JP6805133B2 - Materials for charge-transfer thin films and charge-transfer thin films - Google Patents

Description

The present invention relates to materials for charge-transfer thin films and charge-transfer thin films. More specifically, the present invention relates to a material for a charge-transfer thin film in which light emission derived from a long-wave electromer driven by an electric field is suppressed, and a charge-transfer thin film.

Generally, an electric field is applied to an electronic device such as an organic electroluminescence element (hereinafter, also referred to as "organic EL element"), a solar cell, and an organic transistor to which an electric field is applied, and charge carriers (general term for electrons and holes). A charge-transferring thin film containing an organic material capable of moving the electron is used.
Therefore, the organic material used for the charge-transfer thin film must have a chemical structure in which aromatic rings are combined in order to carry out carrier hopping conduction by π-π interaction. Since the functional organic materials contained in the charge-transfer thin film are required to have various performances, their development has been active in recent years.

As an organic material used for a blue phosphorescent organic EL element, which is an electronic device for which a macroscopic thin film stabilization technology is required, the lowest excited triplet energy level (T ₁ ) is high (in the following, "high T". ₁ ”.) Dibenzofuran skeletons and aromatic compounds having a carbazole skeleton are known (see, for example, Patent Documents 1 and 2). Aromatic compounds have the lowest excited triplet by spatially separating the highest occupied orbital (HOMO) of carbazole and the lowest empty orbital (LUMO) of dibenzofuran distributed on the aromatic compound, which is imaged by molecular orbital calculation. It suppresses the decrease in the term energy level (T ₁ ) (hereinafter, also referred to as "lower T ₁ "), promotes hopping conduction of carriers (electrons and holes), and is suitable for blue phosphorescent materials. It is a peripheral material.

However, it has also been found that these compounds do not function well in terms of luminous efficiency and luminescence lifetime when adapted to shorter wave blue phosphorescent materials. No matter how thermally and electrochemically stable the material is, as the number of times it becomes excited or radical by electric field driving increases, the molecules rotate around the vibration or bond axis, and the form of interaction between the molecules changes. This is because the film state changes.
Examples of changes in the film state include grain boundary formation due to aggregation of contained molecules and HOMO-LUMO stack formation, which is an interaction unfavorable for carrier transport. As a result of such film changes, the life of organic electronic devices using charge-transfer thin films has deteriorated due to changes in film quality.

Japanese Unexamined Patent Publication No. 2013-155153 Special Table 2013-528188

The present invention has been made in view of the above problems and situations, and an object of the present invention is to provide a material for a charge-transfer thin film having a long life and a charge-transfer thin film.

As a result of diligent studies to solve the above problems, the inventor of the present invention spatially determines the highest occupied orbitals and the lowest empty orbitals in which the aromatic compounds are distributed on the aromatic compounds imaged by molecular orbital calculation. The above problem can be solved by satisfying a predetermined formula in the current excitation emission spectrum of a single layer that is separated, has an alkyl group in the range of 3 to 20 carbon atoms, and contains the aromatic compound. We found it and came up with the present invention.
That is, the above problem according to the present invention is solved by the following means.

1. 1. A material for a charge-transfer thin film containing an aromatic compound.
At least two or more aromatic hydrocarbon rings or aromatic heterocycles in which the highest occupied orbitals and the lowest empty orbitals distributed on the aromatic compound imaged by molecular orbital calculation are spatially separated from each other. the a, further have an alkyl group in the range of 3 to 20 carbon atoms, and the current excitation emission spectrum of a single layer containing the aromatic compound, meet the following equation (1),
A material for a charge-transfer thin film, wherein the aromatic compound has a structure represented by the following general formula (1) .
Equation (1): a / b> 1
In the formula (1), a represents the maximum emission intensity appearing at an emission wavelength of 500 nm or less in the current excitation emission spectrum, b represents the maximum emission intensity appearing at an emission wavelength of 550 nm or more, and a represents the energization start. While decaying from the initial value to the value of 1/5, a and b always satisfy the relationship of equation (1).)
General formula (1):
(R ₁ ) _m- A- ( L) _k- B- (R ₂ ) _n
(In the general formula (1), A and B represent an aromatic hydrocarbon ring or an aromatic heterocycle which may have a substituent. R ₁ and R ₂ have a carbon number in the range of 3 to 20. L represents an aromatic hydrocarbon group, an aromatic heterocyclic group or an alkylene group which may have a simple binder or a substituent. M and n are one or more, respectively. Represents an integer. K represents an integer of 1 or more.)

2 . A charge-transfer thin film comprising the material for a charge-transfer thin film according to item 1.

According to the above means of the present invention, a material for a charge-transfer thin film having a long life and a charge-transfer thin film can be provided.

Although the mechanism of expression or mechanism of action of the effect of the present invention has not been clarified, it is inferred as follows.
By using a compound that can obtain a current-excited emission spectrum that satisfies a predetermined relational expression by using effects such as interaction between alkyl groups in addition to π-π interaction, light emission derived from a long-wave electron driven by an electric field can be generated. It is considered that it was possible to provide a material for a charge-transfer thin film having a long life and a charge-transfer thin film which can be suppressed. Furthermore, it is believed that the production suitability of the wet process could be improved due to the secondary effect of improving the solubility of the alkyl group.

Graph showing the photoexcitation spectrum of Comparative Compound 1 A graph showing the time course of the current excitation emission spectrum of Comparative Compound 1. Schematic diagram showing electromer generation by electric field drive Schematic diagram showing the ideal interaction mode Schematic diagram showing HOMO-LUMO of the aromatic compound according to the present invention Schematic diagram showing an ideal interaction form of a compound having an alkyl group Schematic diagram showing the interaction form between two molecules by MD calculation Schematic diagram of the lighting device Cross-sectional view of the lighting device

The material for a charge-transferring thin film of the present invention is a material for a charge-transferring thin film containing an aromatic compound, and the highest cover in which the aromatic compound is distributed on the aromatic compound imaged by molecular orbital calculation. It has at least two or more aromatic hydrocarbon rings or aromatic heterocycles in which the occupied orbital and the lowest empty orbital are spatially separated, and further has an alkyl group having an number of carbon atoms in the range of 3 to 20, and said current excitation emission spectrum of a single layer containing an aromatic compound, wherein meets formula (1), the aromatic compound is characterized by having the structure represented by the general formula (1).
This feature is a technical feature common to the inventions according to each claim.

Further, in the material for a charge-transfer thin film of the present invention, it is preferable that the aromatic compound has a structure represented by the general formula (1) because it easily takes an interaction form suitable for carrier transport.

Further, it is preferable that the charge-transfer thin film of the present invention contains the material for the charge-transfer thin film of the present invention from the viewpoint of exhibiting the effect.

Hereinafter, the present invention, its constituent elements, and modes and modes for carrying out the present invention will be described in detail. In addition, "~" shown in this invention is used in the meaning which includes the numerical values described before and after it as the lower limit value and the upper limit value.

The material for a charge-transferring thin film suitable for the present invention contains an aromatic compound, and the highest occupied orbital and the lowest empty orbital in which the aromatic compound is distributed on the aromatic compound imaged by molecular orbital calculation are determined. A simple substance having at least two or more aromatic hydrocarbon rings or aromatic heterocycles that are spatially separated, having an alkyl group having an number of carbon atoms in the range of 3 to 20, and containing the aromatic compound. further current excitation emission spectrum, meets the following formula (1), the aromatic compound is characterized by having a structure represented by the following general formula (1).
Equation (1): a / b> 1
In the formula (1), a represents the maximum emission intensity appearing at an emission wavelength of 500 nm or less in the current excitation emission spectrum, and b represents the maximum emission intensity appearing at an emission wavelength of 550 nm or more. While a attenuates from the initial value at the start of energization to a value of 1/5, a and b always satisfy the relationship of the equation (1).
General formula (1):
(R ₁ ) _m- A- ( L) _k- B- (R ₂ ) _n
In the general formula (1), A and B represent an aromatic hydrocarbon ring or an aromatic heterocycle which may have a substituent. R ₁ and R ₂ represent an alkyl group having an number of carbon atoms in the range of 3 to 20. L represents an aromatic hydrocarbon group, an aromatic heterocyclic group or an alkylene group which may have a simple bond or a substituent. m and n each represent an integer of 1 or more. k represents an integer of 1 or more.
First, the mechanism by which the aromatic compound according to the present invention does not easily generate light emission derived from an electromer will be described.

≪Expression of Electromer≫
A long-wave electromer expressed by electric field driving in an organic electronic device will be described.
Compounds used in organic electronic devices have a structure containing an aromatic ring for carrier hopping conduction, and when photoexcited, they have a fluorescence spectrum or phosphorus that is unique to each molecule and usually has a maximum intensity at a wavelength of 500 nm or less. The optical spectrum is observed.
For example, in the spectrum (solvent: 2-methylTHF, 285 nm excited) measured by photoexciting Comparative Compound 1 shown in FIG. 1, fluorescence has a maximum emission intensity of 500 nm or less at room temperature and phosphorescence has a maximum emission intensity of 500 nm or less at low temperature. Observed.

On the other hand, when an electric field is driven as a charge-moving thin film, in addition to observing fluorescence and phosphorescence, there are some compounds in which long-wave luminescence that is not observed in the emission spectrum of photoexcitation is observed with the lapse of energization.
The emission of long waves over time of energization is described in Apple. Phys. Lett. , 76, 2355, 2000, it is speculated that it is derived from an electromer formed by the proximity of a molecule having an electron and a molecule having a hole.

In the above document, electromer emission is observed at 600 nm or more (Comparative Compound 1: see FIG. 2), but as a result of examination by the present inventors, emission that is considered to be derived from electromer is observed at 550 nm or more. It became clear. Further, in particular, the organic molecule in which the molecular orbitals of the compound HOMO and LUMO can be spatially separated is a compound suitable for a blue phosphorescent material as described above, but when it is made into a thin film, the film quality changes due to energization. It was found that, as shown in FIG. 3, it is easy to form a π-π stack in which HOMO and LUMO of a certain molecule overlap, and it is easy to generate an electromer.

