JP2012099593A - Organic light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic blue color light-emitting element having a long continuous drive life, a high efficiency, and a high chromatic purity.SOLUTION: The organic light-emitting element operable to emit blue-color light comprises: an anode 2; a cathode 4; and an organic compound layer held between the anode and the cathode, and including at least a luminescent layer 3. The luminescent layer has a first host, a second host, and a guest. The second host is a compound represented by the general formula [1], or a compound resulting from a condensation between the compound represented by the general formula [1] and an aromatic ring selected from a group consisting of a benzene ring, a naphthalene ring, a phenalene ring, an anthracene ring, and a phenanthrene ring, and having seven benzene rings or less. The lowest triplet excitation energy of the second host is smaller than the lowest triplet excitation energy of the first host. In the luminescent layer, a material which is smallest in the lowest singlet excitation energy makes a luminescent material.

Description

  The present invention relates to an organic light emitting device.

  An organic light-emitting device is an electronic device in which a thin film containing a light-emitting organic compound is disposed between an anode and a cathode, and a voltage is applied between the anode and the cathode to inject holes and electrons. To drive. Here, holes and electrons injected from the anode and the cathode recombine in the thin film containing the luminescent organic compound to generate an excited state of the luminescent organic compound, and the excited state of the luminescent compound returns to the ground state. At the same time, the organic light emitting device emits light.

  Recent advances in organic light-emitting devices are remarkable, and their features are high brightness at low applied voltage, variety of emission wavelengths, high-speed response, thin and light-emitting devices. This suggests that the organic light emitting device has a wide range of uses.

  However, when considering application to a full-color display or the like, there is a problem that the light emission efficiency decreases with time, particularly when a blue light emitting element is continuously driven. In addition, the current devices are not sufficient in terms of color purity and luminous efficiency, and further performance improvement is required.

  Various proposals have been made regarding the suppression of the light emission efficiency of organic light emitting devices. For example, Patent Document 1 discloses an organic light-emitting device that includes two types of hosts and a guest (light-emitting dopant) in a light-emitting layer. Further, in the organic light emitting device of Patent Document 1, an organic compound capable of forming both a monomer state and an aggregate state as a first host component is disclosed. Furthermore, an organic compound capable of forming a continuous film substantially free of pinholes as the second host component is disclosed. In the organic light-emitting device disclosed in Patent Document 1, when the first host component is at a low concentration, the state where the materials do not interact with each other (monomer state) is dominant. On the other hand, as the first host component is increased in concentration, the state (aggregate state) formed by the interaction of two or more molecules increases. In connection with this, it is reported in patent document 1 that the suppression degree of luminous efficiency deterioration becomes large.

  Patent Document 2 suggests material deterioration via the excited state of the material in the light-emitting layer as a cause of light emission efficiency deterioration. In particular, material deterioration from a triplet excited state having a long excitation lifetime is suggested among the excited states. For the purpose of suppressing material deterioration from a triplet excited state, a device including a host and a stabilizer having a lowest triplet excitation energy level of less than 130 kJ / mol as a light emitting layer is disclosed. In general, the lower the triplet excitation energy, the faster the conversion from the triplet excited state to the ground state, and the shorter the excitation lifetime. Patent Document 2 suggests that the probability of occurrence of material deterioration can be lowered by this.

Japanese Patent Laid-Open No. 2003-347058 JP 2003-317967 A

  However, in the organic light emitting device disclosed in Patent Document 1, the deterioration of the light emission efficiency is not sufficiently suppressed in the blue organic light emitting device having a low concentration of the first host component. In the organic light-emitting device disclosed in Patent Document 1, the first host component has a structure that satisfies the plane geometric standard and easily causes intermolecular interaction. For this reason, as the first host component is increased in concentration, two or more molecules of the first host component interact with each other, resulting in longer wavelengths of light emission, and blue having high color purity cannot be obtained. There was a problem.

  On the other hand, in the organic light-emitting device disclosed in Patent Document 2, a stabilizer having a lowest triplet excitation energy level of less than 130 kJ / mol has a lower minimum singlet excitation energy due to its extremely low lowest triplet excitation energy. Tend. For this reason, when it mixes with the light emitting layer with a blue light emitting material, there existed a problem that color purity fell by long wavelength light emission of a stabilizer, or luminous efficiency reduced extremely.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a blue organic light-emitting device having a long continuous drive life, a high efficiency and a high color purity.

  The inventors of the present invention have found a method for suppressing the deterioration of light emission efficiency by studying in detail the process of material deterioration occurring in the light emitting layer constituting the organic light emitting element, and have reached the present invention.

The organic light-emitting device of the present invention comprises an anode, a cathode,
An organic compound layer sandwiched between the anode and the cathode and including at least a light emitting layer, and
The light emitting layer has a first host, a second host, and a guest,
An organic light emitting device emitting blue light,
The second host is a compound represented by the following general formula [1] or a compound represented by the following general formula [1] condensed with an aromatic ring selected from a benzene ring, a naphthalene ring, a phenalene ring, an anthracene ring, and a phenanthrene ring. A compound having 7 or less benzene rings (excluding compounds in which the 1st and 12th carbons of benzo [c] phenanthrene are bonded to the same carbon),
The lowest triplet excitation energy of the second host is less than the lowest triplet excitation energy of the first host;
In the light emitting layer, the material having the lowest singlet excitation energy is a light emitting material.

  ADVANTAGE OF THE INVENTION According to this invention, a blue organic light emitting element with a long continuous drive life, high efficiency, and high color purity can be provided.

It is a cross-sectional schematic diagram which shows the example of embodiment in the organic light emitting element of this invention, (a) is a schematic diagram which shows 1st embodiment, (b) is a schematic diagram which shows 2nd embodiment. It is. It is a figure showing the energy relationship of the constituent material contained in a light emitting layer, and the process from the production | generation of an excited state to returning to a ground state. It is a graph which shows the average value of the lowest singlet excitation energy with respect to the total number of benzene rings of a condensed polycyclic aromatic compound. It is a graph which shows the number distribution of the lowest singlet excitation energy which each compound has in the condensed polycyclic aromatic compound whose total benzene ring number is 6 or 7. ¹ is a diagram showing a ¹ H-NMR (CDCl ₃ ) chart of Compound 2. FIG. It is a figure which shows the EL spectrum of the organic EL element produced in Example 1 and the comparative example 1. FIG. 6 is a diagram showing an EL spectrum of an organic EL element produced in Comparative Example 2. FIG.

  The organic light-emitting device of the present invention includes a pair of electrodes, that is, an anode and a cathode, and an organic compound layer that is sandwiched between the anode and the cathode and includes at least a light-emitting layer. The present invention relates to an organic light emitting device that emits blue light.

  Hereinafter, the organic light-emitting device of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of the organic light-emitting device of the present invention. In FIG. 1, (a) shows the first embodiment, and (b) shows the second embodiment.

  In the organic light emitting device 11 in FIG. 1A, an anode 2, a hole transport layer 5, a light emitting layer 3, an electron transport layer 6 and a cathode 4 are sequentially provided on a substrate 1. This is a separation of the carrier transport function and the light emitting function, and the recombination region of holes and electrons is in the light emitting layer. In addition, the organic light emitting device 11 in FIG. 1A can be manufactured by combining materials having hole transporting properties, electron transporting properties, and light emitting properties in a timely manner. For this reason, the freedom of material selection is greatly increased, and a plurality of types of materials having different emission wavelengths can be used. For this reason, diversification of emission hues becomes possible. Further, it is possible to effectively confine each carrier or exciton in the central light emitting layer 3 to improve the light emission efficiency.

  In the organic light emitting device 12 in FIG. 1B, the hole injection layer 7 is inserted between the anode 2 and the hole transport layer 5 in the organic light emitting device 11 in FIG. The insertion of the hole injection layer 7 is effective in lowering the voltage because it is effective in improving the adhesion between the anode 2 and the hole transport layer 5 and the hole injection property.

  However, the organic light-emitting device of the present invention is not limited to the configuration shown in FIGS. 1A and 1B as long as it has the light-emitting layer 3 or the layer having a light-emitting function. Here, examples of the layer having a light emitting function include a hole transport layer 5 and an electron transport layer 6.

