JP2004241374A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an emission-efficient and energy-efficient organic electroluminescent element (organic EL element). <P>SOLUTION: The organic EL element comprises an organic compound that radiates fluorescence and delayed fluorescence at less than 100°C. The above organic compound is a compound that radiates phosphorescence, or a porfyrin compound. The above porfyrin compound is a tin complex or a zinc complex. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescence device (hereinafter, referred to as an organic EL device) 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, and is a display element, a display, a backlight, an electrophotograph, an illumination light source, an exposure light source, a reading light source, a sign, a signboard. It is applied to fields such as interior and interior.
Examples of the fluorescent organic compound used as the organic EL device material include poly (p-phenylenevinylene), starburst molecule, copper phthalocyanine, polyaniline, carbazole-based polymers (Patent Documents 1 and 2), various aryl rings or heteroaryls. An iridium complex having a ring (Patent Document 3) is known.
JP 2000-344777 A JP-A-2000-344873 JP 2001-247859 A

However, these conventional fluorescent organic compounds have a problem that the luminous efficiency is not sufficient due to a fundamental problem concerning the excitation efficiency of the compound.
Accordingly, it is an object of the present invention to provide an organic EL device having a completely new function different from conventional fluorescent organic compounds and having high luminous efficiency.

Therefore, the present inventors 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 the positive and negative electrodes to generate an excited luminescent material (exciton) and emit light.
What matters in this case is the excited state of this exciton. Normally, when a luminescent substance is excited by light irradiation, 100% of the generated excitons are theoretically in an excited singlet state. However, in the case of carrier injection type electroluminescence, only 25% of the generated excitons are excited to an excited singlet state, and the remaining 75% of excitons are excited to an excited triplet state. Has been done. Therefore, simply considering the excitation efficiency alone, it can be seen that using phosphorescence, which is light emission from an excited triplet state, is more efficient in using energy than using fluorescence, which is light emission from an excited singlet. Conceivable. In fact, an external quantum efficiency of 19.5% has been reported for a green light emitting device using an iridium complex which is a phosphorescent compound, suggesting the superiority of the phosphorescent material.
However, phosphorescence, which is a forbidden transition, generally has a quantum yield that is often not so high. It is said that this is because the excited triplet state has a long lifetime, and energy is deactivated due to saturation of the excited state or interaction with an exciton in the excited triplet state (triplet-triplet annihilation). For this reason, in particular, in the case of a red material, the external quantum efficiency reported so far is at most about 7%, slightly exceeding the theoretical value of 5% for a fluorescent material.
In addition, depending on the compound, the emission intensity of phosphorescence is reduced by heat. When such a material is used, in an organic EL element in which heat generation of the device cannot be avoided, the luminous efficiency is further reduced.

As a result of further examining the light emission mechanism of the light emitting material, the present inventors conceived of an organic EL device using a material exhibiting delayed fluorescence. Certain types of fluorescent substances change their energy to the excited triplet state due to intersystem crossing, etc., and then intersect the excited singlet state due to triplet-triplet annihilation or thermal energy absorption, and emit fluorescence. I do. In organic EL, the latter material exhibiting heat-activated delayed fluorescence is considered to be particularly useful.
As described above, the abundance ratio of the excited singlet state and the excited triplet state of the exciton generated in the organic EL element is said to be 25% and 75%, respectively. Here, when a delayed fluorescent material is used for the organic EL element, the exciton in the excited singlet state emits fluorescence as usual. On the other hand, an exciton in an excited triplet state absorbs heat generated by the device, crosses the system to an excited singlet, and emits fluorescence. That is, through the absorption of thermal energy after carrier injection, it is possible to increase the ratio of the compound in the excited singlet state, which usually produces only 25%, to 25% or more. 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 them as luminescent materials.
As a result of further study, it has been clarified that there is a compound that emits strong fluorescence and delayed fluorescence even at a low temperature of less than 100 ° C. When this compound is used, the heat of the device sufficiently causes an intersystem crossing from the excited triplet state to the excited singlet state, and emits delayed fluorescence, so that an organic EL element with significantly improved luminous efficiency can be obtained. And found that the present invention was completed.

  That is, the present invention provides an organic EL device containing an organic compound that emits fluorescence and delayed fluorescence at a temperature lower than 100 ° C.

