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Definitions

• This invention relates to metal-containing phosphorescent dene-rimers with at least one dendron that comprises one or more units that contain a nitrogen atom and light-emitting devices containing them.
• a wide range of luminescent low molecular weight metal complexes are known and have been demonstrated as both light emitting and charge transporting materials in light emitting devices, in particular light-emitting diodes (LEDs) also known as electroluminscent (EL) devices.
• LEDs light-emitting diodes
• EL electroluminscent
• For fluorescent molecules a simple analysis of spin statistics associated with the injection of oppositely charged carriers which pair to form excitons shows that only 25% ofthe excitons formed in the LED are in the singlet state with the remainder forming triplets assuming 100% capture of the charged species.
• the barrier of 25% for singlet excitons may be exceeded for fluorescent polymers but it is still known to be far from 100%.
• the triplet states decay non-rradiativery.
• the possibility to extract luminescence from the triplet excited state has recently been demonstrated by inclusion of phosphorescent guest metallic complexes in host matrices.
• These phosphorescent metal complexes are generally used in a blend with an organic host.
• the organic host plays an important role as it is involved in charge transport but also acts as a triplet source, i.e. it transfers the excited state to the metal complex for emission.
• the main type of hosts used are based on carbazoles, e.g., CBP (4,4'-N,N'-dicarbazole-biphenyl) (H.Z/ Xie et al, Adv.
• TCTA 4,4',4"-t ⁇ is-(carbazol-9-yl) triphenylarnine
• TCTA contains a atylarnine moiety and it has been shown that this can be advantageous.
• blend systems are sensitive to the concentration ofthe guest in the host and only low concentrations ofthe guest can be used before phase separation leads to aggregation or intermolecular interactions ofthe emissive species increases and this leads to emission quenching.
• Dendrimers are branched macromolecules in which branched dendrons (also called dendrites) are attached to a core.
• the properties ofthe dendrimers make them ideal for solution processing and allow incorporation of metal complex chromophores, which have been demonstrated to be effective in light emitting devices (LEDs), into a solution processable system.
• Phosphorescent guest-host emissive layers that are produced by solution processing from a homogeneous solution should have the advantage that the phosphorescent guest is evenly distributed throughout the formed film, assuming of course that there is no phase separation.
• the dendritic structure can be involved in the transportation of charge.
• the single molecule can allow simpler manufacturability. 5.
• the single molecule can give improved electrochemical stability.
• the present invention provides a light emitting device and, in particular, a light emitting diode, which comprises at least one layer that contains a phosphorescent organometallic dendrimer with a metal cation and two or more coordinating groups as part of its core and wherein at least two of said coordinating groups each have a dendron attached, at least one of which dendrons comprises at least one nitrogen atom which forms part of an aromatic ring system or is directly bonded to at least two aromatic groups, as well as the dendrimers used therein.
• a light emitting diode which comprises at least one layer that contains a phosphorescent organometallic dendrimer with a metal cation and two or more coordinating groups as part of its core and wherein at least two of said coordinating groups each have a dendron attached, at least one of which dendrons comprises at least one nitrogen atom which forms part of an aromatic ring system or is directly bonded to at least two aromatic groups, as well as the dendrimers used therein.
• said phosphorescent dendrimer is located between an anode and a cathode.
• the dendrimers typically have the formula (I): CORE - [DENDRON] n CO
• each DENDRON which may be the same or different, represents a dendritic molecular structure comprising at least one nitrogen atom which forms part of an aromatic ring system or is directly attached to at least two aromatic groups such that two or more coordinating groups have different DENDRON attached, CORE terminating in the single bond to the first nitrogen atom or aromatic ring to which more than one dendritic chain is attached, said nitrogen atom or ring forming part of said DENDRON.
• the dendrons are inherently at least partially conjugated.
• the CORE moiety is typically an organometallic moiety.
• an "organometallic” compound or an “organometallic” moiety is a metal-containing compound or moiety.
• Preferred “organometallic” compounds and “organometallic” moieties are compounds and moieties in which a ligand is attached to a metal via a carbon-metal bond.
• the first branching point is an sp 3 hybridised carbon atom.
