JP2011153239A - Luminescent material for organic el, and organic el element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a luminescent material having high light emission efficiency and a long light emission life that is used for an organic EL element. <P>SOLUTION: The luminescent material for organic EL is a metal salen complex compound, for example, a N, N'-bis(salicylidene)ethylenediamine metal complex represented by the formula below, wherein the metal M is Fe, Cr, Mn, Co, Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, Pt, Nd, Sm, Eu or Gd. The metal salen complex of which M is iron emits phosphorescence and gives a blue organic EL element by being doped to the luminescent layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

 The present invention relates to a light emitting material for organic EL, and more particularly to a metal complex that emits blue phosphorescence, and more particularly to a metal salen complex.

 In recent years, a light emitting element and a display device using a light emission principle by organic electroluminescence (Organic Electro-Luminescence: organic EL) have been attracting attention.

  The main part of the organic EL element is a light emitting layer, and light emitting materials used for the light emitting layer are roughly classified into high molecular weight materials and low molecular weight materials. A material using polymer molecules is a high molecular material, and a material using other molecules is a low molecular material.

  It has been screamed that large-sized organic EL devices can be manufactured at low cost by using printing technology using polymer materials as inks. However, the life of polymer materials is difficult, and currently, low molecular materials are generally used. In particular, it is used as a light emitting material.

  Low molecular weight materials have been thinned and laminated by vacuum deposition, and light emitting devices using this as a light emitting layer have been put into practical use. Low molecular materials are roughly classified into fluorescent materials and phosphorescent materials. Fluorescent materials are materials that use singlet light emission, and are excellent in cost, life, durability, film formability, etc. for all three primary colors of red, green, and blue.

  On the other hand, a phosphorescent material is a material using triplet light emission, and has a sufficiently higher light emission efficiency than a fluorescent material, but has a difficulty in life, a decrease in efficiency when current is increased, difficulty in purification, and heat resistance. In particular, blue materials are not yet in practical use. Examples of blue phosphorus materials include platinum complexes described in, for example, JP 2006-232784, JP 2008-37848, and JP 2007-9009.

JP 2006-232784 JP 2008-37848 A Japanese Unexamined Patent Publication No. 2007-9009

  With respect to blue light emission in organic EL, it is a major issue to further improve the light emission efficiency of the light emitting material and to extend the life of the light emitting material. Further, limited materials such as iridium and platinum complexes are used for the blue light emitting material, and there is a demand for a light emitting material that does not use a rare metal.

  An object of the present invention is to provide a novel light-emitting material in the field of organic EL. Another object of the present invention is to provide a blue light emitting material having high luminous efficiency and a long lifetime. Still another object of the present invention is to provide a blue light emitting material that does not use a rare metal. Still another object of the present invention is to provide an organic EL element and an organic EL device using these light emitting materials.

  In order to achieve the above object, the present invention is a light-emitting material for organic EL comprising a metal-salen complex compound. Suitable examples of the metal-salen complex compound according to the present invention include at least one of the following (I), (II), (III) and (IV).

(I)

N, N'-Bis (salicylidene) ethylenediamine metal

(II)

(III)

(IV)

  M is a transition metal, for example, Fe, Cr, Mn, Co, Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, Pt, Nd, Sm, Eu, or Gd.

  The metal salen complex (M is iron) emits blue phosphorescence.

  Furthermore, the present invention is an organic EL device in which the light emitting layer contains the metal-salen complex.

  The light emitting layer may be a host compound doped with the metal complex as a guest compound. The metal complex is preferably doped with 0.5 atomic weight% or more and 5 atomic weight% or less. An example of the host compound is quinolinol aluminum complex (Alq3).

  Furthermore, this invention is an organic EL light emitting device provided with the said organic EL element, It is characterized by the above-mentioned.

  As described above, according to the present invention, a novel light emitting material can be provided in the field of organic EL. In addition, a blue light-emitting material with high emission efficiency and a long lifetime can be provided. Furthermore, a blue light emitting material that does not use a rare metal can be provided. Furthermore, an organic EL element and an organic EL device using these blue light emitting materials can be provided.

