JP2008063399A - Light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting element carrying out light emission with high efficiency and formable by a coating type process. <P>SOLUTION: The light-emitting element is obtained by using a copper dinuclear complex as a light-emitting material. The copper dinuclear complex is represented by general formula (1) [wherein, the ligand A is selected from a pyridine derivative containing nitrogen which is a coordinating atom; X is a halogen atom and selected from Cl, Br or I; and PR<SB>3</SB>is a tertiary phosphine in which the P is a coordinating atom and is selected from structural formula (2) (wherein, R<SB>2</SB>and R<SB>3</SB>are each a ≤6C linear, a ≤6C branched or a ≤6C cyclic alkyl group)]. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light-emitting device using a copper binuclear complex using copper as a light-emitting material, and more particularly, a light-emitting device such as an organic EL device using a halogen-crosslinked binuclear complex, preferably as a light-emitting dopant. It is about.

  Non-patent document 1 describes a light-emitting binuclear copper complex represented by the following chemical formula (4).

  Non-Patent Document 1 shows that the emission wavelength can be controlled by changing the substituent of the pyridine ring and the halogen atom in the above structural formula. Moreover, the light emission quantum yield shows a high value of 0.1 or more.

  In addition, a polymer copper complex having a structure similar to the chemical formula (4) is known (Non-patent Document 2).

First International Symposium on the Photofunctional Chemistry of Complex Systems (ISPCCS), [Kona, Hawaii, USA, 12-14 December 2005] lecture number: IL-05 Emissions of molecular copper dinuclear complexes with halide bridges Yuko Chishina, Kiyoshi Tsuge, Yoichi Sasaki , Shoji Ishizaka, Noboru Kitamura H. Araki, K .; Tsuge, Y .; Sasaki, S .; Ishizaka, and N.I. Kitamura, Inorganic Chemistry, 2005; 44 (26); 9667-9675.

  Non-Patent Document 1 discusses the light emission characteristics of the copper binuclear complex represented by the chemical formula (4). However, there is no description about the application of these complexes as light-emitting materials using light-emitting elements, and it is limited to the study of molecular structure and photophysical properties.

  Moreover, although the copper complex currently disclosed by the nonpatent literature 2 has a high light emission characteristic, it is insoluble in a general organic solvent. Therefore, it is difficult to form a thin film necessary for producing a light-emitting element, and application to the light-emitting element is difficult.

  Therefore, an object of the present invention is to provide a light-emitting element that can emit light with high efficiency and can be formed by a coating process.

  That is, the light-emitting element of the present invention is characterized by using a copper binuclear complex represented by the following general formula (1) as a light-emitting material.

[However, the ligand A is selected from pyridine derivatives containing nitrogen as a coordinating atom, and they may have a substituent. The substituent is selected from an alkyl group, an alkoxyl group, a phenyl group, a benzyl group, a benzoyl group, a dialkylamino group, and a carboxyl group.

  X is a halogen atom and is selected from Cl, Br or I.

PR ₃ is a tertiary phosphine in which P is a coordination atom, and is selected from those shown in the following structural formula (2).

  However, in the structural formula (2), the hydrogen atom of the phenyl group may be substituted with a halogen atom or a branched or straight chain alkyl group or alkoxyl group having 6 or less carbon atoms.

R ₂ and R ₃ are linear, branched or cyclic alkyl groups having 6 or less carbon atoms. ]

  The copper binuclear complex of the present invention is soluble in common organic solvents. Therefore, a light emitting device using the copper binuclear complex of the present invention can be formed by a coating type process.

  In addition, since the copper binuclear complex of the present invention can emit stable high-efficiency light at room temperature, a light-emitting element using this can emit light with high efficiency.

  Furthermore, when the copper binuclear complex of the present invention is used as a luminescent dopant, it can be uniformly dispersed in the host material, concentration quenching is avoided, and highly efficient light emission is possible.

  Hereinafter, the present invention will be described in detail.

  The copper binuclear complex used for the light emitting material of the device of the present invention is represented by the above general formula (1), and the ligand A is preferably selected from the compounds represented by the following structural formula (3).

  Below, the specific example of the copper binuclear complex used for the luminescent material of the element of this invention is shown. In the formula, X represents a halogen atom and is selected from I, Br, and Cl.

