Opto-electrical polymers and devices

Field of the Invention

0001The present invention relates to opto-electrical devices, in particular polymer light-emitting devices, and opto-electrical polymers for use therein.

Background of the Invention

0002One class of opto-electrical devices is those using an organic material for light emission or detection. The basic structure of these devices is a light emissive organic layer, for instance a film of a poly(p-phenylenevinylene) ("PPV") or polyfluorene, sandwiched between a cathode for injecting negative charge carriers (electrons) and an anode for injecting positive charge carriers (holes) into the organic layer. The electrons and holes combine in the organic layer generating photons. In <patcit id="pcit0001" dnum="WO9013148A"><text>WO 90/13148</text></patcit> the organic light- emissive material is a polymer. In <patcit id="pcit0002" dnum="US4539507A"><text>US 4,539, 507</text></patcit> the organic light-emissive material is of the class known as small molecule materials, such as (8-hydroxyquinoline) aluminium("Alq3"). In a practical device one of the electrodes is transparent, to allow the photons to escape the device.

0003A typical organic light-emissive device ("OLED") is fabricated on a glass or plastic substrate coated with a transparent first electrode such as indium-tin-oxide("ITO"). A layer of a thin film of at least one electroluminescent organic material covers the first electrode. Finally, a cathode covers the layer of electroluminescent organic material. The cathode is typically a metal or alloy and may comprise a single layer, such as aluminium, or a plurality of layers such as calcium and aluminium. Other layers can be added to the device, for example to improve charge injection from the electrodes to the electroluminescent material. For example, a hole injection layer such as poly (ethylene dioxythiophene) /polystyrene sulfonate (PEDOT-PSS) or polyaniline may be provided between the anode and the electroluminescent material. When a voltage is applied between the electrodes from a power supply one of the electrodes acts as a cathode and the other as an anode. For organic semiconductors important characteristics are the binding energies, measured with respect to the vacuum level of the electronic energy levels, particularly the "highest occupied molecular orbital" (HOMO) and the "lowest unoccupied molecular orbital" (LUMO) level. These can be estimated from measurements of photoemission and particularly measurements of the electrochemical potentials for oxidation and reduction. It is well understood in this field that such energies are affected by a number of factors, such as the local environment near an interface, and the point on the curve (peak) from which the value is determined. Accordingly, the use of such values is indicative rather than quantitative.

0004In operation, holes are injected into the device through the anode and electrons are injected into the device through the cathode. The holes and electrons combine in the organic electroluminescent layer to form an exciton which then undergoes radiative decay to give light. One way of improving efficiency of devices is to provide hole and electron transporting materials-for example, <patcit id="pcit0003" dnum="WO9948610A"><text>WO 99/48610</text></patcit> discloses blending of hole transporting polymers, electron transporting polymers and electroluminescent polymers. A 1:1 copolymer of dioctylfluorene and triphenylamine is used as the hole transporting polymer in this document.

0005A focus in the field of polymer OLEDs is the development of full colour displays for which red, green and blue emissive materials are required. One drawback with existing polymer OLED displays relevant to this development is the relatively short lifetime of blue emissive materials known to date (by "lifetime" is meant the time for the brightness of the OLED to halve at constant current when operated under DC drive).

0006In one approach, the lifetime of the emissive material may be extended by optimisation of the OLED architecture; for example lifetime of the blue material may in part be dependant on the cathode being used. However, the advantage of selecting a cathode that improves blue lifetime may be offset by disadvantageous effects of the cathode on performance of red and green materials. For example, Synthetic Metals 111-112 (2000), 125-128 discloses a full colour display wherein the cathode is LiF/Ca/Al. The present inventors have found that this cathode is particularly efficacious with respect to the blue emissive material but shows poor performance with respect to green and, especially, red emitters.

0007Another approach is development of novel blue electroluminescent materials. For example, <patcit id="pcit0004" dnum="WO0055927A"><text>WO 00/55927</text></patcit>, which is a development of <patcit id="pcit0005" dnum="WO9948160A"><text>WO 99/48160</text></patcit>, discloses a blue electroluminescent polymer of formula (w): <chemistry id="chem0001" num="0001"><img file="EP2016112B1_D0001.tif" /></chemistry> wherein w + x + y = 1, w ≤ 0.5 , 0 ≤ x + y ≤ 0.5 , and n ≥ 2

0008In essence, the repeat units of the separate polymers disclosed in <patcit id="pcit0006" dnum="WO9948160A"><text>WO 99/48160</text></patcit> are combined into a single molecule. The F8 repeat unit is provided for the purpose of electron injection; the TFB unit is provided for the purpose of hole transport; and the PFB repeat unit is provided as the emissive unit.

