US20020125818A1

US20020125818A1 - Organic electroluminescent device

Info

Publication number: US20020125818A1
Application number: US09/969,758
Authority: US
Inventors: Hideki Sato; Yoshiharu Sato; Masayo Fugono
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 2000-10-04
Filing date: 2001-10-04
Publication date: 2002-09-12
Also published as: US6893743B2; US20030218418A9

Abstract

An organic electroluminescent device is disclosed, comprising a substrate having thereon a light-emitting layer sandwiched by an anode and a cathode, wherein the light-emitting layer comprises at least:

(1) a host material having electron-transporting or hole-transporting property,

(2) Compound A capable of phosphorescence emission at room temperature, and

(3) Compound B capable of phosphorescence emission or fluorescence emission at room temperature and having the maximum light emission wavelength longer than the maximum light emission wavelength of Compound A,

and the maximum light emission wavelength of said device is attributable to said (3). The light emission attributable to (3) is intensified by (2) to elevate the light emission efficiency and by selecting a fluorescent compound as (3), the device can be prevented from aging deterioration of the luminance.

Description

FIELD OF THE INVENTION

The present invention relates to an organic electroluminescent device. More specifically, the present invention relates to a thin film-type device which emits light upon application of an electric field to a light-emitting layer comprising an organic compound.

BACKGROUND OF THE INVENTION

In conventional thin film-type electroluminescent (EL) devices, an inorganic material group II-VI compound semiconductor such as ZnS, CaS and SrS is generally doped with Mn or a rare earth element (e.g., Eu, Ce, Tb, Sm) as a emission center. However, the EL device fabricated from the above-described inorganic material has problems such that:

1) a.c. (alternating current) driving is necessary (from 50 to 1,000 Hz),

2) the driving voltage is high (up to 200 V),

3) full color emission is difficult (particularly blue) and

4) the peripheral driving circuit costs highly.

In recent years, however, for the purpose of improving the above-described problems, studies have been made to develop an EL device using an organic thin film. In order to elevate the light emission efficiency, an organic electroluminescent device has been developed, where the kind of electrode is optimized for the purpose of improving the efficiency of carrier injection from an electrode and a hole-transporting layer comprising an aromatic diamine and a light-emitting layer comprising an aluminum complex of 8-hydroxyquinoline are provide (see, Appl. Phys. Lett., Vol. 51, page 913 (1987)). By this technique, the light emission efficiency is greatly improved as compared with conventional EL devices using a single crystal such as anthracene. Furthermore, for example, an aluminum complex of 8-hydroxyquinoline as a host material is doped with a fluorescence dye for laser, such as coumarin (see, J. Appl. Phys., Vol. 65, page 3610 (1989)), with an attempt to improve the light emission efficiency, convert the light emission wavelength or the like. The devices are coming to have practically usable properties.

In addition to these electroluminescent devices using a low-molecule-weight material, studies are being made to develop an electroluminescent device using a polymer material such as poly(p-phenylenevinylene), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] or poly(3-alkylthiophene) for the light-emitting layer material or to develop a device using a low molecule light-emitting material and an electron-transfer material by mixing these with a polymer such as polyvinylcarbazole.

Also, use of not only fluorescence but also phosphorescence is being studied with an attempt to elevate the light emission efficiency. If phosphorescence is used, that is, light emission from the triplet excitation state is utilized, an improvement of about three times higher efficiency can be expected as compared with conventional devices using fluorescence (singlet). For this purpose, it has been proposed to form the light-emitting layer using a coumarin derivative or a benzophenone derivative (see, The 51th Autumn Meeting. 1990; The Japan Society of Applied Physics, 28a-PB-7 (1990)). However, only an extremely low luminance could be obtained. Thereafter, use of an europium complex is studied with an attempt to utilize the triplet excitation state, however, high light emission efficiency could not be attained either by this use.

Recently, it has been reported that red light emission with high efficiency can be attained by using a platinum complex (T-1) shown below (see, Nature, Vol. 395, page 151 (1998)). Thereafter, the efficiency in green light emission is further greatly improved by doping an iridium complex (T-2) shown below to the light-emitting layer (see, Appl. Phys. Lett., Vol. 75, page 4 (1999)).

For applying the organic electroluminescent device as a display device such as flat panel display, further, as a light source for fluorescent lamp or marker lamp, the light emission efficiency of the device must be more improved.

The organic electroluminescent device using the phosphorescence molecule (T-2) described in the above-described publication emits light with relatively high efficiency, however, the organic electroluminescent device using (T-1) is low in the light emission efficiency as compared with devices using (T-2). The main cause of this is presumed to reside in the relationship between the host material in the light-emitting layer and the phosphorescent substance.

The formation probability of triplet exciton is three times higher than that of singlet exciton and therefore, if light emission from the triplet exciton (namely, phosphorescence) is used, the light emission efficiency is elevated. However, use of a phosphorescent substance alone suffers from bad stability of film and low mobility of electric charge (hole or electron) injected from electrodes and accordingly, the light emission efficiency is not elevated. On the other hand, use of a host material alone cannot provide light emission from a triplet exciton and the material uses its energy mostly for heat and is deactivated, as a result, the light emission efficiency is not elevated. For overcoming this problem, a method of forming a light-emitting layer by dispersing a phosphorescent substance in a host material which exhibits fluorescent property is employed.

According to this method, triplet excitons generated from the host material are used as triplet excitons for the phosphorescent substance to cause light emission therefrom. However, this method involves energy transfer and unless the excited triplet level in the host material is close to the excited triplet level of the phosphorescent substance, the probability of energy transfer decreases and the triplet excitons cannot contribute to the light emission. In the case of the above-described device using (T-1) and (T-2), the excited triplet level of the host material used is considered close to the excited triplet level of (T-2).

Under these circumstances, the present inventors have made investigations on the method for, in an organic electroluminescent device using a phosphorescent emission, attaining high-luminance and high-efficiency light emission from a phosphorescent material which by itself does not emit light with high efficiency.

In order to apply an organic electroluminescent device to a display device such as flat panel display, the device must be ensured with sufficiently high stability at the driving in addition to the improvement of light emission efficiency. However, the organic electroluminescent device using the phosphorescence molecule (T-2) described in the above-described publication, which ensures high-efficiency light emission, is insufficient in the driving stability for practical use (see, Jpn. J. Appl. Phys., Vol. 38, page L1502 (1999)). Thus, a high-efficiency display device cannot be realized.

This driving deterioration is presumed to arise mainly because of deterioration of the light-emitting layer.

Electric charges injected from electrodes form electron-hole pairs (excitons) at a certain probability. In general, the light emission (phosphorescence) by triplet excitons has a longer lifetime as compared with the light emission (fluorescence) by singlet excitons but, on the contrary, the singlet exciton has higher thermal stability than triplet exciton.

With increase of a current applied to a device, electric charges injected to the light-emitting layer increase and accompanying this, the amount of electric charges not participating in the generation of excitons also increase. Also, the amount of excitons which are generated but not contribute to the light emission in the light-emitting layer and are thermally deactivated increases and this causes elevation of the temperature of the light-emitting layer.

At this time, the device is considered to deteriorate because the triple exciton is inferior in the thermal stability as compared with singlet exciton. This can be also verified from the fact that the light emission efficiency of the organic electroluminescent device using the phosphorescence molecule (T-2) greatly decreases with the increase of injected current (see, Appl. Phys. Lett., Vol. 75, page 4 (1999)).

As such, organic electroluminescent devices using a phosphorescence molecule have a serious problem in the device driving stability for the practical use at present.

For applying an organic electroluminescent device to a display device such as flat panel display, polychromatic display must be realized. In recent years, compact display devices such as portable telephone, which are a promising use of the organic electroluminescent device, are also required to have polychromatic display.

For realizing polychromatic display such as multicolor display and full color display by using an organic electroluminescent device, the following methods have been heretofore proposed:

1) a method of providing light emission sub pixel for desired colors such as red (R), green (G) and blue (B),

2) a method of disposing a color filter on a white light-emission layer and coloring the emitted light, and

3) a method of disposing a fluorescence converting layer on a blue light-emitting layer and converting the color of emitted light.

Among these, the method 1) uses no layer of absorbing emitted light, such as color filter, and ensures high use efficiency of light and therefore, this method is ideal for high-efficiency self-light emission-type polychromatic display devices. However, in this method, the materials suitable for respective emitted light colors must be prepared.

