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  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
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  • C07D235/02—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, condensed with other rings condensed with carbocyclic rings or ring systems
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  • Y10S428/917—Electroluminescent

Definitions

• the present invention relates to a novel material for electron transportation and emitting layers, and an organic electroluminescent display using the same.
• An electroluminescent display is a luminescent device using electroluminescence of a solid fluorescent material.
• Current practical technology uses an inorganic electroluminescent display with an inorganic material as an illuminant.
• the conventional inorganic electroluminescent display requires a high voltage of 100 V or more for luminescence, and it is difficult for it to emit blue light. As a result, full colorization by the three colors of RGB (red, green, blue) is difficult.
• Organic electroluminescent displays are based on the theory that electrons and holes injected into an organic thin film of small molecules (sublimable molecules) or a polymer by way of an anode and a cathode form an exciton, and light with a specific wavelength is generated when the high-energy exciton returns to its ground states. This effect was first discovered with a single crystal of anthracene by Pope, et al. in 1965 (M. Pope et al., J. Chem.
• the emitting layer (5) can be composed of two or more different molecules to further increase the device efficiency by separating the roles of light emission and transporting both electrons and holes.
• the molecule transporting both holes and electrons is called a host molecule and the other molecule emitting light is called a dopant molecule.
• the emitting layer (5) is composed of a majority of host molecules and small amounts (1 to 20 %) of dopant molecules.
• the requirements of a dopant molecule include high fluorescent or phosphorescent efficiency with proper band structure relative to the host molecule.
• a small amount of fluorescent or phosphorescent dye is doped on the electron transportation layer (6) or on the hole transportation layer (4) to comprise an emitting layer therein without a separate emitting layer (5).
• it is possible to dope more than one layer such as electron transporting, emitting and hole transporting layers to improve the operational stability or to have multiple emissions.
• Organic thin films between two electrodes are formed by vacuum deposition, spin coating, ink jet printing, roll coating, etc. For efficient injection of electrons from the cathode, a separate electron injection layer is often inserted.
• the reason for manufacturing an organic electroluminescent display with a multi-layered thin film structure includes stabilization of the interfaces between the electrodes and the organic layers.
• the mobility of electrons and holes significantly differ, and thus, if appropriate hole transportation and electron transportation layers are used, holes and electrons can be efficiently transferred to the luminescent layer. Also, if the density of the holes and electrons are balanced in the emitting layer, luminescence efficiency can increase.
• the invention is made in consideration and is directed at overcoming the problems of the conventional art electroluminescent displays.
• An object of the invention in part, is to provide a novel material for electron transport and emitting layers that can largely improve luminescence efficiency, stability, and display lifetime of an organic electroluminescent display using the same.
• the invention in part, provides a compound represented by Chemical Formula 1 , a compound represented by Chemical Formula 2, a compound represented by Chemical Formula 3, a compound represented by Chemical
• R 1 and R 2 are independently or simultaneously a hydrogen atom, a C 1-20 aliphatic hydrocarbon, benzene, naphthalene, biphenyl, anthracene, or a group derived from an aromatic heterocycle or an aromatic ring, and R 1 and R 2 cannot simultaneously be hydrogen atoms;
• Ar is benzene, naphthalene, biphenyl, anthracene, or a group derived from an aromatic heterocycle or an aromatic ring;
• R 3 is a hydrogen atom, a C ⁇ o alkyl or aliphatic hydrocarbon, a substituted or unsubstituted benzene, naphthalene, biphenyl, anthracene, or an aromatic heterocycle or aromatic ring;
• R 4 is a hydrogen atom, a C 1-12 alkyl or aliphatic hydrocarbon, benzene, naphthalene, biphenyl, anthracene, or a group derived from an aromatic heterocycle or aromatic ring.
