JP2011148725A - Light-emitting composition, organic electroluminescent element and benzodifuran derivative - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting composition having high luminance and a long lifetime and an organic electroluminescent element. <P>SOLUTION: The light-emitting composition includes at least a light-emitting dopant and a host material, and at least part of the hydrogen atoms of CH bonds present in the host material is substituted with a deuterium atom. The organic electroluminescent element has at least a substrate (1), an anode (2) and a cathode (8) on the substrate (1), and a light-emitting layer (5) comprising the light-emitting composition in between the both electrodes. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention belongs to the technical field of a luminescent composition used for an organic electroluminescent device and the like, and an organic electroluminescent device using the luminescent composition. The present invention also relates to benzodifuran derivatives useful as host materials.

  In recent years, organic electroluminescence devices have been rapidly researched and developed, and are now commercialized. The organic electroluminescent element generally has a configuration in which a plurality of organic layers such as an electron transport layer, a hole transport layer, and a light emitting layer are laminated between two electrodes. In the light emitting layer, a light emitting material obtained by doping a host material with a light emitting dopant is generally used. Various host materials used for this doping method have been studied. In recent years, various host materials of phosphorescent materials that emit light by triplet excitons have been proposed (for example, Patent Document 1). .

  On the other hand, it has been reported that emission stability and the like are improved by deuterating a hydrogen atom bonded to a conjugated skeleton such as an organic semiconductor compound (for example, Patent Documents 2 and 3). There is no report on the effect of deuteration on light-emitting materials using the doping method. Since the structure of the organic molecule used in the organic electroluminescent device and the performance of the organic device are closely related, the performance of the device itself may be impaired by modifying the structure of the organic molecule.

JP 2008-306168 A JP 2004-99868 A JP-T-2004-515506

An object of the present invention is to provide a technique capable of achieving high luminance and long life without impairing the performance of a luminescent composition and an organic electroluminescent device utilizing a doping method.
More specifically, an object of the present invention is to provide a luminescent composition having high luminance and a long lifetime, and an organic electroluminescent device. It is another object of the present invention to provide a novel benzodifuran derivative useful as a host material of a light-emitting composition utilizing a doping method, particularly a host material of a phosphorescent material.

As a result of various studies to solve the above-mentioned problems, the present inventor has substituted at least a part of the CH-bonded hydrogen atoms present in the host material with deuterium atoms in the luminescent composition utilizing the doping method. Thus, it was found that high brightness and long life can be achieved, and the present invention has been completed. Means for solving the above-mentioned problems are as follows.
[1] A luminescent composition comprising at least a luminescent dopant and a host material, wherein at least a part of CH bond hydrogen atoms present in the host material are substituted with deuterium atoms. object.
[2] The host material has a ring system partial structure including at least one aromatic ring, and a C ₁ or more organic group bonded to the ring system partial structure by a σ bond, and CH in the organic group The luminescent composition according to [1], wherein at least some of the hydrogen atoms in the bond are substituted with deuterium atoms.
[3] The luminescent composition according to [2], wherein at least a part of hydrogen atoms bonded to the α-position carbon atom of the organic group is substituted with a deuterium atom.
[4] The luminescent composition according to [2] or [3], wherein at least part of hydrogen atoms bonded to non-conjugated carbon atoms is substituted with deuterium atoms.
[5] The luminescent composition according to any one of [2] to [4], wherein the organic group is a substituted or unsubstituted alkyl group.
[6] The luminescent composition according to any one of [2] to [5], wherein the ring system partial structure includes at least one benzene ring.

で表される［２］〜［６］のいずれかの発光性組成物。 [7] The ring system partial structure is represented by the following formula (I) or (II):

The luminescent composition in any one of [2]-[6] represented by these.

式中、Ｒ¹〜Ｒ⁴はそれぞれ水素原子又は置換基を表すが、少なくとも１つは、置換もしくは無置換のジアリールアミノ基、又は置換もしくは無置換のＮ−カルバゾリル基を表し；Ｃは炭素原子を表し；Ｄは重水素原子を表し；Ｒ¹¹、Ｒ¹²、Ｒ²¹及びＲ²²はそれぞれ、重水素原子、水素原子、又は置換もしくは無置換のアルキル基を表す；
で表される化合物である［２］〜［７］のいずれかの発光性組成物。 [8] The host material is represented by the following formula (Ia) or (Ib)

In the formula, each of R ^{1 to} R ⁴ represents a hydrogen atom or a substituent, and at least one represents a substituted or unsubstituted diarylamino group or a substituted or unsubstituted N-carbazolyl group; C represents a carbon atom D represents a deuterium atom; R ¹¹ , R ¹² , R ²¹ and R ²² each represent a deuterium atom, a hydrogen atom, or a substituted or unsubstituted alkyl group;
The luminescent composition in any one of [2]-[7] which is a compound represented by these.

