WO2004013252A1

WO2004013252A1 - Electroluminescent materials and devices

Info

Publication number: WO2004013252A1
Application number: PCT/GB2003/003377
Authority: WO
Inventors: Poopathy Kathirgamanathan; Matthew Samuel Kirkham; Alexander Kit Lay; Selvadurai Selvaranjan; Muttulingam Kumaraverl
Original assignee: Elam-T Limited
Priority date: 2002-08-02
Filing date: 2003-08-04
Publication date: 2004-02-12
Also published as: GB2406573B; GB0501866D0; GB0217918D0; AU2003255747A1; GB2406573A

Abstract

An electroluminescent device in which the electroluminescent layer comprises a rare earth, lanthanide or actinide bis[tris(pyrazolyl)borate)mono(acetonate).

Description

Electroluminescent Materials and Devices

The present invention relates to electroluminescent materials and devices incorporating electroluminescent materials.

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 quantum 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.

Hitherto electroluminescent metal complexes have been based on a rare earth, transition metal, lanthanide or an actinide or have been quinolates such as aluminium quinolate.

We have now devised electroluminescent devices based on borate complexes. According to the invention there is provided an electroluminescent device which comprises (i) a first electrode, (ii) a layer of an electroluminescent material which comprises an organo-metallic complex of formula

(I)

and (iii) a second electrode, where R^ R₂ and R₃ are the same or different and are 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; R_1; R and R₃ can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures, can be copolymerisable with a monomer, e.g. styrene, or can be polymer, oligomer or dendrimer substituents, and M is a metal, preferably a transition metal, rare earth, lanthanide or an actinide and m+n is the valency of M.

Preferably m is 1.

Where M is trivalent the compounds can have the formula

Examples of Ri and/or R₂ and/or R 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.

Examples include complexes of formula

or

where R can be selected from groups Ri.

The metal M is preferably selected from Sm(III), Eu(II), Eu(III), Tb(III), Dy(III), Yb(III), Lu(III), Gd (III), U(III), U(VI)O₂, Tm(III), Th(IN), Ce (III), Ce(IV), Pr(III), Νd(III), Pm(III), Dy(III), Ho(πi), Er(III).

The electroluminescent material (I) can be mixed with other electroluminescent materials and, in an embodiment of the invention, the electroluminescent material (I) is mixed with a second electroluminescent material formed of an organo metallic complex in which the metal is preferably a rare earth, actinide or lanthanide which is the same as M in (I) or has a wider band gap than the metal M in (I). There can be more than one other electroluminescent material mixed with (I).

Preferred second electroluminescent materials are described in Patent Application WO98/58037, the contents of which are incorporated by reference, and other electroluminescent materials are described in Patent Applications PCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024, PCT/GB99/04028, PCT/GB00/00268.

The more preferred second electroluminescent materials are of formula M₁(acac)_nOPNP where Mi is a transition metal, rare earth, lanthanide or actinide, acac is a betadiketone of formula

(A) (B) (C) where R_la R 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; Rι_; R 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 thioprienyl groups or nitrile.

Examples of Ri 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;

and OPNP is

Ph Ph

O =P N = P h

Ph Ph

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, perylene or pyrene group. The substituents can be the same or different and can be a substituted and unsubstituted aromatic, heterocyclic and polycyclic ring structure e.g. an alkyl, aralkyl, alkoxy, aromatic, heterocyclic, polycyclic group, halogen such as fluorine, cyano, amino, substituted amino groups etc., hydrocarbyl groups fluorocarbons such as trifluoryl methyl groups, halogens such as fluorine or thiophenyl groups; they can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer e.g. styrene. They can also be unsaturated alkylene groups such as vinyl groups or groups C CH₂=CH₂ — R where R is a substituent as above.

There can be a layer of a hole transmitting material between the first electrode (which. functions as the anode) and the electroluminescent material so the electroluminescent material is deposited on a hole transmitting layer to form an electroluminescent layer. The hole transmitting 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 or entirely takes place in the emitter layer.

Hole transmitting layers are used in small molecule based and polymer electroluminescent devices and in electroluminescent devices based on rare earth, metal complexes and any of the known hole transmitting materials in film form can be used.

The hole transmitting layer can be made of a film of an aromatic 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

(II) where R is in the ortho - or meta-position and is hydrogen, Cl-18 alkyl, Cl-6 alkoxy, amino, chloro, bromo, hydroxy or the group

where R is alky or aryl and R' is hydrogen, Cl-6 alkyl or aryl with at least one other monomer of formula I above.

Polyanilines which can be used in the present invention have the general formula

(HI) 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, BF , PF₆, H PO , H₂PO₄, arylsulphonate, arenedicarboxylate, polystyrenesulphonate, polyacrylate alkysulphonate, vinylsulphonate, vinylbenzene sulphonate, cellulosesulphonate, 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 de-protonated it can be easily evaporated i.e. the polymer is evaporable. Preferably evaporable de-protonated polymers of unsubstituted or substituted polymer of an amino substituted aromatic compound are used. The de-protonated unsubstituted or substituted polymer of an ammo 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. MacDiannid 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 6O% e.g. about 50% for example.

Preferably the polymer is substantially fully de-protonated.

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 x 10^"1 Siemen cm^"1 or higher.

The aromatic rings can be unsubstituted or substituted e.g. by a Cl 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, polyammoanthracenes, polyaminophenanthrenes, etc. and polymers of any other condensed polyaromatic compound. Polyammoanthracenes and methods of making them are disclosed in US Patent 6,153,726. The aromatic rings can be unsubstituted or substituted e.g. by a group R as defined above.

