JP2001240854A - Organic luminescent material and organic luminescent element using the same organic luminescent material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material having a high luminescent quantum yield by reducing non-radiation deactivation form excitation state in an organic luminescent material, to provide a material having a high luminescent quantum yield by reducing non-radiation deactivation from excitation state in an organic luminescent material having a small speed constant of luminescence, to provide a material having a high luminescent quantum yield by reducing non-radiation deactivation from excitation state in an organic luminescent material containing a metal, to provide a material having a high luminescent quantum yield by reducing non-radiation deactivation from excitation state in an organic luminescent material containing a rare earth metal, and to provide a bright luminescent element having a high luminescent quantum yield by using the above luminescent material. SOLUTION: This organic luminescent material is characterized in that the wave number of vibration of molecule contained in the organic luminescent material does not contain >=2,500 intramolecular vibration in the organic luminescent emitting light by imparting energy. This organic luminescent element is obtained by using the above organic luminescent material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an organic light emitting material and an organic light emitting device using the organic light emitting material.

[0002]

2. Description of the Related Art (1) Japanese Patent Application Laid-Open No. H11-80165 The ligand of a specific rare earth complex containing no hydrogen atom is used. The ligands are those in which all of the hydrogen atoms have been halogen-substituted or those which have been substituted with a substituent containing no hydrogen. (2) JP-A-2-247620 N-methoxymethyl-4-nitroaniline molecular crystal and a crystal obtained by substituting this with deuterium. The present invention relates to a non-linear optical material and has a different purpose from the present invention relating to a light emitting material and a light emitting element. (3) Sov. J. Coord. Chem. , 18 , 1
83 (1992) A compound capable of preventing inactivation by water molecules by fluorine substitution of a beta diketone ligand.

[0003] In recent years, the development of functional organic materials has been remarkable, and many organic materials have come to be used for electronic applications where inorganic materials have been mostly used. Above all, organic light-emitting materials have come to the market, and improvements in reliability, durability, etc., which have been problems of organic light-emitting materials in the past, are recognized. Among EL materials, EL materials that emit light when voltage is applied are compared. Organic EL materials can emit light at a lower voltage than inorganic EL materials. This is preferable because it is not necessary to use an inefficient voltage conversion element such as an inverter. Further, as a certain kind of organic EL material, the highest level of luminous efficiency among conventional light emitting devices of 70 lumen / W has been announced, and energy saving can be expected when used not only for portable applications but also for general lighting. .

[0004] These organic light emitting materials can emit light by injecting electric charge by applying a voltage or irradiating ultraviolet light or visible light, but the fundamental and common causes for deteriorating the light emission efficiency are as follows. Non-radiative deactivation from the excited state to emit light. The non-radiative deactivation process in inorganic light-emitting materials is attributed to the coupling between metal atoms, which are luminescence centers, and lattice vibrations [L. A. R
iesberg and H.S. W. Moos,. Ph
y. Rev .. , 174, 429 (1968)].

Generally, the frequency of the lattice vibration (substituted by the wave number ω) is as small as several tens to several hundred cm ^−1, and the energy difference ΔE between the excited state and the deactivated state of the metal is several thousand cm ⁻¹ . Since it is large, the rate of nonradiative deactivation kd becomes small.
The approximate expression of kd is the following expression (1).

Kd = k ₁ exp [−k ₂ ΔE / (hcω)] (1) (where h is Planck's constant, c is the speed of light (cm / sec), k
_l and k ₂ is a positive constant which depends on the lattice structure. In the actual measurement example of kd, Eu is 500 to 10,0.
A value of 500 to 3,000 / sec has been reported for 00 / sec and Tb [J. L. Kropp and
M. W. Windsor, J .; Chem. Phys. ,
42 , 1599 (1965)]. However, this value is a speed that includes not only the coupling with the lattice vibration but also all other deactivation processes, and it can be considered to a first approximation that this deactivation speed.

[0006]

[Problems to be Solved by the Invention] Provided is a material that has high emission quantum yield by reducing non-radiative deactivation from an excited state in an organic light emitting material. 2. Even in organic light-emitting materials with a small light emission rate constant,
Providing a material with high emission quantum yield by reducing non-radiative deactivation from an excited state. 3. Provided is a material that has high emission quantum yield by reducing non-radiative deactivation from an excited state in an organic light emitting material containing a metal. 4. Provided is a rare earth metal-containing organic light-emitting material that has high emission quantum yield by reducing non-radiative deactivation from an excited state. 5. Provided is a bright light emitting element having high luminous efficiency using the light emitting material.