• Dendrons are comprised of branching units and, optionally, linking units. The generation of a dendron is defined by the number of sets of branching units in the dendron. In a second generation dendron, there is a first branching unit, and each ofthe branches stemming from that first branching unit then branches again ("the second branching units"). In a third generation dendron, each ofthe branches stemming from the second branching units would themselves branch again, and so on for higher generation dendrons.
• Suitable branching units include aryl and heteroaryl, which can be fused, and N.
• N-containing fused heteroaryl ring such as carbazole can be considered a branching point.
• the links between branching points include bonding combinations such as aryl-aryl, aryl-vinyl-aryl, aryl-acetylenyl-aryl, aryl-ary -aryl (where aryl' may be different from aryl), N-aryl and N-aryl'-N where aryl and N are branching units.
• Preferred linking units include phenyl and fluorenyl.
• An individual dendron may contain one or more of each type of branching point.
• aryl- vinyl-aryl and aryl-acetylenyl-aryl linkages within the dendron there may be one or more aryl- vinyl or aryl-acetylenyl link between the branching points. Indeed there may be more than one vinyl or acetylenyl or aryl moiety between two aryl branching units but preferably no more than three. Further, there can be advantages in using an asymmetric dendrimer i.e. where the dendrons are not all the same.
• At least one dendron is at least second generation.
• dendrons Inherently at least partially conjugated dendrons (dendrites) indicate that they are made up of alternating double and single bonds or N lone pairs, apart from the surface groups. However this does not mean that the ⁇ system is fully delocalised. The delocalisation ofthe ⁇ system is dependent on the regiochemistry ofthe attachments. In an inherently at least partially conjugated dendron any branching nitrogen will be attached to 3 (hetero)aryl groups. It is preferred that at least one, and especially all, of the dendrons is/are inherently at least partially conjugated.
• the terms aryl, vinyl, acetylenyl etc. refer to such groups that are divalent, trivalent or multivalent as appropriate.
• the dendrons are conjugated.
• at least one dendron comprises a nitrogen atom which forms part of an aromatic ring system.
• at least one dendron is at least second generation and comprises a nitrogen atom which is directly attached to at least two aromatic groups.
• the core or CORE is attached to a nitrogen atom within the dendron which forms part of an aromatic ring system or is attached to two other (hetero) aryl groups.
• the nitrogen atom forms part of an aromatic ring system, especially a carbazole group or is attached to two aromatic groups, preferably phenyl groups or substituted fluorenyl groups such that the nitrogen atom forms part of a di- or tri- arylamine group.
• aromatic groups preferably phenyl groups or substituted fluorenyl groups such that the nitrogen atom forms part of a di- or tri- arylamine group.
• at least two dendrons possess such a nifrogen-containing aromatic ring system.
• the first single bond is attached to an aryl group, preferably a phenyl group.
• the aryl group is attached to at least one carbazole group.
• the N-containing units within the dendron are carbazole units.
• the branching points are carbazole units attached through the N, 3 and 6 positions.
• the carbazole branching points are directly linked whilst in another they are separated by an aryl group, preferably phenyl.
• the dendrons have the nitrogen only included in a carbazole moiety, and all the dendrons attached to the core are of this type.
• the nitrogen atom can be part of an electron-transport or hole-transport or bipolar moiety.
• bipolar properties carbazole units are preferred, for hole-transporting (HT) properties triarylamines are preferred and for electron-transporting (ET) properties either oxadiazole, benzamidazole, quinoxaline or triazole groups are preferred.
• HT hole-transporting
• ET electron-transporting
• R 1 represents an optionally substituted benzene radical
• R 2 represents an optionally substituted alkyl or aryl group.
• the nitrogen-containing rings are either oxadiazoles or imidazoles or triazoles.
• R 1 is typically substituted by one or more surface groups, e.g. 3,5-di-tertiary butyl.
• R 2 is phenyl, which is preferred, or alkyl, for example of 1 to 15 carbon atoms such as methyl or ethyl; these can be substituted, for example when R 2 is phenyl then it can be substituted with, for example, one or more alkyl, alkoxy or halo substituents.