The polyanilines can be deposited on the first electrode by conventional methods e.g. by vacuum evaporation, spin coating, chemical deposition, direct electrodeposition etc. Preferably the thickness of the polyaniline layer is such that the layer is conductive and transparent and is preferably from 20nm to 200nm. The ployanilines can be doped or undoped. When they are doped they can be dissolved in a solvent and deposited as a film; when they are undoped they are solids and can be deposited by vacuum evaporation i.e. by sublimation.

The structural formulae of some other hole transmitting materials are shown in Figures 1, 2, 3, 4 and 5 of the drawings, where R, Ri_, 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; R_1; R 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 Ri and/or R 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.

The hole transporting material can optionally be mixed with the electroluminescent material in a ratio of 5 - 95% of the electroluminescent material to 95 to 5% of the hole transporting compound.

Other hole transporting materials which can be used are conjugated polymers.

US Patent 5807627 discloses an electroluminescence device in which there are conjugated polymers in the electroluminescent layer. The conjugated polymers referred to are defined as polymers for which the main chain is either fully conj ugated possessing extended pi molecular orbitals along the length of the chain or else is substantially conjugated, but with interruptions to conjugation, either random or regular along the main chain. They can be homopolymers or copolymers.

The conjugated polymer used can be any of the conjugated polymers disclosed or referred to in US 5807627, PCT/WO90/13148 and PCT/WO92/03490.

The conjugated polymers disclosed are poly (p-phenylenevinylene)-PPV and copolymers including PPN. Other preferred polymers are poly(2,5 dialkoxyphenylene vinylene) such as poly (2-methoxy-5-(2-methoxypentyloxy-l,4-phenylene vinylene), poly(2-methoxypentyloxy)-l,4-phenylenevinylene), poly(2-methoxy-5-(2- dodecyloxy-l,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, ploythiophenes and oligothiophenes.

In PPN 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 naphthlyene ring and the number of vinylene groups in each polyphenylenevinylene moeity can be increased e.g. up to 7 or higher.

The conjugated polymers can be made by the methods disclosed in US 5807627, PCT/WO90/13148 and PCT/WO92/03490.

The hole transmitting material and the light emitting metal compound can be mixed to form one layer e.g. in a proportion of^" 5 to 95% of the hole transmitting material to 95 to 5% of the light emitting metal compound.

Optionally there is a layer of an electron transmitting material between the second electrode (which functions as the cathode) and the electroluminescent material layer. The electron transmitting material is a material which will transport electrons when an electric current is passed through it; electron transmitting 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 aluminium or chromium. In place of the DBM moiety there can be a Schiffbase.

The electron injecting material can also be a cyano anthracene such as 9,10 dicyano anthracene, a polystyrene sulphonate and compounds of formulae shown in figs. 6 and 7 in wliich the phenyl rings can be substituted with substituents R as defined above.

Instead of being a separate layer the electron transmitting material can be mixed with the electroluminescent material to form one layer e.g. in a proportion of 5 to 95% of the electron transmitting material to 95 to 5% of the light emitting metal compound.

The invention also provides an electroluminescent device comprising (i) a first electrode which is the anode, (ii) a layer of a hole transporting material, (iii) a layer of the electroluminescent material of formula (I) hereinabove, (iv) a layer of an electron transmitting material and (v) a second electrode which is the cathode.

As described above the electroluminescent material of formula (I) can be mixed with a second electroluminescent material.

The electroluminescent layer can comprise a mixture of the electroluminescent material with the hole transmitting material and electron transmitting material.

The electroluminescent material can be deposited on the substrate directly by vacuum evaporation or evaporation from a solution in an organic solvent. The solvent wliich is used will depend on the material but chlorinated hydrocarbons such as dichloromethane and n-methyl pyrrolidone, dimethyl sulphoxide, tetrahydrofuran, dimethylformamide, etc. are suitable in many cases.

Alternatively electroluminescent material can be deposited by spin coating from solution, or by vacuum deposition from the solid state e.g. by sputtering, or any other conventional method can be used. Preferably the first electrode is a transparent substrate such as a conductive glass or plastic material which acts as the anode. Preferred substrates are conductive glass such as indium tin oxide coated glass, but any glass which is conductive or has a transparent 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 second electrode functions as the cathode and can be any low work function metal e.g. aluminium, calcium, lithium, silver/magnesium alloys etc.; aluminium is a preferred metal.

The display of the invention may be a monochromatic or polychromatic electroluminescent display depending on the metal which is selected. Rare earth chelate compounds are known which will emit a range of colours e.g. red, green, and blue light and white light and examples are disclosed in Patent Applications WO98/58037 PCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024, PCT/GB99/04028, PCT/GB00/OO268. By selection the metal M in the electroluminescent materials of the present invention different colour emitting devices can be formed. Thus, a full colour display can be formed by arranging three individual backplanes, each emitting a different primary monochrome colour, on different sides of an optical system, from another side of which a combined colour image can be viewed. Alternatively, displays using rare earth chelate electroluminescent compounds emitting different colours can be fabricated so that adjacent diode pixels in groups of three neighbouring pixels produce red, green and blue light. In a further alternative, field sequential colour filters can be fitted to a white light emitting display. Either or both electrodes can be formed of silicon and the electroluminescent material and intervening layers of a hole transporting and electron transporting materials can be formed as pixels on the silicon substrate. Preferably each pixel comprises at least one layer of a rare earth chelate electroluminescent material and a (at least semi-) transparent electrode in contact with the organic layer on a side thereof remote from the substrate.

