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  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B33/00—Electroluminescent light sources
  • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
  • H05B33/14—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the electroluminescent material, or by the simultaneous addition of the electroluminescent material in or onto the light source
• • C—CHEMISTRY; METALLURGY
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  • C07F5/00—Compounds containing elements of Groups 3 or 13 of the Periodic Table
  • C07F5/02—Boron compounds
  • C07F5/022—Boron compounds without C-boron linkages
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  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/30—Coordination compounds
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/30—Coordination compounds
  • H10K85/321—Metal complexes comprising a group IIIA element, e.g. Tris (8-hydroxyquinoline) gallium [Gaq3]
  • H10K85/322—Metal complexes comprising a group IIIA element, e.g. Tris (8-hydroxyquinoline) gallium [Gaq3] comprising boron
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/30—Coordination compounds
  • H10K85/351—Metal complexes comprising lanthanides or actinides, e.g. comprising europium
• • H—ELECTRICITY
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/30—Coordination compounds
  • H10K85/361—Polynuclear complexes, i.e. complexes comprising two or more metal centers
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  • C09K2211/00—Chemical nature of organic luminescent or tenebrescent compounds
  • C09K2211/10—Non-macromolecular compounds
  • C09K2211/1003—Carbocyclic compounds
  • C09K2211/1011—Condensed systems
• • C—CHEMISTRY; METALLURGY
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  • C09K2211/00—Chemical nature of organic luminescent or tenebrescent compounds
  • C09K2211/10—Non-macromolecular compounds
  • C09K2211/1018—Heterocyclic compounds
  • C09K2211/1025—Heterocyclic compounds characterised by ligands
  • C09K2211/1029—Heterocyclic compounds characterised by ligands containing one nitrogen atom as the heteroatom
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  • C09K2211/00—Chemical nature of organic luminescent or tenebrescent compounds
  • C09K2211/10—Non-macromolecular compounds
  • C09K2211/1018—Heterocyclic compounds
  • C09K2211/1025—Heterocyclic compounds characterised by ligands
  • C09K2211/1044—Heterocyclic compounds characterised by ligands containing two nitrogen atoms as heteroatoms
• • H—ELECTRICITY
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K50/00—Organic light-emitting devices
  • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
  • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers

Definitions

• This invention relates to organometallic complexes, processes for their production, light emitting materials incorporating the complexes and light emitting devices comprising the complexes or the materials.
• the devices of the invention may be flat panel displays.
• Flat panel displays are the critical enabling technology for many current applications, including laptop computers and "heads up" displays, as they offer several potential advantages over conventional cathode ray tube displays, including compactness and low power consumption.
• a flat panel device is a multilayer assembly of structurally important films consisting of a transparent electrode, insulation, phosphor and metal electrode. All are important materials in device fabrication, but the single most important element in the development of a multi-colour electroluminescent device is the phosphor.
• organometallic complexes can be used as phosphors in electroluminescent devices.
• US 5552547 describes complexes of aluminium, gallium and indium in which one of the ligands acts as a "built-in" fluorescent dye. The colour of the light which is emitted from the complex is determined by the Iigand which acts as the dye.
• lanthanide complexes can be used as phosphors in electroluminescent devices.
• the Iigand used in the complexes is a pyrazolone-based molecule in which the binding to the metal by the Iigand occurs via a beta-diketonate-type arrangement.
• the sensitising efficiency of a complex is a measure of the efficiency of the process of energy transfer from the Iigand to the metal during the excitation step associated with electroluminescence.
• the present invention aims to provide organometallic complexes in which the metal is a lanthanide (i.e., organolanthanide complexes) which are more effective phosphors for use in light emitting devices than the known complexes.
• organolanthanide complexes i.e., organolanthanide complexes
• the invention also seeks to provide a Iigand system for organolanthanide complexes which is effective with a range of different lanthanides in order that the same Iigand can provide radiation from different parts of the electromagnetic spectrum, e.g., red, green or blue light and UV or IR radiation, simply by varying the metal in the complex.
• the radiative efficiency of an organometallic complex is a measure of the amount of energy which is radiated from the complex relative to the amount of energy lost via non-radiative pathways.
• the known organolanthanide complexes have the problem that a number of non-radiative pathways are available for energy loss from the metal and their radiative efficiencies can therefore be relatively low.
• the present invention in one embodiment, is based on the finding that pyrazolyl species are highly effective ligands for producing organolanthanide complexes useful as phosphors in light emitting devices. Accordingly, the invention provides a light emitting device comprising a complex containing a lanthanide metal cation complexed with from one to three polydentate ligands, wherein each Iigand comprises one or more pyrazolyl groups, optionally substituted and optionally fused with a substituted or unsubstituted, heterocyclic or carbocyclic, aromatic or non-aromatic, ring system, one of the nitrogen atoms of the pyrazolyl groups forming a coordinate bond to the metal.