The copper binuclear complex of the present invention has a [Cu ₂ X ₂ ] unit bridged by two halogens, and further has a phosphine ligand PR ₃ and a pyridine-based ligand. As representative examples of the emission spectrum of the copper binuclear complex of the present invention, the emission spectra of Exemplified Compounds 001 to 006 are shown in FIG. As shown in FIG. 1, the emission spectra of these complexes can be changed by changing the substituent of the pyridine-based ligand. As shown in FIG. 1A, when X = I, the emission peak wavelength of each complex ranges from 435 nm to 627 nm, and the emission of these complexes covers a wide range of visible light from blue to red. I understand.

  The present inventors have studied the use of these copper binuclear complexes as light emitting dopants for organic EL devices, and obtained highly efficient light emitting devices.

  According to studies by the present inventors, the copper binuclear complex of the present invention is soluble in a general organic solvent. Common organic solvents include, for example, toluene, orthoxylene, metaxylene, paraxylene, tetrahydrofuran, chloroform, methylene chloride, chlorobenzene, carbon tetrachloride, orthodichlorobenzene, metadichlorobenzene, paradichlorobenzene, ethyl acetate and the like. Accordingly, when a light emitting device is produced using the copper binuclear complex of the present invention, it is suitable for a light emitting device using a coating type process in which it is dissolved in an organic solvent and applied to form a light emitting layer.

  Examples of the application type process include spin coating, ink jet, printing, and dispenser methods.

  Usually, when forming a light emitting layer by a coating type process, a mixed solution of a host material and a light emitting dopant is prepared, applied in a desired pattern, and dried to form a film corresponding to the light emitting layer. Accordingly, the light emitting layer is preferably composed of a host material and a light emitting dopant which is the copper binuclear complex of the present invention.

  Specific examples of the organic compound used as the host material of the light emitting layer are shown below. In addition to polyvinyl carbazole (PVK), polyfluorene (PF), polystyrene (PS), and the like, polymethyl methacrylate (PMMA) can also be used. In addition to these polymers, the following compound groups (oligofluorene, TCTB, NPD, TPD) used as organic EL materials are also useful as the host material of the present invention.

  By uniformly dispersing the copper binuclear complex of the present invention in these organic compounds, concentration quenching can be avoided and highly efficient light emission can be achieved. The copper binuclear complex of the present invention can be applied to a light-emitting element because stable and efficient light emission can be obtained at room temperature.

  Luminescence is a radiative transition of excitation energy from the excited state and can be classified by the method of forming the excited state.

1. 1. An electroluminescent device that forms an excited state by combining holes and electrons by current excitation. 2. Photoluminescence element that forms an excited state with an excitation light source. There is a cathode luminescence element that forms an excited state with an electron beam.

  Regarding the electroluminescence element, the application using the copper binuclear complex of the present invention as the light emitting dopant of the organic LED element is possible. An example of the element configuration of the organic LED element is shown in FIG. The organic LED device shown in FIG. 2 comprises a positive electrode / hole injection layer / light emitting layer / electron injection layer / cathode, and the light emitting layer is an organic compound host doped with the copper binuclear complex of the present invention (in FIG. 2, PVK / PBD). The molecular structural formulas of PVK and PBD are shown below.

  By applying a voltage of about 2 V to 20 V to this element, EL light emission is confirmed on the glass substrate side.

  The photoluminescence element can be applied as an emission color conversion material using an organic or inorganic LED as an excitation light source. An example of the configuration of the photoluminescence element is shown in FIG. For example, by applying an electric field to an inorganic LED element that emits ultraviolet light, ultraviolet light (emission peak wavelength = 250 nm to 400 nm) is emitted from the inorganic LED element. The light from inorganic LED is irradiated to the photoluminescent element which has the light emitting layer containing the copper binuclear complex of this invention installed in the front. The photoluminescence element absorbs this light to form an excited state, and light emission from the excited state is observed from the outside.

  The cathode luminescence device can be applied to a cathode ray tube (CRT) phosphor.

  The copper binuclear complex of the present invention is particularly applicable to color mixing or white light emitting materials.

<Example of synthesis experiment>
First, a synthesis experiment example of the copper binuclear complex of the present invention is shown.

