Patent Application
20060269778
The present invention relates to electroluminescent materials and to electroluminescent devices.
Materials which emit light when an electric current is passed through them are well known and used in a wide range of display applications. Liquid crystal devices and devices which are based on inorganic semiconductor systems are widely used; however these suffer from the disadvantages of high energy consumption, high cost of manufacture, low quanta efficiency and the inability to make flat panel displays.
Organic polymers have been proposed as useful in electroluminescent devices, but it is not possible to obtain pure colours; they are expensive to make and have a relatively low efficiency.
Another compound which has been proposed is aluminium quinolate, but this requires dopants to be used to obtain a range of colours and has a relatively low efficiency.
Patent application WO98/58037 describes a range of lanthanide complexes which can be used in electroluminescent devices which have improved properties and give better results. Patent Applications PCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024, PCT/GB99/04028, PCT/GB00/00268 describe electroluminescent complexes, structures and devices using rare earth chelates.
U.S. Pat. No. 5,128,587 discloses an electroluminescent device which consists of an organometallic complex of rare earth elements of the lanthanide series sandwiched between a transparent electrode of high work function and a second electrode of low work function with a hole conducting layer interposed between the electroluminescent layer and the transparent high work function electrode and an electron conducting layer interposed between the electroluminescent layer and the electron injecting low work function anode. The hole conducting layer and the electron conducting layer are required to improve the working and the efficiency of the device. The hole transporting layer serves to transport holes and to block the electrons, thus preventing electrons from moving into the electrode without recombining with holes. The recombination of carriers therefore mainly takes place in the emitter layer.
We have now devised electroluminescent compounds and electroluminescent structures incorporating them.
According to the invention there is provided an electroluminescent diiridium compound of formula
where R1, R2, R3 and R4 can be the same or different and are selected from hydrogen, and substituted and unsubstituted hydrocarbyl groups such as substituted and unsubstituted aliphatic groups, substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorocarbons such as trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups; R1, R2 and R3 can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer, e.g. styrene.
Examples of R1 and/or R2 and/or R3 and/or R4 include aliphatic, aromatic and heterocyclic alkoxy, aryloxy and carboxy groups, substituted and unsubstituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene, naphthyl and fluorene groups, alkyl groups such as t-butyl, heterocyclic groups such as carbazole.
Preferred organic ligands L1 and L2 are phenylpyridine and substituted phenylpryidines.
The invention also provides an electroluminescent device which comprises (i) a first electrode, (ii) a layer of the diiridium complex (A) and (iii) a second electrode.
The first electrode can function as the cathode and the second electrode can function as the anode and preferably there is a layer of a hole transporting material between the anode and the layer of the electroluminescent compound.
The hole transporting material can be any of the hole transporting materials used in electroluminescent devices.
The hole transporting material can be an amine complex such as poly (vinylcarbazole), N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD), an unsubstituted or substituted polymer of an amino substituted aromatic compound, a polyaniline, substituted polyanilines, polythiophenes, substituted polythiophenes, polysilanes etc. Examples of polyanilines are polymers of
where R is in the ortho—or meta-position and is hydrogen, C1-18 alkyl, C1-6 alkoxy, amino, chloro, bromo, hydroxy or the group
where R is alky or aryl and R′ is hydrogen, C1-6 alkyl or aryl with at least one other monomer of formula I above, or the hole transporting material can be a polyaniline; polyanilines which can be used in the present invention have the general formula
where p is from 1 to 10 and n is from 1 to 20, R is as defined above and X is an anion, preferably selected from Cl, Br, SO4, BP4, PF6, H2PO3, H2PO4, arylsulphonate, arenedicarboxylate, polystyrenesulphonate, polyacrylate alkysulphonate, vinylsulphonate, vinylbenzene sulphonate, cellulose sulphonate, camphor sulphonates, cellulose sulphate or a perfluorinated polyanion.
Examples of arylsulphonates are p-toluenesulphonate, benzenesulphonate, 9,10-anthraquinone-sulphonate and anthracenesulphonate; an example of an arenedicarboxylate is phthalate and an example of arenecarboxylate is benzoate.