  By using the low-temperature delayed fluorescent substance of the present invention, an organic EL device having high luminous efficiency can be obtained.

  The compound used as an organic EL device material in the present invention is an organic compound that emits fluorescence and delayed fluorescence at a temperature lower than 100 ° C. (hereinafter, may be referred to as a low-temperature delayed fluorescent substance). The temperature condition of the delayed fluorescence emission is preferably 90 ° C. or less, more preferably 80 ° C. or less, and particularly preferably 0 to 80 ° C., since the delayed fluorescence needs to be generated by normal heat generation of the organic EL device. Further, the low-temperature delayed fluorescent substance may further emit phosphorescence.

  The low-temperature delayed fluorescent substance includes a porphyrin compound. The porphyrin compound is not particularly limited as long as it emits the low-temperature delayed fluorescence described above, but is preferably a tin complex or a zinc complex. In the case of a tin complex, those having a fluoride ion, a sulfate ion, a cyanide ion, an alkyl anion or an aryl anion as a counter ion for neutralizing the electric charge are preferable.

  More preferred porphyrin compounds include the following general formula (1)

(Wherein, R ^{1 to} R ⁸ each represent a hydrogen atom, an alkyl group, an alkenyl group, a carboxyl group, a carboxyalkyl group, a carboxyalkenyl group, an alkoxycarbonylalkyl group, an alkoxycarbonylalkenyl group, a hydroxy group, a hydroxyalkyl group, An alkenyl group, a formyl group, a formylalkyl group, a formylalkenyl group, an alkanoyl group, an alkanoylalkyl group, an alkanoylalkenyl group, a halogen atom, a halogenoalkyl group, a halogenoalkenyl group, or R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ or R ⁷ and R ⁸ may together form an aromatic ring;
R ^{9 to} R ¹² each represent a hydrogen atom, a phenyl group, a halogenophenyl group, a cyanophenyl group, an alkylphenyl group, a sulfonatophenyl group, a carboxyphenyl group, an alkylaminophenyl group, a pyridyl group, or an N-alkylpyridyl group. Show;
M represents Sn ⁴⁺ or Zn ²⁺ ;
X represents a monovalent or divalent anion;
n shows the number of 0-2)
The compound represented by is preferred.

The alkyl group represented by R ^{1 to} R ⁸ is preferably 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 preferably an alkenyl group having 2 to 4 carbon atoms. Specific examples thereof include a vinyl group and an allyl group. As the carboxyalkyl group, a carboxy C _1-6 alkyl group, particularly a carboxy C _1-4 alkyl group, is preferred. Specific examples thereof include a carboxymethyl group, a carboxyethyl group, and a carboxypropyl group. As the carboxyalkenyl group, a carboxy C _2-6 alkenyl group, particularly a carboxy C _2-4 alkenyl group is preferred. Specific examples thereof include a carboxyvinyl group and a carboxyallyl group. The alkoxycarbonyl group, C _1-6 alkoxycarbonyl C _1-6 alkyl group, especially C _1-4 alkoxycarbonyl C _2-4 alkyl group. Specific examples thereof include a methoxycarbonylmethyl group, a methoxycarbonylethyl group, and an ethoxycarbonylethyl group. As the alkoxycarbonylalkenyl group, a C _1-6 alkoxycarbonyl C _2-6 alkenyl group, particularly a C _1-4 alkoxycarbonyl C _2-4 alkenyl group is preferred.

As the hydroxyalkyl group, a hydroxy C _1-6 alkyl group, particularly a hydroxy C _2-4 alkyl group, is preferred. Specific examples thereof include a hydroxyethyl group, a hydroxypropyl group, and a hydroxybutyl group. As the hydroxyalkenyl group, a hydroxy C _2-6 alkenyl group, particularly a hydroxy C _2-4 alkenyl group, is preferred. As the formylalkyl group, a formyl C _2-6 alkyl group, particularly a formyl C _2-4 alkyl group, is preferred. As the alkanoyl group, a C _2-6 alkanoyl group such as an acetyl group and a propionyl group is preferable. As the alkanoylalkyl group, a C _2-6 alkanoyl C _1-6 alkyl group is preferable. As the alkanoylalkenyl group, a C _2-6 alkanoyl C _2-6 alkenyl group is preferable. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. Examples of the halogenoalkyl group include a halogeno C _1-6 alkyl group. Examples of the halogenoalkenyl group include a halogeno C _2-6 alkenyl group.

