JP2005203293A - Luminescent material and organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a long driving life for an organic electroluminescent element which uses a luminescent material using a phosphorescent dopant material having an electron attracting group. <P>SOLUTION: This luminescent material is composed of a host material and the phosphorescent dopant material having the electron attracting group, and the features of this luminescent material is that the lowest unoccupied molecular orbital(LUMO)level is lower than the LUMO level of the dopant material, and the highest occupied molecular orbital(HOMO)level is lower than the HOM of the dopant material. This organic electroluminescent element uses the luminescent material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novel luminescent material and an organic electroluminescent device using the same, and more particularly to a luminescent material for achieving a long driving life.

  In recent years, as a thin film type electroluminescent (EL) element, an organic EL element using an organic thin film has been developed instead of using an inorganic material. In addition, as an attempt to increase the light emission efficiency of the organic EL element, use of phosphorescence (light emission by triplet excitons) instead of fluorescence (light emission by singlet excitons) has been studied. When phosphorescence is used, it is considered that the efficiency is about three times as high as that of an element using fluorescence, and it has been reported that a europium complex, a platinum complex, or the like is used.

  In Non-Patent Document 1, an iridium complex (T-1) having an electron-withdrawing group (fluorine atom) shown below is used as a dopant material, and a carbazole compound is used as a host material, whereby an element that emits blue light is obtained. It has been reported. However, the dopant material is accompanied by a decomposition reaction due to elimination of fluorine atoms during the reduction reaction. Therefore, since the durability against reduction (that is, electrons) is poor, it is unstable with respect to energization driving, and the light emitting layer using this has a problem that it is extremely disadvantageous with respect to driving life.

Appl. Phys. Lett., 79, 2082, 2001

  An object of the present invention is to increase the driving life of an organic electroluminescent device using a light emitting material using a phosphorescent dopant material having an electron withdrawing group.

As a result of intensive studies, the present inventors have found that the lowest unoccupied orbit (hereinafter abbreviated as LUMO) level of the host material is lower than the LUMO level of the dopant material and the highest occupied orbit (hereinafter referred to as HOMO) of the host material. It has been found that the above problem can be solved by using a light emitting material whose level is lower than the HOMO level of the dopant material.
The dopant material having an electron-withdrawing group shifts in a direction in which both the HOMO level and the LUMO level are lower than the dopant material having no electron-withdrawing group due to the introduction of the electron-withdrawing group.

Therefore, when an element is formed using a combination of a conventional host material and a dopant material having an electron withdrawing group as the light emitting layer, the HOMO level of the host material is higher than the HOMO level of the dopant material, and the LUMO level of the host material. The combination is higher than the LUMO level of the dopant material.
In the case where an element formed by such a combination emits light, holes injected into the light emitting layer are transported by the host material, and electrons injected into the light emitting layer are transported by the dopant material. However, as described above, the dopant material having an electron-withdrawing group is poor in durability against electrons, so that it is considered that the driving life is shortened.

  Therefore, it was considered that the problem that the dopant material must transport electrons can be improved by optimizing the HOMO level and the LUMO level of the host material and the dopant material, respectively. Usually, in the case of an organic electroluminescence device, the relationship between the HOMO level and LUMO level of the host material and the dopant material is such that the LUMO level of the host material is higher than the LUMO level of the dopant material and the HOMO level of the host material is It has been considered preferable that it is lower than the HOMO level of the dopant material (Japanese Patent No. 2814435). However, the present inventors dared to determine the length of the light emitting material using the dopant material having an electron-withdrawing group by defining the relationship between the HOMO level and the LUMO level of the host material and the dopant material as described above. Drive life can be achieved.

  That is, the present invention is a light-emitting material comprising a host material and a phosphorescent dopant material having an electron-withdrawing group, wherein the LUMO level of the host material is lower than the LUMO level of the dopant material, and the HOMO of the host material The present invention resides in a light-emitting material and an organic electroluminescent element using the light-emitting material, wherein the level is lower than the HOMO level of the dopant material.

  According to the present invention, a long driving life can be achieved in an organic electroluminescent device using a light emitting material using a phosphorescent dopant material having an electron attractive group.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.
The present invention is a light emitting material comprising a host material and a phosphorescent dopant material having an electron-withdrawing group, wherein the host material has a lowest orbital (hereinafter abbreviated as LUMO) level lower than the LUMO level of the dopant material. The host material has a highest occupied orbital (hereinafter abbreviated as HOMO) level lower than the HOMO level of the dopant material.

  That the LUMO level of the host material is lower than the LUMO level of the dopant material and the HOMO level of the host material is lower than the HOMO level of the dopant material means a state as shown in Table 1-1. That is, when the orbital level A is exactly larger than the orbital level B, it is defined that the orbital level A is lower than the orbital level B.

In order to produce an organic electroluminescence device having excellent driving stability, the HOMO level of the host material is preferably 0.05 V or more lower than the HOMO level of the dopant material, and more preferably 0.1 V or more. The LUMO level of the host material is preferably 0.05 V or more lower than the LUMO level of the dopant material, and more preferably 0.1 V or more.
As described in detail above, conventionally, as the light emitting material of the organic electroluminescent element, as shown in Table 2-1, the LUMO level of the host material is higher than the LUMO level of the dopant material, and the HOMO level of the host material. Is preferably lower than the HOMO level of the dopant material.

However, in the present invention, the light emitting material in which the LUMO level of the host material is lower than the LUMO level of the dopant material having an electron-withdrawing group and the HOMO level of the host material is lower than the HOMO level of the dopant material. By using this, it is possible to achieve a longer driving life of the element.
That is, by using the light emitting material, there can be a relationship in which the phosphorescent dopant material having an electron withdrawing group transports holes and the host material carries electrons in the light emitting layer of the device. Therefore, deterioration due to host oxidation or dopant reduction can be suppressed, and the device can have a long driving life.

The HOMO level and the LUMO level can be measured by electrochemical measurement as described below. Note that the supporting electrolyte, the solvent, and the electrode used for the measurement are not limited to these, and any material that can perform the same level of measurement may be used.
A glassy carbon electrode is used as a working electrode by dissolving about 0.1 to 2 mM of a material to be measured in an organic solvent containing about 0.1 mol / L of tetrabutylammonium perchlorate or tetrabutylammonium hexafluorophosphate as a supporting electrolyte. The oxidation (reduction) potential of the material is calculated by subjecting the platinum electrode as the counter electrode and electrolytic oxidation (reduction) as the working electrode, and comparing the potential with the oxidation-reduction potential of a reference substance such as ferrocene. As the organic solvent, an organic solvent such as acetonitrile, methylene chloride, and tetrahydrofuran, which dissolves the material well and is difficult to be electrolytically oxidized (reduced) by itself, and therefore can take a wide potential window. The oxidation potential calculated by this procedure corresponds to the HOMO level of the material, and the reduction potential corresponds to the LUMO level.

According to the organic electroluminescence device of the present invention, the host material and the phosphorescent dopant material forming the light emitting layer are selected so that the relationship between the HOMO level and the LUMO level is optimal, thereby improving the driving stability. A greatly improved device can be obtained, and excellent performance can be demonstrated in full-color or multi-color panel applications.
The present invention satisfies the relationship that the LUMO level of the host material is lower than the LUMO level of the phosphorescent dopant material having an electron-withdrawing group, and the HOMO level of the host material is lower than the HOMO level of the dopant material. A known host material and dopant material may be used.