• the invention in part, also provides an organic electroluminescent device having an organic layer containing an organic compound selected from compounds represented by the above Chemical Formula 1 , Chemical
• At least one of the organic layers can be located between an anode that injects holes and a cathode that injects electrons. Also, at least one of the organic layers can be an electron injection/transporting layer performing functions of electron injection and transportation. Further, at least one of the organic layers can be an electron injection/transporting and emitting layer performing functions of electron injection and luminescence. Yet further, at least one of the organic layers can be an electron transportation and emitting layer performing functions of electron transportation and light emission. Also, one of the organic layers can be an emitting layer performing the function of light emission.
• the invention in part, pertains to an organic electroluminescent display having a substrate, an anode over the substrate, a hole injection layer over the anode, a hole transportation layer over the hole injection layer, an emitting layer over the transportation layer, an electron transporting layer over the emitting layer and a cathode over the electron transporting layer; and the organic compound is contained in at least the emitting layer.
• the organic electroluminescent display has a substrate, an anode over the substrate, a hole injection layer over the anode, a hole transportation layer over the hole injection layer, an emitting layer over the hole transportation layer, an electron injecting/transporting layer over the emitting layer, and a cathode over the electron transportation layer; and the organic compound is contained in at least one of the electron injecting/transporting layer.
• Fig. 1 is a cross sectional view showing an example of an organic electroluminescent display.
• Fig. 2 shows the brightness of the device of Example 6 as a function of driving time.
• Fig. 3 shows the brightness of the device of Comparative Example 1 as a function of driving time.
• Fig. 4 shows the brightness of the device of Comparative Example 1 as a function of driving time.
• Fig. 5 shows the voltages of Example 6, Comparative Example 1 and Comparative Example 2 as a function of driving time.
• Fig. 6 shows the brightness of the device of Example 7 as a function of driving time.
• Fig. 7 shows the voltages of Example 7 and Comparative Example 3 as a function of driving time.
• the invention provides a novel material in which 1 to 2 imidazole containing groups are introduced at 2 or 2,6-sites of 9,10 substituted anthracene.
• This material is contained in an organic compound layer of organic electroluminescent (EL) devices to improve luminescence efficiency and lifetime, and an organic electroluminescent devices comprising the same in an organic compound layer.
• EL organic electroluminescent
• Fig. 1 is a cross-sectional view showing an example of the applicable structure of an organic electroluminescent display.
• Reference numeral 1 indicates a substrate, 2 an anode, 3 a hole injection layer, 4 a hole transportation layer, 5 an emitting layer, 6 an electron transportation layer, and 7 a cathode.
• the substrate (1) supports of an organic electroluminescent device, and a silicon wafer, a quartz or glass plate, a metal plate, a plastic film or sheet, etc. can be used. Also, the substrate layer can be a thin protective layer on top of the anode when the device fabrication process starts from the cathode side.
• an anode (2) is located on the substrate (1).
• the anode (2) injects holes into a hole injection layer (3) located thereon.
• a metal such as aluminum, gold, silver, nickel, palladium, platinum, etc., or a material with a large work function such as indium-tin oxide (ITO), indium-zinc oxide (IZO), etc.
• ITO indium-tin oxide
• IZO indium-zinc oxide
• a conductive polymer such as carbon black, polythiophene, polypyrrole, or polyaniline, etc.
• a hole injection layer (3) is located over the anode (2).
• Material for the hole injection layer (3) should have high hole injection efficiency from the anode and should efficiently transport injected holes. For this, the material should have a low ionization potential, high transparency to visible light rays and have superior stability for holes.
• a hole transportation layer (4) is located over the hole injection layer (3).
• the hole transportation layer (4) receives holes from the hole injection layer (3) to transport them to an emitting layer (5) located thereon, and it also has a high hole transportation degree, stability for holes and blocks electrons well.
• heat resistance of the display is required, and a material having a glass transition temperature (Tg) over 70°C is preferable.
• NPD NPB
• NPB N',N-di(1- naphthyl)-N,N'-diphenyl-1 ,1 '-diphenyl-4-4' diamine
• spiro-arylamine compounds perylene-arylamine compounds, azacycloheptatriene compounds, bis(diphenylvinylphenyl)anthracene, silicon-germanium oxide compounds, silicon arylamine compounds, etc.