It is a perspective view which concerns on embodiment of the organic EL element concerning this invention. It is a characteristic view which shows the measurement result of the photoluminescence of an iron salen complex. It is a characteristic view which shows the EL spectrum of an organic EL element. It is a characteristic view which shows the 1st measurement result of the IVL characteristic (current voltage illuminance characteristic) of an organic EL element. It is a characteristic view which shows the 2nd measurement result. It is a characteristic view which shows the 3rd measurement result. It is a characteristic view which shows the IVL comparison between the elements in which dope concentrations differ. It is sectional drawing of the light emitting layer which an iron salen complex is doped and achieves blue light emission.

  FIG. 1 is a perspective view of an organic EL element according to the present invention. The organic EL element has a multilayer structure composed of an anode 20, a hole injection layer 18, a hole transport layer 16, a light emitting layer 14, an electron transport layer and an electron injection layer 12, and a cathode 10 in this order from the glass substrate 22. And a sealing layer for sealing them. The arrows in FIG. 1 indicate the direction of light emission by the organic EL.

(1) Substrate In addition to a glass substrate, a plastic substrate is used for the purpose of flexibility. In order to prevent moisture from permeating the substrate, the transparent plastic film has a barrier property.

(2) Anode When light is emitted from the bottom of the substrate, a transparency of 80% or more is required in order to extract the light generated in the element to the outside. In addition, a high work function is required to inject many holes from the anode into the light emitting layer. ITO (Indium Tin Oxide) transparent electrodes are frequently used.

(3) Hole injection layer Holes generated at the anode are injected into the hole transport layer. Polyethylenedioxythiophene (PEDOT: PSS) doped with polystyrene sulfonic acid (PSS) is widely used as the polymer material, and phthalocyanine-based CuPc (copper phthalocyanine) is widely used as the low-molecular material.

(4) Hole transport layer The hole transport layer transports holes injected from the hole injection layer to the light emitting layer. It is necessary to have an appropriate ionization potential and hole mobility, and triphenylamine derivatives are widely used.

(5) Light-Emitting Layer The light-emitting host material and the doping material that is a light-emitting dye function as recombination centers for holes and electrons injected from the anode and the cathode. In addition, doping the luminescent dye into the host material in the luminescent layer obtains high luminous efficiency and converts the emission wavelength.

  The light emitting layer is required to have an appropriate energy level for charge injection, to be excellent in chemical stability and heat resistance, and to be formed of a homogeneous amorphous thin film. In addition, it is required that the type of light emission color and color purity are excellent and that the light emission efficiency is high.

  The light emitting layer is produced by depositing the metal salen complex described above on the hole transport layer or by depositing the metal salen complex together with the host compound on the hole transport layer.

(6) Electron transport layer As the electron transport layer, quinolinol aluminum complex Alq3, oxadiazole derivatives, triazole derivatives, bathophenanthroline derivatives, silole derivatives, and the like are used.

(7) Electron Injection Layer For the same purpose as the hole injection layer, a layer doped with an alkali metal such as Li or Cs is provided at the cathode interface in order to increase electron injection efficiency.

(8) Cathode As the cathode material, an alkaline earth metal or alkali metal, which is a low work function metal, is used so that electrons can be easily injected. A laminated electrode in which Al is deposited on an Al, Mg, Ag co-deposited film, a LiF or Li20 thin film deposited film, or the like is used. In the polymer system, a laminated film of Ca or Ba and Al is used.

(9) Sealing An organic compound or a cathode material may react with moisture or oxygen, which causes dark spots due to oxidation of the cathode material or peeling from the interface with the organic material. In order to prevent this, the element is sealed with a metal sealing can or glass and epoxy. When a metal sealed can is used, the inside of the can is filled with dry nitrogen or a desiccant (getter) is sealed.

(1) Synthesis of metal salen complex (iron salen complex)

Iron salen complex




Complex A


Step 1:

  A mixture of 4-nitrophenol (25 g, 0.18 mol), hexamethylene tetramine (25 g, 0.18 mol), and polyphosphoric acid (200 ml) was stirred at 100 ° C. for 1 hour. The mixture was then taken up in 500 ml ethyl acetate and 1 L water and stirred until completely dissolved. When 400 ml of ethyl acetate was added to the solution, the solution was separated into two phases, the water phase was removed, and the remaining compound was washed twice with a salt solvent and dried over anhydrous MgSO4. , Compound 2 could be synthesized in an amount of 17 g (yield 57%).