The host material preferably has a large HOMO-LUMO band gap, and the phosphorescent dopant material preferably has a high excited triplet energy level. In particular, the host material that can be used in the present invention is compared to the dopant material used in combination.
The HOMO-LUMO band gap is about the same or larger,
Excited triplet energy levels are about the same or higher,
It is preferable that the material has a low reduction potential and a reversible reversibility that is comparable or superior.

  Specifically from the above viewpoint, the host material is preferably a compound represented by the following general formula (I).

In the formula, Ar represents an arbitrary aromatic hydrocarbon group or aromatic heterocyclic group which may have a substituent. n represents an integer of 1 to 10. Z represents a direct bond or an n-valent linking group. However, when n = 1, Z represents an arbitrary substituent or hydrogen atom bonded to Ar. When n ≧ 2, the plurality of Ars contained in one molecule may be the same or different from each other.
When Z is an n-valent linking group, any linking group can be used, and these can be used alone or in combination of the same or different groups. In addition, when Z is a substituent, any substituent can be applied.

Specific examples of Z include the following. In the case of a linking group, these are n-valent groups.
Halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom, preferably fluorine atom),
An alkyl group which may have a substituent (preferably a linear or branched alkyl group having 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, 2 -Propyl, n-butyl, isobutyl, tert-butyl group, etc.),
An alkenyl group which may have a substituent (preferably an alkenyl group having 2 to 8 carbon atoms, more preferably 2 to 4 carbon atoms, such as vinyl, allyl and 1-butenyl groups). ,
An alkynyl group which may have a substituent (preferably an alkynyl group having 2 to 8 carbon atoms, more preferably an alkynyl group having 2 to 4 carbon atoms, such as ethynyl and propargyl groups);
An aralkyl group which may have a substituent (preferably an aralkyl group having 7 to 15 carbon atoms, more preferably 7 to 10 carbon atoms, such as a benzyl group);
An amino group which may have a substituent (preferably an amino group having 0 to 36 carbon atoms, more preferably 0 to 20 carbon atoms, particularly preferably 0 to 12 carbon atoms such as amino, methylamino, dimethylamino, Ethylamino, diethylamino, phenylamino, diphenylamino, dibenzylamino, thienylamino, dithienylamino, pyridylamino, dipyridylamino and the like.
An alkoxycarbonylamino group which may have a substituent (preferably an alkoxycarbonylamino group having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 12 carbon atoms, such as methoxycarbonyl Amino and the like),
An aryloxycarbonylamino group which may have a substituent (preferably an aryloxycarbonylamino group having 7 to 20 carbon atoms, more preferably 7 to 16 carbon atoms, particularly preferably 7 to 12 carbon atoms, Phenoxycarbonyl, etc.),
An optionally substituted heterocyclic oxycarbonylamino group (preferably a C2-C21, more preferably C2-C15, particularly preferably C5-C11 heterocyclic oxycarbonylamino group). For example, thienyloxycarbonylamino).
A sulfonylamino group which may have a substituent (preferably a sulfonylamino group having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms, such as methanesulfonylamino, Benzenesulfonylamino, thiophenesulfonylamino, etc.).
An alkoxy group which may have a substituent (preferably an alkoxy group having 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, particularly preferably 1 to 8 carbon atoms, such as methoxy, ethoxy, isopropoxy , N-butoxy, t-butoxy and the like),
An aryloxy group which may have a substituent (preferably an aryloxy group having 6 to 10 carbon atoms, more preferably 6 to 8 carbon atoms, particularly preferably 6 carbon atoms, such as phenoxy).
A heterocyclic oxy group which may have a substituent (preferably a heterocyclic oxy group having 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, and particularly preferably 4 to 5 carbon atoms. , Pyridyloxy, etc.),
An acyl group which may have a substituent (preferably an acyl group having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as acetyl, benzoyl, formyl, Pivaloyl, tenoyl, nicotinoyl, etc.),
An alkoxycarbonyl group which may have a substituent (preferably an alkoxycarbonyl group having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 12 carbon atoms, such as methoxycarbonyl, ethoxy Carbonyl, etc.).
An aryloxycarbonyl group which may have a substituent (preferably an aryloxycarbonyl group having 7 to 20 carbon atoms, more preferably 7 to 16 carbon atoms, particularly preferably 7 carbon atoms, such as phenoxycarbonyl ),
A heterocyclic oxycarbonyl group which may have a substituent (preferably a heterocyclic oxycarbonyl group having 2 to 20 carbon atoms, more preferably 2 to 12 carbon atoms, particularly preferably 5 to 6 carbon atoms, Thienyloxycarbonyl, pyridyloxycarbonyl, etc.),
An acyloxy group which may have a substituent (preferably an acyloxy group having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 12 carbon atoms, such as acetoxy, ethylcarbonyloxy, Benzoyloxy, pivaloyloxy, thenoyloxy, nicotinoyloxy, etc.),
A sulfamoyl group which may have a substituent (preferably a sulfamoyl group having 0 to 20 carbon atoms, more preferably 0 to 16 carbon atoms, particularly preferably 0 to 12 carbon atoms, such as sulfamoyl and methylsulfamoyl groups. Dimethylsulfamoyl, phenylsulfamoyl, thienylsulfamoyl, etc.),
An optionally substituted carbamoyl group (preferably a carbamoyl group having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as carbamoyl, methylcarbamoyl, diethyl Carbamoyl, phenylcarbamoyl, etc.),
An alkylthio group which may have a substituent (preferably an alkylthio group having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms, such as methylthio, ethylthio, n- Butylthio etc.),
An arylthio group which may have a substituent (preferably an arylthio group having 6 to 26 carbon atoms, more preferably 6 to 20 carbon atoms, and particularly preferably 6 to 12 carbon atoms, and examples thereof include phenylthio and the like. ),
An optionally substituted heterocyclic thio group (preferably a heterocyclic thio group having 1 to 25 carbon atoms, more preferably 2 to 19 carbon atoms, particularly preferably 5 to 11 carbon atoms, thienylthio, pyridylthio Etc.),
A sulfonyl group which may have a substituent (preferably a sulfonyl group having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, and examples thereof include tosyl and mesyl. ),
Sulphenyl group which may have a substituent (preferably a sulfenyl group having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methanesulfinyl, benzene Sulfinyl, etc.),
An ureido group which may have a substituent (preferably a ureido group having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as ureido, methylureido, phenyl Ureido etc.),
An optionally substituted phosphate amide group (preferably a phosphate amide group having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms. Acid amide, phenylphosphoric acid amide, etc.),
Hydroxyl group,
Mercapto group,
A cyano group,
A sulfo group,
Carboxyl group,
Nitro group,
Hydroxamic acid group,
Sulfino group,
A hydrazino group,
Imino group,

(Ra is an arbitrary substituent, preferably an alkyl group, aralkyl group or aryl group having 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, which may have a substituent. Rb is a hydrogen atom or an arbitrary substituent, and preferably 1 carbon atom which may have a substituent.
-10, more preferably an alkyl group having 1 to 6 carbon atoms, an aralkyl group, or an aryl group. ),

(Rc and Rd are each a hydrogen atom or an arbitrary substituent, preferably an optionally substituted alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, an aralkyl group or an aryl group. Any)
A silyl group which may have a substituent (preferably a C1-C10, more preferably a C1-C6 trimethylsilyl group, a triphenylsilyl group, etc.),
A boryl group which may have a substituent (preferably a dimesitylboryl group having 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms),
A phosphino group which may have a substituent (preferably a C1-C10, more preferably a C1-C6 diphenylphosphino group),
An aromatic hydrocarbon group which may have a substituent (preferably an aromatic hydrocarbon group having 6 to 20 carbon atoms, more preferably an aromatic hydrocarbon group having 6 to 14 carbon atoms, a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, A perylene ring, a tetracene ring, a pyrene ring, a benzpyrene ring, a chrysene ring, a triphenylene ring, a group derived from a fluoranthene ring and the like, or a group derived from a 2-5 condensed ring).