式中、Ｒ¹¹、Ｒ¹²、Ｒ²¹及びＲ²²はそれぞれ、重水素原子、水素原子、又は置換もしくは無置換のアルキル基を表す；
で表される化合物である［１］〜［９］のいずれかの発光性組成物。
［１１］ 前記発光性ドーパントが、りん光発光材料である［１］〜［１０］のいずれかの発光性組成物。
［１２］ 前記発光性ドーパントが、イリジウム錯体である［１］〜［１１］のいずれかの発光性組成物。
［１３］ 基板、該基板上に、陽極、陰極、及び該両極間に、［１］〜［１２］のいずれかの発光性組成物からなる発光層を少なくとも有する有機電界発光素子。
［１４］ 下記式（Ｉｄ）で表されるベンゾジフラン系誘導体：

式中、Ｒ¹³〜Ｒ¹⁵及びＲ²³〜Ｒ²⁵はそれぞれ、重水素原子、水素原子、又は置換もしくは無置換のアルキル基を表す。 [9] The luminescent composition according to [8], wherein R ³ and R ⁴ each represent a substituted or unsubstituted diarylamino group or a substituted or unsubstituted N-carbazolyl group; R ¹ and R ² each represent a hydrogen atom. object.
[10] The host material is represented by the following formula (Ib)

In the formula, R ¹¹ , R ¹² , R ²¹ and R ²² each represent a deuterium atom, a hydrogen atom, or a substituted or unsubstituted alkyl group;
The luminescent composition in any one of [1]-[9] which is a compound represented by these.
[11] The luminescent composition according to any one of [1] to [10], wherein the luminescent dopant is a phosphorescent material.
[12] The luminescent composition according to any one of [1] to [11], wherein the luminescent dopant is an iridium complex.
[13] An organic electroluminescent device having at least a light emitting layer made of the light emitting composition of any one of [1] to [12] between a substrate, the substrate, an anode, a cathode, and both electrodes.
[14] A benzodifuran derivative represented by the following formula (Id):

In the formula, R ^{13 to} R ¹⁵ and R ^{23 to} R ²⁵ each represent a deuterium atom, a hydrogen atom, or a substituted or unsubstituted alkyl group.

ADVANTAGE OF THE INVENTION According to this invention, the lifetime of the luminescent composition and organic electroluminescent element using a doping method can be extended.
In addition, according to the present invention, it is possible to provide a luminescent composition having a high luminance and a long lifetime, and an organic electroluminescent element.
In addition, according to the present invention, a novel benzodifuran derivative useful as a host material of a luminescent composition utilizing a doping method, particularly a host material of a phosphorescent material can be provided.

It is a cross-sectional schematic diagram of one Embodiment of the organic electroluminescent element of this invention.

Hereinafter, the present invention will be described in detail.
1. Luminescent composition The present invention is a luminescent composition comprising at least a luminescent dopant and a host material, wherein at least some of the hydrogen atoms in the CH bond present in the host material are substituted with deuterium atoms. The present invention relates to a luminescent composition. The luminescent composition of the present invention is a luminescent composition using a so-called doping method in which a host material is doped with a luminescent dopant. In the doping method, carriers are first transferred from the host to the dopant. As a result, the dopant is electrically excited to excite the dopant, and when the excited dopant returns to the ground state, light is emitted and energy is released. As a result of various studies on the luminescent composition using the doping method by the present inventors, one of the causes of the luminescence decay is that the highly reactive hydrogen atom present in the host molecule is in the flow of this series of luminescence mechanisms. I found out that it would fall out. In the present invention, by deuterating at least some of the hydrogen atoms of the CH bonds present in the host material, the stability of the host material is improved and a long life is achieved. Furthermore, unexpectedly, it has been found that by deuterating the host material, the luminance of the luminescent composition utilizing the doping method can also be improved.

  While removing highly reactive hydrogen atoms from the host molecule and replacing them with less reactive atoms or atomic groups contributes to longer life, the molecular structure of the material is closely related to the emission characteristics and further to the device characteristics. Therefore, the light emission characteristics themselves may be impaired. Actually, as a result of investigation by the present inventor, when a highly reactive hydrogen atom is replaced with a bulky methyl group in order to improve stability, the driving voltage is lower than that of the host material before the introduction of the methyl group. It has been found that the temperature rises excessively, that is, the initial device characteristics themselves are impaired. According to the present invention, it is possible to achieve high brightness and long life while maintaining the light emission characteristics of a light emitting composition using a non-deuterated host material.

Host material:
The molecular structure of the host material used in the present invention is not particularly limited. The present invention is particularly advantageous for extending the lifetime of a luminescent composition using a host material having a highly reactive hydrogen atom. For example, in a host material having a ring system partial structure including at least one aromatic ring, at least a part of hydrogen atoms of a CH bond in a C ₁ or more organic group bonded to the ring system partial structure by a σ bond, It is preferably substituted with a deuterium atom. Since the chain length and structure of the organic group influence the emission color, the organic group may be variously selected according to the color purity. Regardless of which organic group is selected, the effect of the present invention can be obtained by substituting at least a part of the CH bond therein with a deuterium atom.
In particular, in the organic group, a hydrogen atom bonded to the α-position carbon atom with respect to the ring system partial structure is highly reactive, so that at least a part of the hydrogen atoms bonded to the α-position carbon atom is heavy. Substitution with hydrogen atoms is preferred, and substitution with deuterium atoms is more preferred.