As a result, in an organic electronic device using an organic compound in which the molecular orbitals of HOMO and LUMO can be spatially separated as a material for a charge-transfer thin film, the electromers formed over time of energization serve as a carrier quencher. Therefore, it was found that the number of carriers to be passed to the luminescent molecule is reduced, which is one of the major factors for the deterioration of the life. Therefore, we have developed a stable charge-transfer thin film material in which the expression of long-wave electromers by electric field drive is suppressed.

≪Interaction between alkyl groups≫
In the present invention, in addition to the π-π interaction, the technical idea of suppressing a long-wave electromer by electric field driving using an interaction between alkyl groups and the like will be described.
Since the long-wave electromer is generated by the π-π stack of HOMO-LUMO driven by an electric field, a structure in which HOMO-HOMOs and LUMO-LUMOs are π-π stacked as shown in FIG. 4 is expressed in the membrane. Ideally. However, especially in the peripheral material corresponding to the high T ₁ blue light emitting material, HOMO and LUMO have a structure in which charges are separated in order to suppress the reduction of T ₁ and facilitate the transfer of carriers. Is preferable.

As a result, the electrostatic repulsion between HOMO-HOMO and LUMO-LUMO becomes large, and it is considered that it is easy to adopt a structure in which HOMO and LUMO are alternately close to each other as shown in FIG. That is, in the peripheral material corresponding to the blue light emitting material having a high T ₁ , a technique is required in which the HOMO-HOMOs and the LUMO-LUMOs, which originally have a low existence probability, are brought close to each other without reducing the T ₁ .
The technical idea of the present invention is to realize an ideal molecular existence state as shown in FIG. 6 with the assistance of a weak intermolecular force of an alkyl group that does not cause a decrease in T ₁ due to expansion of a conjugated system. Molecular design of.

≪Charge separation of HOMO and LUMO≫
In the present invention, "the highest occupied orbital (HOMO) and the lowest empty orbital (LUMO) are spatially separated" means that the site where HOMO is localized and the site where LUMO is localized in the molecule are different. In the ground state stabilized structure of the aromatic compound according to the present invention, it means that the center of gravity of the electron density distribution of HOMO and the center of gravity of the electron distribution density of LUMO are at different sites (see FIG. 5). ). That is, in the aromatic compound according to the present invention, the electron density distributions of HOMO and LUMO have little overlap or no overlap.
The electron density distribution can be calculated by using the molecular orbital calculation software described later.

[Electronic density distribution]
The distribution state and center of gravity of HOMO and LUMO can be obtained from the electron density distribution when the structure is optimized obtained by molecular orbital calculation.
The structural optimization and the calculation of the electron density distribution by the molecular orbital calculation of the material for the charge transfer thin film in the present invention are for the molecular orbital calculation using B3LYP as a functional and 6-31G (d) as a basis function as the calculation method. It can be calculated using software, and the software is not particularly limited, and any of them can be used in the same manner.
In the present invention, Gaussian 09 (Revision C.01, MJ Frisch, et al, Gaussian, Inc., 2010.) manufactured by Gaussian, USA was used as the software for calculating the molecular orbital.
Regarding the electron density separation state of HOMO and LUMO, from the structure optimization calculation using B3LYP as the functional and 6-31G (d) as the basis function, the time-dependent density functional theory (Time-Dependent DFT) is further obtained. ) Is performed to obtain the energies of S ₁ and T ₁ (E (S ₁ ) and E (T ₁ ), respectively) and calculated as ΔEst = E (S ₁ ) -E (T ₁ ). Is also possible. The smaller the calculated ΔEst, the more separated HOMO and LUMO are. In the present invention, ΔEst calculated by using the same calculation method as described above is preferably 1.0 eV or less, and more preferably 0.5 eV or less.

≪Aromatic compounds≫
The aromatic compound according to the present invention has at least two or more aromatic hydrocarbon rings or fragrances in which the highest occupied orbitals and the lowest empty orbitals distributed on the aromatic compound imaged by molecular orbital calculation are spatially separated. It has a group heterocycle and further has an alkyl group having an number of carbon atoms in the range of 3 to 20. The ring structure and substituents of the aromatic compound according to the present invention will be described with reference to specific examples.

<Aromatic hydrocarbon ring>
The aromatic hydrocarbon ring contained in the aromatic compound according to the present invention may have a structure having an aromatic hydrocarbon ring group, for example, a phenyl group (also referred to as an aryl group), a p-chlorophenyl group, or a mesityl group. , A structure having a tolyl group, a xylyl group, a naphthyl group, an anthryl group, an azulenyl group, an acenaphthenyl group, a fluorenyl group, a phenanthryl group, an indenyl group, a pyrenyl group, a biphenylyl group and the like is preferable.

<Aromatic heterocycle>
The aromatic heterocycle contained in the aromatic compound according to the present invention may have a structure having an aromatic heterocyclic group, for example, a pyridyl group, a pyrimidinyl group, a frill group, a pyrrolyl group, an imidazolyl group, a benzoimidazolyl group, a pyrazolyl group. Group, pyrazinyl group, triazolyl group (for example, 1,2,4-triazole-1-yl group, 1,2,3-triazole-1-yl group, etc.), oxazolyl group, benzoxazolyl group, thiazolyl group, Isooxazolyl group, isothiazolyl group, frazayl group, thienyl group, quinolyl group, benzofuryl group, dibenzofuryl group, benzothienyl group, dibenzothienyl group, indolyl group, carbazolyl group, carborinyl group, diazacarbazolyl group (of the carborinyl group). One of the carbon atoms constituting the carboline ring is replaced with a nitrogen atom), a quinoxalinyl group, a pyridadinyl group, a triazineyl group, a quinazolinyl group, a phthalazinyl group and the like can be used.

<Alkyl group>
Examples of the alkyl group having a carbon number in the range of 3 to 20 in the present invention include a propyl group, an isopropyl group, a pentyl group, a hexyl group, an octyl group, a dodecyl group, a tridecyl group, a tetradecyl group and a pentadecyl group. Can be done.

<Aromatic compound having a structure represented by the general formula (1)>
In the present invention, it is preferable that the aromatic compound has a structure represented by the following general formula (1) because it easily takes an interaction form suitable for carrier transport.
General formula (1):
(R ₁ ) _m- A- (L) _k- B- (R ₂ ) _n
In the above general formula (1), A and B represent an aromatic hydrocarbon ring or an aromatic heterocycle which may have a substituent. R ₁ and R ₂ represent an alkyl group having an number of carbon atoms in the range of 3 to 20. L is a simple bond or an aromatic hydrocarbon group, an aromatic heterocyclic group or an alkylene group which may have a substituent. m and n represent integers of 0 or 1 or more, respectively, and both m and n are never 0. k represents an integer of 1 or more.
As the aromatic hydrocarbon ring, the aromatic heterocycle and the alkyl group, the above-mentioned ones can be used.
In addition, examples of the alkylene group used in the present invention include a propylene group, a pentylene group, a hexylene group, an octylene group, a dodecylene group, a tridecylene group, a tetradecylene group, a pentadecylene group and the like.

Regarding the preferable carbon number of the alkyl group in the general formula (1), it is considered that the interaction between the alkyl groups, for example, the hydrophobic interaction can be obtained by setting the carbon number in the range of 3 to 20. When the number of carbon atoms is 3 or more, the effect of assisting the interaction between alkyl groups can be easily obtained, and when the number of carbon atoms is 20 or less, the synergistic effect with the formation of the π-π stack required for carrier hopping conduction. It is considered that it becomes easy to take a collective structure in which HOMOs and LUMOs are close to each other.

<Observation of luminescence derived from electromer>
The emission derived from the electromer is observed as a light emitter (emission peak) having a maximum emission wavelength in a region longer wavelength side (usually 550 nm or more) than fluorescence or phosphorescence in the current excitation emission spectrum.

(Sample for current excitation emission spectrum measurement)
The measurement of the current excitation emission spectrum is performed using a sample in which a thin film made of only a material for a charge transfer thin film is sandwiched between an anode and a cathode. More specifically, for example, a single layer made of only a material for a charge transfer thin film is formed on a transparent support substrate provided with a transparent electrode such as ITO (indium tin oxide), and aluminum or the like is vapor-deposited on the single layer. A cathode is formed by forming a cathode, and if necessary, another layer may be formed as a sample.

The method for forming the single layer containing the material for the charge transfer thin film may be a vapor deposition method or a coating method such as spin coating. The layer thickness of the single layer is not particularly limited as long as it is a layer thickness that can sufficiently obtain light emission, but if it is 200 nm or less, the driving voltage at the time of measurement does not become too large, and if it is 50 nm or more, the leakage current Is preferably 50 to 200 nm because it makes it difficult for the current to flow.
In addition, when the voltage when applying a current to the measurement sample becomes very large (a state in which charge carriers are difficult to be injected into a single layer), the single layer is located between the anode and the single layer or between the cathode and the single layer. An intermediate layer may be appropriately provided so as to increase the carrier injection efficiency into the layer and reduce the voltage. The material of the intermediate layer is not particularly limited as long as it is a material that does not inhibit light emission from the layer containing the material for a charge-transferring thin film and transports carriers. For example, holes used in an organic electroluminescence device. Transport materials, electron transport materials, and the like are preferably used.

(Measurement method of current excitation emission spectrum)
For the current excitation emission spectrum, the emission spectrum obtained from the sample when the obtained measurement sample is driven with a constant current is measured as the current excitation emission spectrum. The drive current value is not particularly limited as long as the current value is such that light emission from the layer containing the material for the charge transfer thin film can be sufficiently obtained, but it is preferably ¹ to 50 mA / cm ² .
In the obtained current excitation emission spectrum, the value of the maximum emission intensity observed at 500 nm or less is defined as a, and the constant current drive is performed until a is attenuated to 1/5 from the value at the initial stage of drive (initial a). , Measure the current excitation spectrum over time.
In the obtained current excitation spectrum from the initial stage of driving to the end of measurement, the ratio <a / b> of a with time and the maximum emission intensity b observed at 550 nm or more is calculated.