Or an aromatic heterocyclic group consisting of a 5- or 6-membered monocyclic ring or a 2-3 condensed ring which may have a substituent (the hetero atom includes, for example, a nitrogen atom, an oxygen atom, a sulfur atom, etc. Preferably an aromatic heterocyclic group having 1 to 19 carbon atoms, more preferably 3 to 13 carbon atoms, furan ring, benzofuran ring, thiophene ring, benzothiophene ring, pyrrole ring, pyrazole ring, oxazole ring, imidazole ring Oxadiazole ring, indole ring, carbazole ring, pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring, thienopyrrole ring, thienothiophene ring, furopyrrole ring, furofuran ring, thienofuran ring, benzisoxazole ring, benzoisothiazole ring, Benzimidazole ring, pyridine ring, pyrazine ring, pyridazine ring, pyrimidide Derived from a 5- or 6-membered monocyclic or 2-4 condensed ring such as a ring, triazine ring, quinoline ring, isoquinoline ring, sinoline ring, quinoxaline ring, benzimidazole ring, perimidine ring, quinazoline ring, quinazolinone ring, azulene ring Group).
Etc.

Among these, Z is preferably an aromatic hydrocarbon group or an aromatic heterocyclic group from the viewpoint of improving electrical redox durability and improving heat resistance.
In addition, each said group may have a substituent as mentioned above, and may be condensed with another group. Moreover, when there are two or more substituents possessed by each of the above groups, they may be the same or different, and if possible, they may be linked to form a ring.

  The substituent is preferably an alkyl group, aromatic hydrocarbon group, acyl group, alkoxy group, aryloxy group, alkylthio group, arylthio group, alkoxycarbonyl group, aryloxycarbonyl group, halogen atom, arylamino group, alkylamino. Group, an aromatic heterocyclic group, more preferably an alkyl group, an aromatic hydrocarbon group, and an aromatic heterocyclic group, and still more preferably an alkyl group and an aromatic hydrocarbon group. Preferred examples of these substituents are the same as those described as Z above.

The molecular weight of Z is preferably 1000 or less, more preferably 500 or less, including its substituents (excluding Ar). By setting the molecular weight within a preferable range, the vaporization temperature is not excessively increased during film formation using the vapor deposition method, the solubility in a solvent is not impaired during film formation using the wet method, or a wide range. A HOMO-LUMO gap can be obtained.

In the general formula (I), Ar represents an arbitrary aromatic hydrocarbon group or aromatic heterocyclic group which may have a substituent.
The aromatic hydrocarbon group is preferably an aromatic hydrocarbon group having 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms. For example, a benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, perylene ring, tetracene ring, pyrene ring, benzpyrene ring, chrysene ring, triphenylene ring, fluoranthene ring, etc. Groups.

  The aromatic heterocyclic group is preferably an aromatic hydrocarbon group having 1 to 29 carbon atoms, more preferably 3 to 19 carbon atoms. For example, furan ring, benzofuran ring, thiophene ring, benzothiophene ring, pyrrole ring, pyrazole ring, oxazole ring, imidazole ring, oxadiazole ring, indole ring, carbazole ring, pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring, Thienopyrrole ring, thienothiophene ring, furopyrrole ring, furofuran ring, thienofuran ring, benzoisoxazole ring, benzisothiazole ring, benzimidazole ring, pyridine ring, pyrazine ring, pyridazine ring, pyrimidine ring, triazine ring, quinoline ring, isoquinoline ring , Sinoline ring, quinoxaline ring, benzimidazole ring, perimidine ring, quinazoline ring, quinazolinone ring, azulene ring, tetrazole ring, imidazopyridine ring, etc., 5 or 6-membered monocyclic ring or 2-4 condensed ring Ring-derived group.

  Ar is a benzene ring, naphthalene ring, pyridine ring, pyrimidine ring, pyrazine ring, triazine ring, quinoline ring, isoquinoline ring, thiazole ring, oxazole from the viewpoint of electrical redox durability and a wide band gap of HOMO-LUMO. A group derived from a ring, an imidazole ring, an indole ring, a benzimidazole ring, an imidazopyridine ring or a carbazole ring is preferred.

Among these, more preferred are groups derived from a benzene ring, naphthalene ring, pyridine ring, triazine ring, oxazole ring, thiazole ring, imidazole ring, quinoline ring, isoquinoline ring, benzimidazole ring, imidazopyridine ring, and carbazole ring.
More preferred are groups derived from a benzene ring, a pyridine ring, a quinoline ring, an isoquinoline ring, a benzimidazole ring, an imidazopyridine ring and a carbazole ring.

Most preferably, the pyridine ring (especially, the 2,4,6-position is preferably substituted by an arbitrary substituent (preferably an aromatic hydrocarbon group or an aromatic heterocyclic group)), a carbazole ring (among others) In addition, it is preferable not to have an electron donating group (such as an alkyl group, an amino group, or an alkoxy group) as a substituent since the electric reduction durability is not lowered.
In the general formula (I), the aromatic hydrocarbon group or aromatic heterocyclic group represented by Ar may have a substituent. As the substituent, those exemplified as the substituent that Z may have can be similarly applied.

  The molecular weight of Ar is preferably 1000 or less including the substituent (excluding Z), more preferably 500 or less. By setting the molecular weight within a preferable range, the vaporization temperature is not excessively increased during film formation using the vapor deposition method, the solubility in a solvent is not impaired during film formation using the wet method, or a wide range. A HOMO-LUMO gap can be obtained.

  Preferred specific examples of Ar and Z when n = 1 are shown below (R-1 to R-88).

In each of the above structures, L ₁ and L ₂ represent a hydrogen atom or an arbitrary substituent represented by each group exemplified as the substituent that Z may have. In the above table, Z may have an arbitrary substituent other than L ₁ and L ₂ .
Preferred specific examples of Ar and Z when n is 2 or more are as follows (Z-1 to Z-
184).

If it illustrates as a host material represented by general formula (I), as a carbazole type compound (a triarylamine type compound is included), Unexamined-Japanese-Patent No. 63-235946, Unexamined-Japanese-Patent No. 2-285357
JP, JP 2-21889, JP 3-230584, JP 3-232856, JP 5-63073, JP 6-312979, JP 7-053950 JP-A-8-003547, JP-A-957643, JP-A-9-268283, JP-A-965573, JP-A-9-2498
No. 76, JP-A-9-310066, JP-A-10-041069, JP-A-10-168447, EP Patent No. 847228, JP-A-10-208880, JP-A-10-226785 JP-A-10-312073, JP-A-10-316658, JP-A-10-330361, JP-A-11-144866, JP-A-11-144867, JP-A-11-144873, Kaihei 11-149987, JP-A-11-167990, JP-A-11-233260, JP-A-11-241062, WO-00 / 70655, U.S. Pat. -040844, JP2001-313179, JP2001-257076, JP2003-202925, JP2003-204940, JP2003-299512, etc.