[0007]

The organic light-emitting material having a portion that vibrates at a large frequency (wave number) in the molecule is 2900 to 3100 in the case of a carbon-hydrogen bond, and oxygen-hydrogen. Binding can cause fast deactivation. In most cases, the wave number of vibration in an organic molecule is a stretching vibration between hydrogen and another atom. For example, in the case of a carbon-hydrogen bond, 2900 to 3100, In this case, it is 3000 to 3500. Therefore, if the light emitting material does not have a portion that vibrates at the frequency (wave number) as described above, the molecule does not include vibration at a high frequency (wave number), so that excitation is performed to emit light. It is possible to reduce the non-radiative deactivation from the state of being performed, and to obtain a material having high luminous efficiency. That is, the first aspect of the present invention is that, in the organic light emitting material, the wave number of vibration of a large molecule as described above, particularly 2500 cm
An organic light-emitting material that emits light by application of energy with reduced radiationless deactivation, characterized in that it does not contain ⁻¹ or more intramolecular vibrations.

The luminescence yield φ depends on the deactivation rate kd and the rate constant k
It is determined by r and is represented by the following equation (2). Although the deactivation rate does not always occur only by coupling with vibration, it is considered to be a good approximation unless it occurs even by a chemical reaction.

[Formula 2] φ = kr / (kd + kr) (2) Further, the rate constant kr is represented by the following equation (3). In some cases, the range of kr is approximately 10,000,000 to 1,
In the case of an organic light emitting material of a type that emits light at a rate of, 000,000,000,000 / sec, the range of kr is approximately 10
0 to 1,000,000,000,000 / sec.

Kr = φ / τ (3) [where, φ represents the quantum yield of light emission, τ represents the lifetime of light emission, and φ and τ are the amounts that can be actually measured. is there. ]

As can be understood from the equation (2), in order to increase the yield φ of light emission, non-radiative deactivation is suppressed. In particular, when the rate constant kr of light emission is small, non-radiative deactivation is suppressed. It is necessary to suppress as much as possible, and an organic light-emitting material in which the light-emitting material is an organic compound is to obtain an organic light-emitting material having a sufficiently high light-emission yield as compared with an organic light-emitting material in which a metal emits light Is easy. In the first organic light-emitting material of the present invention in which non-radiative deactivation is reduced, an organic light-emitting material having a sufficient light emission yield can be obtained even when the light emission rate constant kr is 100,000 / sec or less. . That is,
The second aspect of the present invention is that the light emission rate constant kr is 100,000.
/ Sec or less in the first organic light emitting material.

The organic light emitting material having reduced non-radiative deactivation may be an organic light emitting material containing a metal having reduced non-radiative deactivation and having both excellent durability and luminous efficiency. That is, the third aspect of the present invention resides in the first and second organic light-emitting materials, wherein a metal is contained as a component constituting an organic substance.

When the emission center is a metal in the organic light-emitting material containing a metal, the rate constant kr of light emission is often about several hundred if the transition accompanying light emission is a forbidden transition. In particular, forbidden transitions of rare earth metals that are currently attracting attention are as small as 100 / sec. In this case, when the coupling between the coordinated organic molecule and the intramolecular vibration is large, the organic molecule is almost completely deactivated without emitting light. By reducing activity,
A sufficient luminescence yield can be obtained. That is, a fourth aspect of the present invention is the third organic luminescent material, wherein the luminescent center is a metal, and the organic ligand is coordinated to the metal. A fifth aspect of the present invention is the third or fourth organic light emitting material, wherein the metal is a rare earth metal.

In each of the organic light-emitting materials, means for preventing intramolecular vibration of 2500 cm ⁻¹ or more from being contained in the organic light-emitting material and reducing non-radiative deactivation include replacing hydrogen atoms of the organic light-emitting material with deuterium. Means. In conventional general organic materials, it is difficult to avoid hydrogen atoms in the material, but in the present invention,
By substituting the hydrogen atoms of the first to fifth organic light emitting materials with deuterium, it is possible to prevent the organic light emitting material from having an intramolecular vibration of 2500 cm ⁻¹ or more. That is, the sixth aspect of the present invention resides in an organic light emitting device in which hydrogen atoms of the first to fifth organic light emitting materials are replaced with deuterium.

Japanese Patent Application Laid-Open No. H11-80165 discloses the use of a group having a chemical structure in which all of the hydrogen atoms of a ligand of a specific rare earth metal complex are replaced with halogen atoms. When all of the hydrogen atoms are replaced with halogen atoms, the chemical properties of the ligand are usually completely different from those of the ligand before replacement, and ordinary materials with hydrogen atoms are synthesized. Substitution with a halogen atom after that makes it difficult to predict the properties of the material. Further, when all hydrogen atoms are replaced with halogen atoms,
Since the coordination force of the ligand to the metal greatly changes, the emission wavelength greatly changes, and the emission rate constant kr also changes greatly, which also makes it difficult to predict the characteristics. On the other hand, when hydrogen is replaced by a deuterium atom as in the present invention, the chemical properties of the ligand of the organic light emitting material do not substantially change, and the organic substance after the deuterium replacement is not used. It is also easy to predict the properties of the light emitting material.