The aromatic ring formed by R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ or R ⁷ and R ⁸ together includes a benzene ring. When these groups form a benzene ring, the pyrrole ring becomes an indole ring.

As the alkylphenyl group represented by R ^{9 to} R ¹² , a C _1-6 alkylphenyl group is preferable. As the alkylaminophenyl group, a C _1-6 alkylaminophenyl group is preferable. As the N- alkylpyridyl group, N-C _1-6 alkyl pyridyl group are preferable.

Particularly preferred R ^{1 to} R ⁸ include a hydrogen atom, an alkyl group, an alkenyl group, a carboxyalkyl group, a carboxyalkenyl group, an alkoxycarbonylalkyl group, and an alkoxycarbonylalkenyl group. As R ^{9 to} R ¹² , a hydrogen atom is particularly preferable.

  Examples of the counter ion in the case of the tin complex include a fluoride ion; a sulfate ion; a cyanide ion; an alkyl anion having 1 to 4 carbon atoms such as a methyl anion and an ethyl anion; and an aryl anion such as a phenyl anion.

These porphyrin compound complexes can be produced by reacting the corresponding porphyrin compound with tin fluoride, zinc fluoride, tin sulfate, zinc sulfate, or the like.
These porphyrin compound complexes (1) emit fluorescence and delayed fluorescence in a wavelength region of 550 nm to 700 nm. Further, phosphorescent light is emitted in a wavelength region of 650 to 900 nm.

  Therefore, when the low-temperature delayed fluorescent substance is used as a light emitting material of an organic EL device, an organic EL device having 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 low-temperature delayed fluorescent substance or a plurality of organic compound thin films containing the light emitting layer is formed between a pair of anode and cathode electrodes. , A hole transport layer, an electron injection layer, an electron transport layer, a protective layer, and the like, and each of these layers may have another function. Various materials can be used for forming each layer.

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

  As the anode, a layer formed on a soda lime glass, a 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, and the like. The cathode, the adhesion between the negative electrode such as the electron injection layer, the electron transport layer, and the light emitting layer, the ionization potential, and the stability. Is taken into consideration. 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.

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

  As the material of the protective layer, any material may be used as long as it has a function of preventing a substance that promotes element deterioration such as moisture or oxygen from entering the element.

  Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1 (protoporphyrin - Synthesis of tin fluoride complex _{(SnF 2 (Proto lX))} )

  50 mg of protoporphyrin disodium salt and 65 mg of tin (II) fluoride are dissolved in 5 mL of dimethyl sulfoxide, and a complex formation reaction is performed at 160 ° C. for 3 hours. The reaction solution was added dropwise to 50 mL of 1% hydrofluoric acid and stirred for 1 hour. The precipitated crystals were separated by filtration, dispersed in 20 mL of ethyl acetate, and washed under reflux for 1 hour. After cooling to room temperature, the crystals were filtered off and dried again to obtain 25 mg of the above complex.

Example 2 (Synthesis of mesoporphyrin-tin fluoride complex (SnF ₂ (Meso IX)))

  170 mg of mesoporphyrin IX dihydrochloride and 208 mg of tin (II) fluoride were dissolved in 15 mL of dimethyl sulfoxide, and a complex formation reaction was performed at 160 ° C. for 3 hours. The reaction solution was added dropwise to 150 mL of 1% hydrofluoric acid and stirred for 1 hour. The precipitated crystals were separated by filtration, dispersed in 60 mL of ethyl acetate, and washed with reflux for 1 hour. After cooling to room temperature, the crystals were filtered off and dried again to obtain 160 mg of the above complex.

Example 3 (Synthesis of hematoporphyrin-tin fluoride complex (SnF ₂ (Hemato IX)))

  50 mg of hematoporphyrin IX and 65 mg of tin (II) fluoride were dissolved in 5 mL of dimethyl sulfoxide, and a complex formation reaction was performed at 160 ° C. for 3 hours. The reaction solution was added dropwise to 50 mL of 1% hydrofluoric acid and stirred for 1 hour. The precipitated crystals were separated by filtration, dispersed in 20 mL of ethyl acetate, and washed under reflux for 1 hour. After cooling to room temperature, the crystals were filtered off and dried again to obtain 38 mg of the above complex.