(Constituent requirements for a and b)
Here, from the reference paper, b is an electromer-derived luminescence in which HOMO and LUMO are close to each other, and a is other interaction forms such as randomly arranged states, HOMOs, and LUMOs. Is the maximum emission intensity when is in close proximity.
That is, when b is stronger than a, as the association state of the compounds in the membrane, the electromers in which HOMO and LUMO are close to each other show other interaction forms (a state in which they are randomly arranged or a state in which HOMO is arranged). It is estimated that the number will be larger than that of (the state where the LUMOs are close to each other). That is, the emission in a state showing other interaction forms (a state in which they are randomly arranged, or a state in which HOMOs and LUMOs are close to each other) is stronger than the emission derived from the electromer, so that the electromer is quenched. It is considered that the carrier can be moved without being done. In the present invention, it has been found that by suppressing the formation of an electromer of an organic material used for an organic electronic device, drive deterioration due to carrier disappearance is suppressed and the device life is improved.

<Synthesis example>
Examples of synthesis of the compound according to the present invention will be described below, but the present invention is not limited thereto. The method for synthesizing HS-3 in Table 1 will be described below as an example.
<< Synthesis of Exemplified Compound HS-3 >>
Exemplified compound HS-3 can be synthesized according to the following scheme.

(Synthesis of Intermediate 1)
Under a nitrogen stream, add 10.0 g (59.8 mmol) of carbazole, 8.77 g (65.8 mmol) of aluminum chloride, and 8.85 g (65.8 mmol) of hexane acid chloride to a flask, add 220 mL of dichloroethane, and add for 1 hour. Stirred at room temperature. The reaction mixture was added to water, extracted with dichloromethane, and concentrated under reduced pressure. The obtained crude product was purified by silica gel column chromatography to obtain 3.4 g (yield 21%) of Intermediate 1. The structure was confirmed by nuclear magnetic resonance spectrum.

(Synthesis of Intermediate 2)
Under a nitrogen stream, add 1.5 g (5.66 mmol) of intermediate 1, 850 mg (17.0 mmol) of hydrazine monohydrate, and 952 mg (17.0 mmol) of potassium hydroxide to the flask, and add 28.2 mL of ethylene glycol. , 110 ° C. for 2 hours, followed by 180 ° C. for 14 hours. After returning the reaction solution to room temperature, water was added, the mixture was extracted with ethyl acetate, and concentrated under reduced pressure. The obtained crude product was purified by silica gel column chromatography to obtain 1.28 g (yield 90%) of Intermediate 2. The structure was confirmed by nuclear magnetic resonance spectrum.

(Synthesis of HS-3)
1.2 g (4.77 mmol) of intermediate 2, 1.79 g (4.34 mmol) of intermediate 3, potassium phosphate 3.32 g (15.6 mmol), copper (I) 0 in a flask under a nitrogen stream. .19 g (1.30 mmol) and 0.48 g (2.60 mmol) of dipivaloyl methane were added, 29 mL of dimethylsulfosoxide was added, and the mixture was heated at 160 ° C. for 7 hours. The reaction mixture was allowed to cool to room temperature, water was added, the mixture was extracted with ethyl acetate, and concentrated under reduced pressure. The obtained crude product was purified by silica gel column chromatography and GPC to obtain 1.15 g (yield 45%) of Exemplified Compound HS-3. The structure was confirmed by nuclear magnetic resonance spectrum. In Examples, this compound was further sublimated and purified.

<Examination of stabilized energy using molecular dynamics (MD) calculation>
Whether or not the aromatic compound according to the present invention easily forms a preferable bimolecular structure as shown in FIG. 6 by the interaction of alkyl groups was examined from the stabilization energy calculated by MD calculation.
It is presumed that the transparent thin film containing the material for the charge transfer thin film of the present invention is amorphous or has low crystallinity as a whole. In order to form a bimolecular structure having a preferable interaction as shown in FIG. 4 in such a thin film, it is considered that a smaller stabilizing energy is preferable.

The stabilization energy of the bimolecular structure can be calculated using molecular dynamics (MD) calculation software. As a typical software, for example, there is Material Studios Studio of Accelrys Ltd. and the like.
Although there are a large number of molecules in the thin film, it is difficult to calculate the stabilization energy using all of these molecules. Therefore, in the present invention, the stabilization of the bimolecular structure using two molecules as a model is performed. It was examined using chemical energy.

The examination method using MD calculation will be described below.
As the calculation software, Material Studios (manufactured by Accelrys Ltd.) was used.
The calculation was performed in the following procedures (1) to (5).
(1) Structural optimization with one molecule is performed using Material Studios.
(2) Create a cell containing two molecules having the structure optimized in (1). In addition, duplicate these cells. The number of duplicates is preferably 100 to 1000.
(3) Relax using molecular dynamics (MD) calculations.
Using Forcite, the temperature was 298 K, NPT: relaxed under certain conditions.
(4) Among the plurality of cells obtained after relaxation, among the energetically most stable bimolecular structure (hereinafter referred to as the most stable structure A) and the bimolecular structure in which alkyl groups are presumed to interact with each other. The most stable structure (hereinafter referred to as the most stable structure B) is extracted.
At this time, as shown in FIG. 7, the distance between the carbon atoms at the base of the alkyl group between the molecules and the carbon atom at the end of the alkyl group is 6 Å for determining whether or not the alkyl groups are interacting with each other. The following are defined in the present invention as interacting. This is because if the alkyl groups are close to each other up to 6 Å or less, it is considered that some kind of interaction is working.
(5) Comparing the energies of the most stable structure A and the most stable structure B, it is considered that the smaller the energy difference is, the easier it is to form a preferable most stable structure B in the thin film.

Table 1 shows the calculation results of HS-1, HS-2, HS-3 and Comparative Compound 2 used in Examples and Reference Examples .

As shown in Table 1, in HS-1 to HS-3 of the aromatic compound and the compound of the reference example according to the present invention, the energy difference between the most stable structures A and B is smaller than that of the comparative compound 2. A calculation result was obtained that the most stable structure B in which alkyl groups interacted energetically is more likely to be formed.

<< Constituent layer of organic electroluminescence element >>
The material for a charge-transfer thin film and the charge-transfer thin film of the present invention can be suitably used for an organic EL device. Typical element configurations in the organic EL element include, but are not limited to, the following configurations.
(1) anode / light emitting layer / cathode (2) anode / light emitting layer / electron transport layer / cathode (3) anode / hole transport layer / light emitting layer / cathode (4) anode / hole transport layer / light emitting layer / electron Transport layer / cathode (5) anode / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode (6) anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode ( 7) Anophode / hole injection layer / hole transport layer / (electron blocking layer /) light emitting layer / (hole blocking layer /) electron transport layer / electron injection layer / cathode Among the above, the configuration of (7) is preferable. It is used, but is not limited to this.

The light emitting layer is composed of a single layer or a plurality of layers, and when there are a plurality of light emitting layers, a non-light emitting intermediate layer may be provided between the light emitting layers.
If necessary, a hole blocking layer (also referred to as a hole barrier layer) or an electron injection layer (also referred to as a cathode buffer layer) may be provided between the light emitting layer and the cathode, and the light emitting layer and the electrode may be provided. An electron blocking layer (also referred to as an electron barrier layer) or a hole injection layer (also referred to as an anode buffer layer) may be provided between the two.

The electron transport layer is a layer having a function of transporting electrons, and in a broad sense, an electron injection layer and a hole blocking layer are also included in the electron transport layer. Further, it may be composed of a plurality of layers.
The hole transport layer is a layer having a function of transporting holes, and in a broad sense, a hole injection layer and an electron blocking layer are also included in the hole transport layer. Further, it may be composed of a plurality of layers.
In the above typical device configuration, the layer excluding the anode and the cathode is referred to as an “organic layer”.

(Tandem structure)
Further, the organic EL element may be an element having a so-called tandem structure in which a plurality of light emitting units including at least one light emitting layer are laminated.
As a typical element configuration of the tandem structure, for example, the following configuration can be mentioned.
Anode / 1st light emitting unit / 2nd light emitting unit / 3rd light emitting unit / cathode Anode / 1st light emitting unit / intermediate layer / 2nd light emitting unit / intermediate layer / 3rd light emitting unit / cathode Here, the first light emitting unit , The second light emitting unit and the third light emitting unit may all be the same or different. Further, the two light emitting units may be the same, and the remaining one may be different.

Further, the third light emitting unit may not be provided, while a light emitting unit or an intermediate layer may be further provided between the third light emitting unit and the electrode.
A plurality of light emitting units may be directly laminated or may be laminated via an intermediate layer, and the intermediate layer is generally an intermediate electrode, an intermediate conductive layer, a charge generation layer, an electron extraction layer, a connection layer, or an intermediate layer. Known materials and configurations can be used as long as they are also called an insulating layer and have a function of supplying electrons to the adjacent layer on the anode side and holes to the adjacent layer on the cathode side.

The material used for the intermediate layer, for example, ITO (indium tin oxide), IZO (indium zinc _{oxide), ZnO 2, TiN, ZrN} , HfN, TiO 2, V 2 O 5, CuI, InN, Conductive inorganic compound layers such as GaN, CuAlO ₂ , CuGaO ₂ , SrCu ₂ O ₂ , LaB ₆ , RuO ₂ , Al, bilayer films such as Au / Bi ₂ O ₃ , SnO ₂ / Ag / SnO ₂ , _{ZnO / Ag / ZnO, Bi 2} O 3 / Au / Bi 2 O 3, TiO 2 / TiN / TiO 2, TiO 2 / ZrN / TiO 2 or the like multilayer film, also fullerenes such as _{C 60,} such as oligothiophene Examples thereof include a conductive organic compound layer, a conductive organic compound layer such as metallic phthalocyanines, metal-free phthalocyanines, metal porphyrins, and metal-free porphyrins, but the present invention is not limited thereto.

Preferred configurations in the light emitting unit include, but are not limited to, the configurations (1) to (7) mentioned in the above typical element configurations, excluding the anode and the cathode.
Specific examples of the tandem organic EL element include, for example, US Pat. No. 6,337,492, US Pat. No. 7,420,203, US Pat. No. 7,473,923, US Pat. No. 6,872,472, and US Pat. No. 6,107,734. Specification, US Pat. No. 6,337,492, International Publication No. 2005/09087, JP-A-2006-228712, JP-A-2006-24791, JP-A-2006-49393, JP-A-2006-49394. , Japanese Patent Application Laid-Open No. 2006-49396, Japanese Patent Application Laid-Open No. 2011-96679, Japanese Patent Application Laid-Open No. 2005-340187, Japanese Patent No. 4711424, Japanese Patent No. 3496681, Japanese Patent No. 3884564, Japanese Patent No. 4213169, Japanese Patent Publication No. Kai 2010-192719, Japanese Patent Application Laid-Open No. 2009-0762929, Japanese Patent Application Laid-Open No. 2008-0784414, Japanese Patent Application Laid-Open No. 2007-059848, Japanese Patent Application Laid-Open No. 2003-272860, Japanese Patent Application Laid-Open No. 2003-045676, International Publication No. Examples thereof include the element configuration and constituent materials described in 2005/094130 and the like, but the present invention is not limited thereto.
Next, the compounds contained in the organic layer will be described, and each layer will be described.