In the present invention, a hydrogen atom bonded to a non-conjugated carbon atom may be substituted with a deuterium atom. In one embodiment of the present invention, the host material includes a ring system partial structure containing at least one aromatic ring, and a substituted or unsubstituted C ₁ or higher alkyl group bonded to the ring system partial structure with a σ bond. And a hydrogen atom bonded to a carbon atom at the α-position of the alkyl group is substituted with a deuterium atom. The alkyl group may be a C ₁ -C ₄ lower alkyl group or a C ₅ or higher alkyl group. Moreover, it may be substituted, and the substituent has a hetero element such as a chain or cyclic alkyl group, an aryl group which may have a substituent, a heteroaryl group, an alkoxy group, an amino group, an alkylsulfanyl group. And silyl groups.

  Examples of the host material used in the present invention are organic compounds having a ring system partial structure having at least one aromatic ring. The ring system partial structure may be a monocyclic structure or a condensed ring structure. The ring system structure preferably contains a benzene ring. Examples of the ring system structure possessed by the host material that can be used in the present invention include the following structures, but are not limited to the following examples.

  An example of the host material is a compound represented by the following formulas (Ia) and (IIa).

In the formula, each of R ^{1 to} R ⁴ represents a hydrogen atom or a substituent, and at least one represents a substituted or unsubstituted diarylamino group or a substituted or unsubstituted N-carbazolyl group; C represents a carbon atom D represents a deuterium atom; R ¹¹ , R ¹² , R ²¹ and R ²² each represent a deuterium atom, a hydrogen atom, or a substituted or unsubstituted alkyl group. The number of carbon atoms of the alkyl group and examples of substituents are the same as described above.

In the examples of the compounds represented by the formulas (Ia) and (IIa), R ³ and R ⁴ each represent a substituted or unsubstituted diarylamino group or a substituted or unsubstituted N-carbazolyl group; R Compounds in which ¹ and R ² represent a hydrogen atom, that is, compounds represented by the following formulas (Ib), (Ic), (IIb) and (IIc) are included.

In the formulas (Ib), (Ic), (IIb) and (IIc), each R represents a substituent (for example, a substituted or unsubstituted C _{1 to} C ₄ alkyl group or alkoxy group), and n Represents an integer of 0 to 5, respectively. However, when n is 2 or more, if possible, a ring (for example, a benzene ring) may be formed. R ¹¹ , R ¹² , R ²¹ and R ²² have the same meanings as those in the above formulas (Ia) and (IIa).

  Since the compounds represented by the above formulas (Ia) to (Ic) and (IIa) to (IIc) have high excited triplet energy levels, they are useful as host materials for the phosphorescent dopant described later.

Luminescent dopant:
There is no restriction | limiting in particular about the luminescent dopant used for this invention. It may be a fluorescent luminescent dopant or a phosphorescent dopant. Each may be doped with one or more dopants, or both light-emitting dopants may be doped with one or more. Examples of the phosphorescent dopant include complex compounds such as iridium complexes and platinum complexes; and benzophenone compounds. Examples of fluorescent light-emitting dopants include various fluorescent dyes such as naphthacene derivatives and various conjugated polymers such as polyfluorene. Use of a phosphorescent dopant is preferable because the internal quantum efficiency is increased. In the embodiment in which the compounds represented by the above formulas (Ia) to (Ic) and (IIa) to (IIc) are used as the host material, the luminescent dopant is preferably a phosphorescent dopant, and in particular, an iridium complex. Is preferred.

  Note that some or all of the CH-bonded hydrogen atoms present in the luminescent dopant may be substituted with deuterium atoms. However, even if only the luminescent dopant is deuterated, the present inventor has confirmed that the effects of the present invention cannot be achieved, that is, that the lifetime cannot be increased, in Examples described later. . That is, the effect of the present invention can be obtained for the first time by deuterating a host material used for a light-emitting material using a doping method. For example, hydrogen bonded directly to a conjugated skeleton in a light-emitting dopant can be obtained. By deuterating atoms, it is distinguished from the prior art which is stabilized.

  The preferred ratio of the luminescent dopant in the luminescent composition of the present invention will vary depending on the type of host material to be combined and the like. In general, the luminescent dopant is preferably about 0.01 to 80 parts by mass, more preferably about 0.1 to 30 parts by mass with respect to 100 parts by mass of the host material. The amount is more preferably about 1 to 15 parts by mass, and still more preferably about 0.1 to 10 parts by mass.

2. TECHNICAL FIELD The present invention also relates to a substrate, an organic electroluminescence device having at least a light emitting layer made of the luminescent composition of the present invention between the anode, the cathode, and both electrodes on the substrate. The organic electroluminescent element of the present invention is required to have an anode, a cathode, and a light emitting layer disposed between them, and in addition, if desired, other components may be provided between the anode and / or the cathode and the light emitting layer. The light emitting layer and / or other functional layers may be included. For example, examples of other functional layers disposed between the anode and the light emitting layer include a hole injection layer, a hole transport layer, and an electron blocking layer. Examples of other functional layers disposed between the cathode and the light emitting layer include an electron injection layer, an electron transport layer, and a hole blocking layer. These layers may have a plurality of functions in one layer.

  A schematic cross-sectional view of one embodiment of the organic electroluminescent device of the present invention is shown in FIG. In FIG. 1, reference numeral 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, 5 is a light emitting layer, 6 is an electron transport layer, 7 is an electron injection layer, and 8 is a cathode. Yes.

