WO2016181844A1

WO2016181844A1 - Π-conjugated compound, delayed fluorescent body, light-emitting thin film, organic electroluminescence element, display device, and illumination device

Info

Publication number: WO2016181844A1
Application number: PCT/JP2016/063217
Authority: WO
Inventors: 康生宮田; 押山　智寛
Original assignee: コニカミノルタ株式会社
Priority date: 2015-05-08
Filing date: 2016-04-27
Publication date: 2016-11-17
Also published as: JPWO2016181844A1

Abstract

In order to provide a π-conjugated compound that increases light-emission efficiency, this π-conjugated compound has: an absolute value for the difference between the lowest excited singlet energy level and the lowest excited triplet energy level that is no more than 0.50 eV; a HOMO energy level for the π-conjugated compound of at least -5.5 eV; and a LUMO energy level of at least -1.8 eV.

Description

π-conjugated compound, delayed phosphor, light-emitting thin film, organic electroluminescence element, display device, and illumination device

The present invention relates to a π-conjugated compound, a delayed phosphor, a light-emitting thin film, an organic electroluminescence element, a display device, and a lighting device.

An organic electroluminescence element (organic EL element (also referred to as “organic electroluminescence element”)) using organic electroluminescence (Electro Luminescence: hereinafter abbreviated as “EL”) is a new one that enables planar light emission. This technology has already been put into practical use as a light emitting system. Organic EL elements are not only applied to electronic displays but also recently applied to lighting equipment, and their development is expected.

When an electric field is applied to the organic EL element, holes and electrons are injected from the anode and the cathode, respectively, and recombine in the light emitting layer to generate excitons. At this time, since singlet excitons and triplet excitons are generated at a ratio of 25%: 75%, phosphorescence using triplet excitons is theoretically higher in internal quantum than fluorescence. It is known that efficiency can be obtained. However, in order to actually obtain high quantum efficiency in the phosphorescence emission method, it is necessary to use a complex using a rare metal such as iridium or platinum as a central metal. There is concern that price will be a major industrial issue.

On the other hand, various developments have been made in order to improve the luminous efficiency in the fluorescent light emitting type, and a new movement has recently appeared. For example, in Patent Document 1, a phenomenon in which singlet excitons are generated by collision of two triplet excitons (triplet-triplet annihilation: hereinafter, abbreviated as “TTA” as appropriate. Triplet-Triplet Fusion: “TTF”) In particular, a technology for increasing the efficiency of a fluorescent element by efficiently causing TTA is disclosed. Although this technology improves the luminous efficiency of fluorescent materials by 2 to 3 times that of conventional fluorescent materials, the theoretical singlet exciton generation efficiency in TTA is only about 40%. Compared with light emission, it has a problem of high light emission efficiency.

Furthermore, in recent years, reverse intersystem crossing from triplet excitons to singlet excitons (hereinafter referred to as “RISC” where appropriate) (thermally activated delayed fluorescence (“ Also referred to as “thermally excited delayed fluorescence”: Thermally Activated Delayed Fluorescence (hereinafter abbreviated as “TADF” as appropriate) and the possibility of use in organic EL devices has been reported (for example, (Refer to Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2.) By using delayed fluorescence by this TADF mechanism, 100% internal quantum is theoretically equivalent to phosphorescence emission even in fluorescence emission by electric field excitation. Efficiency becomes possible.

In order to develop the TADF phenomenon, it is necessary that reverse intersystem crossing from triplet excitons generated by electric field excitation to singlet excitons at room temperature or light emitting layer temperature in the light emitting element occurs. Furthermore, a singlet exciton generated by crossing between inverses emits fluorescence similarly to a 25% singlet exciton generated by direct excitation, so that an internal quantum efficiency of 100% is theoretically possible. To this Gyakuko intersystem crossing occurs, the absolute value of the difference between the lowest excited singlet energy level (S ₁₎ and the lowest triplet excitation energy level (T ₁₎ (hereinafter referred to as Delta] E _ST.) Is very Small is essential.

On the other hand, it is known that when a light emitting layer containing a host material and a light emitting material contains a TADF material as a third component (assist dopant material) in the light emitting layer, it is effective for high light emission efficiency. (Refer nonpatent literature 3). By generating 25% singlet excitons and 75% triplet excitons on the assist dopant by electric field excitation, the triplet excitons generate singlet excitons with reverse intersystem crossing (RISC). be able to. The energy of singlet excitons can be transferred to the luminescent compound by fluorescence resonance energy transfer (Fluorescence resonance energy transfer: hereinafter abbreviated as “FRET” as appropriate), and light can be emitted by the energy transferred by the luminescent compound. It becomes. Therefore, theoretically, it becomes possible to cause the luminescent compound to emit light using 100% exciton energy, and high luminous efficiency is exhibited.

Here, in order to minimize Delta] E _ST in organic compounds are known to be localized without mixing highest occupied molecular orbital of the molecule (HOMO) and the lowest unoccupied molecular orbital (LUMO) is preferred ing.

1 and 2 are schematic diagrams showing energy diagrams of a compound that expresses a TADF phenomenon (TADF compound) and a general fluorescent material. For example, in 2CzPN having the structure shown in FIG. 1, HOMO is localized at the 1st and 2nd carbazolyl groups on the benzene ring, and LUMO is localized at the 4th and 5th cyano groups. Therefore, it is possible to separate the HOMO and LUMO of 2CzPN, ΔE _ST express TADF phenomenon extremely small. On the other hand, in 2CzXy (FIG. 2) in which the cyano group at the 4-position and 5-position of 2CzPN is replaced with a methyl group, the structure is similar, but HOMO and LUMO seen in 2CzPN cannot be clearly separated, so ΔE _ST cannot be reduced, and the TADF phenomenon cannot be expressed.

International Publication No. 2010/134350 JP 2013-116975 A

Conventionally, in order to clearly separate HOMO and LUMO, a technique for introducing a strong electron-donating group or electron-withdrawing group into the molecule is known. However, when a strong electron donating group or electron withdrawing group is introduced, a strong intramolecular charge transfer (CT) excited state is formed, so that the absorption spectrum and emission spectrum of the compound become longer (broader). This causes a problem that it is difficult to control the emission wavelength. Further, in a π-conjugated compound having a strong electron-withdrawing group, the HOMO level is lowered as the LUMO level is lowered. Therefore, when the π-conjugated compound is applied to a light emitting material or the like, the HOMO level or the LUMO level of the light emitting material is low, so that it is difficult to select a host material and the carrier balance during EL driving is lost. .

Conversely, if the electron donating property or the electron withdrawing property is too weak to control the emission wavelength, as described above, the expression of the TADF phenomenon is hindered. Therefore, a new technique for causing the TADF phenomenon to occur while controlling the emission wavelength is desired.

The present invention has been made in view of the above-described problems and situations, and a problem to be solved is to provide a new organic electroluminescence device with improved luminous efficiency. Also provided are a π-conjugated compound used for the organic electroluminescent element, a delay material containing the π-conjugated compound, a light-emitting thin film, and a display device and an illumination device provided with the organic electroluminescent element. It is.

[1] The absolute value of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is 0.50 eV or less, the HOMO energy level is −5.5 eV or more, and the LUMO A π-conjugated compound having an energy level of −1.8 eV or more.

[2] The π-conjugated compound according to [1], comprising an atom selected from the following atomic group A.
Atom group A: hydrogen atom, deuterium atom, fluorine atom, carbon atom forming a single bond, carbon atom forming a double bond, nitrogen atom forming only a single bond, oxygen atom forming only a single bond, single atom A sulfur atom that forms only a bond, a silicon atom that forms only a single bond [3] [1] or [2 having a structure in which two or more of the same or different ring structures selected from the following ring structure group X are linked together ] The π-conjugated compound described in the above.
Ring structure group X: benzene ring, indene ring, naphthalene ring, azulene ring, fluorene ring, phenanthrene ring, anthracene ring, acenaphthylene ring, biphenylene ring, chrysene ring, naphthacene ring, pyrene ring, pentalene ring, asanthrylene ring, heptalene Ring, triphenylene ring, as-indacene ring, s-indacene ring, preaden ring, phenalene ring, fluoranthene ring, perylene ring, acephenanthrylene ring, biphenyl ring, terphenyl ring, tetraphenyl ring, carbazole ring, indolo Indole ring, 9,10-dihydroacridine ring, phenoxazine ring, phenothiazine ring, dibenzothiophene ring, benzofurylindole ring, benzothienoindole ring, indolocarbazole ring, benzofurylcarbazole ring, benzothienocarba Ring, benzothienobenzothiophene ring, benzocarbazole ring, dibenzocarbazole ring, dibenzofuran ring, benzofurylbenzofuran ring, dibenzosilole ring, 5,10-dihydrophenazacillin ring, 10,11-dihydrodibenzoazepine ring [4 A delayed phosphor containing the π-conjugated compound according to any one of [1] to [3].
[5] A light-emitting thin film containing the π-conjugated compound according to any one of [1] to [3].

[6] An anode, a cathode, and a light emitting layer provided between the anode and the cathode, wherein the light emitting layer comprises the π-conjugated compound according to any one of [1] to [3] Including an organic electroluminescence element.

[7] The organic electroluminescent element according to [6], wherein the light emitting layer includes the π-conjugated compound and at least one of a fluorescent material and a phosphorescent material.
[8] The organic electroluminescent element according to [6], wherein the light emitting layer includes the π-conjugated compound, at least one of a fluorescent material and a phosphorescent material, and a host material.
[9] A display device comprising the organic electroluminescence element according to any one of [6] to [8].
[10] A lighting device including the organic electroluminescence element according to any one of [6] to [8].

According to the present invention, it is possible to provide a π-conjugated compound that can increase luminous efficiency, an organic electroluminescence device using the same, and the like.

It is the schematic diagram which showed the energy diagram of the TADF compound. It is the schematic diagram which showed the energy diagram of the general fluorescent material. It is the schematic diagram which showed the energy diagram in case a (pi) conjugated compound functions as an assist dopant material. It is the schematic diagram which showed the energy diagram in case a (pi) conjugated compound functions as a host material. It is the schematic diagram which showed an example of the display apparatus comprised from an organic EL element. It is a schematic diagram of a display device using an active matrix method. It is the schematic which showed the circuit of the pixel. It is a schematic diagram of the display apparatus by a passive matrix system. It is the schematic of an illuminating device. It is a schematic diagram of an illuminating device. It is a graph which shows the relationship between the time from excitation light irradiation and the number of photons at the time of a fluorescence attenuation | damping measurement about the vapor deposition film 4-1 produced in the Example using the (pi) conjugated compound of this invention.

Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In the present application, “˜” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

1. Regarding π-conjugated compounds The present inventors have an absolute value of a difference between the lowest excited singlet energy level and the lowest excited triplet energy level of 0.5 eV or less, and have a relatively weak electron-withdrawing group. It has been found that the luminous efficiency of the organic electroluminescence device is improved by the π-conjugated compound.

In the prior art, radiation of thermally activated delayed fluorescence has been reported by a material comprising a strong electron-withdrawing group such as a nitrogen atom having a double bond, a sulfur atom having a double bond, and an oxygen atom having a double bond. (For example, non-patent literature: Advanced Materials, 2014, 26, 7931-7958.).

In contrast, the π-conjugated compound of the present invention has a relatively weak electron-withdrawing group and exhibits delayed fluorescence emission even though it does not contain a strong electron-withdrawing group. The π-conjugated compound in which the absolute value of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is 0.5 eV or less and does not use an atom constituting a strong electron-withdrawing group Then, the mechanism of expression is inferred when a weak charge separation state is generated in the molecule and thermally activated delayed fluorescence is emitted.

In the conventional material having a strong electron-withdrawing group, the inside of the molecule is in a strong charge separation state. In the method of the present application, since light is emitted from a weak charge separation state, it is possible to suppress an increase in the emission wavelength. Being able to control the emission wavelength is advantageous for the development of organic electroluminescence elements.

The present application relates to an organic electroluminescence device having at least a light emitting layer between an anode and a cathode, wherein at least one of the light emitting layers has a lowest excited singlet energy level and a lowest excited triplet energy of the π-conjugated compound. The absolute value of the difference from the level is 0.50 eV or less, the energy level of HOMO is −5.5 eV or more, and the energy level of LUMO is −1.8 eV or more. This feature is a technical feature common to the claimed invention. Hereinafter, an organic EL light emitting method and a light emitting material related to the technical idea of the present invention will be described.

<Light emitting method of organic EL>
There are two types of organic EL emission methods: “phosphorescence emission” that emits light when returning from the triplet excited state to the ground state, and “fluorescence emission” that emits light when returning from the singlet excited state to the ground state. is there.

When excited by an electric field such as organic EL, triplet excitons are generated with a probability of 75% and singlet excitons with a probability of 25%. Therefore, “phosphorescent light emission” can increase the light emission efficiency compared to fluorescent light emission, and is an excellent method for realizing low power consumption.

On the other hand, even in “fluorescence emission”, triplet excitons that are generated with a probability of 75%, usually exciton energy that only becomes heat due to non-radiative deactivation, should be present at high density. Thus, a TTA (Triplet-Triple Annulation, or Triplet-Triplet Fusion: abbreviated as “TTF”) mechanism that generates singlet excitons from two triplet excitons to improve luminous efficiency is used. A method has been found.

Furthermore, in recent years, the discovery of Adachi et al. Has reduced the energy gap between the singlet excited state and the triplet excited state, so that the energy level of the triplet has a lower energy level due to the Joule heat during light emission and / or the environmental temperature where the light emitting element is placed. A phenomenon in which cross-reverse crossing occurs from a singlet excited state to a singlet excited state and, as a result, enables fluorescence emission nearly 100% (also referred to as thermally excited delayed fluorescence or thermally excited delayed fluorescence: “TADF”) A fluorescent substance that makes this possible has been found (see, for example, Non-Patent Document 1).