  In the organic light emitting device of the present invention, a hole blocking layer, which is a kind of electron transport layer, may be inserted between the light emitting layer 3 and the electron transport layer 6. In particular, by including a material with low HOMO energy in the hole blocking layer, it is possible to suppress the movement of holes from the light emitting layer 3 to the cathode 4 side, which is an effective configuration for improving the light emission efficiency.

The organic light emitting device of the present invention has a first host, a second host, and a guest in the light emitting layer 3 (or a layer having a light emitting function). In the organic light emitting device of the present invention, the following relationships (i) and (ii) are established for the materials contained in the light emitting layer.
(I) The lowest triplet excitation energy of the second host is smaller than the lowest triplet excitation energy of the first host. (Ii) The material having the lowest lowest singlet excitation energy is a light emitting material.

  By satisfying the relationship (i) above, it is possible to prevent deterioration of the first host caused by the generation of triplet excitons. In addition, since the relationship (ii) is satisfied, the lowest singlet excitation energy is selectively transferred to the light emitting material, and thus light emission derived from the light emitting material can be extracted with good color purity. Hereinafter, each material will be described in order.

  In the present invention, the first host is a material that inhibits crystallization of a constituent material that may occur in the light-emitting layer 3 (or a layer having a light-emitting function), and is preferably a material having a substituent in the mother skeleton. As a result, a stable amorphous light emitting layer 3 having a high glass transition temperature can be formed, and a short circuit between electrodes due to crystallization of the light emitting layer can be prevented.

  In the present invention, the first host is a compound having a main skeleton formed by condensing a benzene ring, and the main skeleton is a skeleton formed by condensing four benzene rings (three or more benzene rings are linearly formed). It is preferable that it is a compound which is except when condensing. Here, the main skeleton refers to a skeleton having the lowest lowest singlet excitation energy in a compound formed by a plurality of skeletons connected by a single bond.

  The reason why the first host defined as described above is preferable will be described below. A compound having a main skeleton formed by condensing four benzene rings is preferable because it has the lowest singlet excitation energy suitable as a host of the blue light-emitting layer. However, a skeleton formed by linearly condensing three or more benzene rings in this main skeleton, that is, a compound having a main skeleton containing anthracene as a partial structure, tends to have extremely low minimum triplet excitation energy. It is not preferable.

  On the other hand, a compound having a main skeleton of anthracene and phenanthrene, which is a skeleton formed by condensing three benzene rings, is not preferable as the first host. This is because anthracene has a remarkably low minimum triplet excitation energy, so that the lowest triplet excitation energy tends to be lower than that of the second host, and it is difficult to combine with the second host. In addition, phenanthrene has an extremely large minimum singlet excitation energy, and the minimum singlet excitation energy tends to be larger than materials used for the hole transport layer 5 and the electron transport layer 6. Therefore, energy is easily transferred from the first host in the lowest singlet excited state to the materials used for the hole transport layer 5 and the electron transport layer 6, and the light emission efficiency is likely to be lowered.

  On the other hand, a compound having a skeleton formed by condensing five or more benzene rings as a main skeleton tends to have a minimum singlet excitation energy lower than a minimum singlet excitation energy required as a blue light-emitting material. It is not preferable as a host.

  In particular, among the main skeleton formed by condensing the four benzene rings described above (except when three or more benzene rings are linearly condensed), pyrene and benzo [c] phenanthrene are preferable. As shown in Table 1 below, pyrene and benzo [c] phenanthrene are the lowest in the main skeleton formed by condensing four benzene rings (except when three or more benzene rings are condensed linearly). This is because the singlet excitation energy is in the range of 3.3 eV to 3.7 eV.

  This range is a range of the lowest singlet excitation energy particularly suitable as the main skeleton of the host. The lowest singlet excitation energy shown in Table 1 indicates the longest wavelength among the absorption maximum wavelengths of the skeletons in the solution. Here, the absorption maximum wavelength refers to a literature value (Chemical Handbook revision 4th edition). On the other hand, the solvent used for measuring the absorption spectrum of each skeleton is methanol for pyrene and triphenylene, ethanol for benzo [c] phenanthrene, and cyclohexane for chrysene.

  As a 1st host contained in the light emitting layer 3 (or layer which has a light emission function) which comprises the organic light emitting element of this invention, the compound shown below is mentioned, for example. However, the present invention is not limited to this.

  In the present invention, the second host is a condensed polycyclic hydrocarbon compound having a specific structure. Specifically, the compound represented by the following general formula [1] or the compound represented by the following general formula [1] is any one fragrance selected from a benzene ring, a naphthalene ring, a phenalene ring, an anthracene ring and a phenanthrene ring. It is a compound having 7 or less benzene rings formed by condensation of rings.

  However, in the present invention, the case where the 1st and 12th carbons of the benzo [c] phenanthrene skeleton are combined with the same carbon by the above condensation is excluded.

The second host is a condensed polycyclic aromatic hydrocarbon having no substituent. Here, the second host is a compound in which all carbons constituting the compound are sp ₂ carbons. In general, the bond-dissociation energy of the carbon-carbon bond forming the condensed polycyclic aromatic hydrocarbon is higher than that of the carbon-carbon bond (single bond) connecting the substituent and the mother skeleton. Therefore, the second host is a material that is more resistant to bond dissociation than a material having a substituent in a general mother skeleton.

  In the present invention, the lowest triplet excitation energy of the second host needs to be smaller than the lowest triplet excitation energy of the first host. As a result, energy transfer from the first host to the second host shown in FIG. 2 occurs promptly, so that the second host is more likely to be in a triplet excited state than the first host. Further, as described above, the second host having no substituent is more resistant to bond dissociation than the first host, and thus is easily deactivated without radiation and returns to the ground state. For this reason, deterioration of the material accompanying bond dissociation can be suppressed effectively.

  On the other hand, when the first host and the second host are in a singlet excited state, the excitation energy moves to the light emitting material, so that a light emitting material in a singlet excited state can be efficiently generated. Here, the light emitting material in the singlet excited state emits light (fluorescence) when returning to the ground state.

  By the way, as shown in the following formula [1], the second host is benz [c] phenanthrene or condensed polycyclic aromatic hydrocarbon formed by condensing a specific aromatic ring at a specific position with benz [c] phenanthrene. A compound.

  In the benzo [c] phenanthrene represented by the above formula, the carbon at the 1st position and the carbon at the 12th position are close to each other, so that hydrogen atoms bonded to the respective carbons repel each other. Due to the repulsion between hydrogen atoms, benzo [c] phenanthrene has a three-dimensional twist in its entire structure. Since this three-dimensional twist produces the same effect as steric hindrance, it is easy to suppress an increase in emission wavelength such as excimer emission caused by the interaction between molecules. This three-dimensional twist also has the effect of suppressing crystallization of the material.

  On the other hand, condensed polycyclic hydrocarbon compounds with high planarity that do not have a three-dimensional twist in the overall structure tend to cause crystallization of materials, and also cause intermolecular interactions due to overlapping of π electron clouds. Cheap. For this reason, the condensed polycyclic hydrocarbon compound having high planarity is likely to emit light longer than blue light under the condition of a molecular weight that can be deposited as the concentration in the light emitting layer is increased. For this reason, it becomes difficult to obtain blue light emission with high color purity.

  The three-dimensional twisted structure described above is a compound obtained by condensing an aromatic ring selected from a benzene ring, a naphthalene ring, a phenalene ring, an anthracene ring and a phenanthrene ring at a specific position with benzo [c] phenanthrene. Have. However, a compound in which the 1st and 12th carbons of the benzo [c] phenanthrene skeleton are bonded to the same carbon is a compound having an extremely high planarity without the above-described three-dimensional twisted structure. For example, anthanthrene represented by the following formula [2] and benzo [ghi] perylene represented by the following formula [3] have extremely high planarity of the compound.

  In the present invention, the second host is a condensed polycyclic aromatic compound having a total benzene ring number of 7 or less. The reason is described below.

  FIG. 3 is a graph showing the average value of the lowest singlet excitation energy with respect to the total number of benzene rings of the condensed polycyclic aromatic compound satisfying the structural requirements as the second host in the present invention. From the graph of FIG. 3, as the total number of benzene rings increases, the average value of the lowest singlet excitation energy decreases.