0009In another example, disclosed in <patcit id="pcit0007" dnum="WO03095586A"><text>WO 03/095586</text></patcit>, it was found that the lifetime of a polymer for use in an optical device, in particular an electroluminescent polymer, may be increased by the incorporation of repeat units that increase the glass temperature (Tg) of the polymer. In particular, incorporation of 2,7-linked 9,9-diarylfluorene repeat units into an electroluminescent polymer, particularly a blue emissive electroluminescent polymer, results in significant increase in that polymer's lifetime. Furthermore, it was found to be unnecessary to have separate hole transporting units and blue emissive units; it was found that both functions may be performed by the PFB unit. Surprisingly, the omission of TFB from the prior art polymers described above was found to result in a significant improvement in lifetime. A preferred embodiment disclosed in <patcit id="pcit0008" dnum="WO03095586A"><text>WO 03/095586</text></patcit> is a blue electroluminescent polymer prepared in accordance with the process of <patcit id="pcit0009" dnum="WO0053656A"><text>WO 00/53656</text></patcit> by reaction of 9,9-di-n-octylfluorene-2,7-di(ethylenylboronate) (0.5 equivalents), 2,7-dibromo-9,9-diphenylfluorene (0.35 equivalents) and N,N'-di(4-bromophenyl)-N,N'-di(4-n-butylphenyl)-1,4-diaminobenzene (0.15 equivalents) to give polymer (P1): <chemistry id="chem0002" num="0002"><img file="EP2016112B1_D0002.tif" /></chemistry>

0010In another example, disclosed in <patcit id="pcit0010" dnum="WO04041902A"><text>WO 04/041902</text></patcit>, it was determined that improved electron injection, and therefore improved device performance, may be accomplished by increasing the electron affinity of known polyfluorenes (by providing a deeper LUMO). This was achieved in <patcit id="pcit0011" dnum="WO04041902A"><text>WO 04/041902</text></patcit> by providing fluorene repeat units having electron withdrawing aryl groups. It was also found that increasing electron affinity in this manner lead to better lifetimes for the polymers disclosed therein.

0011<patcit id="pcit0012" dnum="US6309763B"><text>US 6,309,763</text></patcit>, discloses a copolymer comprising 10-90% by weight of the group of formula (y): <chemistry id="chem0003" num="0003"><img file="EP2016112B1_D0003.tif" /></chemistry> wherein R₁ is independently selected in each occurrence from, among other things, C₁-C₂₀ hydrocarbyl. The repeat unit is provided in a copolymer with 10-90% triarylamine. In all the examples each R₁ is C₈H₁₇ as in polymers (w) and (P1) discussed above.

0012<patcit id="pcit0013" dnum="EP1528074A"><text>EP 1528074</text></patcit> also discloses various polymers comprising the above-identified fluorene group in which R₁ is C₈H₁₇. In example 2 of <patcit id="pcit0014" dnum="EP1528074A"><text>EP 1528074</text></patcit>, there is also disclosed a polymer comprising a 9,9-dimethylfluorene unit directly bonded to nitrogen atoms in the backbone as shown in formula (y₂): <chemistry id="chem0004" num="0004"><img file="EP2016112B1_D0004.tif" /></chemistry>

0013<patcit id="pcit0015" dnum="JP2004131700A"><text>JP 2004-131700</text></patcit> also discloses various polymers comprising a fluorene group in which R₁ is C₈H₁₇. In addition, this document also discloses a polymer comprising 9,9-dimethylfluorene directly bonded to silicon in the polymer backbone as shown in formula (y₃): <chemistry id="chem0005" num="0005"><img file="EP2016112B1_D0005.tif" /></chemistry>

0014It is an aim of the present invention to provide a means for increasing the lifetime of polymers for use in an optical device above that of prior art polymers such as those discussed above. It is a further aim of the invention to provide a long-lived polymer for use in an opto-electrical device, particularly a long-lived blue electroluminescent material. It is a yet further aim of the invention to provide a means for increasing the thermal stability of the prior art polymers such as those discussed above. It is yet a further aim of the invention to provide improved device performance.

Summary of the Invention

0015In accordance with a first aspect of the present invention there is provided an opto-electrical device comprising a first electrode, a second electrode, and a semi-conductive region located between the first and second electrodes, the semi-conductive region comprising a polymer comprising aromatically conjugated repeat units of 9,9-dimethylfluorene linked to and conjugated with aromatic rings of adjacent repeat units by a single bond, the polymer further comprising one or more other aromatically conjugated repeat units linked to and conjugated with aromatic rings of adjacent repeat units by a single bond, wherein the one or more different aromatically conjugated repeat units comprise repeat units of formula (b): <chemistry id="chem0006" num="0006"><img file="EP2016112B1_D0006.tif" /></chemistry> wherein each Ar is the same or different and is an optionally substituted phenyl group; m is 0, 1 or 2; and two or more aryl groups Ar may be linked by a direct bond or a divalent group, wherein the 9,9-dimethylfluorene repeat units are 2,7-linked into the polymer as shown in Formula (a): <chemistry id="chem0007" num="0007"><img file="EP2016112B1_D0007.tif" /></chemistry>

0016By "aromatically conjugated" we mean that the six membered aromatic rings in the 9,9-dimethylfluorene repeat unit are linked to aromatic rings in adjacent repeat units by a single bond. Preferably, this linkage is along the backbone of the polymer.

0017The present inventors have surprisingly found that the lifetime of a polymer for use in an opto-electrical device, in particular an electroluminescent polymer, is increased by the incorporation of aromatically conjugated repeat units of 9,9-dimethylfluorene.

0018The aromatically conjugated 9,9-dimethylfluorene surprisingly increases the electron affinity of a polymer when compared to an equivalent polymer comprising 9,9-dioctylfluorene such as prior art polymer P1. The aromatically conjugated 9,9-dimethylfluorene improves electron injection, and therefore improves device performance.

