JP4610918B2 - Compounds having an oxadiazole ring structure substituted with a pyridyl group - Google Patents

Description

The present invention relates to a compound suitable for an organic electroluminescence (EL) element which is a self-luminous element suitable for various display devices, and more specifically, an oxadiazol ring structure substituted with a plurality of linked pyridyl groups. It is related with the compound which has this.

  Since organic EL elements are self-luminous elements, they have been actively researched because they are brighter and more visible than liquid crystal elements and can be clearly displayed.

In 1987, Eastman Kodak's C.I. W. Tang et al. Have made a practical organic EL device using an organic material by developing a laminated structure device in which various roles are assigned to each material. They laminate a phosphor capable of transporting electrons and an organic substance capable of transporting holes, and inject both charges into the phosphor layer to emit light. High luminance of 1000 cd / m 2 or more can be obtained (for example, see Patent Document 1 and Patent Document 2).

JP-A-8-48656 Japanese Patent No. 3194657

  To date, many improvements have been made for practical application of organic EL devices, and various roles have been further subdivided, and sequentially on the substrate, anode, hole injection layer, hole transport layer, light emitting layer, electron transport High efficiency and durability are achieved by an electroluminescent element provided with a layer, an electron injection layer, and a cathode (see, for example, Non-Patent Document 1).

[Non-Patent Document 1] The 9th Seminar of the Japan Society of Applied Physics 55-61 (2001)

  Further, the use of triplet excitons has been attempted for the purpose of further improving the luminous efficiency, and the use of phosphorescent emitters has been studied (for example, see Non-Patent Document 2).

[Non-Patent Document 2] Proceedings of the 9th Workshop of the Japan Society of Applied Physics 23-31 (2001)

The light emitting layer can also be manufactured by doping a phosphor or a phosphorescent light emitter with a charge transporting compound generally called a host material. As described in the above seminar proceedings collection, the selection of an organic material in an organic EL element greatly affects various characteristics such as efficiency and durability of the element.

In the organic EL element, the light injected from both electrodes is recombined in the light emitting layer to obtain light emission. However, since the hole moving speed is faster than the electron moving speed, some of the holes pass through the light emitting layer. There is a problem of efficiency reduction due to passing through. Therefore, an electron transport material having a high electron moving speed is demanded.

Tris (8-hydroxyquinoline) aluminum (hereinafter abbreviated as Alq), which is a typical luminescent material, is generally used as an electron transporting material, but is said to have a low electron moving speed. Therefore, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (hereinafter abbreviated as PBD) has been proposed as a material having a high moving speed. (For example, refer nonpatent literature 3).

Jpn. J. et al. Appl. Phys. , 27, L269 (1988)

However, it has been pointed out that PBD is poor in stability in a thin film state because it tends to cause crystallization, and various oxadiazole derivatives have been proposed (see, for example, Patent Documents 3, 4, and 5).

Japanese Patent No. 2721442 Japanese Patent No. 3316236 Japanese Patent No. 3486994

In these electron transport materials, the stability compared with PBD is improved, but it is still not sufficient, and the electron transfer rate is still insufficient from the viewpoint of balance with the hole transfer rate. . For this reason, Alq having good stability is often used as an electron transport material, but satisfactory device characteristics have not been obtained.

In addition, there is a method of inserting a hole blocking layer as a measure for preventing a part of holes from passing through the light emitting layer and improving the probability of charge recombination in the light emitting layer. As a hole blocking material, triazole derivatives (for example, see Patent Document 6), bathocuproine (hereinafter abbreviated as BCP), aluminum mixed ligand complex (BAlq) (for example, see Non-Patent Document 2). Etc. have been proposed.

Japanese Patent No. 2734341

However, any of the materials has insufficient film stability or insufficient function of blocking holes. Although the hole blocking material generally used at present is BCP, it cannot be said that it is a sufficiently stable material, so it cannot be said that it functions sufficiently as a hole blocking layer, and has satisfactory device characteristics. It was not obtained.

In order to improve the device characteristics of an organic EL device, an organic compound having excellent electron transport performance and hole blocking capability and high stability in a thin film state is required.

An object of the present invention is an organic compound having excellent characteristics of excellent electron transport performance, hole blocking ability and high stability in a thin film state as a material for a highly efficient and durable organic EL device Is to provide. The physical properties of such an organic compound include (1) high electron transfer speed, (2) excellent hole blocking ability, and (3) stable thin film state. it can.