When hydrogen in the organic light emitting material is replaced with deuterium, it is not always necessary to completely replace hydrogen in the organic light emitting material, and partial replacement may be performed as long as a desired emission yield is obtained. When the luminescence center is a metal atom, all hydrogen atoms around or adjacent to the metal atom need to be deuterated. As deuterium, double hydrogen,
Both tritium can be used.

The organic light emitting material of the present invention emits light when various energy is externally applied. Examples of the energy include current, heat, light, and irradiation of an electron beam.

[0016]

Example 1 An organic light-emitting device which emits light by applying a voltage was manufactured using a conventional material. On a glass substrate with a transparent electrode, a hole transport layer, N, N'-diphenyl-N, N'-bis (3
Methylphenyl) -1,1'-biphenyl-4,4'-
Diamine (hereinafter abbreviated as TPD) was deposited to a thickness of 60 nm. Next, a dicyanomethylenepyran-based compound (hereinafter abbreviated as CMP) and a coumarin-based compound were co-evaporated as a light-emitting material to a thickness of 50 nm. The weight ratio of CMP to coumarin compound is 1: 8.
Met. Next, aluminum quinolate (hereinafter abbreviated as Alq) was deposited to a thickness of 25 nm as an electron transport layer, and silver and magnesium were co-deposited thereon to a thickness of 150 nm. The light emitting device thus manufactured emits red light and emits 3 light per 1 cm ^2.
When a current of 0 mA flows, the external quantum yield of light emission is 0.1.
010. Next, a similar light-emitting element was manufactured using deuterated CMP and a coumarin-based compound, and the external quantum yield of light emission when the same current was applied was 0.015. A large amount of the light-emitting material that had been replaced with deuterium and the light-emitting material that had not been replaced were prepared on calcium fluoride by the same vapor deposition method as above, and the infrared absorption spectrum of the material was measured. Did not show absorption at a wave number of 2500 cm ^-1 or more.

The above results can be understood as follows.
The wave number of the stretching vibration of the carbon-hydrogen bond contained in CMP and the coumarin-based compound is about 2500 to 3000 cm ^−1, and such a large wave number vibration causes non-radiative deactivation of the light emitting part. Since the hydrogen atom is the lightest element, the stretching vibration has such a large wave number. However, since there is almost no organic substance having no carbon-hydrogen bond, it is difficult to prevent this. However, if hydrogen atoms are replaced with deuterium, the wave number of this vibration is greatly reduced.
By the deuterium substitution, the wave number of this stretching vibration was reduced to 70%, and became 1700 to 2100 cm ⁻¹ . Even when deuterium substitution is performed, the chemical properties of the compound generally do not change.Therefore, even if synthesis is not performed using expensive deuterium-substituted materials from the beginning, by confirming the chemical properties of the resulting luminescent material, substitution can be performed. It is possible to predict the nature of the case.

Example 2 Pyrazolyl bromide negative ion is coordinated with Tb (III) positive ion as a light emitting material, and CF _{3 is used} as a counter ion.
A material using SO ₃ ⁻ was prepared. Polyvinylcarbazole and 2- (4-biphenylyl) -5- (5-tert-butylbenzene) -1,3,4-oxadiazole (hereinafter B)
BO) and prepare them under dry nitrogen atmosphere.
Dissolved in HF. The weight ratio of the light emitting material, the hole transfer material, and the electron transfer material was 1: 4: 4. Tb contained in the light emitting material used here is a rare earth metal, and it is known that the light emitting center is not an organic compound coordinated but a metal atom. In many cases, a complex of Al and an organic compound has a higher luminous efficiency and durability than a light-emitting material containing only an organic compound. In particular, a complex using a rare-earth metal is superior in both efficiency and durability.

When an organic compound coordinated to a metal is excited, and this energy is transferred to the metal, the metal emits light. In principle, all of the excitation energy may be emitted, but the organic molecule emits light. In this case, only １ ／ of the excited energy can be emitted. This is because when excited organic molecules are generated, the lowest excited singlet and the lowest excited triplet have a ratio of 1: 3, and only the lowest excited singlet can emit light. Next, this mixed solution is
Spin coat on glass with transparent electrode, dry,
And Al were deposited in this order. When a current was applied to the light-emitting element thus configured, green light was emitted. The internal quantum yield of light emission is 0.4 and the rate constant of light emission is 2
00 / sec. When a hydrogen atom directly bonded to the pyrazolyl ring of the light-emitting material and all the hydrogen atoms of the substituents bonded to the pyrazolyl ring were replaced with deuterium, a similar light-emitting element was constructed. .6.
The luminescence rate constant did not change within the measurement error. The reason why the internal quantum yield of light emission is improved even when the light emission rate constant does not change is that the deactivation rate constant kd in Equation (3) is reduced by deuterium substitution.