Preferably, the substrate is of crystalline silicon and the surface of the substrate may be polished or smoothed to produce a flat surface prior to the deposition of electrode, or electroluminescent compound. Alternatively a non-planarised silicon substrate can be coated with a layer of conducting polymer to provide a smooth, flat surface prior to deposition of further materials.

In one embodiment, each pixel comprises a metal electrode in contact with the substrate. Depending on the relative work functions of the metal and transparent electrodes, either may serve as the anode with the other constituting the cathode.

When the silicon substrate is the cathode an indium tin oxide coated glass can act as the anode and light is emitted through the anode. When the silicon substrate acts as the anode, the cathode can be formed of a transparent electrode which has a suitable work function; for example by a indium zinc oxide coated glass in which the indium zinc oxide has a low work function. The anode can have a transparent coating of a metal formed on it to give a suitable work function. These devices are sometimes referred to as top emitting devices or back emitting devices.

The metal electrode may consist of a plurality of metal layers; for example a higher work function metal such as aluminium deposited on the substrate and a lower work function metal such as calcium deposited on the higher work function metal. In another example, a further layer of conducting polymer lies on top of a stable metal such as aluminium. Preferably, the electrode also acts as a mirror behind each pixel and is either deposited on, or sunk into, the planarised surface of the substrate. However, there may alternatively be a light absorbing black layer adjacent to the substrate.

In still another embodiment, selective regions of a bottom conducting polymer layer are made non-conducting by exposure to a suitable aqueous solution allowing formation of arrays of conducting pixel pads which serve as the bottom contacts of the pixel electrodes.

As described in WO00/60669 the brightness of light emitted from each pixel is preferably controllable in an analogue manner by adjusting the voltage or current applied by the matrix circuitry or by inputting a digital signal which is converted to an analogue signal in each pixel circuit. The substrate preferably also provides data drivers, data converters and scan drivers for processing information to address the anay of pixels so as to create images. When an electroluminescent material is used which emits light of a different colour depending on the applied voltage the colour of each pixel can be controlled by the matrix circuitry.

In one embodiment, each pixel is controlled by a switch comprising a voltage controlled element and a variable resistance element, both of which are conveniently formed by metal-oxide-semiconductor field effect transistors (MOSFETs) or by an active matrix transistor.

The devices of the present invention can be used in both active and passive applications such as displays.

The invention is illustrated in the following examples in which examples 1 to 3 are examples of the preparation of the heteroleptic terbium complexes and examples 4 to 11 are examples of the preparation of heteroleptic europium complexes. The main ligand used in all three syntheses is tris(pyrazolyl)borate, which is synthesised as the potassium salt, the preparation of which is given first.

Preparation of potassium tι~is(pyrazolyl)borate

Materials required

Potassium Borohydride 98+% Aldrich

Pyrazole 98% Aldrich

Toluene Analar Aldrich n-Hexane Analar Aldrich

A 500 mL round bottom flask was charged with 6.48 g (0.12 mol) Potassium borohydride, 32.68 g (0.48 mol) pyrazole and a magnetic stirrer bar. A 30 cm long water-cooled condenser was fitted and from the top of this a tube was led (via a trap) to a hydrogen collection vessel (in this case an upturned 10 L flask filled with water in a water bath). The mixture was stirred and heated to 90 °C whereupon the pyrazole melted and hydrogen gas evolution was seen. The temperature was increased steadily to 120 °C until 4 L of H₂ had evolved. The temperature was then raised to 190 °C until the total hydrogen evolution was 9 L (0.36 mol). The tube from the top of the condenser was removed and the flask cooled to 150 °C. The hot solution was decanted into a 250 mL conical flask containing 50 mL of toluene and a magnetic stirrer bar. The solution was stirred and formed a white precipitate on standing. This was filtered off while the solution was still hot, washed with hot toluene (2 x 25 mL) and hot hexane (1 x 25 mL). The white solid was then dried in a vacuum oven at 70°C overnight. Yield of K[HB(C₃H₃N₂)₃].¹/2H₂O was 20.36g (7.7 x 10^"2 mol), 65 %. Melting point 185-187 °C.

The other ligands, wliich have been found to facilitate the formation of the heteroleptic europium species, are shown in Table 1 below.

Table 1

Ligands 1 and 2 were purchased and used without purification

1. 4A4-Trifluoro-l-phenyl-1.3-butanedione Aldrich 99 %

2. 4, 4.4-Trifluoro-l-naphthyl-l,3-butanedione Fluorochem 98+ %

Ligands 3-8 were all prepared by the same procedure, wliich is outlined below. The chemicals used for these syntheses are listed below.

Ethyl trifluoroacetate (3-6) Aldrich 99 %

Ethyl pentafluoropropionate (7-8) Aldrich 98 %

2-Acetylphenanthrene (3) Aldrich 98 %

2-Acetylfluorene (4) Aldrich 98 %

4-Acetylbiphenyl (5) Aldrich 99%

4'-Fluoroaectophenone (6) Aldrich 99 %

3 ' ,4 ' ,5 ' -Trimethoxyacetophenone (7) Aldrich 98 %

Potassium tert-butoxide Lancaster 97 %

Toluene BDH Analar

Diethyl Ether BDH Analar

Deionized water

Ethanol (denatured with 4.8 % methanol) Fluka n-Hexane BDH Analar

I M Hydrochloric Acid

Magnesium sulfate BDH G.P.R.

