JP4764047B2 - Light emitting element - Google Patents

Description

  The present invention relates to a light-emitting element using an organic compound, and more particularly to a light-emitting element using a metal coordination compound as a light-emitting material.

  Organic EL devices have been vigorously studied for application as light-emitting devices with high-speed response and high efficiency (Non-Patent Document 1).

  Since the copper coordination compound is inexpensive, it can be produced at a relatively low cost. If the performance of the copper coordination compound is sufficiently extracted, a low-cost and high-performance organic EL device can be obtained.

  Patent Document 1 and Non-Patent Document 2 disclose organic EL elements using a copper coordination compound. However, these EL devices have remarkably low luminous efficiency, the description of the device efficiency is insufficient, and it is unlikely that the properties of the copper coordination compound can be sufficiently extracted, and are sufficient for use in displays and illumination. It is not a thing of the performance. In addition, when the molecular weight of the light emitting material of the copper coordination compound used in Non-Patent Document 2 is 1600 or more, the molecular weight is too large and the sublimation property is poor, and when vacuum deposition is used for device creation, It is unsuitable.

  Non-Patent Documents 3 to 5 disclose copper coordination compounds having the same structure as some of the compounds of the present invention, but there is no description regarding light emission.

  Non-Patent Document 6 describes a trinuclear copper coordination compound, which has light-emitting properties and suggests application to organic LEDs. However, since the binuclear coordination compound has many metal centers, intermetallic bonds, and metal-ligand bonds that cause instability, there may be a problem in the stability of the coordination compound itself. Moreover, although this trinuclear copper coordination compound can be vapor-deposited, the light emitting characteristics (efficiency) and stability of the device are poor.

Japanese Patent No. 2940514 Macromol. Symp. 125,1-48 (1997) Advanced materials 1999 11 No10 p852 Y.A. Ma et al. Journal of Chemical Society Dalton Transaction 1991 p2859 Journal of Chemical Society Dalton Transaction 1983 p1419 Journal of Chemical Society Dalton Transaction 2001 p3069 Journal of American Chemical Society, 2003 125 (40) p12072

  An object of the present invention is to provide a light-emitting element using a light-emitting material having high luminous efficiency, high stability, and low cost.

That is, the light emitting device of the present invention uses a copper coordination compound represented by any one of the following structural formulas as a light emitting material among mononuclear copper coordination compounds having a partial structure represented by the following general formula (1). Features.

[Cu is a copper ion, and PR ₁ R ₂ APR ₁ 'R ₂ ' is a bidentate phosphine ligand.

L ₁ and L _2-carbon, oxygen, phosphorus, sulfur, a ligand and elements of the coordinating atoms selected from halogen, may be the same or different. ]

L ₁ and L ₂ are ligands having an element selected from carbon, nitrogen, oxygen, phosphorus, sulfur, and halogen as a coordination atom, and may be the same or different. ]

  The copper coordination compound used in the present invention is not only high in luminous efficiency, but also suitable for a vacuum coating process, a spin coating process that is applied as a solution, and a coating method that uses an inkjet nozzle. This makes it possible to create a stable element without any damage. Therefore, the light emitting device of the present invention exhibits high light emission efficiency and high stability and can be manufactured at low cost.

  Hereinafter, the present invention will be described in detail.

  First, it demonstrates from the characteristic of the copper coordination compound which is a luminescent material of this invention.

  The copper coordination compound used in the present invention is a mononuclear copper coordination compound having a partial structure represented by the general formula (1), preferably a partial structure represented by the following general formula (2).