0019Furthermore, the glass transition temperature (Tg) of the polymer is increased when compared to an equivalent polymer comprising 9,9-dioctylfluorene such as the prior art polymer P1, providing a means for increasing the thermal stability of opto-electrical semi-conductive polymers.

0020The other aromatically conjugated repeat units can provide other functionalities such as hole transport and emission.

0021Preferable co-repeat units include amines and/or optionally substituted fluorene units other than 9,9-dimethylfluorene, for example, fluorene units with a C_2-20 alkyl or alkoxy and/or fluorene units with an aryl or heteroaryl.

0022Preferably, m is 0. Preferably, aryl groups in the polymer backbone are linked by a divalent group. Preferred examples of divalent groups include O, S.

0023Very preferably, the optionally substituted repeat unit of formula (b) has the structure: <chemistry id="chem0008" num="0008"><img file="EP2016112B1_D0008.tif" /></chemistry>

0024The repeat unit (b) is provided as an emissive unit in the copolymer and can also provide hole transport functionality. A small amount of optionally substituted -Ar-N(Ar)-Ar- may also be present in the copolymer. Preferably, this repeat unit is in a molar ratio of no greater than 5 %. However, since the repeat unit of formula (b) fulfils both emission and hole transport functions, no other nitrogen containing hole transport repeat units are required. Accordingly, in a preferred embodiment the polymer comprises no repeat units comprising nitrogen atoms in the repeat unit backbone other than the repeat unit of formula (b).

0025Each Ar is preferably an optionally substituted phenyl.

0026Another example is a repeat unit of formula (c): <chemistry id="chem0009" num="0009"><img file="EP2016112B1_D0009.tif" /></chemistry> wherein each R' is independently selected from hydrogen or a solubilising group.

0027Another example is an, optionally substituted, repeat unit of formula (d) that is optionally substituted with one or more substituents: <chemistry id="chem0010" num="0010"><img file="EP2016112B1_D0010.tif" /></chemistry> wherein each R is the same or different, and the two R groups together may form a ring and / or at least one R group may form a ring with the at least one optional substituent, for example as shown in the structure below: <chemistry id="chem0011" num="0011"><img file="EP2016112B1_D0011.tif" /></chemistry>

0028Preferred groups R are independently selected from the group consisting of alkyl, alkoxy, aryl and heteroaryl, each of which may optionally be further substituted.

0029Very preferably, the optionally substituted, repeat unit of formula (d) has the structure: <chemistry id="chem0012" num="0012"><img file="EP2016112B1_D0012.tif" /></chemistry> wherein each Ar' is the same or different and comprises an optionally substituted aryl or heteroaryl group. Preferably, each Ar' is optionally substituted phenyl. Optionally, one or both of the Ar' comprise electron withdrawing groups. Optionally, one or both of the Ar' comprise solubilising groups.

0030The provision of solubilising groups can be particularly useful in embodiments of the present invention. This is because the 9,9-dimethylfluorene is less soluble in organic solvents than 9,9-dioctylfluorene, for example. Accordingly, it is advantageous in some applications to improve the solution processability of a polymer comprising this repeat unit by providing co-repeat units which are more soluble than 9,9-dimethylfluorene. This may be achieved by, for example, providing aryl co-repeat units having solubilising side groups thereon. Examples of suitable solubilising side groups include optionally substituted C₄-C₂₀ alkyl or alkoxy groups, more preferably C₄-C₁₀ alkyl groups, and most preferably C₆-C₈ alkyl groups. The solubilising substituents may be provided, for example, in the 9-position of a fluorene repeat unit or bound to the pendant aryl groups in the case of, for example, 9,9-diphenylfluorene or PFB.

0031Preferably, the polymer is an electroluminescent polymer, more preferably a polymer capable of emitting light in the wavelength range 400-500 nm, most preferably 430-500 nm. It has been found that polymers comprising 9,9-dimethylfluorene are particularly useful as blue emitters which have a longer lifetime than the prior art blue emitters disclosed in the background section.

0032In accordance with a second aspect of the present invention there is provided an opto-electrical device comprising a first electrode, a second electrode, and a semi-conductive region located between the first and second electrodes, the semi-conductive region comprising a polymer according to the first aspect of the invention.

0033The polymer according to the first aspect of the invention may be provided in a blended layer with other polymers, dendrimers or small molecules. Alternatively, it may be provided in a layer on its own, the polymer comprising all moieties necessary to perform the function of the layer.

0034Preferably, the polymer is provided in an electroluminescent layer of the semiconductive region.

0035In one embodiment the electroluminescent layer comprises one or more phosphorescent moieties, the polymer according to the first aspect of the invention acting as a host for the one or more phosphorescent moieties. It has been found that polymers comprising 9,9-dimethylfluorene are particularly useful as host materials which do not quench emission from phosphorescent moieties.

0036The polymer may be provided in a charge transporting layer of the semi-conductive region, e.g. an electron transporting layer disposed between the electroluminescent layer and the cathode or a hole transporting layer disposed between the electroluminescent layer and the anode. For the avoidance of doubt, it will be appreciated that, where present, a hole injection material (such as PEDOT-PSS or polyaniline), a hole transporting layer or an electron transporting layer separate from the electroluminescent layer do not constitute a part of the electroluminescent layer.