Ligand Syntheses

3. 4,4, 4-Trifluoro-l-(phenanhren-2-yl)-l,3-butanedione

2-acetylphenanthrene (lOg. 0.045 mol) and Potassium tert-butoxide (5.61 g, 0.050 mol) of which were stirred in 200 mL toluene under an atmosphere of argon; to the stirred suspension, ethyl trifluoroacetate (5.4 mL, 0.045 mol) was added. The mixture was stirred overnight, after which the toluene was removed. 100 mL of diethyl ether and 100 mL of IM HCl were added to the residue and stirred until the solid dissolved giving a coloured ether layer. The ether layer was separated and washed three times with 50 mL deionsed water, and dried over magnesium sulfate. The solution was filtered and rotary evaporated and the residue recrystallised from hot ethanol to give a yellow crystalline product. Yield 8.5 g (60 %).

4. 4,4, 4-Trifluoro-l-(phenanthren-2-yl)-l,3-butanedione

Prepared as for 3 but using 2-acetylfluorene. Yellow crystalline product obtained. Yield 10.2 g (69 %).

5. 4,4, 4-Trifluoro-l-(biphenyl-4-yl)-l, 3-butanedione

Prepared as for 3 but using 4-acetylbiphenyl. Off-white crystalline product obtained. Yield 11.8 g (79 %).

6. 4,4, 4-Trifluoro-l-(4 -fluorophenyl)- 1, 3-butanedione

Prepared as for 3 but using 4'-Fluoroacetophenone. Product is oily in nature so is extracted with hot hexane, filtered and cooled in the fridge to give a pale yellow crystalline product. Yield 6.3 g (37 %).

7. 4,4,5,5, 5-Pentafluoro-l-π.4.5-trimethoxyphenyl)-l,3-pentanedione

Prepared as for 3 but using 3',4',5'-triinethoxyacetophenone and 1 equivalent of ethyl pentafluoropropionate instead of ethyl trifluoroacetate. Product obtained as a yellow solid. Yield 8.7 g (51 %). 8. 4, 4,5,5,5-Pentafluoro-l-(fluoren-2-yl)-l, 3-pentanedione

Prepared as for 7 but using 2-acetyl.fluorene. Product obtained as a yellow/orange solid. Yield 1 1.2 g (66 %).

Example 1. Preparation of terbium(III) bis(tris(pyrazolvD borate) mono (4- butyryl-5-methyl-2-phenyl-2, 4-dihydro-pyrazol-3-onate) - Compound A

fi) Ligand synthesis

Materials required

3-Methyl-l -phenyl-2-pyrazolin-5-one 99% Aldrich n-Butyryl chloride 99+% Aldrich

Calcium hydroxide 95+% Aldrich

Dioxane (dried over sodium) 99+% Aldrich

Hydrochloric Acid (2 M)

- diluted from cone. HCl (s.g. 1.18) Analar BDH

Diethyl Ether Analar BDH

The synthesis of this ligand was done in a fumehood due to the strong smell. In a large round bottom flask, 3-Methyl-l-phenyl-2-pyrazolin-5-one (5.0 g, 0.029 mol) was dissolved in dry dioxane, heating as necessary. The solution was cooled and calcium hydroxide (6.4 g, 0.086 mol) added to the stirred solution, followed by dropwise addition of n-butyryl chloride (3.36 g, 0.032 mol). The mixture was then refluxed for 4 hours giving an orange mixture. The mixture was then poured into 400 mL of 2 M HCl whereupon a brown solid was precipitated. This was filtered off and washed copiously with water. Recrystallisation from diethyl ether yielded 2.5 g (36 %) of 4-butyryl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3 -one as a light brown solid. (ii) Complex synthesis

Materials required

Terbium(III) chloride hexahydrate 98% Avocado

Potassium hydrotris(l -pyrazolyl)borate see above

4-butyryl-5 -methyl-2-phenyl-2,4-dihydro-pyrazol-3 -one see above

Sodium Hydroxide GPR BDH

Deionised water

Dichloromethane Analar BDH n-Hexane Analar BDH

Magnesium sulfate dried GPR BDH

4-butyl-5-methyl-2-phenyl 2,4 dihydropyrazol-3-one (2.33 g, 9.6x10 mol) and sodium hydroxide (0.383 g, 9.6x10^" mol) were added to 100 mL of deionised water and the mixture warmed and stirred until the solution was homogeneous. Potassium tris(pyrazolyl)borate (5.00 g, 1.91 x 10^" mol) was dissolved in 100 mL of deionised water, added to the aqueous ligand solution and stirred for a further 10 mins. Slightly less than 1 equivalent (with respect to the pyrazolone) of terbium(III) chloride hexahydrate (3.50 g, 9.37xl0^"3 mol) was dissolved in deionised water. The ligand solution was added slowly to the stirred terbium solution to give an immediate white ppt. The crude product is collected by filtration.

The white solid was dissolved into 200 mL of a 50:50 mix of deionised water/dichloromethane and stirred for 15 mins until the solid had mostly dissolved into the dichloromethane phase. The mixture was transferred to a separating funnel and the dichloromethane fraction collected. Dry magnesium sulfate was added to remove any remaining water and filtered off. The dry dichloromethane solution was then evaporated to dryness to give a white solid, which was then recrystallised using a minimum amount of dichloromethane and layering with n-hexane. The crystals were collected by filtration and washed with cold n-hexane. Terbium(flι) bis(fris(pyrazolyl)borate)mono(4-butyryl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3- onate) is obtained as a white crystalline solid, (1st crop, 6.2 g, 80%). DSC:- Mpt 257.3 -262.2 °C, Tg 98.0°C.