[A X ₁ BX ₂ is a bidentate ligand, X ₁ and X ₂ is an atom selected from carbon-containing, oxygen, phosphorus, sulfur, may be the same or different. ]

  In general, in the stability of metal coordination compounds, a process in which bond cleavage occurs and breaks down by the attack of an external small molecule such as oxygen or water on the bond between the central metal or metal-ligand is important. One of the factors. The copper coordination compound of the present invention is a tetracoordinate copper coordination compound, and since the ligand is arranged so as to surround the central metal, the central metal can be three-dimensionally protected. The compound can be stabilized. Furthermore, it is most suitable if it is a mononuclear copper coordination compound in which two bidentate ligands are bonded to a copper atom. The copper coordination compound of the present invention is thermally stable and exhibits high luminous efficiency and is suitable for a light emitting material. In particular, it is characterized in that it emits stronger light than other compounds in the solid powder state.

  In general, there are many compounds that emit light strongly in a dilute solution, but the emission becomes extremely weak in a solid powder state. These are phenomena in which aggregates are formed in the ground state by interaction between luminescent material molecules, or excited aggregates are formed, and the original light emission characteristics cannot be obtained. This is a “concentration quenching” phenomenon. Are known. The copper coordination compound in the present invention can be said to be a light emitting material that is strong against concentration quenching. Therefore, when considering the light-emitting layer in the light-emitting device, concentration quenching is generally avoided by adding a small amount of light-emitting material as a guest material in the host material. However, the copper coordination compound of the present invention has this concentration quenching. Therefore, the concentration can be increased or a 100% light emitting layer can be formed, and a light emitting element having high light emission efficiency and high productivity can be manufactured. In addition, since the concentration dependency of the light emission characteristics is small, production variation and the like can be suppressed, and a light-emitting element with high productivity can be manufactured from this viewpoint.

  It is preferable to use a positive monovalent copper ion as the central metal of the copper coordination compound. Considering the electron arrangement of copper atoms, plus monovalent copper contains 10 d electrons. In general, a transition metal having an even number of d electrons often shows good emission characteristics.

  The vacuum deposition method is generally used as a method for producing an organic LED element because a thin film having a stable and good film quality can be produced. From our experiments, as the molecular weight increases, the sublimation properties drop and this vapor deposition method cannot be used. In our experiments, in order to enable vacuum deposition, the molecular weight of the compound is preferably 1500 or less, and more preferably 1200 or less. In particular, a mononuclear coordination compound can be suppressed in molecular weight as compared with a binuclear coordination compound, and therefore it is generally very advantageous when a vacuum deposition method is used.

  The ligand used for the copper coordination compound of the present invention will be described.

The chemical structural formulas of ligands that can be used in the present invention are listed below. These structural formulas may be used as they are, or they may be used with further substituents. For example, the following structural formula is a condensed ring group, a halogen atom, a linear, branched or cyclic alkyl group (the CH ₂ group of the alkyl group is —O— or —NR— (where R is an alkyl group or substituted) May be substituted with an aromatic ring group), and the H atom may be substituted with an aromatic ring group or a halogen atom), or an aromatic ring group which may have a substituent. May be.

  The ligands shown in Chemical Formulas 3 to 8 are zero-valent phosphine bidentate ligands.

In the ligand represented by Chemical Formula 9, the hydrogen atom of “CH”, “CH ₂ ”, “NH”, “SH” or “OH” shown in the structural formula is extracted, and a minus monovalent bidentate is formed. Become a rank. The coordination atom with respect to the copper atom of these ligands is a carbon atom, a nitrogen atom, a sulfur atom, a phosphorus atom, and an oxygen atom. G12 to G19 can also be converted to zero-valent monodentate ligands by using “NH”, “SH” or “OH” without extracting hydrogen atoms. The coordination atom for the copper atom of these ligands is a phosphorus atom.

  In the ligand represented by Chemical formula 10, H01 to H12 are zero-valent monodentate ligands. The coordination atom for the copper atom of these ligands is a phosphorus atom, a carbon atom and a nitrogen atom. In the ligands represented by H13 to H15, a hydrogen atom of “SH” or “OH” is withdrawn and becomes a monovalent monodentate ligand. The coordination atom with respect to the copper atom of these ligands is a sulfur atom and an oxygen atom. In H16 to H18, the halogen atom acts as a minus monovalent monodentate ligand as it is.