• an emitting layer (5) is located.
• the emitting layer (5) holes and electrons respectively injected from the anode (2) and a cathode (7) recombine to emit light, and the emitting layer (5) is formed from a material with high quantum efficiency.
• One method to evade such a condition is to dope a fluorescent or phosphorescent material that can accept and transport the problematic carriers instead of the host material.
• Another method is to introduce an excessive amount of the opposite carrier to minimize the chance of having the problematic carrier to attack the neutral host material. Therefore, it is very difficult to produce such conditions while maintaining optimum balancing of both carriers and introducing the proper amount of dopant material to maximize the quantum efficiency. Also, the choice of dopants capable of producing such a condition would be limited. For this reason, it is very important to have emitting material having stabilities to both carriers.
• Materials used for emitting layers include, for green, Alq3; and for blue, Balq (8-hydroxyquinoline beryllium salt), DPVBi (4,4'-bis(2.2- diphenylethyenyl)-1 ,1 '-biphenyl), spiro-DPVBi (spiro-4,4'-bis(2,2- diphenylethyenyl) 1 ,1 '-biphenyl), LiPBO (2-2(-benzoxazoyl)-phenol lithium salt), aluminum-quinoline metal complexes, derivatives of imidazole, thiazole, and oxazole and also their metal complexes, etc.
• Balq 8-hydroxyquinoline beryllium salt
• DPVBi 4,4'-bis(2.2- diphenylethyenyl)-1 ,1 '-biphenyl
• spiro-DPVBi spiro-4,4'-bis(2,2- diphenylethyenyl) 1
• a small amount of perylene and BczVBi (3,3'[(1 ,1 '- biphenyl)-4,4'-diyldi-2,1-ethenediyl]bis(9-ethyl)-9H-carbazole, or DSA (distrylamine), can be doped therein.
• a small amount of material such as DCJTB ([2-(1 ,1-dimethylethyl)-6-[2-(2,3,6,7-tetrahydro-1 , 1 ,7,7- tetramethyl-1 H,5H-benzo(l,j)quinolizin-9-yl)ethenyl]4H-pyran-4-ylidene]- propanedinitrile) is doped on green emitting material.
• the emitting layer is formed by a process such as ink jet printing, roll coating, spin coating, etc., a polypheylenevinylene (PPV) polymer or polyfluorene, etc. can be used for the emitting layer (5).
• PPV polypheylenevinylene
• An electron transportation layer (6) is located over the emitting layer (5).
• the electron transportation layer (6) requires a material that has a high electron injection efficiency from a cathode (7) located thereon and that can efficiently transport the injected electrons. For this, it should be made of a material having a high electron affinity and mobility and superior stability for electrons. Also, the electron transportation layer (6) requires stable interface formation with the cathode material, otherwise delamination of the cathode layer and inefficient electron injection during operation occurs, resulting in a significant voltage increase. A voltage increase due to inefficient electron injection makes the display device less efficient and requires more power consumption.
• doping of the electron transportation layer with conductive metals having low work-functions enhances the electron injection from the cathode and forms a stable interface with metallic cathode layers.
• Materials used for the electron transportation layer include aromatic compounds such as tetraphenyl butadiene, etc. (Japanese Laid Open Patent Publication No. Sho 57-51781); metal complexes such as 8-hydroxyquinoline, etc. (Japanese Laid Open Patent Publication No. Sho 59-194393); metal complexes of 10-hydroxy benzo[h] quinoline (Japanese Laid Open Patent Publication No. Hei 6-322362); cyclopentadiene derivatives (Japanese Laid Open Patent Publication No.
• a cathode (7) is located over the electron transportation layer (6).
• the cathode (7) injects electrons into the electron transportation layer (6).
• a metal having a low work function is preferable.
• an appropriate metal such as tin, magnesium, indium, calcium, sodium, lithium, aluminum, silver, etc., or an appropriate alloy thereof can be used.