Example 4 (Synthesis of Coproporphyrin Tetramethyl Ester-Tin Fluoride Complex (SnF ₂ (Copro III-4Me)))

  50 mg of coproporphyrin III tetramethyl ester and 55 mg of tin (II) fluoride were dissolved in 5 mL of dimethyl sulfoxide, and a complex formation reaction was carried out at 160 ° C. for 3 hours. The reaction solution was added dropwise to 50 mL of 1% hydrofluoric acid and stirred for 1 hour. The precipitated crystals were separated by filtration, dispersed in 20 mL of ethyl acetate, and washed under reflux for 1 hour. After cooling to room temperature, the crystals were filtered off and dried again to obtain 22 mg of the above complex.

Example 5 (Synthesis of octaethylporphyrin-tin fluoride complex (SnF ₂ (OEP)))

  Octaethylporphyrin (50 mg) and tin (II) fluoride (73 mg) were dissolved in dimethyl sulfoxide (5 mL), and a complex formation reaction was performed at 160 ° C. for 3 hours. The reaction solution was added dropwise to 50 mL of 1% hydrofluoric acid and stirred for 1 hour. The precipitated crystals were separated by filtration, dispersed in 20 mL of ethyl acetate, and washed under reflux for 1 hour. After cooling to room temperature, the crystals were filtered off and dried again to obtain 19 mg of the above complex.

Example 6 (Synthesis of Ethioporphyrin-tin Fluoride Complex (SnF ₂ (Etio I)))

  Ethioporphyrin I 100 mg of dihydrobromide and 122 mg of tin (II) fluoride were dissolved in 10 mL of dimethyl sulfoxide, and a complex formation reaction was carried out at 160 ° C. for 3 hours. The reaction solution was added dropwise to 100 mL of 1% hydrofluoric acid and stirred for 1 hour. The precipitated crystals were separated by filtration, dispersed in 40 mL of ethyl acetate, and washed under reflux for 1 hour. After cooling to room temperature, the crystals were filtered off and dried again to obtain 55 mg of the above complex.

Test example 1
The delayed fluorescence spectra of the porphyrin complexes obtained in Examples 1 to 6 were measured.
(1) Preparation of measurement sample (filter paper) 1 mg of each of the above porphyrin complexes was dissolved in 1 mL of dimethyl sulfoxide. Then, using a 10 μL micro syringe manufactured by Hamilton, 10 μL of the above-described complex solution was added to No. 1 manufactured by ADVANTEC. The solution was dropped on 5C filter paper, and then dried with hot air at 160 ° C. The spots after dropping and drying were circular, and each had a diameter of about 1 cm. A spot portion of the filter paper was cut out and used for measuring a delayed fluorescence spectrum.
(2) Confirmation of Delayed Fluorescence When the above-mentioned measurement samples were irradiated with ultraviolet rays (wavelength 365 nm), strong red fluorescence derived from the tin fluoride-porphyrin complex was observed from all the samples. Further, when a hot air at 60 ° C. was blown to these samples under ultraviolet irradiation, a clear increase in the luminescence intensity (approximately 2 to 3 times visually) was observed in all the samples. The results revealed that all of these tin fluoride-porphyrin complexes emit heat-activated delayed fluorescence.
(3) Apparatus and Measurement Conditions For the measurement, an R928 photomultiplier tube was attached to an LS55 luminescence spectrophotometer manufactured by Perkin Elmer. With the excitation-side slit width set to 15 nm and the detection-side slit width set to 20 nm, all spectra were measured in the phosphorescence measurement mode (Delay = 1 ms, Gate = 1 ms).
(4) Results As shown in FIGS. 1 to 6, a strong delayed fluorescence spectrum and a phosphorescent spectrum at a wavelength of 520 to 750 nm were observed at room temperature (25 ° C.) for all porphyrin complexes.