<Phosphorescent compound>
As described above, phosphorescence is theoretically 3 times more advantageous than fluorescence in terms of light emission efficiency, but energy deactivation (= phosphorescence) from triplet excited state to singlet ground state is forbidden. It is a transition. Similarly, since the intersystem crossing from the singlet excited state to the triplet excited state is also a forbidden transition, its rate constant is usually small. That is, since the transition is difficult to occur, the exciton lifetime is increased from millisecond to second order, and it is difficult to obtain desired light emission.

However, when a complex using a heavy metal such as iridium or platinum emits light, the rate constant of the forbidden transition increases by 3 digits or more due to the heavy atom effect of the central metal. % Phosphorescence quantum yield can be obtained.

However, in order to obtain such ideal light emission, it is necessary to use a rare metal called a white metal such as iridium, palladium, or platinum, which is a rare metal. The price of the metal itself is a major industrial issue.

<Fluorescent compound>
A general fluorescent compound is not necessarily a heavy metal complex like a phosphorescent compound, and is a so-called organic compound composed of a combination of general elements such as carbon, oxygen, nitrogen and hydrogen. Is applicable. Furthermore, other non-metallic elements such as phosphorus, sulfur and silicon can be used, and complexes of typical metals such as aluminum and zinc can be used. However, since only 25% of excitons can be applied to light emission as described above with conventional fluorescent compounds, high efficiency light emission such as phosphorescence emission cannot be expected.

<Delayed fluorescent compound>
[Excited triplet-triplet annihilation (TTA) delayed fluorescent compound]
In order to solve the problems of fluorescent compounds, a light emission method using delayed fluorescence has appeared. The TTA method that originates from collisions between triplet excitons can be described by the following general formula. That is, there is a merit that a part of triplet excitons, in which the energy of excitons has been converted only to heat due to non-radiation deactivation, can cross back to singlet excitons that can contribute to light emission. Even in an actual organic EL device, it is possible to obtain an external extraction quantum efficiency approximately twice that of a conventional fluorescent light emitting device.
General formula: T ^* + T ^* → S ^* + S (wherein T ^* represents a triplet exciton, S ^* represents a singlet exciton, and S represents a ground state molecule)
However, as can be seen from the above equation, since only one singlet exciton that can be used for light emission is generated from two triplet excitons, it is impossible in principle to obtain 100% internal quantum efficiency.

[Thermal activated delayed fluorescence (TADF) compound]
The TADF method, which is another highly efficient fluorescent emission, is a method that can solve the problems of TTA. As described above, the fluorescent compound has the advantage that the molecule can be designed infinitely. That is, among the molecularly designed compounds, there are compounds in which the energy level difference between the triplet excited state and the singlet excited state is extremely close.

Such compounds, even though in the molecule does not have a heavy atom, reverse intersystem crossing from a triplet excited state is usually not occur because Delta] E _ST is smaller to the singlet excited state occurs. Furthermore, since the rate constant of deactivation from singlet excited state to ground state (= fluorescence emission) is extremely large, triplet excitons themselves are thermally deactivated to ground state (non-radiative deactivation). It is more kinetically advantageous to return to the ground state while emitting fluorescence via the singlet excited state. Therefore, TADF theoretically enables 100% fluorescence emission.

<Molecular design concepts related to ΔE _ST>
It explained molecular design for reducing the Delta] E _ST.
ΔE in order to reduce the _ST is highest occupied molecular orbital in principle molecules (Highest Occupied Molecular Orbital: HOMO) and lowest unoccupied molecular orbital (Lowest Unoccupied Molecular Orbital: LUMO) spatial overlap the small to most effects of Is.

In general, it is known that HOMO is distributed in electron donating sites and LUMO is distributed in electron withdrawing sites in the electron orbit of the molecule. By introducing an electron donating and electron withdrawing skeleton into the molecule, HOMO is distributed. It is possible to move away the position where LUMO exists.

For example, in the application physics volume 82, No. 6, 2013, "Organic optoelectronics at the stage of practical use", electron donating skeletons such as cyano groups and triazines, and electron donations such as carbazole and diphenylamino groups By introducing a sex skeleton, LUMO and HOMO are localized.

It is also effective to reduce the molecular structure change between the ground state and triplet excited state of the compound. As a method for reducing the structural change, for example, making the compound rigid is effective. Rigidity described here means that there are few sites that can move freely in the molecule, for example, by suppressing free rotation in the bond between the rings in the molecule or by introducing a condensed ring with a large π conjugate plane. means. In particular, it is possible to reduce the structural change in the excited state by making the portion involved in light emission rigid.

<General problems with TADF compounds>
TADF compounds have various problems in terms of their light emission mechanism and molecular structure. The following describes some of the problems generally associated with TADF compounds.
In TADF compound, it is necessary to release as possible sites present in the HOMO and LUMO in order to reduce the Delta] E _ST, Therefore, the electronic state of the molecule of the donor / acceptor type HOMO site and LUMO sites separated It becomes a state close to intramolecular CT (intramolecular charge transfer state).

When there are a plurality of such molecules, stabilization is achieved by bringing the donor part of one molecule and the acceptor part of the other molecule close to each other. Such a stabilization state is not limited to the formation between two molecules, but can also be formed between a plurality of molecules such as three or five molecules. As a result, various stabilization states with a wide distribution are obtained. As a result, the shape of the absorption spectrum and emission spectrum becomes broad. In addition, even when a multimolecular assembly exceeding two molecules is not formed, various existence states can be taken depending on the direction and angle of interaction between the two molecules. The shape of the emission spectrum becomes broad.

The broad emission spectrum causes two major problems. One problem is that the color purity of the emitted color is lowered. This is not a big problem when applied to lighting applications, but when used for electronic displays, the color gamut is small and the color reproducibility of pure colors is low. It becomes difficult.

Another problem is that the rising wavelength on the short wavelength side of the emission spectrum (referred to as “fluorescence 0-0 band”) is shortened, that is, the S _{1 is} increased (the lowest excited singlet energy level is increased). It is to do.
Naturally, when the wavelength of the fluorescent 0-0 band is shortened, the phosphorescent 0-0 band derived from T ₁ having lower energy than S ₁ is also shortened (increased in the T ₁ level). Therefore, the compound used for the host compound needs to have a high S ₁ level and a high T ₁ level in order to prevent reverse energy transfer from the dopant.
This is a very big problem. A host compound consisting essentially of an organic compound takes a plurality of active and unstable chemical species such as a cation radical state, an anion radical state, and an excited state in an organic EL device. By expanding the π-conjugated system, it can exist relatively stably.

However, in order to impart a high S ₁ level and high T ₁ level position to molecule requires to or cut off it to reduce the π conjugated system in the molecule, and high S ₁ level and high T ₁ level position It becomes difficult to achieve both stability and the life of the light emitting element is shortened as a result.

In addition, in a TADF compound that does not contain a heavy metal, a transition that is deactivated from a triplet excited state to a ground state is a forbidden transition, and therefore the existence time (exciton lifetime) in the triplet excited state is from several hundred microseconds to millisecond. It is very long with second order. For this reason, even if the T ₁ energy level of the host compound is higher than that of the fluorescent compound, the triplet excited state of the fluorescent compound from the triplet excited state to the host compound is determined from the length of the existence time. The probability of causing reverse energy transfer increases. As a result, the reverse reverse energy transfer from the triplet excited state to the singlet excited state of the originally intended TADF compound does not occur sufficiently, and unfavorable reverse energy transfer to the host compound becomes the mainstream, resulting in sufficient luminous efficiency. Inconvenience that cannot be obtained.

In order to solve the above problems, it is necessary to sharpen the emission spectrum shape of the TADF compound and reduce the difference between the emission maximum wavelength and the rising wavelength of the emission spectrum. This can be basically achieved by reducing the change in the molecular structure of the singlet excited state and the triplet excited state.

In order to suppress reverse energy transfer to the host compound, it is effective to shorten the existence time (exciton lifetime) of the triplet excited state of the TADF compound. To achieve this, it is necessary to take measures such as reducing the molecular structure change between the ground state and the triplet excited state and introducing suitable substituents and elements to undo the forbidden transition. Can be solved.

Hereinafter, various measurement methods related to the π-conjugated compound according to the present invention will be described.

[Electron density distribution]
Π conjugated compound of the present invention, from the viewpoint of reducing the Delta] E _ST, it is preferable that HOMO and LUMO are substantially separated in the molecule. The distribution states of these HOMO and LUMO can be obtained from the electron density distribution when the structure is optimized by molecular orbital calculation.

In the present invention, structure optimization and calculation of electron density distribution by molecular orbital calculation of a π-conjugated compound are performed by using molecular orbital calculation software using B3LYP as a functional and 6-31G (d) as a basis function as a calculation method. There is no particular limitation on the software, and any of them can be similarly calculated.
In the present invention, Gaussian 09 (Revision C.01, MJ Frisch, et al, Gaussian, Inc., 2010.) manufactured by Gaussian, USA was used as molecular orbital calculation software.

Further, “HOMO and LUMO are substantially separated” means that the HOMO orbital distribution calculated by the above molecular calculation and the central part of the LUMO orbital distribution are separated, more preferably the HOMO orbital distribution and the LUMO orbital. This means that the distributions of do not overlap.
As for the separation state of HOMO and LUMO, from the above-mentioned structure optimization calculation using B3LYP as the functional and 6-31G (d) as the basis function, the time-dependent density functional method (Time-Dependent DFT) is used. An excited state calculation is performed to obtain energy levels of S ₁ and T ₁ (E (S ₁ ) and E (T ₁ ), respectively), and ΔE _ST = | E (S ₁ ) −E (T ₁ ) | It is also possible to calculate. As calculated Delta] E _ST is small, indicating that the HOMO and LUMO are more separated. In the present invention, it is Delta] E _ST calculated using the calculation method similar to that described above or less 0.50EV, preferably not more than 0.30 eV, more preferably not more than 0.10 eV.

[Lowest excitation singlet energy level S ₁ ]
The lowest excited singlet energy level S ₁ of the π-conjugated compound of the present invention is defined in the present invention as calculated in the same manner as in a normal method. That is, a sample to be measured is deposited on a quartz substrate to prepare a sample, and the absorption spectrum (vertical axis: absorbance, horizontal axis: wavelength) of this sample is measured at room temperature (300 K). A tangent line is drawn with respect to the rising edge of the absorption spectrum on the long wavelength side, and is calculated from a predetermined conversion formula based on the wavelength value at the intersection of the tangent line and the horizontal axis.

However, when the molecules themselves of the π-conjugated compound used in the present invention have a relatively high aggregation property, an error due to aggregation may occur in the measurement of the thin film. Considering that the Stokes shift of the π-conjugated compound of the present invention is relatively small and that the structural change between the excited state and the ground state is small, the lowest excited singlet energy level S ₁ in the present invention is room temperature (25 ° C. The peak value of the maximum emission wavelength in the solution state of the π-conjugated compound in (1) was used as an approximate value.
Here, as the solvent to be used, a solvent that does not affect the aggregation state of the π-conjugated compound, that is, a solvent having a small influence of the solvent effect, for example, a nonpolar solvent such as cyclohexane or toluene can be used.

[Lowest excited triplet energy level T ₁ ]
The lowest excited triplet energy level (T ₁ ) of the π-conjugated compound of the present invention is calculated from the photoluminescence (PL) characteristics of the solution or thin film. For example, as a calculation method in a thin film, after making a dispersion of a dilute π-conjugated compound into a thin film, using a streak camera, the transient PL characteristics are measured to separate the fluorescent component and the phosphorescent component, the absolute value of the energy difference can be determined the lowest excited triplet energy level of the lowest excited singlet energy level as Delta] E _ST.

In measurement and evaluation, an absolute PL quantum yield measurement apparatus C9920-02 (manufactured by Hamamatsu Photonics) was used for measurement of the absolute PL quantum yield. The light emission lifetime was measured using a streak camera C4334 (manufactured by Hamamatsu Photonics) while exciting the sample with laser light.

[HOMO and LUMO energy levels]
The LUMO energy level of the π-conjugated compound of the present invention is −1.8 eV or more, preferably −1.7 to −0.6 eV, more preferably −1.5 to −1.1 eV. The LUMO energy level of −1.8 eV or more indicates that the π-conjugated compound of the present invention does not have a strong electron-withdrawing group, that is, the HOMO energy level does not become excessively low. In a conventional π-conjugated compound having a strong electron-withdrawing group, the HOMO level is lowered as the LUMO level is lowered. Therefore, when the π-conjugated compound is a light-emitting material, for example, the HOMO level and the LUMO level of the light-emitting material are low, so that it is difficult to select a host material and the carrier balance during EL driving is lost. On the other hand, in the π-conjugated compound of the present invention, since the LUMO level is relatively high, the HOMO level is not excessively lowered, and excitons are easily generated on the π-conjugated compound. can get. The energy level of HOMO of the π-conjugated compound of the present invention is −5.5 eV or more, preferably −5.3 to −4.0 eV, more preferably −5.0 to −4.5 eV. The energy levels of HOMO and LUMO are calculated by structure optimization calculation using B3LYP as the functional and 6-31G (d) as the basis function.

[Structure of π-conjugated compound of the present invention]
The π-conjugated compound of the present invention is not particularly limited as long as it satisfies the above-mentioned requirements, but can be a compound having a π-conjugated structure and not containing a strong electron-withdrawing group. Such a π-conjugated compound can be a compound composed only of atoms selected from the following atomic group A.

Atomic group A:
Hydrogen atom, deuterium atom, fluorine atom, carbon atom forming only single bond, carbon atom forming double bond, nitrogen atom forming only single bond, oxygen atom forming only single bond, only single bond Sulfur atoms to be formed, silicon atoms having only a single bond

Among the atomic group A, a hydrogen atom, a fluorine atom, a carbon atom that forms only a single bond, a carbon atom that forms a double bond, a nitrogen atom that forms only a single bond, an oxygen atom that forms only a single bond, a single atom Sulfur atoms that form only bonds are preferred.