  The substrate 1 serves as a support for a plurality of organic layers formed thereon. There is no restriction | limiting in particular about the material. A quartz plate, a glass plate, a metal plate, a metal foil, a plastic film, a plastic sheet, or the like is used. In particular, a transparent substrate is preferable, and a glass plate and plastic films such as polyester, polymethacrylate, polycarbonate, polysulfone and the like are preferable. When a plastic film is used as the substrate 1, it is necessary to pay attention to the gas barrier property. In order to improve the gas barrier property, the gas barrier property is provided by a method such as providing a dense silicon oxide film on at least one surface. May be improved.

  An anode 2 is provided on the substrate 1 so that holes can be injected from the anode 2 into the hole injection layer 3. This anode is usually a metal such as aluminum, gold, silver, nickel, palladium, platinum, or a metal oxide such as an oxide of indium, tin and / or zinc (for example, indium tin oxide (ITO), indium zinc oxide (IZO). )), Metal halides such as copper iodide, carbon black, or conductive polymers such as poly (3-methylthiophene), polypyrrole, and polyaniline.

The anode 2 can be formed by, for example, a sputtering method or a vacuum deposition method. In addition, metal fine particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, and conductive polymer fine powder are dispersed in an appropriate binder resin solution and applied onto the substrate 1. The anode 2 can also be formed by Further, when a conductive polymer is used as the material of the anode 2, a thin film may be formed directly on the substrate 1 by electrolytic polymerization, or the anode 2 may be formed by applying a conductive polymer on the substrate 1. Is possible. The anode 2 may have a laminated structure of layers made of different materials.
There is no particular limitation on the thickness of the anode 2. From the viewpoint of transparency, it is generally 5 to 1000 nm, preferably about 10 to 500 nm.

  A hole injection layer 3 is disposed on the anode 2. The conditions required for the material of the hole injection layer 3 are that the hole injection efficiency from the anode 2 is high and the injected holes can be efficiently transported. For this purpose, a small difference between the ionization potential of the hole injection material and the work function of the anode is required. Moreover, it is also preferable that transparency is high with respect to visible light. From these viewpoints, the hole injection layer 3 is made of, for example, an organic material such as a porphyrin derivative, a phthalocyanine compound (Japanese Patent Laid-Open No. 63-295695), a starburst aromatic triamine (Japanese Patent Laid-Open No. 4-308688) Compounds, sputtered carbon films (Japanese Patent Laid-Open No. 8-31573), metal oxides such as vanadium oxide, ruthenium oxide, molybdenum oxide (The 43rd Joint Conference on Applied Physics, 27a-SY- 9, 1996). The porphyrin compound and the phthalocyanine compound may have a central metal or may be metal-free. Specific examples of phthalocyanine compounds include 29H, 31H-phthalocyanine, copper (II) phthalocyanine, zinc (II) phthalocyanine, titanium phthalocyanine oxide, copper (II) 4,4 ', 4 ", 4' ''-tetraaza-29H , 31H-phthalocyanine, etc. Other examples of the material of the hole injection layer 3 include a system in which an electron-accepting compound is mixed with a hole-transporting polymer. Examples of the molecule include polythiophene (Japanese Patent Laid-Open No. 10-92584), polyaniline, and aromatic amine-containing polyether (Japanese Patent Laid-Open No. 2000-36390).

There is no restriction | limiting in particular about the formation method of the positive hole injection layer 3. FIG. A preferred method will be selected depending on the material. Vacuum deposition when using compounds with sublimation, wet coating such as spin coating and ink jet when using compounds that are soluble in solvents, sputtering, electron beam evaporation, plasma when using inorganics A CVD method can be used.
The film thickness of the hole injection layer 3 thus formed is usually about 3 to 200 nm, preferably about 10 to 100 nm.

A hole transport layer 4 is provided on the hole injection layer 3. It is desirable that the material of the hole transport layer 4 has a high hole injection efficiency from the hole injection layer 3 and can efficiently transport the injected holes to the light emitting layer 5. For that purpose, the difference between the ionization potential of the hole injection material and the ionization potential of the hole transport material is small, the transparency to visible light is high, the hole mobility is large, and the stability against oxidation is excellent. In addition, it is required that impurities that become traps are less likely to be generated during manufacture and use. In consideration of applications for in-vehicle display, in addition to these requirements, the element is required to have heat resistance. In order to satisfy the heat resistance of the element, it is preferable to use a material having a glass transition temperature (Tg) of 100 ° C. or higher. Examples of materials constituting the hole transport layer include carbazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino Substituted chalcone derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, polysilane compounds, poly (N- Vinylcarbazole) derivatives, organosilane derivatives, and polymers containing these structures.
There is no restriction | limiting in particular about the formation method of a positive hole transport layer, It is the same as that of the formation method of a positive hole injection layer, A various method can be utilized according to material. The film thickness of the hole transport layer 4 is usually about 10 to 300 nm, preferably about 30 to 100 nm.

A light emitting layer 5 is disposed on the hole transport layer 4. The light emitting layer 5 is made of the light emitting composition of the present invention. Although there is no restriction | limiting in particular about the formation method of the light emitting layer 5, It is preferable to utilize a vapor deposition method at the point which can form a thin layer uniformly.
Although there is no restriction | limiting in particular also about the film thickness of the light emitting layer 5, Usually, about 10-200 nm, Preferably it is about 30-100 nm.