《Light emitting layer》
The organic layer preferably contains the aromatic compound according to the present invention, and is also preferably contained in the light emitting layer.
Further, the organic layer has a light emitting layer, and is a layer that provides a place where electrons and holes injected from an electrode or an adjacent layer are recombined and emit light via excitons. It may be in the layer of the light emitting layer or at the interface between the light emitting layer and the adjacent layer. The structure of the light emitting layer is not particularly limited as long as it satisfies the requirements specified in the present invention.

The total thickness of the light emitting layer is not particularly limited, but from the viewpoint of homogeneity of the formed layer, prevention of applying an unnecessary high voltage at the time of light emission, and improvement of the stability of the light emitting color with respect to the drive current. Therefore, it is preferably adjusted in the range of 2 nm to 5 μm, more preferably in the range of 2 to 500 nm, and further preferably in the range of 5 to 200 nm.
Further, in the present invention, the layer thickness of each light emitting layer is preferably adjusted within the range of 2 nm to 1 μm, more preferably adjusted within the range of 2 to 200 nm, and further preferably within the range of 3 to 150 nm. Is adjusted to.
The light emitting layer according to the present invention preferably contains a light emitting dopant (a luminescent dopant compound, a dopant compound, also simply referred to as a dopant) and a host compound (a matrix material, a host compound, also simply referred to as a host).

<Host compound>
The host compound used in the present invention is a compound mainly responsible for injection and transport of electric charges in the light emitting layer, and its own light emission is not substantially observed in the organic EL device.
A compound having a phosphorescent quantum yield of less than 0.1 at room temperature (25 ° C.) is preferable, and a compound having a phosphorescent quantum yield of less than 0.01 is more preferable. Further, among the compounds contained in the light emitting layer, the mass ratio in the layer is preferably 20% or more.
Further, the excited state energy of the host compound is preferably higher than the excited state energy of the light emitting dopant contained in the same layer.
The host compound may be used alone or in combination of two or more. By using a plurality of types of host compounds, it is possible to adjust the movement of electric charges, and it is possible to improve the efficiency of the organic EL device.

The host compound that can be used in the present invention is not particularly limited, and compounds conventionally used in organic EL devices can be used. It may be a low molecular weight compound, a high molecular weight compound having a repeating unit, or a compound having a reactive group such as a vinyl group or an epoxy group.
As a known host compound, it has hole transporting ability or electron transporting ability, prevents the wavelength of light emission from being lengthened, and is stable against heat generation when the organic EL device is driven at a high temperature or during device driving. From the viewpoint of operation, it is preferable to have a high glass transition temperature (Tg). Tg is preferably 90 ° C. or higher, and more preferably 120 ° C. or higher.
Here, the glass transition point (Tg) is a value obtained by a method based on JIS K 7121-2012 using DSC (Differential Scanning Colorimetry: differential scanning calorimetry).

Specific examples of known host compounds include, but are not limited to, the compounds described in the following documents.
JP 2001-257076, 2002-308855, 2001-313179, 2002-319491, 2001-357977, 2002-334786, 2002-8860, 2002-334787A, 2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75645, 2002-338579, 2002. 2002-105445, 2002-343568, 2002-141173, 2002-352957, 2002-203683, 2002-363227, 2002-231453, 2003 No. 3165, No. 2002-234888, No. 2003-27048, No. 2002-255934, No. 2002-260861, No. 2002-280183, No. 2002-299060, No. 2002- 302516, 2002-305083, 2002-305084, 2002-308837, US Patent Publication No. 2003/0175553, US Patent Publication No. 2006/0280965, US Patent Publication 2005/0112407, US Patent Publication No. 2009/0017330, US Patent Publication No. 2009/0030202, US Patent Publication No. 2005/02389919, International Publication No. 2001/039234, International. Publication No. 2009/021126, International Publication No. 2008/056746, International Publication No. 2004/093207, International Publication No. 2005/089025, International Publication No. 2007/063796, International Publication No. 2007/0637554, International Publication No. 2004/107822, International Publication No. 2005/030900, International Publication No. 2006/114966, International Publication No. 2009/086028, International Publication No. 2009/003898, International Publication No. 2012/0293947, JP-A-2008-074939 No., JP-A-2007-254297, European Patent No. 2034538 and the like.

<Light emitting dopant>
As the light emitting dopant used in the present invention, a fluorescent dopant (also referred to as a fluorescent dopant or a fluorescent compound) and a phosphorescent dopant (also referred to as a phosphorescent dopant or a phosphorescent compound) are preferably used. In the present invention, it is preferable that at least one light emitting layer contains a phosphorescent dopant.
The concentration of the light emitting dopant in the light emitting layer can be arbitrarily determined based on the specific dopant used and the requirements of the device, and is contained at a uniform concentration with respect to the layer thickness direction of the light emitting layer. It may have an arbitrary concentration distribution.

Further, as the light emitting dopant used in the present invention, a plurality of types may be used in combination, a combination of dopants having different structures, or a combination of a fluorescent light emitting dopant and a phosphorescent light emitting dopant may be used. Thereby, an arbitrary emission color can be obtained.
The luminescent colors of the organic EL element of the present invention and the compound used in the present invention are spectrally radiated in FIG. It is determined by the color when the result measured by the luminometer CS-1000 (manufactured by Konica Minolta Co., Ltd.) is applied to the CIE chromaticity coordinates.

In the present invention, it is also preferable that the light emitting layer of one layer or a plurality of layers contains a plurality of light emitting dopants having different light emitting colors and exhibits white light emission.
The combination of luminescent dopants showing white color is not particularly limited, and examples thereof include a combination of blue and orange, a combination of blue and green and red, and the like.
The white color in the organic EL element of the present invention is not particularly limited and may be white color closer to orange or white color closer to blue, but when the 2 degree viewing angle front luminance is measured by the above method. , It is preferable that the chromaticity in the CIE 1931 color system at 1000 cd / m ² is within the region of x = 0.39 ± 0.09 and y = 0.38 ± 0.08.

(Phosphorescent dopant)
The phosphorescent dopant according to the present invention (hereinafter, also referred to as “phosphorescent light emitting dopant”) is a compound in which light emission from the lowest excited triple term is observed, and specifically, at room temperature (25 ° C.). It is a compound that emits phosphorescence and is defined as a compound having a phosphorescence quantum yield of 0.01 or more at 25 ° C., but a preferable phosphorescence quantum yield is 0.1 or more.
The phosphorus photon yield can be measured by the method described on page 398 (1992 edition, Maruzen) of Spectroscopy II of the 4th edition Experimental Chemistry Course 7. The phosphorescence quantum yield in a solution can be measured using various solvents, but the phosphorescence dopant according to the present invention can achieve the above phosphorescence quantum yield (0.01 or more) in any of any solvents. Just do it.

There are two types of light emission of the phosphorescent dopant in principle. One is that carrier recombination occurs on the host compound to which the carrier is transported to generate an excited state of the host compound, and this energy is transferred to the phosphorescent dopant. It is an energy transfer type that obtains light emission from a phosphorescent dopant. The other is a carrier trap type in which the phosphorescent dopant serves as a carrier trap, carriers are recombined on the phosphorescent dopant, and light emission from the phosphorescent dopant is obtained. In either case, the excited state energy of the phosphorescent dopant is required to be lower than the excited state energy of the host compound.
As the phosphorescent dopant that can be used in the present invention, it can be appropriately selected from known ones used for the light emitting layer of the organic EL element.

Specific examples of known phosphorescent dopants that can be used in the present invention include compounds described in the following documents.
Nature, 395, 151 (1998), Apple. Phys. Lett. , 78, 1622 (2001), Adv. Mater. , 19, 739 (2007), Chem. Mater. , 17, 3532 (2005), Adv. Mater. , 17, 1059 (2005), International Publication No. 2009/100991, International Publication No. 2008/101842, International Publication No. 2003/040257, US Patent Publication No. 2006/835469, US Patent Publication No. 2006/20202194. , US Patent Publication No. 2007/0087321, US Patent Publication No. 2005/0244673, Inorg. Chem. , 40, 1704 (2001), Chem. Mater. , 16, 2480 (2004), Adv. Mater. , 16, 2003 (2004), Angew. Chem. lnt. Ed. , 2006, 45, 7800, Apple. Phys. Lett. , 86, 153505 (2005), Chem. Lett. , 34,592 (2005), Chem. Commun. , 2906 (2005), Inorg. Chem. , 42, 1248 (2003), International Publication No. 2009/050290, International Publication No. 2002/015645, International Publication No. 2009/000673, US Patent Publication No. 2002/0034656, US Pat. No. 7,332232. , US Patent Publication No. 2009/01087737, US Patent Publication No. 2009/00397776, US Patent No. 6921915, US Patent No. 6687266, US Patent Publication No. 2007/0190359, US Patent Publication No. 2006/0008670, US Patent Publication No. 2009/015846, US Patent Publication No. 2008/0015355, US Patent No. 7250226, US Patent No. 7396598, US Publication No. 2006/0263635, US Patent Publication No. 2003/0138657, US Patent Publication No. 2003/0152802, US Patent No. 70090928, Angew. Chem. lnt. Ed. , 47, 1 (2008), Chem. Mater. , 18, 5119 (2006), Inorg. Chem. , 46,4308 (2007), Organometallics, 23,3745 (2004), Apple. Phys. Lett. , 74,1361 (1999), International Publication No. 2002/002714, International Publication No. 2006/090024, International Publication No. 2006/056418, International Publication No. 2005/019373, International Publication No. 2005/123873, International Publication No. 2007/004380, International Publication No. 2006/082742, US Patent Publication No. 2006/0251923, US Patent Publication No. 2005/0260441, US Patent No. 7393599, US Patent No. 75334505 Book, US Patent No. 7445855, US Patent Publication No. 2007/0190359, US Patent Publication No. 2008/0297033, US Patent No. 7338722, US Patent Publication No. 2002/0134984. , US Patent No. 7279704, US Patent Publication No. 2006/098120, US Patent Publication No. 2006/103874, International Publication No. 2005/076380, International Publication No. 2010/032663, International Publication No. 2008/140115, International Publication No. 2007/052431, International Publication No. 2011/134013, International Publication No. 2011/157339, International Publication No. 2010/086089, International Publication No. 2009/113646, International Publication No. 2012 / 020327, International Publication No. 2011/051404, International Publication No. 2011/004639, International Publication No. 2011/073149, US Patent Publication No. 2012/228583, US Patent Publication No. 2012/212126, Special Open 2012-069737, Japanese Patent Application Laid-Open No. 2012-195554, Japanese Patent Application Laid-Open No. 2009-114086, Japanese Patent Application Laid-Open No. 2003-81988, Japanese Patent Application Laid-Open No. 2002-302671 and Japanese Patent Application Laid-Open No. 2002-363552.
Among them, preferred phosphorescent dopants include organometallic complexes having Ir as the central metal. More preferably, a complex containing at least one coordination mode among a metal-carbon bond, a metal-nitrogen bond, a metal-oxygen bond and a metal-sulfur bond is preferable.