• the ligands are trispyrazolylborate anions, the pyrazolyl groups being optionally substituted and optionally fused with a substituted or unsubstituted, heterocyclic or carbocyclic, aromatic or non-aromatic, ring system, optionally substituted at the boron atom.
• Suitable complexes for use in the invention are desirably those having the formula (I):
• Z is a carbon atom or R 1 - B fragment p is 1 , 2 or 3 q is 3-p
• A is a counterion
• R 1 is: (i) hydrogen, aryl or aralkyl each optionally substituted with from one to five halogen or C, to C 6 alkyl groups; or (ii) C, to C 6 alkyl, C, to C 6 alkenyl or C, to C 6 alkynyl each optionally substituted with one or more halogen atoms each L is covalently bound to Z and is independently selected from a group of the formula (II) or
• R 2 , R 3 and R 4 are independently selected from: (i) halogen, cyano, nitro, sulphono, amino, C, to C 6 alkylamino, C, to C 6 alkylamido, carboxyl, C ⁇ to C 6 alkyloxycarbonyl, hydroxy, C, to C 6 alkoxy, C, to C 6 alkylcarbonyloxy, C, to C 6 alkylcarbonyl C, to C 6 haloalkoxy and hydrogen; (ii) aryl or aralkyl each optionally substituted on the aryl ring or, for aralkyl, on the alkylene chain with from one or more of the groups mentioned under (i) above; and (iii) C, to C 6 alkyl, C* to C 6 alkenyl or C, to C 6 alkynyl each optionally substituted with one or more of the groups mentioned under (i) and (ii) above
• R 2 and R 3 or R 3 and R 4 are linked so as to form a fused, aromatic or non-aromatic, ring system with the pyrazolyl ring of L
• M is a trivalent lanthanide metal ion.
• p is suitably 1 or 2 and is preferably 2.
• the light emitting device of the invention may be a flat panel display.
• R 4 and/or R 2 is -(CX 2 ) n X wherein n is 0 or a positive integer from 1 to 6 and X is halogen; or R 4 and/or R 2 is orthodihalogenated or orthodihalomethylated aryl, optionally further substituted on the aryl ring (e.g., with from one to three halogen atoms or C to C 6 alkyl groups) or in which R 2 and R 3 or R 3 and R 4 are linked so as to form a fused, aromatic or non- aromatic, ring system with the pyrazolyl ring of L are believed to be novel and are also provided by the invention.
• alkyl as used herein is intended to cover branched and unbranched C, to C 6 groups and alicyclic compounds for the C 3 to C 6 groups.
• aryl covers C 6 to C 10 aromatic groups such as phenyl and naphthyl as well as heterocycles such as pyridyl, furyl and thiophenyl.
• aralkyl means C, to C 3 alkyl substituted with aryl, such as benzyl.
• halogen means fluorine, chlorine, bromine or iodine. Of these, fluorine is the preferred halogen for the complexes of the invention.
• M is terbium (Tb), cerium (Ce), europium (Eu), erbium (Er), gadolinium (Gd), thulium (Tm), samarium (Sm) or neodymium (Nd).
• M may be another lanthanide metal such as praesodymium (Pr), for example.
• Pr praesodymium
• the complexes with cerium, europium, erbium and gadolinium are preferred because they provide emissions of blue light, red light, IR radiation and UV radiation, respectively, and thus range across the electromagnetic spectrum.
• the complex with terbium unexpectedly gives blue light rather than the green light which is normally expected for terbium complexes. This is particularly advantageous since cerium complexes which are conventionally used to produce blue light have the problem of a relatively wide bandwidth for the emitted light.
• the terbium complex of the present invention emits blue light with a narrower bandwidth than the previously used cerium compounds and so provides an improved alternative source of blue light for light emitting devices.
• the trispyrazolyl ligands used in the invention have been found to be particularly effective in terms of their sensitising efficiency i.e., in transferring energy to the metal in the excitation step of the light emitting (e.g., electroluminescence) process. They also impart high radiative efficiencies to the complexes by providing few non- radiative pathways for relaxation (i.e., energy loss from the metal in its excited state).
• the ligands have been reported. Dias et al, Inorg Chem. 1 995, 34, 1 975 and 1 996, 35, 267 and Renn et al Helv Chim Acta ( 1 995), 10., 993 describe the synthesis of the fluorinated trispyrazolyl borate ligands. Julia et al., Organic Preparations and Procedures International, 1 6, 299, 1 984, discloses the preparation of the trispyrazolylmethane-derived ligands.
• complexes of the invention are generally called "organometallic” herein. However, it will be understood by those skilled in the art that this term is used synonymously with the term “coordination”. Also, the term “complex” as used herein covers both neutral species and compounds containing a charged organolanthanide species as part of a complex salt.