Step 2:

Compound 2 (17 g, 0.10 mol) Compound 2 (17 g, 0.10 mol), acetic anhydride (200 ml) and H ₂ SO ₄ (a little) were stirred at room temperature for 1 hour. The resulting solution was hydrolyzed by mixing in ice water (2 L) for 0.5 hour. The obtained solution was filtered and dried in the air to obtain a white powder. When the powder was recrystallized using a solution containing ethyl acetate, 24 g of Compound 3 (yield 76%) of white crystals could be obtained.

Step 3:

  Compound 3 (24 g, 77 mmol and a mixture of carbon (2.4 g) supporting 10% palladium in methanol (500 ml) was reduced overnight in a hydrogen reducing atmosphere at 1.5 atmospheres. Compound 4 (21g) was synthesized.

Step 4, 5:

  Compound 4 (21 g, 75 mmol) and di (tert-butyl) dicarbonate (18 g, 82 mmol) were stirred in anhydrous dichloromethane (DCM) (200 ml) overnight in a nitrogen atmosphere. The resulting solution was evaporated in vacuo and then dissolved with methanol (100 ml). Thereafter, sodium hydroxide (15 g, 374 mmol) and water (50 ml) were added and refluxed for 5 hours. Thereafter, the mixture was cooled, filtered through a filter, washed with water, and then dried in vacuo to obtain a brown compound. The obtained compound was subjected to flash chromatography using silica gel twice to obtain 10 g of compound 6 (yield 58%).

Step 6:

  Compound 6 (10 g, 42 mmol) was placed in 400 ml of absolute ethanol, refluxed with heating, and ethylenediamine (1.3 g, 21 mmol) was added to 20 ml of absolute ethanol with stirring for several hours with a few drops. The mixed solution was cooled in an ice container and stirred for 15 minutes. Thereafter, it was washed with 200 ml of ethanol, filtered, and dried under vacuum. Compound 7 was synthesized in 8.5 g (yield 82%).

Step 7:

Compound 7 (8.2 g, 16 mmol) and triethylamine (22 ml, 160 mmol) in anhydrous methanol (50 ml) were added, and a solution of FeCl ₃ (2.7 g, 16 mmol) in 10 ml methanol was mixed under a nitrogen atmosphere. . When mixed for 1 hour in a nitrogen atmosphere at room temperature, a brown compound was obtained. Then, it was dried in vacuum. The obtained compound was diluted with 400 ml of dichloromethane, washed twice with a salt solution, dried with Na2SO4, and dried in vacuo to obtain complex A. The obtained compound was recrystallized in a solution of diethyl ether and paraffin and measured by high performance liquefaction chromatography to obtain 5.7 g of complex A (iron-salen complex) having a purity of 95% or more (yield 62%).

Similarly, the synthesis of the compound of formula (II) is performed by Khairul I. Ansari, James D. Grant, Getachew A. Woldemarian, Sahba Kasiri and Subhrangsu S. Mandal, 'Iron (III) -salen complexes wigth less DNA cleavage activity exhibitor. more efficient apoptosis in MCF7 cells ', Org. Biomol. Chem. 7 (2009) 926-932, or Sheila M. Crawford,' The ultra-violet and visible spectra of some transition metal chelates with N, N'-bis- This is possible by referring to (o-hydroxybenzylidene) ethylenediamine and N, N'-bis- (o-hydroxybenzylidene) -o-phenylenediamine and related compounds', Spectrochimica Acta, 19 (1963) 255-270.

Furthermore, the synthesis of the compound of formula (III)
GV Panova, NK Vikulova and VM Potapov, 'Stereochemistry of Four-coordinate Chelate Compounds of Schiff Bases and Their Analogues', Russian Chemical Reviews, 49 (1980) 655-667, Alexander V. Wiznycia, John Desper and Chistopher J. Levy, It is possible by referring to 'Monohelical Iron (II) and Zinc (II) Complexes of a (1R, 2R) -Cyclohexyl Salen Ligand with Benz [a] anthryl Sidearms', Inorganic Chemistry 45 (2006) 10034-10036.