(Fluorescent dopant)
The fluorescent dopant used in the present invention (hereinafter, also referred to as “fluorescent luminescent dopant”) is a compound capable of emitting light from the excited singlet, and is not particularly limited as long as light emission from the excited singlet is observed.
Examples of the fluorescent dopant used in the present invention include anthracene derivatives, pyrene derivatives, chrysene derivatives, fluoranthene derivatives, perylene derivatives, fluorene derivatives, arylacetylene derivatives, styrylarylene derivatives, styrylamine derivatives, arylamine derivatives, boron complexes, and coumarins. Examples thereof include derivatives, pyran derivatives, cyanine derivatives, croconium derivatives, squalium derivatives, oxobenzanthracene derivatives, fluorescein derivatives, rhodamine derivatives, pyrylium derivatives, perylene derivatives, polythiophene derivatives, and rare earth complex compounds.

Further, in recent years, light emitting dopants using delayed fluorescence have also been developed, and these may be used.
Specific examples of the light emitting dopant using delayed fluorescence include the compounds described in International Publication No. 2011/156793, Japanese Patent Application Laid-Open No. 2011-213643, Japanese Patent Application Laid-Open No. 2010-93181, and the like. Is not limited to these.

《Electron transport layer》
In the present invention, the electron transport layer may be made of a material having a function of transporting electrons and may have a function of transmitting electrons injected from the cathode to the light emitting layer.
The total thickness of the electron transport layer used in the present invention is not particularly limited, but is usually in the range of 2 nm to 5 μm, more preferably in the range of 2 to 500 nm, and further preferably in the range of 5 to 200 nm. It is within the range.
Further, in the organic EL element, when the light generated in the light emitting layer is taken out from the electrode, the light taken out directly from the light emitting layer and the light taken out after being reflected by the electrode located at the opposite electrode to the electrode that takes out the light interfere with each other. It is known to wake up. When light is reflected by the cathode, this interference effect can be efficiently utilized by appropriately adjusting the layer thickness of the electron transport layer between several nm and several μm.

On the other hand, if the layer thickness of the electron transport layer is increased, the voltage tends to increase. Therefore, especially when the layer thickness is thick, the electron mobility of the electron transport layer should be 1 × ^10-5 cm ² / Vs or more. Is preferable.
The material used for the electron transport layer (hereinafter referred to as an electron transport material) may have any of electron injection property, transport property, and hole barrier property, and is among conventionally known compounds. Any one can be selected and used.

For example, nitrogen-containing aromatic heterocyclic derivatives (carbazole derivatives, azacarbazole derivatives (one or more of the carbon atoms constituting the carbazole ring substituted with nitrogen atoms), pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, pyridazine derivatives, Triazine derivative, quinoline derivative, quinoxalin derivative, phenanthroline derivative, azatriphenylene derivative, oxazole derivative, thiazole derivative, oxadiazole derivative, thiadiazol derivative, triazole derivative, benzimidazole derivative, benzoxazole derivative, benzthiazole derivative, etc.), dibenzofuran derivative, Examples thereof include dibenzothiophene derivatives, silol derivatives, aromatic hydrocarbon ring derivatives (naphthalene derivatives, anthracene derivatives, triphenylene, etc.).

Further, a metal complex having a quinolinol skeleton or a dibenzoquinolinol skeleton as a ligand, for example, tris (8-quinolinol) aluminum (Alq), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-) Dibromo-8-quinolinol) aluminum, tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), etc., and metal complexes thereof. A metal complex in which the central metal is replaced with In, Mg, Cu, Ca, Sn, Ga or Pb can also be used as an electron transport material.

In addition, metal-free or metal phthalocyanine, or those whose terminals are substituted with an alkyl group, a sulfonic acid group, or the like can also be preferably used as an electron transport material. Further, the distyrylpyrazine derivative exemplified as the material of the light emitting layer can also be used as an electron transport material, and an inorganic semiconductor such as n-type-Si or n-type-SiC is used like the hole injection layer and the hole transport layer. Can also be used as an electron transport material.
Further, it is also possible to use a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain.

In the electron transport layer used in the present invention, the electron transport layer may be doped with a doping material as a guest material to form an electron transport layer having a high n property (electron rich). Examples of the doping material include n-type dopants such as metal compounds and metal compounds such as metal halides. Specific examples of the electron transport layer having such a structure include, for example, JP-A-4-2970776, JP-A-10-270172, JP-A-2000-196140, JP-A-2001-102175, J. Mol. Apple. Phys. , 95, 5773 (2004) and the like.

Specific examples of known and preferable electron transporting materials used in organic EL devices include, but are not limited to, the compounds described in the following documents.
U.S. Patent No. 6528187, U.S. Patent No. 7230107, U.S. Patent Publication No. 2005/0025993, U.S. Patent Publication No. 2004/0036077, U.S. Patent Publication No. 2009/0115316, U.S. Pat. Patent Publication No. 2009/0101870, US Patent Publication No. 2009/0179554, International Publication No. 2003/060956, International Publication No. 2008/132805, Appl. Phys. Lett. , 75, 4 (1999), Apple. Phys. Lett. , 79,449 (2001), Apple. Phys. Lett. , 81, 162 (2002), Apple. Phys. Lett. , 81, 162 (2002), Apple. Phys. Lett. , 79,156 (2001), U.S. Pat. No. 7,964,293, U.S. Patent Publication No. 2009/030202, International Publication No. 2004/080975, International Publication No. 2004/063159, International Publication No. 2005/085387. , International Publication No. 2006/067931, International Publication No. 2007/0865552, International Publication No. 2008/114690, International Publication No. 2009/0694242, International Publication No. 2009/0667779, International Publication No. 2009/054253, International Publication No. 2011/086935, International Publication No. 2010/150593, International Publication No. 2010/047707, EP23111826, JP-A-2010-251675, JP-A-2009-209133, JP-A-2009-124114, JP-A-2008-277810, JP-A-2006-156445, JP-A-2005-340122, JP-A-2003-45662, JP-A-2003-31367, JP-A-2003-282270, International Publication No. 2012/115034 and the like.

More preferable electron transporting materials in the present invention include pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, triazine derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, carbazole derivatives, azacarbazole derivatives, and benzimidazole derivatives.
Specific examples of compounds used in the electron transport layer of the organic EL device are given below, but the present invention is not limited thereto.
The electron transport material may be used alone or in combination of two or more.

《Hole blocking layer》
The hole blocking layer is a layer having a function of an electron transporting layer in a broad sense, and is preferably made of a material having a function of transporting electrons and a small ability to transport holes, and is positive while transporting electrons. By blocking the holes, the probability of recombination of electrons and holes can be improved.
In addition, the structure of the electron transport layer described above can be used as the hole blocking layer used in the present invention, if necessary.
The hole blocking layer provided in the organic EL element is preferably provided adjacent to the cathode side of the light emitting layer.
The layer thickness of the hole blocking layer used in the present invention is preferably in the range of 3 to 100 nm, and more preferably in the range of 5 to 30 nm.
As the material used for the hole blocking layer, the material used for the electron transport layer described above is preferably used, and the material used as the host compound described above is also preferably used for the hole blocking layer.

《Electron injection layer》
The electron injection layer (also referred to as “cathode buffer layer”) used in the present invention is a layer provided between the cathode and the light emitting layer in order to reduce the driving voltage and improve the emission brightness, and is an “organic EL element”. And its industrialization forefront (published by NTS Co., Ltd. on November 30, 1998), Volume 2, Chapter 2, "Electrode Materials" (pages 123-166).
In the present invention, the electron injection layer may be provided as needed and may be present between the cathode and the light emitting layer or between the cathode and the electron transport layer as described above.
The electron injection layer is preferably a very thin film, and the layer thickness is preferably in the range of 0.1 to 5 nm, although it depends on the material. Further, it may be a non-uniform film in which the constituent material is intermittently present.

The details of the electron-injected layer are also described in JP-A-6-325871, JP-A-9-17574, JP-A-10-74586, etc., and specific examples of materials preferably used for the electron-injected layer , Metals such as strontium and aluminum, alkali metal compounds such as lithium fluoride, sodium fluoride and potassium fluoride, alkaline earth metal compounds such as magnesium fluoride and calcium fluoride, oxidation Examples thereof include metal oxides typified by aluminum, metal complexes typified by lithium 8-hydroxyquinolate (Liq) and the like. It is also possible to use the above-mentioned electron transport material.
Further, the material used for the above-mentioned electron injection layer may be used alone or in combination of two or more.

《Hole transport layer》
In the present invention, the hole transport layer may be made of a material having a function of transporting holes and may have a function of transmitting holes injected from the anode to the light emitting layer.
The total thickness of the hole transport layer used in the present invention is not particularly limited, but is usually in the range of 5 nm to 5 μm, more preferably in the range of 2 to 500 nm, and further preferably in the range of 5 to 200 nm. Is within the range of.
The material used for the hole transport layer (hereinafter, also referred to as a hole transport material) may have any of hole injection property, transport property, and electron barrier property, and is a conventionally known compound. Any one can be selected and used from the above.