The complex had the formula

Example 2. Preparation of terbium (III) bisCtris(pyrazolyl) borate) monod- indol-l-yl-butane-l,3-dionate - Compound B

(D Ligand synthesis

Materials required Indole 99% Lancaster 2,2,6-Trimethyl-4H- l,3-dioxin-4-one (TMDO) 95% Aldrich Xylenes (isomers plus ethylbenzene) 98.5+% Aldrich Ethanol (denatured with 4.8 % methanol) -96%* Fluka * based on denaturant-free substance

Indole (20.0 g, 0.17 mol) and TMDO (23.5 mL, 0.18 mol) were stirred in 35 mL of xylenes in a 100 mL conical flask. The flask was immersed in an oil bath at 155°C and stirred for 30 mins during which time acetone was evolved. The mixture was cooled and poured into 200 mL of ethanol. A colourless solid was fomied. This was collected by filtration and recrystallised from hot ethanol to yield 20.0 g (58 %) of I - indol-l-yl-butane-l,3-dione as colourless crystals.

(ii) Complex synthesis

Materials required

Terbium(III) chloride hexahydrate 98% Avocado

Potassium hydrotris(l -pyrazolyl)borate see above

1 -indol- 1 -yl-butane- 1 ,3 -dione see above

Sodium Hydroxide GPR BDH

Deionised water

Dichioromethane Analar BDH n-Hexane Analar BDH

Magnesium sulfate dried GPR BDH

1 -indol- 1 -yl-butane- 1,3 -dione (1.93 g, 9.6xl0^"3 mol) and sodium hydroxide (0.383 g, 9. 6x10^"3 mol) were added to 100 mL of deionised water and the mixture warmed and stirred until the solution was homogeneous. Potassium tris(pyrazolyl)borate (5.00g, 1.91xl0^"2 mol) was dissolved in 100 mL of deionised water, added to the aqueous ligand solution and stirred for a further 10 mins. Slightly less than 1 equivalent (with respect to 1 -indol- l-yl-butane-1,3 -dione) of terbium(III) chloride hexahydrate (3.50 g, 9.37x10^"3 mol) was dissolved in deionised water. The ligand solution was added slowly to the stirred terbium solution to give an immediate white precipitate. The crude product is collected by filtration.

The white solid was dissolved into 200 mL of a 50:50 mix of deionised water/dichloromethane and stirred for 15 mins until the solid had mostly dissolved - 26 -

into the dichloromethane phase. The mixture was transferred to a separating funnel and the dichloromethane fraction collected. Dry magnesium sulfate was added to remove any remaining water and filtered off. The dry dichloromethane solution was then evaporated to dryness to give a white solid, which was then recrystallised using a minimum amount of dichloromethane and layering with n-hexane. The crystals were collected by filtration and washed with cold n-hexane. Terbium(III)bis(trispyrazolyl)borate)mono( 1 -indol- 1 -yl-butane- 1 ,3 -dionate) is obtained as a white crystalline solid, (1st crop, 4.9 g, 65 %). DSC:- Mpt 232.2- 236.0°C, Tg 97.8 °C.

The complex had the formula

Example 3. Preparation of terbium (III) bis(tris(pyrazoIyl) borate) mono (acetylacetonate) - Compound C

Materials required

Terbium(III) chloride hexahydrate 98% Avocado Potassium hydrotris(l -pyrazolyl)borate see above

Acetylacetone (pentane-2,4-dione) 99+% Aldrich

Sodium Hydroxide GPR BDH

Deionised water

Dichioromethane Analar BDH n-Hexane Analar BDH

Magnesium sulfate dried GPR BDH

Acetylacetone (0.959 g, 9.57xl0^"3 mol) and sodium hydroxide (0.383 g, 9.57xl0^"3 mol) were added to 100 mL of deionised water and the mixture stirred at room temperature for 15 mins or until the solution became homogeneous. Potassium tris(pyrazolyl)borate (5.00g, 1.91x10^" mol) was dissolved in 100 mL of deionised water, added to the aqueous acetylacetone and stirred for a further 10 mins. Slightly less than 1 equivalent (with respect to acetylacetone) of terbium(III) chloride hexahydrate (3.50 g, 9.37x 10^"3 mol) was dissolved in deionised water. The ligand solution was added slowly to the stirred terbium solution to give an immediate white ppt. The crude product is collected by filtration.

The white solid was dissolved into 200 mL of a 50:50 mix of deionised water/dichloromethane and stirred for 15 mins until the solid had mostly dissolved into the dichloromethane phase. The mixture was transferred to a separating funnel and the dichloromethane fraction collected. Dry magnesium sulfate was added to remove any remaining water and filtered off. The dry dichloromethane solution was then evaporated to dryness to give a white solid, which was then recrystallised using a minimum amount of dichloromethane and layering with n-hexane. The crystals were collected by filtration and washed with cold n-hexane. Terbium(III) bis(tris(pyrazolyl)borate)mono(acetylacetonate) is obtained as a white crystalline solid, (1st crop, 5.13 g, 80%). DSC:- Mpt. 167.1- 173.7°C, Tg 73.6 °C. The complex had the formula

Examples 4 to 11

Synthetic procedures for the preparation of heteroleptic europium tris(pyrazolyl)borate complexes.

The main ligand used in all the following syntheses is tris(pyrazolyl)borate, which is synthesised as the potassium salt as described above.

Complex Synthesis

Materials required (other than those previously described) Europium(III) chloride hexahydrate Acros 99.9 %

Dichloromethane BDH Analar

Example 4 Preparation of Europium(IH) bis(tris(pyrazolyl)borate)mono(4,4,4- trifluoro-l-phenyl-1, 3-butanedionate) Compound D

4,4,4-Trifluoro-l-phenyl-l,3-butanedionate (2.07 g, 0.009 mol) and potassium-tert- butoxide (1.08 g, 0.009 mol) were added to 100 mL of ethanol and the mixture stirred until the solution became homogeneous, heating where required. Potassium tris(pyrazolyl)borate (5.0 g, 0.01 9 mol) was dissolved in 100 mL of deionised water, added to the ethanolic solution and stirred for a further 10 mins. Slightly less than 1 equivalent (with respect to the diketone) of europium (III) chloride hexahydrate (3.29 g, 0.009 mol) was dissolved in deionised water. The ligand solution was added slowly to the stirred europium solution to give an immediate pale yellow precipitate. The mixture was stirred overnight.