(1) First, a method for synthesizing a complex [Cu ₂ I ₂ (PPh ₃ ) ₃ ], which is a raw material for the copper complex of the present invention, is shown. This method is reported in reference 1.
(Reference 1: G. Costa, E. Reisenhofer, L. Stefani J. Inorg. Nucl. Chem., 1965, 27, 2581.)

Melt the PPh ₃ 104.9mg (0.4mmol) in CHCl ₃ 20ml. To this, 38.1 mg (0.2 mmol) of CuI is added and stirred for about 4 hours. After concentrating with an evaporator to about 1 ml and diffusing ether vapor, colorless crystals are precipitated (yield 58.4 mg (yield 50% vs. PPh ₃ )).

The results of elemental analysis are as follows, and it was confirmed that the obtained compound was a complex [Cu ₂ I ₂ (PPh ₃ ) ₃ ].

Found (%) C: 55.77, H: 3.97, N: 0.00
Calcd. (%) For [Cu ₂ I ₂ (PPh ₃ ) ₃ ] C: 55.54, H: 3.88, N: 0

(2) A method for synthesizing a raw material complex [Cu ₂ Br ₂ (PPh ₃ ) ₃ ] will be described.

Melt the PPh ₃ 104.9mg (0.4mmol) in CHCl ₃ 20ml. To this, 8.7 mg (0.2 mmol) of CuBr ₂ is added and stirred for about 4 hours. After concentrating with an evaporator to about 1 ml and diffusing ether vapor, colorless crystals are deposited (yield 65.2 mg (yield 60.7% vs. PPh ₃ )).

The results of elemental analysis are as follows, and it was confirmed that the obtained compound was a complex [Cu ₂ Br ₂ (PPh ₃ ) ₃ ].

Found C: 60.67, H: 4.30, N: 0.00
Calcd. for [Cu ₂ Br ₂ (PPh ₃ ) ₃ ] C: 60.40, H: 4.22, N: 0

(3) Synthesis of [Cu ₂ X ₂ (PPh ₃ ) ₂ (L) ₂ ] using [Cu ₂ X ₂ (PPh ₃ ) ₃ ] synthesized in (1) and (2) as a starting compound Then, [Cu ₂ X ₂ (PPh ₃ ) ₃ ] is reacted with 10 times the amount of pyridine analog ligand L to obtain [Cu ₂ X ₂ (PPh ₃ ) ₂ (L) ₂ ]. A specific synthesis example is shown below.

(3-1) Synthesis of Copper Binuclear Complex [Cu ₂ I ₂ (PPh ₃ ) ₂ (4-Mepy) ₂ ] (Exemplary Compound 002 (X═I)) [Cu ₂ I ₂ (PPh ₃ ) ₃ ] 35 mg ( 0.03 mmol) was dissolved in 1.0 ml of CHCl _3, and ₃₀ μl (0.3 mmol) of 4-Mepy was added thereto, and left to stand to leave colorless crystals after several days (yield 22.2 mg (yield 67.8%)). ).

  The results of elemental analysis are as follows, and it was confirmed that the obtained compound was the target complex.

Found C: 52.68, H: 4.00, N: 2.50
Calcd. for [Cu ₂ I ₂ (PPh ₃ ) ₂ (3-Mepy) ₂ ] C: 52.81, H: 4.06, N: 2.57

(3-2) Synthesis of a copper binuclear complex [Cu ₂ Br ₂ (PPh ₃ ) ₂ (3-Mepy) ₂ ] (Exemplary Compound 003 (X = Br)) [Cu ₂ Br ₂ (PPh ₃ ) ₃ ] Dissolve 7 mg (0.05 mmol) in 1.0 ml of CHCl ₃ , add 50 μl (0.5 mmol) of 3-Mepy here, add hexane and let stand, and after a few days, colorless crystals are precipitated (yield 26.8 mg (yield 26.8 mg)). Yield 53.7%)).

  The results of elemental analysis are as follows, and it was confirmed that the obtained compound was the target complex.