As the phenylanthracene derivative, a host material described in JP 2000-344691 A, etc.,
As the starburst type compound of fused ring arylene, host materials described in JP2001-192651A, JP2002-324677A, and the like,
Examples of condensed imidazole compounds include Appl. Phys. Lett., 78, 1622, 2001, JP 2001-335776, JP 2002-338579, JP 2002-319491, JP The host materials described in 2002-367785, JP 2002-367786, etc.
As the azepine-based compound, a host material described in JP-A-2002-235075 and the like,
As the condensed triazole-based compound, a host material described in JP-A-2002-356489 and the like,
As propeller type arylene compounds, host materials described in JP 2003-027048 A, etc.,

Examples of the monotriarylamine type compound include host materials described in JP 2002-175883 A, JP 2002-249765 A, JP 2002-324676 A, and the like.
Examples of the arylbenzidine compounds include host materials described in JP 2002-329577 A,
As the triaryl boron compound, host materials described in JP2003-031367A, JP2003-031368A, etc.,
Examples of indole compounds include host materials described in JP 2002-305084 A, JP 2003-008866 A, JP 2002-015871 A, and the like.
Examples of indolizine compounds include host materials described in JP 2000-311787 A, and the like.
As pyrene compounds, host materials described in JP-A-2001-118682, etc.,
Examples of dibenzoxazole (or dibenzothiazole) compounds include host materials described in JP-A-2002-231453,
As the bipyridyl-based compound, a host material described in JP 2003-123983 A, etc.,
Examples of the pyridine compound include host materials described in Japanese Patent Application No. 2003-347307, Japanese Patent Application No. 2003-374430, and the like.

  From the viewpoint of excellent light emitting characteristics as an element, preferably a carbazole compound (including a triarylamine compound), a starburst type compound of a condensed ring arylene, a condensed ring imidazole compound, a propeller type arylene compound, a monotria They are a reelamine type compound, an indole compound, an indolizine compound, a bipyridyl compound, and a pyridine compound.

  Furthermore, a carbazole compound or a phenylpyridine compound is preferable from the viewpoint of driving life as an element. Specific examples of particularly preferred compounds are shown below.

Among them, H-A1 to A6, A8 to A11, A14 to A18, A20 to A25 are preferable, and H-A1, A3, A4, A6, A8
-A10, A15-A18, A20-A25 are particularly preferred.
Table A-1 shows the HOMO level, LUMO level, band gap, melting point, and vaporization temperature of some particularly preferred host materials.

  As the host material, the band gap is preferably 3.0 V or more, more preferably 3.2 V or more, and most preferably 3.5 V or more. The glass transition point is usually 75 ° C. or higher, preferably 100 ° C. or higher, more preferably 130 ° C. or higher, and most preferably 150 ° C. or higher. The vaporization temperature is usually 300 ° C. or higher, preferably 350 ° C. or higher, most preferably 400 ° C. or higher, usually 700 ° C. or lower, preferably 600 ° C. or lower, most preferably 550 ° C. or lower, under normal pressure conditions. .

  The molecular weight of the host material represented by the general formula (I) is usually about 4000 or less, preferably about 3000 or less, more preferably about 2000 or less, usually about 300 or more, preferably about 400 or more, more preferably 500 or more. Degree. If the molecular weight is too large, the sublimation property is lowered, for example, it tends to be difficult to form a thin film by vapor deposition, or in the process of synthesis, it tends to generate impurities that are difficult to remove, which can impair the driving life of the device. Therefore, as described later, there is a possibility that it may become a problem when used for a layer constituting the organic electroluminescent element. On the other hand, if the molecular weight is too small, for example, the sublimation temperature becomes too low, so that it is difficult to form a thin film by vapor deposition, the melting point and the glass transition point are lowered, the heat resistance is lowered, or crystallization is easy. May occur and the film forming property (amorphous property) may be deteriorated.

  Examples of the phosphorescent dopant material having an electron-withdrawing group include phosphorescent organometallic complexes containing a metal of Groups 7 to 11 of the periodic table. Preferred examples of the metal include ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold. Preferred examples of these organometallic complexes include compounds represented by the following general formulas (V) and (VI).

In formula (V), M ⁴ represents a metal, and m + n represents the valence of the metal. n is an integer of 1 or more, and m is an integer of 0 or more. When m is 0, a combination of different CN bidentate ligands may be used. L represents a monovalent bidentate ligand. Ring a represents an aromatic hydrocarbon group or an aromatic heterocyclic group which may have a substituent. Ring b represents an aromatic heterocyclic group which may have a substituent. Either ring a or ring b has at least one electron withdrawing group. Both ring a and ring b may have an electron-withdrawing group.

In formula (VI), M ⁷ represents a metal, and T represents a carbon atom or a nitrogen atom. At least one of R ¹² to R ¹⁵ is an electron withdrawing group. When T is a nitrogen atom, R ¹⁴ and R ¹⁵ are absent. When T is a carbon atom, R ¹⁴ and R ¹⁵ are each independently a hydrogen atom, halogen atom, alkyl group, aralkyl group, alkenyl group, cyano group, amino group, acyl group, alkoxycarbonyl group, carboxyl group, Represents an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group, an aromatic hydrocarbon group or an aromatic heterocyclic group; Each of the groups may have a substituent.

R ¹² and R ¹³ are hydrogen atom, halogen atom, alkyl group, aralkyl group, alkenyl group, cyano group, amino group, acyl group, alkoxycarbonyl group, carboxyl group, alkoxy group, alkylamino group, aralkylamino group, haloalkyl Represents a group, a hydroxyl group, an aryloxy group, an aromatic hydrocarbon group or an aromatic heterocyclic group, and may be linked to each other to form a ring. Moreover, each said group may have a substituent.

The ring a of the compound represented by the general formula (V) is preferably phenyl, biphenyl, naphthyl, anthryl, phenanthryl, thienyl, furyl, benzothienyl, benzofuryl, pyridyl, quinolyl. Group, or an isoquinolyl group.
The ring b is preferably a pyridyl group, pyrimidyl group, pyrazyl group, triazyl group, benzothiazole group, benzoxazole group, benzimidazole group, pyrazoyl group, quinolyl group, isoquinolyl group, quinoxaline group, or phenanthridine group. It is done.

A preferred combination of ring a and ring b is a phenyl group as ring a and a pyridyl group as ring b from the viewpoint of stability.
As the substituent that the compound represented by the general formula (V) may have,
A halogen atom such as a fluorine atom or a chlorine atom, preferably a fluorine atom;
An alkyl group having 1 to 6, preferably 1 to 4 carbon atoms, such as a methyl group or an ethyl group;
An alkenyl group having 2 to 6 carbon atoms, preferably 1 to 4 carbon atoms, such as a vinyl group;
An alkoxycarbonyl group having 2 to 6 carbon atoms, preferably 2 to 4 carbon atoms, such as a methoxycarbonyl group and an ethoxycarbonyl group;
An alkoxy group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, such as a methoxy group and an ethoxy group;
An aryloxy group having 6 to 24 carbon atoms, preferably 6 to 12 carbon atoms, such as a phenoxy group and a benzyloxy group;
A dialkylamino group having 2 to 12, preferably 2 to 6 carbon atoms, such as a dimethylamino group or a diethylamino group;
An acyl group having 2 to 12, preferably 2 to 6 carbon atoms, such as an acetyl group;
A haloalkyl group having 1 to 6, preferably 1 to 4 carbon atoms, such as a trifluoromethyl group;
An aromatic hydrocarbon group having 6 to 18 carbon atoms, preferably 6 to 12 carbon atoms, such as a phenyl group;
A cyano group and the like, and these may be linked to each other to form a ring.

In addition, the substituent which the ring a has, and the substituent which the ring b has may couple | bond together, and one condensed ring may be formed, for example, 1-phenanthridine etc. are mentioned.
As the substituent of ring a and ring b, the above alkyl group, alkoxy group, aromatic hydrocarbon group (particularly phenyl group), cyano group, halogen atom, or haloalkyl group is more preferable in terms of sublimability.