For this purpose, as described above, for example, a fluorescence dye for laser, such as coumarin, is doped into an aluminum complex of 8-hydroxyquinoline used as a host material to convert the light emission wavelength (see, J. Appl. Phys., Vol. 65, page 3610 (1989)).

However, since conventionally proposed methods of doping a fluorescence dye all utilize the light emission by singlet excitons, the probability of generating excitons is theoretically low as described above and a sufficiently high light emission efficiency cannot be attained. Furthermore, the method of using a phosphorescence molecule such as (T-1) or (T-2) has a problem in that the number of molecules known to emit phosphorescence at room temperature is very small and desired colors cannot be afforded.

By taking account of these circumstances, the present inventors have studied on the method for attaining high efficiency, high driving stability and capability of polychromatic display, and succeeded in reaching the present invention.

SUMMARY OF THE INVENTION

The organic electroluminescent device of the present invention is characterized by that in an organic electroluminescent device comprising a substrate having thereon a light-emitting layer sandwiched by an anode and a cathode, the light-emitting layer comprises at least

(1) a host material having electron-transporting and/or hole-transporting property,

(2) Compound A capable of phosphorescence emission at room temperature, and

(3) Compound B capable of phosphorescence emission or fluorescence emission at room temperature and having the maximum light emission wavelength longer than the maximum light emission-wavelength of Compound A, and the maximum light emission wavelength of the device is attributable to (3).

More specifically, the present inventors have found that when the constituent element (2), namely, Compound A capable of phosphorescence emission at room temperature is used in combination with the constituent element (3), namely, Compound B which is (a) a phosphorescent compound of not emitting light with high efficiency by itself or (b) a fluorescent compound of emitting light in various colors but incapable of ensuring light emission efficiency as high as that of the phosphorescent compound for any of those colors, Compound A plays a role of sensitizer and the light emission of Compound B is intensified.

As a result, a device capable of emitting light in various colors can be obtained and accordingly, this is very useful in realizing a flat panel display of multi-color display or full-color display using an organic electroluminescent device.

In the case where Compound B is a compound capable of fluorescence emission at room temperature, an effect of inhibiting the deterioration of luminance and the decrease in a light emission efficiency can also be provided and this is preferred. By the combination use with the phosphorescence emission Compound A, a light emission color attributable to the fluorescent Compound B and light emission efficiency close to the phosphorescence emission can be realized and at the same time, the aging deterioration of luminance and the decrease in the light emission efficiency when the device emits light at a high luminance, which occurs very often in phosphorescence emission devices, can be inhibited to elevate the driving stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing one example of the organic electroluminescent device according to the present invention. [0038]
FIG. 2 is a schematic sectional view showing another example of the organic electroluminescent device according to the present invention. [0039]
FIG. 3 is a schematic sectional view showing another example of the organic electroluminescent device according to the present invention. [0040]
FIG. 4 is a graph showing the change in a luminance when the devices fabricated in Example 4 or Comparative Example 5 emitted light at a high luminance. [0041]
FIG. 5 is a graph showing the change in a luminance when the devices fabricated in Example 5 or Comparative Example 5 emitted light at a high luminance. [0042]
FIG. 6 is a graph showing the change in a luminance when the devices fabricated in Example 6 or Comparative Example 5 emitted light at a high luminance. [0043]
FIG. 7 is a graph showing the change in a luminance when the devices fabricated in Example 4 or Comparative Example 5 were driven continuously. [0044]
FIG. 8 is a graph showing the change in a luminance when the devices fabricated in Example 5 or Comparative Example 5 were driven continuously. [0045]
FIG. 9 is a graph showing the change in a luminance when the devices fabricated in Example 6 or Comparative Example 5 were driven continuously.[0046]