  FIG. 4 is a graph showing the number distribution of the lowest singlet excitation energy of each compound in the condensed polycyclic aromatic compound having 6 or 7 total benzene rings. In FIG. 4, the white bar is a condensed polycyclic aromatic compound having 6 total benzene rings, and the black bar is a condensed polycyclic aromatic compound having 7 total benzene rings.

  3 and 4, the average of the lowest singlet excitation energy of the condensed polycyclic aromatic compound having 6 total benzene rings is about 3.1 eV. On the other hand, the average of the lowest singlet excitation energy of the condensed polycyclic aromatic compound having 7 total benzene rings is about 2.9 eV. Considering the tendency of FIG. 3, the average of the lowest singlet excitation energy of the condensed polycyclic aromatic compound having 8 total benzene rings is predicted to be about 2.7 eV. On the other hand, considering that the minimum singlet excitation energy of the blue light emitting material is generally about 2.9 eV, the condensed polycyclic aromatic compound contained in the organic light emitting device of the present invention as the second host of the light emitting layer is: It can be said that the total number of benzene rings is preferably 7 or less.

  Because the condensed polycyclic aromatic compound that is the second host is a condensed polycyclic hydrocarbon compound having a total number of benzene rings of 7 or less, the lowest singlet excitation energy of the second host is a light emitting material that emits blue light. It becomes difficult to become lower than the lowest singlet excitation energy. For this reason, it is possible to suppress a decrease in color purity and a decrease in luminous efficiency caused by the second host itself emitting light.

  However, the minimum singlet excitation energy with respect to the total number of benzene rings of the condensed polycyclic aromatic compound satisfying the structural requirements as the second host in the present invention used in FIGS. 3 and 4 is calculated using the following calculation method. Asked.

(A) Structure optimized density functional theory (DFT)
Functional: B3LYP
Basis function: 6-31G *
(B) S ₁ (absorption) excitation energy time-dependent density functional theory (TDDFT)
Density functional theory (DFT)
Functional: B3LYP
Basis function: 6-31G *

(Software etc.)
Software: Gaussian 03, Revision E. 01:
Gaussian 03, Revision E .; 01,
M.M. J. et al. Frisch, G.M. W. Trucks, H.C. B. Schlegel, G.M. E. Scuseria, M .; A. Robb, J .; R. Cheeseman, J. et al. A. Montgomery, JR. , T. Vreven, K.M. N. Kudin, J .; C. Burant, J .; M.M. Millam, S.M. S. Iyengar, J. et al. Tomasi, V.M. Barone, B.M. Mennucci, M .; Cossi, G .; Scalmani, N.M. Rega, G .; A. Petersson, H.C. Nakatsuji, M .; Hada, M .; Ehara, K .; Toyota, R.A. Fukuda, J. et al. Hasegawa, M .; Ishida, T .; Nakajima, Y .; Honda, O .; Kitao, H .; Nakai, M .; Klene, X .; Li, J. et al. E. Knox, H .; P. Hratchian, J. et al. B. Cross, V.M. Bakken, C.I. Adamo, J .; Jaramillo, R.A. Gomperts, R.M. E. Stratmann, O.M. Yazyev, A .; J. et al. Austin, R.A. Cammi, C.I. Pomeri, J .; W. Ochterski, P.M. Y. Ayala, K .; Morokuma, G .; A. Voth, P.M. Salvador, J .; J. et al. Dannenberg, V.M. G. Zakrzewski, S .; Dapprich, A.D. D. Daniels, M.M. C. Strain, O .; Farkas, D.C. K. Malick, A.M. D. Rabuck, K.M. Raghavachari, J. et al. B. Foresman, J.M. V. Ortiz, Q. Cui, A .; G. Baboul, S.M. Cliffford, J. et al. Cioslowski, B.M. B. Stefanov, G.M. Liu, A .; Liashenko, P.A. Piskorz, I .; Komaromi, R.A. L. Martin, D.M. J. et al. Fox, T.M. Keith, M.C. A. Al-Laham, C.I. Y. Peng, A.M. Nanayakara, M .; Challacombe, P.M. M.M. W. Gill, B.M. Johnson, W.M. Chen, M.C. W. Wong, C.I. Gonzalez, and J.M. A. Pople, Gaussian, Inc. , Wallingford CT, 2004.

  Even if benzo [c] phenanthrene itself forms a three-dimensional twisted structure, if many aromatic rings are condensed with benzo [c] phenanthrene, the area of the planar portion in the molecule becomes large, and the emission wavelength is reduced. It becomes easy to invite long wave. Considering this, it can be said that the condensed polycyclic aromatic compound contained in the organic light emitting device of the present invention as the second host of the light emitting layer preferably has a total number of benzene rings of 7 or less.

  By the way, when an aromatic ring is condensed to benzo [c] phenanthrene, the relationship between the condensed aromatic ring and carbon in the benzo [c] phenanthrene skeleton assumed to be involved in the condensation of the aromatic ring is shown in Table 2 below. Street.

  As shown in Table 2, the compound used as the second host includes a compound formed by condensation of benzo [c] phenanthrene and a phenalene ring. Here, when the benzo [c] phenanthrene and the phenalene ring are condensed, at least the 1-position carbon in the phenalene ring represented by the following formula [4] must participate in the condensation.

  In the present invention, the lowest singlet excitation energy of the second host is preferably larger than the lowest singlet excitation energy of the first host. This makes it difficult for the excitation energy in the singlet excited state generated in the first host to transfer energy to the second host due to recombination of holes and electrons in the first host. That is, the second host is unlikely to be in a singlet excited state. Thereby, excimer emission from the second host can be suppressed, and blue with high color purity can be extracted. Here, excimer light emission refers to light generated by the interaction between a compound in a singlet excited state and the same kind of compound in a ground state. In addition, excimer emission light has a characteristic that it has a longer wavelength than light emitted when a compound in a singlet excited state returns to the ground state.

  In the present invention, the HOMO (maximum occupied orbit) energy of the second host is lower than the HOMO energy of the first host, and the LUMO (lowest orbital) energy of the second host is lower than the LUMO energy of the first host. Is preferably high. Thereby, since holes and electrons are more likely to exist in the first host than in the second host, the probability of recombination of holes and electrons in the first host is greater than in the second host. As a result, since the second host is less likely to be in a singlet excited state, excimer emission from the second host can be suppressed, and blue with high color purity can be obtained.

  Examples of the condensed polycyclic hydrocarbon used as the second host include materials represented by the following structural formulas. However, the present invention is not limited to these.

  In addition, as shown in Table 3 below, the exemplified compounds shown above are particularly excellent in any of color purity, suppression of crystallization, and output of blue light emission that suppresses longer emission wavelength. .

  In Table 3, the compound of group 1 has singlet excitation energy suitable as a host of a blue organic light emitting device, and is preferable as a second host. This enables a combination with a light emitting material having a large singlet excitation energy of the light emitting material, which is advantageous for obtaining a blue color with higher color purity.

  In Table 3, since the compound of group 2 contains an anthracene skeleton in the molecule, the lowest triplet excitation energy is small, which is preferable as the second host. This enables combination with a first host having a low minimum triplet excitation energy. In particular, Group 2 compounds can be easily combined with a first host having a pyrene skeleton suitable for forming a stable amorphous layer, and prevent short-circuiting between electrodes due to crystallization of the material. It is advantageous.

  In Table 3, the compound of Group 3 has two or more three-dimensional twist structures resulting from the benzo [c] phenanthrene skeleton. Thereby, since the planar area | region in the whole compound becomes small, it is preferable as a 2nd host. Thereby, it is possible to suppress an increase in the emission wavelength due to the intermolecular interaction between the materials.

  In Table 3, a compound of Group 4 is preferable as the second host because it has a skeleton derived from phenanthro [3,4-c] phenanthrene represented by the following general formula [5].

  Here, since the distance between the carbon at the 1-position and the carbon at the 14-position of phenanthro [3,4-c] phenanthrene is small and the repulsive force between hydrogen atoms bonded to each carbon is large, the three-dimensional structure Twist increases. Thereby, it is possible to suppress an increase in the emission wavelength due to the intermolecular interaction between the materials.