Therefore, in order to achieve the above-mentioned object, the present inventors pay attention to the fact that the nitrogen atom of the pyridine ring, which has electron affinity, has the ability to coordinate to the metal, and a plurality of linked pyridine rings are formed. As a result of designing and chemically synthesizing a novel organic compound linked to an oxadiazole ring, experimentally producing various organic EL devices, and intensively evaluating the characteristics of the devices, the present invention has been completed.

That is, the present invention is a compound having an oxadiazole ring structure substituted with a plurality of linked pyridyl groups represented by the general formula (1).

[In the formula, Ar represents an unsubstituted or substituted aromatic hydrocarbon group, an unsubstituted or substituted aromatic heterocyclic group, or an unsubstituted or substituted condensed polycyclic aromatic group; R1, R2, R3 , R4 and R5, one of them is a linking group, the other independently represents a hydrogen atom, a fluorine atom, a cyano group, an alkyl group, a trifluoromethyl group, a phenyl group, a tolyl group, a naphthyl group, R6, R7, R8, R9, R10, two of them are bonding groups, and the others are each independently a hydrogen atom, fluorine atom, cyano group, alkyl group, trifluoromethyl group, phenyl group, tolyl group, A naphthyl group is represented, m represents an integer of 1 to 3, and n represents an integer of 1 to 4. ]

Moreover, this invention is a compound for organic electroluminescent elements which has the oxadiazole ring structure substituted by the some connected pyridyl group represented by General formula (1).

  Specific examples of the aromatic hydrocarbon group, aromatic heterocyclic group, and condensed polycyclic aromatic group that are the group Ar in the general formula (1) include the following groups. Phenyl group, biphenylyl group, terphenyl group, tetrakisphenyl group, styryl group, naphthyl group, anthryl group, acenaphthenyl group, fluorenyl group, phenanthryl group, indenyl group, pyrenyl group, pyridyl group, pyrimidyl group, furanyl group, pyronyl group, Thiophenyl group, quinolyl group, benzofuranyl group, benzothiophenyl group, indolyl group, carbazolyl group, benzoxazolyl group, quinoxalyl group, benzimidazolyl group, pyrazolyl group, dibenzofuranyl group, dibenzothiophenyl group.

Specific examples of the substituent for the ring of these groups Ar include the following. Fluorine atom, chlorine atom, cyano group, hydroxyl group, nitro group, alkyl group, alkoxy group, amino group, substituted amino group, trifluoromethyl group, phenyl group, tolyl group, naphthyl group, aralkyl group.

  Specific examples of the linked pyridyl group in the general formula (1) include a dipyridyl group and a terpyridyl group.

  The organic compound having an oxadiazole ring structure substituted with a plurality of linked pyridyl groups of the present invention has faster electron transfer than conventional electron transport materials, excellent hole blocking ability, and a thin film state. Is stable. As a result, it is clear that an organic EL element with high efficiency and high durability can be realized.

The present invention is an organic compound having an oxadiazole ring structure substituted with a plurality of linked pyridyl groups, useful as a constituent material of an electron transport layer, a hole blocking layer, or a light emitting layer of an organic EL device. By using the material of the invention, the light emission efficiency and durability of the conventional organic EL device can be remarkably improved.

The organic compound having an oxadiazole ring structure substituted with a plurality of linked pyridyl groups of the present invention is a novel compound, for example, 6- (2H-tetrazol-5-yl) -2,2 ′. It can be synthesized by condensing bipyridine or the corresponding terpyridine with various chloroformates.

These compounds were purified by column purification, recrystallization with a solvent, or crystallization. The structure of the compound was identified by hydrogen NMR analysis. As physical properties, DSC measurement (Tg) and melting point were measured. The melting point is an index of vapor deposition, and the glass transition point (Tg) is an index of stability in a thin film state.

  The melting point and glass transition point were measured using a differential scanning calorimeter DSC6200 manufactured by Seiko Instruments Inc. using powder.

The work function was measured using an atmospheric photoelectron spectrometer AC2 manufactured by Riken Keiki Co., Ltd. after a 100 nm thin film was formed on the ITO substrate. The work function is an index of hole blocking ability.

The speed of electron transfer of the organic compound having an oxadiazol ring structure substituted with a plurality of linked pyridyl groups of the present invention was deduced by comparing the device characteristics of an actual organic EL device.

The structure of the organic EL device suitable for the compound of the present invention includes, on the substrate, an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode, and an anode, a hole injection layer, a positive electrode. Examples include a hole transport layer, a light emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode. In these multilayer structures, several organic layers can be omitted.