• Specific examples of dendrimers with such a dendron are shown in Figure 9. It will be appreciated that the dendrons in a dendrimer can contain mixtures of ET, HT and bipolar components, and these are preferably in separate dendrons so that they are not in conjugation with each other.
• the distal aryl groups possess one or more surface groups that are not hydrogen atoms. It is further preferred in this case that the dendrons are at least inherently partially conjugated.
• DENDRON comprises in part an aromatic unit which contains a nitrogen atom.
• This nitrogen atom either forms part of an aromatic ring system or is directly attached to two or three aromatic groups.
• the nitrogen is part of a ring system, it is preferably in a carbazole group, and when it is attached to aromatic groups, the aromatic groups are preferably phenyl or substituted fluorenyl or heteroaryl groups.
• the dendrimer comprises a dendron having a plurality of nitrogen atoms. More preferably, said dendron has a plurality of nitrogen atoms, each being part of a carbazole group. Further, all the nitrogen atoms in said dendron are preferably part of carbazole groups. , In a preferred embodiment the dendrimer comprises 3-21 carbazole units.
• the present invention also provides a device which comprises at least one layer that contains a phosphorescent organometallic compound with a metal cation and two or more co-ordinating groups as part of its core and wherein at least two of said coordinating groups each have a substituent attached, at least one of which substituents comprises at least one nitrogen atom which forms part of an aromatic ring system or is directly bonded to at least two aromatic groups, said nitrogen atom being linked to the co-ordinating group by a direct bond or an optionally substituted hydrocarbyl group.
• said substituent is a carbazole group.
• said optionally substituted hydrocarbyl group is a C 2 -C 12 hydrocarbyl group.
• said optionally substituted hydrocarbyl group is phenyl or C 2 -C 12 alkylene, for example ethylene.
• the host which often contains carbazole units can transfer its energy to the phosphorescent guest for emission.
• the host In the case of green and red emission the host has been reported to have higher energy levels than the guest and for blue emission the energy levels ofthe host are reported to be lower than the guest.
• the dendron singlet or triplet energy should preferably be such that it can, if formed, be transferred to the core for emission. Therefore whilst the singlet or triplet energy ofthe dendrons is normally greater than the emission energy of the core it can be below that of the core providing the energy difference is small enough to allow the transfer of energy to the core. To aid this it is preferred that the triplet excited states ofthe dendrons must be longer lived than the emissive state ofthe core.
• the dendrimers ofthe invention are preferably luminescent in the, solid state.
• the luminescent moiety may be partially or wholly within the core itself.
• the luminescence is preferably from the metal cation containing core.
• Suitable surface groups for the dendrimers which are preferably present, and are attached to the distal (hetero)aryl group include branched and unbranched alkyl, especially t-butyl, branched and unbranched alkoxy, for example 2-ethylhexyloxy, hydroxy, alkylsilane, carboxy, carbalkoxy, and vinyl.
• a more comprehensive list include a further-reactable alkene, (meth)acrylate, sulphur-containing, or silicon-containing group; sulphonyl group; polyether group; C r to-C 15 alkyl (preferably t-butyl) group; amine group; mono-, di- or alkyl arnine group; -COOR group wherein R is hydrogen or C,-to-C ⁇ 5 alkyl; -OR group wherein R is hydrogen, aryl, or -to-C ⁇ alkyl or alkenyl; -O 2 SR group wherein R is C,-to-C 15 alkyl or alkenyl; -SR group wherein R is aryl, or C,-to-C ls alkyl or alkenyl; -SiR 3 group wherein the R groups are the same or different and are hydrogen, C,-to-C 15 alkyl or alkenyl, or -SR' group (R' is aryl or Ci-to-
• t-butyl and alkoxy groups are used. Different surface groups may be present on different dendrons or different distal groups of a dendron. In one embodiment, there are surface groups present on the dendron which comprises the N atom which forms part of an aromatic group or is attached to at least two aromatic groups. It is preferred that the dendrimer is solution processable i.e. the surface groups are such that the dendrimer can be dissolved in a solvent.
• the surface group can be chosen such that the dendrimer can be processed to the required form, for example a thin film for an OLED.