• an electrode with a double-layered structure such as lithium fluoride and aluminum, lithium oxide and aluminum, strontium oxide and aluminum, etc. can be used.
• aluminum is known to have a work function of 4.2 eV, which is not low enough for efficient electron injection, a thin layer of insulating material enhances the electron injection by tunneling effect. Also, it is possible to co-deposit the cathodic metals with the electron transporting layer to enhance interfacial strength and electron injection.
• the four layer organic structure located between opposite electrodes can be altered. Adding more organic layers such as a hole-blocking or an electron blocking layer can improve the performance of the organic electroluminescence devices. Also, using less than four layers can simplify device structure.
• At least one organic compound layer comprising the organic compound represented by the above Chemical Formulas 1 to 5 of the invention is located between an anode and a cathode.
• the novel material of the invention is contained in an organic compound layer between an anode and a cathode, preferably an electron, transportation, and emitting layers, thereby largely improving efficiency and device lifetime of an organic electroluminescent device.
• an organic electroluminescent device that lowers operation voltage and has superior stability can be provided.
• a suitable dopant can be added to the material used in the invention to simultaneously perform functions of the electron transportation layer and the emitting layer without a separate emitting layer.
• 5,766,779, 2 to 8 of such hetero functional groups are contained in one molecule that was applied for an electron transportation layer of an organic electroluminescent device.
• U.S. Patent No. 5,645,948 used an organic material comprising 3 to 8 of the same heterofunctional groups in one molecule applied for an emitting layer.
• the invention has 1 to 2 heterofunctional groups are introduced at 2- or 2,6- positions of a 9,10-substituted anthracene moiety for use as a material for electron injection, transportation and light emitting layers.
• TPBI (Chemical Formula 6) was introduced by Kodak Company in 1996 and discussed in U.S. Patent Nos. 5,645,948 and 5,766,779 has been known as a representative material for electron transportation and blue emission.
• TPBI has an imidazole group, and as shown in the following Chemical Formula 6, it contains three N-phenyl benzimidazole groups in 1 ,3,5-substitution sites of benzene and performs functions for transporting electrons or as an emitting layer.
• TPBI has lower operational stability as an electron transporting material as well as an emitting material than the material claimed in the invention, as is shown in the experimental parts the disclosure. (Chemical Formula 6)
• Japanese Laid Open Patent Publication Hei 11-345686 discusses a material for electron transportation disclosed in containing an oxazole group and a thiazole group as shown in the following Chemical Formulas 7 to 10, and it has been reported to be applicable for a luminescence layer. However, if put to practical use, it is not satisfactory in terms of operation voltage, brightness, and life cycle of a display.
• any organic material except an organometal complex such as Alq3 is difficult to practically use for a display.
• the present inventors synthesized a novel organic material represented by the above Chemical Formulas 1 to 5, selected appropriate hole injection and hole transportation, and emitting layers, and then applied it for electron injection and transportation layers. Therefore, they could obtain much superior results in terms of operation voltage, efficiency and lifetime of the display. Also, when the organic material represented by the above Chemical Formulas 1 to 5 is used as an emitting layer with a proper selection of hole injection, hole transportation and electron transporting layers, one could obtain an organic electroluminescent devices with superior operation voltage, and lifetime of the display
• the anthracene moiety used for novel emitting layers by the present inventors had been studied by Kodak Company, TDK, etc. in the U.S. and disclosed in various patents, but the historical origin of this anthracene technology had already begun in the early 1960's. Helfrich and Pope first announced the organic electroluminescence phenomenon using anthracene single crystals, but there was a lot of problems in practical use because the luminescence efficiency was low and a high voltage was required (W. Helfrich, W. G. Schneider, Phys. Rev. Lett. 14, 229, 1965. M. Pope, H. Kallmann, J. Giachino, J. Chem. Phys., 42,2540, 1965).
• anthracene derivatives announced by Kodak Company and TDK, etc. are characterized by only being used for a luminescent layer of an organic electroluminescent device.