An electron transport layer 6 is disposed on the light emitting layer 5. The electron transport layer 6 is made of a material that contributes to the improvement of luminous efficiency, facilitates electron injection from the cathode 8, and has a large electron transport capability. Examples of such an electron transport material include an aluminum complex of 8-hydroxyquinoline, an oxadiazole derivative (J. Appl. Phys., 65, 3610, 1989), a phenanthroline derivative (Japanese Patent Laid-Open No. 5-33159). Publication), starburst type benzimidazole compounds (Japanese Patent Laid-Open No. 10-106749), silole compounds (Appl. Phys. Lett., 55, 1489, 1989), and the like. Furthermore, since the electron transport layer 6 contains an alkali metal, the electron transport material is reduced by a reaction with the alkali metal, and an anion radical serving as a charge carrier can be efficiently generated. It can be greatly improved. (Japanese Patent Laid-Open No. 10-270171). Li, Na, K, Cs etc. are used as an alkali metal. The content of the alkali metal in the electron transport layer 6 is preferably 1 to 50% by weight. As a method of mixing the alkali metal with the electron transport material, co-evaporation of the electron transport material and the alkali metal can be used.
As a method for forming the electron transport layer 6, a thin film formation method similar to that exemplified above as a method for forming the hole injection layer can be used. The film thickness of the electron transport layer 6 is usually about 5 to 200 nm, preferably about 10 to 100 nm.

  An electron injection layer 7 is disposed on the electron transport layer 6. The electron injection layer 7 is a layer having a function of improving the electron injection efficiency from the cathode 8. The example of the material constituting the electron injection layer 7, the example of the formation method, and the thickness are the same as those of the electron transport layer 6.

In a mode in which the light emitting layer 5 is doped with a phosphorescent dopant, it is effective to provide a hole blocking layer between the light emitting layer and the cathode 8 in order to further improve the phosphorescence efficiency. is there. The material used for the hole blocking layer is required to have a HOMO-LUMO gap wider than that of the electron transport layer material as well as the electron transport property. Examples of materials that satisfy such conditions include phenanthroline derivatives.
Note that the electron transport layer 6 or the electron injection layer 7 may also function as a hole blocking layer.

The cathode 8 serves to inject electrons into the light emitting layer 5. As the material of the cathode 8, those exemplified above as materials used for the anode 2 can be used. However, in order to perform electron injection efficiently, a metal having a low work function is preferable. Specific examples of these include metals such as tin, magnesium, indium, calcium, aluminum, and silver, or alloys thereof. More specifically, a magnesium-silver alloy, a magnesium-indium alloy, an aluminum-lithium alloy, or the like can be given.
The example of the forming method and the thickness are the same as those of the anode.

Furthermore, an ultrathin insulating film (thickness of 0.1 to 5 nm) such as Li complex of LiF, MgF ₂ , Li ₂ O, Cs ₂ CO ₃ , 8-hydroxyquinoline or the like is formed at the interface between the cathode 8 and the electron injection layer 7. Is also an effective method for improving the efficiency of the device (Appl. Phys. Lett., 70, 152, 1997, IEEE Trans. Electron. Devices, 44, 1245, 1997). SID 04 Digest, page 154, 2004, JP 11-233262 A).

FIG. 1 shows an embodiment of the organic electroluminescence device according to the present invention, and the present invention is not limited to the illustrated configuration. For example, a stacked structure opposite to that shown in FIG. 1 is adopted, that is, a cathode 8, an electron injection layer 7, an electron transport layer 6, a light emitting layer 5, a hole transport layer 4, a hole injection layer 3, an anode on the substrate 1. Stacking in the order of 2 is also possible. Other configuration examples are shown below, but are not limited to the following examples. Further, as described above, the substrate may be disposed on either side.
Anode / hole transport layer / light emitting layer / cathode Anode / light emitting layer / electron transport layer / cathode Anode / hole transport layer / light emitting layer / electron transport layer / cathode Anode / hole injection layer / light emitting layer / cathode Anode / light emitting Layer / electron injection layer / cathode anode / hole injection layer / emission layer / electron injection layer / cathode anode / hole injection layer / hole transport layer / emission layer / cathode anode / emission layer / electron transport layer / electron injection layer / Cathode Anode / hole transport layer / light emitting layer / electron injection layer / cathode Anode / hole injection layer / light emitting layer / electron transport layer / cathode Anode / hole injection layer / hole transport layer / light emitting layer / electron injection layer / Cathode Anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode Anode / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode Anode / hole injection layer / light emitting layer / Electron transport layer / electron injection layer / cathode

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

3. Benzodifuran derivative The present invention also relates to a benzodifuran derivative represented by the following formula (Id). The benzodifuran derivative of the present invention is useful as a host material for a luminescent composition utilizing a doping method, particularly as a host material for a phosphorescent material (for example, an iridium complex). In particular, in the following formula (Id), at least one of R ^{13 to} R ¹⁵ is a deuterium atom (preferably 2 or more, more preferably all are deuterium atoms), and at least one of R ^{23 to} R ²⁵ is a deuterium atom. A compound (preferably 2 or more, more preferably all deuterium atoms) not only is useful as a host material, but also contributes to the extension of the lifetime of a luminescent composition utilizing a doping method. Further, the benzodifuran derivative represented by the following formula (Id) is expected to be used not only as a host material of a luminescent composition but also as a hole transport material or a charge transport material of an organic electroluminescent element.