• the surface groups are groups which contain at least two carbon atoms, for example C 2 -C 15 alkyl or OR where R is aryl or C 2 -C 15 alkyl or alkenyl. More preferably, the surface groups will contain 4 or more carbons for example tert-butyl.
• the surface group can be chosen such that the dendrimer can be patterned. For example, a cross-linkable group is present which can be cross-linked upon irradiation or by chemical reaction.
• the surface group comprises a protecting group which can be removed to leave a group which can be cross-linked.
• the surface groups are selected so the dendrirners are soluble in solvents suitable for solution processing.
• the aryl groups within the dendrons can be typically benzene, napthalene, biphenyl (in which case an aryl group is present in the link between adjacent branching points) anthracene, fluorene, pyridine, oxadiazole, triazole, triazine, thiophene, carbazole, quinoxaline and where appropriate substituted variations.
• Typical substituents include C, to C 15 alkyl or alkoxy groups.
• the aryl groups at the branching points are preferably benzene rings, preferably coupled at ring positions 1, 3 and 5, triazinyl or carbazole rings. These groups may optionally be substituted.
• the carbazole units are typically connected at the 3-, 6- and N positions.
• one or more ofthe dendrons attached to the core can be unconjugated.
• dendrons include ether-type aryl dendrons, for example where benzene rings are connected via a methyleneoxy hnk.
• generation level is determined by the number of sets of branching points. It may be advantageous for at least one dendron to be of .the second, or higher, generation to provide the required solution processing properties. Second, or higher, generation dendrons are particularly useful in the cases when the nitrogen atom is attached to aryl groups and the nitrogen atom acts as the branching unit in the dendron, e.g.
• the nitrogen atom is directly attached to 2 or 3 aryl groups and the dendron containing the nitrogen atom is of second, or higher, generation.
• the branching unit is a nitrogen atom
• the dendrons are relatively small (that is incorporate a relatively small number of atoms) compared to a dendron in which the branching unit is an aromatic ring incorporating a nitrogen atom (e.g. carbazole). Larger dendrons can improve film forming properties and increase the spacing ofthe luminescent cores.
• the cores typically comprise a metal cation and attached ligands; the metal is central in the core and the core is luminescent.
• the core is emissive the attachment of, and the regiochemistry of attachment of, the dendrons can directly affect the emissive properties ofthe core.
• the core normally comprises the metal cation and the aryl and heteroaryl units directly attached to the metal.
• the heteroaryl and aryl can also form a branching point, e.g. if a second dendron is attached to the aryl or heteroaryl unit that is connected to the metal cation.
• the dendrons attached to the (hetero)aryl unit that is bound to the metal cation must themselves contain at least one nitrogen atom which forms part of an aromatic ring system or is directly bonded to at least two aromatic groups.
• metal ion or "metal cation”, as used herein, describes the charge state the metal would have without ligands attached (the oxidation state), hi the dendrimers that contain a metal cation the overall charge ofthe dendrimer is neutral and the metal-ligand bonding will have more or less covalent character depending on the metal and ligand involved.
• the core comprises a metal cation and attached ligands it is typically a complex of a metal cation and two or mtire coordinating groups, at least two ofthe coordinating groups being bound to dendrons. Typically the luminescence ofthe dendrimer will derive from that complex.
• CORE is typically a complex of a metal cation and two or more coordinating groups, at least one and preferably two or more ofthe said groups each being bound to a DENDRON moiety as defined in formula (I) by the single bond in which CORE in this formula terminates.
• dendrons in particular DENDRONS are attached to all ofthe coordinating groups forming part of the CORE.
• DENDRONS are attached to all three coordinating groups.
• CORE may be represented as a complex ofthe following formula (TT):
• each [X-], which are the same or different, is a coordinating group X attached to a single bond in which CORE terminates
• each Y which may be the same or different, is a coordinating group
• q is an integer of 2 or more and r is 0 or an . integer, the sum of (a.q) + (b.r) being equal to the number of coordination sites available on M, wherein a is the number of coordination sites on [X-] and b is the number of coordination sites on Y.
• the single bond to the branching group may be directly from the co-ordinating group or via an intervening group, typically an ethylene, substituted ethylene, vinylene, substituted vinylene or acetylethyl group.