• the present invention is also based on the wider finding that non-radiative pathways for relaxation in organolanthanide complexes can be provided by carbon-hydrogen bonds in the Iigand which are relatively close to the metal and the discovery that these pathways can be blocked by fluorinating the Iigand to replace the carbon- hydrogen bonds by carbon-fluorine bonds or otherwise designing the Iigand such that there are no carbon-hydrogen bonds within 5 A, preferably 8 A, more preferably 10 A, of the metal centre (i.e., the centre of the metal atom).
• the invention provides light emitting material comprising an organometallic complex either as a film or dispersed within a matrix of a polymer, the organometallic complex being a complex wherein the ligands are optionally fluorinated and arranged about the metal such that there are no carbon-hydrogen bonds within 5 A of the metal centre.
• the light emitted from the light emitting devices of the invention may be produced by various mechanisms such as electroluminescence, photoluminescence or cathodoluminescence with electroluminescence being preferred.
• the matrix is preferably of the type conventionally used in light emitting (e.g., electroluminescent) devices and based on polymer systems such as polyvinylcarbazole (PVK) or polymethylmethacrylate (PMMA) with a hole transporting material such as 2-(4-biphenylyl)-5-(5-tertbutylbenzene)-1 ,3,4-oxadiazole (BBO).
• PVK polyvinylcarbazole
• PMMA polymethylmethacrylate
• BBO hole transporting material
• the organolanthanide complexes used in the invention may themselves act as electron transporting materials, separately from or in addition to being a phosphor, in the light emitting devices.
• the ligands ZL 3 used in the complexes of the present invention in which R 4 and/or R 2 is -(CX 2 ) n X or optionally substituted orthodihalogenated or orthodiperhalomethylated aryl are particularly advantageous for use in the electroluminescent material of the invention since they provide complexes with no carbon-hydrogen (C- H) bonds within 5 A of the metal centre.
• C- H carbon-hydrogen
• R 4 and/or R 2 is conveniently trifluoromethyl.
• R 3 may be hydrogen and R 2 trifluoromethyl.
• ZL 3 may be:
• the increased conjugation of the fused bi- and poly- cyclic systems can be advantageous for electron transfer within the complex.
• the complexes used in the invention are positively charged, they will be provided by compounds containing the complex and a counterion.
• the counterion preferably should not provide non- radiative pathways for relaxation of the metal. Therefore, it is preferred that the counterion should not contain bonds between hydrogen and other atoms, such as carbon-hydrogen bonds.
• Trifluoromethylsulphonate, CF 3 SO 3 ⁇ , halide (fluoride, chloride, bromide or iodide), nitrate, NO 3 " , and perchlorate, CI0 4 " are suitable counterions for this purpose.
• the present invention provides a process for producing the complex of the invention which comprises the steps of reacting M 3 + ions (i.e., trivalent lanthanide ions) with ZL 3 anions in solution and separating the complex from the reaction mixture.
• the process is carried out in a suitable solvent at about or above room temperature up to the boiling point of the solvent for a time sufficient to form an extractable amount of the complex, preferably with stirring.
• the complex is separated from the reaction mixture by solvent extraction.
• the process is preferably carried out under anhydrous conditions. It is also advantageous to exclude oxygen from the reaction mixture by carrying out the process under an inert gas atmosphere e.g., of nitrogen or argon.
• the process may be carried out via the following reaction:
• M' is a monovalent metal such as an alkali metal e.g., sodium or potassium, or thallium or silver (as Tl + and Ag + , respectively)
• two equivalents of M'ZL 3 are suspended or dissolved in a solvent and are treated with one equivalent of a trivalent lanthanide salt.
• the reaction mixture is stirred for a period of time between one and 1 00 hours either at room temperature or at the boiling point of the solvent under standard conditions.
• the solvent is removed (for example, by evaporation under reduced pressure) and the complex separated from by-products by extraction into a solvent with a different polarity from that of the reaction solvent.
• the product is purified by crystallisation from either the extraction solvent or a combination of solvents with different polarities.
• Figure 1 shows a simplified cross-sectional view of an electroluminescent device according to the invention, such as an organic flat panel display;
• Figure 2 is a current versus voltage plot for an electroluminescent device according to the invention.
• Figures 3, 4 and 5 are photoluminescence plots for europium, terbium and cerium complexes of the invention.
• Figure 6 is a plot of electroluminescence intensity versus wavelength for an electroluminescent device of the invention containing a terbium complex of the invention.
• the device 10 of Figure 1 includes a substrate 1 which generally has a substantially planar surface 1 a and may be a glass plate, although other suitable materials can be used for this purpose.