Brief Description of the Drawings

0037The present invention will now be described in further detail, by way of example only, with reference to the accompanying drawings in which: <ul id="ul0001" list-style="none"><li><figref idref="f0001">FIGURE 1</figref> shows an electroluminescent device;</li><li><figref idref="f0001">FIGURE 2</figref> shows a graph illustrating how the glass transition temperature of two different polymers changes with 9,9-dimethylfluorene content; and</li><li><figref idref="f0002">FIGURE 3</figref> shows a graph illustrating how the LUMO level of the two different polymers changes with 9,9-dimethylfluorene content.</li></ul>

Detailed Description of the Invention

General device architecture

0038With reference to <figref idref="f0001">Figure 1</figref>, the standard architecture of an electroluminescent device according to the invention comprises a transparent glass or plastic substrate 1, an anode of indium tin oxide 2 and a cathode 4. The polymer according to the invention is located in layer 3 between anode 2 and cathode 4. Layer 3 may comprise the polymer according to the invention alone or a plurality of polymers.

0039Electroluminescent devices may be monochrome devices or full colour devices (i.e. formed from red, green and blue electroluminescent materials). By "red electroluminescent material" is meant an organic material that by electroluminescence emits radiation having a wavelength in the range of 600-750 nm, preferably 600-700 nm, more preferably 610-650 nm and most preferably having an emission peak around 650-660 nm. By "green electroluminescent material" is meant an organic material that by electroluminescence emits radiation having a wavelength in the range of 510-580 nm, preferably 510-570 nm. By "blue electroluminescent material" is meant an organic material that by electroluminescence emits radiation having a wavelength in the range of 400-500 nm, more preferably 430-500 nm.

Charge transporting layers

0040Further layers may be located between anode 2 and cathode 4, such as charge transporting, charge injecting or charge blocking layers.

0041In particular, it is desirable to provide a conductive hole injection layer formed of a doped organic material located between the anode 2 and the electroluminescent layer 3 to assist hole injection from the anode into the layer or layers of semiconducting polymer. Examples of doped organic hole injection materials include poly(ethylene dioxythiophene) (PEDT), in particular PEDT doped with polystyrene sulfonate (PSS) as disclosed in <patcit id="pcit0016" dnum="EP0901176A"><text>EP 0901176</text></patcit> and <patcit id="pcit0017" dnum="EP0947123A"><text>EP 0947123</text></patcit>, or polyaniline as disclosed in <patcit id="pcit0018" dnum="US5723873A"><text>US 5723873</text></patcit> and <patcit id="pcit0019" dnum="US5798170A"><text>US 5798170</text></patcit>.

0042If present, a hole transporting layer located between anode 2 and electroluminescent layer 3 preferably has a HOMO level of less than or equal to 5.5 eV, more preferably around 4.8-5.5 eV.

0043If present, an electron transporting layer located between electroluminescent layer 3 and cathode 4 preferably has a LUMO level of around 3-3.5 eV.

Electrodes

0044Cathode 4 is selected from materials that have a workfunction allowing injection of electrons into the electroluminescent layer. Other factors influence the selection of the cathode such as the possibility of adverse interactions between the cathode and the electroluminescent material. The cathode may consist of a single material such as a layer of aluminium. Alternatively, it may comprise a plurality of metals, for example a bilayer of calcium and aluminium as disclosed in <patcit id="pcit0020" dnum="WO9810621A"><text>WO 98/10621</text></patcit>, elemental barium disclosed in <patcit id="pcit0021" dnum="WO9857381A"><text>WO 98/57381</text></patcit>, <nplcit id="ncit0001" npl-type="s"><text>Appl. Phys. Lett. 2002, 81(4), 634</text></nplcit> and <patcit id="pcit0022" dnum="WO0284759A"><text>WO 02/84759</text></patcit> or a thin layer of dielectric material to assist electron injection, for example lithium fluoride disclosed in <patcit id="pcit0023" dnum="WO0048258A"><text>WO 00/48258</text></patcit> or barium fluoride, disclosed in <nplcit id="ncit0002" npl-type="s"><text>Appl. Phys. Lett. 2001, 79(5), 2001</text></nplcit>. In order to provide efficient injection of electrons into the device, the cathode preferably has a workfunction of less than 3.5 eV, more preferably less than 3.2 eV, most preferably less than 3 eV.

0045In a practical device, at least one of the electrodes is semi-transparent in order that light may be absorbed (in the case of a photoresponsive device) or emitted (in the case of an OLED). Where the anode is transparent, it typically comprises indium tin oxide. Examples of transparent cathodes are disclosed in, for example, <patcit id="pcit0024" dnum="GB2348316A"><text>GB 2348316</text></patcit>.

0046The embodiment of <figref idref="f0001">Figure 1</figref> illustrates a device wherein the device is formed by firstly forming an anode on a substrate followed by deposition of an electroluminescent layer and a cathode, however it will be appreciated that the device of the invention could also be formed by firstly forming a cathode on a substrate followed by deposition of an electroluminescent layer and an anode.

Encapsulation

0047Optical devices tend to be sensitive to moisture and oxygen. Accordingly, the substrate preferably has good barrier properties for prevention of ingress of moisture and oxygen into the device. The substrate is commonly glass, however alternative substrates may be used, in particular where flexibility of the device is desirable. For example, the substrate may comprise a plastic as in <patcit id="pcit0025" dnum="US6268695B"><text>US 6268695</text></patcit> which discloses a substrate of alternating plastic and barrier layers or a laminate of thin glass and plastic as disclosed in <patcit id="pcit0026" dnum="EP0949850A"><text>EP 0949850</text></patcit>.