For example, porphyrin derivatives, phthalocyanine derivatives, oxazole derivatives, oxadiazole derivatives, triazole derivatives, imidazole derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, hydrazone derivatives, stillben derivatives, polyarylalkane derivatives, triarylamine derivatives, carbazole derivatives. , Indolocarbazole derivatives, isoindole derivatives, acene derivatives such as anthracene and naphthalene, fluorene derivatives, fluorenone derivatives, and polymer materials or oligomers in which polyvinylcarbazole and aromatic amines are introduced into the main chain or side chains, polysilane, conductivity. Examples thereof include sex polymers or oligomers (for example, PEDOT / PSS, aniline-based copolymers, polyaniline, polythiophene, etc.).

Examples of the triarylamine derivative include a benzidine type represented by α-NPD, a starburst type represented by MTDATA, and a compound having fluorene or anthracene in the triarylamine connecting core portion.
Hexaazatriphenylene derivatives as described in JP-A-2003-591432 and JP-A-2006-135145 can also be used as the hole transport material.
Further, a hole transport layer having a high p property doped with impurities can also be used. Examples thereof include JP-A-4-297076, JP-A-2000-196140, and JP-A-2001-102175. Apple. Phys. , 95, 5773 (2004) and the like.

In addition, JP-A-11-251067, J. Hung et. al. Use so-called p-type hole transport materials and inorganic compounds such as p-type-Si and p-SiC as described in the author's literature (Appl. Phys. Lett., 80 (2002), p.139). You can also do it. Further, an orthometalated organometallic complex having Ir or Pt in the central metal as represented by Ir (ppy) ₃ is also preferably used.

As the hole transport material, the above-mentioned materials can be used, but a triarylamine derivative, a carbazole derivative, an indolocarbazole derivative, an azatriphenylene derivative, an organic metal complex, and an aromatic amine are introduced into the main chain or side chain. High molecular weight materials or oligomers are preferably used.
Specific examples of known and preferable hole transporting materials used in organic EL devices include, but are not limited to, the compounds described in the following documents in addition to the documents mentioned above.
For example, Apple. Phys. Lett. , 69, 2160 (1996), J. Mol. Lumin. , 72-74, 985 (1997), Apple. Phys. Lett. , 78,673 (2001), Apple. Phys. Lett. , 90, 183503 (2007), Apple. Phys. Lett. , 90, 183503 (2007), Apple. Phys. Lett. , 51, 913 (1987), Synth. Met. , 87, 171 (1997), Synth. Met. , 91, 209 (1997), Synth. Met. , 111,421 (2000), SID Symposium Digital, 37,923 (2006), J. Mol. Mater. Chem. , 3,319 (1993), Adv. Mater. , 6,677 (1994), Chem. Mater. , 15, 3148 (2003), US Patent Publication No. 2003/0162053, US Patent Publication No. 2002/0158242, US Patent Publication No. 2006/0240279, US Patent Publication No. 2008/0220265 , U.S. Patent Publication No. 5061569, International Publication No. 2007/002683, International Publication No. 2009/01809, EP650955, U.S. Patent Publication No. 2008/01245772, U.S. Patent Publication No. 2007/0278938, U.S. Patent Publication No. 2008/0106190, U.S. Patent Publication No. 2008/0018221, International Publication No. 2012/115034, Japanese Patent Application Laid-Open No. 2003-591432, Japanese Patent Application Laid-Open No. 2006-135145, US Patent Application No. No. 13/585981 and the like.
The hole transporting material may be used alone or in combination of two or more.

《Electronic blocking layer》
The electron blocking layer is a layer having a function of a hole transporting layer in a broad sense, and is preferably made of a material having a function of transporting holes but having a small ability to transport electrons, while transporting holes. By blocking the electrons, the probability of recombination of electrons and holes can be improved.
Further, the structure of the hole transport layer described above can be used as an electron blocking layer used in the present invention, if necessary.
The electron blocking layer provided on the organic EL element is preferably provided adjacent to the anode side of the light emitting layer.
The layer thickness of the electron blocking layer used in the present invention is preferably in the range of 3 to 100 nm, and more preferably in the range of 5 to 30 nm.
As the material used for the electron blocking layer, the material used for the hole transporting layer described above is preferably used, and the material used as the host compound described above is also preferably used for the electron blocking layer.

《Hole injection layer》
The hole injection layer (also referred to as “anode buffer layer”) used in the present invention is a layer provided between the anode and the light emitting layer in order to reduce the driving voltage and improve the emission brightness, and is an “organic EL”. It is described in detail in Volume 2, Chapter 2, "Electrode Materials" (pages 123-166) of "Elements and the Forefront of Industrialization of Elements" (published by NTS Co., Ltd. on November 30, 1998).
In the present invention, the hole injection layer may be provided as needed and may be present between the anode and the light emitting layer or between the anode and the hole transport layer as described above.
The details of the hole injection layer are also described in JP-A-9-45479, 9-2660062, 8-288609, etc., and examples of the material used for the hole injection layer include. Examples thereof include materials used for the hole transport layer described above.

Among them, phthalocyanine derivatives typified by copper phthalocyanine, hexaazatriphenylene derivatives as described in JP-A-2003-591432 and JP-A-2006-135145, metal oxides typified by vanadium oxide, amorphous carbon. , Polyaniline (emeraldine), polythiophene and other conductive polymers, tris (2-phenylpyridine) iridium complexes and the like, orthometallated complexes, triarylamine derivatives and the like are preferable.
The material used for the hole injection layer described above may be used alone or in combination of two or more.

<< Other additive compounds >>
The organic layer described above may further contain other additive-containing substances.
Examples of the additive-containing substances include halogen elements such as bromine, iodine and chlorine, halogenated compounds, alkali metals and alkaline earth metals such as Pd, Ca and Na, compounds and complexes of transition metals, salts and the like.
The content of the additive content can be arbitrarily determined, but is preferably 1000 ppm or less, more preferably 500 ppm or less, still more preferably 50 ppm or less, based on the total mass% of the contained layer. is there.
However, it is not within this range depending on the purpose of improving the transportability of electrons and holes and the purpose of favoring the energy transfer of excitons.

<< Method of forming organic layer >>
A method for forming an organic layer (hole injection layer, hole transport layer, light emitting layer, hole blocking layer, electron transport layer, electron injection layer, etc.) according to the present invention will be described.
The method for forming the organic layer according to the present invention is not particularly limited, and conventionally known methods such as a vacuum vapor deposition method and a wet method (also referred to as a wet process) can be used, but the organic layer is formed by a wet method. Is more preferable.
The wet method includes a spin coating method, a casting method, an inkjet method, a printing method, a die coating method, a blade coating method, a roll coating method, a spray coating method, a curtain coating method, an LB method (Langmuir-Blogget method), and the like. From the viewpoint of easy obtaining a homogeneous thin film and high productivity, a method having high suitability for the roll-to-roll method such as a die coating method, a roll coating method, an inkjet method, and a spray coating method is preferable.

Examples of the liquid medium for dissolving or dispersing the organic EL material include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene, xylene, mesitylene, cyclohexylbenzene and the like. Aromatic hydrocarbons of the above, aliphatic hydrocarbons such as cyclohexane, decalin and dodecane, and organic solvents such as DMF and DMSO can be used.
Further, as a dispersion method, dispersion can be performed by a dispersion method such as ultrasonic waves, high shear force dispersion, or media dispersion.

Further, a different film forming method may be applied to each layer. When a thin-film deposition method is used for film formation, the vapor deposition conditions vary depending on the type of compound used, but generally, the boat heating temperature is 50 to 450 ° C., the degree of vacuum is 1 × 10 ^-6 to 1 × 10 ^-2 Pa, and the deposition rate is high. It is desirable to appropriately select in the range of 0.01 to 50 nm / sec, substrate temperature -50 to 300 ° C., layer thickness 0.1 nm to 5 μm, preferably 5 to 200 nm.
The formation of the organic layer according to the present invention is preferably carried out consistently from the hole injection layer to the cathode by one vacuuming, but it may be taken out in the middle and a different film forming method may be applied. In that case, it is preferable to carry out the work in a dry inert gas atmosphere.

"anode"
As the anode in the organic EL element, a metal, an alloy, an electrically conductive compound having a large work function (4 eV or more, preferably 4.5 eV or more) and a mixture thereof as an electrode material are preferably used. Specific examples of such an electrode material include metals such as Au and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO.
Further, a material such as IDIXO (In ₂ O _3- ZnO) which is amorphous and can produce a transparent conductive film may be used.

For the anode, a thin film may be formed by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering, and a pattern of a desired shape may be formed by a photolithography method, or when pattern accuracy is not required so much (about 100 μm or more) , The pattern may be formed through a mask having a desired shape during vapor deposition or sputtering of the electrode material.
Further, when a coatable substance such as an organic conductive compound is used, a wet film forming method such as a printing method or a coating method can also be used. When light emission is taken out from this anode, it is desirable to increase the transmittance to more than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less.
The film thickness of the anode depends on the material, but is usually selected within the range of 10 nm to 1 μm, preferably 10 to 200 nm.

"cathode"
As the cathode, a metal having a small work function (4 eV or less) (referred to as an electron-injectable metal), an alloy, an electrically conductive compound, or a mixture thereof as an electrode material is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O). ₃ ) Examples thereof include a mixture, indium, a lithium / aluminum mixture, aluminum, and a rare earth metal. Among these, from the viewpoint of electron injectability and durability against oxidation and the like, a mixture of an electron injectable metal and a second metal which is a stable metal having a larger work function value, for example, a magnesium / silver mixture, Magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, lithium / aluminum mixture, aluminum and the like are suitable.

The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. The sheet resistance of the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm.
In order to transmit the emitted light, it is convenient that the emission brightness is improved if either the anode or the cathode of the organic EL element is transparent or translucent.
Further, a transparent or translucent cathode can be produced by producing the above metal on the cathode having a thickness of 1 to 20 nm and then producing the conductive transparent material mentioned in the description of the anode on the cathode. By applying the above, it is possible to manufacture an element in which both the anode and the cathode are transparent.