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an organic electroluminescent device containing a host material, Compound A capable of phosphorescence emission at room temperature and Compound B capable of phosphorescence emission or fluorescence emission at room temperature in the light-emitting layer, and having a maximum light emission wavelength attributable to Compound B. In the organic electroluminescent device, the light-emitting layer preferably contains the host material as a main component and Compound A and Compound B as sub-components. [0047]
The term “main component” as used herein means a material occupying 50% by weight or more in the materials constituting the layer and the term “sub-component” means a material occupying less than 50% by weight in the materials constituting the layer. That is, the term “contains Compounds A and B as sub-components” means that the total amount of Compound A and Compound B is less than 50% by weight based on the materials for forming the light-emitting layer. [0048]
The host material preferably has an excited triplet level in an energy state higher than the excited triplet level of Compound A and the excited triplet level (when Compound B is a phosphorescent compound) or excited singlet level (when Compound B is a fluorescent compound) of Compound B, contained in the light-emitting layer. [0049]
Also, the host material must be a compound ensuring a stable thin film shape, having a high glass transition temperature (Tg) and being capable of efficiently transporting holes and/or electrons. [0050]
Furthermore, the host material must be a compound which is electrochemically and chemically stable and does not easily allow the generation of impurities working out to a trap or quenching the emitted light during the production or use. [0051]
Examples of the host material satisfying these requirements include the compounds represented by the following formula (I) or (II), or the compounds having the group represented by the following formula (III): [0052]
(wherein the carbazolyl group and the phenylene group each may have an arbitrary substituent, and Z[0053] ¹represents a direct bond or a divalent linking group).
(wherein M represents a metal selected from [0054] Groups 1, 2, 3, 12 and 13 of the periodic table, n represents a valence number of the metal, L represents an arbitrary substituent, j represents a number of the substituent L and is 0 or 1, X²represents a carbon atom or a nitrogen atom, the ring A represents a nitrogen-containing heterocyclic ring and may have a substituent, and the ring B represents an aromatic hydrocarbon ring group or an aromatic heterocyclic group and may have a substituent).
(wherein R[0055] ⁵¹to R⁵⁴each independently represents a hydrogen atom or an arbitrary substituent, each of the pairs R⁵¹and R⁵², and R⁵³and R⁵⁴may combine to form a ring, and X³represents an oxygen atom or a sulfur atom).
Preferred examples of the compound having an N-phenylcarbazole skeleton, represented by formula (I) include the compounds represented by the following formula (I-1): [0056]
(wherein R[0057] ¹to R¹⁶each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the adjacent substituents R¹and R², R³and R⁴, R⁵and R⁶, R⁷and R⁸, R⁹and R¹⁰, R¹¹and R¹², R¹³and R¹⁴, and R¹⁵and R¹⁶may combine to form a ring, and z¹represents a direct bond or a divalent linking group).
Specific examples of R[0058] ¹to R¹⁶in formula (I-1) include a hydrogen atom; a halogen atom such as chlorine atom and fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an aralkyl group such as benzyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; a cyano group; an amino group; an acyl group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; a carboxyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an alkylamino group such as diethylamino group and diisopropylamino group; an aralkylamino group such as dibenzylamino group and diphenethylamino group; a haloalkyl group such as trifluoromethyl group; a hydroxyl group; an aryloxy group such as phenoxy group and benzyloxy group; an aromatic hydrocarbon ring group such as phenyl group or naphthyl group, which may have a substituent; and an aromatic heterocyclic group such as thienyl group and pyridyl group, which may have a substituent.
Examples of the substituent which the aromatic hydrocarbon ring group and the aromatic heterocyclic group each can have include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aryloxy group such as phenoxy group and benzyloxy group; an alkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. [0059]
Each pair of the adjacent substituents R[0060] ¹and R², R³and R⁴, R⁵and R⁶, R⁷and R⁸, R⁹and R¹⁰, R¹¹and R¹², R¹³and R¹⁴, and R¹⁵and R¹⁶may be combine to form a 5-, 6- or 7-membered ring such as benzene ring or cyclohexane ring.
R[0061] ¹to R¹⁶each is particularly preferably a hydrogen atom, an alkyl group or a cyano group.
Z[0062] ¹in formula (I) or (I-1) is preferably a direct bond, an oxygen atom, a sulfur atom, a linking group shown below:
a divalent aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, or any one of the following linking groups: [0063]
(any benzene ring moiety in the each structure may have an arbitrary substituent, and Ar[0064] ¹to Ar⁶each represents an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent or a group represented by the following formula (I-2):
wherein the carbazolyl group and the phenylene group each may have an arbitrary substituent). [0065]
Among the preferred linking groups for Z[0066] ¹in formula (I) or (I-1), examples of the aromatic hydrocarbon ring group include a 5- or 6-membered monocyclic ring and a 2-, 3- or 4-condensed ring, such as phenylene group, naphthylene group, anthranyl group and naphthacene, and examples of the aromatic heterocyclic group include a 5- or 6-membered monocyclic ring and a 2- or 3-condensed ring, such as divalent thiophene ring residue, furan ring residue, pyridine ring residue, pyrimidine ring residue and quinoline ring residue.
These aromatic hydrocarbon ring group and aromatic heterocyclic group may have a substituent such as an alkyl group having from 1 to 6 carbon atoms (e.g. methyl, ethyl), a halogen group (e.g. fluorine) or an a-haloalkyl group (e.g. trifluoromethyl). [0067]
Examples of Ar[0068] ¹to Ar⁶include an aromatic hydrocarbon ring group which is a 5- or 6-membered monocyclic ring or a 2-, 3- or 4-condensed ring, such as phenylene group, naphthylene group, anthranyl group and naphthacene, and an aromatic heterocyclic ring which is a 5- to 6-membered monocyclic ring or a 2- or 3-condensed ring, such as thienyl group, furan group, pyridyl group, pyrimidinyl group and quinolyl group. These aromatic hydrocarbon ring group and aromatic heterocyclic group may have a substituent such as an alkyl group (e.g. methyl, ethyl), a halogen group (e.g. fluorine) or an α-haloalkyl group (e.g. trifluoromethyl).
The structure represented by formula (I-2) is preferably represented by the following formula (I-3): [0069]
(wherein R[0070] ¹⁷to R²⁴each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group which may have a substituent, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group, or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the pairs R¹⁷and R¹⁸, R¹⁹and R²⁰, R²¹and R²², and R²³and R²⁴may combine with each other to form a ring).
Specific examples of R[0071] ¹⁷to R²⁴in formula (I-3) include a hydrogen atom; a halogen atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an aralkyl group such as benzyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; a cyano group; an amino group; an acyl group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; a carboxyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an alkylamino group such as diethylamino group and diisopropylamino group; an aralkylamino group such as dibenzylamino group and diphenethylamino group; a haloalkyl group such as trifluoromethyl group; a hydroxyl group; an aryloxy group such as phenoxy group and benzyloxy group; an aromatic hydrocarbon ring group such as phenyl group and naphthyl group, which may have a substituent; and an aromatic heterocyclic group such as thienyl group and pyridyl group, which may have a substituent.
Examples of the substituent which the aromatic hydrocarbon ring group and the aromatic heterocyclic group each can have include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aryloxy group such as phenoxy group and benzyloxy group; a dialkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. [0072]
Each pair of the adjacent substituents R[0073] ¹⁷and R¹⁸, R¹⁹and R²⁰, R²¹and R²², and R²³and R²⁴may combine to form a 5-, 6- or 7-membered ring such as benzene ring or cyclohexane ring.
Specific preferred examples of the compound represented by formula (I) are set forth below, however, the present invention is not limited thereto. [0074]
In the light-emitting layer, these compounds may be used individually or, if desired, in combination of two or more thereof. [0075]
In the organic electroluminescent device of the present invention, an organic metal complex compound represented by formula (II) may be used as the host material of the light-emitting layer. An organic metal complex represented by the following formula (II-1), a mixed ligand complex represented by the following formula (II-2) and a binuclear metal complex represented by the following formula (II-3) are particularly preferred. [0076]
[Organic Metal Complex] [0077]
(wherein M[0078] ¹is a mono-, di- or trivalent metal, n, X²and the rings A and B have the same meanings as in formula (II));
[Mixed Ligand Complex] [0079]
(wherein M[0080] ²represents a trivalent metal, X²and the rings A and B have the same meanings as in formula (II), and L¹represents the following formula (II-2a), (II-2b) or (II-2c)):
(wherein Ar[0081] ¹¹to Ar¹⁵each represents an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocyclic group which may have a substituent, and Z²represents silicon or germanium); [Binuclear Metal Complex]
(wherein M[0082] ³and M³′ each represents a trivalent metal, X²and the rings A and B have the same meanings as in formula (II), X²′ rings A′ and B′ have the same meanings as X²and the rings A and B, respectively).
A plurality of the following structural moieties: [0083]
(in formula (II-3), the following structural moieties each present in a couple in one compound: [0084]
namely, the rings A, the rings B and X[0085] ²s (in the case of formula (II-3), the rings A, the rings A′, the rings B, the rings B′, X²s and X²'s), contained in one molecule of the compound represented by formula (II), (II-1), (II-2) or (II-3) may be the same or different. From the standpoint that the synthesis is facilitated, all of these are preferably the same.
Similarly, M[0086] ³and M³′ in the compound represented by formula (II-3) may be the same or different and from the standpoint that the synthesis is facilitated, both of these are preferably the same.
The ring A, the ring A′, the ring B and the ring B′ in the compounds represented by formula (II), (II-1), (II-2) or (II-3) each is preferably selected from the following rings. [0087]
[Ring A and Ring A′][0088]
5-Membered or 6-membered nitrogen-containing aromatic heterocyclic rings which may have a substituent. One or two 5- or 6-membered aromatic hydrocarbon ring or aromatic heterocyclic ring may be condensed to the ring to form a condensed ring. [0089]
[Ring B and ring B′][0090]
6-Membered aromatic hydrocarbon rings or aromatic heterocyclic rings, which may have a substituent. One or two 5- or 6-membered aromatic hydrocarbon ring or aromatic heterocyclic ring may be condensed to the ring to form a condensed ring. [0091]
The ring A, the ring A′, the ring B and the ring B′ in the compounds represented by formula (II), (II-1), (II-2) or (II-3) each is more preferably a monocyclic ring and particularly preferably a ring selected from the following rings. [0092]
[Ring A and Ring A′][0093]
Diazole ring, thiazole ring, oxazole ring, thiadiazole ring, oxadiazole ring, triazole ring, pyridine ring, diazine ring and triazine ring, which may have a substituent. [Ring B and Ring B′][0094]
Benzene ring, pyridine ring, diazine ring and triazine ring, which may have a substituent. [0095]
The ring A, the ring A′, the ring B and the ring B′ in the compounds represented by the formula (II), (II-1), (II-2) or (II-3) each is most preferably a ring selected from the following structural formulae: [0096]
[Ring A and Ring A′] [0097]
(wherein R[0098] ³¹to R³⁷each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group, an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, or each of the pairs R³¹and R³², R³¹and R³³, R³⁴and R³⁵, R³⁵and R³⁶, and R³⁶and R³⁷may combine with each other to form a ring).
[Ring B and Ring B′] [0099]
(wherein R[0100] ³⁸to R⁴¹each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group, an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocyclic group that may have a substituent, or each of the pairs R³⁸and R³⁹, R³⁹and R⁴⁰, and R⁴⁰and R⁴¹may combine with each other to form a ring).
In each structure of [Ring B and Ring B′] shown above, two bonds either may be bonded to either the oxygen atom or the atom X on the ring A or the ring A′ insofar as the definitions of the ring B and ring B′ structures in formulae (II) and (II-1) to (II-3) are satisfied. [0101]
R[0102] ³¹to R⁴¹each specifically represents a hydrogen atom; a halogen atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group or ethyl group; an aralkyl group such as benzyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; a cyano group; an amino group; an acyl group; a carboxyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group or ethoxy group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group or ethoxycarbonyl group; an aryloxy group such as phenoxy group or benzyloxy group; a dialkylamino group such as diethylamino group or diisopropylamino group; a diaralkylamino group such as dibenzylamino group or diphenethylamino group; an α-haloalkyl group such as trifluoromethyl group; a hydroxyl group; an aromatic hydrocarbon ring group such as phenyl group or naphthyl group, which may have a substituent; or an aromatic heterocyclic group such as thienyl group or pyridyl group, which may have a substituent.
Examples of the substituent which the aromatic hydrocarbon ring group and the aromatic heterocyclic group each can have include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aryloxy group such as phenoxy group and benzyloxy group; a dialkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. [0103]
Examples of the ring formed by combining each pair of the adjacent substituents R[0104] ³¹and R³², R³¹and R³³, R³⁴and R³⁵, R³⁵and R³⁶, R³⁶and R³⁷, R³⁸and R³⁹, R³⁹and R⁴⁰, and R⁴⁰and R⁴¹include a benzene ring and a cyclohexane ring.
R[0105] ³¹to R⁴¹each is preferably a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a haloalkyl group or an aromatic hydrocarbon group which may have a substituent, or each combine with the adjacent substituent to form a ring.
The metal M (M[0106] ¹, M², M³and M³′) in the compounds represented by formula (II), (II-1), (II-2) or (II-3) is not particularly limited insofar as the metal is selected from Groups 1, 2, 3, 12 and 13 of the periodic table, however, preferred examples thereof include zinc, aluminum, gallium, beryllium and magnesium.
Specific examples of the compounds represented by formula (II), (II-1), (II-2) or (II-3) are set forth below, however, the present invention is not limited thereto. [0107]
In the light-emitting layer, these compounds may be used individually as a main component or, if desired, may be used in combination. [0108]
In the organic electroluminescent device of the present invention, the host material used in the light-emitting layer may be a compound having a group represented by formula (III) (structural formula shown below): [0109]
(wherein R[0110] ⁵¹to R⁵⁴each independently represents a hydrogen atom or an arbitrary substituent, each of the pairs R⁵¹and R⁵², and R⁵³and R⁵⁴may combine to form a ring, and X³represents an oxygen atom or a sulfur atom).
Examples of the ring formed by combining each of the pairs R[0111] ⁵¹and R⁵², and R⁵³and R⁵⁴include a benzene ring and a cyclohexane ring.
R[0112] ⁵¹to R⁵⁴each specifically represents a hydrogen atom; a halogen atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group or ethyl group; an aralkyl group such as benzyl group; an alkenyl group such as vinyl group; a cyano group; an amino group; an acyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group or ethoxy group; an alkoxycarbonyl group having from 1 to 6 carbon atoms such as methoxycarbonyl group or ethoxycarbonyl group; an aryloxy group such as phenoxy group or benzyloxy group; a dialkylamino group such as diethylamino group or diisopropylamino group; a diaralkylamino group such as dibenzylamino group or diphenethylamino group; an a-haloalkyl group such as trifluoromethyl group; a hydroxyl group; an aromatic hydrocarbon ring group such as phenyl group or naphthyl group, which may have a substituent; or an aromatic heterocyclic group such as thienyl group or pyridyl group, which may have a substituent. Examples of the substituent include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group such as vinyl group; an alkoxycarbonyl group having from 1 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aryloxy group such as phenoxy group and benzyloxy group; a dialkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. Among these substituents, the alkyl, alkoxy or alkoxycarbonyl group having from 1 to 6 carbon atoms may be liner and branched. The same applies to the substituents exemplified below.
Specific preferred examples of the group represented by formula (III) are set forth below, however, the present invention is not limited thereto. [0113]
The compound having a group represented by formula (III) may be a low molecular compound or a polymer compound. In the case of a polymer compound, the group may be contained in the main chain or may be contained as a side chain. [0114]
This compound is preferably a low molecular compound having a molecular weight of approximately from 400 to 1,200. In the compound having a group represented by formula (III), the total number of rings as the entire compound is preferably from 6 to 20, more preferably from 7 to 18. The compound having a group represented by formula (III) is preferably a compound having from 2 to 3 units represented by formula (III) within the molecule. [0115]
In particular, the group represented by formula (III) is preferably (S-1) or (S-2). [0116]
The compound having a group represented by formula (III) is preferably a compound represented by the following formula (III-1) or (III-2): [0117]
(wherein R[0118] ⁵⁵to R⁶²each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an α-haloalkyl group, a hydroxyl group, or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the pairs R⁵⁵and R⁵⁶, R⁵⁷and R⁵⁸, R⁵⁹and R⁶⁰, and R⁶¹and R⁶²may combine with each other to form a ring, X⁴and X⁵each independently represents an oxygen group or a sulfur group, and Q¹represents a divalent linking group comprising an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent);
(wherein R[0119] ⁶³to R⁷⁴each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an α-haloalkyl group, a hydroxyl group, or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the adjacent substituents R⁶³and R⁶⁴, R⁶⁵and R⁶⁶, R⁶⁷and R⁶⁸, R⁶⁹and R⁷⁰, R⁷¹and R⁷², R⁷³and R⁷⁴may combine to form a ring, X⁶to X⁸each independently represents an oxygen atom or a sulfur atom, and Q²represents a trivalent linking group comprising an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent).
In formula (III-1), R[0120] ⁵⁵to R⁶²each independently represents a hydrogen atom; a halogen atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group or ethyl group; an aralkyl group such as benzyl group; an alkenyl group such as vinyl group; a cyano group; an amino group; an acyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group or ethoxy group; an alkoxycarbonyl group having from 1 to 6 carbon atoms such as methoxycarbonyl group or ethoxycarbonyl group; an aryloxy group such as phenoxy group or benzyloxy group; a dialkylamino group such as diethylamino group or diisopropylamino group; a diaralkylamino group such as dibenzylamino group or diphenethylamino group; an α-haloalkyl group such as trifluoromethyl group; a hydroxyl group; an aromatic hydrocarbon ring group such as phenyl group or naphthyl group, which may have a substituent; or an aromatic heterocyclic group such as thienyl group or pyridyl group, which may have a substituent. Examples of the substituent include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group such as vinyl group; an alkoxycarbonyl group having from 1 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aryloxy group such as phenoxy group and benzyloxy group; a dialkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. Each of the pairs R⁵⁵and R⁵⁶, R⁵⁷and R⁵⁸, R⁵⁹and R⁶⁰and R⁶¹and R⁶²may combine with each other to form a benzene ring or a cyclohexane group. X⁴and X⁵each independently represents an oxygen group or a sulfur group. Q¹represents a divalent linking group comprising an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent. Preferred examples of the linking group Q¹are set forth below.
Among these, the linking group Q[0121] ¹is preferably (A-2), (A-6), (A-8), (A-10) or (A-12). The compound is most preferably a compound having this linking group Q¹and having the ring structure (S-1) or (S-2).