  In the present invention, the content of the second host contained in the light emitting layer is light emission in order to prevent the other materials from being brought into the triplet excited state while the second host in the triplet excited state is concentrated. It is preferable to set it to 25 to 75 weight% of the whole layer. Here, when the concentration of the second host is higher than 75% by weight, the light emitting layer is easily crystallized.

  In the present invention, the light emitting material is preferably a compound having a five-membered ring structure. Since a material having a five-membered ring structure tends to have low LUMO energy, electrons are easily trapped in the light-emitting material dispersed in the light-emitting layer. This facilitates recombination of holes and electrons in the light emitting material. Here, the light emitting material in a singlet excited state generated by recombination of holes and electrons emits light as it is and returns to the ground state, so that a second host in a singlet excited state is unlikely to exist. Therefore, excimer emission from the second host can be suppressed, and blue with high color purity can be obtained. In particular, a material having a fluoranthene skeleton, a benzo [k] fluoranthene skeleton, or an acenaphtho [1,2-k] benzo [e] acephenanthrene skeleton is preferable because of its low LUMO energy.

  Here, among the luminescent materials, examples of the compound having a fluoranthene skeleton, a benzo [k] fluoranthene skeleton, or an acenaphtho [1,2-k] benzo [e] acephenanthrene skeleton include the compounds shown below. Can be mentioned. However, the present invention is not limited to these.

  The content of the light emitting material contained in the light emitting layer 3 is preferably lower than the contents of the first host and the second host contained in the light emitting layer 3. Thereby, concentration quenching of the light emitting material can be avoided and the light emission efficiency can be improved. Further, by reducing the content, the probability that the light emitting material is in a triplet excited state is low, and the influence on the deterioration of the light emission efficiency is small.

  In the present invention, a compound having a benzo [c] phenanthrene skeleton is used as the first host, a compound of Exemplary Compound 7 or 9 is used as the second host, and a compound having a fluoranthene skeleton in the partial structure is used as the light emitting material. Is particularly preferred. This is because this combination easily satisfies the conditions of the present invention.

  On the other hand, in the present invention, it is preferable to use a material having the lowest singlet excitation energy among the materials in the light emitting layer as the light emitting material because the light emitting material is suitable for light emission in the light emitting layer. .

  On the other hand, the light emitting material is preferably a compound having a substituent in the basic skeleton. Thereby, the rotatable substituent acts as a steric hindrance of the compound itself, and concentration quenching can be avoided. For this reason, high luminous efficiency can be realized.

  By the way, the light emitting layer which comprises an organic light emitting element is generally comprised by mixing the host which occupies most light emitting layers, and the light emitting material contained in a small amount in a light emitting layer. The light emitting layer is a stable amorphous layer having a high glass transition temperature. If the light emitting layer loses its amorphous property and crystallizes, there is a problem such as a short circuit between electrodes caused by a crystal grain boundary. Therefore, generally, a host having a substituent in the mother skeleton is used for the light emitting layer. For example, a material in which an aryl group or an alkyl group is bonded to the mother skeleton of the condensed polycyclic hydrocarbon can be used. These materials are suitable for forming a stable amorphous layer having a high glass transition temperature because a rotatable substituent causes a steric hindrance.

  Here, the present inventors conducted research by paying attention to a process in which a host having a substituent in a mother skeleton generally used in a light emitting layer deteriorates. As a result, the following phenomenon was newly clarified. Specifically, when a host having a substituent on the mother skeleton is in a triplet excited state by obtaining excitation energy, a single bond connecting the mother skeleton and the substituent is easily dissociated therefrom. And that is an important factor of deterioration of luminous efficiency in the organic light emitting device.

  Hereinafter, a verification experiment will be described in which a host having a substituent in the mother skeleton undergoes bond dissociation degradation from a triplet excited state.

(Verification experiment)
(1) Preparation of sample for verification experiment <Preparation of sample 1>
An indium tin oxide (ITO) film was formed on a glass substrate by sputtering to form an anode. At this time, the film thickness of the anode was 130 nm. Next, this anode-attached substrate was ultrasonically washed successively with acetone and isopropyl alcohol (IPA), then boiled and washed with IPA and then dried. Further, UV / ozone cleaning was performed. The substrate treated as described above was used as a transparent conductive support substrate in the following steps.

  Next, the following sample compound 1 (host) and the following sample compound 2 (luminescent material) are simultaneously vacuum-deposited from different boats on the anode by a vacuum evaporation method to form an organic compound layer (luminescent layer). Formed. At this time, the mixing ratio of sample compound 1 and sample compound 2 was 95: 5 (weight ratio), and the film thickness of the organic compound layer was 50 nm.

  Next, a cathode was formed by depositing aluminum on the organic compound layer by vacuum vapor deposition. At this time, the thickness of the cathode was set to 150 nm.

  Finally, a protective glass plate was placed in a nitrogen atmosphere with a dew point of −70 ° C. or lower so that the sample did not adsorb moisture, and sealed with an epoxy adhesive. In addition, it dug into the adhesion surface side of protective glass, and enclosed the sheet | seat for water | moisture-content adsorption | suction (Organic EL water | moisture content getter sheet | seat, Dynic Co., Ltd. product). Sample 1 was produced as described above.

<Creation of sample 2>
When preparing Sample 1, Sample 2 was prepared in the same manner as Sample 1, except that the following sample compound 3 was used instead of sample compound 1 as the host.

<Creation of sample 3>
In preparing Sample 1, when forming the organic compound layer, Sample Compound 1 (Host), Sample Compound 3 (Host), and Sample Compound 2 (Luminescent Material) were mixed at a ratio of 47.5: 47. Co-deposited at 5: 5 (weight ratio). Except for this, Sample 3 was produced in the same manner as Sample 1.

(2) Details of Verification Experiment Sample 1 was irradiated with light having a wavelength of 365 nm from the glass substrate side for 168 hours. The irradiation intensity at this time was 5.4 W / cm ² . Moreover, when irradiating light, the voltage between both electrodes is maintaining 0V, and it is in the state which is not energized. The light to be irradiated is absorbed by the organic compound layer, and molecules in an excited state (not only in a singlet excited state but also partially in a triplet excited state due to intersystem crossing) are generated. Further, when the photoluminescence of the organic compound layer was measured, the intensity after irradiation for 168 hours was about 15% with respect to that before irradiation.

  The organic compound contained in the organic compound layer of Sample 1 after light irradiation was identified by normal layer LC-APPI-FTMS / DAD / FLD. The apparatus was measured using Agilent 1100 manufactured by Agilent and LTQ Orbitrap XL manufactured by thermofischer.

  As a result, compounds other than sample compound 1 and sample compound 2, specifically, a phenyl group deficiency of sample compound 1 and a naphthyl group deficiency of sample compound 1 were detected. These detected substances, in particular, a deficiency of sample compound 1, cannot occur unless the anthracene skeleton, which is the basic skeleton of sample compound 1, and the carbon-carbon bond (single bond) connecting the phenyl group or the naphthyl group are dissociated. Is. Further, a phenyl group adduct of sample compound 1, a naphthyl group adduct of sample compound 1, and isomers thereof were also detected. In these detected substances, a phenyl group or a naphthyl group separated by bond dissociation is generated by rebinding to another sample compound 1. Moreover, the above detection object was not detected from the sample 1 which has not been irradiated with light. From this experiment, it is clear that when a material having a substituent on the mother skeleton is in an excited state, dissociation of the carbon-carbon bond (single bond) connecting the mother skeleton and the substituent occurs, thereby deteriorating the compound itself. It was.

Next, Sample 1, Sample 2, and Sample 3 were irradiated with light having a wavelength of 365 nm from the glass substrate side. Each irradiation intensity ^{1W / cm 2, 1.2W / cm} 2, a 2.7 W / cm ^2. Each irradiation intensity was set so that the number of photons absorbed per unit time by the organic compound layer of each sample was about the same. Moreover, when irradiating light, the voltage between both electrodes is maintaining 0V, and it is in the state which is not energized.