《Support board》
The types of support substrates (hereinafter, also referred to as substrates, substrates, substrates, supports, etc.) that can be used for organic EL elements are not particularly limited, such as glass and plastic, and even if they are transparent, they are opaque. It may be. When light is taken out from the support substrate side, the support substrate is preferably transparent. Examples of the transparent support substrate preferably used include glass, quartz, and a transparent resin film. A particularly preferable support substrate is a resin film capable of imparting flexibility to the organic EL element.

Examples of the resin film include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyethylene, polypropylene, cellophane, cellulose diacetate, cellulose triacetate (TAC), cellulose acetate butyrate, and cellulose acetate propionate. CAP), cellulose acetate phthalate, cellulose esters such as cellulose nitrate or derivatives thereof, polyvinylidene chloride, polyvinyl alcohol, polyethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide , Polyether sulfone (PES), polyphenylene sulfide, polysulfones, polyetherimide, polyetherketoneimide, polyamide, fluororesin, nylon, polymethylmethacrylate, acrylic or polyarylates, Arton (trade name: JSR) or Appel Examples thereof include films such as cycloolefin resins (trade name: manufactured by Mitsui Kagaku Co., Ltd.).

A film of an inorganic substance, an organic substance, or a hybrid film of both of them may be formed on the surface of the resin film, and the water vapor permeability (25 ± 0.5 ° C.) measured by a method according to JIS K 7129-1992. it is preferable that the relative humidity of (90 ± 2)%) is 0.01g ^/ (m 2 · 24h) or less of a gas barrier film was further measured by a method conforming to JIS K 7126-1987 oxygen the ^{permeability, 1 × 10 -3 ml / (} m 2 · 24h · atm) or less, that the water vapor permeability is ^{1 × 10 -5 g / (m} 2 · 24h) or less of a high gas barrier film preferable.

The material for forming the gas barrier film may be any material having a function of suppressing infiltration of a material that causes deterioration of the element such as moisture and oxygen, and for example, silicon oxide, silicon dioxide, silicon nitride and the like can be used. Further, in order to improve the brittleness of the film, it is more preferable to have a laminated structure of these inorganic layers and layers made of an organic material. The stacking order of the inorganic layer and the organic layer is not particularly limited, but it is preferable to stack the inorganic layer and the organic layer alternately a plurality of times.

The method for forming the gas barrier film is not particularly limited, and for example, vacuum deposition method, sputtering method, reactive sputtering method, molecular beam epitaxy method, cluster ion beam method, ion plating method, plasma polymerization method, atmospheric pressure plasma weight. Although legal, plasma CVD method, laser CVD method, thermal CVD method, coating method and the like can be used, the atmospheric pressure plasma polymerization method as described in JP-A-2004-68143 is particularly preferable.

Examples of the opaque support substrate include a metal plate such as aluminum and stainless steel, a film or opaque resin substrate, and a ceramic substrate.
The external extraction quantum efficiency of the light emission of the organic EL device at room temperature is preferably 1% or more, and more preferably 5% or more.
Here, the external extraction quantum efficiency (%) = the number of photons emitted to the outside of the organic EL element / the number of electrons passed through the organic EL element × 100.
Further, a hue improving filter such as a color filter may be used in combination, or a color conversion filter that converts the color emitted from the organic EL element into multiple colors by using it as a phosphor may be used in combination.

<< Other configurations >>
As a sealing means, a protective film, a protective plate, a technique for improving light extraction efficiency, and a condensing sheet that can be used in the present invention, known techniques described in JP-A-2014-152151 can be used. ..

《Use》
The organic EL element using the material for a charge transfer thin film of the present invention can be used as a display device, a display, and various light emitting light sources.
As the light source, for example, a lighting device (household lighting, in-car lighting), a backlight for a clock or a liquid crystal, a signboard advertisement, a traffic light, a light source of an optical storage medium, a light source of an electrophotographic copying machine, a light source of an optical communication processor, light Examples thereof include, but are not limited to, a light source of a sensor, but the light source can be effectively used as a backlight of a liquid crystal display device and a light source for lighting.
If necessary, the organic EL element may be patterned by a metal mask, an inkjet printing method, or the like at the time of film formation. In the case of patterning, only the electrode may be patterned, the electrode and the light emitting layer may be patterned, or all the layers of the device may be patterned. In the fabrication of the device, a conventionally known method is used. Can be done.

《Display device》
The organic EL element using the material for a charge transfer thin film of the present invention can be used in a display device. The display device may be monochromatic or multicolored, but here, a multicolor display device will be described.
In the case of a multicolor display device, a shadow mask is provided only when the light emitting layer is formed, and a film can be formed on one surface by a vapor deposition method, a casting method, a spin coating method, an inkjet method, a printing method, or the like.
When patterning only the light emitting layer, the method is not limited, but a vapor deposition method, an inkjet method, a spin coating method, or a printing method is preferable.

The configuration of the organic EL element provided in the display device is selected from the above-mentioned configuration examples of the organic EL element, if necessary.
The method for manufacturing the organic EL device is as shown in the above-described embodiment of manufacturing the organic EL device.
When a DC voltage is applied to the multicolor display device thus obtained, light emission can be observed by applying a voltage of about 2 to 40 V with the positive polarity of the anode and the negative polarity of the cathode. Further, even if a voltage is applied with the opposite polarity, no current flows and no light emission occurs. When an AC voltage is further applied, light is emitted only when the anode is in the + state and the cathode is in the-state. The waveform of the alternating current to be applied may be arbitrary.

The multicolor display device can be used as a display device, a display, and various light emitting light sources. Full-color display is possible by using three types of organic EL elements that emit blue, red, and green in the display device and display.
Examples of display devices and displays include televisions, personal computers, mobile devices, AV devices, teletext displays, information displays in automobiles, and the like. In particular, it may be used as a display device for reproducing a still image or a moving image, and the driving method when used as a display device for reproducing a moving image may be either a simple matrix (passive matrix) method or an active matrix method.
Light sources include household lighting, interior lighting, backlights for clocks and liquid crystals, signboard advertisements, traffic lights, light sources for optical storage media, light sources for electrophotographic copying machines, light sources for optical communication processors, light sources for optical sensors, etc. However, the present invention is not limited thereto.

≪One aspect of lighting equipment≫
An aspect of a lighting device including an organic EL element using the material for a charge-transfer thin film of the present invention will be described.
The non-light emitting surface of the organic EL element is covered with a glass case, a glass substrate with a thickness of 300 μm is used as a sealing substrate, and an epoxy-based photocurable adhesive (Luxtrac LC0629B manufactured by Toa Synthetic Co., Ltd.) is used as a sealing material around it. Is applied, and this is laminated on the cathode and brought into close contact with the transparent support substrate, irradiated with UV light from the glass substrate side, cured, and sealed to form an illuminating device as shown in FIGS. 8 and 9. can do.
FIG. 8 shows a schematic view of the lighting device, in which the organic EL element 101 is covered with a glass cover 102 (note that the sealing work with the glass cover is a nitrogen atmosphere without bringing the organic EL element 101 into contact with the atmosphere. It was performed in the lower glove box (in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more).
FIG. 9 shows a cross-sectional view of the lighting device, in which 105 is a cathode, 106 is an organic EL layer, and 107 is a glass substrate with a transparent electrode. The glass cover 102 is filled with nitrogen gas 108, and a water catching agent 109 is provided.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the examples, the indication of "parts" or "%" is used, but unless otherwise specified, it indicates "parts by mass" or "% by mass". The compounds used in the examples are shown below.

<< Preparation of sample for current excitation emission spectrum observation >>
Samples 1-1 to 1-6 for observing the current excitation emission spectrum were prepared and incorporated into a lighting device for evaluation.
<Preparation of sample 1-1>
(Formation of anode)
After patterning on a substrate (NA45 manufactured by NH Technoglass Co., Ltd.) in which ITO (indium tin oxide) was deposited at 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, the ITO transparent electrode was provided. The transparent support substrate was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes.

(Formation of hole injection layer)
The ITO surface was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes. On this, a solution obtained by diluting poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (abbreviated as PEDOT / PSS, manufactured by Bayer, Baytron P Al 4083) with pure water was formed by a slit coating method, and then formed. It was dried at 140 ° C. for 1 hour to provide a hole injection layer having a layer thickness of 40 nm.

This transparent support substrate is fixed to the substrate holder of a commercially available vacuum vapor deposition apparatus, while 200 mg of molybdenum oxide is placed in a molybdenum resistance heating boat, 200 mg of compound EB-1 is placed in another molybdenum resistance heating boat, and another molybdenum product is used. 200 mg of Comparative Compound 1 was placed in a resistance heating boat, 200 mg of Compound HB-1 was placed in another molybdenum resistance heating boat, and 200 mg of Compound ET-1 was placed in another molybdenum resistance heating boat, which was attached to a vacuum vapor deposition apparatus. ..

(Formation of hole transport layer)
Next, the vacuum chamber was depressurized to 4 × 10 ^-4 Pa, and then the heating boat containing molybdenum oxide was energized to heat it. A hole transport layer was provided.

(Formation of electron blocking layer)
Further, the heating boat containing the compound EB-1 was energized and heated, and the holes were vapor-deposited on the hole transport layer at a vapor deposition rate of 0.1 nm / sec to provide an electron blocking layer of 10 nm.

(Formation of light emitting layer)
Further, the heating boat containing the comparative compound 1 was energized and heated, and a 60 nm light emitting layer was provided by co-depositing on the hole transport layer at a vapor deposition rate of 0.1 nm / sec.

(Formation of hole blocking layer)
Further, the heating boat containing the compound HB-1 was energized and heated, and a hole blocking layer having a diameter of 10 nm was provided by vapor deposition on the light emitting layer at a vapor deposition rate of 0.1 nm / sec.

(Formation of electron transport layer)
Further, the heating boat containing the compound ET-1 was energized and heated, and the hole was vapor-deposited on the hole blocking layer at a vapor deposition rate of 0.1 nm / sec to provide an electron transport layer of 30 nm.

(Formation of electron injection layer and cathode layer)
Subsequently, 2 nm of potassium fluoride was vapor-deposited as an electron injection layer, and 100 nm of aluminum was further deposited to form a cathode to prepare Sample 1-1.

<Preparation of samples 1-2-1-6>
In the preparation of Sample 1-1, Samples 1-2 to 1-6 were prepared in the same manner except that Comparative Compound 1 was changed to the compounds shown in Table 2.