In the formula (Id), R ^{13 to} R ¹⁵ and R ^{23 to} R ²⁵ each represent a deuterium atom, a hydrogen atom, or a substituted or unsubstituted alkyl group. The alkyl group may be a C ₁ -C ₄ lower alkyl group or a C ₅ or higher alkyl group. Examples of the substituent of the alkyl group include those having a hetero element such as an aryl group and a heteroaryl group, an alkoxy group, an amino group, and an alkylsulfanyl group, which may have a substituent, and a silyl group. Examples of the substituted or unsubstituted alkyl group, an unsubstituted C ₁ -C ₄ lower alkyl groups (e.g. methyl group).

  The present invention will be described more specifically with reference to the following examples. The materials, reagents, amounts and ratios of substances, operations, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples.

1. Production Examples of Benzodifuran Derivatives (CZBDF-1 to 3) The following benzodifuran cyclization precursors Pre-1, Pre-2, and Pre-3 were synthesized using known compounds as starting materials.

As an example, a synthesis example of Pre-1 is described below.

To a solution of 5.18 g (16 mmol) of Pre-1a dissolved in tetrahydrofuran (48 mL), a 1.56 mol / L hexane solution of normal butyl lithium (n-BuLi) was added dropwise at 0 ° C. The reaction was allowed to proceed with stirring for minutes. Next, 4.03 mL (64.0 mmol) of CD ₃ I was added to the reaction solution, and the reaction was allowed to proceed at room temperature for 22 hours to obtain Pre-1b. The yield was 94%.
1.08 g of Pre-1b, 28.5 mg of p-toluenesulfonic acid monohydrate, and a 2: 1 mixed solvent of CH ₂ Cl ₂ and methanol were mixed and reacted at room temperature for 30 minutes. -1 was obtained. The yield was 95%.

Below, a synthesis scheme is also simply shown for Pre-2 and Pre-3.

  Using each of the benzodifuran cyclization precursors Pre-1, Pre-2, and Pre-3 as starting materials, benzodifuran derivatives CZBDF-1 to 3 were synthesized according to the following scheme.

The synthesis of CZBDF-1 is shown as an example. After dropping 3.85 mL of n-BuLi (1.56 mol / L hexane solution) at 0 ° C. into a solution of Pre-1 in 577 mg (3.0 mmol) in dehydrated tetrahydrofuran (3.0 mL), the reaction mixture was cooled to room temperature. The mixture was heated up to a total of 30 minutes. To this reaction mixture, 6.0 mL of a 1.0 mol / L tetrahydrofuran solution of zinc chloride and 6.0 mL of dehydrated toluene were added, and the temperature was raised to 120 ° C. and stirred for 3 hours. The reaction solution was cooled to room temperature, the N- methylpyrrolidone 1.5 mL, the _{Pd 2 (dba) 3 · CHCl} 3 31.1mg (0.3mmol), P (t-Bu) ₃ in 1.0 mol / L 1.2 mL (1.2 mmol) of the toluene solution and 2.32 g (7.2 mmol) of Agent-1 were added, and the mixture was stirred at 60 ° C. for 20 hours. After cooling to room temperature, methanol was added to the reaction solution to precipitate a precipitate, and the filtered product was washed with ethyl acetate and dried to obtain a crude product.
By repeating this isolation and purification several times with a sublimation purification apparatus, the target product CZBDF-1 was obtained in a yield of 27%. Identification was performed by ¹ H and ¹³ C-NMR.
¹ H NMR (500 MHz, CDCl ₂ CDCl ₂ ) δ7.29 (t, J = 7.5 Hz, 4H), 7.43 (t, J = 7.5 Hz, 4H), 7.52 (d, J = 7.5 Hz, 4H), 7.67 (d, J = 8.0 Hz, 4H), 7.72 (s, 2H), 7.75 (d, J = 8.0 Hz, 4H), 8.13 (d, J = 7.5 Hz, 4H).
¹³ C NMR (125 MHz, CDCl ₂ CDCl ₂ ) δ100.4, 110.1, 116.4, 120.3, 120.5, 123.3, 126.1, 126.3, 127.3, 130.3, 136.3, 140.8, 151.3, 152.6.

CZBDF-2 and 3 were also obtained in a yield of 54 to 67% by the same method. Identification was performed by ¹ H NMR and elemental analysis.
CZBDF-2:
¹ H NMR (500 MHz, CDCl ₂ CDCl ₂ ) δ 2.63 (s, 6H), 7.29 (t, J = 7.5 Hz, 4H), 7.43 (t, J = 7.5 Hz, 4H), 7.52 (d, J = 8.0 Hz, 4H), 7.67 (d, J = 8.0 Hz, 4H), 7.72 (s, 2H), 7.75 (d, J = 8.0 Hz, 4H), 8.13 (d, J = 8.0 Hz, 4H).
Elemental analysis C ₄₈ H ₃₂ N ₂ O ₆ : Calculated value (wt%) C 86.20; H 4.82; N 4.19. Found C 86.32; H 4.67; N 4.06
CZBDF-3:
¹ H NMR (500 MHz, CDCl ₂ CDCl ₂ ) δ1.31 (s, 18H), 7.29 (t, J = 7.5 Hz, 4H), 7.31 (s, 2H), 7.44 (t, J = 7.5 Hz, 4H ), 7.52 (d, J = 8.0 Hz, 4H), 7.58-7.63 (m, 8H), 8.13 (d, J = 8.0 Hz, 4H).
Elemental analysis C ₅₄ H ₄₄ N ₂ O ₆ : Calculated value (% by weight) C 86.14; H 5.89; N 3.72. Found C 86.21; H 5.99; N 3.51

2. Basic physical properties of benzodifuran derivatives For the benzodifuran derivatives CZBDF-1 to 3 obtained above, the orbital energy levels (HOMO, LUMO) were determined by cyclic voltammetry and UV-visible absorption spectra, respectively, and excited triplet energy levels (T ₁ ). Was measured by phosphorescence, and the hole mobility (μ _h ) was measured by a time-of-flight method using an amorphous film. The result is shown in the following formula.