• the single bond in the or each [X-] moiety being a bond in which CORE terminates, connects to a dendron.
• a dendron Preferably there are at least two dendrons in a dendrimer, in which case q in formula (H) is an integer of 2 or more.
• the said two or more dendrons typically have the structures represented by DENDRON as defined above.
• the coordinating groups Y when present, are neutral or charged chelated ligands which are not attached to dendrons and which serve to fulfil the coordination requirements ofthe metal cation. Suitable Y include arylpyridines and heteroaryl pyridines and substituted variants.
• Y ligands include ⁇ -diketonates, 2- carboxylpyridines, such as picolinic acid triaiylphosphines, such as triphenylphosphine, triall-ylphosphines, ethylenediamine, cyanide, carbon monoxide and carbon monosulfide.
• Suitable metals include metals in the second or third row ofthe transition metals especially iridium, rhenium, rhodium and platinum.
• the second or third row transition metals form organometallic complexes with carbon or nitrogen donors. These can include for example porphyrin and arylpyridines.
• the nitrogen donor is generally part of a heteroaromatic ring, such as pyridine or substituted pyridine, and the aryl is a phenyl, fused aryl, or more than one aromatic ring, or a heteroaryl, or a substituted equivalent.
• the dendron can be attached to either of the rings.
• the two rings of the "ligand" are normally in conjugation, so that the metal forms a 5 membered cyclometallated ring.
• the rings can be attached in such a way that they can form a 6-membered cyclometallated ring with the metal cation.
• the at least two said dendrons are attached to ligands that are bonded to the metal by at least a carbon-metal bond. It is further preferred that the carbon-metal bond forms part of a cyclometallated ring.
• the emission colour is governed by the lowest energy ligand.
• a suitable ligand and dendron attachment is shown in figure A of Figure 6.
• red emission it is appropriate to have 3 coordinating ligands each with a dendron attached to pyridine, for example as in Figure B.
• red emission there could be one ligand as in Figure B and two dendritic ligands as in Figure A and the Figure B type ligand may or may not have a dendron attached.
• the blue emission it is suitable to have 3 coordinating ligands each with a dendron attached to the pyridine via say an ethylene link with, for example, fluoro groups on the phenyl, as shown in Figure C.
• the dendrimers can be built in a convergent or divergent route, but a convergent route is preferred.
• the dendrons are attached to the appropriate ligands and these are subsequently attached to the metal cation to form the dendritic metal complex.
• the. synthetic route allows other non-dendritic ligands can subsequently I i v ⁇
• a ligand with a suitably reactive functional group can be complexed to the metal ion, and then reacted with appropriately functionalised dendrons.
• this latter method not all ligands have to have the reactive functional groups, and thus this method allows the attachment of dendrons to some but not all ofthe ligands complexed to the metal.
• a key property ofthe dendrons is to impart solution processibility to the metal complex and therefore allow the formation of good quality thin films suitable for use in light-emitting diodes.
• the dendritic metal complexes may be homoleptic or contain more than one type of dendritic ligand, as discussed above.
• the metal complex may contain two or preferably more than two, e.g. 3, dendritic ligands plus one or more no ⁇ -dendritic ligands.
• two dendritic phenylpyridine ligands with the third ligand a non-dendritic arylpyridine ligand. It is desirable that the number and/or generation of dendritic ligands is sufficient to provide the required solution processing.
• the method of preparation may give rise to a statistical mixture of all complex types. This is not necessarily disadvantageous providing that the optical, electronic, and processing properties are satisfactory.
• the moieties forming the attachment point to metal are all the same or have similar binding constants.
• at least one should desirably be a conjugated dendron.
• the conjugated dendrons can be comprised of a number of different types of branching units, as discussed above.
• the surface groups and dendrites can be varied so the dendrimers are soluble in solvents, such as toluene, THF, water and alcoholic solvents such as methanol, suitable for the solution processing technique of choice. Typically t-bufyl and alkoxy groups have been used.
• the choice of dendron and/or surface group can allow the formation of blends with dendrimers (organic or organometallic), polymer or molecular compounds.