M ⁴ in the formula (V) is preferably ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum or gold in terms of high luminance. In particular, iridium, platinum, and gold are preferable.
L in the formula (V) represents a monovalent bidentate ligand, and specific examples thereof include the following bidentate ligands, but are not limited thereto.

  Among the above, the following are preferable in terms of stability.

M ⁷ in the formula (VI) is preferably ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum or gold, and particularly preferably a divalent metal such as platinum or palladium. Is mentioned.
The electron withdrawing group in formula (V) and formula (VI) is the [β group] substituted with at least one group selected from the following [α group] and [α group], and [α group]: [Γ group] which may be substituted with at least one group selected from

[Α group] fluorine atom, chlorine atom, carbonyl group, carboxyl group, cyano group, nitro group,
[Β group]
An alkyl group having 1 to 15 carbon atoms, preferably 1 to 6 carbon atoms,
An alkoxy group having 1 to 15 carbon atoms, preferably 1 to 6 carbon atoms,
An alkoxyalkyl group having 2 to 30 carbon atoms, preferably 2 to 15 carbon atoms,
An alkoxyalkoxy group having 2 to 30 carbon atoms, preferably 2 to 15 carbon atoms,
An alkylamino group having 1 or 2 alkyl group moieties of 1 to 10 carbon atoms, preferably 2 to 15 carbon atoms,
An arylamino group having 1 or 2 aromatic hydrocarbon groups having 6 to 18 carbon atoms, preferably 6 to 12 carbon atoms,
An acylamino group having 1 or 2 acyl groups having 2 to 30 carbon atoms, preferably 2 to 15 carbon atoms,
An alkylthio group having 1 to 15 carbon atoms, preferably 1 to 8 carbon atoms,
An aromatic hydrocarbon group having 6 to 18 carbon atoms, preferably 6 to 12 carbon atoms,
-R ¹⁰¹ COR ¹⁰² , -OR ¹⁰³ COR ¹⁰⁴ , -COR ¹⁰⁵ , -OCOR ¹⁰⁶
(However, R < ¹⁰¹ > -R < ¹⁰⁶ > represents a C1-C15 alkyl group or alkylene group each independently.)

[Γ group]
An alkylboryl group having 1 or 2 alkyl groups having 1 to 15 carbon atoms, preferably 1 to 6 carbon atoms,
An arylboryl group having 1 or 2 aromatic hydrocarbon groups having 6 to 18 carbon atoms, preferably 6 to 12 carbon atoms,
An alkylsulfonyl group having 1 or 2 alkyl group moieties of 1 to 15 carbon atoms, preferably 1 to 8 carbon atoms,
An arylsulfonyl group having 1 or 2 aromatic hydrocarbon groups having 6 to 18 carbon atoms, preferably 6 to 12 carbon atoms
Specific examples of the electron-withdrawing group include the following groups, but are not limited thereto.
(In the following structure, Me represents a methyl group and Bu represents a butyl group.)

Of the electron-withdrawing groups, a halogen atom is preferable from the viewpoint of stability, and a fluorine atom is more preferable.
Specific examples of the organometallic complex represented by the general formula (V) are shown below, but are not limited to the following compounds.

  (In the above structure, Me represents a methyl group, Bu represents a butyl group, and Mes represents a mesityl group.)

  Specific examples of the organometallic complex represented by the general formula (VI) are shown below, but are not limited to the following compounds.

The molecular weight of the dopant material used in the present invention is usually 400 or more, preferably 600 or more, and usually 1200 or less, preferably 1000 or less.
In addition, although the light emission maximum wavelength of dopant material is 400-1200 nm normally, since the dopant material which can be used by this invention has an electron withdrawing group, a 500 nm or less thing is used suitably.

The present invention is a light emitting material containing the host material and the dopant material, and the light emitting material is usually used for a light emitting layer in an organic electroluminescent device.
The amount of the organometallic complex contained as a dopant material in the light emitting layer is preferably 0.1% by weight or more and 30% by weight or less. If it is less than 0.1% by weight, it cannot contribute to the improvement of the light emission efficiency of the device, and if it exceeds 30% by weight, concentration quenching occurs due to the formation of a dimer between organometallic complexes, leading to a decrease in light emission efficiency.

  There is a tendency that a slightly larger amount than the amount of the fluorescent dye (dopant) contained in the light emitting layer of a device using conventional fluorescence (singlet) is preferable. In addition to the organometallic complex, when the fluorescent dye is contained in the light emitting layer, the amount is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, and preferably 10% by weight or less, 8% by weight or less is more preferable. These organometallic complexes may be partially contained in the light emitting layer in the film thickness direction, or may be unevenly distributed.

In order to efficiently emit light from the dopant material, the excited triplet energy level of the dopant material is preferably lower than the excited triplet energy level of the host. When the former is higher than the latter, energy transfer from the triplet level of the dopant formed in the light emitting layer to the triplet level of the host occurs, leading to a decrease in light emission efficiency.
An element using the light-emitting material of the present invention is an element having a long driving life, but can specifically achieve about 150 hours (room temperature, initial luminance 500 cd / m ² ) depending on conditions and the like. It is.

Hereinafter, the organic electroluminescent element of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing a structural example of a general organic electroluminescence device used in the present invention. 1 is a substrate, 2 is an anode, 4 is a hole transport layer, 5 is a light emitting layer, and 6 is a light emitting layer. A hole blocking layer, 8 represents a cathode.
The substrate 1 serves as a support for the organic electroluminescent element, and a quartz or glass plate, a metal plate or a metal foil, a plastic film, a sheet, or the like is used. In particular, a glass plate or a transparent synthetic resin plate such as polyester, polymethacrylate, polycarbonate, or polysulfone is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too small, the organic electroluminescent element may be deteriorated by the outside air that has passed through the substrate, which is not preferable. For this reason, a method of providing a gas barrier property by providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate is also a preferable method.

An anode 2 is provided on the substrate 1, and the anode 2 plays a role of hole injection into the hole transport layer. This anode is usually made of metal such as aluminum, gold, silver, nickel, palladium, platinum, metal oxide such as oxide of indium and / or tin, metal halide such as copper iodide, carbon black, or poly It is composed of conductive polymers such as (3-methylthiophene), polypyrrole and polyaniline. In general, the anode 2 is often formed by sputtering, vacuum deposition, or the like. Further, in the case of metal fine particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, and conductive polymer fine powders, they are dispersed in an appropriate binder resin solution and placed on the substrate 1. It is also possible to form the anode 2 by applying to. Further, in the case of a conductive polymer, a thin film can be directly formed on the substrate 1 by electrolytic polymerization, or the anode 2 can be formed by applying a conductive polymer on the substrate 1 (Appl. Phys. Lett. 60, 2711, 1992). The anode 2 can also be formed by stacking different materials. The thickness of the anode 2 varies depending on the required transparency. When transparency is required, the visible light transmittance is usually 60% or more, preferably 80% or more. In this case, the thickness is usually 5 to 1000 nm, preferably 10 to It is about 500 nm. If it can be opaque, the anode 2 may be the same as the substrate 1. Furthermore, it is also possible to laminate different conductive materials on the anode 2 described above.

  A hole transport layer 4 is provided on the anode 2. As conditions required for the material of the hole transport layer, it is necessary that the material has a high hole injection efficiency from the anode and can efficiently transport the injected holes. For this purpose, the ionization potential is small, the transparency to visible light is high, the hole mobility is high, the stability is high, and impurities that become traps are less likely to be generated during manufacturing and use. Required. Further, in order to contact the light emitting layer 5, it is required not to quench the light emitted from the light emitting layer or to form an exciplex with the light emitting layer to reduce the efficiency. In addition to the above general requirements, when the application for in-vehicle display is considered, the element is further required to have heat resistance. Therefore, a material having a Tg value of 85 ° C. or higher is desirable.