Found C: 57.64, H: 4.40, N: 2.85
Calcd. for [Cu ₂ Br ₂ (PPh ₃ ) ₂ (3-Mepy) ₂ ] C: 57.78, H: 4.45, N: 2.81

(3-3) Synthesis of Cu binuclear complex [Cu ₂ Br ₂ (PPh ₃ ) ₂ (4-Phypy) ₂ ] (Exemplary Compound 006 (X = Br)) [Cu ₂ Br ₂ (PPh ₃ ) ₃ ] 2 mg (0.03 mmol) is dissolved in 0.8 ml of CHCl ₃ , 46.5 mg (0.3 mmol) of 4-Phypy is added to the solution, and left to stand for a while. .6 mg (yield 55.3%)).

  The results of elemental analysis are as follows, and it was confirmed that the obtained compound was the target complex.

Found C: 62.24, H: 4.41, N: 2.45
Calcd. for [Cu ₂ Br ₂ (PPh ₃ ) ₂ (4-Phypy) ₂ ] C: 62.09, H: 4.31, N: 2.50

The emission spectrum at room temperature of the solid powder of the copper binuclear complex obtained by the synthesis method of the above synthesis experiment example is shown in FIG. FIG. 1A shows an emission spectrum of [Cu ₂ I ₂ (PPh ₃ ) ₂ (L) ₂ ] (exemplary compounds 001 to 006 (X = I)) containing an iodine atom, and FIG. The emission spectrum of [Cu ₂ Br ₂ (PPh ₃ ) ₂ (L) ₂ ] containing the atoms (Exemplary compounds 001 to 006 (X = Br)) was shown. The emission peak wavelength of each complex is 435 nm to 627 nm when X = I, and 472 nm to 650 nm when X = Br. It can be seen that a wide range of visible light region can be covered by changing the ligand. Comparing the iodine complex and bromine complex having the same ligand, it can be seen that the emission peak wavelength of the iodine complex is shorter.

  Even if it was made to emit light by excitation light for 2 hours or more, light emission with high luminance can be obtained, and it was found that the copper complex of the present invention can obtain stable light emission.

<Example 1>
A copper binuclear complex of the present invention (Exemplary Compounds 002 to 006 (X = Br)) including the complex synthesized in the synthetic experiment example described above was dispersed in a polymer to prepare a photoluminescence device using an excitation light source. .

  Polystyrene (manufactured by ACROS ORGANIC) was dissolved in chloroform at a concentration of 14% by weight. The copper complex was dissolved at the same concentration of 1.4% by weight. Thereafter, the polystyrene solution and the copper complex solution were mixed at a ratio of 1: 1. A few drops of this solution were dropped on a glass substrate washed with acetone, and dried for 2 hours to form a cast film. The photoluminescence spectrum of this polystyrene-copper complex mixed film was measured with excitation light having a wavelength of 355 nm. Moreover, the spectrum was similarly measured about the cast film only of polystyrene. The emission spectrum is shown in FIG.

  It can be seen that each emission spectrum is an emission spectrum derived from a copper binuclear complex, unlike the emission from a cast film of only polystyrene. Exemplified compound 004 (X = Br) and Exemplified compound 005 (X = Br) having a large emission wavelength have an emission spectrum extending to the short wavelength side. This is thought to be due to the fact that polystyrene-derived light emission was observed simultaneously with the light emission of the copper complex because the energy transfer of excitation energy from polystyrene was insufficient. Accordingly, by appropriately selecting the copper complex and the host compound, it is possible to obtain multicolor light emission or white light emission by color mixture with the light emission of the host material.

  Emission is considered to be because the copper complex was uniformly dispersed in polystyrene by using a copper complex that was confirmed to be uniform throughout the cast film and could be dissolved in chloroform. From this example, it is possible to obtain stable photoluminescence with high luminance by excitation light by dispersing in a host and emitting a copper complex, and the copper binuclear complex of the present invention is useful for a photoluminescence device having an excitation light source. Clarified that there is.

<Example 2>
In this example, an organic EL element was created using a copper complex.

The element configuration is shown in FIG. The element configuration is
ITO / PEDOT (30 nm) / light emitting layer (100 nm) / Cs ₂ CO ₃ (2 nm) / Al (70 nm)
It is. PEDOT was AI1083 manufactured by Baytron.