• the other blend component can be a charge transport material. If it is blended with another component the dendrimer ofthe current invention is preferably the major component in the blend by either weight % and/or mole %. If the dendrimer is blended with a polymer it is preferred that the polymer is a conjugated polymer or itself contains N as part of an aromatic ring or directly bonded to at least 2 aromatic rings.
• the organometallic dendrimer can be incorporated into a light emitting diode as either a homogeneous layer or as a blend with at least one dendrimer (organic or organometallic), polymer or molecular compound.
• the organometallic dendrimers can be incorporated into an LED in a conventional manner.
• an organic light emitting or electroluminescent device can be formed from a light emitting layer sandwiched between two electrodes, at least one of which must be transparent to the emitted light.
• Such a device can have a conventional arrangerhent comprising a transparent substrate layer, a transparent electrode layer, a light emitting layer and a back electrode.
• the standard materials can be used.
• the transparent substrate layer is typically made of glass although other transparent materials such as PET, can be used..
• the anode which is generally transparent is preferably made from indium tin oxide (ITO) although other similar materials including indium oxide/tin oxide, tin oxide/antimony, zinc. oxide/aluminum, gold and platinum can also be used.
• ITO indium tin oxide
• Conducting polymers such as PANI (polyaniline) or PEDOT can also be used.
• the cathode is normally made of a low work function metal or alloy such as Al, Ca, Mg, Li, or MgAl or optionally with an additional layer of LiF.
• a low work function metal or alloy such as Al, Ca, Mg, Li, or MgAl or optionally with an additional layer of LiF.
• other layers may also be present, including a hole transporting material and/or an electron transporting material.
• a hole-blocking/electron-transporting layer between the light emitting dendrimer layer and the cathode.
• the substrate may be an opaque material such as silicon and the light is emitted through the opposing electrode.
• An advantage ofthe present invention is that the layer containing the dendrimer can be deposited from solution.
• Conventional solution processing techniques such as spin coating, ink-jet printing, printing, and dip-coating can be used to deposit the dendrimer layer.
• a solution containing the dendrimer is applied over the transparent electrode layer, the solvent evaporated, and then subsequent layers applied.
• the film thickness is typically lOnm to lOOOnm, preferably less than 200nm, more preferably 30-120nm.
• Fig. 1 illustrates the preparation of carbazolyl dendritic arylpyridine ligands (Examples 1 to 3) and a first generation iridium dendrimer. (Example 11).
• Fig. 2 illustrates the preparation of another carbazolyl arylpyridine dendritic ligand (Examples 4 to 8).
• Fig. 3 illustrates the preparation of a second generation carbazolyl dendritic ligand and a first generation iridium dendrimer (Examples 9, 10).
• Fig. 4 illustrates the preparation of a second generation iridium dendrimer (Example 12).
• Fig. 5 illustrates the preparation of another first generation iridium dendrimer (Example 13-15).
• Fig. 6 illustrates suitable ligand and dendron attachments.
• Fig. 7 illustrates the preparation of a second generation iridium dendrimer.
• Fig. 8 show the current- voltage and luminance- voltage characteristics of a device containing a second generation iridium dendrimer (Examples 18-20).
• Example 1 DEHP-Car (1
• 3,6-Dif4'-(2"-ethylhexyloxy phenyllcarbazole A mixture of 3,6-dibromocarbazole (12.0 g, 37.1 mmol), the boronic compound GO- BX 2 , see below; (24.1 g, 96.4 mmol), tefr- ⁇ kis(triphenylphosphine) palladium (0) (800 mg, 0.692 mmol), 2 M Na 2 CO 3(aq) (40 cm 3 ), EtOH (40 cm 3 ) and toluene (100 cm 3 ) was degassed and then heated at reflux (with bath temperature of 100 °C) under argon for 42 h.
• rert-butyl lithium (1.7 M, 66.0 cm 3 , 112 mmol) was added carefully to a cold (dry- ice/acetone bath) solution of GO-Br (20.0 g, 70.1 mmol) in 300 cm 3 of anhydrous THF under an argon atmosphere. The mixture was stirred at -78 °C for 1 h and then tri-methyl borate (57.2 cm 3 , 421 mmol) was added slowly to the cold mixture. The reaction was stirred at -78 °C for 2 h before being removed from the dry-ice/acetone bath. The mixture was then stirred at room temperature for further 2.5 h before being quenched with 3 M HCl (aq) (30 cm 3 ). The two layers were separated.