  As a result, the time for the photoluminescence of sample 1 to reach the initial 90% emission luminance is about 13 hours later, and the time for the photoluminescence of sample 2 to reach the initial emission luminance of 90% is about 1.5 hours later. It was.

  Since sample 1 and sample 2 have the same luminescent material, the difference in resistance to bond dissociation between sample compound 1 and sample compound 3 as a host is reflected in the difference in time at which photoluminescence becomes 90% of the initial value. It is thought that.

  Moreover, it was after about 14 hours that the photoluminescence of the sample 3 reached the initial light emission luminance of 90%. This time is closer to the result of Sample 1 than Sample 2.

  Here, the reason why the time when the photoluminescence of the sample 3 becomes 90% of the initial luminance is close to the time of the sample 1 is due to bond dissociation degradation from the excited state of the host, particularly from the triplet excited state, Specifically, it can be explained as follows.

  In Sample 1 and Sample 2, triplet excitation energy generated in the organic compound layer diffuses into Sample Compound 1 or Sample Compound 3, which is a host that occupies most of each organic compound layer. On the other hand, the sample 3 has two types of hosts (sample compound 1 and sample compound 3). Here, in the case of Sample 3, the triplet excited state rapidly transfers energy from a material having a high minimum triplet excitation energy to a material having a low minimum triplet excitation energy, and thus has a high probability of being present in a material having a low minimum triplet excitation energy. When the lowest triplet excitation energy was obtained by calculation using the density functional method, sample compound 1 was 1.66 eV and sample compound 3 was 2.34 eV, so in sample 3, the probability that sample compound 1 would be in a triplet excited state. Is expensive. Therefore, in both sample 1 and sample 3, since the bond dissociation degradation occurs from the triplet excited state of sample compound 1, the time when the photoluminescence of sample 3 is 90% of the initial time is interpreted as being close to the time of sample 1 it can. From this experiment, it was found that bond dissociation degradation occurs when the host is in a triplet excited state.

  As a result of examining in detail the degradation process of the material used for the organic light emitting element through the series of experiments described above, the present inventors have found that the material having a substituent in the mother skeleton passes through the triplet excited state, A new degradation process has been clarified in which the bond connecting the substituent and the dissociation is dissociated.

  The present invention has been made based on the above findings. Further, the present invention can effectively suppress the bond dissociation deterioration of the material.

  Next, other constituent members constituting the organic light emitting device of the present invention will be described.

  The hole transport material contained in the hole transport layer 5 or the hole injection layer 7 has excellent mobility for facilitating the injection of holes from the anode 2 and transporting the injected holes to the light emitting layer. It is preferable. Low molecular and high molecular weight materials having hole injection and transport performance include triarylamine derivatives, phenylenediamine derivatives, triazole derivatives, oxadiazole derivatives, imidazole derivatives, pyrazoline derivatives, pyrazolone derivatives, oxazole derivatives, fluorenone derivatives, hydrazone derivatives. , Stilbene derivatives, phthalocyanine derivatives, porphyrin derivatives, and poly (vinyl carbazole), poly (silylene), poly (thiophene), and other conductive polymers, but are not limited thereto.

  The electron injecting / transporting material contained in the electron transporting layer 6 can be arbitrarily selected from those having the function of facilitating the injection of electrons from the cathode 4 and transporting the injected electrons to the light emitting layer. It is selected considering the balance with the carrier mobility of the material. Materials having electron injection and transport performance include oxadiazole derivatives, oxazole derivatives, thiazole derivatives, thiadiazole derivatives, pyrazine derivatives, triazole derivatives, triazine derivatives, perylene derivatives, quinoline derivatives, quinoxaline derivatives, fluorenone derivatives, anthrone derivatives, phenanthroline derivatives. And organometallic complexes, but of course not limited to these. A material having a high ionization potential can be used as a constituent material of the hole block layer.

  As a constituent material of the anode 2, a material having a work function as large as possible is preferable. For example, single metal such as gold, platinum, silver, copper, nickel, palladium, cobalt, selenium, vanadium, tungsten, or an alloy composed of a combination of these, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO) Metal oxides such as zinc indium oxide can be used. In addition, conductive polymers such as polyaniline, polypyrrole, polythiophene, and polyphenylene sulfide can also be used. These electrode materials may be used alone or in combination of two or more. The anode 2 may be composed of a single layer or a plurality of layers.

  On the other hand, the constituent material of the cathode 4 is preferably a material having a small work function. For example, simple metals such as lithium, sodium, potassium, calcium, magnesium, aluminum, indium, ruthenium, titanium, manganese, yttrium, silver, lead, tin, and chromium can be used. In addition, an alloy in which a plurality of these metal simple substances are combined, for example, lithium-indium, sodium-potassium, magnesium-silver, aluminum-lithium, aluminum-magnesium, magnesium-indium and the like can be used. Further, it is possible to use a metal oxide such as indium tin oxide (ITO). These electrode materials may be used alone or in combination of two or more. The cathode 4 may be composed of a single layer or a plurality of layers.

  Further, it is desirable that at least one of the anode 2 and the cathode 4 is transparent or translucent.

  Although it does not specifically limit as the board | substrate 1 used with the organic light emitting element of this invention, Transparent substrates, such as opaque board | substrates, such as a metal board | substrate and a ceramic board | substrate, glass, quartz, a plastic sheet, are used. It is also possible to control the color light by using a color filter film, a fluorescent color conversion filter film, a dielectric reflection film or the like on the substrate.

  Further, regarding the light extraction direction of the element, either a bottom emission configuration (a configuration in which light is extracted from the substrate side) or a top emission (a configuration in which light is extracted from the opposite side of the substrate) is possible.

  In the organic light emitting device of the present invention, the layer made of an organic material (organic compound layer), that is, the light emitting layer 3 and other layers can be formed by various methods. In general, a thin film of each layer is formed by vacuum vapor deposition, ionized vapor deposition, sputtering, or plasma CVD. Alternatively, it is dissolved in an appropriate solvent, and a thin film is formed by a known coating method (for example, spin coating, dipping, casting method, LB method, ink jet method, etc.). In particular, when a film is formed by a coating method, the film can be formed in combination with an appropriate binder resin.

  The binder resin can be selected from a wide range of binder resins. For example, polyvinyl carbazole resin, polycarbonate resin, polyester resin, polyarylate resin, polystyrene resin, ABS resin, polybutadiene resin, polyurethane resin, acrylic resin, methacrylic resin, butyral resin, polyvinyl acetal resin, polyamide resin, polyimide resin, polyethylene resin, Examples include, but are not limited to, polyethersulfone resins, diallyl phthalate resins, phenol resins, epoxy resins, silicone resins, polysulfone resins, urea resins, and the like. These resins may be homopolymers or copolymers. Furthermore, these resin may be used individually by 1 type, and 2 or more types may be mixed and used for it. Furthermore, you may use together additives, such as a well-known plasticizer, antioxidant, and an ultraviolet absorber, as needed.

  Note that a protective layer or a sealing layer can be provided for the manufactured element in order to prevent contact with oxygen, moisture, or the like. Examples of protective layers include diamond thin films, inorganic material films such as metal oxides and metal nitrides, polymer films such as fluororesins, polyparaxylene, polyethylene, silicone resins, and polystyrene resins, and photocurable resins. Can be mentioned. Further, it is possible to cover glass, a gas-impermeable film, a metal, etc., and to package the element itself with an appropriate sealing resin.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(Compounds used in Examples)
The main compounds used in the examples are shown below.

(Synthesis example)
Synthesis examples of compounds 1 and 3 to 6 used in Example 1 are described below.

  <Synthesis Example of Compound 1>

(1) Synthesis of 4-bromo-7,12-diphenylbenzo [k] fluoranthene The following reagents and solvent were charged in a reaction vessel.
5-Bromoacenaphthylene: 14.5 g (62.8 mmol)
Diphenylisobenzofuran: 17.1 g (63.3 mmol)
Xylene: 200ml

  Next, the reaction solution was stirred for 5 hours while refluxing. Next, after cooling the reaction solution to room temperature, the solvent was distilled off under reduced pressure. Next, 26 ml of trifluoroacetic anhydride and 260 ml of chloroform were further added, and the reaction solution was stirred for 1 hour while refluxing. Next, after cooling the reaction solution to room temperature, the solvent was distilled off under reduced pressure to obtain a crude product. Next, the crude product was purified by silica gel column chromatography (mobile phase; toluene: heptane = 1: 3) to obtain 16 g of 4-bromo-7,12-diphenylbenzo [k] fluoranthene as a yellow solid. It was.