As an anode of the organic EL element, an electrode material having a large work function such as ITO or gold is used. In addition to copper phthalocyanine (hereinafter abbreviated as CuPc), a material such as a starburst type triphenylamine derivative can be used for the hole injection layer. The hole transport layer includes N, N′-diphenyl-N, N′-di (m-tolyl) -benzidine (hereinafter abbreviated as TPD) and N, N′-diphenyl-N, N ′, which are benzidine derivatives. -Di (α-naphthyl) -benzidine (hereinafter abbreviated as NPD), various triphenylamine tetramers, and the like can be used. Also, a coating type polymer material such as PEDOT / PSS can be used for the hole injection / transport layer.

In addition to organic compounds having an oxadiazole ring structure substituted with a plurality of linked pyridyl groups, the light-emitting layer, hole blocking layer, and electron transport layer of organic EL devices are aluminum complexes, styryl derivatives, oxazole derivatives, carbazols. -Lu derivatives and polydialkylfluorene derivatives can be used. Alternatively, a dopant that is a phosphor such as quinacridone, coumarin, or rubrene, or a phosphorescent material such as an iridium complex of phenylpyridine can be used.

As the electron injection layer of the organic EL element, lithium fluoride or the like can be used. As the cathode, an electrode material having a low work function such as an alloy of aluminum and magnesium or silver, such as an aluminum magnesium electrode, is used.

Embodiments of the present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
Synthesis Example 1 Synthesis of 6- (2H-tetrazol-5-yl) -2,2′-bipyridine 10.0 g of 6-cyano-2,2′-bipyridine, 5.4 g of sodium azide, and ammonium chloride in 50 ml of DMF 4.4g was added and it stirred at 100 degreeC for 6 hours. After cooling to room temperature, the reaction solution was poured into 500 ml of 20% aqueous hydrochloric acid solution, and the precipitated white solid was taken out by suction filtration and washed with water. It vacuum-dried at 80 degreeC for 20 hours, and obtained 11.6 g of white powder.

Synthesis Example 2 Synthesis of 1,3-bis [2- (2,2′-bipyridin-6yl) -1,3,4-oxadiazol-5-yl] benzene (hereinafter referred to as BpyOXDm) [ Synthetic Example 1], 0.63 g of tetrazoylbipyridine intermediate was dissolved in 10 ml of dehydrated pyridine, and 0.29 g of isophthaloyl dichloride was slowly added. The mixture was heated to 115 ° C. and stirred under reflux for 6 hours. After cooling to room temperature, the reaction solution was poured into water, and the precipitated white solid was taken out by suction filtration and washed with water. After vacuum drying at 80 ° C. for 20 hours, the obtained solid was purified by column chromatography (carrier: silica gel, eluent: chloroform / methanol = 20/1), and 1,3-bis [2- ( 2,2′-bipyridin-6yl) -1,3,4-oxadiazol-5-yl] benzene, 0.62 g (yield 81%) was obtained.

  The structure of the obtained powder was identified using NMR. 1H-NMR measurement results are shown in FIG.

  The structure was identified by detecting the following 18 hydrogen signals by 1H-NMR (CDCl 3). δ (ppm) = 9.071 (s, 1H), 8.639-8.714 (m, 6H), 8.325-8.477 (m, 4H), 8.037 (t, 2H), 7 .756-7.854 (m, 3H), 7.330 (t, 2H).

[Synthesis Example 3] 1,4-bis [2- (2,2′-bipyridin-6-yl) -1,3,4-oxadiazol-5-yl] benzene (hereinafter abbreviated as BpyOXDp) Synthesis [Synthesis Example 1], an intermediate of 0.67 g of tetrazoylbipyridine, was dissolved in 10 ml of dehydrated pyridine, and 0.32 g of terephthaloyl dichloride was added. The mixture was heated to 110 ° C. and stirred under reflux for 5 hours. After cooling to room temperature, the reaction solution was poured into water, and the precipitated white solid was taken out by suction filtration and washed with water. Vacuum drying at 80 ° C. for 20 hours gave a white crude product. Purification by column chromatography yielded 0.58 g (yield 74%) of the desired product.

  The structure of the obtained powder was identified using NMR. 1H-NMR measurement results are shown in FIG.

The structure was identified by detecting the following 18 hydrogen signals by 1H-NMR (CDCl 3). δ (ppm) = 8.736 (s, 2H), 8.640 (d, 4H), 8.463 (s, 3H), 8.260-8.384 (m, 4HH), 8.060 (t , 2H), 7.932 (s, 2H), 7.380 (d, 1H).