  For the light emitting layer, a mixed host material of PVK and PBD was mixed with a copper complex. Here, the copper complex is Exemplified Compound 005 (X = Br). PVK is a hole transport property, and PBD is an electron transport property. Therefore, by mixing these to form a light emitting layer, electrons and holes can be efficiently injected into the light emitting layer when a voltage is applied. As for the mixing ratio of these materials in the light emitting layer, the mixing weight ratio of the mixed host material was PVK: PBD = 7: 3. Devices having light-emitting layers in which Example Compound 005 (X = Br) was mixed at a ratio of 3% by weight, 5% by weight, and 10% by weight to the mixed host material were respectively prepared.

For device preparation, first, PEDOT was spin-coated on ITO at 4000 rotations / minute (60 seconds) and dried at 200 ° C. for 10 minutes. Next, a mixed solution of orthodichlorobenzene in which 3% by weight, 5% by weight and 10% by weight of the exemplified compound 005 (X = Br) is added to the mixed host material (mixing weight ratio is PVK: PBD = 7: 3). Was adjusted respectively. Each of these solutions was spin-coated on PEDOT at 1000 revolutions / minute (60 seconds) and dried at 70 ° C. for 30 minutes. Then, set the substrate in a vacuum deposition apparatus, and vapor deposition are continuously Cs ₂ CO ₃ and aluminum.

  The electroluminescence (EL) characteristic at the time of voltage application in these elements was evaluated. First, FIG. 5 shows EL spectra in which the concentration of the copper complex (Exemplary Compound 005 (X = Br)) is 3 wt%, 5 wt%, and 10 wt%. In FIG. 5, the light emission band near 420 nm is derived from PVK, and the light emission band near 550 nm is light emission derived from the exemplary compound 005 (X = Br). It can be seen that the higher the concentration of the exemplified compound 005 (X = Br), the stronger the emission intensity of the exemplified compound 005 (X = Br) relative to the emission intensity of PVK.

  From this emission spectrum, by changing the concentration of the copper complex, the ratio of emission from the host material and the copper complex can be changed, and the emission color due to the color mixture can be changed. Further, white light emission can be obtained by appropriately selecting the ratio of the copper complex.

  FIG. 6 shows a voltage-luminance curve and a current-power efficiency curve when the copper complex doping concentrations are 5% and 10%. There is no significant difference between these properties at concentrations of 5% and 10%. The EL luminous efficiency was 0.7 lm / (5%) 0.4 lm / W (10%) at maximum. From this result, it turned out that the copper binuclear complex of this invention is useful as a light emission dopant of an organic EL element.

It is a figure which shows the emission spectrum of exemplary compound 001 thru | or 006. It is a figure which shows an example of the element structure of the organic LED element of this invention. It is a figure which shows an example of a structure of the photo-luminescence element of this invention. It is a figure which shows the emission spectrum of the photo-luminescence element manufactured in the Example. It is a figure which shows the emission spectrum of the organic EL element manufactured in the Example. It is a figure which shows the voltage-luminance curve of the organic EL element manufactured in the Example, and a current-power efficiency curve.

Claims (4)

A light-emitting element using a copper binuclear complex represented by the following general formula (1) as a light-emitting material.

[However, the ligand A is selected from pyridine derivatives containing nitrogen as a coordinating atom, and they may have a substituent. The substituent is selected from an alkyl group, an alkoxyl group, a phenyl group, a benzyl group, a benzoyl group, a dialkylamino group, and a carboxyl group.
X is a halogen atom and is selected from Cl, Br or I.
PR ₃ is a tertiary phosphine in which P is a coordination atom, and is selected from those shown in the following structural formula (2).

However, in the structural formula (2), the hydrogen atom of the phenyl group may be substituted with a halogen atom or a branched or straight chain alkyl group or alkoxyl group having 6 or less carbon atoms.
R ₂ and R ₃ are linear, branched or cyclic alkyl groups having 6 or less carbon atoms. ] The light emitting device according to claim 1, wherein the ligand A is selected from compounds represented by the following structural formula (3).

  A light-emitting layer, the light-emitting layer is formed of a mixture of a light-emitting dopant and a host material, the copper binuclear complex represented by the general formula (1) is used as the light-emitting dopant, and an organic compound is used as the host material. The light emitting device according to claim 1, wherein the light emitting device is characterized in that   The light emitting device according to claim 3, wherein the light emitting dopant and the host material emit light simultaneously to obtain mixed light emission.

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