We have found that protonated polymers of the unsubstituted or substituted polymer of an amino substituted aromatic compound such as a polyaniline are difficult to evaporate or cannot be evaporated. However we have surprisingly found that if the unsubstituted or substituted polymer of an amino substituted aromatic compound is deprotonated then it can be easily evaporated, i.e. the polymer is evaporable.
Preferably evaporable deprotonated polymers of unsubstituted or substituted polymers of an amino substituted aromatic compound are used. The de-protonated unsubstituted or substituted polymer of an amino substituted aromatic compound can be formed by deprotonating the polymer by treatment with an alkali such as ammonium hydroxide or an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide.
The degree of protonation can be controlled by forming a protonated polyaniline and de-protonating. Methods of preparing polyanilines are described in the article by A. G. MacDiarmid and A. F. Epstein, Faraday Discussions, Chem Soc. 88 P319 1989.
The conductivity of the polyaniline is dependent on the degree of protonation with the maximum conductivity being when the degree of protonation is between 40 and 60%, e.g. about 50%.
Preferably the polymer is substantially fully deprotonated.
A polyaniline can be formed of octamer units, i.e. p is four, e.g.
The polyanilines can have conductivities of the order of 1×10−1 Siemen cm−1 or higher.
The aromatic rings can be unsubstituted or substituted, e.g. by a C1 to 20 alkyl group such as ethyl.
The polyaniline can be a copolymer of aniline and preferred copolymers are the copolymers of aniline with o-anisidine, m-sulphanilic acid or o-aminophenol, or o-toluidine with o-aminophenol, o-ethylaniline, o-phenylene diamine or with amino anthracenes.
Other polymers of an amino substituted aromatic compound which can be used include substituted or unsubstituted polyaminonapthalenes, polyaminoanthracenes, polyaminophenanthrenes, etc. and polymers of any other condensed polyaromatic compound. Polyaminoanthracenes and methods of making them are disclosed in U.S. Pat. No. 6,153,726. The aromatic rings can be unsubstituted or substituted, e.g. by a group R as defined above.
Other hole transporting materials are conjugated polymers and the conjugated polymers which can be used can be any of the conjugated polymers disclosed or referred to in U.S. Pat. No. 5,807,627, PCT/WO90/13148 and PCT/WO92/03490.
The preferred conjugated polymers are poly (p-phenylenevinylene)-PPV and copolymers including PPV. Other preferred polymers are poly(2,5 dialkoxyphenylene vinylene) such as poly (2-methoxy-5-(2-methoxypentyloxy-1,4-phenylene vinylene), poly(2-methoxypentyloxy)-1,4-phenylenevinylene), poly(2-methoxy-5-(2-dodecyloxy-1,4-phenylenevinylene) and other poly(2,5 dialkoxyphenylenevinylenes) with at least one of the alkoxy groups being a long chain solubilising alkoxy group, poly fluorenes and oligofluorenes, polyphenylenes and oligophenylenes, polyanthracenes and oligo anthracenes, polythiophenes and oligothiophenes.
In PPV the phenylene ring may optionally carry one or more substituents, e.g. each independently selected from alkyl, preferably methyl, alkoxy, preferably methoxy or ethoxy.
Any poly(arylenevinylene) including substituted derivatives thereof can be used and the phenylene ring in poly(p-phenylenevinylene) may be replaced by a fused ring system such as anthracene or naphthylene ring and the number of vinylene groups in each polyphenylenevinylene moiety can be increased, e.g. up to 7 or higher.
The conjugated polymers can be made by the methods disclosed in U.S. Pat. No. 5,807,627, PCT/WO90/13148 and PCT/WO92/03490.
The thickness of the hole transporting layer is preferably 20 nm to 200 nm.
The polymers of an amino substituted aromatic compound such as polyanilines referred to above can also be used as buffer layers with or in conjunction with other hole transporting materials.
The structural formulae of some other hole transporting materials are shown in FIGS. 12 to 16 of the drawings, where R1, R2 and R3 can be the same or different and are selected from hydrogen, and substituted and unsubstituted hydrocarbyl groups such as substituted and unsubstituted aliphatic groups, substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorocarbons such as trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups; R1, R2 and R3 can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer, e.g. style. X is Se, S or O, Y can be hydrogen, substituted or unsubstituted hydrocarbyl groups, such as substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorine, fluorocarbons such as trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups or nitrile.