[Synthesis Example 4] 2,6-bis [2- (2,2′-bipyridin-6-yl) -1,3,4-oxadiazol-5-yl] pyridine (hereinafter abbreviated as BpyOXDmPy) Synthesis Intermediate 0.50 g of tetrazoylbipyridine synthesized in [Synthesis Example 1] was dissolved in 10 ml of dehydrated pyridine, and 0.26 g of 2,6-pyridinedicarbonyl dichloride was added. The mixture was heated to 110 ° C. and stirred for 9 hours under reflux. After cooling to room temperature, the reaction solution was poured into water, and the precipitated white solid was taken out by suction filtration and washed with water. Vacuum drying at 80 ° C. for 20 hours gave a white crude product. Purification by column chromatography yielded 0.12 g (yield 24%) of the desired product.

  The structure of the obtained powder was identified using NMR. The result of 1H-NMR measurement is shown in FIG.

The structure was identified by detecting the following 17 hydrogen signals by 1H-NMR (CDCl 3).
δ (ppm) = 8.005-8.648 (m, 13H), 7.667 (t, 2H), 7.256 (d, 2H).

About the compound of this invention, melting | fusing point and glass transition point were calculated | required with the differential scanning calorimetry apparatus (The Seiko Instruments make, DSC6200 type DSC).
Melting point Glass transition point
Compound of Invention Example 2 243 ° C. 106 ° C.
Compound of Invention Example 3 271 ° C. Not observed
Compound of Invention Example 4 253 ° C. 114 ° C.

The compound of the present invention that exhibits a glass transition point exhibits a value of 100 ° C. or higher, and can be deduced that the thin film state is stable.

Using the compound of the present invention, a deposited film having a film thickness of 100 nm was prepared on an ITO substrate, and the work function was measured with an atmospheric photoelectron spectrometer (AC2 type, manufactured by Riken Keiki Co., Ltd.). The compounds of Examples 2, 3, and 4 all had values exceeding the measurement limit of 6.8 eV.

Thus, the compound of the present invention has a clearly deeper work function than the hole transport material, and can be deduced as having a large hole blocking ability.

As shown in FIG. 4, the organic EL element has a hole transport layer 3, a light emitting layer 4, an electron transport layer 5, a cathode (on a glass substrate 1 on which an ITO electrode is previously formed as a transparent anode 2. An aluminum magnesium electrode) 6 was deposited in this order.
The glass substrate 1 on which ITO with a film thickness of 150 nm was formed was cleaned with an organic solvent, and then the surface was cleaned with oxygen plasma treatment. This was attached in a vacuum vapor deposition machine and depressurized to 0.001 Pa or less.

Subsequently, as the hole transport layer 3, TPD was formed to a thickness of about 50 nm at a deposition rate of 6 nm / min. Next, about 20 nm of Alq was formed as the light emitting layer 4 at a deposition rate of 6 nm / min. On this light emitting layer 4, BpyOXDm which is the compound of Example 1 of this invention as the electron carrying layer 5 was formed about 30 nm with the vapor deposition rate of 6 nm / min. The vapor deposition so far was continuously performed without breaking the vacuum. Finally, a cathode vapor deposition mask was inserted, and an MgAg alloy was vapor deposited at a ratio of 10: 1 to about 200 nm to form the cathode 6. The prepared element was stored in a vacuum desiccator, and the characteristics were measured at room temperature in the air.

  The characteristics of the organic EL device of the present invention thus formed are as follows: the applied voltage at which light emission of 100 cd / m 2 is obtained, the light emission luminance when a current of 200 mA / cm 2 is loaded, and the light emission efficiency defined by the light emission luminance / voltage. evaluated.

As a result of applying a direct current voltage to the organic EL element, light emission of 3.7 to 100 cd / m 2 was observed. At 7.8 V, a current of 200 mA / cm 2 flowed, and stable green light emission of 11900 cd / m 2 was obtained. The luminous efficiency at this luminance was as high as 6.0 cd / A.

In the device shown in FIG. 1, the organic EL device was used under the same conditions as in Example 5 in place of BpyOXDm used in Example 7 as the material for the electron transport layer 5 instead of BpyOXDmPy which is the compound of Example 4 of the present invention. It was fabricated and its characteristics were examined. Light emission from 4.0 V to 100 cd / m 2 was observed, and at 8.5 V, a current of 200 mA / cm 2 flowed, and a stable green light emission of 11500 cd / m 2 was obtained. The luminous efficiency at this luminance was as high as 5.8 cd / A.