Example 7
Glass in which indium tin oxide (ITO) was deposited to a thickness of about 1600 ° was spin-coated with an aqueous solution of a mixture of poly (ethylenedioxy) thiophene (PEDOT) and polystyrenesulfonic acid (PSS) as a hole injection layer. Next, a dichloromethane solution of a mixture of the compound SnF ₂ (OEP) and polyvinyl carbazole (PVCz) in an amount of 2% by weight was applied as a light emitting material by spin coating. On this polymer thin film, bathocuproine (BCP) was formed as a hole blocking layer by vacuum evaporation at 100 °, and as an electron transport layer, aluminum-8-hydroxyquinoline complex (Alq3) was formed at 400 ° by vacuum evaporation. Finally, a 10% by weight silver-magnesium alloy was co-deposited at 1000 ° as a metal electrode, and then silver was deposited to a thickness of 200 °. When a DC voltage of 12 V was applied to the device obtained by the above operation, a current of 0.1 mA / cm ² flowed, strong red light emission derived from porphyrin having peaks at wavelengths of 570 nm and 623 nm, and a wavelength around 400 nm to 550 nm. , Weak blue emission due to exciplex formation between BCP and PVCz was observed.

SnF is a diagram showing the delayed fluorescence spectra of ₂ (Proto lX). Dotted line: excitation spectrum, solid line: delayed fluorescence spectrum (550-650 nm) and phosphorescence spectrum (650-750 nm) at an excitation wavelength of 407 nm. FIG. 3 is a view showing a delayed fluorescence spectrum of SnF ₂ (MesolX). Dotted line: excitation spectrum, solid line: delayed fluorescence spectrum (520-670 nm) and phosphorescence spectrum (670-750 nm) at an excitation wavelength of 399 nm. SnF is a diagram showing the delayed fluorescence spectra of ₂ (Hemato IX). Dotted line: excitation spectrum, solid line: delayed fluorescence spectrum (520-670 nm) and phosphorescence spectrum (670-750 nm) at an excitation wavelength of 404 nm. FIG. 3 is a view showing a delayed fluorescence spectrum of SnF ₂ (Copro III). Dotted line: excitation spectrum, solid line: delayed fluorescence spectrum (500-670 nm) and phosphorescence spectrum (670-750 nm) at an excitation wavelength of 399 nm. FIG. 3 is a view showing a delayed fluorescence spectrum of SnF ₂ (OEP). Dotted line: excitation spectrum, solid line: delayed fluorescence spectrum (500-670 nm) and phosphorescence spectrum (670-750 nm) at an excitation wavelength of 398 nm. FIG. 3 is a view showing a delayed fluorescence spectrum of SnF ₂ (Etio I). Dotted line: excitation spectrum, solid line: delayed fluorescence spectrum (500-670 nm) and phosphorescence spectrum (670-750 nm) at an excitation wavelength of 398 nm.

Claims (5)

  An organic electroluminescence device comprising an organic compound that emits fluorescence and delayed fluorescence at a temperature of less than 100 ° C.   The organic electroluminescent device according to claim 1, wherein the organic compound emitting fluorescence and delayed fluorescence at a temperature lower than 100 ° C is a compound emitting phosphorescence.   3. The organic electroluminescent device according to claim 1, wherein the organic compound that emits fluorescence and delayed fluorescence at a temperature lower than 100 ° C. is a porphyrin compound.   The organic electroluminescent device according to claim 3, wherein the porphyrin compound is a tin complex or a zinc complex. The porphyrin compound has the following general formula (1)

(Wherein, R ^{1 to} R ⁸ each represent a hydrogen atom, an alkyl group, an alkenyl group, a carboxyl group, a carboxyalkyl group, a carboxyalkenyl group, an alkoxycarbonylalkyl group, an alkoxycarbonylalkenyl group, a hydroxy group, a hydroxyalkyl group, An alkenyl group, a formyl group, a formylalkyl group, a formylalkenyl group, an alkanoyl group, an alkanoylalkyl group, an alkanoylalkenyl group, a halogen atom, a halogenoalkyl group, a halogenoalkenyl group, or R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ or R ⁷ and R ⁸ may together form an aromatic ring;
R ^{9 to} R ¹² each represent a hydrogen atom, a phenyl group, a halogenophenyl group, a cyanophenyl group, an alkylphenyl group, a sulfonatophenyl group, a carboxyphenyl group, an alkylaminophenyl group, a pyridyl group, or an N-alkylpyridyl group. Show;
M represents Sn ⁴⁺ or Zn ²⁺ ;
X represents a monovalent or divalent anion;
n shows the number of 0-2)
The organic electroluminescent device according to claim 3, which is a compound represented by the formula:

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