Examples of such a hole transporting material include two or more tertiary amines represented by 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl, and two or more Aromatic diamines having a starburst structure such as aromatic diamines having condensed aromatic rings substituted with nitrogen atoms (Japanese Patent Laid-Open No. 5-234681), 4,4 ', 4 "-tris (1-naphthylphenylamino) triphenylamine Group amine compounds (J. Lumin., 72-74, 985, 1997), aromatic amine compounds consisting of tetramers of triphenylamine (Chem. Commun., 2175, 1996), 2,2 Spiro compounds such as', 7,7'-tetrakis- (diphenylamino) -9,9'-spirobifluorene (Synth. Metals, 91, 209, 1997) and the like. They may be used alone or in combination as necessary.

In addition to the above-mentioned compounds, polyarylene ether sulfone (Polym. Adv. Tech.) Containing polyvinylcarbazole, polyvinyltriphenylamine (JP-A-7-53953), and tetraphenylbenzidine as materials for the hole transport layer 4. , Vol. 7, p. 33, 1996).
In the case of the coating method, one or more hole transport materials and, if necessary, additives such as a binder resin and a coating property improving agent that do not trap holes are added and dissolved to prepare a coating solution. Then, it is applied on the anode 2 by a method such as spin coating, and dried to form the hole transport layer 4. Examples of the binder resin include polycarbonate, polyarylate, and polyester. When the binder resin is added in a large amount, the hole mobility is lowered. Therefore, it is desirable that the binder resin be less, and usually 50% by weight or less is preferable.

In the case of the vacuum deposition method, the hole transport material is put in a crucible installed in a vacuum vessel, and after the inside of the vacuum vessel is evacuated to about 10 ⁻⁴ Pa with a suitable vacuum pump, the crucible is heated, The hole transport material is evaporated and the hole transport layer 4 is formed on the substrate 1 on which the anode is formed, which is placed facing the crucible.
The thickness of the hole transport layer 4 is usually 5 to 300 nm, preferably 10 to 100 nm. In order to uniformly form such a thin film, a vacuum deposition method is generally used.

In the present invention, a hole transport layer is preferably provided between the anode and the light emitting layer in that holes can be efficiently injected into the light emitting layer.
A light emitting layer 5 is provided on the hole transport layer 4. The light-emitting layer 5 contains the above-described light-emitting material, and moves between the electrodes applied with an electric field from the anode to move through the hole transport layer and from the cathode to move through the hole blocking layer 6. Excited by recombination with electrons that emit strong light. The light emitting layer 5 may contain other components such as a host material other than those defined in the present invention as long as the performance of the present invention is not impaired.

The thickness of the light emitting layer 5 is usually 10 nm or more, preferably 20 nm or more, usually 200 nm or less, preferably 100 nm or less. A hole blocking layer 6 formed as a thin film by the same method as the hole transport layer 4 is laminated on the light emitting layer 5. The holes moving from the hole transport layer reach the cathode. It is formed from a compound capable of blocking and transporting electrons injected from the cathode toward the light emitting layer efficiently. The physical properties required for the material constituting the hole blocking layer are required to have high electron mobility and low hole mobility. The hole blocking layer 6 has a function of confining holes and electrons in the light emitting layer and improving luminous efficiency.

  As a hole blocking material satisfying such conditions, a mixed ligand complex represented by the following general formula (VII) is preferably exemplified.

(In the formula, R ^{16 to} R ²¹ represent a hydrogen atom or an arbitrary substituent. M ⁸ represents a metal atom selected from aluminum, gallium, and indium. L ³ represents the following general formula (VIIa), ( It is represented by either VIIb) or (VIIc).

(In the formula, Ar ^{11 to} Ar ¹⁵ represent an aromatic hydrocarbon group which may have a substituent or an aromatic heterocyclic group which may have a substituent, and Z ³ represents silicon or germanium. Represents.)
In the general formula (VII), R ^{16 to} R ²¹ represent a hydrogen atom or an arbitrary substituent, preferably a hydrogen atom; a halogen atom such as chlorine or bromine; a carbon number of 1 to 6 such as a methyl group or an ethyl group. An aralkyl group such as a benzyl group; an alkenyl group having 2 to 6 carbon atoms such as a vinyl group; a cyano group; an amino group; an acyl group; an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; A C2-C6 alkoxycarbonyl group such as a carbonyl group or an ethoxycarbonyl group; a carboxyl group; an aryloxy group such as a phenoxy group or a benzyloxy group; a dialkylamino group such as a diethylamino group or a diisopropylamino group; a dibenzylamino group; Diaralkylamino groups such as diphenethylamino groups; α-haloalkyl groups such as trifluoromethyl groups; hydroxyl groups; substituents Represents an aromatic hydrocarbon group such as a phenyl group and naphthyl group which may have a substituent; an aromatic heterocyclic group such as a thienyl group and a pyridyl group which may have a substituent.

  Examples of the substituent that the aromatic hydrocarbon group and the aromatic heterocyclic group may have include: a halogen atom such as a fluorine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; and a carbon number such as a vinyl group. An alkenyl group having 2 to 6 carbon atoms; an alkoxycarbonyl group having 2 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group; an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; a phenoxy group and a benzyloxy group Aryloxy groups; dialkylamino groups such as dimethylamino groups and diethylamino groups; acyl groups such as acetyl groups; haloalkyl groups such as trifluoromethyl groups; cyano groups and the like. R16 to R21 are more preferably a hydrogen atom, an alkyl group, a halogen atom or a cyano group. R19 is particularly preferably a cyano group.

In the above formula (VII), Ar11 to Ar15 are specifically aromatic hydrocarbon groups such as a phenyl group, biphenyl group and naphthyl group which may have a substituent, or aromatics such as thienyl group and pyridyl group. Represents a heterocyclic group.
Preferred specific examples of the compound represented by the general formula (VII) are shown below, but are not limited thereto.

In addition, these compounds may be used independently in a hole-blocking layer, and may be mixed and used as needed.
As the hole blocking material, in addition to the mixed ligand complex of the general formula (VII), a compound having at least one 1,2,4-triazole ring residue represented by the following structural formula may be used. it can.

  Specific examples of the compound having at least one 1,2,4-triazole ring residue represented by the above structural formula are shown below.

  Examples of the hole blocking material further include compounds having at least one phenanthroline ring represented by the following structural formula.

  Specific examples of the compound having at least one phenanthroline ring represented by the above structural formula are shown below.

  Further, as the hole blocking material, a compound having at least one pyridine ring substituted at the 2,4,6-position represented by the following structural formula can also be used.

(In the formula, R ⁴¹ , R ⁴² and R ⁴³ each independently represents a hydrogen atom or an arbitrary substituent. The linking group Q represents an n-valent linking group, and the pyridine ring and the linking group Q are pyridine rings. (It is directly bonded to any one of positions 2 to 6. n is an integer of 1 to 8.)
Specific examples of the compound having at least one pyridine ring substituted at the 2,4,6-position represented by the above structural formula are shown below, but are not limited thereto.