0048The device is preferably encapsulated with an encapsulant (not shown) to prevent ingress of moisture and oxygen. Suitable encapsulants include a sheet of glass, films having suitable barrier properties such as alternating stacks of polymer and dielectric as disclosed in, for example, <patcit id="pcit0027" dnum="WO0181649A"><text>WO 01/81649</text></patcit> or an airtight container as disclosed in, for example, <patcit id="pcit0028" dnum="WO0119142A"><text>WO 01/19142</text></patcit>. A getter material for absorption of any atmospheric moisture and / or oxygen that may permeate through the substrate or encapsulant may be disposed between the substrate and the encapsulant.

Electroluminescent layer

0049Electroluminescent layer 3 may consist of the electroluminescent material alone or may comprise the electroluminescent material in combination with one or more further materials. In particular, the electroluminescent material may be blended with hole and/or electron transporting materials as disclosed in, for example, <patcit id="pcit0029" dnum="WO9948160A"><text>WO 99/48160</text></patcit>. Alternatively, the electroluminescent material may be covalently bound to a charge transporting material

Polymers according to embodiments of the present invention

0050Polymers according to embodiments of the present invention may comprise an arylene co-repeat unit Ar such as a fluorene, particularly 2,7-linked 9,9-dialkylfluorene or 2,7- linked 9,9-diarylfluorene; a spirofluorene such as 2,7-linked 9,9-spirofluorene; an indenofluorene such as a 2,7-linked indenofluorene; or a phenyl such as alkyl or alkoxy substituted 1,4-phenylene. Each of these groups may be substituted.

0051Further suitable Ar groups are known in this art, for example as disclosed in <patcit id="pcit0030" dnum="WO0055927A"><text>WO00/55927</text></patcit>, <patcit id="pcit0031" dnum="WO0046321A"><text>WO 00/46321</text></patcit>, <patcit id="pcit0032" dnum="WO03095586A"><text>WO03/095586</text></patcit> and <patcit id="pcit0033" dnum="WO2004041902A"><text>WO 2004/041902</text></patcit>.

0052A polymer according to the present invention may comprise a homopolymer, copolymer, terpolymer or higher order polymer.

0053A copolymer, terpolymer or higher order polymer according to the present invention includes regular alternating, random and block polymers where the percentage of each monomer used to prepare the polymer may vary.

0054For ease of processing, it is preferred that the polymer is soluble. Substituents such as C_1-10 alkyl or C_1-10 alkoxy may usefully be selected to confer on the polymer solubility in a particular solvent system. Typical solvents include mono-or polyalkylated benzenes such as toluene and xylene or THF.

0055A polymer comprising the aromatically conjugated 9,9-dimethylfluorene may provide one or more of the functions of hole transport, electron transport and emission depending on which layer of the device it is used in and the nature of co-repeat units.

0056A homopolymer of the aromatically conjugated 9,9-dimethylfluorene may be utilised to provide electron transport.

0057A copolymer comprising the aromatically conjugated 9,9-dimethylfluorene and a triarylamine repeat unit, in particular a repeat unit selected from formulae 1-6, may be utilised to provide hole transport and/or emission: <chemistry id="chem0013" num="0013"><img file="EP2016112B1_D0013.tif" /></chemistry><chemistry id="chem0014" num="0014"><img file="EP2016112B1_D0014.tif" /></chemistry><chemistry id="chem0015" num="0015"><img file="EP2016112B1_D0015.tif" /></chemistry> wherein X, Y, A, B, C and D are independently selected from H or a substituent group. More preferably, one or more of X, Y, A, B, C and D is independently selected from the group consisting of optionally substituted, branched or linear alkyl, aryl, perfluoroalkyl, thioalkyl, cyano, alkoxy, heteroaryl, alkylaryl and arylalkyl groups. Most preferably, X, Y, A and B are C_1-10 alkyl. Optionally, any two of the aromatic rings may be linked by a direct bond or a divalent group such as an oxygen or sulphur atom.

0058Particularly preferred hole transporting polymers of this type are AB copolymers of the aromatically conjugated 9,9-dimethylfluorene and a triarylamine repeat unit.

0059A copolymer comprising an aromatically conjugated 9,9-dimethylfluorene and a heteroarylene repeat unit may be utilised for charge transport or emission. Preferred heteroarylene repeat units are selected from formulae 7-21: <chemistry id="chem0016" num="0016"><img file="EP2016112B1_D0016.tif" /></chemistry> wherein R₆ and R₇ are the same or different and are each independently hydrogen or a substituent group, preferably alkyl, aryl, perfluoroalkyl, thioalkyl, cyano, alkoxy, heteroaryl, alkylaryl or arylalkyl. For ease of manufacture, R₆ and R₇ are preferably the same. More preferably, they are the same and are each a phenyl group. <chemistry id="chem0017" num="0017"><img file="EP2016112B1_D0017.tif" /></chemistry><chemistry id="chem0018" num="0018"><img file="EP2016112B1_D0018.tif" /></chemistry><chemistry id="chem0019" num="0019"><img file="EP2016112B1_D0019.tif" /></chemistry><chemistry id="chem0020" num="0020"><img file="EP2016112B1_D0020.tif" /></chemistry><chemistry id="chem0021" num="0021"><img file="EP2016112B1_D0021.tif" /></chemistry><chemistry id="chem0022" num="0022"><img file="EP2016112B1_D0022.tif" /></chemistry><chemistry id="chem0023" num="0023"><img file="EP2016112B1_D0023.tif" /></chemistry><chemistry id="chem0024" num="0024"><img file="EP2016112B1_D0024.tif" /></chemistry><chemistry id="chem0025" num="0025"><img file="EP2016112B1_D0025.tif" /></chemistry>