(2) Synthesis of Compound 1 After the reaction vessel was filled with a nitrogen atmosphere, the following reagents and solvent were charged.
4-Bromo-7,12-diphenylbenzo [k] fluoranthene: 0.7 g (1.45 mmol)
2- (Fluoranthen-3-yl) -4,4,5,5-tetramethyl- [1,3,2] dioxaborolane: 0.48 g (1.45 mmol)
Toluene: 100ml
Ethanol: 50ml

  Next, after adding an aqueous cesium carbonate solution prepared by mixing 0.95 g (2.90 mmol) of cesium carbonate and 15 ml of distilled water, the reaction solution was heated to 50 ° C. and stirred at this temperature (50 ° C.) for 30 minutes. did.

  Next, tetrakis (triphenylphosphine) palladium (0.17 g, 0.145 mmol) was added, and the reaction solution was stirred for 5 hours while heating on a silicone oil bath heated to 90 ° C. Next, the reaction solution was cooled to room temperature. Next, water, toluene and ethyl acetate were added, solvent extraction operation was performed, and the organic layer was separated. Next, the organic layer obtained when the solvent extraction operation with a mixed solvent of toluene and ethyl acetate was performed twice for the aqueous layer was added to the organic layer separated first. Next, the organic layer was washed with saturated saline and then dried over sodium sulfate. Next, the residue (crude product) obtained by distilling off the solvent of the organic layer under reduced pressure was purified by silica gel column chromatography (mobile phase; toluene: heptane = 1: 3). Next, the purified product was vacuum dried at 120 ° C., and further purified by sublimation to obtain 0.6 g of Compound 2 as a pale yellow solid.

MALDI-TOF MS (Matrix Assisted Ionization-Time of Flight Mass Spectrometry) confirmed the M ⁺ of this material 604.2.

Furthermore, the NMR chart shown in FIG. 5 was obtained by ¹ H-NMR measurement, and the structure of this material was confirmed. The identification results are as follows.
[ ¹ H-NMR (400 Hz, CDCl ₃ )]
δ 8.01 (d, 1H), 7.91-7.95 (m, 3H), 7.58-7.71 (m, 13H), 7.39-7.54 (m, 8H), 7 .22 (q, 1H), 6.74 (d, 1H), 6.63 (d, 1H)

  The purity of the compound 2 obtained in this manner was measured using high performance liquid chromatography (HPLC) manufactured by JASCO Corporation under the sample concentration, analytical column, and various measurement conditions shown below. As a result, it was confirmed that the purity was 99.9% or more in both UV and fluorescence detectors.

[Sample] (Compound 2): 1 mg / THF: 10 g
[Analysis column] YMC M80
[Column temperature setting] 40 ℃
[Injection volume] 5.0 μl
[Developing solvent] MeOH: CHCl ₃ = 90: 10
[Flow rate] 1.0 ml / min
[Measurement time] 20 min
[HPLC detection conditions]
UV absorption wavelength 254nm
Fluorescence excitation wavelength 350nm
Fluorescence detection wavelength 450nm

  <Synthesis Example of Compound 3>

The following reagents and solvents were charged into a 50 mL eggplant flask.
3-chlorobenzo [c] phenanthrene: 400 mg (1.52 mmol)
2FLPB: 819 mg (1.60 mmol)
Palladium (II) acetate: 34 mg (152 μmol)
Dicyclohexyl (2 ′, 6′-dimethoxybiphenyl-2-yl) phosphine: 156 mg (381 μmol)
Potassium phosphate: 0.97 g (4.57 mmol)
Toluene: 20 mL
Water: 0.5mL

Next, after putting the inside of the reaction system under a nitrogen atmosphere, the reaction solution was heated to 100 ° C. and stirred at this temperature (100 ° C.) for 4 and a half hours. After completion of the reaction, water was added to the reaction solution and further stirred to filter the precipitated product to obtain a gray powder crude product. Next, this crude product was dissolved in heated toluene, passed through a short silica gel column to remove the remaining catalyst, and then recrystallized with a toluene / octane mixed solvent to obtain crystals. Next, the obtained crystals were vacuum-dried at 150 ° C., and then purified by sublimation under conditions of 1.0 × 10 ⁻⁴ Pa and 345 ° C., whereby 518 mg (yield 56) %)Obtained.

The obtained compound was identified. The results are shown below.
[MALDI-TOF-MS]
Actual measurement value: m / z = 612.35, calculation value: C ₄₈ H ₃₆ = 612.28
[ ₁ H-NMR (400 MHz, CDCl ₃ )]
δ 9.24 (d, 1H), 9.19 (d, 1H), 8.32 (s, 1H), 8.15-7.95 (m, 3H), 7.95-7.53 (m , 15H), 7.53-7.28 (m, 3H), 1.68 (s, 6H), 1.58 (s, 6H).

  <Synthesis Example of Compound 4>

The following reagents and solvents were charged into a 100 ml eggplant flask.
N, N′-diphenylbenzidine: 4.88 g (14.5 mmol)
2-Iodo-9,9-dimethylfluorene: 6.40 g (20 mmol)
Potassium carbonate: 4.00g
Copper powder: 3.0g
Orthodichlorobenzene: 30ml

  Next, after attaching a condenser tube to the eggplant flask, the reaction solution was stirred for 20 hours while refluxing. Next, the reaction solution was cooled. Next, the reaction solution was filtered, and orthodichlorobenzene as a solvent was removed under reduced pressure, and then crude crystals that precipitated when methanol was added were collected by filtration. Next, the obtained crude crystals were purified by silica gel column chromatography (developing solvent: toluene / hexane mixed solvent) to obtain 7.32 g (yield 70%) of Compound 4 as white crystals.

  <Synthesis Example of Compound 5>

(1) Synthesis of Intermediate Compound 1-1 Intermediate compound 1-1 is obtained by using the method described in Non-Patent Document 3 using 2,7-ditertiarybutylfluorene (Sigma-Aldrich) as a raw material. It is done.

(2) Synthesis of Compound 5 The following reagents and solvent were charged into a 200 ml three-necked flask.
Intermediate compound 1-1: 4.56 g (12.0 mmol)
Compound 1-2: 0.828 g (4.00 mmol)
Sodium tersalibutoxide: 0.96 g (10.0 mmol)
Xylene: 100ml

  Next, the atmosphere in the reaction system was changed to a nitrogen atmosphere. Next, 34.4 mg (0.17 mmol) of tritertiary butylphosphine was added while stirring the reaction solution at room temperature. Next, 48.9 mg (0.085 mmol) of palladium dibenzylideneacetone was added. Next, the reaction solution was heated to 125 ° C. and stirred at this temperature (125 ° C.) for 3 hours. After completion of the reaction, the organic layer was extracted with toluene and dried over anhydrous sodium sulfate, and then the solvent was distilled off under reduced pressure to obtain a crude product. Next, this crude product was purified by silica gel column chromatography (developing solvent: heptane / toluene mixed solvent) to obtain 2.53 g (yield 78.0%) of Compound 7 as white crystals.

Mass spectrometry confirmed 817.5, the M ⁺ of this material. Further, a melting point of 267 ° C. and a glass transition point of 143 ° C. were confirmed by DSC differential scanning calorimetry.

  <Synthesis Example of Compound 6>

The following reagents and solvents were charged into a 300 ml three-necked flask.
2-Iodo-9,9-dimethylfluorene (Compound 8A): 5.8 g (18.1 mmol)
Diethyl ether: 80ml

  Next, after making the reaction system into a nitrogen atmosphere, the reaction solution was cooled to −78 ° C., and then the reaction solution was stirred at this temperature (−78 ° C.), while n-butyllithium (15% hexane solution) 11. 7 ml (18.1 mmol) was added dropwise. Next, the reaction solution was warmed to room temperature and then stirred at this temperature (room temperature) for 1 hour. Next, after cooling the reaction solution to −20 ° C., a dispersion prepared by mixing 0.81 g (4.51 mmol) of phenanthroline (Compound 8B) and 100 ml of toluene was added dropwise. Next, the reaction solution was stirred at room temperature for 12 hours, and then water was added. Next, the organic layer was extracted with chloroform and dried over anhydrous sodium sulfate, and then the solvent was distilled off under reduced pressure to obtain a crude product. Next, the crude product was purified by alumina column chromatography (developing solvent: hexane / chloroform mixed solvent) to obtain 2.04 g (yield 80%) of Compound 6 as white crystals.