• anthracene derivatives disclosed in Japanese Laid Open Patent Publication No. Hei 11 -345686 were asserted to be applicable for a luminescent layer and an electron transportation material, it was only included in the broad claims of the patent, and there was no mention in the Synthesis example or Examples, and so far there have been no examples for practically using it for electron injection and transportation materials.
• Japanese Laid Open Patent Publication No. Hei 11 -345686 is characterized in that two substitution sites of 1 and 5, 1 and 8, or 2 and 6 were used, and the 9, 10 sites were substituted by hydrogen atoms.
• Anthracene has 10 substitution sites, and the present inventors focused on discovering an optimal compound while varying the four substitution sites of 2, 6, 9, 10 of anthracene, which is most characteristic in the present invention.
• aromatic hydrocarbons such as phenyl, naphthyl, biphenyl, etc. were independently or simultaneously substituted.
• imidazole groups were independently or simultaneously substituted, or aromatic hydrocarbons such as phenyl, etc. were substituted, and then imidazole groups were independently or simultaneously substituted to synthesize the material.
• Representative materials of the present invention having electron transporting and emitting capacity are compounds of the following Chemical Formulas 1-1 to 1-10, Chemical Formulas 2-1 to 2-5, Chemical Formulas 3-1 to 3-5, Chemical Formulas 4-1 to 4-5, and Chemical Formulas 5-1 to 5-5.
• the aromatic moiety of the imidazole group can be substituted with groups such as C 1 -C 20 alkyl, alkoxy or aromatic hydrocarbons, substituted or unsubstituted heterocyclic or aromatic groups, or halides such as CI, Br, F or I.
• the imidazole group can have more than one substitution on the benzene ring, and this substitution can have an ortho, meta or para substitution. That is, the imidazole group can be substituted as is shown below:
• R 5 can be C C 20 alkyl, alkoxy or aromatic hydrocarbons, aryl- substituted silicon groups, aryl-substituted boron groups, substituted or unsubstituted heterocyclic or aromatic groups, or halides such as CI, Br, F or I.
• anthracene moiety can be further substituted with additional functional groups, as is shown below:
• R 6 can be C C 20 alkyl, alkoxy or aromatic hydrocarbons, substituted or unsubstituted heterocyclic or aromatic groups, or halides such as CI, Br, F or I.
• Example 5 (6.00 g, 10.1 mmol) was dispersed in 300 mL of acetic acid under a nitrogen atmosphere, and then potassium iodide (16.8 g, 101 mmol) and sodium hypophosphite hydrate (17.7g, 167 mmol) were added, and the mixture was agitated while boiling for 3 hours. After cooling to room temperature, the mixture was filtered and washed with water and methanol, and then vacuum dried to obtain a light yellow compound of the Chemical Formula f (5.0 g, 88%).
• Preparation Example 7 (Preparation of starting material represented by Chemical Formula g) The compound of the Chemical Formula e prepared in Preparation Example 5 (9.5 g, 16 mmol) was dispersed in 100 mL of acetic acid, and 5 drops of concentrated sulfuric acid were added thereto, and the mixture was refluxed for 3 hours. The mixture was cooled to room temperature, and the precipitate was filtered, washed with acetic acid, and then washed with water and ethanol in this order. After drying, the solid was purified by sublimation to obtain a white solid compound of the Chemical Formula g (8.0 g, 89%).
• Example 7 (10.0 g, 17.9 mmol) was completely dissolved in 150 mL of dry
• Example 3 (0.40 g, 0.62 mmol) and 4-formylphenylboronic acid (1.10 g, 7.34 mmol) were added to a solution of 10 mL of 2 N potassium carbonate solution and 30 mL of toluene, and Pd(PPh 3 ) 4 (0.16 g, 0.14 mmol) was added while stirring, and the mixture was refluxed for 3 days.
• the organic layer was separated, washed with water, dried over magnesium sulfate, passed through a silica gel column, and concentrated under reduced pressure.