More specifically, the π-conjugated compound of the present invention preferably contains a structure in which two or more ring structures selected from the following ring structure group X are connected to each other. In the π-conjugated compound of the present invention, these ring structures may be substituted with a substituent.
Ring structure group X:
Benzene ring, indene ring, naphthalene ring, azulene ring, fluorene ring, phenanthrene ring, anthracene ring, acenaphthylene ring, biphenylene ring, chrysene ring, naphthacene ring, pyrene ring, pentalene ring, asanthrylene ring, heptalene ring, triphenylene ring, as-indacene ring, chrysene ring, s-indacene ring, preaden ring, phenalene ring, fluoranthene ring, perylene ring, acephenanthrylene ring, biphenyl ring, terphenyl ring, tetraphenyl ring, carbazole ring, indoloindole ring 9,10-dihydroacridine ring, phenoxazine ring, phenothiazine ring, dibenzothiophene ring, benzofurylindole ring, benzothienoindole ring, indolocarbazole ring, benzofurylcarbazole ring, benzothienocarba Lumpur ring, benzothiophene thieno benzothiophene ring, benzocarbazole ring, dibenzothiophene carbazole ring, a dibenzofuran ring, benzo furyl benzofuran ring, dibenzosilole ring, 5,10-dihydrophenanthrene Naza cylindrical ring, 10,11-dihydro-dibenzo azepine ring

Among the ring structures selected from the above ring structure group, preferred are benzene ring, naphthalene ring, fluorene ring, phenanthrene ring, biphenylene ring, pyrene ring, triphenylene ring, chrysene ring, fluoranthene ring, perylene ring, biphenyl ring, Terphenyl ring, carbazole ring, indoloindole ring, 9,10-dihydroacridine ring, phenoxazine ring, phenothiazine ring, benzofurylindole ring, benzothienoindole ring, indolocarbazole ring, benzothienobenzothiophene ring, dibenzocarbazole Ring, dibenzofuran ring, benzofurylbenzofuran ring, 5,10-dihydrophenazacillin ring, and 10,11-dihydrodibenzazepine ring.

The substituent of the ring structure is preferably an atom selected from the atomic group A or a substituent composed of a combination thereof. Specific examples include a fluorine atom, an alkyl group which may be substituted with fluorine, an alkoxy group which may be substituted with fluorine, and an amino group which may be substituted. Preferred are a fluorine atom, an alkyl group which may be substituted with fluorine, and an amino group which may be substituted.

The alkyl group of the “alkyl group optionally substituted with fluorine” which may be a substituent of a ring structure may be an alkyl group having any of a linear, branched, or cyclic structure. Examples of the alkyl group include linear, branched or cyclic alkyl groups having 1 to 20 carbon atoms. Specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, s-butyl group, t-butyl group, n-pentyl group, neopentyl group, n-hexyl group, cyclohexyl group, 2-ethylhexyl group, n-heptyl group, n-octyl group, 2-hexyloctyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group N-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group and n-icosyl group. Preferred are methyl group, ethyl group, isopropyl group, t-butyl group, cyclohexyl group, 2-ethylhexyl group, and 2-hexyloctyl group.

The alkoxy group of the “alkoxy group which may be substituted with fluorine” which may be a substituent of a ring structure may be an alkoxy group having any of a linear structure, a branched structure or a cyclic structure. Examples of the alkoxy group include a linear, branched or cyclic alkoxy group having 1 to 20 carbon atoms. Specifically, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, t-butoxy group, n-pentyloxy group, neopentyloxy group, n-hexyloxy group, Cyclohexyloxy group, n-heptyloxy group, n-octyloxy group, 2-ethylhexyloxy group, nonyloxy group, decyloxy group, 3,7-dimethyloctyloxy group, n-undecyloxy group, n-dodecyloxy group, n-tridecyloxy, n-tetradecyloxy, 2-n-hexyl-n-octyloxy, n-pentadecyloxy, n-hexadecyloxy, n-heptadecyloxy, n-octadecyl Examples thereof include an oxy group, an n-nonadecyloxy group, and an n-icosyloxy group. Among these, a methoxy group, an ethoxy group, an isopropoxy group, a t-butoxy group, a cyclohexyloxy group, a 2-ethylhexyloxy group, and a 2-hexyloctyloxy group are preferable.

Examples of the substituent of the “optionally substituted amino group” which may be a substituent of the ring structure include a fluorine atom, an alkyl group optionally substituted with fluorine, a ring structure selected from the ring structure group X, etc. Is mentioned. The alkyl group and the ring structure selected from the ring structure group X can be the same as those specifically shown above.

Here, the conjugated compound of the present invention contains at least an “electron donating group” and an “electron withdrawing group”. Among the ring structures included in the aforementioned ring structure group X, those that can be “electron-withdrawing groups” include benzene ring, indene ring, naphthalene ring, azulene ring, fluorene ring, phenanthrene ring, anthracene ring, acenaphthylene ring, biphenylene Ring, chrysene ring, naphthacene ring, pyrene ring, pentalene ring, acanthrylene ring, heptalene ring, triphenylene ring, as-indacene ring, s-indacene ring, preaden ring, phenalene ring, fluoranthene ring, perylene ring, aceph An aromatic ring that is unsubstituted or substituted with an “electron-withdrawing group” such as a nanthrylene ring, biphenyl ring, terphenyl ring, or tetraphenyl ring; may be an aromatic heterocyclic ring such as a dibenzofuran ring or a dibenzosilole ring . Examples of the “electron withdrawing group” include the aforementioned fluorine atom, an alkyl group substituted with a fluorine atom, and the like.

On the other hand, among the ring structures included in the aforementioned ring structure group X, those that can be “electron-donating groups” are carbazole ring, indoloindole ring, 9,10-dihydroacridine ring, phenoxazine ring, phenothiazine ring. , Dibenzothiophene ring, benzofurylindole ring, benzothienoindole ring, indolocarbazole ring, benzofurylcarbazole ring, benzothienocarbazole ring, benzothienobenzothiophene ring, benzocarbazole ring, dibenzocarbazole ring, benzofurylbenzofuran ring, 5 , 10-dihydrophenazacillin ring, aromatic heterocycle such as 10,11-dihydrodibenzazepine ring; and the above-mentioned aromatic ring substituted with “electron donating group”. Examples of the “electron-donating group” include the aforementioned alkyl group, alkoxy group, and optionally substituted amino group.

Specific preferred examples of the π-conjugated compound of the present invention are shown below, but these compounds may further have a substituent, may be a structural isomer thereof, and the like, and are not limited to this description. .

The π-conjugated compound of the present invention can be the aforementioned fluorescent compound in an organic EL device. Further, the π-conjugated compound of the present invention can be used as a host compound for an organic EL device. In this case, the light emitting layer preferably contains the π-conjugated compound of the present invention and at least one of a fluorescent light emitting compound and a phosphorescent light emitting compound from the viewpoint of high light emission. Furthermore, the π-conjugated compound of the present invention can be used as the assist dopant described above in the organic EL device. In this case, the π-conjugated compound of the present invention, the fluorescent compound, and the phosphorescence are included in the light emitting layer. From the viewpoint of high light emission, it is preferable to contain at least one of the light emitting compounds and a host compound.

Also, [pi conjugated compound of the present invention, the absolute value of the aforementioned Delta] E _ST is less 0.50EV, likely indicates TADF properties. Therefore, the π-conjugated compound of the present invention can be used for various applications as a delayed phosphor. Here, exhibiting delayed fluorescence means that there are two or more types of components having different decay rates of emitted fluorescence when fluorescence decay measurement is performed. In general, the slow decay component generally has a decay time of sub-microseconds or more. However, the decay time is not limited because the decay time differs depending on the material. In general, fluorescence decay measurement can be performed as follows. A solution or thin film of a π-conjugated compound (luminescent compound) or a co-deposition film of the π-conjugated compound and the second component is irradiated with excitation light in a nitrogen atmosphere, and the number of photons at a certain emission wavelength is measured. At this time, the π-conjugated compound exhibits delayed fluorescence when there are two or more types of components having different decay rates of emitted fluorescence.

Furthermore, since the π-conjugated compound of the present invention has bipolar properties and can cope with various energy levels, it can be used as a fluorescent compound, a light-emitting host, an assist dopant, as well as hole transport and electron transport. It can also be used as a suitable compound. Therefore, the π-conjugated compound of the present invention is not limited to use in the light-emitting layer of the organic EL device, and will be described later as a hole injection layer, a hole transport layer, an electron blocking layer, a hole blocking layer, an electron transport layer, an electron It can be used for an injection layer, an intermediate layer, and the like.

Further, the π-conjugated compound of the present invention can also be used as a light-emitting thin film containing the π-conjugated compound.

<Synthesis Method of π-Conjugated Compound>
Examples of the π-conjugated compound include International Publication No. 2010/113755, Organic Letters, 2010, 12, 3438-3441. , Angew. Chem. Int. Ed. 2008, 47, 6338-6361., Or by referring to the methods described in the references described in these documents.

2. About organic EL element << Constitutional layer of organic EL element >>
The organic EL device of the present invention is an organic electroluminescence device having at least a light emitting layer between an anode and a cathode, wherein at least one of the light emitting layers contains the above-described π-conjugated compound. . The organic EL element of the present invention can be suitably included in a lighting device and a display device.
As typical element structures in the organic EL element of the present invention, the following structures can be exemplified, but the invention is not limited thereto.
(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) Anode / hole injection layer / hole transport layer / (electron blocking layer /) luminescent layer / (hole blocking layer /) electron transport layer / electron injection layer / cathode Among the above, the configuration of (7) is preferable. Although used, it is not limited to this.
The light emitting layer used in the present invention is composed of a single layer or a plurality of layers. 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 blocking 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. 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 therebetween.
The electron transport layer used in the present invention 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. Moreover, you may be comprised by multiple layers.
The hole transport layer used in the present invention 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. Moreover, you may be comprised by multiple layers.
In the above-described typical element configuration, the layer excluding the anode and the cathode is also referred to as “organic layer”.

(Tandem structure)
The organic EL element of the present invention may be a so-called tandem element in which a plurality of light emitting units including at least one light emitting layer are stacked.
As typical element configurations of the tandem structure, for example, the following configurations can be given.
Anode / first light emitting unit / intermediate layer / second light emitting unit / intermediate layer / third light emitting unit / cathode Here, the first light emitting unit, the second light emitting unit and the third light emitting unit are all the same, May be different. Two light emitting units may be the same, and the remaining one may be different.
A plurality of light emitting units may be laminated directly or 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, an intermediate layer. A known material structure can be used as long as it is also called an insulating layer and has a function of supplying electrons to the anode-side adjacent layer and holes to the cathode-side adjacent layer.

Examples of materials used for the intermediate layer include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO ₂ , TiN, ZrN, HfN, TiOx, VOx, CuI, InN, GaN, CuAlO ₂ , Conductive inorganic compound layers such as CuGaO ₂ , SrCu ₂ O ₂ , LaB ₆ , RuO ₂ and Al, two-layer 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 and} other multilayer films, C _{60 and} other fullerenes, conductive organic layers such as oligothiophene, Examples include conductive organic compound layers such as metal phthalocyanines, metal-free phthalocyanines, metal porphyrins, metal-free porphyrins, etc. The invention is not limited to these.
Preferred examples of the configuration within the light emitting unit include, for example, those obtained by removing the anode and the cathode from the configurations (1) to (7) mentioned in the above representative device configurations. It is not limited.

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, US Pat. No. 6,107,734, US Pat. No. 6,337,492, International JP 2005/009087, JP 2006-228712, JP 2006-24791, JP 2006-49393, JP 2006-49394, JP 2006-49396, JP 2011. No. -96679, JP 2005-340187, JP 47114424, JP 34966681, JP 3884564, JP 4213169, JP 2010-192719, JP 2009-076929, JP Open 2008-078 No. 14, JP 2007-059848 A, JP 2003-272860 A, JP 2003-045676 A, International Publication No. 2005/094130, and the like. The present invention is not limited to these.

Hereinafter, each layer constituting the organic EL element of the present invention will be described.

<Light emitting layer>
The light-emitting layer used in the present invention is a layer that provides a field in which electrons and holes injected from an electrode or an adjacent layer are recombined to emit light via excitons, and the light-emitting portion is the light-emitting layer. Even in the layer, it may be the interface between the light emitting layer and the adjacent layer. If the light emitting layer used for this invention satisfy | fills the requirements prescribed | regulated by this invention, there will be no restriction | limiting in particular in the structure.
The total thickness of the light emitting layer is not particularly limited, but it prevents the uniformity of the film to be formed, the application of unnecessary high voltage during light emission, and the improvement of the stability of the emission color against the drive current. From the viewpoint, it is preferably adjusted to a range of 2 nm to 5 μm, more preferably adjusted to a range of 2 to 500 nm, and further preferably adjusted to a range of 5 to 200 nm.
The thickness of each light emitting layer used in the present invention is preferably adjusted to a range of 2 nm to 1 μm, more preferably adjusted to a range of 2 to 200 nm, and further preferably in a range of 3 to 150 nm. Adjusted.
The light emitting layer used in the present invention may be a single layer or a plurality of layers. When the π-conjugated compound of the present invention is used in the light emitting layer, it may be used alone or in combination with a host material, a fluorescent light emitting material, a phosphorescent light emitting material, etc. described later. At least one layer of the light-emitting layer contains a light-emitting dopant (a light-emitting compound, a light-emitting dopant, or simply a dopant), and further contains a host compound (a matrix material, a light-emitting host compound, or simply a host). preferable. In the π-conjugated compound of the present invention, it is preferable that at least one layer of the light-emitting layer contains the π-conjugated compound of the present invention and a host compound because the light emission efficiency is improved. It is preferable that at least one layer of the light emitting layer contains the π-conjugated compound of the present invention and at least one of a fluorescent light emitting compound and a phosphorescent light emitting compound because the light emission efficiency is improved. It is preferable that at least one layer of the light emitting layer contains the π-conjugated compound of the present invention, at least one of a fluorescent light emitting compound and a phosphorescent light emitting compound, and a host compound because the light emission efficiency is improved.