Example 3 A light-emitting device similar to that of Example 2 was manufactured by changing the metal ion of the light-emitting material to Ce. The same hole transport material, electron transfer material, and electrode material were used. When a current was applied to the device, blue light emission was observed. The internal quantum yield of light emission was 0.9, and the rate constant of light emission was 1,800,000 / sec. Next, hydrogen was directly bonded to the pyrazolyl ring, and all the hydrogens of the substituents bonded to the pyrazolyl ring were replaced with deuterium. No change was observed in the yield and the rate constant of the luminescence. In this case, it can be understood that the contribution of nonradiative deactivation caused by the influence of vibration of the coordinated organic compound is already sufficiently small even before the deuterium substitution, because the emission rate constant is very large. Since the emission transition of Ce ion is an allowable transition, the emission rate constant is large as described above. However, since the Tb ion is spin-forbidden and parity-forbidden, its value is as small as about 200 / sec. Become. When only one side of the spin or parity forbidden rule exists, the magnitude of the emission rate constant is 100,
Although it is 000 / sec, the effect of the deuterium substitution can be expected up to the case of such a light emission rate constant.

Example 4 In Example 2, only the luminescent material was dissolved in THF, and the luminescence quantum yield and the luminescence rate constant were compared when irradiating ultraviolet rays without containing oxygen or water.

[0022]

[Table 1] The quantum efficiency was improved when deuterium substitution was performed, and the effect of deuterium substitution could be confirmed also on the luminescence yield by ultraviolet irradiation.

[0023]

[Effect] 1. Claims 1 and 2 Since a molecule having no large frequency (wave number) is included in a molecule, it is possible to reduce non-radiative deactivation from a state excited to emit light, and a material having high luminous efficiency. Could be obtained. 2. Claim 3 Even if the light emission rate constant is 100,000 / sec or less,
Non-radiative deactivation due to the influence of intramolecular vibration of the organic light emitting material can be reduced, and a material having high luminous efficiency can be obtained. 3. Claim 4 By using a material containing a metal, an organic light emitting material excellent in both durability and luminous efficiency could be obtained. 4. Claim 5 Since the luminescent center is a metal, the excited energy can be used with high efficiency, and a luminescent material with high luminous efficiency can be obtained. 5. Claim 6 In the organic light emitting material containing a metal, by using a rare earth metal as the light emission center, it is possible to use the excited energy with high efficiency, and to obtain a light emitting material with high light emission efficiency. 6. Claims 7 to 9 By reducing the wave number of intramolecular vibration and reducing non-radiative deactivation due to the influence of this vibration, a material having high luminous efficiency could be obtained. 7. Claims 10 to 14 Since a high-efficiency light-emitting material is obtained by reducing non-radiative deactivation, and a light-emitting element using this material is formed, a bright light-emitting element with high luminous efficiency can be obtained.

Claims (14)

[Claims] 1. An organic light-emitting material which emits light by the application of energy, wherein the organic light-emitting material does not include intramolecular vibration in which the number of vibrations of molecules contained in the organic light-emitting material is 2500 cm ⁻¹ or more. 2. The organic light emitting material according to claim 1, wherein the material does not have a carbon-hydrogen bond and / or an oxygen-hydrogen bond. 3. An organic light emitting material having a light emission rate constant kr of 1
2. The method according to claim 1, wherein the speed is not more than 00,000 / sec.
Or the organic light-emitting material according to 2. 4. The method according to claim 1, further comprising a metal.
3. The organic light emitting material according to any one of 3. 5. The organic luminescent material according to claim 4, wherein the luminescent center is a metal and has a structure in which an organic ligand is coordinated with the metal. 6. The organic light emitting material according to claim 4, wherein the metal is a rare earth metal. 7. The organic light emitting material according to claim 1, wherein a hydrogen atom of the organic light emitting material is substituted with deuterium. 8. The organic light emitting material according to claim 7, wherein a hydrogen atom is partially substituted with deuterium. 9. The organic luminescent material according to claim 8, wherein all hydrogen atoms around the metal at the luminescent center are substituted with deuterium. 10. An organic light emitting device using the organic light emitting material according to claim 1. 11. The organic light emitting device according to claim 10, wherein light is emitted by heat. 12. The organic light emitting device according to claim 10, wherein the organic light emitting device emits light by light. 13. The organic light emitting device according to claim 10, wherein light is emitted by an electron beam. 14. The organic light emitting device according to claim 10, wherein light is emitted by an electric current.