[Comparative example]
For comparison, the material of the electron transport layer 5 was changed to Alq, an organic EL element was produced under the same conditions as in Example 5, and the characteristics were examined. That is, about 50 nm of Alq3 was formed at a deposition rate of 6 nm / min as the light emitting and electron transporting layers 3 and 4. Emission from 7.2 V to 100 cd / m 2 was observed. At 13.3 V, a current of 200 mA / cm 2 flowed, and a green emission of 9600 cd / m 2 was obtained. The luminous efficiency at this luminance was 4.6 cd / A.

As is clear from these results, the organic EL device using the compound having an oxadiazol ring structure substituted with a plurality of linked pyridyl groups according to the present invention is an Alq used as a general electron transport material. It was found that the device was superior in light emission efficiency as compared with the device using, and further excellent in durability because a significant decrease in driving voltage could be achieved.

In the comparative test described above, a clear decrease in the driving voltage is observed. Therefore, the rate of electron transfer of the organic compound having an oxadiazol ring structure substituted with a plurality of linked pyridyl groups of the present invention is It can be deduced that each stage is faster than Alq, which is an electron transport material.

  The compound having an oxadiazol ring structure substituted with a plurality of linked pyridyl groups of the present invention is excellent as a compound for an organic EL device because it has a high electron transfer rate and a stable thin film state. Luminous efficiency and durability can be remarkably improved by producing an organic EL device using the compound of the present invention. For example, it has become possible to develop home appliances and lighting.

It is a 1H-NMR chart of BpyOXDm. It is a 1H-NMR chart of BpyOXDp. It is a 1H-NMR chart of BpyOXDmPy. 7 is a diagram showing an EL element configuration of Example 7. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Transparent anode 3 Hole transport layer 4 Light emitting layer 5 Electron transport layer 6 Cathode

Claims (6)

A compound having an oxadiazole ring structure substituted with a plurality of linked pyridyl groups represented by the general formula (1).
[In the formula, Ar represents an unsubstituted or substituted aromatic hydrocarbon group, an unsubstituted or substituted aromatic heterocyclic group, or an unsubstituted or substituted condensed polycyclic aromatic group; R1, R2, R3 , R4 and R5, one of them is a linking group, the other independently represents a hydrogen atom, a fluorine atom, a cyano group, an alkyl group, a trifluoromethyl group, a phenyl group, a tolyl group, a naphthyl group, R6, R7, R8, R9, R10, two of them are bonding groups, and the others are each independently a hydrogen atom, fluorine atom, cyano group, alkyl group, trifluoromethyl group, phenyl group, tolyl group, A naphthyl group is represented, m represents an integer of 1 to 3, and n represents an integer of 1 to 4. ]   2. The compound having an oxadiazole ring structure substituted with a pyridyl group according to claim 1, wherein n = 1 in the general formula (1), and a plurality of linked pyridyl groups are dipyridyl groups.   The compound having an oxadiazole ring structure substituted with a pyridyl group according to claim 1, wherein n = 2 in the general formula (1), and a plurality of linked pyridyl groups are terpyridyl groups. The compound for organic electroluminescent elements which has the oxadiazole ring structure substituted by the several linked pyridyl group represented by General formula (1).
[In the formula, Ar represents an unsubstituted or substituted aromatic hydrocarbon group, an unsubstituted or substituted aromatic heterocyclic group, or an unsubstituted or substituted condensed polycyclic aromatic group; R1, R2, R3 , R4 and R5, one of them is a linking group, the other independently represents a hydrogen atom, a fluorine atom, a cyano group, an alkyl group, a trifluoromethyl group, a phenyl group, a tolyl group, a naphthyl group, R6, R7, R8, R9, R10, two of them are bonding groups, and the others are each independently a hydrogen atom, fluorine atom, cyano group, alkyl group, trifluoromethyl group, phenyl group, tolyl group, A naphthyl group is represented, m represents an integer of 1 to 3, and n represents an integer of 1 to 4. ]   The compound for organic electroluminescence devices having an oxadiazole ring structure substituted with a pyridyl group according to claim 4, wherein n = 1 in the general formula (1), and a plurality of linked pyridyl groups are dipyridyl groups.   The compound for organic electroluminescence devices having an oxadiazole ring structure substituted with a pyridyl group according to claim 4, wherein n = 2 in the general formula (1), and a plurality of linked pyridyl groups are terpyridyl groups.