JP2006024830A - Organic electroluminescent device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL device of high luminescent efficiency having a completely new function which is different from a conventional fluorescent organic compound. <P>SOLUTION: The organic electroluminescence device includes a compound expressed by general formula (1) (wherein R<SP>1</SP>to R<SP>8</SP>shows a hydrogen atom, an alkyl group or an alkenyl group respectively; M shows Pt<SP>4+</SP>, In<SP>3+</SP>or Pd<SP>4+</SP>, X shows a monovalent or a bivalent anion, and n shows a number of 0 to 2). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescence element (hereinafter referred to as an organic EL element) having extremely high luminous efficiency and high energy efficiency.

An organic EL element is basically an element that excites and emits light by applying an electric field to a fluorescent organic compound. Display element, display, backlight, electrophotography, illumination light source, exposure light source, reading light source, sign, signboard Applications are being made in fields such as interiors.
Examples of the fluorescent organic compound used as the organic EL element material include poly (p-phenylene vinylene), starburst molecules, metal phthalocyanine complexes, polyaniline, and carbazole polymers (Patent Documents 1 and 2). As compounds that emit phosphorescence instead of fluorescence, iridium complexes having various aryl rings or heteroaryl rings (Patent Document 3) are known.
JP 2000-344777 A JP 2000-344873 A JP 2001-247859 A

However, these conventional fluorescent or phosphorescent organic compounds have a problem that the light emission efficiency is not sufficient at a current density at which a light emission intensity that can withstand practical use can be obtained due to a fundamental problem regarding the excitation efficiency of the compound. .
Accordingly, an object of the present invention is to provide an organic EL element having a completely new function different from conventional fluorescent organic compounds and having high luminous efficiency.

Therefore, the present inventor reexamined the light emission mechanism of the organic EL element. That is, in the organic EL, carriers (electrons and holes) are injected into the luminescent material from both positive and negative electrodes to generate an excited luminescent material (exciton) and emit light.
The problem in this case is the excited state of the exciton. Normally, when a luminescent substance is excited by light irradiation, theoretically, 100% of the generated excitons are in an excited singlet state. However, in the case of carrier injection type electroluminescence, only 25% of the generated excitons are excited to the excited singlet state, and the remaining 75% are excited to the excited triplet state. It has been broken. Therefore, if only the excitation efficiency is considered, the energy utilization efficiency is higher when using phosphorescence emitted from the excited triplet state than when using fluorescence emitted from the excited singlet. Conceivable. Actually, in a green light emitting device using an iridium complex which is a phosphorescent compound, an external quantum efficiency of 19.5% has been reported, suggesting the superiority of phosphorescent materials.
However, phosphorescence, which is a forbidden transition, generally has a quantum yield that is often not very high, and the lifetime of the excited triplet state is also long. For this reason, energy deactivation is likely to occur due to saturation of the excited state or interaction with the exciton of the excited triplet state (triplet-triplet annihilation).
Some compounds cause the phosphorescence intensity to decrease due to heat. When such a material is used, the luminous efficiency of the organic EL element, in which the heat generation of the device cannot be avoided, is further reduced.
For these reasons, particularly in an organic EL element using a red phosphorescent material, a significant decrease in light emission efficiency called Roll-off is caused with an increase in current density. Actually, the organic EL devices using the red phosphorescent material reported so far show an external quantum efficiency of 7% to 8%, which is slightly higher than the theoretical value of 5% of the fluorescent material in the low current density region. However, in the current density region where the emission intensity that can withstand practical use is obtained, the external quantum efficiency is reduced to about 2%, which is about a quarter.