(1) Luminescent dopant As the luminescent dopant, a fluorescent luminescent dopant (also referred to as a fluorescent luminescent compound or a fluorescent dopant) and a phosphorescent dopant (also referred to as a phosphorescent luminescent compound or a phosphorescent dopant) are preferably used. It is done. In the present invention, the light-emitting layer contains the π-conjugated compound according to the present invention as a fluorescent light-emitting compound or an assist dopant in a range of 0.1 to 50% by mass, particularly in a range of 1 to 30% by mass. It is preferable to contain within.

In the present invention, the light emitting layer contains the light emitting compound within a range of 0.1 to 50% by mass, and particularly preferably within a range of 1 to 30% by mass.
The concentration of the light-emitting compound in the light-emitting layer can be arbitrarily determined based on the specific light-emitting compound used and the requirements of the device, and is uniform in the thickness direction of the light-emitting layer. It may be contained and may have any concentration distribution.
Moreover, the luminescent compound used in the present invention may be used in combination of a plurality of types, or a combination of fluorescent luminescent compounds having different structures, or a combination of a fluorescent luminescent compound and a phosphorescent luminescent compound. Good. Thereby, arbitrary luminescent colors can be obtained.

The absolute value (ΔE _ST ) of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is 0.50 eV or less, a π-conjugated compound according to the present invention, a luminescent compound, and a host compound. When contained in the light emitting layer, the π-conjugated compound according to the present invention acts as an assist dopant. On the other hand, when the light emitting layer contains the π-conjugated compound and the luminescent compound according to the present invention and does not contain the host compound, the π-conjugated compound according to the present invention acts as a host compound. When the light emitting layer contains only the π-conjugated compound according to the present invention, the π-conjugated compound according to the present invention acts as a host compound / light-emitting compound.
The mechanism for producing the effect is the same in any case, and the triplet exciton generated on the π-conjugated compound according to the present invention is converted into a singlet exciton by reverse intersystem crossing (RISC). It is in.
As a result, all the exciton energies generated on the π-conjugated compound according to the present invention can be transferred to the luminescent compound by fluorescence resonance energy transfer (FRET), thereby realizing high luminous efficiency.
Therefore, when the light emitting layer contains the three components of the π-conjugated compound, the luminescent compound, and the host compound according to the present invention, the energy levels of S ₁ and T ₁ of the π-conjugated compound are S of the host compound. ₁ and T ₁ of the lower than the energy level, it is preferably higher than the energy level of the S ₁ and T ₁ of the light-emitting compound.
Similarly, light emitting layer, the energy level of the S ₁ and T ₁ of the case containing the two components of the light emitting compound and [pi conjugated compound according to the present invention, [pi-conjugated compounds, S ₁ luminescent compound higher than the energy level of T ₁ and is preferable.

FIG. 3 and FIG. 4 show schematic diagrams when the π-conjugated compound of the present invention acts as an assist dopant and a host compound, respectively. 3 and 4 are examples, and the generation process of the triplet exciton generated on the π-conjugated compound according to the present invention is not limited to the electric field excitation, and the energy transfer from the light emitting layer or the peripheral layer interface. And electronic transfer.
Further, in FIGS. 3 and 4, a fluorescent compound is used as a light-emitting material, but the present invention is not limited to this, and a phosphorescent compound may be used, or a fluorescent compound and a phosphorescent compound may be used. Both of the functional compounds may be used.

When the π-conjugated compound according to the present invention is used as an assist dopant, the light-emitting layer contains a host compound in a mass ratio of 100% or more with respect to the π-conjugated compound, and the fluorescent compound and / or phosphorescent compound. Is preferably contained within a range of 0.1 to 50% by mass with respect to the π-conjugated compound.

When the π-conjugated compound according to the present invention is used as a host compound, the light emitting layer has a mass ratio of 0.1 to 50% of the fluorescent compound and / or phosphorescent compound with respect to the π-conjugated compound. It is preferable to contain.

When the π-conjugated compound according to the present invention is used as an assist dopant or a host compound, the emission spectrum of the π-conjugated compound according to the present invention and the absorption spectrum of the luminescent compound preferably overlap.

The light emission color of the organic EL device of the present invention and the compound used in the present invention is shown in FIG. 3.16 on page 108 of “New Color Science Handbook” (edited by the Japan Color Society, University of Tokyo Press, 1985). It is determined by the color when the result measured with a luminance meter 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 emission colors and emits white light.
There are no particular limitations on the combination of light-emitting dopants that exhibit white, and examples include blue and orange, and a combination of blue, green, and red.
The white color in the organic EL device of the present invention means that the chromaticity in the CIE 1931 color system at 1000 cd / m ² is x = 0.39 ± 0.09 when the 2 ° viewing angle front luminance is measured by the method described above. Y = 0.38 ± 0.08.

(1.1) Fluorescent luminescent dopant The fluorescent luminescent dopant (fluorescent dopant) may be the π-conjugated compound of the present invention, or a known fluorescent dopant or delayed fluorescence used in the light emitting layer of the organic EL device. You may use it selecting suitably from a dopant.

Specific examples of known fluorescent dopants that can be used in the present invention include, for example, anthracene derivatives, pyrene derivatives, chrysene derivatives, fluoranthene derivatives, perylene derivatives, fluorene derivatives, arylacetylene derivatives, styrylarylene derivatives, styrylamine derivatives, arylamine derivatives. , Boron complexes, coumarin derivatives, pyran derivatives, cyanine derivatives, croconium derivatives, squalium derivatives, oxobenzanthracene derivatives, fluorescein derivatives, rhodamine derivatives, pyrylium derivatives, perylene derivatives, polythiophene derivatives, rare earth complex compounds, and the like. In recent years, light emitting dopants utilizing delayed fluorescence have been developed, and these may be used. Specific examples of the luminescent dopant using delayed fluorescence include, for example, compounds described in International Publication No. 2011/156793, Japanese Patent Application Laid-Open No. 2011-213643, Japanese Patent Application Laid-Open No. 2010-93181, Japanese Patent No. 5366106, and the like. However, the present invention is not limited to these.

(1.2) Phosphorescent dopant The phosphorescent dopant used in the present invention will be described.
The phosphorescent dopant used in the present invention is a compound in which light emission from an excited triplet is observed, specifically, a compound that emits phosphorescence at room temperature (25 ° C.), and a phosphorescence quantum yield. Is defined as a compound of 0.01 or more at 25 ° C., but a preferable phosphorescence quantum yield is 0.1 or more.
The phosphorescence quantum yield can be measured by the method described in Spectroscopic II, page 398 (1992 edition, Maruzen) of Experimental Chemistry Course 4 of the 4th edition. Although the phosphorescence quantum yield in a solution can be measured using various solvents, the phosphorescence dopant used in the present invention achieves the phosphorescence quantum yield (0.01 or more) in any solvent. Just do it.

The phosphorescent dopant can be appropriately selected from known materials used for the light emitting layer of the organic EL device. 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), Appl. 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 Application Publication No. 2006/835469, US Patent Application Publication No. 2006 /. No. 0202194, U.S. Patent Application Publication No. 2007/0087321, U.S. Patent Application 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, Appl. 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 Application Publication No. 2002/0034656, US Pat. No. 7,332,232, US Patent Application Publication No. 2009/0108737, United States Patent Application Publication No. 2009/0039776, United States Patent No. 6921915, United States Patent No. 6,687,266, United States Patent Application Publication No. 2007/0190359, United States Patent Application Publication No. 2006/0008670, United States Patent Application Publication No. 2009/0165846, United States Patent Application Publication No. 2008/0015355, United States Patent No. 7250226, United States Patent No. 7396598, United States Patent Application Publication No. 2006 0263635 Pat, U.S. Patent Application Publication No. 2003/0138657, U.S. Patent Application Publication No. 2003/0152802, U.S. Patent No. 7090928, Angew. Chem. lnt. Ed. 47, 1 (2008), Chem. Mater. 18, 5119 (2006), Inorg. Chem. 46, 4308 (2007), Organometallics 23, 3745 (2004), Appl. Phys. Lett. 74, 1361 (1999), International Publication No. 2002/002714, International Publication No. 2006/009024, International Publication No. 2006/056418, International Publication No. 2005/019373, International Publication No. 2005/123873, International Publication No. 2005/123873, International Publication No. 2007/004380, International Publication No. 2006/082742, US Patent Application Publication No. 2006/0251923, US Patent Application Publication No. 2005/0260441, US Pat. No. 7,393,599. , US Pat. No. 7,534,505, US Pat. No. 7,445,855, US Patent Application Publication No. 2007/0190359, US Patent Application Publication No. 2008/0297033, US Pat. No. 7,338,722, US Patent Application Publication No. 2002 / 0 No. 34984, U.S. Pat. No. 7,279,704, U.S. Patent Application Publication No. 2006/098120, U.S. Patent Application Publication No. 2006/103874, WO 2005/076380, WO 2010/032663. International Publication No. 2008140115, 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 Application Publication No. 2012/228583, US Patent Application Publication No. 2012/21211. No. 6, JP 2012-069737 A, Japanese Patent Application No. 2011-181303, JP 2009-114086, JP 2003-81988, JP 2002-302671, JP 2002-363552. No. gazette.
Among these, a preferable phosphorescent dopant includes an organometallic complex having Ir as a central metal. More preferably, a complex containing at least one coordination mode of metal-carbon bond, metal-nitrogen bond, metal-oxygen bond, and metal-sulfur bond is preferable.

(2) Host compound The host compound used in the present invention is a compound mainly responsible for charge injection and transport in the light emitting layer, and its own light emission is not substantially observed in the organic EL device.
The host compound preferably has a mass ratio in the layer of 20% or more among the compounds contained in the light emitting layer.
A host compound may be used independently or may be used together with multiple types. By using a plurality of types of host compounds, it is possible to adjust the movement of electric charge, and the efficiency of the organic electroluminescence element can be improved.
The host compound that is preferably used in the present invention will be described below.

As the host compound, the π-conjugated compound of the present invention may be used as described above, but there is no particular limitation. From the viewpoint of reverse energy transfer, those having an excitation energy larger than the excitation singlet energy of the dopant are preferred, and those having an excitation triplet energy larger than the excitation triplet energy of the dopant are more preferred.
The host compound is responsible for carrier transport and exciton generation in the light emitting layer. Therefore, it can exist stably in all active species states such as cation radical state, anion radical state, and excited state, and does not cause chemical changes such as decomposition and addition reaction. It is preferable not to move at the angstrom level.

In particular, when the luminescent dopant used in combination exhibits TADF emission, the existence time of the triplet excited state of the TADF compound is long, so that the T ₁ energy level of the host compound itself is high, and the host compounds are associated with each other. Molecules in which the host compound does not decrease in T ₁ , such as not forming a low T ₁ state in the state, TADF compound and the host compound do not form an exciplex, or the host compound does not form an electromer due to an electric field. Appropriate design of the structure is required.
In order to satisfy these requirements, the host compound itself must have high electron hopping mobility, high hole hopping movement, and small structural change when it is in a triplet excited state. It is. Preferred examples of host compounds that satisfy such requirements include those having a high T ₁ energy level such as a carbazole skeleton, an azacarbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, or an azadibenzofuran skeleton.

In addition, the host compound has a hole transporting ability or an electron transporting ability, prevents the emission of light from becoming longer, and further stabilizes the organic electroluminescence device against heat generation during high temperature driving or during device driving. From the viewpoint of operating, it is preferable to have a high glass transition temperature (Tg). Tg is preferably 90 ° C. or higher, more preferably 120 ° C. or higher.
Here, the glass transition point (Tg) is a value determined by a method based on JIS K 7121-2012 using DSC (Differential Scanning Colorimetry).

As the host compound used in the present invention, it is also preferable to use the π-conjugated compound according to the present invention as described above. The π-conjugated compound according to the present invention has a high T ₁ and can be suitably used for a light-emitting material having a short emission wavelength (that is, a high energy level of T ₁ and S ₁ ). It is.

When a known host compound is used for the organic EL device of the present invention, specific examples thereof include compounds described in the following documents, but the present invention is not limited thereto. JP-A-2001-257076, 2002-308855, 2001-313179, 2002-319491, 2001-357777, 2002-334786, 2002-8860, 2002-334787, 2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75645, 2002-338579, 2002-105445 gazette, 2002-343568 gazette, 2002-141173 gazette, 2002-352957 gazette, 2002-203683 gazette, 2002-363227 gazette, 2002-231453 gazette, No. 003-3165, 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, U.S. Patent Application Publication No. 2003/0175553, U.S. Patent Application Publication No. 2006/0280965, US Patent Application Publication No. 2005/0112407, US Patent Application Publication No. 2009/0017330, US Patent Application Publication No. 2009/0030202, US Patent Application Publication No. 2005/0238919, International Publication First 001/039234, 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. 2007/2007 / No. 063754, 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. 2012/023947 JP 2008-074939 A, JP 2007-254297 A, European Patent No. 2034538, International Publication No. 2011/055933, International Publication No. 2012/035853, and the like. Specific examples of the host compound used in the present invention include compounds represented by H-1 to H230 described in paragraphs [0255] to [0293] of JP-A-2015-38941. And a compound represented by the following chemical formula H-231 or H-234 is included, but the host compound is not limited thereto.