Addition of dichloromethane to the mixture and stirring for 10 mins allows extraction of the europium complex. The mixture was transferred to a separating funnel and the dichloromethane fraction collected. Dry magnesium sulfate was added to remove any remaining water and filtered off. The dry dichloromethane solution was then evaporated to dryness to give a yellow solid, which was then recrystallised using a minimum amount of dichloromethane and layering with n-hexane. The crystals were collected by filtration and washed with cold n-hexane. Europium(Ill) bis(tris(pyrazolyl)borate)mono(4,4,4-trifluoro- 1 -phenyl- 1 ,3 -butanedionate) is obtained as an off white crystalline solid, (1st crop, 4.35 g, 61 %). DSC:- Mpt. 227.0- 228.9 °C, Tg 88.6 °C. PL:- 0.097 cdm^μW^"1 CIE:- (x,y) 0.66, 0.34.

Example 5 Preparation of Europium (III) bis(tris(pyrazolyl) borate) mono(4, 4, 4-trifluoro-l -naphthyl-1, 3-butanedionate) Compound E

This complex is prepared in the same way as Compound D but with 4,4,4-trifluoro-l- naphthyl-1, 3-butanedione used as the second ligand. Europium(III) bis(tris(pyrazo 1 yl)borate)mono(4,4,4~trifluoro~I-napthyl- 1 ,3 -butanedionate) is obtained as a pale yellow crystalline solid, (1st crop, 5.23 g, 69 %). DSC:- Mpt. 229.0-231.9 °C, Tg 99.7 °C. PI:- 0.137 cdm^"2μW^_1; CIE:- (x,y) 0.66,0.34. Example 6 Preparation of EuropiumdII) bis(tris(pyrazolyl)borate)mono(4. 4. 4- trifluoro- l-(phenanthren-2-yl)-l, 3-butanedionate) Compound F

This complex is prepared in the same way as Compound D but with 4,4,4-trifluoro-l- phenanthren-2-yl- 1 ,3 -butanedione used as the second ligand.

Europium(III) bis(tris(pyrazolyl)borate)mono(4,4,4.trifluoro-l-(phenanthren-2-yl)- 1,3 -butanedionate) is obtained as a yellow crystalline solid, (1st crop, 5.89 g, 73 %). DSC:- Mpt. 291.2 -296.7 °C. PL:- 0.129 cdm^μW^CIE:- (x,y) 0.66, 0.34.

Example 7 Preparation of EuropiumdII) bis(tris(pyrazolyl)borate)mono(4, 4, 4- trifluoro-l-(fluoren-2-yI)-l, 3-butanedionate) Compound G

This complex is prepared in the same way as Compound D but with 4,4,4-trifluoro-l- (fluoren-2-yl)-l,3 -butanedione used as the second ligand. EuropiumdII) bis(tris(pyrazolyl)borate)mono(4,4,4-trifluoro-l-(fluoren-2-yl)-l ,3 -butanedioflate) is obtained as a yellow crystalline solid, (1st crop, 4.85 g, 61 %). DSC:- Mpt. 281.5 - 285.6 °C. PL:- 0.124 cdm^"2μW^_1; CIE:- (x,y) 0.66,0.34.

Example 8 Preparation of EuropiumdII) bis(tris(pyrazolyl)borate)mono(4,4,4- trifluoro-l-(biphenyl-4-yl)-l,3-butanedionate) Compound H

This complex is prepared in the same way as Compound D but with 4,4,4-trifluoro-l- (biphenyl-4-yl)-l,3 -butanedione used as the second ligand. Europium(lll) bis(tris(pyrazolyl)borate)mono(4,4,4-trifluoro-l -(biphenyl-4-yl)-l, ,3 -butanedionate) is obtained as a pale yellow crystalline solid, (1st crop, 3.25 g, 42%). DSC:-. Mpt. 241.6 - 244.4 °C, Tg 107,5 °C. PL:- 0.114 cdrn W^"1; CIE:- (x,y) 0.66,0.34. Example 9 Preparation of EuropiumdII) bis(tris(pyrazolyl)borate)mono(4. 4. 4trifluoro-l-(4-fluorophenyl) -1 ,3-butanedionate) Compound I

This complex is prepared in the same way as Compound D but with 4,4,4-trifluoro-l- (4-fluorophenyl)-l,3 -butanedione used as the second ligand. Europium(III) bis(tris(pyrazolyl)borate)mono(4, 4, 4trifluoro-l-(4-fluorophenyl) -1 ,3- butanedionate) is obtained as a pale yellow crystalline solid, 1st crop. 2.68 g, 37 %). DSC:- Mpt. 225.7-231.5 °C, Tg 90.2°C PL:- 0.100 cdm^μW^"1 ; CIE:-(x,y) 0.66, 0.34.

Example 10 Preparation of Europium (III) bis(tris (pyrazolyl) borate) mono (4,4,5,5,5-pentafluoro-1 -(3 .4,5-trimethoxyphenvD-l, 3-pentanedionate Compound J

This complex is prepared in the same way as Compound D but with 4,4,5,5,5- pentaflluoro-l-(3,4,5-trimethoxyphenyl)-l,3-pentanedione used as the second ligand.