Specific preferred examples of the compound represented by formula (III-1) are shown in Table 1, however, the present invention is not limited thereto.

TABLE 1

Compound	R⁵⁵-R⁵⁸,	R⁵⁹-R⁶²,	Linking
Number	Substituted Moiety	Substituted Moiety	group Q¹

(H-101)	(S-1)	(S-1)	(A-1)
(H-102)	(S-2)	(S-2)	(A-1)
(H-103)	(S-1)	(S-1)	(A-2)
(H-104)	(S-2)	(S-2)	(A-2)
(H-105)	(S-3)	(S-3)	(A-2)
(H-106)	(S-1)	(S-2)	(A-2)
(H-107)	(S-4)	(S-4)	(A-2)
(H-108)	(S-5)	(S-5)	(A-2)
(H-109)	(S-6)	(S-6)	(A-2)
(H-110)	(S-7)	(S-7)	(A-2)
(H-111)	(S-8)	(S-8)	(A-2)
(H-112)	(S-2)	(S-9)	(A-2)
(H-113)	(S-10)	(S-10)	(A-2)
(H-114)	(S-11)	(S-11)	(A-2)
(H-115)	(S-12)	(S-12)	(A-2)
(H-116)	(S-13)	(S-13)	(A-2)
(H-117)	(S-13)	(S-2)	(A-2)
(H-118)	(S-14)	(S-14)	(A-2)
(H-119)	(S-13)	(S-14)	(A-2)
(H-120)	(S-15)	(S-15)	(A-2)
(H-121)	(S-2)	(S-16)	(A-2)
(H-122)	(S-16)	(S-16)	(A-2)
(H-123)	(S-1)	(S-1)	(A-3)
(H-124)	(S-2)	(S-2)	(A-3)
(H-125)	(S-1)	(S-1)	(A-4)
(H-126)	(S-2)	(S-2)	(A-4)
(H-127)	(S-2)	(S-2)	(A-5)
(H-128)	(S-1)	(S-1)	(A-6)
(H-129)	(S-2)	(S-2)	(A-6)
(H-130)	(S-3)	(S-3)	(A-6)
(H-131)	(S-1)	(S-1)	(A-7)
(H-132)	(S-2)	(S-2)	(A-7)
(H-133)	(S-1)	(S-1)	(A-8)
(H-134)	(S-2)	(S-2)	(A-8)
(H-135)	(S-3)	(S-3)	(A-8)
(H-136)	(S-1)	(S-1)	(A-9)
(H-137)	(S-2)	(S-2)	(A-9)
(H-138)	(S-1)	(S-1)	(A-10)
(H-139)	(S-2)	(S-2)	(A-10)
(H-140)	(S-1)	(S-2)	(A-10)
(H-141)	(S-3)	(S-3)	(A-10)
(H-142)	(S-4)	(S-4)	(A-10)
(H-143)	(S-7)	(S-7)	(A-10)
(H-144)	(S-10)	(S-10)	(A-10)
(H-145)	(S-13)	(S-13)	(A-10)
(H-146)	(S-14)	(S-14)	(A-10)
(H-147)	(S-1)	(S-2)	(A-11)
(H-148)	(S-2)	(S-2)	(A-11)
(H-149)	(S-1)	(S-1)	(A-12)
(H-150)	(S-2)	(S-2)	(A-12)
(H-151)	(S-2)	(S-2)	(A-13)
(H-152)	(S-2)	(S-2)	(A-14)
(H-153)	(S-2)	(S-2)	(A-15)
(H-154)	(S-1)	(S-1)	(A-16)
(H-155)	(S-2)	(S-2)	(A-17)