  Furthermore, the synthesis of the compound of formula (IV) is described in GV Panova, NK Vikulova and VM Potapov, 'Stereochemistry of Four-coordinate Chelate Compounds of Schiff Bases and Their Analogues', Russian Chemical Reviews, 49 (1980) 655-667. It is possible by reference.

Luminescence test of iron salen (chemical formula (I))
First, the iron-salen complex was dissolved in a chloroform solution at a concentration of 250 mg / ml. Thereafter, photoluminescence was measured using a SPECBOS1201M apparatus manufactured by JETI of Germany. As shown in FIG. 2, an emission spectrum was observed at a light wavelength of 280 nm to 480 nm as follows. An experiment was conducted to emit light from green to blue by mixing 1% atomic weight and 5% atomic weight with a host compound composed of a quinolinol aluminum complex Alq3 that emits light at 450 nm to 600 nm.

(2) Manufacture of organic EL elements, electrical and optical characteristics evaluation Manufacturing conditions for organic EL devices
The ITO substrate cleaning process was as follows. The ITO cleaning environment was performed in a class 100 clean booth installed in a class 1000 clean room.
As the solvent used for washing, isopropyl alcohol (IPA), an organic alkali aqueous solution, and ultrapure water (18 MΩ, TOC: ˜10 ppb) were used. For cleaning, an ultrasonic washer (frequency used was 40 kHz and 950 kHz) and a UV ozone washer were used.

This was performed by a vacuum deposition method in which the raw material compound was heated and evaporated in a vacuum chamber. The conditions for the vapor deposition process are the degree of vacuum (1-2 × 10 ⁻⁴ Pa).
First, an ITO film was prepared, and 2-TNATA, which is a hole injection layer, was formed to a thickness of 30 nm on the ITO film at a deposition film speed of 0.1 to 0.2 nm / sec. Thereafter, the raw material was changed from 2-TNATA to NPD, and NPD was deposited on the 2-TNATA film as a hole transport layer at a deposition film speed of 0.1 to 0.2 nm / sec. Thereafter, the raw material was changed from NPD to a mixture of Alq3 and iron salen, and a film was formed as a light emitting layer with a film thickness of 30 nm at a vapor deposition film rate of 0.1 to 0.2 nm / sec.

  Next, the raw material was changed to Alq3 alone, and Alq3 was formed as an electron transport layer with a film thickness of 30 nm at a deposition film speed of 0.1 to 0.2 nm / sec. Thereafter, the raw material was changed to LiF, and a film was formed as an electron injection layer at a deposition film thickness rate of 0.01 nm / sec and a film thickness of 0.8 nm. Finally, aluminum was deposited as an electrode material with a film thickness of 150 nm at a deposition film speed of 0.1 to 0.2 nm / sec.

The organic EL structure has the following three patterns.
(1) ITO / 2-TNATA (30nm) / NPD (50nm) / Selenium 0% @ Alq3 (30nm) /
Alq3 (30nm) / LiF (0.8nm) / Al (150nm)
(2) ITO / 2-TNATA (30nm) / NPD (50nm) / iron salen 1% @ Alq3 (30nm) /
Alq3 (30nm) / LiF (0.8nm) / Al (150nm)
(3) ITO / 2-TNATA (30nm) / NPD (50nm) / Salen 5% @ Alq3 (30nm) /
Alq3 (30nm) / LiF (0.8nm) / Al (150nm)
The light emitting area was 2.0 × 2.0 mm ² .

b. Luminescence test Sealed in a glove box (H ₂ O and O ₂ are less than 10 ppm). UV curing was carried out by sticking out a glass sealing can and taking it out of the glow box. The curing temperature was 80 ° C. and the curing time was 3 hours. The desiccant (getter) introduced into the device was a CaO-based Dynic 10 mm square, and the adhesive for sealing was a three-bond UV curable epoxy resin.