Examples of R1 and/or R2 and/or R3 include aliphatic, aromatic and heterocyclic alkoxy, aryloxy and carboxy groups, substituted and substituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene, naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclic groups such as carbazole.
In an embodiment of the invention the hole transporting material is mixed with the electroluminescent compound in the electroluminescent layer and a preferred electroluminescent compound is CBP which has the formula of
There can be a buffer layer between the anode and the hole sporting layer and any of the hole transporting materials listed above can be used.
Optionally there is a layer of an electron injecting material between the cathode and the electroluminescent material layer. The electron injecting material is a material which will transport electrons; when an electric current is passed through electron injecting materials include a metal complex such as a metal quinolate, e.g. an aluminium quinolate, lithium quinolate, Mx(DBM)n where Mx is a metal and DBM is dibenzoyl methane and n is the valency of Mx, e.g Mx is chromium. The electron injecting material can also be a cyano anthracene such as 9,10 dicyano anthracene, cyano substituted aromatic compounds, tetracyanoquinidodimethane a polystyrene sulphonate or a compound with the structural formulae shown in FIGS. 9 or 10 of the drawings in which the phenyl rings can be substituted with substituents R as defined above. Instead of being a separate layer the electron injecting material can be mixed with the electroluminescent material and co-deposited with it.
Optionally the hole transporting material can be mixed wit the electroluminescent material and co-deposited with it.
The hole transporting materials, the electroluminescent material and the electron injecting materials can be mixed together to form one layer, which simplifies the construction.
The anode is preferably a transparent substrate such as a conductive glass or plastic material which acts as the anode. Preferred substrates are conductive glasses such as indium tin oxide coated glass, but any glass which is conductive or has a conductive layer such as a metal or conductive polymer can be used. Conductive polymers and conductive polymer coated glass or plastics materials can also be used as the substrate.
The cathode is preferably a low work function metal, e.g. aluminiuni, calcium, lithium, magnesium and alloys thereof such as silver/magnesium alloys, rare earth metal alloys, etc; aluminium is a preferred metal. A metal fluoride such as an alkali metal, rare earth metal or their alloys can be used as the second electrode, for example by having a metal fluoride layer formed on a metal.
The diiridium compound (A) can be mixed with other electroluminescent compounds, for example europium complexes and the invention also provides an electroluminescent device which comprises (i) a first electrode, (ii) a layer of an electroluminescent europium organo metallic or organic complex mixed with an iridium organo metallic or organic complex and (iii) a second electrode.
There is preferably also a layer of an electroluminescent europium organo metallic or organic complex and the invention also provides electroluminescent devices of structures: (i) a first electrode, (ii) a layer of an electroluminescent europium organo metallic or organic complex, (iii) a layer of an electroluminescent europium organo metallic or organic complex mixed with diiridium compound and (iv) a second electrode.
The electroluminescent europium organo metallic or organic complex preferably has the formula (Lα)3Eu where Lα is an organic complex.
Preferred electroluminescent compounds which can be used in the present invention are of formula
(Lα)3 Eu←Lp
where Lα and Lp are organic ligands and Lp is a neutral ligand. The ligands Lα can be the same or different and there can be a plurality of ligands Lp which can be the same or different.
For example (L1)(L2)(L3)Eu (Lp) where (L1)(L2)(L3) are the same or different organic complexes and (Lp) is a neutral ligand and the different groups (L1)(L2)(L3) may be the same or different.
Lp can be monodentate, bidentate or polydentate and there can be one or more ligands Lp.
Further electroluminescent compounds which can be used in the present invention are of general formula (Lα)nEuM2 where M2 is a non rare earth metal, Lα is a as above and n is the combined valence state of Eu and M2. The complex can also comprise one or more neutral ligands Lp so the complex has the general formula (Lα)n Eu M2 (Lp), where Lp is as above. The metal M2 can be any metal which is not a rare earth, transition metal, lanthanide or an actinide. Examples of metals which can be used include lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, copper (I), copper (II), silver, gold, zinc, cadmium, boron, aluminium, gallium, indium, germanium, tin (II), tin (IV), antimony (II), antimony (IV), lead (II), lead (IV) and metals of the first, second and third groups of transition metals in different valence states, e.g. manganese, iron, ruthenium, osmium, cobalt, nickel, palladium(II), palladium(IV), platinum(II), platinum(IV), cadmium, chromium. titanium, vanadium, zirconium, tantulum, molybdenum, rhodium, iridium, titanium, niobium, scandium, yttrium.