In formula (III-2), R[0123] ⁶³to R⁷⁴each independently represents a hydrogen atom; a halogen atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group or ethyl group; an aralkyl group such as benzyl group; an alkenyl group such as vinyl group; a cyano group; an amino group; an acyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group or ethoxy group; an alkoxycarbonyl group having from 1 to 6 carbon atoms such as methoxycarbonyl group or ethoxycarbonyl group; an aryloxy group such as phenoxy group or benzyloxy group; a dialkylamino group such as diethylamino group or diisopropylamino group; a diaralkylamino group such as dibenzylamino group or diphenethylamino group; an α-haloalkyl group such as trifluoromethyl group; a hydroxyl group; an aromatic hydrocarbon ring group such as phenyl group or naphthyl group, which may have a substituent; or an aromatic heterocyclic group such as thienyl group or pyridyl group, which may have a substituent. Examples of the substituent include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group such as vinyl group; an alkoxycarbonyl group having from 1 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aryloxy group such as phenoxy group and benzyloxy group; a dialkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. Each of the pairs R⁶³and R⁶⁴, R⁶⁵and R⁶⁶, R⁶⁷and R⁶⁸, R⁶⁹and R⁷⁰, R⁷¹and R⁷², and R⁷³and R⁷⁴may combine with each other to form a benzene ring or a cyclohexane group. X⁶to X⁸each independently represents an oxygen group or a sulfur group, and Q²represents a trivalent linking group comprising an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent. Preferred examples of the linking group Q are set forth below.
Among these, the linking group Q[0124] ²is preferably (B-1), (B-2) or (B-7). The compound is most preferably a compound having this linking group and having the ring structure (S-1) or (S-2).

Specific preferred examples of the compound represented by formula (III-2) are shown in Table 2, however, the present invention is not limited thereto.

TABLE 2

	R⁶³-R⁶⁶,	R⁶⁷-R⁷⁰,	R⁷¹-R⁷⁴,
Compound	Substituted	Substituted	Substituted	Linking
No.	Moiety	Moiety	Moiety	Group Q²

(H-201)	(S-1)	(S-1)	(S-1)	(B-1)
(H-202)	(S-2)	(S-2)	(S-2)	(B-1)
(H-203)	(S-1)	(S-1)	(S-1)	(B-2)
(H-204)	(S-2)	(S-2)	(S-2)	(B-2)
(H-205)	(S-3)	(S-3)	(S-3)	(B-2)
(H-206)	(S-1)	(S-1)	(S-2)	(B-2)
(H-207)	(S-4)	(S-4)	(S-4)	(B-2)
(H-208)	(S-13)	(S-13)	(S-13)	(B-2)
(H-209)	(S-14)	(S-14)	(S-14)	(B-2)
(H-210)	(S-15)	(S-15)	(S-15)	(B-2)
(H-211)	(S-16)	(S-16)	(S-16)	(B-2)
(H-212)	(S-1)	(S-1)	(S-1)	(B-3)
(H-213)	(S-2)	(S-2)	(S-2)	(B-3)
(H-214)	(S-1)	(S-1)	(S-1)	(B-4)
(H-215)	(S-13)	(S-13)	(S-13)	(B-4)
(H-216)	(S-1)	(S-1)	(S-1)	(B-5)
(H-217)	(S-2)	(S-2)	(S-2)	(B-5)
(H-218)	(S-2)	(S-2)	(S-2)	(B-6)
(H-219)	(S-4)	(S-4)	(S-4)	(B-6)
(H-220)	(S-1)	(S-1)	(S-1)	(B-7)
(H-221)	(S-2)	(S-2)	(S-2)	(B-7)
(H-222)	(S-3)	(S-3)	(S-3)	(B-7)
(H-223)	(S-7)	(S-7)	(S-7)	(B-7)
(H-224)	(S-1)	(S-2)	(S-2)	(B-7)
(H-225)	(S-10)	(S-10)	(S-10)	(B-7)
(H-226)	(S-13)	(S-13)	(S-13)	(B-7)
(H-227)	(S-14)	(S-14)	(S-14)	(B-7)
(H-228)	(S-15)	(S-15)	(S-15)	(B-7)
(H-229)	(S-16)	(S-16)	(S-16)	(B-7)
(H-230)	(S-1)	(S-1)	(S-1)	(B-8)
(H-231)	(S-2)	(S-2)	(S-2)	(B-8)
(H-232)	(S-1)	(S-1)	(S-1)	(B-9)
(H-233)	(S-2)	(S-2)	(S-2)	(B-9)
(H-234)	(S-1)	(S-1)	(S-1)	(B-10)
(H-235)	(S-2)	(S-2)	(S-2)	(B-10)
(H-236)	(S-13)	(S-13)	(S-13)	(B-10)
(H-237)	(S-14)	(S-14)	(S-14)	(B-10)