《Electron transport layer》
In the present invention, the electron transport layer is 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 according to the present invention is not particularly limited, but is usually in the range of 2 nm to 5 μm, more preferably 2 to 500 nm, and further preferably 5 to 200 nm.
Further, in the organic EL element, when the light generated in the light emitting layer is extracted from the electrode, the light extracted directly from the light emitting layer interferes with the light extracted after being reflected by the electrode from which the light is extracted and the electrode located at the counter electrode. It is known to wake up. When light is reflected by the cathode, this interference effect can be efficiently utilized by appropriately adjusting the total thickness of the electron transport layer between several nanometers and several micrometers.
On the other hand, when the layer thickness of the electron transport layer is increased, the voltage is likely to increase. Therefore, particularly when the layer thickness is large, the electron mobility of the electron transport layer is preferably 10 ⁻⁵ cm ² / Vs or more. .
The material used for the electron transport layer (hereinafter referred to as an electron transport material) may be any of electron injecting or transporting properties and hole blocking properties, and can be selected from conventionally known compounds. Can be selected and used.

For example, nitrogen-containing aromatic heterocyclic derivatives (carbazole derivatives, azacarbazole derivatives (one or more carbon atoms constituting the carbazole ring are substituted with nitrogen atoms), pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, pyridazine derivatives, Triazine derivatives, quinoline derivatives, quinoxaline derivatives, phenanthroline derivatives, azatriphenylene derivatives, oxazole derivatives, thiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, triazole derivatives, benzimidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, etc.), dibenzofuran derivatives, Dibenzothiophene derivatives, silole derivatives, aromatic hydrocarbon ring derivatives (naphthalene derivatives, anthracene derivatives, triphenylene derivatives, etc.) It is.

In addition, a metal complex having a quinolinol skeleton or a dibenzoquinolinol skeleton as a ligand, such as 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 their metal complexes A metal complex in which the central metal is replaced with In, Mg, Cu, Ca, Sn, Ga, or Pb can also be used as the electron transport material.
In addition, metal-free or metal phthalocyanine, or those having terminal ends substituted with an alkyl group or a sulfonic acid group can be preferably used as the electron transport material. In addition, the distyrylpyrazine derivative exemplified as the material for the light emitting layer can also be used as an electron transport material, and an inorganic semiconductor such as n-type-Si, n-type-SiC, etc. as in the case of the hole injection layer and the hole transport layer. Can also be used as an electron transporting material.
Further, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

In the electron transport layer according to 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 complexes and metal compounds such as metal halides. Specific examples of the electron transport layer having such a structure include, for example, JP-A-4-297076, JP-A-10-270172, JP-A-2000-196140, 2001-102175, J. Pat. Appl. Phys. , 95, 5773 (2004) and the like.

Specific examples of known preferable electron transport materials used in the organic EL device of the present invention include compounds described in the following documents, but the present invention is not limited thereto.
US Pat. No. 6,528,187, US Pat. No. 7,230,107, US Patent Application Publication No. 2005/0025993, US Patent Application Publication No. 2004/0036077, US Patent Application Publication No. 2009/0115316, US Patent Application Publication No. 2009/0101870, United States Patent Application Publication No. 2009/0179554, International Publication No. 2003/060956, International Publication No. 2008/132805, Appl. Phys. Lett. 75, 4 (1999), Appl. Phys. Lett. 79, 449 (2001), Appl. Phys. Lett. 81, 162 (2002), Appl. Phys. Lett. 81, 162 (2002), Appl. Phys. Lett. 79,156 (2001), US Patent No. 7964293, US Patent Application Publication No. 2009/030202, International Publication No. 2004/080975, International Publication No. 2004/063159, International Publication No. 2005/085387, International Publication No. Public Publication No. 2006/067931, International Publication No. 2007/086552, International Publication No. 2008/114690, International Publication No. 2009/066942, International Publication No. 2009/066779, International Publication No. 2009/054253, International Publication No. 2011/086935, International Publication No. 2010/150593, International Publication No. 2010/047707, European Patent No. 2311826, Japanese Unexamined Patent Publication No. 2010-251675, Japanese Unexamined Patent Publication No. 2009-209133, Japanese Unexamined Patent Publication No. 2009-124114. issue 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.

More preferable known electron transport materials in the present invention include aromatic heterocyclic compounds containing at least one nitrogen atom and compounds containing a phosphorus atom. For example, pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, triazine derivatives, dibenzofurans. Derivatives, dibenzothiophene derivatives, azadibenzofuran derivatives, azadibenzothiophene derivatives, carbazole derivatives, azacarbazole derivatives, benzimidazole derivatives, arylphosphine oxide derivatives, and the like.
An electron transport material may be used independently and may use multiple types together.

《Hole blocking layer》
The hole blocking layer is a layer having a function of an electron transport layer in a broad sense, and is preferably made of a material having a function of transporting electrons while having a small ability to transport holes, and transporting electrons while transporting holes. The probability of recombination of electrons and holes can be improved by blocking.
Moreover, the structure of the electron carrying layer mentioned above can be used as a hole-blocking layer concerning this invention as needed.
The hole blocking layer provided in the organic EL device of the present invention is preferably provided adjacent to the cathode side of the light emitting layer.
The layer thickness of the hole blocking layer according to the present invention is preferably in the range of 3 to 100 nm, more preferably in the range of 5 to 30 nm.
As the material used for the hole blocking layer, the material used for the above-described electron transport layer is preferably used, and the material used as the above-described host compound is also preferably used for the hole blocking layer.

《Electron injection layer》
The electron injection layer (also referred to as “cathode buffer layer”) according to the present invention is a layer provided between the cathode and the light emitting layer in order to lower the driving voltage and improve the light emission luminance. It is described in detail in Chapter 2 “Electrode Materials” (pages 123 to 166) of the second edition of “The Forefront of Industrialization (issued by NTT Corporation on November 30, 1998)”.
In the present invention, the electron injection layer may be provided as necessary, 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 depending on the material. Moreover, the nonuniform layer (film | membrane) in which a constituent material exists intermittently may be sufficient.

Details of the electron injection layer are also described in JP-A-6-325871, JP-A-9-17574, JP-A-10-74586, and the like. Specific examples of materials preferably used for the electron injection layer are as follows. , Metals typified by strontium and aluminum, alkali metal compounds typified by lithium fluoride, sodium fluoride, potassium fluoride, etc., alkaline earth metal compounds typified by magnesium fluoride, calcium fluoride, etc., oxidation Examples thereof include metal oxides typified by aluminum, metal complexes typified by 8-hydroxyquinolinate lithium (Liq), and the like. Further, the above-described electron transport material can also be used.
Moreover, the material used for said electron injection layer may be used independently, and may use multiple types together.

《Hole transport layer》
In the present invention, the hole transport layer is 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 according to the present invention is not particularly limited, but is usually in the range of 5 nm to 5 μm, more preferably 2 to 500 nm, and further preferably 5 to 200 nm.
As a material used for the hole transport layer (hereinafter referred to as a hole transport material), any material that has either a hole injection property or a transport property or an electron barrier property may be used. Any one can be selected and used.
For example, porphyrin derivatives, phthalocyanine derivatives, oxazole derivatives, oxadiazole derivatives, triazole derivatives, imidazole derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, hydrazone derivatives, stilbene derivatives, polyarylalkane derivatives, triarylamine derivatives, carbazole derivatives , Indolocarbazole derivatives, isoindole derivatives, acene derivatives such as anthracene and naphthalene, fluorene derivatives, fluorenone derivatives, and polyvinyl carbazole, polymer materials or oligomers with aromatic amines introduced into the main chain or side chain, polysilane, conductive And polymer (for example, PEDOT / PSS, aniline copolymer, polyaniline, polythiophene, etc.).

Triarylamine derivatives include benzidine type typified by α-NPD (4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl), starburst type typified by MTDATA, Examples include compounds having fluorene or anthracene in the triarylamine-linked core.
In addition, hexaazatriphenylene derivatives such as those described in JP-T-2003-519432 and JP-A-2006-135145 can also be used as hole transport materials.
Furthermore, 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, JP-A-2001-102175, J. Pat. Appl. Phys. 95, 5773 (2004), and the like.

JP-A-11-251067, J. Org. Huang et. al. It is also possible to use so-called p-type hole transport materials and inorganic compounds such as p-type-Si and p-type-SiC, as described in the literature (Applied Physics Letters 80 (2002), p. 139). Further, ortho-metalated organometallic complexes having Ir or Pt as the central metal represented by Ir (ppy) 3 are also preferably used.
Although the above-mentioned materials can be used as the hole transport material, a triarylamine derivative, a carbazole derivative, an indolocarbazole derivative, an azatriphenylene derivative, an organometallic complex, or an aromatic amine is introduced into the main chain or side chain. The polymer materials or oligomers used are preferably used.

Specific examples of known preferred hole transport materials used in the organic EL device of the present invention include the compounds described in the following documents in addition to the documents listed above, but the present invention is not limited thereto. Not.
For example, Appl. Phys. Lett. 69, 2160 (1996), J. MoI. Lumin. 72-74,985 (1997), Appl. Phys. Lett. 78, 673 (2001), Appl. Phys. Lett. 90, 183503 (2007), Appl. Phys. Lett. 90, 183503 (2007), Appl. Phys. Lett. 51, 913 (1987), Synth. Met. 87, 171 (1997), Synth. Met. 91, 209 (1997), Synth. Met. 111, 421 (2000), SID Symposium Digest, 37, 923 (2006), J. Am. Mater. Chem. 3,319 (1993), Adv. Mater. 6, 677 (1994), Chem. Mater. 15, 3148 (2003), U.S. Patent Application Publication No. 2003/0162053, U.S. Patent Application Publication No. 2002/0158242, U.S. Patent Application Publication No. 2006/0240279, U.S. Patent Application Publication No. 2008/2008. No. 0220265, US Pat. No. 5,061,569, WO 2007/002683, WO 2009/018009, EP 650955, US Patent Application Publication No. 2008/0124572, US Patent Application Publication No. 2007/0278938, U.S. Patent Application Publication No. 2008/0106190, U.S. Patent Application Publication No. 2008/0018221, International Publication No. 2012/115034, Special Table No. 2003-519432, Special Publication No. Open 2006-135 45 No. is US Patent Application No. 13/585981 Patent like.
The hole transport material may be used alone or in combination of two or more.

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

《Hole injection layer》
The hole injection layer (also referred to as “anode buffer layer”) according to the present invention is a layer provided between the anode and the light emitting layer for the purpose of lowering the driving voltage and improving the light emission luminance. It is described in detail in Volume 2, Chapter 2, “Electrode Materials” (pages 123 to 166) of “The Forefront of Industrialization (issued by NTT Corporation on November 30, 1998)”.
In the present invention, the hole injection layer may be provided as necessary, 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 described in JP-A-9-45479, JP-A-9-260062, JP-A-8-288069, etc. Examples of materials used for the hole injection layer include: Examples thereof include materials used for the above-described hole transport layer.
Among them, phthalocyanine derivatives typified by copper phthalocyanine, hexaazatriphenylene derivatives, metal oxides typified by vanadium oxide, amorphous carbon as described in JP-T-2003-519432 and JP-A-2006-135145, etc. Preferred are conductive polymers such as polyaniline (emeraldine) and polythiophene, orthometalated complexes represented by tris (2-phenylpyridine) iridium complex, and triarylamine derivatives.
The materials used for the aforementioned hole injection layer may be used alone or in combination of two or more.

"Additive"
The organic layer in the present invention described above may further contain other additives.
Examples of the additive include halogen elements such as bromine, iodine and chlorine, halogenated compounds, alkali metals such as Pd, Ca and Na, alkaline earth metals, transition metal compounds, complexes, and salts.
The content of the additive can be arbitrarily determined, but is preferably 1000 ppm or less, more preferably 500 ppm or less, and further preferably 50 ppm or less with respect to the total mass% of the contained layer. .
However, it is not within this range depending on the purpose of improving the transportability of electrons and holes or the purpose of favoring the exciton energy transfer.

<Method for 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, intermediate 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 a conventionally known method such as a vacuum deposition method or a wet method (also referred to as a wet process) can be used.
Examples of the wet method include spin coating method, casting method, ink jet method, printing method, die coating method, blade coating method, roll coating method, spray coating method, curtain coating method, and LB method (Langmuir-Blodgett method). From the viewpoint of obtaining a homogeneous thin film easily and high productivity, a method with high roll-to-roll method suitability such as a die coating method, a roll coating method, an ink jet method and a spray coating method is preferable.

Examples of the liquid medium for dissolving or dispersing the organic EL material used in the present invention include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene, xylene, Aromatic hydrocarbons such as mesitylene and cyclohexylbenzene, aliphatic hydrocarbons such as cyclohexane, decalin, and dodecane, and organic solvents such as DMF and DMSO can be used.
Moreover, as a dispersion method, it can disperse | distribute by dispersion methods, such as an ultrasonic wave, high shear force dispersion | distribution, and media dispersion | distribution.
Further, different film forming methods may be applied for each layer. When a vapor deposition method is employed for film formation, the vapor deposition conditions vary depending on the type of compound used, but generally a boat heating temperature of 50 to 450 ° C., a degree of vacuum of 10 ⁻⁶ to 10 ⁻² Pa, and a vapor deposition rate of 0.01 to It is desirable to select appropriately within the range of 50 nm / second, substrate temperature −50 to 300 ° C., layer (film) thickness 0.1 nm to 5 μm, preferably 5 to 200 nm.
The organic layer according to the present invention is preferably formed from the hole injection layer to the cathode consistently by a single evacuation, but it may be taken out halfway and subjected to different film formation methods. In that case, it is preferable to perform the work in a dry inert gas atmosphere.