  As shown in the above table, it can be understood that any of CZBDF-1 to 3 functions as a phosphorescent dopant host material.

3. Production and Evaluation of Organic Electroluminescence Device (Device Nos. 1 to 3) An organic electroluminescence device having the structure shown in FIG. 1 was produced by the following method. An indium tin oxide (ITO) transparent conductive film is deposited on the glass substrate 1 by sputtering at 145 nm to form an ITO film (sheet resistance 10Ω, average surface roughness 1.5 nm). The anode 2 was formed by patterning into stripes having a width of 2 mm using hydrochloric acid etching. The patterned ITO substrate is subjected to ultrasonic cleaning with a surfactant (Semi-clean M-LO, manufactured by Yokohama Oil & Fat Co., Ltd.), ultrasonic cleaning with ultrapure water, and running water cleaning, followed by drying with nitrogen blow. Finally, ultraviolet ozone cleaning was performed.

  On the anode 2 subjected to the above cleaning treatment, PEDOT: PSS (product name: Baytron CH 8000 manufactured by Starck Vitec), which is a conductive polymer (polythiophene), was spin-coated as a hole injection layer 3 with a film thickness of 70 nm. Then, it was heat-dried at 120 ° C. for 10 minutes in the atmosphere, and then heat-treated at 180 ° C. for 3 minutes in nitrogen.

Next, the ITO substrate on which the hole injection layer 3 was formed was placed in a vacuum deposition apparatus. After roughly exhausting the apparatus with an oil rotary pump, the apparatus was exhausted with a cryopump until the degree of vacuum in the apparatus was 2 × 10 ⁻⁴ Pa or less.
The following aromatic amine compound (α-NPD) placed in a metal boat arranged in the above apparatus was heated to deposit on the ITO substrate on which the hole injection layer 3 was formed. The degree of vacuum during deposition is 2.4 × 10 ⁻⁴ Pa, the deposition rate is 0.15 nm / second, and a hole transport layer 4 is formed by laminating a 45 nm film on the hole injection layer 3. did.

Subsequently, as a material of the light emitting layer 5, any one of CZBDF-1 to CZBDF-1 to 3 is used as a host material, and 4.3 to 4.5% by mass of the iridium complex (Ir (ppy) ₃ shown below) based on the host material. Each of the light-emitting compositions doped with) was prepared, and the light-emitting layers 5 were formed by vapor deposition in the same manner as the hole transport layer 4. The deposition was performed under the conditions of a deposition rate of 0.07 to 0.12 nm / second and a vacuum degree during deposition of 2.5 to 2.7 × 10 ⁻⁴ Pa. The thickness of the deposited light emitting layer 5 was 30 nm.

An electron transport layer 6 made of BCP having the following structure was formed on the light emitting layer 5 in the same manner as the hole transport layer 4 by vapor deposition. The deposition was performed under the conditions of a deposition rate of 0.05 to 0.10 nm / second and a degree of vacuum of 2.4 to 2.5 × 10 ⁻⁴ Pa during deposition. The film thickness of the electron transport layer 6 was 10 nm.

An electron injection layer 7 made of aluminum 8-hydroxyquinoline complex Al (C ₉ H ₆ NO) ₃ was formed on the electron transport layer 6 in the same manner as the hole transport layer 4 by vapor deposition. The film thickness of the electron injection layer 7 was 20 nm.

Thereafter, the element on which the vapor deposition up to the electron injection layer 7 has been performed is moved to a vacuum chamber for metal vapor deposition in a vacuum, and a 2 mm wide striped shadow mask is used as the cathode vapor deposition mask and the ITO stripe on the anode 2. Were in close contact with the element so as to be orthogonal to each other, and evacuated with a cryopump until the degree of vacuum in the apparatus was 3 × 10 ⁻⁴ Pa or less in the same manner as in the case of the organic layer.

In order to facilitate electron injection from the cathode 8 on the electron injection layer 7, a lithium complex of 8-hydroxyquinoline is deposited as a cathode interface layer at a deposition rate of 0.008 nm / second and a degree of vacuum of 2.2 at the time of deposition. The film was formed with a film thickness of 1.0 nm under the condition of × 10 ⁻⁴ Pa.
Subsequently, aluminum was formed to a thickness of 80 nm on the cathode interface layer at a deposition rate of 0.5 nm / second. The degree of vacuum at the time of deposition was 2.3 × 10 ⁻⁴ Pa.