In the light-emitting layer, only one compound having a group represented by formula (III) may be contained or two or more thereof may be contained. [0126]
In addition to formulae (I) to (III), the host material which can be used includes the following compounds. [0127]
For the host material, a plurality of compounds which can be represented by the same formula may be used in combination as described above, or compounds which cannot be represented by the same formula may also be used in combination. [0128]
In the organic electroluminescent device of the present invention, the host material of the light-emitting layer is most preferably the compound represented by formula (I). [0129]
The constituent element (2) of the present invention, namely, Compound A capable of phosphorescence emission at room temperature is described below. [0130]
Compound A preferably has an excited triplet level lying between the excited triplet level of the host material and the excited triplet level (when Compound B is a phosphorescent compound) or excited singlet level (when Compound B is a fluorescent compound) of Compound B which is described later. [0131]
In view of the structure, an organic metal complex containing a metal selected from [0132] Groups 7 to 11 of the periodic table is preferred.
From the standpoint that the charge transfer between the center metal and the ligand readily occurs, the metal is preferably a metal of the fifth or sixth period of the periodic table. Specific examples thereof include ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum and gold. [0133]
Examples of the complex thereof include the compounds represented by the following formula (IV): [0134]
(wherein the ring D represents an aromatic hydrocarbon ring which may have a substituent or an aromatic heterocyclic ring which may have a substituent, the ring E represents a nitrogen-containing aromatic heterocyclic ring which may have a substituent, a group on the ring D and a group on the ring E may combine to form a ring condensed to these rings, M[0135] ⁴represents a metal selected from Groups 7 to 11 of the periodic table, L²represents an arbitrary bidentate ligand, m represents a valence number of M⁴, and k represents an integer satisfying 0≦k<m).
In the ligand [0136]
the ring D represents an aromatic hydrocarbon ring or aromatic heterocyclic ring which may have a substituent, preferably a phenyl group, a naphthyl group, an anthryl group, a thienyl group, a pyridyl group, a furyl group, a benzothienyl group, a benzofuryl group, a quinolyl group or an isoquinolyl group. [0137]
Examples of the substituent which these aromatic hydrocarbon ring group and aromatic heterocyclic group may have include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aromatic hydrocarbon ring group such as phenyl group and naphthyl group; an aryloxy group such as phenoxy group and benzyloxy group; a dialkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. [0138]
The ring E represents a nitrogen-containing aromatic heterocyclic group, preferably a pyridyl group, a pyrimidyl group, a pyrazine group, a triazine group, a benzothiazole group, a benzoxazole group, a benzimidazole, a quinolyl group, an isoquinolyl group, a quinoxaline group or phenanthridine group, which may have a substituent. [0139]
Examples of the substituent which this aromatic heterocyclic group may have include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aromatic hydrocarbon ring group such as phenyl group and naphthyl group; an aryloxy group such as phenoxy group and benzyloxy group; a dialkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. [0140]
The substituent of the ring D and the substituent of the ring E may combine to form one condensed ring as a whole. Examples of the condensed ring include 7,8-benzoquinoline. [0141]
More preferred examples of the substituent of the ring D and the ring E include an alkyl group, an alkoxy group, an aromatic hydrocarbon ring group and a cyano group. [0142]
Examples of the ligand [0143]
include the following structures, however, the present invention is not limited thereto. In the following examples, the substituents in the ring D and the ring E are omitted but, as described above, these rings each may have a substituent. [0144]
The arbitrary bidentate ligand L[0145] ²in formula (IV) is not particularly limited insofar as it is a monovalent bidentate ligand, however, when the steric hindrance is considered, the ligand is preferably not so bulky and examples thereof include the following ligands.
(wherein R, R′, R″ and R′″ each independently represents an alkyl group having from 1 to 4 carbon atoms or a haloalkyl group having from 1 to 4 carbon atoms, and the substituents in the aromatic hydrocarbon ring and the aromatic heterocyclic ring are omitted.) [0146]
Among the ligands L[0147] ², the following ligands are particularly preferred.
As long as the valence number of the center metal M[0148] ⁴in formula (IV) is satisfied, any combination of the ligand containing the ring D and the ring E with the arbitrary ligand L²may be used and how many ligands may be coordinated, however, the compound represented by the following formula (IV-1) or (IV-2) is preferred:
(wherein the rings D[0149] ¹and D²have the same meanings as the ring D in formula (IV), the rings E¹and E²have the same meanings as the ring E in formula (IV), M⁵and M⁶have the same meanings as M⁴in formula (IV) and m has the same meaning as in formula (IV)).
Specific examples of the phosphorescent Compound A represented by formula (IV) are set forth below, however, the present invention is not limited thereto. [0150]
For Compound B, an organic metal complex represented by the following formula (V) can be used in addition to the organic metal complex represented by formula (IV). [0151]
(wherein R[0152] ⁸¹to R⁹²each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the pairs R⁸¹and R⁸², R⁸⁴and R⁸⁵, R⁸⁷and R⁸⁸, and R⁹⁰and R⁹¹may combine with each other to form a ring, M⁷represents a metal selected from Groups 7 to 11 of the periodic table, X⁹to X¹²each represents carbon or nitrogen, provided that when any one of X⁹to X¹²is a nitrogen atom, R⁸³, R⁸⁶, R⁸⁹or R⁹²bonded to the nitrogen atom is absent).
Similarly to M[0153] ⁵and M⁶in formulae (IV-1) and (IV-2), M⁷in formula (V) is preferably a metal of the fifth or sixth period of the periodic table. Specific examples thereof include ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum and gold. Among these, preferred are divalent metals such as platinum and palladium.
Specific examples of the organic metal complex represented by formula (V) are set forth below, however, the present invention is not limited thereto. [0154]
The constituent element (3) of the present invention, that is, Compound B capable of phosphorescence emission or fluorescence emission at room temperature is described below. [0155]
The case where Compound B is a phosphorescent compound is described below. [0156]
The organic electroluminescent device of the present invention is characterized in that Compound A fills the role of sensitizer in the light-emitting layer and therefore, the light emission attributable to Compound B is intensified. Accordingly, it is important that the phosphorescent Compound B has an excited triplet level in the energy state lower than the excited triplet level of the phosphorescent Compound A. [0157]
Examples of the phosphorescent Compound B include the same compounds as described above for Compound A. Among those, a compound having an energy level satisfying the above-described relationship with Compound A is preferably selected. [0158]
In view of the energy transfer, at least one complex containing iridium is preferably contained as Compound A or B. In particular, it is preferred to contain at least one iridium complex as Compound A and also at least one iridium complex as Compound B or to contain at least one iridium complex as either one of Compound A and Compound B and contain at least one platinum complex as the other compound. [0159]
As described above, in order to realize the smooth energy transfer from Compound A to Compound B, it is important that the maximum light emission wavelength of Compound B is longer than the maximum light emission wavelength of Compound A. The term “the maximum light emission wavelength of Compound A” means the maximum light emission wavelength at a phosphorescence emission spectrum of Compound A. The term “the maximum light emission wavelength of Compound B” means the maximum light emission wavelength at a phosphorescence emission spectrum when Compound B is a phosphorescent compound, and the maximum light emission wavelength at a fluorescence emission spectrum when Compound B is a fluorescent compound. [0160]
The conditions for measuring the maximum emission wavelength of Compound A or Compound B are not particularly limited, the maximum emission wavelength of Compound A and Compound B may be measured under the same conditions and the thus obtained value for Compound A may be compared with that for Compound B. For example, Compound A is compared with Compound B with respect to light emission spectra of solutions dissolving Compound A or B in the same solvent, single-layer films made from each compound alone, organic electroluminescent devices having the same structure except for doping each compound to the light-emitting layer, or the like. [0161]
The case where Compound B is a fluorescent compound is described below. [0162]
In the organic electroluminescent device of the present invention, for letting Compound A to fill the role of sensitizer in the light-emitting layer, it is important, as described above, that the fluorescent Compound B has an excited singlet level in the energy state lower than the excited triplet level of Compound A. Examples of the fluorescent Compound B include compounds which present blue light emission, such as perylene, pyrene, anthracene and derivatives thereof; compounds which present green light emission, such as quinacridone derivatives and coumarin derivatives; compounds which present yellow light emission, such as rubrene and perimidone derivatives; and compounds which present red light emission, such as coumarin derivatives, benzopyran derivatives, rhodamine derivatives, phenoxazone derivatives, benzothioxanthene derivatives and azabenzothioxanthene. [0163]
In addition to these fluorescent compounds, the fluorescent compounds described in [0164] Laser Kenkyu (Laser Research), Vol. 8, pages 694, 803 and 958 (1980); and ibid., Vol. 9, page 85 (1981) can be used as the fluorescent Compound B according to host material and the phosphorescent Compound A.
Among these, the fluorescent compounds of presenting green light emission, yellow light emission or red light emission are preferred. [0165]
The construction of the organic electroluminescent device of the present invention is described below by referring to the drawings, however, the present invention is not limited thereto. [0166]
FIGS. [0167] 1 to 3 each is a sectional view schematically showing an embodiment of the organic electroluminescent device of the present invention, where 1 denotes a substrate, 2 denotes an anode, 3 denotes an anode buffer layer, 4 denotes a hole-transporting layer, 5 denotes a light-emitting layer, 6 denotes a hole-blocking layer, 7 denotes an electron-transporting layer and 8 denotes a cathode. The construction is described mainly by referring to the device shown in FIG. 1.
The [0168] substrate 1 works out to a support of the organic electroluminescent device and for example, a plate of quartz or glass, a metal sheet or foil, or a plastic film or sheet is used therefor. Particularly, a glass plate or a transparent synthetic resin plate such as polyester, polymethacrylate, polycarbonate or polysulfone is preferred. In the case of using a synthetic resin substrate, it is necessary to take notice of the gas-barrier property. If the substrate has excessively low gas-barrier property, the organic electroluminescent device may disadvantageously deteriorate due to outside air passing through the substrate. Accordingly, a dense silicon oxide film or the like is provided at least on one surface of the synthetic resin substrate to ensure the gas-barrier property and this is one of the preferred methods.