"anode"
As the anode in the organic EL element, a material having a work function (4 eV or more, preferably 4.5 eV or more) of a metal, an alloy, an electrically conductive compound, or a mixture thereof is preferably used. Specific examples of such electrode substances include metals such as Au, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO. Alternatively, an amorphous material such as IDIXO (In ₂ O ₃ —ZnO) capable of forming a transparent conductive film may be used.
The anode may be formed by depositing a thin film of these electrode materials by vapor deposition or sputtering, and a pattern having a desired shape may be formed by photolithography, or when pattern accuracy is not so high (about 100 μm or more) A pattern may be formed through a mask having a desired shape at the time of vapor deposition or sputtering of the electrode material.
Or when using the substance which can be apply | coated like an organic electroconductivity compound, wet film-forming methods, such as a printing system and a coating system, can also be used. When light emission is extracted from the anode, it is desirable that the transmittance be greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less.
Although the film thickness of the anode depends on the material, it is usually selected within the range of 10 nm to 1 μm, preferably 10 to 200 nm.

"cathode"
As the cathode, a material having a work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and 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 ) Mixtures, indium, lithium / aluminum mixtures, aluminum, rare earth metals and the like. Among these, from the point of durability against electron injection and oxidation, etc., a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function than this, for example, a magnesium / silver mixture, Magnesium / aluminum mixtures, magnesium / indium mixtures, aluminum / aluminum oxide (Al ₂ O ₃ ) mixtures, lithium / aluminum mixtures, aluminum and the like are preferred.

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 as 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, if either one of the anode or the cathode of the organic EL element is transparent or translucent, the emission luminance is advantageously improved.
In addition, a transparent or translucent cathode can be produced by producing a conductive transparent material mentioned in the description of the anode on the cathode after producing the above metal with a thickness of 1 to 20 nm. By applying the above, it is possible to manufacture a device in which both the anode and the cathode are transparent.

[Support substrate]
The support substrate (hereinafter also referred to as a substrate or a substrate) that can be used in the organic EL device of the present invention is not particularly limited in the type of glass, plastic and the like, and is transparent or opaque. May be. When extracting light 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 giving 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, cellulose acetate propionate ( CAP), cellulose esters such as cellulose acetate phthalate, cellulose nitrate or derivatives thereof, polyvinylidene chloride, polyvinyl alcohol, polyethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide , Polyethersulfone (PES), polyphenylene sulfide, polysulfones Cycloolefin resins such as polyetherimide, polyetherketoneimide, polyamide, fluororesin, nylon, polymethylmethacrylate, acrylic or polyarylate, Arton (trade name, manufactured by JSR) or Appel (trade name, manufactured by Mitsui Chemicals) Can be mentioned.

The surface of the resin film may be formed with an inorganic film, an organic film, or a hybrid film of both, and the water vapor permeability (25 ± 0.5 ° C.) measured by a method according to JIS K 7129-1992. , Relative humidity (90 ± 2)% RH) is preferably 0.01 g / m ² · 24 h or less, and further, oxygen permeability measured by a method according to JIS K 7126-1987. However, it is preferably a high-barrier film having 1 × 10 ⁻³ ml / m ² · 24 h · atm or less and a water vapor permeability of 1 × 10 ⁻⁵ g / m ² · 24 h or less.

As a material for forming the barrier film, any material may be used as long as it has a function of suppressing intrusion of elements that cause deterioration of elements such as moisture and oxygen. For example, silicon oxide, silicon dioxide, silicon nitride, or 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 organic material layers. Although there is no restriction | limiting in particular about the lamination | stacking order of an inorganic layer and an organic layer, It is preferable to laminate | stack both alternately several times.
The method for forming the barrier film is not particularly limited. For example, vacuum deposition, sputtering, reactive sputtering, molecular beam epitaxy, cluster ion beam, ion plating, plasma polymerization, atmospheric pressure plasma polymerization A plasma CVD method, a laser CVD method, a thermal CVD method, a coating method, or the like can be used, but an atmospheric pressure plasma polymerization method as described in JP-A-2004-68143 is particularly preferable.

Examples of the opaque support substrate include metal plates such as aluminum and stainless steel, films, opaque resin substrates, and ceramic substrates.
The external extraction quantum efficiency at room temperature (25 ° C.) of light emission of the organic EL device of the present invention is preferably 1% or more, and more preferably 5% or more.
Here, external extraction quantum efficiency (%) = number of photons emitted to the outside of the organic EL element / number of electrons flowed to the organic EL element × 100.
In addition, a hue improvement filter such as a color filter may be used in combination, or a color conversion filter that converts the emission color from the organic EL element into multiple colors using a phosphor may be used in combination.

[Sealing]
Examples of the sealing means used for sealing the organic EL element of the present invention include a method of bonding a sealing member, an electrode, and a support substrate with an adhesive. As a sealing member, it should just be arrange | positioned so that the display area | region of an organic EL element may be covered, and it may be concave plate shape or flat plate shape. Moreover, transparency and electrical insulation are not particularly limited.
Specific examples include a glass plate, a polymer plate / film, and a metal plate / film. Examples of the glass plate include soda-lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of the polymer plate include polycarbonate, acrylic, polyethylene terephthalate, polyether sulfide, and polysulfone. Examples of the metal plate include those made of one or more metals or alloys selected from the group consisting of stainless steel, iron, copper, aluminum, magnesium, nickel, zinc, chromium, titanium, molybdenum, silicon, germanium, and tantalum.

In the present invention, a polymer film and a metal film can be preferably used because the organic EL element can be thinned. Furthermore, the polymer film has an oxygen permeability measured by a method according to JIS K 7126-1987 of 1 × 10 ⁻³ ml / m ² · 24 h or less, and measured by a method according to JIS K 7129-1992. The water vapor permeability (25 ± 0.5 ° C., relative humidity 90 ± 2%) is preferably 1 × 10 ⁻³ g / m ² · 24 h or less.
For processing the sealing member into a concave shape, sandblasting, chemical etching, or the like is used.

Specific examples of the adhesive include photocuring and thermosetting adhesives having reactive vinyl groups of acrylic acid oligomers and methacrylic acid oligomers, and moisture curing adhesives such as 2-cyanoacrylates. be able to. Moreover, heat | fever and chemical curing types (two-component mixing), such as an epoxy type, can be mentioned. Moreover, hot-melt type polyamide, polyester, and polyolefin can be mentioned. Moreover, a cationic curing type ultraviolet curing epoxy resin adhesive can be mentioned.
In addition, since an organic EL element may deteriorate by heat processing, what can be adhesive-hardened from room temperature to 80 degreeC is preferable. A desiccant may be dispersed in the adhesive. Application | coating of the adhesive agent to a sealing part may use commercially available dispenser, and may print like screen printing.

In addition, it is also preferable that the electrode and the organic layer are coated on the outside of the electrode facing the support substrate with the organic layer interposed therebetween, and an inorganic or organic layer is formed in contact with the support substrate to form a sealing film. . In this case, the material for forming the film may be any material that has a function of suppressing intrusion of elements that cause deterioration of elements such as moisture and oxygen. For example, silicon oxide, silicon dioxide, silicon nitride, or the like may be used. it can.
Further, in order to improve the brittleness of the film, it is preferable to have a laminated structure of these inorganic layers and layers made of organic materials. There are no particular limitations on the method of forming these films. For example, vacuum deposition, sputtering, reactive sputtering, molecular beam epitaxy, cluster ion beam, ion plating, plasma polymerization, atmospheric pressure plasma A combination method, a plasma CVD method, a laser CVD method, a thermal CVD method, a coating method, or the like can be used.

In the gap between the sealing member and the display area of the organic EL element, an inert gas such as nitrogen or argon, or an inert liquid such as fluorinated hydrocarbon or silicon oil can be injected in the gas phase and liquid phase. preferable. A vacuum can also be used. Moreover, a hygroscopic compound can also be enclosed inside.
Examples of the hygroscopic compound include metal oxides (for example, sodium oxide, potassium oxide, calcium oxide, barium oxide, magnesium oxide, aluminum oxide) and sulfates (for example, sodium sulfate, calcium sulfate, magnesium sulfate, cobalt sulfate). Etc.), metal halides (eg calcium chloride, magnesium chloride, cesium fluoride, tantalum fluoride, cerium bromide, magnesium bromide, barium iodide, magnesium iodide etc.), perchloric acids (eg perchloric acid) Barium, magnesium perchlorate, and the like), and anhydrous salts are preferably used in sulfates, metal halides, and perchloric acids.

[Protective film, protective plate]
In order to increase the mechanical strength of the element, a protective film or a protective plate may be provided outside the sealing film or the sealing film on the side facing the support substrate with the organic layer interposed therebetween. In particular, when sealing is performed by the sealing film, the mechanical strength is not necessarily high, and thus it is preferable to provide such a protective film and a protective plate. As a material that can be used for this, the same glass plate, polymer plate / film, metal plate / film, etc. used for the sealing can be used, but the polymer film is light and thin. Is preferably used.

[Light extraction improvement technology]
An organic EL element emits light inside a layer having a refractive index higher than that of air (within a refractive index of about 1.6 to 2.1), and is about 15% to 20% of light generated in the light emitting layer. It is generally said that it can only be taken out. This is because light incident on the interface (interface between the transparent substrate and air) at an angle θ greater than the critical angle causes total reflection and cannot be taken out of the device, or between the transparent electrode or light emitting layer and the transparent substrate. This is because light is totally reflected between the light and the light is guided through the transparent electrode or the light emitting layer, and as a result, the light escapes in the direction of the side surface of the device.

As a technique for improving the light extraction efficiency, for example, a method of forming irregularities on the surface of the transparent substrate to prevent total reflection at the transparent substrate and the air interface (for example, US Pat. No. 4,774,435), A method for improving efficiency by providing light condensing property (for example, Japanese Patent Laid-Open No. 63-134795), a method for forming a reflective surface on the side surface of an element (for example, Japanese Patent Laid-Open No. 1-220394), a substrate A method of forming an antireflection film by introducing a flat layer having an intermediate refractive index between the substrate and the light emitter (for example, Japanese Patent Laid-Open No. 62-172691), lower refractive index than the substrate between the substrate and the light emitter A method of introducing a flat layer having a refractive index (for example, Japanese Patent Application Laid-Open No. 2001-202827), a method of forming a diffraction grating between any one of the substrate, the transparent electrode layer, and the light emitting layer (including between the substrate and the outside) ( JP 1 No. -283751 Publication), and the like.

In the present invention, these methods can be used in combination with the organic EL device of the present invention. However, a method of introducing a flat layer having a lower refractive index than the substrate between the substrate and the light emitter, or a substrate, transparent A method of forming a diffraction grating between any layers of the electrode layer and the light emitting layer (including between the substrate and the outside) can be suitably used.
In the present invention, by combining these means, it is possible to obtain an element having higher luminance or durability.

When a low refractive index medium is formed between the transparent electrode and the transparent substrate with a thickness longer than the wavelength of light, the light extracted from the transparent electrode has a higher extraction efficiency to the outside as the refractive index of the medium is lower. Become.
Examples of the low refractive index layer include aerogel, porous silica, magnesium fluoride, and a fluorine-based polymer. Since the refractive index of the transparent substrate is generally in the range of about 1.5 to 1.7, the low refractive index layer preferably has a refractive index of about 1.5 or less. Furthermore, it is preferable that it is 1.35 or less.
The thickness of the low refractive index medium is preferably at least twice the wavelength in the medium. This is because the effect of the low refractive index layer is diminished when the thickness of the low refractive index medium is about the wavelength of light and the electromagnetic wave exuded by evanescent enters the substrate.

The method of introducing a diffraction grating into an interface that causes total reflection or in any medium has a feature that the effect of improving the light extraction efficiency is high. This method uses the property that the diffraction grating can change the direction of light to a specific direction different from refraction by so-called Bragg diffraction, such as first-order diffraction or second-order diffraction. The light that cannot be emitted due to total internal reflection between layers is diffracted by introducing a diffraction grating into any layer or medium (in the transparent substrate or transparent electrode). , Trying to extract light out.

The introduced diffraction grating desirably has a two-dimensional periodic refractive index. This is because light emitted from the light-emitting layer is randomly generated in all directions, so in a general one-dimensional diffraction grating having a periodic refractive index distribution only in a certain direction, only light traveling in a specific direction is diffracted. The light extraction efficiency does not increase so much.
However, by making the refractive index distribution a two-dimensional distribution, light traveling in all directions is diffracted, and light extraction efficiency is increased.
The position where the diffraction grating is introduced may be in any of the layers or in the medium (in the transparent substrate or the transparent electrode), but is preferably in the vicinity of the organic light emitting layer where light is generated. At this time, the period of the diffraction grating is preferably in the range of about 1/2 to 3 times the wavelength of light in the medium. The arrangement of the diffraction gratings is preferably two-dimensionally repeated, such as a square lattice, a triangular lattice, or a honeycomb lattice.

[Condensing sheet]
The organic EL device of the present invention is front-facing to a specific direction, for example, the light emitting surface of the device by combining a so-called condensing sheet, for example, by providing a structure on the microlens array on the light extraction side of the support substrate (substrate). By condensing in the direction, the luminance in a specific direction can be increased.
As an example of the microlens array, quadrangular pyramids having a side of 30 μm and an apex angle of 90 degrees are arranged two-dimensionally on the light extraction side of the substrate. One side is preferably within a range of 10 to 100 μm. If it becomes smaller than this, the effect of diffraction will generate | occur | produce and color, and if too large, thickness will become thick and is not preferable.
As the condensing sheet, for example, a sheet that is put into practical use in an LED backlight of a liquid crystal display device can be used. As such a sheet, for example, a brightness enhancement film (BEF) manufactured by Sumitomo 3M Limited can be used. As the shape of the prism sheet, for example, the base material may be formed by forming a △ -shaped stripe having a vertex angle of 90 degrees and a pitch of 50 μm, or the vertex angle is rounded and the pitch is changed randomly. Other shapes may be used.
Moreover, in order to control the light emission angle from an organic EL element, you may use a light-diffusion plate and a film together with a condensing sheet. For example, a diffusion film (light-up) manufactured by Kimoto Co., Ltd. can be used.