• the crude product was dispersed in 40 mL of ethanol, filtered, and recrystallized from chloroform to obtain dialdehyde (155 mg, 36%).
• Dialdehyde (120 mg, 0.17 mmol) and N-phenyl-1,2-phenylenediamine (83 mg, 0.45 mmol) were introduced into a solution of 20 ml of toluene and 10 ml of acetic acid. The mixture was refluxed for 2 days, cooled to room temperature, filtered off with suction, and washed with ethanol. The obtained solid was washed with 100 ml of chloroform and dried to obtain a pure compound represented by Chemical Formula 2-2 (120 mg, 68%).
• the analysis result of the compound is as follows:
• Example 9 (4.00 g, 7.85 mmol) and 4-formylphenylboronic acid (3.53 g, 23.5 mmol) were introduced into a solution of 20 mL of 2 N potassium carbonate solution and 60 mL of toluene, Pd(PPh 3 ) 4 (0.27 g, 0.23 mmol) was added while stirring, and the mixture was refluxed for 3 days.
• the organic layer was separated, washed with water, dried over magnesium sulfate, and passed through a silica gel layer, and concentrated to obtain a solid compound.
• the solid was dispersed in 100 mL of ethanol, filtered, and recrystallized from ethyl acetate to obtain anthracene phenylaldehyde (2.00 g,
• dialcohol 4.10 g, 82%.
• a mixture of the dialcohol (4.10 g, 6.59 mmol), potassium iodide (10.9 g, 65.9 mmol), and sodium hypophosphite hydrate (11.6 g, 109 mmol) was refluxed in acetic acid (200 mL) for 24 hours.
• the mixture was cooled to room temperature, filtered, washed with water and petroleum ether in this order, and dried to obtain 2,6-dibromo-9,10-dinaphthalene-2-yl-anthracene (3.15 g, 81%).
• 2,6-Dibromo-9,10-dinaphthalene-2-yl-anthracene (3.15 g, 5.35 mmol) and 4-formylphenylboronic acid (2.81 g, 18.7 mmol) were introduced into a solution of 20 mL of 2 N potassium carbonate solution and 100 mL of toluene, Pd(PPh 3 ) 4 (0.25 g, 0.22 mmol) was introduced while agitating, and the mixture was refluxed for 15 hours. The organic layer was separated, washed with water, dried over magnesium sulfate. Purification by column chromatography yielded dinaphthyl anthracene phenyldialdehyde (2.77 g, 81%).
• the dialcohol (0.70 g, 1.00 mmol) was dispersed in 60 mL of acetic - acid under a nitrogen atmosphere, and potassium iodide (1.66 g, 10 mmol) and sodium hypophosphite hydrate (1.66 g, 15.7 mmol) were added, and then the mixture was agitated while boiling. The mixture was cooled to room temperature, filtered, washed with water and methanol, and dried to obtain a light yellow compound of Chemical Formula 3-2 (0.45 g, 67%).
• the analysis result of the compound is as follows:
• a glass substrate on which ITO (indium tin oxide) was coated in a thin film at a thickness of 1 ,50 ⁇ A was introduced into distilled water in which detergent was dissolved, and it was washed using ultrasonic waves.
• As the detergent a Fischer Co. product was used, and the distilled water was filtered twice with a filter from Millipore Co.
• the ITO was washed for 30 minutes, and ultrasonic cleaning was conducted twice in sequence with distilled water for 10 minutes each time. After washing with distilled water, ultrasonic cleaning was conducted with a solvent such as isopropyl alcohol, acetone, methanol, etc, and the substrate was dried and transferred to a plasma cleaning apparatus. The substrate was then cleaned using oxygen plasma for 5 minutes, and transferred to a vacuum deposition apparatus.
• hexanitrile hexaazatriphenylene was thermal-vacuum deposited with a thickness of 500A to form a hole injection layer.
• NPB which transports holes, was vacuum deposited thereon (600A), and Alq3 that performs a function of the emitting layer was vacuum deposited with a thickness of 300A.
• a compound of the Chemical Formula 1 -4 that performs functions of injecting and transporting electrons, was vacuum deposited with a thickness of 200A to form a thin film of an organic material layer.
• lithium fluoride (LiF) with a thickness of 5A and aluminum with a thickness of 2500A were sequentially deposited to form a cathode using shadow mask to fabricate 6 mm 2 of test pixel.
• the deposition rate of the organic material was maintained at 1 A /sec, that of lithium fluoride was 0.2A /sec, and that of aluminum was 3-7A /sec.
• the half-lifetime of the device was measured by applying 200 mA/cm 2 of constant DC current density.
• the changes of brightness and driving voltage were monitored to evaluate the performance of the claiming compounds relative to the existing compounds.
• the brightness of the device drops to a 53 % level and the driving voltage was increased to 6.4 V, which corresponds to 102 % of the initial driving voltage (See Fig. 5).
• hexanitrile hexaazatriphenylene was thermal-vacuum deposited with a thickness of 50 ⁇ A to form a hole injection layer.
• NPB which transports holes, was vacuum deposited thereon (600A)
• Alq3 that performs functions of both emitting layer and electron transporting layer was vacuum deposited with a thickness of 500A.
• LiF lithium fluoride
• Alq3 lithium fluoride
• aluminum with a thickness of 2.500A were sequentially deposited to form a cathode using shadow mask to fabricate 6 mm 2 of test pixel.
• the deposition rate of the organic material was maintained at 1 A /sec, that of lithium fluoride was 0.2A /sec, and that of aluminum was 3-7A /sec.
• the half-lifetime of the device was measured by applying 200 mA/cm 2 of constant DC current density. As shown in Fig. 3, after 38 hours of driving, the brightness of the device drops to 50 % level and the driving voltage was increased to 7.7 V, which corresponds to 102 % of the initial driving voltage (See Fig. 5). Comparative Example 2
• hexanitrile hexaazatriphenylene was thermal-vacuum deposited with a thickness of 50 ⁇ A to form a hole injection layer.
• NPB which transports holes, was vacuum deposited thereon (60 ⁇ A), and Alq3 that performs a function of the emitting layer was vacuum deposited with a thickness of 30 ⁇ A.
• TPBI that performs functions of injecting and transporting electrons was vacuum deposited with a thickness of 20 ⁇ A to form a thin film of an organic material layer.
• lithium fluoride (LiF) with a thickness of 5A and aluminum with a thickness of 2,50 ⁇ A were sequentially deposited to form a cathode using shadow mask to fabricate 6 mm 2 of test pixel.
• the deposition rate of the organic material was maintained at 1 /sec, that of lithium fluoride was 0.2 A /sec, and that of aluminum was 3-7A /sec.
• the half-lifetime of the device was measured by applying 200 mA/cm 2 of constant DC current density. As shown in Fig. 4, after 40 hours of driving, the brightness of the device drops to 50 % level and the driving voltage was increased to 7.2 V, which corresponds to 113 % of the initial driving voltage (See Fig. 5).
• This comparative result shows that the electron transporting material of the invention provides an organic electroluminescent device which can minimize driving voltage increase during operation.
• hexanitrile hexaazatriphenylene was thermal-vacuum deposited with a thickness of 50 ⁇ A to form a hole injection layer.
• NPB which transports holes, was vacuum deposited thereon (60 ⁇ A), and a compound of Chemical Formula 1-4 that performs a function of the emitting layer was vacuum deposited with a thickness of 40 ⁇ A.
• Alq3 that performs functions of injecting and transporting electrons was vacuum deposited with a thickness of 20 ⁇ A to form a thin film of an organic material layer.
• lithium fluoride (LiF) with a thickness of ⁇ A and aluminum with a thickness of 2,500 A were sequentially deposited to form a cathode using shadow mask to fabricate 6 mm 2 of test pixel.