Example 1
(1) Fabrication / Evaluation of Element The organic light-emitting element shown in FIG. 2 was fabricated by the method described below. First, by sputtering, indium tin oxide (ITO) as an anode was formed on a glass substrate (substrate 1) to form an anode 2. At this time, the film thickness of the anode 2 was 130 nm. Next, the substrate 1 on which the anode 2 was formed was ultrasonically cleaned successively with acetone and isopropyl alcohol (IPA), then boiled and cleaned with IPA, and then dried. Further, UV / ozone cleaning was performed. The substrate treated as described above was used as a transparent conductive support substrate in the following steps.

  Next, Compound 4 (hole injection material) and chloroform were mixed to prepare a 0.1 wt% toluene solution. Next, this toluene solution was dropped on the anode 2, and a film was formed by first performing spin coating at a rotational speed of 500 RPM for 10 seconds and then at a rotational speed of 1000 RPM for 1 minute. Next, it was dried in a vacuum oven at 80 ° C. for 10 minutes to completely remove the solvent in the thin film. The thickness of the hole injection layer 7 formed by the above method was 11 nm.

  Next, the compound 5 was formed on the hole injection layer 7 by vacuum deposition to form the hole transport layer 5. At this time, the thickness of the hole transport layer 5 was set to 15 nm.

  Next, the compound 3 (first host), the compound 2 (second host, manufactured by Tokyo Chemical Industry), and the compound 1 (guest) are simultaneously transferred from different boats onto the hole transport layer 5 by vacuum deposition. The light emitting layer 3 was formed by vapor deposition. At this time, the deposition rate was adjusted so that the concentrations of Compound 3, Compound 2 and Compound 1 contained in the light emitting layer 3 were 50 wt%, 45 wt% and 5 wt%, respectively, and the film thickness of the light emitting layer 3 was 30 nm. It was.

  Next, the electron transport layer 6 was formed by depositing the compound 6 on the light emitting layer 3 by vacuum deposition. At this time, the thickness of the electron transport layer 6 was set to 30 nm.

When forming the organic compound layer (hole injection layer 7, hole transport layer 5, light emitting layer 3, electron transport layer 6) constituting the organic light emitting device of this example, the degree of vacuum during vapor deposition is set to 7. 0 × 10 ^-5 Pa or less, and the deposition rate was less than 0.08 nm / sec or more 0.10 nm / sec. However, the light emitting layer 3 has a vapor deposition rate that combines both the host and the dopant. The vacuum state was maintained from the completion of the vapor deposition of the hole transport layer 5 until the vapor deposition of the light emitting layer 3 was started, and the time between them was within 10 minutes. Furthermore, the vacuum state was maintained from the completion of the deposition of the light emitting layer 4 to the start of the deposition of the electron transport layer 6, and the time between them was within 10 minutes.

Next, lithium fluoride (LiF) was formed on the electron transport layer 6 by a vacuum deposition method to form a LiF film. At this time, the thickness of the LiF film was 0.5 nm, the degree of vacuum during vapor deposition was 1.0 × 10 ⁻⁴ Pa, and the film formation rate was 0.05 nm / sec. Next, an aluminum film was formed on the LiF film by vacuum deposition to form an Al film. At this time, the film thickness of the Al film was set to 150 nm, the degree of vacuum during vapor deposition was set to 1.0 × 10 ⁻⁴ Pa, and the film formation rate was set to 1.0 nm / sec or more and 1.2 nm / sec or less. The LiF film and the Al film function as an electron injection electrode (cathode 4).

  Finally, a protective glass plate was placed in a nitrogen atmosphere with a dew point of −70 ° C. or lower so that the device did not adsorb moisture in the atmosphere, and the device was sealed with an epoxy adhesive. In addition, it dug into the adhesion surface side of protective glass, and the sheet | seat for water | moisture-content adsorption | suction (The water | moisture-content getter sheet | seat for organic EL, the product made from Dynic Co., Ltd.) was enclosed. An organic light emitting device was obtained as described above.

The obtained device was applied with a voltage of 5.6 V using the ITO electrode (anode 2) as a positive electrode and the aluminum electrode (cathode 4) as a negative electrode. As a result, blue light emission having a maximum emission wavelength of 463 nm derived from Compound 1 with emission luminance of 1917 cd / m ² , emission efficiency of 9.0 cd / A, and CIExy chromaticity (1.51, 2.6) was observed (FIG. 6). ).

Further, when a voltage was continuously applied to the organic light emitting device of this example while maintaining a current density of 100 mA / cm ² , a luminance half time (light emission luminance of 50% of the initial luminance after the voltage application was started). The time taken to become 306 hours was 306 hours, and the durability performance was good.

(2) Evaluation of lowest triplet excitation energy of host Next, the lowest triplet excitation energy of the first host was measured. First, the sample for a measurement was produced by co-evaporating the compound 5 and the compound 7 (triplet sensitizer) shown below, and forming a thin film on a slide glass. At this time, the concentration of Compound 7 (triplet sensitizer) in the thin film was 10% by weight, and the film thickness was 100 nm.

  Next, the fluorescence spectrum was measured about the produced sample. Specifically, the photoluminescence of the sample was measured with a Hitachi Fluorometer F4500.

Next, the phosphorescence spectrum of the sample was measured, and the lowest triplet excitation energy was determined from the obtained phosphorescence spectrum. Here, the phosphorescence spectrum was measured at a low temperature such as liquid nitrogen temperature (77 K). The lowest triplet excitation energy (T ₁ ) was determined from the first emission peak (shortest wavelength peak) of the measured phosphorescence spectrum.

  In addition, the thing which cannot obtain phosphorescence emission (it cannot measure phosphorescence weakly) was calculated | required in consideration of the energy transfer from a triplet sensitizer. In addition, when phosphorescence cannot be measured by the above method because phosphorescence efficiency is very low, a method that can obtain the lowest triplet excitation energy using triplet-triplet energy transfer to the acceptor was used. . Furthermore, when the lowest triplet excitation energy could not be obtained by any of the above experimental methods, the lowest triplet excitation energy was obtained using the following calculation method.

(A) Structure optimized density functional theory (DFT)
Functional: B3-LYP
Basis function: def2-SV (P)
(B) S ₁ (absorption), T ₁ (absorption) excitation energy time-dependent density functional method (TDDFT)
Density functional theory (DFT)
Functional: B3-LYP
Basis function: def2-SV (P)

(Software etc.)
Software: TURBOMOLE Version 5.10:
TURBOMOLE:
R. Ahlrichs, M.A. Baer, M.M. Haeser, H .; Horn, and C.L. Koelmel, Electronic structure calibrations on workstation computers: the program system TURBOMOLE Chem. Phys. Lett. 162: 165 (1989)

  As a result, the lowest triplet excitation energy of the first host was 2.18 eV.

  The lowest triplet excitation energy of the second host was measured by the same method and found to be 2.1 eV. Therefore, in the present Example, it turned out that the lowest triplet excitation energy of a 2nd host is smaller than the lowest triplet excitation energy of a 1st host.

(3) Evaluation of HOMO energy and LUMO energy of host A thin film of two kinds of hosts (first host and second host) included in the light emitting layer was prepared by vacuum deposition. Next, each physical property was evaluated by the method shown below about the produced thin film. The lowest singlet excitation energy of the luminescent material was also evaluated in the same manner.

(3-1) Minimum singlet excitation energy Using a Hitachi spectrophotometer U-3010, the visible light-ultraviolet absorption spectrum of the sample is measured, and the energy gap is determined from the absorption edge of the obtained visible light-ultraviolet absorption spectrum. Asked. The obtained energy gap corresponds to the lowest singlet excitation energy.