[Usage]
The organic EL element of the present invention can be used as an electronic device such as a display device, a display, and various light emitting devices.
Examples of light emitting devices include lighting devices (home lighting, interior lighting), clocks and backlights for liquid crystals, billboard advertisements, traffic lights, light sources of optical storage media, light sources of electrophotographic copying machines, light sources of optical communication processors, light Although the light source of a sensor etc. are mentioned, It is not limited to this, Especially, it can use effectively for the use as a backlight of a liquid crystal display device, and a light source for illumination.
In the organic EL element of the present invention, patterning may be performed by a metal mask, an ink jet printing method, or the like as needed during film formation. In the case of patterning, only the electrode may be patterned, the electrode and the light emitting layer may be patterned, or the entire layer of the element may be patterned. In the fabrication of the element, a conventionally known method is used. Can do.

<Display device>
The display device including the organic EL element of the present invention may be single color or multicolor, but here, the multicolor display device will be described.

In the case of a multicolor display device, a shadow mask is provided only at the time of forming a light emitting layer, and a film can be formed on one surface by vapor deposition, casting, spin coating, ink jet, printing, or the like.
In the case of patterning only the light emitting layer, there is no limitation on the method, but a vapor deposition method, an inkjet method, a spin coating method, and a printing method are preferable.

The configuration of the organic EL element included in the display device is selected from the above-described configuration examples of the organic EL element as necessary.

Moreover, the manufacturing method of an organic EL element is as having shown in the one aspect | mode of manufacture of the organic EL element of said this invention.

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 when a voltage is applied with the opposite polarity, no current flows and no light emission occurs. Further, when an AC voltage is applied, light is emitted only when the anode is in the + state and the cathode is in the-state. The alternating current waveform to be applied may be arbitrary.

The multicolor display device can be used as a display device, a display, or various light emission sources. In a display device or display, full-color display is possible by using three types of organic EL elements of blue, red, and green light emission.

Examples of the display device or display include a television, a personal computer, a mobile device, an AV device, a character broadcast display, and an information display in a car. In particular, it may be used as a display device for reproducing still images and moving images, and the driving method when used as a display device for reproducing moving images may be either a simple matrix (passive matrix) method or an active matrix method.

Light-emitting devices include household lighting, interior lighting, clock and liquid crystal backlights, billboard advertisements, traffic lights, optical storage media light sources, electrophotographic copying machine light sources, optical communication processor light sources, optical sensor light sources, etc. However, the present invention is not limited to these.

Hereinafter, an example of a display device having the organic EL element of the present invention will be described with reference to the drawings.
FIG. 5 is a schematic view showing an example of a display device composed of organic EL elements. It is a schematic diagram of a display such as a mobile phone that displays image information by light emission of an organic EL element.

The display 1 includes a display unit A having a plurality of pixels, a control unit B that performs image scanning of the display unit A based on image information, a wiring unit C that electrically connects the display unit A and the control unit B, and the like.
The control unit B is electrically connected to the display unit A via the wiring unit C, and sends a scanning signal and an image data signal to each of a plurality of pixels based on image information from the outside. Sequentially emit light according to the image data signal, scan the image, and display the image information on the display unit A.

FIG. 6 is a schematic diagram of a display device using an active matrix method.
The display unit A includes a wiring unit C including a plurality of scanning lines 5 and data lines 6, a plurality of pixels 3 and the like on a substrate. The main members of the display unit A will be described below.
FIG. 6 shows a case where the light emitted from the pixel 3 is extracted in the direction of the white arrow (downward).

The scanning line 5 and the plurality of data lines 6 in the wiring portion are each made of a conductive material, and the scanning lines 5 and the data lines 6 are orthogonal to each other in a grid pattern and are connected to the pixels 3 at the orthogonal positions (details are illustrated Not)
When a scanning signal is applied from the scanning line 5, the pixel 3 receives an image data signal from the data line 6 and emits light according to the received image data.
Full-color display is possible by appropriately arranging pixels in the red region, the green region, and the blue region on the same substrate.

Next, the light emission process of the pixel will be described. FIG. 7 is a schematic diagram showing a pixel circuit.
The pixel includes an organic EL element 10, a switching transistor 11, a driving transistor 12, a capacitor 13, and the like. A full color display can be performed by using red, green, and blue light emitting organic EL elements as the organic EL elements 10 in a plurality of pixels, and juxtaposing them on the same substrate.

7, an image data signal is applied from the control unit B to the drain of the switching transistor 11 via the data line 6. When a scanning signal is applied from the control unit B to the gate of the switching transistor 11 via the scanning line 5, the driving of the switching transistor 11 is turned on, and the image data signal applied to the drain is supplied to the capacitor 13 and the driving transistor 12. Is transmitted to the gate.

By transmitting the image data signal, the capacitor 13 is charged according to the potential of the image data signal, and the drive transistor 12 is turned on. The drive transistor 12 has a drain connected to the power supply line 7 and a source connected to the electrode of the organic EL element 10, and the power supply line 7 connects to the organic EL element 10 according to the potential of the image data signal applied to the gate. Current is supplied.

When the scanning signal is moved to the next scanning line 5 by the sequential scanning of the control unit B, the driving of the switching transistor 11 is turned off. However, since the capacitor 13 holds the charged potential of the image data signal even if the driving of the switching transistor 11 is turned off, the driving of the driving transistor 12 is kept on and the next scanning signal is applied. Until then, the light emission of the organic EL element 10 continues. When the scanning signal is next applied by sequential scanning, the driving transistor 12 is driven according to the potential of the next image data signal synchronized with the scanning signal, and the organic EL element 10 emits light.
That is, the organic EL element 10 emits light by the switching transistor 11 and the drive transistor 12 that are active elements for the organic EL element 10 of each of the plurality of pixels, and the light emission of the organic EL element 10 of each of the plurality of pixels 3. It is carried out. Such a light emitting method is called an active matrix method.

Here, the light emission of the organic EL element 10 may be light emission of a plurality of gradations by a multi-value image data signal having a plurality of gradation potentials, or by turning on / off a predetermined light emission amount by a binary image data signal. Good. The potential of the capacitor 13 may be held continuously until the next scanning signal is applied, or may be discharged immediately before the next scanning signal is applied.
In the present invention, not only the active matrix method described above, but also a passive matrix light emission drive in which the organic EL element emits light according to the data signal only when the scanning signal is scanned.

FIG. 8 is a schematic view of a passive matrix display device. In FIG. 8, a plurality of scanning lines 5 and a plurality of image data lines 6 are provided in a lattice shape so as to face each other with the pixel 3 interposed therebetween.
When the scanning signal of the scanning line 5 is applied by sequential scanning, the pixels 3 connected to the applied scanning line 5 emit light according to the image data signal.
In the passive matrix system, the pixel 3 has no active element, and the manufacturing cost can be reduced.
By using the organic EL element of the present invention, a display device with improved luminous efficiency was obtained.

<Lighting device>
The organic EL element of the present invention can also be used for a lighting device.
The organic EL element of the present invention may be used as an organic EL element having a resonator structure. Examples of the purpose of use of the organic EL element having such a resonator structure include a light source of an optical storage medium, a light source of an electrophotographic copying machine, a light source of an optical communication processing machine, and a light source of an optical sensor. It is not limited. Moreover, you may use for the said use by making a laser oscillation.
Further, the organic EL element of the present invention may be used as a kind of lamp for illumination or exposure light source, a projection device for projecting an image, or a type for directly viewing a still image or a moving image. It may be used as a display device (display).
The driving method when used as a display device for reproducing a moving image may be either a passive matrix method or an active matrix method. Alternatively, it is possible to produce a full-color display device by using two or more organic EL elements of the present invention having different emission colors.

Further, the π-conjugated compound used in the present invention can be applied to a lighting device including an organic EL element that emits substantially white light. For example, when a plurality of light emitting materials are used, white light emission can be obtained by simultaneously emitting a plurality of light emission colors and mixing the colors. The combination of a plurality of emission colors may include three emission maximum wavelengths of three primary colors of red, green, and blue, or two of the complementary colors such as blue and yellow, blue green and orange, etc. The thing containing the light emission maximum wavelength may be used.

In addition, the organic EL device forming method of the present invention may be simply arranged by providing a mask only when forming a light emitting layer, a hole transport layer, an electron transport layer, or the like, and separately coating with the mask. Since the other layers are common, patterning of a mask or the like is unnecessary, and for example, an electrode film can be formed on one surface by a vapor deposition method, a cast method, a spin coating method, an ink jet method, a printing method, or the like, and productivity is improved.
According to this method, unlike a white organic EL device in which light emitting elements of a plurality of colors are arranged in parallel in an array, the elements themselves emit white light.

[One Embodiment of Lighting Device of the Present Invention]
One aspect of the lighting device of the present invention that includes the organic EL element of the present invention will be described.
The non-light emitting surface of the organic EL device of the present invention is covered with a glass case, a 300 μm thick glass substrate is used as a sealing substrate, and an epoxy photocurable adhesive (LUX The track LC0629B) is applied, and this is overlaid on the cathode and brought into close contact with the transparent support substrate, irradiated with UV light from the glass substrate side, cured, sealed, and illuminated as shown in FIG. 9 and FIG. A device can be formed.
FIG. 9 shows a schematic diagram of a lighting device, and the organic EL element (organic EL element 101 in the lighting device) of the present invention is covered with a glass cover 102 (note that the sealing operation with the glass cover is performed by lighting. This was carried out in a glove box under a nitrogen atmosphere (in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or higher) without bringing the organic EL element 101 in the apparatus into contact with the air).
FIG. 10 is a cross-sectional view of the lighting device, 105 is a cathode, 106 is an organic 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.
By using the organic EL element of the present invention, a lighting device with improved luminous efficiency can be obtained.

<Light-Emitting Thin Film> The light-emitting thin film according to the present invention contains the above-described π-conjugated compound according to the present invention, and can be produced in the same manner as the method for forming the organic layer.
The light-emitting thin film of the present invention can be produced in the same manner as the organic layer forming method.

The method for forming the light-emitting thin film of the present invention is not particularly limited, and a conventionally known method such as a vacuum deposition method or a wet method (also referred to as a wet process) can be used.
Examples of the wet method include spin coating method, casting method, ink jet method, printing method, die coating method, blade coating method, roll coating method, spray coating method, curtain coating method, and LB method (Langmuir-Blodgett method). From the viewpoint of obtaining a homogeneous thin film easily and high productivity, a method with high roll-to-roll method suitability such as a die coating method, a roll coating method, an ink jet method and a spray coating method is preferable.

Examples of the liquid medium for dissolving or dispersing the light emitting material used in the present invention include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene, xylene, and mesitylene. Aromatic hydrocarbons such as cyclohexylbenzene, aliphatic hydrocarbons such as cyclohexane, decalin, and dodecane, and organic solvents such as DMF and DMSO can be used.

Moreover, as a dispersion method, it can disperse | distribute by dispersion methods, such as an ultrasonic wave, high shear force dispersion | distribution, and media dispersion | distribution.
Further, different film forming methods may be applied for each layer. When a vapor deposition method is employed for film formation, the vapor deposition conditions vary depending on the type of compound used, but generally the boat heating temperature is in the range of 50 to 450 ° C., and the degree of vacuum is in the range of 10 ⁻⁶ to 10 ⁻² Pa. Of these, the deposition rate is within the range of 0.01 to 50 nm / second, the substrate temperature is within the range of −50 to 300 ° C., the layer thickness is within the range of 0.1 to 5 μm, and preferably within the range of 5 to 200 nm. desirable.
Further, when the spin coat method is adopted for film formation, it is preferable to perform the spin coater within a range of 100 to 1000 rpm and within a range of 10 to 120 seconds in a dry inert gas atmosphere.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto. In addition, although the display of "%" is used in an Example, unless otherwise indicated, "mass%" is represented.

1. Synthesis of π-conjugated compound of the present invention (Synthesis of Compound T-3)
In the same manner as described in Angew. Chem. Int. Ed. 2008, 47, 6338-6361., Compound T-3 was synthesized. Specifically, 2,8-dibromodibenzofuran and 9,9-dimethyl-9,10-dihydroacridine were refluxed in toluene in the presence of a palladium catalyst and a basic reagent. The obtained precipitate was collected to obtain compound T-3 represented by the following chemical formula.

(Synthesis of other compounds)
In the same manner as described above, the compounds represented by the following chemical formulas T-6, T-8, T-16, T-17, T-23, T-45, T-51, T-53, T-54, T-55, T-63, T-81, T-91, T-92, T-109, T-122, T-126, T-131, T-134, and Comparative compound 2 were synthesized.

Further, as Comparative Compound 1 and Comparative Compound 3, compounds represented by the following chemical formulas were prepared.

ΔE _ST , HOMO and LUMO, and the emission wavelength of the obtained compound were determined by the following method.

(Calculation of energy levels of ΔE _ST , HOMO and LUMO)
The energy levels of HOMO and LUMO were calculated from the structure optimization calculation using B3LYP as the functional and 6-31G (d) as the basis function. Further, using the optimized structure, the excited state calculation is performed by the time-dependent density functional method (Time-Dependent DFT) using B3LYP as the functional and 6-31G (d) as the basis function, and S ₁ , energy levels of T ₁ (respectively _{_{E (S 1), E (}} T 1)) of seeking _{_{ΔE ST = | E (S 1}} ) -E (T 1) | is calculated as.

2. Preparation of organic EL device [Example 1]
(Preparation of organic EL element 1-1)
An ITO (indium tin oxide) film having a thickness of 150 nm was formed on a 50 mm × 50 mm × 0.7 mm thick glass substrate, followed by patterning to form an ITO transparent electrode as an anode. The transparent substrate provided with the ITO transparent electrode was subjected to ultrasonic cleaning with isopropyl alcohol and dried with dry nitrogen gas, followed by UV ozone cleaning for 5 minutes. The obtained transparent substrate was fixed to a substrate holder of a commercially available vacuum deposition apparatus.

Each of the deposition crucibles in the vacuum deposition apparatus was filled with the constituent material of each layer in an amount optimal for device fabrication. As the evaporation crucible, a crucible made of a resistance heating material made of molybdenum or tungsten was used.