As described above, an organic electroluminescent element having a light emitting area portion having a size of 2 mm × 2 mm was obtained.
For each fabricated device, the voltage was varied to track the LV characteristics, and from the LV curve, the maximum luminance (L _max ) and the maximum external quantum efficiency (EQE _max ) based on the Lambertian assumption, and drive The voltage (V ₁₀₀₀ ) and luminance efficiency (η ₁₀₀₀ ) were determined. The results are shown in the table below.

Subsequently, the device No. For 1 and 2, the half-life t _1/2 was measured with the current density constant at 12.5 mA / cm ² . The results are shown in the table below.

As shown in the above two tables, Device No. 1 uses a luminescent composition in which a deuterated host material (CZBDF-1) is doped with a phosphorescent dopant as the material of the luminescent layer 5. Therefore, as a material for the light-emitting layer 5, as compared with the device No. 2 using a light-emitting composition in which a non-deuterated host material (CZBDF-2) is doped with a phosphorescent dopant, It can be understood that the maximum brightness is remarkably improved and the half-life is five times that a long life is achieved. That is, it can be understood that by deuterating the host material, the luminance was improved and the lifetime was improved without deteriorating the device characteristics.
On the other hand, the device No. 3 is a device using CZBDF-3 in which R is a t-butyl group as a host material of the light-emitting layer 5, and is more reactive than CZBDF-2 in which R is a methyl group. The light emitting layer 5 uses a highly stable host material in which high hydrogen atoms (hydrogen atoms bonded to α-position carbon atoms) are substituted with methyl groups. As a result, the maximum luminance is improved to the same extent as device No. 1. On the other hand, it can be understood that the mobility is lowered and the driving voltage is remarkably increased. Therefore, although device No. 3 is stabilized as compared with No. 2, it can be understood that it is inferior in terms of drive voltage.

4). Production and evaluation of organic electroluminescence element (device No. 4) In production of device No. 2, CZBDF-2 was used as a host material as the material of the light-emitting layer 5, and 4.3 mass% of the host material below. Device No. 4 was produced in the same manner as Device No. 2 except that the luminescent composition doped with the deuterium iridium complex (Ir (Dppy) ₃ ) shown in FIG.

As for device No. 4, various device characteristics were measured in the same manner as described above. 1 and 2 and initial device characteristics (driving voltage and maximum efficiency) were the same. Next, the half-life t _1/2 was measured with the current density kept constant at 12.5 mA / cm ² . The results are shown in the table below.

  As shown in the above table, device No. 4 was almost the same as device No. 2 in terms of lifetime, and it was not possible to achieve a longer lifetime. That is, for a luminescent composition using a doping method, even if the dopant is deuterated, it is impossible to achieve a long lifetime, and it is possible to achieve a long lifetime only by deuterating the host material. Understandable.

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

Claims (14)

A luminescent composition comprising at least a luminescent dopant and a host material, wherein at least a part of CH bond hydrogen atoms present in the host material are substituted with deuterium atoms. The host material has a ring system partial structure including at least one aromatic ring, and a C ₁ or more organic group bonded to the ring system partial structure by a σ bond, and at least CH bonds in the organic group The luminescent composition according to claim 1, wherein some of the hydrogen atoms are substituted with deuterium atoms. The luminescent composition according to claim 2, wherein at least a part of hydrogen atoms bonded to the α-position carbon atom of the organic group is substituted with a deuterium atom. The luminescent composition according to claim 2 or 3, wherein at least a part of hydrogen atoms bonded to non-conjugated carbon atoms is substituted with deuterium atoms. The luminescent composition according to claim 2, wherein the organic group is a substituted or unsubstituted alkyl group. The luminescent composition according to any one of claims 2 to 5, wherein the ring system partial structure contains at least one benzene ring. The ring system partial structure is represented by the following formula (I) or (II)

The luminescent composition of any one of Claims 2-6 represented by these. The host material is represented by the following formula (Ia) or (Ib)

In the formula, each of R ^{1 to} R ⁴ represents a hydrogen atom or a substituent, and at least one represents a substituted or unsubstituted diarylamino group or a substituted or unsubstituted N-carbazolyl group; C represents a carbon atom D represents a deuterium atom; R ¹¹ , R ¹² , R ²¹ and R ²² each represent a deuterium atom, a hydrogen atom, or a substituted or unsubstituted alkyl group;
The luminescent composition according to claim 1, which is a compound represented by the formula: The luminescent composition according to claim 8, wherein R ³ and R ⁴ each represent a substituted or unsubstituted diarylamino group or a substituted or unsubstituted N-carbazolyl group; and R ¹ and R ² each represent a hydrogen atom. . The host material is represented by the following formula (Ib)

In the formula, R ¹¹ , R ¹² , R ²¹ and R ²² each represent a deuterium atom, a hydrogen atom, or a substituted or unsubstituted alkyl group;
The luminescent composition according to claim 1, which is a compound represented by the formula: The luminescent composition according to claim 1, wherein the luminescent dopant is a phosphorescent material. The luminescent composition according to claim 1, wherein the luminescent dopant is an iridium complex. The organic electroluminescent element which has at least the light emitting layer which consists of a luminescent composition of any one of Claims 1-12 between a board | substrate and this board | substrate between an anode, a cathode, and this both electrodes. A benzodifuran derivative represented by the following formula (Id):

In the formula, R ^{13 to} R ¹⁵ and R ^{23 to} R ²⁵ each represent a deuterium atom, a hydrogen atom, or a substituted or unsubstituted alkyl group.

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