<< Evaluation of Samples 1-1 to 1-6 >>
When evaluating the obtained samples 1-1 to 1-6, the non-emissive surface of each sample after production is covered with a glass case, and a glass substrate having a thickness of 300 μm is used as a sealing substrate to seal the periphery. An epoxy-based photocurable adhesive (Luxtrac LC0629B manufactured by Toa Synthetic Co., Ltd.) is applied as a material, which is placed on the cathode and brought into close contact with the transparent support substrate, and cured by irradiating UV light from the glass substrate side. And sealed, and a lighting device as shown in FIGS. 8 and 9 was prepared and evaluated. Using the lighting device thus produced, the fluorescence intensity half-life was evaluated for samples 1-1 to 1-6. The evaluation results are shown in Table 2 together with the comparative compounds. The half-life of fluorescence intensity in the present specification means that when each lighting device is driven with a constant current of 200 μA, the maximum emission intensity a that appears at an emission wavelength of 500 nm or less is from the initial value at the start of energization to 1/2. The time until decay (unit: hr) was calculated, and this was used as a measure of half-life.

As shown in Table 2, it is a material for a charge-transfer thin film containing an aromatic compound having an alkyl group having an alkyl group in the range of 3 to 20, and according to the present invention, the minimum value of a / b is larger than 1. It has been clarified that the aromatic compounds HS-1 and HS-2 are materials for charge-transfer thin films having a longer half-life of fluorescence emission than the comparative compounds 1 to 4.

[ Reference example 2]
<< Fabrication of organic EL element >>
<Manufacturing of organic EL element 2-1>
(Formation of anode)
After patterning a substrate (NA45 manufactured by NH Technoglass Co., Ltd.) in which ITO was deposited at 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, the transparent support substrate provided with the ITO transparent electrode was treated with isopropyl alcohol. It was ultrasonically washed, dried with dry nitrogen gas, and UV ozone washed for 5 minutes.

(Formation of hole injection layer)
The ITO surface was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes. On this, a solution obtained by diluting poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (abbreviated as PEDOT / PSS, manufactured by Bayer, Baytron P Al 4083) with pure water was formed by a slit coating method, and then formed. It was dried at 140 ° C. for 1 hour to provide a hole injection layer having a layer thickness of 40 nm.
This transparent support substrate is fixed to the substrate holder of a commercially available vacuum vapor deposition apparatus, while 200 mg of compound HT-1 is placed in a molybdenum resistance heating boat, 200 mg of compound EB-1 is placed in another molybdenum resistance heating boat, and another 200 mg of Comparative Compound 2 in a molybdenum resistance heating boat, 200 mg of Compound BD-1 in another molybdenum resistance heating boat, 200 mg of Compound HB-2 in another molybdenum resistance heating boat, and another molybdenum product. 200 mg of compound ET-2 was placed in a resistance heating boat and attached to a vacuum vapor deposition apparatus.

(Formation of hole transport layer)
Next, the vacuum chamber was depressurized to 4 × 10 ^-4 Pa, and then the heating boat containing HT-1 was energized and heated, and a hole of 10 nm was deposited on a transparent support substrate at a vapor deposition rate of 0.1 nm / sec. A transport layer was provided.

(Formation of electron blocking layer)
Further, the heating boat containing the compound EB-1 was energized and heated, and the holes were vapor-deposited on the hole transport layer at a vapor deposition rate of 0.1 nm / sec to provide an electron blocking layer of 5 nm.

(Formation of light emitting layer)
Next, a resistance heating boat containing Comparative Compound 2 and BD-1 was energized and heated, and co-deposited on the hole transport layer at vapor deposition rates of 0.1 nm / sec and 0.01 nm / sec, respectively, to achieve a layer thickness. A light emitting layer of 30 nm was formed.

(Formation of hole blocking layer)
Further, the heating boat containing the compound HB-2 was energized and heated, and a hole blocking layer having a diameter of 5 nm was provided by vapor deposition on the light emitting layer at a vapor deposition rate of 0.1 nm / sec.

(Formation of electron transport layer)
Further, the heating boat containing the compound ET-2 was energized and heated, and the hole was vapor-deposited on the hole blocking layer at a vapor deposition rate of 0.1 nm / sec to provide an electron transport layer of 30 nm.

(Formation of electron injection layer and cathode)
Subsequently, potassium fluoride 2 nm was vapor-deposited as an electron injection layer, and aluminum 100 nm was further vapor-deposited to form a cathode to produce an organic EL element 2-1.

<Manufacturing of organic EL elements 2-2 and 2-3>
In the production of the organic EL element 2-1 the comparative compound 2 was changed to HS-1 and HS-3. Other than that, the organic EL elements 2-2 and 2-3 were manufactured in the same manner.

<< Evaluation of organic EL elements 2-1 to 2-3 >>
The following evaluation was performed for each organic EL element. The evaluation results are shown in Table 3.

<Half life>
The half-life was evaluated according to the measurement method shown below.
Each organic EL element was driven with a constant current with a current giving an initial brightness of 8000 cd / m ^2, and the time to be halved of the initial brightness was obtained, which was used as a measure of half life. The half-life was expressed as a relative value with the organic EL element 2-1 as 1.
The larger the value, the better the durability.

As shown in Table 3, it is a material for a charge-transferring thin film containing an aromatic compound having an alkyl group having an alkyl group in the range of 3 to 20 carbon atoms, and the minimum value of a / b is larger than 1, and electromer formation is generated. It was found that the suppressed organic EL device using HS-1 and HS-3 as a host had an excellent half-life as compared with the organic EL device of the comparative example.

[ Reference example 3]
<Manufacturing of organic EL element 3-1>
After patterning a substrate (NA-45 manufactured by NH Technoglass Co., Ltd.) in which ITO was deposited at 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, the transparent support substrate provided with the ITO transparent electrode was isopropyl. Ultrasonic cleaning with alcohol, drying with dry nitrogen gas, and UV ozone cleaning was performed for 5 minutes.

(Formation of hole transport layer)
A solution of poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT / PSS, Bayer, Baytron P Al 4083) diluted to 70% with pure water was used on this transparent support substrate at 3000 rpm. A thin film was formed by a spin coating method under the condition of 30 seconds, and then dried at 200 ° C. for 1 hour to provide a hole transport layer having a layer thickness of 20 nm.

(Formation of second hole transport layer)
This substrate was transferred to a nitrogen atmosphere, and a mixed solution of 5 mg of HT-2 and 45 mg of the hole transport material HT-3 dissolved in 10 ml of toluene was positively prepared on the hole transport layer at 2000 rpm for 30 seconds. A thin film was formed by spin coating on the hole transport layer. Under a nitrogen atmosphere, ultraviolet light was irradiated at 120 ° C. for 90 seconds to perform photopolymerization and cross-linking to form a second hole transport layer having a layer thickness of about 15 nm.

(Formation of light emitting layer)
A thin film was formed on the second hole transport layer by a spin coating method at 600 rpm for 30 seconds using a solution of 100 mg of Comparative Compound 2 and 10 mg of BD-2 dissolved in 10 ml of toluene. It was vacuum dried at 60 ° C. for 1 hour to obtain a light emitting layer having a layer thickness of about 70 nm.

(Formation of electron transport layer)
Subsequently, this substrate is fixed to the substrate holder of the vacuum vapor deposition apparatus, the vacuum chamber is depressurized to 4 × 10 ^-4 Pa, and then the heating boat containing ET-3 is energized to heat the substrate. An electron transport layer having a layer thickness of 30 nm was provided by vapor deposition on the light emitting layer at 1 nm / sec. The substrate temperature at the time of vapor deposition was room temperature.

(Cathode formation)
Subsequently, 0.5 nm of lithium fluoride was vapor-deposited as the cathode buffer layer, and 110 nm of aluminum was further vapor-deposited to form a cathode, thereby producing an organic EL element 3-1.

<Manufacturing of organic EL elements 3-2 and 3-3>
In the production of the organic EL element 3-1 the organic EL elements 3-2 and 3-3 were produced in the same manner except that the comparative compound 2 was changed to HS-1 and HS-3.

<< Evaluation of organic EL elements >>
The half-life of the organic EL elements 3-1 to 3-3 was evaluated in the same manner as in Example 2.

As shown in Table 4, it is clear that the organic EL elements 3-2 and 3-3 containing the material for the charge transfer thin film of the reference example are superior in life to the organic EL element 3-1 of the comparative example. Is.
From the above, it was found that it is useful to include the aromatic compound of the reference example in the light emitting layer formed by the wet process.

According to the present invention, it is possible to obtain a charge-transfer thin film material having a long life and a charge-transfer thin film material, and an organic EL element using the charge-transfer thin film material is a display device. , Display, and various light emitting light sources.

101 Organic EL element 102 Glass cover 105 Cathode 106 Organic EL layer 107 Glass substrate with transparent electrode 108 Nitrogen gas 109 Water trapping agent

Claims (2)

A material for a charge-transfer thin film containing an aromatic compound.
At least two or more aromatic hydrocarbon rings or aromatic heterocycles in which the highest occupied orbitals and the lowest empty orbitals distributed on the aromatic compound imaged by molecular orbital calculation are spatially separated from each other. the a, further have an alkyl group in the range of 3 to 20 carbon atoms, and the current excitation emission spectrum of a single layer containing the aromatic compound, meet the following equation (1),
A material for a charge-transfer thin film, wherein the aromatic compound has a structure represented by the following general formula (1) .
Equation (1): a / b> 1
In the formula (1), a represents the maximum emission intensity appearing at an emission wavelength of 500 nm or less in the current excitation emission spectrum, b represents the maximum emission intensity appearing at an emission wavelength of 550 nm or more, and a represents the energization start. While decaying from the initial value to the value of 1/5, a and b always satisfy the relationship of equation (1).)
General formula (1):
(R ₁ ) _m- A- ( L) _k- B- (R ₂ ) _n
(In the general formula (1), A and B represent an aromatic hydrocarbon ring or an aromatic heterocycle which may have a substituent. R ₁ and R ₂ have a carbon number in the range of 3 to 20. L represents an aromatic hydrocarbon group, an aromatic heterocyclic group or an alkylene group which may have a simple binder or a substituent. M and n are one or more, respectively. Represents an integer. K represents an integer of 1 or more.) A charge-transfer thin film comprising the material for a charge-transfer thin film according to claim 1 .

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