• jert-butyl lithium (1.7 M, 36.6 cm 3 , 62.1 mmol) was added to a cold (dry-ice/acetone bath) solution of 2-(3'-BrPh)Py (8.10 g, 34.6 mmol) in 130 cm 3 of anhydrous THF under an argon atmosphere.
• the mixture was stirred at -78 °C for 2 h and then 2- isopropoxy-4,4,5,5-tetramethyl-l,3,2-dioxaborolane (9 cm 3 ) was added rapidly to the cold mixture.
• the reaction was stirred at -78 °C for 2 h and the dry-ice/acetone bath was removed.
• the mixture was then stirred at room temperature for further 20 h before being quenched with H 2 O (30 cm 3 ). The two layers were separated. The aqueous layer was extracted with ether (3 x 40 cm 3 ). To the aqueous layer, NaCHO 3(sat) (40 cm 3 ) was added and the aqueous layer was further extracted with ether (2 X 40 cm 3 ). The organic layer and the ether extracts were combined and dried over anhydrous sodium sulfate, filtered and the solvents removed.
• Tris(dibenzylideneacetone)di-palladium (0) [Pd 2 (dba) 3 ] (125 mg, 0.137 mmol) and tri- tert-butylphosphine (10% in hexane, 0.5 cm 3 ) were added to a degassed (Schlenk line, evacuated and back-filled with argon) mixture of carbazolyl compound 1 [Example 1] (3.14 g, 5.45 mmol), 1,4-dibromobenzene (12.3 g, 52.2 mmol), sodium tert-butoxide (1.00 g, 10.4 mmol), and distilled xylenes (15 cm 3 ).
• the mixture was degassed again before being heated (with bath temperature of 135 °C) under argon for 115 h.
• the mixture was allowed to cool to ambient temperature and quenched with H 2 O (0.5 cm 3 ).
• the mixture was purified by column chromatography over silica using light petroleum as eluent to give 1.46 g (37%) of 8; (Found: C, 76.1; H, 7.1, N, 2.1.
• the mixture was degassed again before being heated (with bath temperature of 131 °C) under argon for 27 h.
• the resultant was allowed to cool to room temperature and quenched with H 2 O (0.5 cm 3 ).
• the mixture was purified by column chromatography over silica using DCM-light petroleum (0:1 to 1:20) as eluent to give 476 mg (60%) of 8 as an oil; characterization data as above.
• the mixture was degassed again before being heated (with bath temperature of 135 °C) under argon for 118 h.
• the mixture was allowed to cool to ambient temperature and quenched with H 2 O (0.5 cm 3 ).
• the mixture was purified by column chromatography over silica using DCM-light petroleum (0: 1 to 1 :30) and then ethyl acetate-light petroleum (1 :20) as eluent to give 835 mg (100%) of 12; ⁇ H (200 MHz; CDC1 3 ) 7.21-7.92 (11 H, m, PyH, CarH & ArH), 8.12-8.33 (4 H, m, PyH, CarH & ArH), and 8.75 (1 H, m, PyH); m/z [APCr] 321, 322, 323 (MH+).
• the mixture was degassed again before being heated (with bath temperature of 133 °C) under argon for one week.
• the mixture was allowed to cool to room temperature and quenched with H 2 O (0.5 cm 3 ).
• the crude was purified by column chromatography over silica using DCM-light petroleum (0:1 to 1 : 10) as eluent to give
• iridium (HT) A mixture of 2-(3'-Car G2-Ph)Py 3 (734 mg, 0.532 mmol), iridium chloride tri-hydrate (38 mg, 0.106 mmol), H 2 O (1.5 cm 3 ) and 2-butoxyethanol (6.5 cm 3 ) was heated (bath temperature: 140 °C) under argon for 3 days before being cooled.
• the yellow precipitate was filtered off and washed with 95% of EtOH (-10 cm 3 ).