Europium (III) bis(tris (pyrazolyl) borate) mono (4,4,5,5,5-pentafluoro-] -(3 .4,5- trimethoxyphenyl)-l,3-pentanedionate)is obtained as a yellow crystalline solid, (1st crop, 6.54 & 82 %). DSC:- Mpt. 235.2 - 237.9 °C, Tg 88.0 °C.

PL:- 0.118 cdm^'VW^"1; CIE:- (x,y) 0.66,0.33.

Example 11 Preparation of EuropiumdII) bis(tris(pyrazolyl) borate) mono

(4,4,5, 5,5-pentafluoro-l-(fluoren-2-yl)-l,3-pentanedionate) Compound K

This complex is prepared in the same way as Compound D but with 4,4,5,5,5- pentafluoro-l-(fluoren-2-yl)-l,3-pentanedione used as the second ligand. Europium(III) bis(tris(pyrazolyl) borate) mono (4,4,5, 5,5-pentafluoro-l-(fluoren-2- yl)-l, 3-pentanedionate) is obtained as a yellow crystalline solid, (1st crop, PL :- 6.02 cdm^μW^"1; CIE:- (x,y) 0.66,0.33.

Crystalline products contain traces of occluded dichloromethane. Therefore the crystals are ground to a powder and dried in a vacuum oven at 60°C for 24 hours to give the pure products.

Example 12 Device Construction

An ITO coated glass piece (1 x 1cm² ) had a portion etched out with concentrated hydrochloric acid to remove the ITO and was cleaned and dried. The device was fabricated by sequentially forming on the ITO, by vacuum evaporation, layers of TPD, Compound C and aluminium quinolate to form a structure of :- ITO(10Ω/sqr)/TPD(40nm)/ Compound C (80nm)/Alq3(40mn)/Al where ITO is an indium coated glass substrate anode; TPD is as shown in fig. 4 ; Compound C is the terbium complex of Example 3; Alq3 is aluminium quinolate and Al is an aluminium cathode.

The device is shown schematically in fig. 8 where (1) is the ITO anode; (2) is the TPD layer; (3) is the Compound C layer; (4) is an aluminium quinolate layer and (5) is an aluminium cathode.

The organic coating on the portion which had been etched with the concentrated hydrochloric acid was wiped with a cotton bud.

The coated electrodes were stored in a vacuum desiccator over a molecular sieve and phosphorous pentoxide until they were loaded into a vacuum coater (Edwards, 10^"6 torr) and aluminium top contacts made. The active area of the LED's was 0.08 cm by 0.1 cm the devices were then kept in a vacuum desiccator until the electroluminescence studies were performed.

The ITO electrode was always connected to the positive terminal. The current vs. voltage studies were carried out on a computer controlled Keithly 2400 source meter. The electroluminescent properties were measured and shown in fig. 9. Example 13

A device was fabricated as in Example 12 which had the structure ITO/DDPANI(8ιιm)/TPD(40nm)/Tb(tmhd)₃OPNP:Tp₂Tb(acac)/Liq(32nm)/Al where Tb(tmhd)₃OPNP is

Tb(tmhd)₃OPNP

Tp Tb(acac) is

Tp₂Tb(acac) DDPANI is di-dedoped polyaniline. The /Tb(tmhd)₃OPNP:Tp₂Tb(acac)/layer was formed by concurrent vacuum deposition to form the mixed layer. The weight ratio of the Tb(tmhd)₃OPNP andTp₂Tb(acac) is conveniently shown by a relative thickness measurement.

The electroluminescent properties were measured as in Example 12 and are shown in figs. 10 to 14 of the drawings.

Example 14

A device was made as in fig. 13 of structure ITO/DDPANI(5nm)/α- PB(40nm)/Tb(tmhd)₃OPNP:Tp₂Tb(indacac)(3:2)(71nm)/Alq3(20nm)/AI where Tp Tb(indacac) is

Tp₂Tb(indacac)

The electroluminescent properties were measured as in Example 12 and are shown in figs. 15 and 16 of the drawings. Example 15

A device as in example 14 was fabricated in which Tp₂Tb(pyr) was used in place of the Tp₂(indacac) to give a device structure ITO/DDPANI(5nm)/TPD(40nm)/Tb(tm d)₃OPNP:Tp₂(pyr)(3:2)(74nm)/Alq3(20nm)/AI, where Tp (pyr) is

Tp₂Tb(pyr)

and TPD is as shown in Fig. 4. The electroluminescent properties were measured as in Example 12 and are shown in figs. 17 and 18 of the drawings.

Example 16

A device of structure ITO/α-NPB(40mn)/Tρ₂Eu(tfnapacac)(l OOnm)/BCP(30mn)/Al was fabricated as in Example 12 where BCP is bathocupron and Tp Eu(tfnapacac) is

Tp₂Eu(tfnapacac) The electroluminescent properties were measured as in Example 12 and the results shown in figs. 19 and 20.

Example 17

A device of structure ITO/α-NPB(40nm)/Eu(dbm)₃:Tp₂Eu(tfnapacac)(l:l)(100nm)/Alq₃(40nm)/Al

Tp₂Eu(tfhapacac) was fabricated as in Example 13.

The electroluminescent properties were measured as in Example 12 and the resnlts shown in figs. 21 and 22. Example 18

A device of structure ITO/ -NPB(30nm)/Tp₂Eu(tfbiphenacac)(70nm)/BCP(25nm)/Al where Tp₂Eu(tfbiphenacac) is

Tp₂Eu(tfbiphenacac)

was fabricated by the process of Example 12 and the spectrum measured as in Example 12 and the results shown in fig. 23.