0060Electroluminescent copolymers may comprise an electroluminescent region and at least one of a hole transporting region and an electron transporting region as disclosed in, for example, <patcit id="pcit0034" dnum="WO0055927A"><text>WO 00/55927</text></patcit> and <patcit id="pcit0035" dnum="US6353083B"><text>US 6353083</text></patcit>. If only one of a hole transporting region and electron transporting region is provided then the electroluminescent region may also provide the other of hole transport and electron transport functionality.

0061The different regions within such a polymer may be provided along the polymer backbone, as per <patcit id="pcit0036" dnum="US6353083B"><text>US 6353083</text></patcit>, or as groups pendant from the polymer backbone as per <patcit id="pcit0037" dnum="WO0162869A"><text>WO 01/62869</text></patcit>.

Polymerisation methods

0062Preferred methods for preparation of these polymers are Suzuki polymerisation as described in, for example, <patcit id="pcit0038" dnum="WO0053656A"><text>WO 00/53656</text></patcit> and Yamamoto polymerisation as described in, for example, <nplcit id="ncit0003" npl-type="s"><text>T. Yamamoto, "Electrically Conducting And Thermally Stable □ - Conjugated Poly(arylene)s Prepared by Organometallic Processes", Progress in Polymer Science 1993, 17, 1153-1205</text></nplcit>. These polymerisation techniques both operate via a "metal insertion" wherein the metal atom of a metal complex catalyst is inserted between an aryl group and a leaving group of a monomer. In the case of Yamamoto polymerisation, a nickel complex catalyst is used; in the case of Suzuki polymerisation, a palladium complex catalyst is used.

0063For example, in the synthesis of a linear polymer by Yamamoto polymerisation, a monomer having two reactive halogen groups is used. Similarly, according to the method of Suzuki polymerisation, at least one reactive group is a boron derivative group such as a boronic acid or boronic ester and the other reactive group is a halogen. Preferred halogens are chlorine, bromine and iodine, most preferably bromine.

0064It will therefore be appreciated that repeat units and end groups comprising aryl groups as illustrated throughout this application may be derived from a monomer carrying a suitable leaving group.

0065Suzuki polymerisation may be used to prepare regioregular, block and random copolymers. In particular, homopolymers or random copolymers may be prepared when one reactive group is a halogen and the other reactive group is a boron derivative group. Alternatively, block or regioregular, in particular AB, copolymers may be prepared when both reactive groups of a first monomer are boron and both reactive groups of a second monomer are halogen.

0066As alternatives to halides, other leaving groups capable of participating in metal insertion include groups include tosylate, mesylate and triflate.

Solution processing

0067A single polymer or a plurality of polymers may be deposited from solution to form layer 5. Suitable solvents for polyarylenes, in particular polyfluorenes, include mono-or poly-alkylbenzenes such as toluene and xylene. Particularly preferred solution deposition techniques are spin-coating and inkjet printing.

0068Spin-coating is particularly suitable for devices wherein patterning of the electroluminescent material is unnecessary - for example for lighting applications or simple monochrome segmented displays.

0069Inkjet printing is particularly suitable for high information content displays, in particular full colour displays. Inkjet printing of OLEDs is described in, for example, <patcit id="pcit0039" dnum="EP0880303A"><text>EP 0880303</text></patcit>.

0070If multiple layers of the device are formed by solution processing then the skilled person will be aware of techniques to prevent intermixing of adjacent layers, for example by crosslinking of one layer before deposition of a subsequent layer or selection of materials for adjacent layers such that the material from which the first of these layers is formed is not soluble in the solvent used to deposit the second layer.

0071Where a plurality of polymers are deposited, they may comprise a blend of at least two of a hole transporting polymer, an electron transporting polymer and, where the device is a PLED, an emissive polymer as disclosed in <patcit id="pcit0040" dnum="WO9948160A"><text>WO 99/48160</text></patcit>. Alternatively, layer 3 may be formed from a single polymer that comprises regions selected from two or more of hole transporting regions, electron transporting regions and emissive regions as disclosed in, for example, <patcit id="pcit0041" dnum="WO0055927A"><text>WO 00/55927</text></patcit> and <patcit id="pcit0042" dnum="US6353083B"><text>US 6353083</text></patcit>. Each of the functions of hole transport, electron transport and emission may be provided by separate polymers or separate regions of a single polymer. Alternatively, more than one function may be performed by a single region or polymer. In particular, a single polymer or region may be capable of both charge transport and emission. Each region may comprise a single repeat unit, e.g. a triarylamine repeat unit may be a hole transporting region.

0072Alternatively, each region may be a chain of repeat units, such as a chain of polyfluorene units as an electron transporting region. The different regions within such a polymer may be provided along the polymer backbone, as per <patcit id="pcit0043" dnum="US6353083B"><text>US 6353083</text></patcit>, or as groups pendant from the polymer backbone as per <patcit id="pcit0044" dnum="WO0162869A"><text>WO 01/62869</text></patcit>.