  When the optical surface was magnified and observed with a microscope, good light emission without dark spots was obtained with an element having a doping concentration of 0%. In the 1% device, fine dark spots were seen on the entire light emitting surface. Although 5% of the elements were photographed, the light was emitted but the amount of light was not enough to capture a photograph, resulting in a blackout image as follows.

c. EL Spectrum Measurement FIG. 3 shows the EL spectrum (@ 5 mA) in the devices of the structures (1) to (3) produced this time. For the element (3), since the emission intensity was insufficient for the measurement, the drive current was increased to 13 mA, but the intensity was still insufficient and the S / N spectrum was slightly worse. It was also confirmed that the EL spectrum blue-shifted as the doping concentration increased.

d. Evaluation of Current / Voltage / Luminance (IVL) Characteristics IVL characteristics (current / voltage illuminance characteristics) were measured for the fabricated elements (1) to (3). For the measurement of voltage and current, a source measure unit GS610 made by Yokogawa Electric was used. The luminance meter used BM-9 made by Topcon. W32-G610IVL2-R manufactured by System House Sunrise was used as the automatic measurement control software for current, voltage, and brightness. In this time, devices with each structure were prepared for three substrates, and one device having a good light emitting surface was selected for each substrate, and IVL measurement was performed. The evaluation number (N) was set to “3” for each element. The result of (1) is shown in FIG. 4, the result of (2) is shown in FIG. 5, and the result of (6) is shown in FIG.

e. IVL comparison between devices with different doping concentrations (maximum value comparison)
This is shown in FIG. For each graph representing the measurement results of each material, the graph showing the maximum value in the current efficiency-current density characteristics was selected from among the measured values of N = 3.

  As described above, as shown in FIGS. 4 to 7, an organic EL element that emits blue light can be provided by adding an iron-salen complex to Alq3 that is a light-emitting layer.

(3) Life of the organic EL The current, voltage and luminance were measured again after 3 months from the production of the title organic EL, but no deterioration was observed.

(4) Possibility of light emission of other compounds The iron-salen complex of the chemical formula (I) achieves blue light emission as a result of being blue-shifted by doping into the light-emitting layer shown in FIG. For blue shift, HOMO (Highest Occupied Molecular Orbital) is preferably −3.90 eV to −4.50 eV, and LUMO (Lowest Occupied Molecular Orbital) is preferably −3.4 eV to −3.0 eV. Good.

  The chemical formulas (II) to (IV) were examined in the same manner as the compound (I), and it was found that blue organic EL light emission was possible. When HOMO and LUMO of (I), (II), (III), and (IV) were calculated using DMol3 of Accelrys, the results were as follows.

Compound (I)
HOMO -3.991 eV
LUMO -3.320 eV

Compound (II)
HOMO -4.495 eV
LUMO -3.012 eV

Compound (III)
HOMO -4.195 eV
LUMO -3.165 eV

Compound (IV)
HOMO -4.134 eV
LUMO -3.325 eV
Since HOMO and LUMO of the chemical formulas (II), (III), and (IV) satisfy the requirements for blue shift, it was found that they can be used as additives for organic EL as in the chemical formula (I).

Claims (9)

  A light emitting material for organic EL comprising a metal-salen complex compound. The light-emitting material for organic EL according to claim 1, wherein the metal-salen complex combination part is composed of at least one of the following (I), (II), (III) and (IV).

(I)



N, N'-Bis (salicylidene) ethylenediamine metal

(II)



(III)


(IV)




M is Fe, Cr, Mn, Co, Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, Pt, Nd, Sm, Eu, or Gd.   The light emitting material for organic EL according to claim 2, wherein the metal-salen complex (M is iron) emits blue phosphorescence.   The organic electroluminescent element in which a light emitting layer contains the metal salen complex of any one of Claims 1 thru | or 3.   The organic EL device according to claim 4, wherein the light emitting layer is a host compound doped with the metal complex as a guest compound.   The organic EL device according to claim 5, wherein the metal-salen complex is doped with 0.5 atomic weight% or more and 5 atomic weight% or less.   An organic EL light-emitting device comprising the organic EL element according to claim 4.   The light emitting material for organic EL of Claim 1 whose HOMO (Highest Occupied Molecular Orbital) is -3.90 eV --4.50 eV.   The light emitting material for organic EL according to claim 1 or 8, wherein LUMO (Lowest Occupied Molecular Orbital) is -3.4 eV to -3.0 eV.