Preferably Lα is selected from β diketones such as those of formulae
where R1, R2 and R3 can be the same or different and are selected from hydrogen, and substituted and unsubstituted hydrocarbyl groups such as substituted and unsubstituted aliphatic groups, substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorocarbons such as trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups. R1, R2 and R3 can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer, e.g. styrene. X is Se, S or O, Y can be hydrogen, substituted or unsubstituted hydrocarbyl groups, such as substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structures, fluorine, fluorocarbons such as trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups or nitrile.
Examples of R1 and/or R2 and/or R3 include aliphatic, aromatic and heterocyclic alkoxy, aryloxy and carboxy groups, substituted and substituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene, naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclic groups such as carbazole.
Some of the different groups Lα may also be the same or different charged groups such as carboxylate groups so that the group L1 can be as defined above and the groups L2, L3 . . . can be charged groups such as
where R is R1 as defined above or the groups L1, L2 can be as defined above and L3 . . . etc. are other charged groups
R1, R2 and R3 can also be
where X is O, S, Se or NH.
A preferred moiety R1 is trifluoromethyl CF3 and examples of such diketones are, banzoyltrifluoroacetone, p-chlorobenzoyltrifluoroacetone, p-bromotrifluoroacetone, p-phenyltrifluoroacetone, 1-naphthoyltrifluoroacetone, 2-naphthoyltrifluoroacetone, 2-phenathoyltrifluoroacetone, 3-phenanthoyltrifluoroacetone, 9-anthroyltrifluoroacetonetrifluoroacetone, cinnamoyltrifluoroacetone, and 2-thenoyltrifluoroacetone.
The different groups Lα may be the same or different ligands of formulae
where X is O, S, or Se and R1 R2 and R3 are as above.
The different groups Lα may be the same or different quinolate derivatives such as
where R is hydrocarbyl, aliphatic, aromatic or heterocyclic carboxy, aryloxy, hydroxy or alkoxy, e.g. the 8 hydroxy quinolate derivatives or
where R, R1, and R2 are as above or are H or F e.g. R1 and R2 are alkyl or alkoxy groups
As stated above, the different groups Lα may also be the same or different carboxylate groups, e.g.
where R5 is a substituted or unsubstituted aromatic, polycyclic or heterocyclic ring a polypyridyl group, R5 can also be a 2-ethyl hexyl group so Ln is 2-ethylhexanoate or R5 can be a chair structure so that Ln is 2-acetyl cyclohexanoate or Lα can be
where R is as above, e.g. alkyl, allenyl, amino or a fused ring such as a cyclic or polycyclic ring.
The different groups Lα may also be
where R, R1 and R2 are as above or
The groups Lp in the formula (A) above can be selected from
where each Ph which can be the same or different and can be a phenyl (OPNP) or a substituted phenyl group, other substituted or unsubstituted aromatic group, a substituted or unsubstituted heterocyclic or polycyclic group, a substituted or unsubstituted fused aromatic group such as a naphthyl, anthracene, phenanthrene or pyrene group. The substituents can be, for example, an alkyl, aralkyl, alkoxy, aromatic, heterocyclic, polycyclic group, halogen such as fluorine, cyano, amino, substituted amino etc. Examples are given in
—C—CH2═CH2—R
where R is as above.
Lp can also be compounds of formulae
where R1, R2 and R3 are as referred to above; for example bathophen shown in
where R1, R2 and R3 are as referred to above.
Lp can also be
where Ph is as above.
Other examples of Lp chelates are as shown in
Specific examples of Lα and Lp are tripyridyl and TMHD, and TMHD complexes, α, α′, α″ tripyridyl, crown ethers, cyclans, cryptans phthalocyanans, porphoryins ethylene diamine tetramine (EDTA), DCTA, DTPA and TTHA. Where TMHD is 2,2,6,6-tetramethyl-3,5-heptanedionato and OPNP is diphenylphosphonimide triphenyl phosphorane. The formulae of the polyamines are shown in
A preferred europium complex is Eu(DBM)3OPNP.