Hosts for phosphorescent emitters

0073Numerous hosts are described in the prior art including "small molecule" hosts such as 4,4'-bis(carbazol-9-yl)biphenyl), known as CBP, and (4,4',4"-tris(carbazol-9-yl)triphenylamine), known as TCTA, disclosed in <nplcit id="ncit0004" npl-type="s"><text>Ikai et al. (Appl. Phys. Lett., 79 no. 2, 2001, 156</text></nplcit>); and triarylamines such as tris-4-(N-3-methylphenyl-N-phenyl)phenylamine, known as MTDATA. Polymers are also known as hosts, in particular homopolymers such as poly(vinyl carbazole) disclosed in, for example, <nplcit id="ncit0005" npl-type="s"><text>Appl. Phys. Lett. 2000, 77(15), 2280</text></nplcit>; polyfluorenes in <nplcit id="ncit0006" npl-type="s"><text>Synth. Met. 2001, 116, 379</text></nplcit>, <nplcit id="ncit0007" npl-type="s"><text>Phys. Rev. B 2001, 63, 235206</text></nplcit> and <nplcit id="ncit0008" npl-type="s"><text>Appl. Phys. Lett. 2003, 82(7), 1006</text></nplcit>; poly[4-(N-4-vinylbenzyloxyethyl, N-methylamino)-N-(2,5-di-tert-butylphenylnapthalimide] in <nplcit id="ncit0009" npl-type="s"><text>Adv. Mater. 1999, 11(4), 285</text></nplcit>; and poly(para-phenylenes) in <nplcit id="ncit0010" npl-type="s"><text>J. Mater. Chem. 2003, 13, 50-55</text></nplcit>. Copolymers are also known as hosts.

0074It is envisaged that polymers according to the present invention will be useful as hosts for phosphorescent emitters due to the large band gap of polymers comprising aromatically conjugated 9,9-dimethylfluoride.

Metal complexes

0075Preferred metal complexes comprise optionally substituted complexes of formula (V):         ML¹_qL²_rL³_s     (V) wherein M is a metal; each of L¹, L² and L³ is a coordinating group; q is an integer; r and s are each independently 0 or an integer; and the sum of (a. q) + (b. r) + (c.s) is equal to the number of coordination sites available on M, wherein a is the number of coordination sites on L¹, b is the number of coordination sites on L² and c is the number of coordination sites on L³.

0076Heavy elements M induce strong spin-orbit coupling to allow rapid intersystem crossing and emission from triplet states (phosphorescence). Suitable heavy metals M include: <ul id="ul0002" list-style="dash"><li>lanthanide metals such as cerium, samarium, europium, terbium, dysprosium, thulium, erbium and neodymium; and</li><li>d-block metals, in particular those in rows 2 and 3 i.e. elements 39 to 48 and 72 to 80, in particular ruthenium, rhodium, pallaidum, rhenium, osmium, iridium, platinum and gold.</li></ul>

0077Suitable coordinating groups for the f-block metals include oxygen or nitrogen donor systems such as carboxylic acids, 1,3-diketonates, hydroxy carboxylic acids, Schiff bases including acyl phenols and iminoacyl groups. As is known, luminescent lanthanide metal complexes require sensitizing group(s) which have the triplet excited energy level higher than the first excited state of the metal ion. Emission is from an f-f transition of the metal and so the emission colour is determined by the choice of the metal. The sharp emission is generally narrow, resulting in a pure colour emission useful for display applications.

0078The d-block metals form organometallic complexes with carbon or nitrogen donors such as porphyrin or bidentate ligands of formula (VI): <chemistry id="chem0026" num="0026"><img file="EP2016112B1_D0026.tif" /></chemistry> wherein Ar⁴ and Ar⁵ may be the same or different and are independently selected from optionally substituted aryl or heteroaryl; X¹ and Y¹ may be the same or different and are independently selected from carbon or nitrogen; and Ar⁴ and Ar⁵ may be fused together. Ligands wherein X¹ is carbon and Y¹ is nitrogen are particularly preferred.

0079Examples of bidentate ligands are illustrated below: <chemistry id="chem0027" num="0027"><img file="EP2016112B1_D0027.tif" /></chemistry><chemistry id="chem0028" num="0028"><img file="EP2016112B1_D0028.tif" /></chemistry>

0080Each of Ar⁴ and Ar⁵ may carry one or more substituents. Particularly preferred substituents include fluorine or trifluoromethyl which may be used to blue-shift the emission of the complex as disclosed in <patcit id="pcit0045" dnum="WO0245466A"><text>WO 02/45466</text></patcit>, <patcit id="pcit0046" dnum="WO0244189A"><text>WO 02/44189</text></patcit>, <patcit id="pcit0047" dnum="US2002117662A"><text>US 2002-117662</text></patcit> and <patcit id="pcit0048" dnum="US2002182441A"><text>US 2002-182441</text></patcit>; alkyl or alkoxy groups as disclosed in <patcit id="pcit0049" dnum="JP2002324679A"><text>JP 2002-324679</text></patcit>; carbazole which may be used to assist hole transport to the complex when used as an emissive material as disclosed in <patcit id="pcit0050" dnum="WO0281448A"><text>WO 02/81448</text></patcit>; bromine, chlorine or iodine which can serve to functionalise the ligand for attachment of further groups as disclosed in <patcit id="pcit0051" dnum="WO0268435A"><text>WO 02/68435</text></patcit> and <patcit id="pcit0052" dnum="EP1245659A"><text>EP 1245659</text></patcit>; and dendrons which may be used to obtain or enhance solution processability of the metal complex as disclosed in <patcit id="pcit0053" dnum="WO0266552A"><text>WO 02/66552</text></patcit>.