Specific examples of the metal coordination compound of the present invention are shown below (in the table, the bidentate ligand PR ₁ R ₂ APR ₁ 'R ₂ ' is represented as A and X ₁ BX ₂ is represented as B). .

  Tables 1 to 3 show copper coordination compounds having one zero-valent phosphine bidentate ligand and one minus monovalent bidentate ligand, and having an overall valence of zero. Show.

  Tables 4 to 10 have one zero-valent phosphine bidentate ligand, one zero-valent monodentate ligand, and one minus monovalent monodentate ligand. Represents a zero-valent copper coordination compound.

Tables 11 and 12 show copper coordination compounds having two zero-valent phosphine bidentate ligands and having a total monovalence of plus one. In the case of these ionic copper coordination compounds, PF ₆ ⁻ , ClO ₄ ⁻ , BF ₄ ⁻ , halogen ions and the like can be used as counter anions.

  Among the specific examples, the structural formulas of preferred copper coordination compounds are shown below.

According to the study of the present inventor, the exemplified compound 1067 is [Cu (PPh ₂ C ₆ H ₄ PPh ₂ ) PPh ₂ (C ₆ H ₄ O)] having a pseudo tetrahedral structure by X-ray crystal structure analysis. confirmed. The exemplified compound 2073 was also confirmed to be [Cu (PPh ₂ C ₆ H ₄ PPh ₂ ) PPh ₂ (C ₆ H ₄ OH) Cl] having a pseudo tetrahedral structure by X-ray crystal structure analysis.

  In addition, ligands that are monodentate coordinate to the copper atom and those that coordinate to copper in the bidentate are shown, but the bidentate ligand is coordinated to copper compared to the monodentate ligand. The mononuclear tetracoordinate copper coordination compound has a chelate effect (when a multidentate ligand such as a bidentate or a tridentate ligand is coordinated to a metal, a chelate ring is formed, resulting in the stability of the complex. The stability is improved due to the effect of increasing the degree). Furthermore, as shown in Tables 1 to 3, Table 11, and Table 12, mononuclear tetracoordinate copper coordination compounds in which two bidentate ligands are coordinated further increase the stability. preferable.

  Since the light emitting material of the present invention emits light well in a solid, it can be used at a high concentration in the light emitting layer. However, when the coordination compound is composed of the same ligand, the coordination compound is relatively easily crystallized, and when used as a light-emitting element, there is a possibility that problems such as deterioration easily occur. Therefore, crystallization can be suppressed by reducing the symmetry of the molecule. Since the mononuclear tetracoordinate copper coordination compounds shown in Tables 1 to 10 and Table 12 have a plurality of ligands having different structures, the symmetry of the molecular structure is low. Those having such a molecular structure are more desirable for a light-emitting material of an organic LED element because of high amorphousness and low crystallinity.

There are several possibilities for the light emission mechanism of the copper coordination compound of the present invention.
(1) LMCT (ligand-to-metal-charge-transfer) excited state (2) MLCT (metal-to-ligand-charge-transfer) excited state (3) metal center excited state (4) ligand center (ππ ^* ) Excited state

  The following description of light emission is a model for our light emission mechanism. The luminescent minimum excited state of the copper coordination compound of the present invention is caused by LMCT (charge transfer from ligand to metal), particularly when it has only a strong electron donor ligand as typified by a phosphine ligand. The resulting triplet state is expected. Or a metal center excited state is also considered.

In the case of those directly coordinated to a copper atom via an N atom, such as pyridine, pyrazine, pyrimidine, pyridazine, quinoline, and isoquinoline ring, an electron transitions from the ground state to a higher orbital when it enters an excited state. The heterocycle is easy to accept electrons due to electron deficiency. Therefore, the heterocyclic ring often accepts electrons at the time of excitation transition from the copper atom. These ligands having a heterocyclic ring accept electrons from a copper atom during excitation transition. When electrons are transferred from the metal to the ligand during the excitation transition, the excited state is referred to as an MLCT excited state. A ligand center (ππ ^* ) excited state is also conceivable.

  Among the coordination compounds of the present invention, there are those in which an electron-deficient heterocyclic ring such as a pyridine, pyrazine, pyrimidine, pyridazine, quinoline, or isoquinoline ring is directly coordinated to a copper atom via an N atom. In this case, it is necessary to consider the possibility of the above-mentioned several luminescent minimum excited states ((1) to (4)).

  The light emission lifetime of the copper coordination compound of the present invention is 0.1 μs to 100 μs in the solid state, light emitted via the triplet excited state, and delayed fluorescence or phosphorescence.

  For high luminous efficiency, it is important to have a ligand structure that suppresses the structural change between the ground state and the excited state. The copper coordination compound of the present invention is considered to produce strong light emission because the above structural change is suppressed in a solid compared to a solution. This is one reason why the copper coordination compound emits light well in a solid state.

  The aluminum quinolinol derivatives, coumarin derivatives, quinacridone derivatives, and the like that have been used so far can obtain very strong luminescence in a solution, and the strong luminescence properties are maintained as they are even in solid dispersion. This characteristic worked effectively also in the organic EL element, and high luminous efficiency of the element was obtained. However, in the copper coordination compound of the present invention, light emission in a solid is much stronger than light emission in a solution. The present inventors focused on this characteristic and found that the organic EL device is useful for high-efficiency and stable light emission.

  The copper coordination compound of the present invention is useful as a light emitting material for an organic EL device. Needless to say, it has high luminous efficiency, and is also suitable for a vacuum deposition process, a spin coat process in which a solution is applied, and a coating method using an inkjet nozzle.

  Next, the light emitting device of the present invention will be described. In the light emitting device of the present invention, the light emitting material is preferably contained in the light emitting layer.

  The basic structure of the organic EL device of the present invention is shown in FIGS.

  As shown in FIG. 1, the organic EL element is generally composed of a single layer or a plurality of organic film layers sandwiched between a transparent electrode 14 and a metal electrode 11 on a transparent substrate 15.

  FIG. 1A shows the simplest configuration in which the organic layer is composed only of the light emitting layer 12.

  In FIG. 1B and FIG. 1C, the organic layer is composed of two layers, which are composed of the light emitting layer 12, the hole transport layer 13, the light emitting layer 12 and the electron transport layer 16, respectively.

  In FIG. 1D, the organic layer is composed of three layers, and is composed of the hole transport layer 13, the light emitting layer 12, and the electron transport layer 16.

  For the light emitting layer 12, an aluminum quinolinol complex having electron transporting properties and light emitting properties (a typical example is Alq shown below) is used.

  For the light-emitting layer 12, a guest host type in which the light-emitting copper coordination compound of the present invention is mixed in the carrier transport material, a method of using only the light-emitting copper coordination compound at 100%, or the light-emitting copper coordination A compound is a main component, and a small amount of additives (such as a carrier transport material and an anti-crystallization material) can also be added. Furthermore, among the guest host types, two carrier transport materials of electron transport property and hole transport property can be used for the guest, and a luminescent copper coordination compound can be added therein. Therefore, the light emitting layer of the present invention can be composed of a material having one component or two or more components in consideration of performance improvement and productivity.

  For the hole transport layer 13, for example, a triphenylamine derivative (a typical example is αNPD shown below) is mainly used. In the case of a polymer, PVK is used. PVK is mainly hole transportable, and PVK itself exhibits blue EL emission.

  As the electron transport layer 16, for example, an oxadiazole derivative or the like, or Alq, Bphen, or BCP shown below can be used.

