of such a hole-transporting material.
Under these circumstances, extensive studies have recently been made on the molecular structure of such a hole-transporting material to improve the heat resistance thereof.
For example, Adachi et al. attempted to improve the heat resistance by polymerizing a triphenylamine derivative known as a hole-transporting material such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (hereinafter abbreviated as “TPD”, which represents a dimer of triphenylamine) represented by the following formula (3-1).
As a result, it was reported that a triphenylamine trimer (hereinafter referred to as “HTM1”) represented by the following formula (4):
exhibits a high heat resistance and an excellent hole-transporting capacity (C. Adachi, K. Nagai and N. Tamoto, “Appl. Phys. Lett.”, 66 (20), 2679 (1995)).
Further, Tokito et al. also attempted to improve the heat resistance by polymerizing a triphenylamine derivative in a similar manner as described above.
As a result, it was clarified that a triphenylamine tetramer (hereinafter referred to as “TPTE”) represented by the following formula (5-1):
exhibits a high heat resistance and an excellent hole-transporting capacity (S. Tokito, H. Tanaka, A. Okada and Y. Taga, “Appl. Phys. Lett.”, 69(7), 878 (1996); S. Tokito, H. Tanaka, K. Noda, A. Okada and Y. Taga, “Macromol. Symp.”, 125, 181-188 (1997); JP-A-10-25473 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”)).
Further, JP-A-7-126226 discloses that a benzidine compound obtained by normalizing the biphenyl ring in the center of the foregoing TPTE into various divalent groups containing the biphenyl ring and normalizing the kind of substituents on various rings and the substitution positions therefor exhibits an excellent stability at the time of light emission and storage, as compared with low molecular weight hole-transporting materials such as the foregoing TPD.
The inventors made studies on the foregoing problems. It was found that the foregoing various polymerized compounds or their peripheral compounds certainly exhibit a stabilized heat resistance and stability as compared with the conventional TPD but leave something to be desired in their effects. In particular, these compounds cannot satisfy the high heat resistance required for on vehicle display devices.
In other words, on vehicle display devices must operate without any trouble even when continuously driven at a temperature as high as 85° C. and a humidity as high as 85% RH for 240 hours. Thus, the on vehicle display device, if it is in the form of organic electroluminescence device, must not show a drastic drop of luminance or stop light emission even when continuously operated under the foregoing high temperature and humidity conditions for 240 hours.
However, HTM1 (a trimer of triphenylamine) represented by the foregoing formula (4) exhibits a glass transition temperature Tg of about 110° C. and hence shows a difference as small as 25° C. from the foregoing ambient temperature, demonstrating that it exhibits an insufficient heat resistance. Thus, if continuously operated at such a high temperature and humidity, the foregoing generation of Joule's heat causes the temperature of the device itself to exceed the glass transition temperature Tg of HTM1 in an extremely short period of time, resulting in deterioration of the foregoing organic compound itself, i.e., HTM1 itself, or reduction in the injection efficiency between layers.
Further, the thickness of the organic layer constituting the device is as extremely small as about 0.1 &mgr;m in total, even if the organic layer comprises a plurality of layers. Thus, if there is some dispersion of thickness, current is concentrated into the section having the smallest thickness to cause local rise in temperature, resulting in the cracking and peeling of the organic layers that cause short-circuiting between the cathode and the anode.
It is thus expected that a device comprising HTM1 shows a drastic drop in luminance or stops light emission in a short period of time due to the foregoing defects.
The insufficient heat resistance of the organic electroluminescence device using HTM1 is also apparent from the fact described in the report by Tokito et al. that a device comprising TPTR, which is different from HTM1 only in the substitution position of terminal methyl group, has a critical temperature as described below of about 110° C.
This is also applicable to TPTE represented by the foregoing formula (5-1). In other words, TPTE exhibits a glass transition temperature Tg of 130° C. and hence shows a temperature difference as small as 45° C. from the foregoing ambient temperature of 85° C. Thus, if continuously operated at such a high temperature and humidity, it can be expected that the resulting deterioration of TPTE itself or the injection efficiency between layers or the short-circuiting between the cathode and the anode causes the device to show a drastic drop of luminance or to stop light emission in a short period of time.
The above described reference discloses that the upper limi
Okuda Nobuyuki
Ueba Yoshinobu
Uemura Takashi
Barts Samuel
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
LandOfFree
Triphenylamine derivative and organic electroluminescence... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Triphenylamine derivative and organic electroluminescence..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Triphenylamine derivative and organic electroluminescence... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3159979