After reducing the vacuum inside the vacuum evaporation system to 1 × 10 ⁻⁴ Pa, energize the evaporation crucible containing HAT-CN (1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile). Then, HAT-CN was deposited on the ITO transparent electrode at a deposition rate of 0.1 nm / second to form a 10 nm thick hole injecting and transporting layer.

Next, α-NPD (4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) was deposited on the hole injection layer at a deposition rate of 0.1 nm / second, and the thickness was 40 nm. A hole transport layer was formed.

MCP (1,3-bis (N-carbazolyl) benzene) as the host material and Comparative Compound 1 as the light-emitting compound were deposited at a deposition rate of 0.1 nm / second so as to be 94% and 6% by volume, respectively. Co-evaporation was performed to form a light emitting layer having a thickness of 30 nm.

Thereafter, BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) was deposited at a deposition rate of 0.1 nm / second to form an electron transport layer having a thickness of 30 nm.

Further, lithium fluoride was vapor-deposited with a thickness of 0.5 nm, and then 100 nm of aluminum was further vapor-deposited to form a cathode.

The non-light-emitting surface side of the obtained element was covered with a can-shaped glass case in an atmosphere of high-purity nitrogen gas with a purity of 99.999% or more, and an electrode lead-out wiring was installed to produce an organic EL element 1-1. did.

(Preparation of organic EL elements 1-2 to 1-23)
Organic EL devices 1-2 to 1-23 were produced in the same manner as the organic EL device 1-1 except that the luminescent compound was changed as shown in Table 1.

(Evaluation)
The relative luminous efficiency (%) of the obtained organic EL element was measured by the following method.

Measurement of relative luminous efficiency The obtained organic EL device was allowed to emit light at room temperature (about 25 ° C.) and a constant current of ^2.5 mA / cm ² . Then, the light emission luminance of the organic EL element immediately after the start of light emission was measured using a spectral radiance meter CS-2000 (manufactured by Konica Minolta).
The obtained light emission luminance was applied to the following formula, and the relative light emission luminance with respect to the light emission luminance of the organic EL element 1-1 was determined.
Relative light emission luminance (%) = (light emission luminance of each organic EL element / light emission luminance of organic EL element 1-1) × 100

The obtained results are shown in Table 1.

The organic EL devices 1-4 to 1-23 containing the π-conjugated compound of the present invention as the light emitting compound have higher emission luminance than the organic EL devices 1-1, 1-2, and 1-3 containing the comparative compound. You can see that The π-conjugated compounds of the Examples for Delta] E _ST is 0.50 or less, tends to occur reverse intersystem crossing, it is presumed that the luminous efficiency has increased. Further, since these are in a range where the energy levels of HOMO and LUMO are relatively high, it is presumed that the carrier balance in the EL element is good and the light emission efficiency is increased.

[Example 2]
(Preparation of organic EL element 2-1)
An ITO layer of an ITO (indium tin oxide) substrate having a thickness of 100 nm formed on a 100 mm × 100 mm × 1.1 mm glass substrate (NA Techno Glass NA45) was patterned to form an ITO transparent electrode as an anode. Next, the transparent substrate provided with the ITO transparent electrode was subjected to ultrasonic cleaning with isopropyl alcohol and dried with dry nitrogen gas, and then UV ozone cleaning was performed for 5 minutes.

On this transparent substrate, a solution obtained by diluting poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT / PSS, Bayer, Baytron P Al 4083) to 70% with pure water at 3000 rpm for 30 seconds. After coating by the spin coat method under the above conditions, it was dried at 200 ° C. for 1 hour to form a hole injection layer having a thickness of 20 nm. The obtained transparent substrate was fixed to a substrate holder of a commercially available vacuum deposition apparatus.

In addition, each of the deposition crucibles in the vacuum deposition apparatus was filled with the optimum amount of the constituent material of each layer for device fabrication. The evaporation crucible used was made of a resistance heating material made of molybdenum or tungsten.

After reducing the vacuum inside the vacuum deposition apparatus to a vacuum degree of 1 × 10 ⁻⁴ Pa, α-NPD was deposited on the hole injection layer at a deposition rate of 0.1 nm / second to form a 40 nm thick hole transport layer.

Next, CDBP as the host material and 2,5,8,11-tetra-t-butylperylene as the light-emitting compound were deposited at a deposition rate of 0.1 nm / second so as to be 97% and 3% by volume, respectively. Co-evaporation was performed to form a light emitting layer having a thickness of 30 nm.

Thereafter, TPBi (1,3,5-tris (N-phenylbenzimidazol-2-yl) was deposited at a deposition rate of 0.1 nm / second to form an electron transport layer having a thickness of 30 nm.

Furthermore, after sodium fluoride was vapor-deposited with a thickness of 1 nm, 100 nm of aluminum was further vapor-deposited to form a cathode.

The non-light emitting surface side of the above element was covered with a can-shaped glass case in an atmosphere of high purity nitrogen gas having a purity of 99.999% or more, and an electrode lead-out wiring was installed to prepare an organic EL element 2-1.

(Preparation of organic EL element 2-2)
CDBP as the host material, 2,5,8,11-tetra-t-butylperylene as the luminescent compound, and comparative compound 1 as the assist dopant, each in a volume percentage of 82%, 3%, and 15% A light emitting layer was formed in the same manner as in the production of the organic EL element 2-1, except that co-evaporation was performed so that the organic EL element 2-2 was produced.

(Production of organic EL elements 2-3 to 2-12)
Organic EL devices 2-3 to 2-12 were produced in the same manner as the organic EL device 2-2 except that the assist dopant was changed as shown in Table 2.

In the same manner as described above, the light emission luminance of the organic EL element 2-1 was measured, and the relative light emission luminance of each organic EL element with respect to the light emission luminance of the organic EL element 2-1 was determined. The obtained measurement results are shown in Table 2.

It can be seen that the organic EL devices 2-5 to 2-12 containing the π-conjugated compound of the present invention as the assist dopant show higher emission luminance than the organic EL device 2-1 containing no assist dopant. Π conjugated compound of the present invention, Delta] E _ST is small. Therefore, triplet excitons are likely to be singlet excitons with reverse intersystem crossing (RISC). As a result, it became possible to cause the luminescent compound to emit light using the exciton energy, and it is assumed that high luminous efficiency was developed in the above examples. On the other hand, the comparative compound 2, is greater than 0.50 Delta] E _ST, reverse intersystem crossing hardly occurs, emission efficiency is presumed that was lower than that of Example. In Comparative Compounds 1 and 2, it is presumed that the luminous efficiency was slightly higher than that of the organic EL element 2-1, because the carrier transport property in the light emitting layer was slightly improved. On the other hand, it is surmised that in Comparative Compound 3, the LUMO level and the HOMO level are both low, so that the carrier balance is lost and the light emission efficiency is lower than that of the organic EL element 2-1.

[Example 3]
(Preparation of organic EL element 3-1)
An ITO (indium tin oxide) film having a thickness of 150 nm was formed on a 50 mm × 50 mm × 0.7 mm thick glass substrate, followed by patterning to form an ITO transparent electrode as an anode. The transparent substrate provided with the ITO transparent electrode was subjected to ultrasonic cleaning with isopropyl alcohol and dried with dry nitrogen gas, followed by UV ozone cleaning for 5 minutes. The obtained transparent substrate was fixed to a substrate holder of a commercially available vacuum deposition apparatus.

Each of the resistance heating boats for vapor deposition in the vacuum vapor deposition apparatus was filled with an optimum amount for each element of the constituent material of each layer. The resistance heating boat was made of molybdenum or tungsten.

After depressurizing the inside of the vacuum evaporation system to a vacuum degree of 1 × 10 ⁻⁴ Pa, HAT-CN (1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile) represented by the following formula was contained. A resistance heating boat was energized and heated, and deposited on the ITO transparent electrode at a deposition rate of 0.1 nm / second to form a 15 nm thick hole injection layer.

Next, α-NPD (4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) HT-1 was deposited at a deposition rate of 0.1 nm / second, and a hole transport with a thickness of 30 nm was performed. A layer was formed.

Subsequently, a resistance heating boat containing comparative compound 1 as a host material and GD-1 as a luminescent compound was energized and heated, and the hole transport layer was deposited at a deposition rate of 0.1 nm / second and 0.010 nm / second, respectively. Co-evaporated on top to form a 40 nm thick light emitting layer.

Next, HB-1 was deposited at a deposition rate of 0.1 nm / second to form a first electron transport layer having a thickness of 5 nm.

Further, ET-1 was deposited thereon at a deposition rate of 0.1 nm / second to form a second electron transport layer having a thickness of 45 nm.

Then, after vapor-depositing lithium fluoride to a thickness of 0.5 nm, aluminum 100 nm was vapor-deposited to form a cathode, and an organic EL element 3-1 was produced.

(Production of organic EL elements 3-2 to 3-12)
A light emitting layer was formed in the same manner as the organic EL element 3-1, except that the host material was changed as shown in Table 3, and organic EL elements 3-2 to 3-12 were produced.

In the same manner as described above, the light emission luminance of the organic EL element 3-1 was measured, and the relative light emission luminance of each organic EL element with respect to the light emission luminance of the organic EL element 3-1 was obtained. The obtained measurement results are shown in Table 3.

In the organic EL element 3-4 ~ 3-12 containing π-conjugated compounds of the present invention Delta] E _ST is less than 0.50eV as a host material, organic EL devices 31 and 32 includes a comparative compound, and 3 It can be seen that the emission luminance is higher than −3.

[Example 4]
(Preparation of vapor deposition film 4-1)
A quartz substrate having a size of 50 mm × 50 mm and a thickness of 0.7 mm is ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes. Fixed to.
A vapor deposition crucible in a vacuum vapor deposition apparatus was filled with π-conjugated compound T-55. The evaporation crucible used was made of a resistance heating material made of molybdenum.
After reducing the vacuum to 1 × 10 ⁻⁴ Pa, π-conjugated compound T-55 was deposited at a deposition rate of 0.1 nm / second to form a deposited film 4-1 having a layer thickness of 40 nm.

(Measurement of delayed fluorescence of deposited film 4-1)
Under a nitrogen atmosphere, the deposited film 4-1 was irradiated with excitation light of 355 nm, and fluorescence decay measurement was performed at the maximum emission wavelength.
FIG. 11 shows a graph showing the relationship between time and the number of photons for the deposited film 4-1.

As shown in FIG. 11, in the π covalent compound (T-55) of the present invention, two or more kinds of components having different fluorescence decay rates were confirmed, and delayed fluorescence emission was confirmed.

This application claims priority based on Japanese Patent Application No. 2015-095819 filed on May 8, 2015. The contents described in the application specification and the drawings are all incorporated herein.

According to the present invention, it is possible to provide a π-conjugated compound that can increase the light emission efficiency without increasing the light emission wavelength.

DESCRIPTION OF SYMBOLS 1 Display 3 Pixel 5 Scan line 6 Data line 7 Power supply line 10 Organic EL element 11 Switching transistor 12 Drive transistor 13 Capacitor 101 Organic EL element in a lighting device 102 Glass cover 105 Cathode 106 Organic layer 107 Glass substrate 108 with transparent electrode 108 Nitrogen gas 109 Water trapping agent A Display part B Control part C Wiring part

Claims

The absolute value of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is 0.50 eV or less,
A π-conjugated compound having a HOMO energy level of −5.5 eV or more and a LUMO energy level of −1.8 eV or more.
The π-conjugated compound according to claim 1, comprising an atom selected from the following atomic group A.
Atom group A: hydrogen atom, deuterium atom, fluorine atom, carbon atom forming only a single bond, carbon atom forming a double bond, nitrogen atom forming only a single bond, oxygen atom forming only a single bond, Sulfur atoms that form only single bonds, silicon atoms that form only single bonds
The π-conjugated compound according to claim 1, comprising a structure in which two or more of the same or different ring structures are selected from the following ring structure group X.
Ring structure group X: benzene ring, indene ring, naphthalene ring, azulene ring, fluorene ring, phenanthrene ring, anthracene ring, acenaphthylene ring, biphenylene ring, chrysene ring, naphthacene ring, pyrene ring, pentalene ring, asanthrylene ring, heptalene Ring, triphenylene ring, as-indacene ring, s-indacene ring, preaden ring, phenalene ring, fluoranthene ring, perylene ring, acephenanthrylene ring, biphenyl ring, terphenyl ring, tetraphenyl ring, carbazole ring, indolo Indole ring, 9,10-dihydroacridine ring, phenoxazine ring, phenothiazine ring, dibenzothiophene ring, benzofurylindole ring, benzothienoindole ring, indolocarbazole ring, benzofurylcarbazole ring, benzothienocarba Lumpur ring, benzothiophene thieno benzothiophene ring, benzocarbazole ring, dibenzothiophene carbazole ring, a dibenzofuran ring, benzo furyl benzofuran ring, dibenzosilole ring, 5,10-dihydrophenanthrene Naza cylindrical ring, 10,11-dihydro-dibenzo azepine ring
A delayed phosphor containing the π-conjugated compound according to claim 1.
A delayed phosphor containing the π-conjugated compound according to claim 2.
A light-emitting thin film containing the π-conjugated compound according to claim 1.
An anode, a cathode, and a light emitting layer provided between the anode and the cathode,
The organic electroluminescent element in which at least one layer of the light emitting layer contains the π-conjugated compound according to claim 1.
The organic light-emitting device according to claim 7, wherein the light-emitting layer includes the π-conjugated compound and at least one of a fluorescent material and a phosphorescent material.
The organic light-emitting device according to claim 7, wherein the light-emitting layer includes the π-conjugated compound, at least one of a fluorescent material and a phosphorescent material, and a host material.
A display device comprising the organic electroluminescence element according to claim 7.
A lighting device including the organic electroluminescence element according to claim 7.