As a result of further verifying the light emission mechanism in the light emitting material, the present inventors have conceived an organic EL element using a material exhibiting delayed fluorescence. Certain types of fluorescent substances, after energy transition to the excited triplet state due to crossing between systems, etc., are then crossed back to the excited singlet state due to triplet-triplet annihilation or absorption of thermal energy, and emit fluorescence. To do. In organic EL, the latter material that exhibits thermally activated delayed fluorescence is considered to be particularly useful.
As described above, the existence ratios of the excited singlet state and the excited triplet state of excitons generated in the organic EL element are said to be 25% and 75%, respectively. Here, when a delayed fluorescent material is used for the organic EL element, excitons in the excited singlet state emit fluorescence as usual. On the other hand, excitons in the excited triplet state absorb the energy of other triplet excitons or the heat generated by the device and cross the system to the excited singlet to emit fluorescence. That is, by absorbing energy such as heat after carrier injection, it is possible to increase the ratio of the compound in an excited singlet state, which normally generated only 25%, to 25% or more. In particular, the latter thermally activated delayed fluorescence phenomenon is expected to appear more prominently in a high current density region where the calorific value of the element increases. However, many delayed fluorescent materials reported so far cannot obtain strong delayed fluorescence unless heat exceeding 100 ° C. is applied, and it has been difficult to use as a luminescent material.
As a result of further investigation, it has been clarified that there exist porphyrin compounds that emit strong fluorescence and delayed fluorescence even at a low temperature of less than 100 ° C. If this porphyrin compound is used, the system crossing from the excited triplet state to the excited singlet state will occur sufficiently by the heat of the device, and delayed fluorescence will be emitted, greatly reducing Roll-off in the high current density region And it discovered that the organic EL element which shows the stable high luminous efficiency in a wide current density area | region was obtained, and came to complete this invention.

  That is, the present invention provides the following general formula (1)

(Wherein R ^{1 to} R ⁸ each represents a hydrogen atom, an alkyl group or an alkenyl group;
M represents Pt ⁴⁺ , In ³⁺ or Pd ⁴⁺ ;
X represents a monovalent or divalent anion;
n represents a number from 0 to 2)
The organic electroluminescent element containing the compound represented by this is provided.

  When the low-temperature delayed fluorescent material of the present invention is used, an organic EL device having a high light emission efficiency in a wide current density region can be obtained with almost no decrease in light emission efficiency accompanying an increase in current density.

The porphyrin compound used in the organic EL device of the present invention has Pt ⁴⁺ , In ³⁺ or Pd ⁴⁺ as a central metal ion. In the general formula (1), the alkyl group represented by R ¹ to R ^8, an alkyl group having 1 to 6 carbon atoms, particularly preferably an alkyl group having 1 to 4 carbon atoms. Specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and an n-butyl group. The alkenyl group is preferably an alkenyl group having 2 to 6 carbon atoms, particularly an alkenyl group having 2 to 4 carbon atoms. Specific examples thereof include a vinyl group and an allyl group.

  The counter ion of the platinum (IV) complex, indium (III) complex or palladium (IV) complex includes chloride ion; fluoride ion; sulfate ion; cyanide ion; C1-C4 such as methyl anion and ethyl anion. An anion such as a phenyl anion.

  These porphyrin compound complexes are obtained by reacting the corresponding porphyrin compound with platinum chloride (IV) acid or a salt thereof, indium chloride (III), hexachloropalladium (IV) acid or a salt thereof, and, if necessary, anion exchange. It can manufacture by performing reaction.

  These porphyrin compound complexes (1) emit fluorescence and delayed fluorescence at a temperature of less than 100 ° C. The temperature condition of delayed fluorescence emission is preferably 90 ° C. or less, more preferably 80 ° C. or less, particularly preferably 0 to 80 ° C., because delayed fluorescence needs to be generated by normal heat generation of the organic EL element device. These porphyrin compound complexes (1) emit fluorescence and delayed fluorescence in the wavelength region of 550 nm to 700 nm. Further, phosphorescence may be emitted in a wavelength region of 650 to 1000 nm.

  Therefore, when the porphyrin compound complex (1) is used as a light emitting material for an organic EL device, an organic EL device with extremely high luminous efficiency can be formed.

  The organic EL device of the present invention is a device in which a light emitting layer containing a porphyrin compound complex (1) or a plurality of organic compound thin films containing the light emitting layer is formed between a pair of electrodes of an anode and a cathode. An injection layer, a hole transport layer, an electron injection layer, an electron transport layer, a protective layer, and the like may be included, and each of these layers may have other functions. Various materials can be used for forming each layer.

  The anode supplies holes to a hole injection layer, a hole transport layer, a light emitting layer, and the like, and a metal, an alloy, a metal oxide, an electrically conductive compound, or a mixture thereof can be used. Is a material having a work function of 4 eV or more.

  As the anode, a layer formed on a soda-lime glass, non-alkali glass, a transparent resin substrate or the like is usually used.