• An electrically conductive layer 2 is deposited on the planar surface 1 a so as to form a relatively uniform electrical contact.
• Layers 3, 4 and 5 may be a single layer (for example, of the electroluminescent material of the present invention) comprising a mixture of conductive materials and luminescent dopant (such as a complex of the invention).
• a more efficient working device consists of a first organic layer 3 of a hole transporting material, the host emissive material 4 (such as the electroluminescent material of the invention), a second organic layer 5 of electron transporting material (which may comprise an organolanthanide of the invention also useful as a phosphor) and a second electrically conductive layer 6 to form a second electrical contact.
• substrate 1 is formed of glass and conductive layer 2 is formed of organic and inorganic conductors, such as conductive polyaniline (PANI) or indium-tin-oxide (ITO), which are substantially transparent to visible light so that the emitted light exits downwardly through substrate 1 as the device 10 is shown in the Figure.
• PANI conductive polyaniline
• ITO indium-tin-oxide
• Device 10 has a potential applied between layers 2 and 6 by means of a potential source 7.
• conductive layer 2 is a p-type contact and conductive layer 6 is an n-type contact.
• the negative terminal of potential source 7 is connected to conductive layer 6 and the positive terminal is connected to conductive layer 2.
• Electrons injected through the n-type contact are transported through organic layer 5 and into organometallic layer 4 (the emissive layer). Holes injected from the p-type contact are transported through the organic layer 3 and into the organometallic layer 4 where, upon an electron and hole recombination, a photon is emitted.
• An electroluminescent device was prepared using this complex as a phosphor.
• the device had a single layer structure consisting of a homogeneous mixture of the organometallic phosphor, an electron carrying material and a hole carrying material.
• This layer was deposited by spin-coating a stock solution of these materials onto an indium-tin oxide coated glass substrate in a dry nitrogen atmosphere.
• the stock solution was prepared in a dry nitrogen atmosphere using a mixture of the organometallic phosphor, polyvinylcarbazole (PVK) and 2-(4-biphenylyl)-5-(5-tertbutylbenzene)-1 ,3,4-oxadiazole (BBO).
• PVK polyvinylcarbazole
• BBO 2-(4-biphenylyl)-5-(5-tertbutylbenzene)-1 ,3,4-oxadiazole
• Tm(OTf) 3 (0.62 g, 1 .0 mmol) and KBpz (0.67 g, 2.0 mmol) were dissolved in THF (50 mL) and the solution was stirred for 1 2 h at room temperature. A fine colourless precipitate developed within 1 h. After 1 2 h the THF was removed under vacuum and the product extracted from the resulting colourless solid with CH2CI2 (50 mL). Removal of the CH2CI2 in vacuo afforded the product as a colourless solid (0.72 g, 79 %).
• Tm(OTf) 3 (0.62 g, 1 .0 mmol) and KT ind (0.81 g , 2.0 mmol) were dissolved in THF (50 mL) and the orange solution was stirred for 1 5 h at room temperature. The solvent was removed from the resulting cloudy solution and the yellow residue was washed with CH2CI2 (50 mL). The yellow filtrate was evaporated to dryness under reduced pressure, affording the product as a pale yellow solid (0.68 g, 65 %).
• Nd(OTf) 3 (1 .1 8 g, 2.0 mmol) and KT ind (1 .61 g , 4.0 mmol) were dissolved in THF (50 mL) and the lilac solution was stirred for 24 h at room temperature. The solvent was removed from the resulting cloudy solution and the lilac residue was washed with CH2CI2 (50 mL). The lilac filtrate was evaporated to dryness under reduced pressure, affording the product as a lilac solid (1 .27 g, 62 %).
• Tb(OTf) 3 (1 .20 g, 2.0 mmol) and KBpz 1 2 (2.23 g, 4.0 mmol) were suspended in THF (50 mL) and allowed to stir for 14 h. The initial colourless cloudy mixture cleared and became yellow during this time. Analysis of the product at this time showed only 1 Iigand coordinated to the metal centre The mixture was then heated at 85 °C for 6 h after which time the mixture was cooled to room temperature and the solvent was removed under reduced pressure to give a yellow solid residue, which was extracted into CH2CI2 (50 mL). The filtrate was concentrated to dryness to give the product as a pale yellow solid.
• EXAMPLE 21 Tb(Bpz 1 2 ) 2 (OTf)
• Tb(OTf) 3 (1 .20 g, 2.0 mmol) and KBpz 1 2 (2.23 g, 4.0 mmol) were suspended in THF (30 mL) and the mixture heated to reflux. After 6 h the mixture was cooled to room temperature and the solvent was removed under reduced pressure to give a yellow solid residue, which was extracted into CH2CI2 (50 mL)and filtered from any insoluble residue. The filtrate was concentrated to dryness to give the product as a pale yellow solid.

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