The film thickness of the hole blocking layer 6 is usually 0.3 to 100 nm, preferably 0.5 to 50 nm. The hole blocking layer can also be formed by the same method as the hole transporting layer, but usually a vacuum deposition method is used.
The cathode 8 serves to inject electrons into the light emitting layer 5 through the hole blocking layer 6. The material used for the cathode 8 can be the material used for the anode 2, but a metal having a low work function is preferable for efficient electron injection, and tin, magnesium, indium, calcium, A suitable metal such as aluminum or silver or an alloy thereof is used. Specific examples include low work function alloy electrodes such as magnesium-silver alloy, magnesium-indium alloy, and aluminum-lithium alloy. Furthermore, inserting an ultra-thin insulating film (0.1-5 nm) such as LiF, MgF2, Li2O at the interface between the cathode and the light emitting layer or the electron transport layer is also an effective method for improving the efficiency of the device (Appl. Phys Lett., 70, 152, 1997; JP-A-10-74586; IEEE Trans. Electron. Devices, 44, 1245, 1997). The film thickness of the cathode 8 is usually the same as that of the anode 2. For the purpose of protecting the cathode made of a low work function metal, further laminating a metal layer having a high work function and stable to the atmosphere increases the stability of the device. For this purpose, metals such as aluminum, silver, copper, nickel, chromium, gold, platinum are used.

For the purpose of further improving the luminous efficiency of the device, it is conceivable to provide an electron transport layer 7 between the hole blocking layer 6 and the cathode 8 (see FIG. 2). The electron transport layer 7 is formed of a compound that can efficiently transport electrons injected from the cathode between the electrodes to which an electric field is applied in the direction of the hole blocking layer 6.
The electron transporting compound used for the electron transporting layer 7 is a compound that has high electron injection efficiency from the cathode 8 and that can efficiently transport injected electrons with high electron mobility. is necessary.

Materials satisfying such conditions include metal complexes such as aluminum complexes of 8-hydroxyquinoline (JP 59-194393 A), metal complexes of 10-hydroxybenzo [h] quinoline, oxadiazole derivatives, Styryl biphenyl derivative, silole derivative, 3- or 5-hydroxyflavone metal complex, benzoxazole metal complex, benzothiazole metal complex, trisbenzimidazolylbenzene (US Pat. No. 5,645,948), quinoxaline compound (JP-A-6-207169) Phenanthroline derivatives (JP-A-5-331459), 2-t-butyl-9,10-N, N'-dicyanoanthraquinonediimine, n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type Examples include zinc selenide.

Electron transport with enhanced electron transport capability by doping alkali metals into phenanthroline derivatives and metal complexes, or by doping organic substances with high electron transport properties such as oxadiazole derivatives, quinoxaline compounds, and phenanthroline derivatives. Layers can also be formed.
The thickness of the electron transport layer 7 is usually 5 to 200 nm, preferably 10 to 100 nm.

The electron transport layer 7 is formed by laminating on the hole blocking layer 6 by a coating method or a vacuum deposition method in the same manner as the hole transport layer 4. Usually, a vacuum deposition method is used.
In order to efficiently inject electrons from the cathode into the light emitting layer and to facilitate recombination of holes and electrons in the light emitting layer, the present invention provides a hole blocking layer and / or between the cathode and the light emitting layer. Or it is preferable to have an electron carrying layer.

  The hole injection layer 3 may be inserted between the hole transport layer 4 and the anode 2 for the purpose of further improving the efficiency of hole injection and improving the adhesion of the entire organic layer to the anode. (See FIG. 3). By inserting the hole injection layer 3, the driving voltage of the initial element is lowered, and at the same time, an increase in voltage when the element is continuously driven with a constant current is suppressed. The conditions required for the material used for the hole injection layer include that the contact with the anode is good and a uniform thin film can be formed, and that it is thermally stable, that is, the melting point and glass transition temperature are high, and the melting point is 300 ° C. or higher. The glass transition temperature is required to be 100 ° C or higher. Furthermore, the ionization potential is low, hole injection from the anode is easy, and the hole mobility is high.

For this purpose, a talocyanine compound such as copper phthalocyanine (JP-A 63-295695), polyaniline (Appl. Phys. Lett., 64, 1245, 1994), polythiophene (Optical Materials, 9, 125, 1998) and other organic compounds, sputtered carbon films (Synth. Met., 91, 73, 1997), metals such as vanadium oxide, ruthenium oxide, molybdenum oxide Oxides (J. Phys. D, 29, 2750, 1996) have been reported. Moreover, hole injection can be facilitated by doping an electron-accepting group such as DDQ into an aromatic diamine-containing polyether.

In the case of the hole injection layer, a thin film can be formed in the same manner as the hole transport layer, but in the case of an inorganic material, a sputtering method, an electron beam evaporation method, or a plasma CVD method is further used.
The thickness of the hole injection layer 3 formed as described above is usually 3 to 100 nm, preferably 5 to 50 nm.
In addition, it is also possible to laminate | stack the cathode 8, the hole-blocking layer 6, the light emitting layer 5, the positive hole transport layer 4, and the anode 2 in order on the board | substrate contrary to FIG. 1, and as already stated. It is also possible to provide the organic electroluminescent element of the present invention between two substrates, at least one of which is highly transparent. Similarly, it is also possible to laminate in a structure opposite to that of each of the layers shown in FIGS.

  The present invention can be applied to any of an organic electroluminescent element having a single element, an element having a structure arranged in an array, and a structure having an anode and a cathode arranged in an XY matrix.

EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited to description of a following example, unless the summary is exceeded.
(Measurement of HOMO and LUMO levels of materials)
The oxidation / reduction potentials of the host materials H-1, H-2, H-3, H-4 and the dopant materials D-1, D-2, D-3 shown below were measured under the following conditions.
Reference electrode: Silver wire (ferrocene is used as an internal standard substance, oxidation potential of ferrocene = 0.4 V vs. SCE)
Working electrode: Glassy carbon Counter electrode: Platinum wire Measurement solvent: 0.1 mol / L Tetra (normal butyl) ammonium perchlorate Methylene chloride solution (or acetonitrile solution, acetonitrile-tetrahydrofuran mixed solution)
Sweep speed: 100mV / sec
Sample concentration: 1mmol / L
Table 1 shows the results obtained by converting the obtained potential using a saturated sweet potato electrode (SCE) as a reference electrode.

<Example 1>
An organic electroluminescent element having the structure shown in FIG. 3 was produced by the following method.
An indium tin oxide (ITO) transparent conductive film 2 deposited on a glass substrate 1 with a thickness of 150 nm (sputtered film; sheet resistance 15 Ω) is formed into a 2 mm wide stripe using normal photolithography and hydrochloric acid etching. An anode was formed by patterning. The patterned ITO substrate was cleaned in the order of ultrasonic cleaning with acetone, water with pure water, and ultrasonic cleaning with isopropyl alcohol, dried with nitrogen blow, and finally subjected to ultraviolet ozone cleaning.

Next, an aromatic diamine-containing polyether (P-1) (weight average molecular weight 25,300; glass transition temperature 171 ° C.) having the following structure as the hole injection layer 3 and 10% by weight of the following compound based on (P-1) (P-2) was spin coated on the glass substrate under the following conditions.

Solvent ethyl benzoate
P-1 concentration 20 [mg / ml]
P-2 concentration 2 [mg / ml]
Spinner speed 1500 [rpm]
Spinner rotation time 30 [seconds]
Drying condition 100 ° C. for 1 hour A uniform thin film having a thickness of 30 nm was formed by the above spin coating.

Next, the substrate 1 coated with the hole injection layer 3 was placed in a vacuum evaporation apparatus. After rough evacuation of the apparatus using an oil rotary pump, the apparatus was evacuated using a cryopump until the degree of vacuum in the apparatus was 8 × 10 ⁻⁵ Pa or less.
4,4′-bis [N- (1-phenanthyl) -N-phenylamino] biphenyl represented by the following structural formula (HT-1), placed in a ceramic crucible arranged in the above apparatus.