<Production Example 1 (Production of Exemplified Compound 1067)>
Under a nitrogen atmosphere, CuCl (100 mg, 1.0 mmol) and toluene (10 ml) were added to a 50 ml flask. To this solution was added 1,2-diphenylphosphinobenzene (450 mg, 1.0 mmol), and the mixture was heated to reflux with stirring for 2 hours. The solution gradually became a yellow suspension. After the produced yellow suspension was filtered, the obtained yellow solid was washed with toluene and hexane in this order, and dried under reduced pressure. This yellow solid is dissolved in a small amount of methylene chloride, and hexane is gently placed on the solution and recrystallized, whereby the following compound (A) [Cu (PPh ₂ C ₆ H ₄ PPh ₂ ) Cl] _{2 is obtained.} Was obtained in a yield of 75% (413 mg).

Compound (A) (110 mg, 0.2 mmol) and toluene (10 ml) were added to a 50 ml flask under a nitrogen atmosphere. PPh ₂ (C ₆ H ₄ OH) (56 mg, 0.2 mmol) was added to this solution and stirred at room temperature for 1 hour. The solution gradually became a homogeneous clear solution. After distilling off the solvent, the obtained white solid was washed with a small amount of hexane, and dried under reduced pressure, whereby exemplary compound 2073 [Cu (PPh ₂ C ₆ H ₄ PPh ₂ ) ClPPh ₂ (C ₆ H ₄ OH) ] Was obtained in a yield of 69% (110 mg).

Exemplified compound 2073 (110 mg, 0.2 mmol) and tetrahydrofuran (10 ml) were added to a 50 ml flask under a nitrogen atmosphere. After cooling this solution to -40 degreeC, the normal butyl lithium-hexane solution (1.6M) was added slowly, and it heated up gradually to room temperature, and stirred for 1 hour. The pale yellow solid obtained by distilling off the solvent of the obtained solution was dissolved in a small amount of methylene chloride, and hexane was gently put on the solution and recrystallized to re-exemplify Exemplified Compound 1067 [Cu (PPh ₂ C ₆ H ₄ PPh ₂ ) PPh ₂ (C ₆ H ₄ O)] was obtained in a yield of 55% (53 mg).

<Production Example 2 (Production of Exemplified Compound 2520)>
Under a nitrogen atmosphere, CuI (190 mg, 1.0 mmol) and toluene (10 ml) were added to a 50 ml flask. To this solution was added 1,2-diphenylphosphinobenzene (450 mg, 1.0 mmol), and the mixture was heated to reflux with stirring for 2 hours. The solution gradually became a yellow suspension. After the produced yellow suspension was filtered, the obtained yellow solid was washed with toluene and hexane in this order, and dried under reduced pressure. This yellow solid was dissolved in a small amount of methylene chloride, and hexane was gently put on the solution, followed by recrystallization, whereby the following compound (B) [Cu (PPh ₂ C ₆ H ₄ PPh ₂ ) I] ₂ In 71% yield (454 mg).

Compound (B) (130 mg, 0.2 mmol) and toluene (10 ml) were added to a 50 ml flask under a nitrogen atmosphere. PPh ₃ (53 mg, 0.2 mmol) was added to this solution and stirred at room temperature for 1 hour. The solution gradually became a homogeneous clear solution. After distilling off the solvent, the obtained white solid was washed with a small amount of hexane, and dried under reduced pressure to obtain Exemplified Compound 2520 [Cu (PPh ₂ C ₆ H ₄ PPh ₂ ) IPPh ₃ ] in a yield of 90% ( 165 mg).