Example 19

A. device of structure

ITO/α-NPB(30nm)/Eu(dbm)₃OPNP:Tp₂Eu(tfbiphenapacac)(3:2)(70nm)/BCP(25nm)/Al by the process of example 13 where Eu(dbm)₃OPNP is

Eu(dbm)₃OPNP The electroluminescent spectrum was measured as in Example 12 and the results shown in fig. 24.

Example 20

A comparison of the devices of Examples 18 and 19 and are shown in Table 2.

Table 2

Tp₂Eu(tfbiphenacac) as Emissive Layer

ITO/α-NPB (30 nm)/Tp₂Eu(tfbiphenacac) (70 nm)/BCP (25 nm)/Al

Eu(dbm)₃OPNP + Tp₂Eu(tfbiphenacac) as Emissive Layer

ITO/α-NPB (30 nm)/Eu(dbm)₃OPNP:Tp₂Eu(tfbiphenacac) (3 :2) (70 nm)/BCP (25 nm)/Al

Claims

1. An electroluminescent device which comprises (i) a first electrode, (ii) a layer of an electroluminescent material which comprises an organo-metallic complex of formula

(I)

and (iii) a second electrode where Ri and R₂ are the same or different and are 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; R_1; R₂ and R are the same or different and are 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, -CH₂CH₃ groups halogens such as fluorine or thiophenyl groups; R_1; R and R₃ can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures, can be copolymerisable with a monomer e.g. styrene or can be polymer, oligomer or dendrimer substituents, M is a transition metal, rare earth, lanthanide or an actinide, and m +n is the valency of M.

2. An electroluminescent device as claimed in claim 1 in which the organometallic complex (I) is

3. An electroluminescent device as claimed in claim 2 in which the organometallic complex is

or

or

where R can be selected from groups Ri

4. An electroluminescent device as claimed in any one of claims 1 to 3 in which M is Sm(III), Eu(II), Eu(III), Tb(III), Dy(III), Yb(III), Lu(III), Gd (III), U(III), U(VI)O₂, Tm(III), Th(IN), Ce (III), Ce(IN), Pr(III), Νd(III), Pm(III), Dy(III), Ho(III), Er(III).

5. An electroluminescent device as claimed in any one of claims 1 to 4 in which the electroluminescent material (I) is mixed with a second electroluminescent organo metallic complex.

6. An electroluminescent device as claimed in claim 5 in which the metal in the second electroluminescent organometallic complex is the same as M in (I) or has a wider band gap than the metal M in (I).

7. An electroluminescent device as claimed in claim 5 or 6 in which the second elctroluminescent organometallic complex is of formula M₁(acac)_nOPNP where Mi is a transition metal, rare earth, lanthanide or actinide, acac is a betadiketone of formula (A), (B) or (C) herein and OPNP is as defined herein.

8. An electroluminescent device as claimed in any one of claims 1 to 7 which comprises (i) a first electrode which is the anode, (ii) a layer of a hole transporting material, (iii) a layer of the electroluminescent material, (iv) a layer of an electron transmitting material and (v) a second electrode which is the cathode.

9. An electroluminescent device as claimed in claim 8 in which the hole transmitting layer is an aromatic amine complex.

10. An electroluminescent device as claimed in claim 9 in which the hole transmitting layer is formed from a poly(vinylcarbazole), N,N'-diphenyl-N,N'-bis (3- methylphenyl) -1,1' -biphenyl -4,4 '-diamine (TPD), polyaniline, or a substituted polyaniline.

11. An electroluminescent device as claimed in claim 9 in which the hole transmitting layer has a formula (II) or (III) herein or as in figs. 1 to 5 of the drawings.

12. An electroluminescent device as claimed in claim 9 in which the hole transmitting layer is a conjugated polymer as herein specified.

13. An electroluminescent device as claimed in claim 8 in which the hole transmitting layer is selected from poly (p-phenylenevinylene)-PPN and copolymers including PPV, poly(2,5 dialkoxyphenylene vinylene), 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, ploythiophenes and oligothiophenes.

14. An electroluminescent device as claimed in any one of claims 8 to 13 in which the hole transmitting material and the electroluminescent material are mixed to form one layer in a proportion of 5 to 95% of the hole transmitting material to 95 to 5% of the light emitting metal compound.

15. An electroluminescent device as claimed in any one of claims 8 to 14 in which the electron transmitting material is a metal quinolate, a compound of formula Mx(DBM)_n where Mx is a metal and DBM is dibenzoyl methane and n is the valency of Mx or as in figs. 6 or 7 of the drawings.

16. An electroluminescent device as claimed in claim 15 in which the metal quinolate is lithium, sodium, potassium, zinc, magnesium or aluminium quinolate.

17. An electroluminescent device as claimed in any one of claims 8 to 16 in wliich the electron transmitting material and the electroluminescent material are mixed to form one layer in a proportion of 5 to 95% of the electron transmitting material to 95 to 5% of the light emitting metal compound.

18. An electroluminescent device as claimed in any one of claims 8 to 17 in which the anode and/or cathode is formed on a substrate of crystalline silicon and the surface of the substrate may be polished or smoothed to produce a flat surface prior to the deposition of electrode, or electroluminescent compound.

19. An electroluminescent device as claimed in any one of claims 8 to 17 in which the anode and/or cathode is formed on a substrate of a non-planarised silicon substrate.

20. An electroluminescent device as claimed in any one of claims 8 to 19 in which there is a copper phthalocyanine layer on the first electrode and a lithium fluoride layer on the second electrode.