• the yellow solid was dissolved into 5 cm 3 of DCM and purified by column chromatography over silica using DCM-light petroleum (0:1 to 1:4) as eluent to give 85.2 mg (27 %) of a brown yellow solid as the dichloro-bridged dimer 6; m/z [MALDI] 2949 (broad) (C 194 H 212 IrN 6 O 8 -Cl + ).
• a light yellow-brown solid was isolated (589 mg, 80%) as the excess ligand 3.
• Tris(dibenzylideneacetone)di-palladium (0) [Pd 2 (dba) 3 ] (50 mg, 0.055 mmol) and tri- tert-butylphosphine (10% in hexane, 0.8 cm 3 ) were added to a degassed (Schlenk line, evacuated and back-filled with argon) mixture of DEHP-Car (1) (1.90 g, 3.30 mmol), Br-btp (22) (300 mg, 1.03 mmol), sodium tert-butoxide (348 mg, 3.62 mmol), and distilled toluene (from sodium under nitrogen) (2.0 cm 3 ).
• the device was prepared as follows:
• the table shows the performance of devices made with two types of dendrimer according to the current invention (compounds 5 and 7) and a comparative example for a device made with an Ir-cored dendrimer (Ir-Gl) that does not have N atoms as part of units in the dendrons.
• Ir-G2 is/ c tris ⁇ 2-[3'-(3",5"-di ⁇ 3'",5'"-di[4""-2""- ethylhexyloxy)phenyl]phenyl ⁇ phenyl)
• Ir-Gl is fac tris [2-(3 '- ⁇ 3 ",5 ' '-di[4" '-(2" ' '-ethylhexyloxy)phenyl]phenyl ⁇ phenyl)pyridine]iridium (III) which is a first generation dendrimer. (The synthesis of these dendrimers is given in the PCT application claiming priority from GB 0104175.5).
• the solid was purified by a silica gel column using DCM-light petroleum (1:10 to 1:4) as eluent to give the chloro-bridged dimer 32 (141 mg) as a yellow solid; d H (200 MHz; CDC1 3 ) 5.83 (4 H, m, ArH), 6.50- 7.85 (112 H, m, PyH & ArH), and 9.15 (4 H, m, PyH); m/z [MALDI] 1320, 1321, 1322, 1323, 1324, 1325, (C S2 H 60 IrN 6 + ), 1356, 1357, 1358, 1359, 1360 (C 82 H 60 ClIrN 6 )._
• Single-layer OLED devices were made with dendrimer 33 using the procedure described in Example 16, except that at step 5 the oxygen plasma treatment was for 4 minutes at 70 W.
• the concentration ofthe solution for spin-coating was 20 mg/ml of 33 in CHC1 3 and it was spun at 1800 rpm for 60 sec:
• the device structure was ITO / 33 / Ca (20 nm) / Al (60 nm).
• the device passed a relatively large current (see figure 8) showing the dendrimer has good charge transporting properties, but in this simple device structure charge recombination was inefficient leading to arelatively low efficiency of 0.01 cd/A at 100 cd/m 2 and 10.5 N.
• Example 21 Bi-layer OLED devices were made with a light emitting layer containing dendrimer 33 and an evaporated electron transporting layer of 2,2 ,2 -(l,3,5-phenylene)tris[l-phenyl-lH- benzimidazolyl) (TPBI).
• the devices were fabricated following the method described in example 16, except that the oxygen plasma treatment was for 4 min at 70 watts, and there was the additional step of vacuum depositing a layer of TPBI prior to deposition of the cathode layers.
• the concentration ofthe solutions of light emitting material was 10 mg/ml in CHC1 3 and the spin speed was 2300 rpm for 60 sec.
• the structures ofthe two types of devices are shown below in which 33 was used as a neat layer, and 33 was blended with 4,4'- ⁇ , ⁇ '-dicarbazole-biphenyl (CBP), respectively.
• CBP 4,4'- ⁇ , ⁇ '-dicarbazole-biphenyl
• the peak efficiency was 0.4 cd/A at 6 V and ⁇ 1000 cd/m 2 for the neat bi-layer device.
• the peak efficiency was 9 cd/A at 7.9 V and -7000 cd m 2 for the 33.CBP blended bi-layer device. Neither of these device structures had been optimised for efficiency.

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