On the [0169] substrate 1, an anode 2 is provided. The anode 2 fills the role of injecting holes into the hole-transporting layer 4. This anode 2 is generally composed of a metal such as aluminum, gold, silver, nickel, palladium or platinum, a metal oxide such as indium oxide and/or tin oxide, a metal halide such as copper iodide, a carbon black or an electrically conductive polymer such as poly(3-methyl thiophene), polypyrrole or polyaniline. The anode 2 is usually formed by sputtering or vacuum vapor deposition. In the case where a metal fine particle of silver, a fine particle of copper iodide, carbon black, an electrically conductive metal oxide fine particle or an electrically conductive polymer fine particle is used, the anode 2 can be formed by dispersing this in an appropriate binder resin solution and applying the dispersion solution on the substrate 1. Furthermore, in the case of using an electrically conductive polymer, the anode 2 can be provided by forming a thin film directly on the substrate 1 using electrolytic polymerization or by coating the electrically conductive polymer on the substrate 1 (see, Appl. Phys. Lett., Vol. 60, page 2711 (1992)).
The [0170] anode 2 may also be a stacked layer structure formed by stacking layers comprising different materials.
The thickness of the [0171] anode 2 varies depending on the required transparency. In the case where the transparency is necessary, the transmittance of visible ray is usually set to 60% or more, preferably 80% or more, and in this case, the thickness is usually from 5 to 1,000 nm, preferably on the order of 10 to 500 nm. In the case where the transparency is not required, the anode 2 may have substantially the same thickness as the substrate 1. On this anode 2, a different electrically conductive material can also be further stacked.
On the [0172] anode 2, a hole-transporting layer 4 is provided. The material for the hole-transporting layer 4 is required to ensure high efficiency in the hole injection from the anode 2 and efficient transportation of the injected holes. To satisfy these requirements, the material is required to have a small ionization potential, a high transparency to visible ray, a high hole mobility, excellent stability and difficulty of generating impurities serving as a trap during the production or use. Since the hole-transporting layer 4 contacts with the light-emitting layer 5, the material is also required not to quench the light emission from the light-emitting layer 5 or not to form an exciplex between the hole-transporting layer 4 and the light-emitting layer 5 and thereby reduce the efficiency. In addition to these general requirements, when an application to a display for the mounting on vehicles is considered, since the device is further required to have heat resistance, the material preferably has a Tg of 75° C. or more, more preferably 85° C. or more.
Examples of the hole-transporting material include aromatic diamines containing two or more tertiary amines and having two or more condensed aromatic rings substituted to nitrogen atoms, represented by 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (see, JP-A-5-234681); aromatic amine compounds having a star burst structure, such as 4,4′,4″-tris(1-naphthylphenylamino)triphenylamine (see, [0173] J. Lumin., Vol. 72-74, page 985 (1997)); aromatic amine compounds comprising a tetramer of triphenylamine (see, Chem. Commun., page 2175 (1996)); and spiro compounds such as 2,2′,7,7′-tetrakis(diphenylamino)-9,9′-spirobifluorene (see, Synth. Metals, Vol. 91, page 209 (1997)). These compounds may be used individually or, if desired, in combination.
In addition to the above-described compounds, examples of the material for the hole-transporting [0174] layer 4 include polymer materials such as polyvinylcarbazole, polyvinyltriphenylamine (see, JP-A-7-53953), polyarylene ether sulfone containing tetraphenylbenzidine (see, Polym. Adv. Tech., Vol. 7, page 33 (1996)).
In the case of forming the hole-transporting [0175] layer 4 by the coating method, one or more hole-transporting material is, if desired, after adding additives which do not become a trap for the holes, such as binder resin and coatability improving agent, dissolved to prepare a coating solution and the coating solution is coated on the anode 2 by spin coating or the like and dried to form the hole-transporting layer 4. Examples of the binder resin include polycarbonate, polyarylate and polyester. If the amount of the binder resin added is large, the hole mobility is reduced. Therefore, the amount added thereof is preferably as low as possible and in terms of the content in the hole-transporting layer 4, preferably 50% by weight or less.
In the case of forming the hole-transporting [0176] layer 4 by the vacuum vapor deposition method, the hole-transport material is placed in a crucible disposed within a vacuum container, the inside of the vacuum chamber is evacuated to about 10⁻⁴Pa by an appropriate vacuum pump and then the crucible is heated to evaporate the hole-transport material, whereby the hole-transporting layer 4 is formed on the substrate 1 having formed thereon the anode 2 and being disposed to face the crucible.
The thickness of the hole-transporting [0177] layer 4 is usually from 5 to 300 nm, preferably from 10 to 100 nm. In order to uniformly form such a thin film, the vacuum vapor deposition method is generally used in many cases.
On the hole-transporting [0178] layer 4, the light-emitting layer 5 is provided. The light-emitting layer 5 comprises at least (1) a host material having electron-transporting property or hole-transporting property, (2) Compound A capable of phosphorescence emission at room temperature and (3) Compound B capable of phosphorescence emission or fluorescence emission at room temperature. Between the electrodes applied with an electric field, a hole injected from the anode 2 and transferring through the hole-transporting layer 4 and an electron injected from the cathode 8 and transferring through the hole-blocking layer 6 are recombined and thereby the light-emitting layer is excited and emits strong light. The maximum light emission wavelength in the light emission spectrum is attributable to the above-described Compound B.
The light-emitting [0179] layer 5 may contain components other than the above-described (1) to (3) within the range of not impairing the performance of the present invention.
The content of Compound A capable of phosphorescence emission is preferably from 0.1 to 30% by weight based on the entire light-emitting layer. If the content is less than 0.1% by weight, Compound A may fail in sufficiently contributing to the improvement of light emission efficiency of the device, whereas if it exceeds 30% by weight, concentration quenching may occur to cause reduction of the light emission efficiency. [0180]
In the case of using a compound capable of phosphorescence emission as Compound B, the content thereof is also preferably from 0.1 to 30% by weight based on the entire light-emitting layer but more preferably, the total amount of Compounds A and B is from 0.1 to 30% by weight based on the entire light-emitting layer. In view of the energy transfer, the ratio of Compound B to Compound A (compound B)/(compound A) is preferably from 0.3 to 3 (molar ratio). [0181]
In the case of using a compound capable of fluorescence emission as Compound B, the content thereof is preferably from 0.05 to 10% by weight, more preferably from 0.05 to 2% by weight, based on the entire light-emitting layer. [0182]
Compound A and Compound B may be uniformly distributed within the light-emitting layer or may be non-uniformly present by having a distribution in the film thickness direction. [0183]
The thickness of the light-emitting [0184] layer 5 is usually from 10 to 200 nm, preferably from 20 to 100 nm. This thin film is formed by the same method as the hole-transporting layer 4.
The hole-[0185] blocking layer 6 is stacked on the light-emitting layer 5 to come into contact with the interface of the light-emitting layer 5 in the cathode side and fills the role of inhibiting the holes transferring from the hole-transporting layer 4, from reaching the cathode 8. The hole-blocking layer 6 is formed of a compound capable of transporting the electrons injected from the cathode 8 toward the direction of the light-emitting layer 5 with good efficiency. The material constituting the hole-blocking layer 6 is required to have high electron mobility and low hole mobility. The hole-blocking layer 6 has a function of enclosing holes and electrons within the light-emitting layer 5 and thereby improving the light emission efficiency.
Preferred examples of the hole-blocking material satisfying these requirements include mixed ligand complexes represented by the following formula (VI): [0186]
(wherein R[0187] ¹⁰¹to R¹⁰⁶each represents a hydrogen atoms or an arbitrary substituent, Q³represents a metal atom selected from aluminum, gallium and indium, and Y¹is represented by any one of the following formulae (VI-1), (VI-2) and (VI-3):
(wherein Ar[0188] ²¹to Ar²⁵each represents an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocyclic group which may have a substituent, and Y²represents silicon or germanium).
In formula (VI), R[0189] ¹⁰¹to R¹⁰⁶each independently represents a hydrogen atom or an arbitrary substituent, preferably a hydrogen atom; a halogen atom such as chlorine or bromine; an alkyl group having from 1 to 6 carbon atoms such as methyl group or ethyl group; an aralkyl group such as benzyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; a cyano group; an amino group; an acyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group or ethoxy group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group or ethoxycarbonyl group; a carboxyl group; an aryloxy group such as phenoxy group or benzyloxy group; an alkylamino group such as diethylamino group or diisopropylamino group; an aralkylamino group such as dibenzylamino group or diphenethylamino group; a haloalkyl group such as trifluoromethyl group; a hydroxyl group; an aromatic hydrocarbon ring group such as phenyl group or naphthyl group, which may have a substituent; or an aromatic heterocyclic group such as thienyl group or pyridyl group, which may have a substituent.
Examples of the substituent which these aromatic hydrocarbon ring group and aromatic heterocyclic group can have include a halogen atom such as fluorine atom; an alkyl group having from 1 to 6 carbon atoms such as methyl group and ethyl group; an alkenyl group having from 2 to 6 carbon atoms such as vinyl group; an alkoxycarbonyl group having from 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; an alkoxy group having from 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aryloxy group such as phenoxy group and benzyloxy group; an alkylamino group such as dimethylamino group and diethylamino group; an acyl group such as acetyl group; a haloalkyl group such as trifluoromethyl group; and a cyano group. [0190]
R[0191] ¹⁰¹to R¹⁰⁶each is more preferably a hydrogen atom, an alkyl group, a halogen atom or a cyano group. R¹⁰⁴is particularly preferably a cyano group.
Specific examples of Ar[0192] ²¹to Ar²⁵in formula (VI) include an aromatic hydrocarbon ring group such as phenyl group, biphenyl group and naphthyl group, which may have a substituent, and an aromatic heterocyclic group such as thienyl group and pyridyl group. Among these, preferred are those resulting from condensation of two or three 5-membered rings, 6-membered rings or 5-membered and/or 6-membered rings, or those resulting from direct bonding of two or more of these rings. Between the aromatic hydrocarbon ring group and the aromatic heterocyclic group, the aromatic hydrocarbon ring group is preferred.
Examples of the substituent which Ar to Ar can have include the same groups as described above for the substituent of the aromatic hydrocarbon ring group or aromatic heterocyclic group represented by, for example, R[0193] ¹⁰¹to R¹⁰⁶.
Specific preferred examples of the compound represented by formula (VI) are set forth below, however, the present invention is not limited thereto. [0194]