In one embodiment of the invention there is provided a structure which comprises (i) a few electrode, (ii) a layer of a hole transporting, (iii) a layer of an electroluminescent europium organo metallic or organic complex mixed with an iridium organo metallic or organic complex (A), (iv) an electron transmitting layer and (v) a second electrode and preferably there is also one or more layers of a europium electroluminescent organo metallic or organic complex adjacent to the layer (iii).
Optionally there can be other layers such as buffer layers in order that the holes and electrons combine in the electroluminescent layer and to improve the overall performance of the device.
The invention is illustrated in the examples which exemplify the synthesis of the diiridium complex and a device incorporating it.
A three-necked 1 litre round-bottomed flask under an inert atmosphere (nitrogen) was charged with sodium tert-butoxide (30.0 g, 310 mmol) and a magnetic stirrer-bar. Thf (dried and distilled over Na/benzophenone, 500 mL) was introduced, the temperature reduced to −78° C. and pentane-2,4-dione (30.0 g, 300 mmol) in Thf (dried and distilled over Nalbenzophenone, 100 mL) added over 30 min. The reaction was allowed to warm to around 0° C. and cooled with an ice-bath to maintain the temperature below 5° C. Iodine (38.0 g, 150 mmol) in Thf (dried and distilled over Na/benzophenone, 100 mL) was added dropwise. The reaction mixture was stirred for a further 30 min. with the ice-bath and then for 1 hour once the ice-bath had been removed. Diethylether (300 mL) was added to the reaction mixture, which was then poured into 200 mL saturated ammonium chloride solution (the pH was measured to ensure that the product had been neutralised). The organic layer was washed with 0.25M sodium thiosulfate solution (2×200 mL) and then brine (200 mL). The volatiles were removed in vacuo and the product recrystallised from ethanol (95%) to yield colourless crystals (19.3 g, 65%). M.p. 193-4° C. The product was used without further purification.
Iridium trichloride hydrate (0.388 g) was combined with 2-phenylpyridine (0.76 g), dissolved in a mixture of 2-ethoxyethanol (30 mL, dried and distilled over MgSO4) and water (10 mL), and refluxed for 24 hours. The solution was cooled to room temperature and the yellow/green precipitate collected on a glass sinter. The precipitate was washed with ethanol (60 mL, 95%), acetone (60 mL), and then dissolved in dichloromethane (75 mL) and filtered. Toluene (25 mL) and hexane (10 mL) were added to the filtrate and the volume reduced in vacuo to about 50 mL. Cooling yielded crystals (yellow/green) of the desired product (0.43 g, 72%). This was used without further purification.
Tetrakis(2-phenylpyridine-C2,N′)(μ-chloro) diiridium (II) (0.5 g, 0.47 mmol), 3,4-diacetyl-2,5-hexanedione (I) (0.092 g, 0.47 mmol) and sodium carbonate (dried at 100° C., 200 mg, 1.9 mmol) were refluxed under an inert atmosphere (nitrogen) in 2-ethoxyethanol (dried and distilled over magnesium sulfate, 50 mL) for 12 hours. On cooling to room temperature, a yellow precipitate was collected on a sinter (porosity 3) and washed with water (50 mL), hexane (50 mL) and diethylether (50 mL). The crude product was flash chromatographed on a silica column using dichioromethane as eluent. The dichloromethane was reduced in volume to about 5 mL and then methanol (100 mL) was added. The solution was, once more, reduced in volume to about 50 mL and the yellow product filtered (sinter, porosity 3) and washed with further methanol (100 mL). The product was dried in a vacuum oven at 80° C. for 2 hours. Yield (030 g, 46%).
Device Construction
An electroluminescent device is shown in
ITO/CuPc(8 nm)α-NPB(40 nm)/CBP+Ir2(diacac)2(dpp)2(12%)(20 nm)/BCP(6 mm)/Alq3(20 nm)/LiF(0.7 mn)Al
where CBP is shown in
An electric current was passed through the device and the properties of the emitted light measured and the results are shown in FIGS. 18 to 20 of the drawings.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0230076.2 | Dec 2002 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB03/05660 | 12/23/2003 | WO | 7/25/2005 |