(3-2) Maximum Occupied Orbit (HOMO) Energy Measurement was performed using atmospheric photoelectron spectroscopy (measuring instrument name AC-2, manufactured by Riken Kikai). Note that what is obtained by measurement is an ionization potential, which corresponds to the highest occupied orbital (HOMO) energy.

(3-3) Lowest empty orbit (LUMO) energy Using the energy gap and ionization potential obtained in (3-1) and (3-2), the electron affinity was determined by the following calculation formula. The electron affinity corresponds to the lowest orbital (LUMO) energy.
Electron affinity = ionization potential-energy gap

  As a result, the lowest singlet excitation energy of the first host is 3.03 eV, the lowest singlet excitation energy of the second host is 3.22 eV, and the lowest singlet excitation energy of the light emitting material is 2.81 eV. there were. Therefore, it was found that the lowest singlet excitation energy of the light emitting material is the smallest among the materials contained in the light emitting layer, and the lowest singlet excitation energy of the second host is larger than the lowest singlet excitation energy of the first host. .

  The HOMO energy of the first host was 5.8 eV, and the HOMO energy of the second host was 5.93 eV. On the other hand, the LUMO energy of the first host was 2.77 eV, and the LUMO energy of the second host was 2.71 eV.

  Therefore, the HOMO energy of the second host is lower than the HOMO energy of the first host, and the LUMO energy of the second host is higher than the LUMO energy of the first host. I understood it.

(Comparative Example 1)
In Example 1, when forming the light emitting layer 3, the compound 2 (second host) was not used, and the contents of the compound 3 and the compound 1 contained in the light emitting layer 3 were 95% by weight and 5% by weight, respectively. The deposition rate was adjusted so that Except for this, an organic light emitting device was fabricated in the same manner as in Example 1.

About the obtained element, the voltage of 5.4V was applied by setting the ITO electrode (anode) as a positive electrode and the aluminum electrode (cathode) as a negative electrode. As a result, blue emission with a maximum emission wavelength of 463 nm derived from Compound 2 was observed with emission luminance of 1288 cd / m ² , emission efficiency of 8.5 cd / A, CIExy chromaticity (1.52, 2.52) (FIG. 6). ).

  Next, the luminance half-life of the element of this comparative example was evaluated in the same manner as in Example 1. As a result, the luminance half-life was about 195 hours, and a result inferior in durability performance compared to Example 1 was obtained.

  In the organic light-emitting device of this comparative example, since the second host is not included in the light-emitting layer, the first host in the triplet excited state is present with a higher probability than the device of Example 1. As a result, it is assumed that more material deterioration occurs due to bond dissociation of the first host, and this is assumed to be a cause of inferior durability performance of the organic light emitting device of this comparative example.

  Further, FIG. 4 shows that the emission spectrum of Comparative Example 1 is almost the same as that of Example 1, and that in Example 1, excimer emission of the second host is not generated and only blue emission is performed.

(Example 2)
In Example 1, when the light emitting layer 3 was formed, the deposition rate was such that the concentrations of the compound 3, the compound 2 and the compound 1 contained in the light emitting layer 3 were 90 wt%, 5 wt% and 5 wt%, respectively. Adjusted. Except for this, an organic light emitting device was fabricated in the same manner as in Example 1.

About the obtained element, the voltage of 5.2V was applied, making an ITO electrode (anode) a positive electrode and an aluminum electrode (cathode) a negative electrode. As a result, blue emission derived from the compound 2 having an emission luminance of 1423 cd / m ² , an emission efficiency of 8.9 cd / A, CIExy chromaticity (1.48, 2.5), and a maximum emission wavelength of 463 nm was observed.

  Next, the luminance half time was evaluated in the same manner as in Example 1. As a result, the luminance half time was about 215 hours later.

(Example 3)
In Example 1, when the light emitting layer 3 was formed, the deposition rate was such that the concentrations of the compound 3, the compound 2 and the compound 1 contained in the light emitting layer 3 were 70% by weight, 25% by weight and 5% by weight, respectively. Adjusted. Except for this, an organic light emitting device was fabricated in the same manner as in Example 1.

About the obtained element, the voltage of 5.2V was applied, making an ITO electrode (anode) a positive electrode and an aluminum electrode (cathode) a negative electrode. As a result, blue light emission derived from the compound 3 having an emission luminance of 1571 cd / m ² , an emission efficiency of 9.4 cd / A, CIExy chromaticity (1.48, 2.55), and a maximum emission wavelength of 463 nm was observed.

  Next, the luminance half time was evaluated in the same manner as in Example 1. As a result, the luminance half time was about 280 hours later.

  From the results of Examples 1 to 3 and Comparative Example 1, it was found that the luminance half time was increased as the concentration of the second host was increased. This is because if the concentration of the second host is low, the second host cannot be intensively brought into the triplet excited state, and the number of first hosts in the triplet excited state increases. This is because dissociation degradation is likely to occur. In the present invention, the concentration of the second host in the light emitting layer 3 is preferably 25% by weight or more in order to bring the second host into a triplet excited state intensively and to obtain excellent driving durability performance.

(Comparative Example 2)
In Example 1, an organic light emitting device was produced in the same manner as in Example 1 except that Compound 8 shown below was used instead of Compound 2 as the second host.

  Compound 8 does not have benzo [c] phenanthrene as a partial structure, and has a highly planar structure.

With respect to the obtained device, a voltage of 4.8 V was applied with the ITO electrode (anode) as the positive electrode and the aluminum electrode (cathode) as the negative electrode. As a result, in addition to the blue light emission derived from the light emission luminance of 1063 cd / m ² , the light emission efficiency of 5.5 cd / A, CIExy chromaticity (2.64, 4.77) and compound 2, the maximum light emission wavelength longer than that A green light emission of 524 nm was observed (FIG. 7). Since this green light emission is not observed in the device having the second host (compound 10) concentration of 1%, the concentration of the compound 10 in the light-emitting layer is increased to 45%, so that the interaction between the compound 1 and the compound 8 occurs. The emission of longer wavelength due to was observed.

When a voltage was applied to the device under a nitrogen atmosphere while maintaining a current density of 100 mA / cm ² , the voltage dropped sharply and light emission was not performed when 1 hour had elapsed after driving. This is presumably because the compound 8 has a high planarity structure, so that the crystallization of the compound 8 or the like occurred in the light emitting layer, causing a short circuit between the anode 2 and the cathode 4.

  1: substrate, 2: anode, 3: light emitting layer, 4: cathode, 5: hole transport layer, 6: electron transport layer, 7: hole injection layer

Claims (5)

An anode and a cathode;
An organic compound layer sandwiched between the anode and the cathode and including at least a light emitting layer, and
The light emitting layer has a first host, a second host, and a guest,
An organic light emitting device emitting blue light,
The second host is a compound represented by the following general formula [1] or a compound represented by the following general formula [1] condensed with an aromatic ring selected from a benzene ring, a naphthalene ring, a phenalene ring, an anthracene ring, and a phenanthrene ring. And a compound having 7 or less benzene rings (excluding compounds in which the 1st and 12th carbons of the benzo [c] phenanthrene skeleton are bonded to the same carbon).
The lowest triplet excitation energy of the second host is less than the lowest triplet excitation energy of the first host;
The organic light-emitting element, wherein a material having the lowest singlet excitation energy in the light-emitting layer is a light-emitting material.

  2. The organic light emitting device according to claim 1, wherein the concentration of the second host contained in the light emitting layer is 25 wt% or more and 75 wt% or less.   The organic light emitting device according to claim 1 or 2, wherein the lowest singlet excitation energy of the second host is larger than the lowest singlet excitation energy of the first host. The HOMO energy of the second host is lower than the HOMO energy of the first host;
4. The organic light emitting device according to claim 1, wherein the LUMO energy of the second host is higher than the LUMO energy of the first host. 5. The first host has a main skeleton formed by condensing a benzene ring,
5. The structure according to claim 1, wherein the main skeleton is a skeleton formed by condensing four benzene rings (except when three or more benzene rings are linearly condensed). The organic light-emitting device described in 1.

Images