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Aluminum chelate complex for organic el materialRelated Patent Categories: Stock Material Or Miscellaneous Articles, Composite (nonstructural Laminate), Of Inorganic Material, Metal-compound-containing Layer, Fluroescent, Phosphorescent, Or Luminescent LayerAluminum chelate complex for organic el material description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070054148, Aluminum chelate complex for organic el material. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF TECHNOLOGY [0001] This invention relates to an aluminum chelate complex useful as a material to be incorporated in an organic electroluminescent element (hereinafter referred to as an organic EL element) and its emissive layer and other parts. BACKGROUND TECHNOLOGY [0002] An organic EL element constituting a display panel using an organic material is generally formed from a glass substrate as a display surface, an anode as a transparent electrode, plural layers of organic materials containing an organic emissive layer and a cathode consisting of a metal electrode, each prepared in thin film and stacked one upon another. The layers of organic materials contain layers capable of transporting holes such as a hole injecting layer and a hole transporting layer and layers capable of transporting electrons such as an electron transporting layer and an electron injecting layer in addition to an organic emissive layer and organic EL elements comprising such layers of organic materials have also been proposed. An inorganic compound may as well constitute an electron injecting layer. [0003] When an electrical field is applied to an organic EL element comprising an organic emissive layer and an electron or hole transporting layer, holes are injected from the anode and electrons from the cathode. These electrons and holes recombine together in the organic emissive layer to form excitons which return to the ground state with emission of light and an organic EL element utilizes this emission of light. The emissive layer is often doped with a colorant as a guest material to raise the luminous efficiency or to operate the element stably. [0004] In recent years, the use of phosphorescent materials besides fluorescent materials in the emissive layer has been proposed. In the emissive layer of an organic EL element, the probability of generating singlet excitons and triplet excitons after recombination of electrons and holes is thought to be 1:3 and an element utilizing phosphorescence by triplet excitons as well is thought to attain luminous efficiency three to four times greater than that of an element utilizing fluorescence by singlet exictons. [0005] On the other hand, for the purposes of reducing the power requirement and improving the luminous efficiency and operating stability of an organic EL element, a proposal has been made to provide a hole blocking layer between the organic emissive layer and the cathode to restrict the migration of holes from the organic emissive layer. This hole blocking layer accumulates holes efficiently inside the emissive layer thereby improving the probability of recombination of holes with electrons and raising the luminous efficiency. Phenanthroline derivatives and triazole derivatives have been reported to be effective as hole-blocking materials. [0006] Patent literature 1: JP4-206685A [0007] Patent literature 2: JP2001-237079A [0008] Patent literature 3: JP2001-284056A [0009] It is reported in JP04-206685A that a complex of aluminum with a hydroxyquinoline compound and a phenolic compound (hereinafter referred to as AlQ2OR) is useful as an organic EL material emitting blue light. This AlQ2OR has a structure in which one aluminum atom is complexed with two molecules of 8-hydroxyquinoline compounds and one molecule of a phenolic compound. In an example disclosed in JP04-206685A, AlQ2OR is incorporated in the electron transporting layer to emit light. [0010] A phosphorescent or fluorescent organic EL element reported in JP2001-237079A has AlQ2OR in the hole blocking layer. Further, a phosphorescent organic EL element reported in JP2002-284056A has a hole blocking layer comprising AlQ2OR between the emissive layer containing a phosphorescent material and the electron transporting layer. [0011] A compound cited in JP2001-237079A and JP2001-284056A for AlQ2OR is (1,1'-biphenyl)-4-olato)bis(2-methyl-8-quinolinolato-N1,08)aluminum (hereinafter referred to as BAlq) obtained from 2-methyl-8-hydroxyquinoline as a hydroxyquinoline compound and 4-phenyphenol as a phenolic compound. Although BAlq