• the deposition rate of the organic material was maintained at 1A /sec, that of lithium fluoride was 0.2A /sec, and that of aluminum was 3-7A /sec.
• the half-lifetime of the device was measured by applying 50 mA/cm 2 of constant DC current density. As shown in Fig. 6, after 140 hours of driving, the brightness of the device drops to a 67% level and the driving voltage was increased to 6.5 V, which corresponds to 103% of the initial driving voltage (See Fig. 7). This result shows that the material claiming in this patent application is stable to hole carriers and also can be used as an blue emitting source with enhanced device lifetime.
• An electroluminescent device was prepared in the same manner as Example 6, except the TPBI is used as an emitting material instead of a compound of the Chemical Formula 1 -4.
• a forward electric field of 6.9 V was added, and as result, a blue light emission with a brightness of 354 nit (peak max. located at 440 nm), was observed at a current density of 50 mA/cm 2 .
• the half-lifetime of the device was measured by applying 50 mA/cm 2 of constant DC current density.
• the brightness of the device drops to a 20% level of the initial brightness and the driving voltage was increased to 8.2 V, which corresponds to 124% of the initial driving voltage (See Fig. 7).
• This comparative result shows that the material of the invention is stable to hole carriers and also can be used as a blue emitting source with enhanced device lifetime.
• hexanitrile hexaazatriphenylene was thermal-vacuum deposited with a thickness of 50 ⁇ A to form a hole injection layer.
• NPB which transports holes, was vacuum deposited thereon (60 ⁇ A), and a compound represented by the Chemical Formula j that performs a function of the emitting layer was vacuum deposited with a thickness of 10 ⁇ A.
• a compound of the Chemical Formula 1 -2 that performs functions of injecting and transporting electrons was vacuum deposited with a thickness of 20 ⁇ A to form a thin film of an organic material layer.
• lithium fluoride (LiF) with a thickness of ⁇ A and aluminum with a thickness of 2,50 ⁇ A were sequentially deposited to form a cathode using shadow mask to fabricate 6mm 2 of test pixel.
• the deposition rate of the organic material was maintained at 1 A /sec, that of lithium fluoride was 0.2A
• hexaazatriphenylene was vacuum deposited with a thickness of 500 A to
• NPB 60 ⁇ A
• a compound represented by the Chemical Formula I that performs a function of a emitting layer was vacuum deposited with a thickness of 20 ⁇ A.
• a compound represented by the Chemical Formula 2-2 that performs functions of electron injection and transportation was vacuum deposited with a thickness of 20 ⁇ A to form a thin film of an organic material layer.
• lithium fluoride (LiF) with a thickness of 5A and aluminum with a thickness of 2,50 ⁇ A were sequentially deposited to form a cathode using shadow mask to fabricate 6 mm 2 of test pixel.
• the deposition rate of the organic material was maintained at 1A /sec, that of lithium fluoride was 0.2A/sec, and that of aluminum was 3-7A/sec.
• hexanitrile hexaazatriphenylene was thermal vacuum deposited with a thickness of 50 ⁇ A to form a hole injection layer.
• NPB which transports holes, was vacuum deposited thereon (60 ⁇ A), and a compound represented by the Chemical Formula k functioning as a emitting layer was vacuum deposited with a thickness of 20 ⁇ A.
• a compound represented by the Chemical Formula 3-2 that performs functions of electron injection and transportation was vacuum deposited with a thickness of 200A to form a thin film of an organic material layer.
• lithium fluoride (LiF) with a thickness of 5A and aluminum with a thickness of 2,50 ⁇ A were sequentially vacuum deposited to form a cathode using shadow mask to fabricate 6 mm 2 of test pixel.
• the deposition rate of the organic material was maintained at 1A /sec, that of lithium fluoride was 0.2A /sec, and that of aluminum was 3-7A /sec.
• novel material of the present invention can be contained in an organic compound layer of an organic electroluminescent display to realize improvement in luminescence, efficiency, and life cycle, as well as low- voltage operation.

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