Claims

What is claimed is:

1. An organic electroluminescent device comprising a substrate having thereon a light-emitting layer sandwiched by an anode and a cathode, wherein said light-emitting layer comprises at least:

(1) a host material having electron-transporting or hole-transporting property,

(2) Compound A capable of phosphorescence emission at room temperature, and

and the maximum light emission wavelength of said device is attributable to said (3).

2. The organic electroluminescent device as claimed in claim 1, wherein Compound A is an organic metal complex containing a metal selected from Groups 7 to 11 of the periodic table.

3. The organic electroluminescent device as claimed in claim 1, wherein Compound B is an organic metal complex of presenting phosphorescence emission at room temperature and containing a metal selected from Groups 7 to 11 of the periodic table.

4. The organic electroluminescent device as claimed in claim 2 or 3, wherein the metal of Groups 7 to 11 of the periodic table is selected from ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum and gold.

5. The organic electroluminescent device as claimed in claim 2 or 3, wherein the organic metal complex is a compound represented by the following formula (IV):

wherein the ring D represents an aromatic hydrocarbon ring which may have a substituent or an aromatic heterocyclic ring which may have a substituent, the ring E represents a nitrogen-containing aromatic heterocyclic ring which may have a substituent, a group on the ring D and a group on the ring E may combine to form a ring condensed to these rings, M⁴represents a metal selected from Groups 7 to 11 of the periodic table, L²represents an arbitrary bidentate ligand, m represents a valence number of M⁴, and k represents an integer satisfying 0·k<m.

6. The organic electroluminescent device as claimed in claim 2 or 3, wherein the organic metal complex is selected from the compounds represented by the following formula (IV-1) or (IV-2):

wherein M⁵and M⁶each represents a metal selected from Groups 7 to 11 of the periodic table, m represents a valence number of said metal, the rings D¹and D²each represents an aromatic hydrocarbon ring or aromatic heterocyclic ring which may have a substituent, the rings E¹and E²each represents a nitrogen-containing aromatic heterocyclic ring which may have a substituent, a substituent on the ring D¹and a substituent on the ring E¹may combine to form a ring condensed to these rings, or a substituent on the ring D²and a substituent on the ring E²may combine to form a ring condensed to these rings.

7. The organic electroluminescent device as claimed in claim 2 or 3, wherein the organic metal complex is selected from the compounds represented by the following formula (V):

wherein R⁸¹to R⁹²each represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the pairs R⁸¹and R⁸², R⁸⁴and R⁸⁵, R⁸⁷and R⁸⁸, and R⁹⁰and R⁹¹may combine with each other to form a ring, M⁷represents a metal selected from Groups 7 to 11 of the periodic table, X⁹to X¹²each represents carbon or nitrogen, provided that when any one of X⁹to X¹²is a nitrogen atom, R⁸³, R⁸⁶, R⁸⁹or R⁹²bonded to said nitrogen atom is absent.

8. The organic electroluminescent device as claimed in claim 1, which contains an iridium complex as Compound A and/or Compound B.

9. The organic electroluminescent device as claimed in claim 1, which contains at least one iridium complex and at least one platinum complex, one as Compound A and the other as Compound B.

10. The organic electroluminescent device as claimed in claim 1, which contains one iridium complex as Compound A and one iridium complex as Compound B.

11. The organic electroluminescent device as claimed in claim 1, wherein the host material is a compound represented by the following formula (I):

wherein the carbazolyl group and the phenylene group each may have an arbitrary substituent, and Z¹represents a direct bond or a divalent linking group.

12. The organic electroluminescent device as claimed in claim 10, wherein the compound represented by formula (I) is represented by the following formula (I-1):

wherein R¹to R¹⁶each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the adjacent substituents R¹and R², R³and R⁴, R⁵and R⁶, R⁷and R⁸, R⁹and R¹⁰, R¹¹and R¹², R¹³and R¹⁴, and R¹⁵and R¹⁶may combine to form a ring, and Z¹represents a direct bond or a divalent linking group.

13. The organic electroluminescent device as claimed in claim 10, wherein in formula (I), Z¹is a direct bond, an oxygen atom, a sulfur atom, a linking group shown below:

a divalent aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, or any one of the following linking groups:

any benzene ring moiety in the each structure may have an arbitrary substituent, and Ar¹to Ar⁶each represents an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent or a group represented by the following formula (I-2):

wherein the carbazolyl group and the phenylene group each may have an arbitrary substituent.

14. The organic electroluminescent device as claimed in claim 12, wherein the group represented by formula (1-2) is a group represented by the following formula (1-3):

wherein R¹⁷to R²⁴each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group which may have a substituent, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group, or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the pairs R¹⁷and R¹⁸, R¹⁹and R²⁰, R²¹and R²², and R²³and R²⁴may combine with each other to form a ring.

15. The organic electroluminescent device as claimed in claim 1, wherein the host material is a compound represented by the following formula (II):

wherein M represents a metal selected from Groups 1, 2, 3, 12 and 13 of the periodic table, n represents a valence number of said metal, L represents an arbitrary substituent, j represents a number of the substituent L and is 0 or 1, X²represents a carbon atom or a nitrogen atom, the ring A represents a nitrogen-containing heterocyclic ring and may have a substituent, and the ring B represents an aromatic hydrocarbon ring group or an aromatic heterocyclic group and may have a substituent.

16. The organic electroluminescent device as claimed in claim 14, wherein the compound represented by formula (IT) is represented by any one of the following formulae (II-1), (II-2) and (II-3):

[Organic Metal Complex]

wherein M¹is a mono-, di- or trivalent metal, n, X²and the rings A and B have the same meanings as in formula (II);

[Mixed Ligand Complex]

wherein M²represents a trivalent metal, X²and the rings A and B have the same meanings as in formula (II), and L¹represents the following formula (II-2a), (II-2b) or (II-2c):

wherein Ar¹¹to Ar¹⁵each represents an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocyclic group which may have a substituent, and Z²represents silicon or germanium;

[Binuclear Metal Complex]

wherein M³and M³, each represents a trivalent metal, X²and the rings A and B have the same meanings as in formula (II), X²′ and the rings A′ and B′ have the same meanings as X²and the rings A and B, respectively.

17. The organic electroluminescent device as claimed 3in claim 1, wherein a host material is a compound having a group represented by the following formula (III):

wherein R⁵¹to R⁵⁴each independently represents a hydrogen atom or an arbitrary substituent, each of the pairs R⁵¹and R⁵², and R⁵³and R⁵⁴may combine to form a ring, and X³represents an oxygen atom or a sulfur atom.

18. The organic electroluminescent device as claimed in claim 16, wherein the compound having a group represented by formula (III) has a molecular weight of approximately from 400 to 1,200.

19. The organic electroluminescent device as claimed in claim 16, wherein the compound represented by formula (III) is represented by the following formula (III-1) or (III-2):

wherein R⁵⁵to R⁶²each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an α-haloalkyl group, a hydroxyl group, or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the pairs R⁵⁵and R⁵⁶, R⁵⁷and R⁵⁸, R⁵⁹and R⁶⁰, and R⁶¹and R⁶²may combine with each other to form a ring, X⁴and X⁵each independently represents an oxygen group or a sulfur group, and Q¹represents a divalent linking group comprising an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent;

wherein R⁶³to R⁷⁴each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an α-haloalkyl group, a hydroxyl group, or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, each of the adjacent substituents R⁶³and R⁶⁴, R⁶⁵and R⁶⁶, R⁶⁷and R⁶⁸, R⁶⁹and R⁷⁰, R⁷¹and R⁷², R⁷³and R⁷⁴may combine to form a ring, X⁶to X⁸each independently represents an oxygen atom or a sulfur atom, and Q²represents a trivalent linking group comprising an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent.

20. The organic electroluminescent device as claimed in claim 1, wherein Compound B is a fluorescent compound of presenting green light emission, yellow light emission or red light emission.

21. The organic electroluminescent device as claimed in claim 1, which has a hole-blocking layer between said light-emitting layer and a cathode.