shows excellent durability, it has a shortcoming of inferior hole-blocking ability as its ionization potential (Ip) is not sufficiently large. Consequently, in the cases where BAlq is used in the hole blocking layer and tris(8-hydroxyquinolinato-N1,08)aluminum (hereinafter referred to as Alq3) is used in the electron transporting layer, it is the electron transporting layer that emits light. In an organic EL element utilizing red phosphorescence, the emission of light (green) by Alq3 leads to degradation of chromaticity. Now, it has been found in some cases that, in an organic EL element whose emissive layer comprises a phosphorescent material as a guest material, the use of AlQ2OR as a host material is capable of attaining a long operating life while maintaining good luminous characteristics. [0012] However, the life of an element using AlQ2OR disperses a great deal and this has become a large obstacle in putting an element of this kind into practical use. The cause of this dispersion of life has not been elucidated at all. As a result, there has not been a clue for setting up guidelines not only for the control of materials essential for the manufacture of highly reliable commercial elements but also for improvement of life. DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention [0013] An object of this invention is to elucidate the causes affecting the life of an organic EL element comprising AlQ2OR, offer remedial means, set up a guideline for the control of materials essential for the manufacture of highly reliable commercial elements and provide an organic EL material which constitutes an organic EL element capable of manifesting excellent performance with little deterioration of luminance with passage of time, excellent reliability and high product quality acceptable to practical use and an organic EL element utilizing said organic EL material. Means to Solve the Problems [0014] The inventors of this invention have conducted extensive studies in the development of commercially viable organic EL materials comprising AlQ2OR, found that AlQ2OR prepared by the usual method contains specific impurities, clarified the relationship between the content of these impurities and the durability of an organic EL element and completed this invention. [0015] This invention relates to an aluminum chelate complex for an organic EL material represented by general formula (1) in which a compound represented by general formula (2) is present as an impurity in an amount of 350 wt ppm or less. [0016] In general formulas (1) and (2), Ar.sub.1 is a mono- or bicyclic arylene group, Ar.sub.2 is a mono- or bicyclic aryl group, the total number of aromatic rings in Ar.sub.1 and Ar.sub.2 is 2 to 4, and where Ar.sub.1 or Ar.sub.2 contains 2 or more aromatic rings, these aromatic rings may be condensed. The groups R.sub.1--R.sub.6 are independently hydrogen or hydrocarbon groups containing 1-8 carbon atoms. The group X is a halogen. In general formulas (1) and (2), the same symbols mean the same thing. [0017] Here, the arylene and aryl groups or Ar.sub.1 and Ar.sub.2 need to be linked together directly, that is, Ar.sub.2 is substituted at the nucleus of Ar.sub.1. The groups Ar.sub.1 and Ar.sub.2, when represented respectively by H--Ar.sub.1--H and Ar.sub.2--H, are exemplified by benzene, naphthalene, biphenyl and their alkyl-substituted derivatives. The substituent alkyl groups here are preferably those containing 1-6 carbon atoms (lower alkyl groups) and the number of substituents is preferably 3 or less. More preferably, Ar.sub.1 is naphthylene or phenylene and Ar.sub.2 is naphthyl or phenyl. The total number of aromatic rings in Ar.sub.1 and Ar.sub.2 is preferably 2 or 3. [0018] In general formulas (1) and (2), the groups R.sub.1--R.sub.6 are independently hydrogen or hydrocarbon groups containing 1-8 carbon atoms such as alkyl and alkenyl and alkyl groups containing 1-3 carbon atoms are preferred. However, hydrocarbon groups containing aryl groups or aryl-containing groups are excluded. The group X is preferably Br, I or Cl. [0019] The aforementioned aluminum chelate complex can be obtained by reacting aluminum isopropoxide successively with a quinolinol derivative and a phenolic compound represented by HO--Ar.sub.1--Ar.sub.2. This aluminum chelate complex can be used as the aforementioned host material of the emissive layer in an organic EL element comprising an organic emissive layer between the anode and the cathode. Continue reading about Aluminum chelate complex for organic el material... 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