<Production Example 3 (Production of Exemplary Compound 3004)>
Under a nitrogen atmosphere, [Cu (CH ₃ CN) ₄ ] PF ₆ (185 mg, 0.5 mmol) and acetonitrile (10 ml) were added to a 50 ml flask. To this solution was added 1,2-diphenylphosphinobenzene (450 mg, 1.0 mmol), and the mixture was stirred at room temperature for 2 hours. The solid obtained by distilling off the solvent from the obtained reaction solution was recrystallized from chloroform / hexane to give a PF ₆ salt of Exemplary Compound 3004 [Cu (PPh ₂ C ₆ H ₄ PPh ₂ ). ₂ ] (PF ₆ ) was obtained in a yield of 80% (432 mg).

<Luminescent properties of compound>
The emission characteristics in the powder state of the compounds produced in Production Examples 1 to 3 were measured using a Hitachi F4500 fluorometer. The results are shown in Table 13. Each emission spectrum is shown in FIG.

<Example 1>
In this example, an element having three organic layers as shown in FIG. 1D was used as the element structure.

100 nm ITO (transparent electrode 14) was patterned on the glass substrate (transparent substrate 15) so that the opposing electrode area was 3 mm ² . On the ITO substrate, the following organic layer and electrode layer were vacuum-deposited by resistance heating in a vacuum chamber of 10 ⁻⁴ Pa to form a continuous film.
Hole transport layer 13 (40 nm): Compound FL1
Light emitting layer 12 (40 nm): exemplary compound 1067
Electron transport layer 16 (50 nm): BPhen
Metal electrode layer 11-1 (1 nm): KF
Metal electrode layer 11-2 (120nm): Al
The structural formula of compound FL1 is shown below.

<Example 2>
In this example, an element having three organic layers as shown in FIG. 1D was used as the element structure.

  On the ITO substrate produced in the same manner as in Example 1, PEDOT (for organic EL) manufactured by Bayer was applied as a hole transport layer 13 to a film thickness of 40 nm by spin coating at 1000 rpm (20 seconds), and 120 ° C. For 1 hour.

A light emitting layer 12 having a film thickness of 50 nm is formed thereon by spin-coating with the following solution at 2000 rpm for 20 seconds in a nitrogen atmosphere, and dried under the same conditions as those for forming the hole transport layer 13. did.
Dehydrated chlorobenzene: 10g
Polyvinylcarbazole (average molecular weight 9600): 92 mg
Illustrative compound 2520: 8 mg

  This substrate was mounted in a vacuum deposition chamber, and Bphen was deposited as a film having a thickness of 40 nm as the electron transport layer 16.

Next, a cathode (metal electrode 11) having the following configuration was formed.
Metal electrode layer 11-1 (15 nm): AlLi alloy (Li content 1.8 wt%)
Metal electrode layer 11-2 (100 nm): Al
<Element characteristics>
The device characteristics were evaluated by applying a DC voltage with the metal electrode 11 minus and the transparent electrode 14 plus.

  The voltage / current characteristics showed good rectification. The emission spectrum and emission intensity were measured with a spectrum measuring machine SR1 and BM7 manufactured by Topcon Corporation. The current value at the time of voltage application was measured with 4140B manufactured by Hured Packard. The light emission efficiency cd / A was calculated from the light emission luminance and the current measurement value. The results are shown in Table 14.

In Example 1, EL light emission showed good light emission when emitted at 600 cd / cm ² .

  Further, the EL emission spectrum of Example 2 gave a spectrum similar to the emission spectrum of the exemplary compound 2520 shown in FIG. 2 in the solid state, and showed good and stable emission.

It is sectional drawing which shows an example of the light emitting element of this invention. It is a figure which shows the emission spectrum of the exemplary compound manufactured in the Example.

Explanation of symbols

11 Metal electrode 12 Light emitting layer 13 Hole transport layer 14 Transparent electrode 15 Transparent substrate 16 Electron transport layer

Claims (2)

Emitting device characterized by using a copper coordination compound following Ru indicated by any one of structural formulas as the luminescent material.

The light-emitting element according to claim 1, wherein the copper coordination compound is represented by any one of the following structural formulas .

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