  The cathode supplies electrons to the electron injection layer, the electron transport layer, the light emitting layer, etc., and the adhesion, ionization potential, stability, etc., between the negative electrode and the adjacent layer such as the electron injection layer, electron transport layer, light emitting layer, etc. Selected in consideration of As a material for the cathode, a metal, an alloy, a metal halide, a metal oxide, an electrically conductive compound, or a mixture thereof can be used.

  The material of the hole injection layer and the hole transport layer may be any one having a function of injecting holes from the anode, a function of transporting holes, or a function of blocking electrons injected from the cathode. Good. The material for the electron injection layer and the electron transport layer may be any material having any one of a function of injecting electrons from the cathode, a function of transporting electrons, and a function of blocking holes injected from the anode.

  As a material for the protective layer, any material may be used as long as it has a function of preventing substances that promote device deterioration such as moisture and oxygen from entering the device.

  EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these at all.

Example 1 (Synthesis of octaethylporphyrin-platinum chloride complex (PtCl ₂ OEP) (1))

  In a 100 mL eggplant-shaped flask, 550 mg of octaethylporphyrin (OEP), 1.0 g of chloroplatinic acid hexahydrate, and 0.5 g of lithium carbonate were weighed. To this, 20 mL of N, N-dimethylacetamide was added and refluxed for 3 hours under a nitrogen atmosphere. After confirming the disappearance of the raw material spots by thin layer chromatography, 50 mL of 0.1 M hydrochloric acid aqueous solution was added to the reaction solution, and the precipitated crystals were filtered. The obtained crystals were vacuum-dried to obtain 591 mg of the desired product (yield 72%).

Example 2 (Synthesis of PtCl ₂ OEP (2))
Buchler, Johann W .; Lay, Kiong-Lam; Stoppa, Harald. "Metal complexes with tetrapyrrole ligands.XXIV.Knowledge of platinum (IV) porphyrins." According to 35B (4), 433-438 (Germany), commercially available PtOEP was oxidized with hydrogen peroxide to synthesize the target compound.
From the absorption spectrum and fluorescence spectrum of the obtained compound, it was confirmed that it was the same compound as the compound obtained in Example 1.

Test example 1
The delayed fluorescence spectrum of the porphyrin complex obtained in Example 1 was measured.
(1) Preparation of measurement sample 1 mg of the above porphyrin complex was dissolved in 1 mL of a 10 wt% polyvinyl acetate-tetrahydrofuran solution. Next, 10 μL of the above complex solution was dropped and applied to a glass plate, and then dried by blowing hot air at 160 ° C. In addition, the spot after application | coating and drying was circular, and the diameter was about 1 cm. Using this glass plate, the delayed fluorescence spectrum was measured.

(2) Apparatus and measurement conditions For measurement, an R928 photomultiplier tube and a front surface accessory were attached to a Perkin Elmer LS55 type luminescence spectrophotometer. The spectrum was measured in a phosphorescence measurement mode (Delay = 1 ms, Gate = 1 ms) with an excitation-side slit width of 15 nm and a detection-side slit width of 20 nm.
The excitation spectrum (dotted line) and delayed fluorescence spectrum (solid line) of the obtained PtCl ₂ OEP are shown in FIG.

(3) Results As shown in FIG. 1, a strong delayed fluorescence spectrum was observed in the porphyrin complex (1) at a wavelength of 520 to 750 nm at room temperature (25 ° C.).
Further, when the temperature of the glass plate was changed from room temperature to 80 ° C. using a resistance heating type hot plate under the irradiation of ultraviolet rays having a wavelength of 365 nm, an increase in fluorescence intensity was confirmed visually.

Is a diagram showing the delayed fluorescence spectra of PtCl ₂ OEP. Dotted line: excitation spectrum, solid line: delayed fluorescence spectrum (550 to 650 nm) at an excitation wavelength of 407 nm.

Claims (2)

The following general formula (1)

(Wherein R ^{1 to} R ⁸ each represents a hydrogen atom, an alkyl group or an alkenyl group;
M represents Pt ⁴⁺ , In ³⁺ or Pd ⁴⁺ ;
X represents a monovalent or divalent anion;
n represents a number from 0 to 2)
The organic electroluminescent element containing the compound represented by these.   The organic electroluminescence device according to claim 1, wherein the compound represented by the general formula (1) emits fluorescence and delayed fluorescence at a temperature of less than 100 ° C.

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