Vapor deposition was performed by heating with a tantalum wire heater around the crucible. At this time, the temperature of the crucible was controlled in the range of 319 to 331 ° C. A hole transport layer 4 having a thickness of 60 nm was obtained at a vacuum degree of 8 × 10 ⁻⁵ Pa and a deposition rate of 0.1 nm / second during the deposition.
Subsequently, as the light emitting layer 5, the above H-3 as a host material and the above D-2 as a dopant material were placed in separate ceramic crucibles, and film formation was performed by a binary simultaneous vapor deposition method.

The crucible temperature of H-3 was controlled at 284 ° C., and the deposition rate was controlled at 0.07 nm / second. The crucible temperature of D-2 was controlled at 248 ° C. and the deposition rate was 0.004 nm / sec. A light emitting layer 5 made of a light emitting material having a thickness of 30 nm and containing 5 wt% of dopant material D-2 in the host material H-3 was laminated. The degree of vacuum during vapor deposition was 9 × 10 ⁻⁵ Pa.
Further, a compound shown as (HB-12) in the text as a hole blocking layer 6 was laminated with a crucible temperature of 275 ° C. and a film thickness of 10 nm at a deposition rate of 0.1 nm / second. The degree of vacuum during the deposition was 7 × 10 ⁻⁵ Pa.

On the hole blocking layer 6, an aluminum 8-hydroxyquinoline complex represented by the following structural formula (ET-1) as an electron transport layer 7, Al (C ₉ H ₆ NO) ₃

Was deposited in the same manner. The crucible temperature of the aluminum 8-hydroxyquinoline complex at this time was 250 ° C., the degree of vacuum was 7 × 10 ⁻⁵ Pa, the deposition rate was controlled at 0.2 nm / second, and the film thickness was 35 nm.
The substrate temperature when vacuum-depositing the hole transport layer, the light emitting layer, the hole blocking layer, and the electron transport layer was maintained at room temperature.
Here, the element on which the electron transport layer 7 has been deposited is once taken out from the vacuum deposition apparatus into the atmosphere, and a 2 mm wide stripe-shaped shadow mask is used as a cathode deposition mask. The device was placed in close contact with each other so as to be orthogonal to each other, placed in another vacuum vapor deposition apparatus, and evacuated until the degree of vacuum in the apparatus was 5 × 10 ⁻⁴ Pa or less in the same manner as the organic layer. As the cathode 8, first, lithium fluoride (LiF) is vapor deposited at a rate of 0.01 nm / second using a molybdenum boat.
The film was formed on the electron transport layer 7 at a vacuum degree of 5 × 10 ⁻⁴ Pa and a film thickness of 0.5 nm. Next, aluminum was similarly heated by a molybdenum boat to form an aluminum layer having a thickness of 80 nm at a deposition rate of 0.5 nm / second and a degree of vacuum of 1 × 10 ⁻³ Pa, thereby completing the cathode 8. The substrate temperature at the time of vapor deposition of the above two-layer cathode 8 was kept at room temperature.

As described above, an organic electroluminescent element having a light emitting area portion having a size of 2 mm × 2 mm was obtained.
When the obtained device was continuously driven at a constant current at an initial luminance of 500 cd / m ² at room temperature, the luminance half-life was as shown in the following table.
In other words, it has been found that an element using a light emitting material composed of a host material and a dopant material having a relationship between the HOMO level and the LUMO level defined in the present invention has a long driving life.

<Example 2>
A device was fabricated in the same manner as in Example 1 except that the host material H-3 of the light emitting layer was replaced with H-4 and the dopant material D-2 was replaced with D-3. evaluated. The results are as shown in the following table.
In other words, it has been found that an element using a light emitting material composed of a host material and a dopant material having a relationship between the HOMO level and the LUMO level defined in the present invention has a long driving life.

<Comparative Example 1>
An element was produced in the same manner as in Example 1 except that the host material H-3 of the light emitting layer was replaced with the host material H-1, and the obtained element was evaluated in the same manner as in Example 1. The results are as shown in the following table. It could not be said to be an element with a short luminance half-life and a long driving life.
<Comparative example 2>
An element was produced in the same manner as in Example 1 except that the dopant material D-2 of the light emitting layer was replaced with the dopant material D-1, and the obtained element was evaluated in the same manner as in Example 1. The results are as shown in the following table.
It could not be said that the device had a short luminance half time and a long driving life.

<Comparative Example 3>
A device was fabricated in the same manner as in Example 1 except that the dopant material D-2 of the light emitting layer was replaced by D-1 and the host material H-3 was replaced by H-1, and the resulting device was fabricated in the same manner as in Example 1. evaluated. The results are as shown in the following table.
It could not be said that the device had a short luminance half time and a long driving life.

<Comparative example 4>
A device was produced in the same manner as in Example 1 except that the host material H-3 of the light emitting layer was replaced with H-2, and the obtained device was evaluated in the same manner as in Example 1. The results are as shown in the following table.
It could not be said that the device had a short luminance half time and a long driving life.
<Comparative Example 5>
A device was fabricated in the same manner as in Example 1 except that the dopant material D-2 of the light emitting layer was replaced by D-1 and the host material H-3 was replaced by H-2. evaluated. The results are as shown in the following table.
It could not be said that the device had a short luminance half time and a long driving life.

<Comparative Example 6>
A device was fabricated in the same manner as in Example 2 except that Compound H-4, which is a host material for the light emitting layer, was replaced with H-2, and the resulting device was evaluated in the same manner as in Example 2. The results are as shown in the following table.
It could not be said that the device had a short luminance half time and a long driving life.

The schematic cross section which showed an example of the organic electroluminescent element. The schematic cross section which showed another example of the organic electroluminescent element. The schematic cross section which showed another example of the organic electroluminescent element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole injection layer 4 Hole transport layer 5 Light emitting layer 6 Hole blocking layer 7 Electron transport layer 8 Cathode

Claims (10)

A light-emitting material comprising a host material and a phosphorescent dopant material having an electron-withdrawing group, wherein the host material has a lowest orbital (hereinafter abbreviated as LUMO) level lower than the LUMO level of the dopant material, and the host A light-emitting material characterized in that the highest occupied orbital (hereinafter abbreviated as HOMO) level of the material is lower than the HOMO level of the dopant material. The luminescent material according to claim 1, wherein the electron-withdrawing group of the dopant material is a halogen atom. The luminescent material according to claim 2, wherein the halogen atom is a fluorine atom. 4. The luminescent material according to claim 1, wherein an emission maximum wavelength of the dopant material is 500 nm or less. 5. The luminescent material according to claim 1, wherein the host material is represented by the following general formula (I).

(In the formula, Ar represents an arbitrary aromatic hydrocarbon group or aromatic heterocyclic group which may have a substituent. N represents an integer of 1 to 10. Z represents a direct bond or n. Represents a valent linking group, provided that when n = 1, Z represents any substituent or hydrogen atom bonded to Ar, and when n ≧ 2, a plurality of Ars contained in one molecule are each They may be the same or different.) The light emitting material according to claim 5, wherein the host material represented by the general formula (I) is a carbazole compound. The luminescent material according to claim 5, wherein the host material represented by the general formula (I) is a phenylpyridine-based compound. An organic electroluminescent element having an anode, a cathode, and a light emitting layer provided between both electrodes on a substrate, wherein the light emitting layer contains the light emitting material according to any one of claims 1 to 7. Light emitting element. The organic electroluminescence device according to claim 8, further comprising a hole blocking layer and / or an electron transport layer between the cathode and the light emitting layer. 10. The organic electroluminescent device according to claim 8, further comprising a hole transport layer between the anode and the light emitting layer.

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