0081Other ligands suitable for use with d-block elements include diketonates, in particular acetylacetonate (acac); triarylphosphines and pyridine, each of which may be substituted.

0082Main group metal complexes show ligand based, or charge transfer emission. For these complexes, the emission colour is determined by the choice of ligand as well as the metal.

0083The host material and metal complex may be combined in the form of a physical blend. Alternatively, the metal complex may be chemically bound to the host material. In the case of a polymeric host, the metal complex may be chemically bound as a substituent attached to the polymer backbone, incorporated as a repeat unit in the polymer backbone or provided as an end-group of the polymer as disclosed in, for example, <patcit id="pcit0054" dnum="EP1245659A"><text>EP 1245659</text></patcit>, <patcit id="pcit0055" dnum="WO0231896A"><text>WO 02/31896</text></patcit>, <patcit id="pcit0056" dnum="WO0318653A"><text>WO 03/18653</text></patcit> and <patcit id="pcit0057" dnum="WO0322908A"><text>WO 03/22908</text></patcit>.

0084A wide range of fluorescent low molecular weight metal complexes are known and have been demonstrated in organic light emitting devices [see, e. g., <nplcit id="ncit0011" npl-type="s"><text>Macromol. Sym. 125 (1997) 1-48</text></nplcit>, <patcit id="pcit0058" dnum="US5150006A"><text>US-A 5,150,006</text></patcit>, <patcit id="pcit0059" dnum="US6083634A"><text>US-A 6,083,634</text></patcit> and <patcit id="pcit0060" dnum="US5432014A"><text>US-A 5,432,014</text></patcit>], in particular tris-(8-hydroxyquinoline)aluminium. Suitable ligands for di or trivalent metals include: oxinoids, e. g. with oxygen-nitrogen or oxygen-oxygen donating atoms, generally a ring nitrogen atom with a substituent oxygen atom, or a substituent nitrogen atom or oxygen atom with a substituent oxygen atom such as 8-hydroxyquinolate and hydroxyquinoxalinol-10-hydroxybenzo (h) quinolinato (II), benzazoles (III), schiff bases, azoindoles, chromone derivatives, 3-hydroxyflavone, and carboxylic acids such as salicylato amino carboxylates and ester carboxylates. Optional substituents include halogen, alkyl, alkoxy, haloalkyl, cyano, amino, amido, sulfonyl, carbonyl, aryl or heteroaryl on the (hetero) aromatic rings which may modify the emission colour.

0085It is envisaged that polymers according to the present invention will be useful as hosts for fluorescent emitters, again due to the large band gap of polymers comprising aromatically conjugated 9,9-dimethylfluoride.

Polymer Examples

0086Two electroluminescent polymers were prepared using standard Suzuki polymerisation to make polymers from PFB, optionally substituted 9,9-dimethlyfluorene, F8 and optionally substituted 9,9-diphenylfluorene,

0087As can be seen in <figref idref="f0001">Figure 2</figref>, by increasing the proportion of 9,9-dimethylfluorene repeat unit in the opto-electrical semi-conductive polymers the glass transition temperature is increased thus increasing the thermal stability of the opto-electrical semi-conductive polymers.

0088As can be seen in <figref idref="f0002">Figure 3</figref>, by increasing the proportion of 9,9-dimethylfluorene repeat unit in the opto-electrical semi-conductive polymers the LUMO level is lowered increasing the electron affinity of the polymers. This improves electron injection and thus device performance as discussed below. The LUMO level was measured using cyclic voltammetry as is known in the art.

Device Example

0089Onto indium tin oxide supported on a glass substrate (available from Applied Films, Colorado, USA) was deposited a layer of PEDT / PSS, available from Bayer ® as Baytron P ® by spin coating. A hole transporting layer comprising fluorene and triarylamine units was deposited over the PEDOT layer according to the method described in <patcit id="pcit0061" dnum="WO2004023573A"><text>WO 2004/023573</text></patcit>. A layer of opto-electrical semi-conductive polymer was deposited over the PEDT / PSS layer by spin-coating from xylene solution. Onto the opto-electrical semi-conductive polymer was deposited a Ba/Al cathode.

0090A comparision between two devices where one device included a layer of opto-electrical semi-conductive polymer according to the present invention and the other device comprised a polymer of aromatically conjugated 9,9-diethylfluorene repeat unit clearly illustrated that the half life starting at 1600 cd/m² of the polymer according to the present invention was at least 300 hrs compared to the known polymer of aromatically conjugated 9,9-diethylfluorene repeat unit where the half life starting at 1600 cd/m² was no greater than 200 hrs. The driving conditions used to generate the lifetime data were operated using a DC drive at constant current.

0091Although the present invention has been described in terms of specific exemplary embodiments, it will be appreciated that various modifications, alterations and/or combinations of features disclosed herein will be apparent to those skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims.