Summary of the Invention

This invention relates to polymers, organic optoelectronic devices comprising said polymers, and methods of making said polymers and devices.

Background of the Invention

Electronic devices comprising active organic materials are attracting increasing attention for use in devices such as organic light emitting diodes, organic photoresponsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory array devices. Devices comprising organic materials offer benefits such as low weight, low power consumption and flexibility. Moreover, use of soluble organic materials allows use of solution processing in device manufacture, for example inkjet printing or spin-coating.

An organic optoelectronic device may comprise a substrate carrying an anode, a cathode and an organic semiconducting layer between the anode and cathode comprising a light- emitting material.

The organic semiconductor layer is an organic light-emitting layer in the case where the device is an organic light-emitting device (OLED). Holes are injected into the device through the anode (for example indium tin oxide, or ITO) and electrons are injected through the cathode during operation of the device. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of the light combine to form an exciton that releases its energy as light.

Suitable light-emitting materials include small molecule, polymeric and dendrimeric materials. Suitable light-emitting polymers for use in the light-emitting layer include poly(arylene vinylenes) such as poly(p-phenylene vinylenes) and polyarylenes such as polyfluorenes. Alternatively or additionally, the light-emitting layer may comprise a host material and a light-emitting dopant, for example a fluorescent or phosphorescent dopant.

The operation of an organic photovoltaic device or photosensor entails the reverse of the above-described process in that photons incident on the organic semiconducting layer generate excitons that are separated into holes and electrons. In order to facilitate the transfer of holes and electrons into the light-emitting layer of an OLED (or transfer of separated charges towards the electrodes in the case of a photovoltaic or photosensor device) additional layers may be provided between the anode and the cathode, such as a hole -transporting layer between the anode and the light- emitting layer and / or an electron-transporting layer between the cathode and the light- emitting layer.

One known class of hole transporting materials is electron-rich triphenylamines. WO 01/66618 discloses an organic light-emitting device in which triphenylamine repeat units of a hole transporting polymer are substituted with electron-withdrawing trifiuoromethyl groups to adjust the HOMO level of those repeat units.

Additionally, or alternatively, a hole-injection layer may be provided between the anode and the light-emitting layer. Known hole injection layers include conductive organic materials such as poly(ethylene dioxythiophene) (PEDT), in particular PEDT doped with a charge-balancing polyacid such as polystyrene sulfonate (PSS) as disclosed in EP 0901 176, and conductive inorganic materials such as VOx, MoOx and RuOx as disclosed in Journal of Physics D: Applied Physics (1996), 29(11), 2750-2753.

Bardecker et al, Adv. Funct. Mater. 2008, 1 , 3964-3971 discloses an OLED having a self- assembled monolayer (SAM) on the surface of an ITO anode and a hole -transporting layer over the SAM comprising crosslinked 4,4',4"-tris( -carbazolyl)triphenylamine bis(vinylbenzyl-ether), or "BVB-TCTA". Devices were formed using SAMs having phosphonic acid groups to bind to ΓΓΌ.

Polymers comprising pendant hole -transporting groups and single layer devices are described in J. Mater. Chem., 2001, 1 1, 3023-3030, which discloses

polypheny lenevinylene derivatives with carbazole pendant groups.

Adv. Mater. 2009, 21, 1972-1975 discloses polystyrene with pendant hole transporting groups cross-linked on top of an anode / hole injection bilayer of ITO / PEDT:PSS.

Photo-cross linkable hole transporting polymers comprising triarylamine and oxetane- functionalized styrenes copolymerized by radical polymerization are disclosed in

Macromolecules 2005, 38, 1640-1647. Macromolecules 2009, 42, 4053^1-062 discloses polyfluorene with pendant charge transporting groups.

Chem. Mater. 2007, 19, 4827-4832 discloses an interlayer formed by crosslinking of a non-conjugated backbone with pendant benzocyclobutane (BCB) cross-linker and hole transporting groups.

WO 03/086026 discloses a hole transport polymer comprising a polyacrylate, polymethacrylate or polystyrene polymeric backbone, and a pendant fused aromatic hole transport unit.

EP0712171, EP0850960, EP0851017, FR2736061, FR2785615, WO0002936,

W09965961 disclose hole -transport, electron-transport, and emissive units used as active pendant groups. Examples of active pendant groups include nathylimide, carbazole, pyrazoline, benzoxazole, benzothiazole, anthracene, phenanthrene are disclosed. Polymer backbones include polyacrylate, polystyrene, polyethylene. Thermally and photo-induced cross-linking units are also described.

Preparation and use of polymers with pendant active units are also described in the following references:

J. Mat. Chem., 2007, 17, 4122-4135 describes tatrathiafulvalene (TTF) derivatives used as pendant groups for electron-donating polymers.

J. Mat. Chem, 1993, 3(1), 1 13-114 describes polymers containing pendant

oligothiophenes as a novel class of electrochromic materials.

Macromolecules, 1995, 28, 723-729 describes synthesis of polythiophenes, as pendant groups of vinyl-type electrochemically doped polymers.

Appl. Phys Lett., 2006, 88, 093505 describes tetraphenyldiamine as well as carbazole and triphenylamine derivatives for phosphorescent polymer LED. Proc. Of SPIE, vol 6333 63330G-1 describes hole-transporting and emitting pendant polymers for OLED.

Synthetic Metals, 2008, 158, 670-675 describes synthesis of new hole-transport molecular glass with pendant carbazoyl moieties. J. Mat. Chem., 2008, 18, 4495-4509 discloses crosslinkable hole transporting materials for solution-processed OLEDs.

Summary of the Invention

In a first aspect the invention provides a polymer comprising a repeat unit of formula (X):

(X) wherein R 10 in each occurrence represents H or a substituent; Sp 2 represents a spacer group; t is 0 or 1 ;and POZ represents an optionally substituted, optionally fused phenoxazine group.

Optionally, the polymer comprises a repeat unit of formula (Xa):

wherein R ¹⁰ in each occurrence represents H or a substituent; Sp ² represents a spacer group; t is 0 or 1 ; d in each occurrence is independently 0, 1, 2, 3 or 4; R in each occurrence represents a substituent; and two substituents R ⁸ attached to the same phenyl ring may form a saturated or unsaturated ring.

Optionally, R ⁸ and R ¹⁰ are independently in each occurrence selected from the group consisting of, H, optionally substituted aryl, optionally substituted heteroaryl and alkyl, optionally C _1-20 alkyl wherein one or more non-adjacent C atoms of the alkyl may be replaced with O, S, substituted N, -C=0 and -COO-, -Si- and one or more H atoms of alkyl may be replaced with F or an aryl or heteroaryl group. Preferred groups R include Ci-20 alkyl and phenyl that may be unsubstituted or substituted with one or more C _1-20 alkyl groups. Preferred groups R ¹⁰ include H, C _1-20 alkyl and phenyl that may be unsubstituted or substituted with one or more C _1-20 alkyl groups.

Optionally, Sp2 comprises at least one non-ring atom spacing the phenoxazine unit from the polymer backbone.

Optionally, Sp comprises an aryl group, optionally a phenyl group.

Optionally, Sp comprises an alkyl chain, optionally a C _1-20 alkyl chain, an alkoxy group or an ether group.

Optionally, the polymer comprises one or more further repeat units different to the repeat unit of formula (X).

Optionally, the one or more further repeat units include a crosslinkable repeat unit.

Optionally, the one or more further repeat units include a repeat unit comprising a charge transporting unit having a HOMO level different to the repeat unit of formula (X).

In a second aspect, the invention provides an organic electronic device comprising a polymer according to the first aspect.

Optionally, the organic electronic device is an organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and the cathode.

Optionally, the light-emitting layer comprises the polymer according to the first aspect.

Optionally, the light-emitting layer further comprises a light-emitting dopant. Optionally, a charge-transporting layer is provided between the anode and light-emitting layer or between the cathode and light-emitting layer, the charge transporting layer comprising the polymer according to the first aspect. The charge transporting layer is optionally a hole transporting layer.

A composition comprising the polymer of the first aspect and at least one solvent may be provided, and this composition may be used to form a layer of the organic electronic device by depositing the composition from a solution in a solvent and evaporating the solvent. If the polymer of the first aspect comprises a crosslinkable repeat unit then that unit may be crosslinked. A further layer may then be deposited onto the crosslinked layer from a solution.

In a third aspect the invention provides a polymer having a backbone and comprising first and second repeat units, wherein:

the first repeat unit comprises a first backbone segment and a first charge-transporting group pendant from the first backbone segment and spaced apart from the first backbone segment by a first spacer group comprising at least 4 non-ring atoms in a path linking the first charge-transporting group to the polymer backbone; and

the second repeat unit comprises a second backbone segment and a cross-linkable group pendant from the second backbone segment and spaced apart from the second backbone segment by a second spacer group.

Optionally according to the third aspect, the backbone is substantially non-conjugated. Optionally according to the third aspect, the first repeat unit has formula (I):

(I)

wherein, each R independently represents H or a substituent; Sp represents the first spacer group; and CT represents the first charge transporting group.

Optionally according to the third aspect, the second repeat unit has formula (II):

(II)

wherein each R independently represents H or a substituent; Sp represents the second spacer group; and XL represents the crosslinkable group.

Optionally according to the third aspect, Sp 1 comprises at least one non-ring atom spacing XL from the second backbone segment.

Optionally according to the third aspect, the polymer comprises one or more further repeat units.

Optionally according to the third aspect, the polymer comprises one or more further repeat units, each of the one or more further repeat units comprising a further charge- transporting group that is different from the first charge transporting group.

Optionally according to the third aspect, the further repeat units have formula (XI): (Sp3) _w

CT2

(XI)

wherein R9 is H or a substituent which in each occurrence may be the same or different; Sp3 is a spacer group; w is 0 or 1 ; and CT2 is the further charge-transporting group.

Optionally according to the third aspect, the polymer comprises a further repeat unit that is not substituted with a charge-transporting group or a crosslinkable group.

Optionally according to the third aspect, the further repeat unit is a styryl repeat unit optionally substituted with one or more substituents selected from C _1-20 alkyl groups wherein one or more non-adjacent C atoms of the alkyl groups may be replaced by O or S.

Optionally according to the third aspect, R and R ¹ are independently in each occurrence selected from the group consisting of, H, optionally substituted aryl, optionally substituted heteroaryl and alkyl wherein one or more non-adjacent C atoms of the alkyl may be replaced with O, S, substituted N, -C=0 and -COO-, -Si- and one or more H atoms of alkyl may be replaced with F or an aryl or heteroaryl group.

Optionally according to the third aspect, Sp comprises an alkyl chain, optionally a C4-20 alkyl chain, an alkoxy group or an ether group.

Optionally according to the third aspect, Sp ¹ comprises an alkyl chain, optionally a C _1-20 alkyl chain, an alkoxy group or an ether group.

Optionally according to the third aspect, the first charge-transporting group is a hole transporting group, an electron transporting group or a bipolar group.

Optionally according to the third aspect, the crosslinkable group contains a polymerisable double bond, an optionally substituted benzocyclobutane group or an oxetane group. Optionally according to the third aspect, the first spacer group contains no more than 8 non-ring atoms spacing the first charge transporting group from the first backbone segment.

Optionally according to the third aspect, the second spacer group comprises no more than 8 non-ring atom spacing the crosslinkable group from the second backbone segment.

Optionally according to the third aspect, the number of the non-ring atoms of Sp plus the number of the non-ring atoms of Spl is not more than 10.

The polymer of the first aspect may comprise, in addition to repeat units of formula (X), one or more repeat units described in the third aspect of the invention that are different from repeat units of formula (X).

In a fourth aspect the invention provides a composition comprising the polymer of the third aspect and at least one solvent.

Optionally according to the fourth aspect, the at least one solvent is selected from mono- or poly-alky lated benzenes.

In a fifth aspect the invention provides a method of forming the polymer according to the third aspect by copolymerising a first monomer to form the first repeat unit and a second monomer to form the second repeat unit.

In a sixth aspect the invention provides an optoelectronic device comprising a layer comprising the polymer of the third aspect.

Optionally according to the sixth aspect, the device is an organic light-emitting device.

Optionally according to the sixth aspect, the layer is a hole -transporting layer.

In a seventh aspect the invention provides a method of forming an optoelectronic device comprising the steps of:

providing a first electrode;

forming a charge-transporting layer by depositing the polymer of the first aspect over the first electrode;

crosslinking the crosslinkable group; depositing an organic semiconducting layer over the charge transporting layer; and

forming a second electrode over the organic semiconducting layer.

Optionally according to the seventh aspect, the charge-transporting layer is a hole- transporting layer.

Optionally according to the seventh aspect, a hole injection layer is deposited between the first electrode and the hole transporting layer.

Optionally according to the seventh aspect, the surface of the first electrode is modified by a self-assembled monolayer.

Optionally according to the seventh aspect, the step of forming the charge-transporting layer comprises deposition of a composition according to the fourth aspect and evaporation of the at least one solvent.

Description of the Drawings

The invention will now be described in more detail with reference to the drawings, in which:

Figure 1 illustrates an organic light-emitting device according to an embodiment of the invention.

Detailed Description of the Invention

Polymer backbone

The backbone of inventive polymers may be formed from atoms that are linked together to form a non-conjugated chain.

A non-conjugated backbone may be formed by polymerization of a reactive monomer or monomers comprising reactive unsaturated group such as carbon-carbon unsaturated bonds, in particular carbon-carbon double bonds, to provide a backbone formed of a chain of carbon atoms.

Exemplary reactive monomers for forming repeat units that together form a non- conjugated backbone include optionally substituted styrenes, acrylates including alkylacrylates, for example methacrylates, and vinyl groups. These monomers may be polymerized by methods known to the skilled person such as free radical polymerization, ring-opening metathesis polymerization (ROMP) and cationic or anionic polymerization.

The polymer backbone may further comprise substituents selected from the group consisting of optionally substituted aryl, optionally substituted heteroaryl and alkyl wherein one or more non-adjacent C atoms of the alkyl group may be replaced with O, S, substituted N, -C=0 and -COO-, -Si- and one or more H atoms of the alkyl group may be replaced with F or aryl or heteroaryl groups. The backbone substituents may be solubilising groups such as alkyl groups.

Charge transporting polymer side chain

The polymer backbone may carry charge-transporting side chains of formula (la):

-Sp-CT

(la)

Sp and the charge-transporting group CT are described in more detail below.

The polymer side chain (la) may be attached to the polymer after formation of the polymer backbone. Alternatively, the monomers used to form the polymer backbone may be substituted with the side chain (la).

In one arrangement, the charge-transporting side chains of the polymer may be the same. In another arrangement, two or more different charge-transporting side chains may be provided. Different side chains may differ in respect of one or both of Sp and CT.

The polymer may carry a phenoxazine side group, which may or may not be linked to the polymer backbone by a spacer group such as spacer group Sp ² as described above. The phenoxazine side group may be linked to a spacer group through one of the aromatic carbon atoms of the phenoxazine unit or through the N atom of the phenoxazine unit.

Crosslinking polymer side chain

The polymer backbone may carry crosslinking side chains of formula (Ila):

-Sp ^! -XL (Ila)

wherein Sp ¹ is a spacer group described in more detail below and XL is a crosslinkable group.

Exemplary crosslinkable groups XL include groups comprising a polymerisable double bond such as a vinyl or acrylate group; an optionally a substituted benzocyclobutane (BCB) group or an oxetane group.

The XL group may be capable of undergoing cross-linking under thermal conditions following a ring-opening and a subsequent cyclisation without generating any side- products.

Charge transporting groups

The one or more charge transporting groups of the polymer may each be a hole transporting group, an electron transporting group or a bipolar group capable of transporting both holes and electrons.

A hole transporting group may have a low electron affinity (2 eV or lower) and low ionisation potential (5.8 eV or lower, preferably 5.7 eV or lower, more preferred 5.6 eV or lower).

An electron-transporting group may have a high electron affinity (1.8 eV or higher, preferably 2 eV or higher, even more preferred 2.2 eV or higher) and high ionisation potential (5.8 eV or higher) Suitable electron transport groups include groups disclosed in, for example, Shirota and Kageyama, Chem. Rev. 2007, 107, 953-1010.

Electron affinities and ionisation potentials may be measured by cyclic voltammetry (CV)

One exemplary class of charge-transporting groups are fused thiophenes each optionally substituted with one or more substituents R3 described below, . Exemplary fused thiophenes include the following groups:

R ³ in each occurrence is H or a substituent, as described in more detail below.

Exemplary substituents R ³ include optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl, preferably optionally substituted alkyl, for example Ci_2o alkyl.

The thiophenes may be substituted with one or more further substituents R ³ .

Another exemplary class of charge-transporting groups are fused polycyclic aromatics, for example three to seven fused benzene rings each optionally substituted with one or more substituents R described below, for example alkyl, including for example an optionally substituted pentacene.

Another exemplary class of charge-transporting groups are hole-transporting amine - containing groups, for example (hetero)arylamine groups of general formula (III):

(III)

wherein Ar ¹ and Ar ² in each occurrence are independently selected from optionally substituted aryl or heteroaryl groups, m is greater than or equal to 1 , preferably 1 or 2, R is H, and x and y are each independently 1 , 2 or 3.

Any of the aryl or heteroaryl groups in the repeat unit of Formula (III) may be linked by a direct bond or a divalent linking atom or group.

Substituents R ² are preferably selected from alkyl, for example C _1-20 alkyl, Ar ³ , or a branched or linear chain of Ar 3 groups, for example -(Ar 3 ) _r , wherei*n Ar3 i*n each occurrence is independently selected from aryl or heteroaryl and r is at least 1 , optionally l , 2 or 3. 1 2 3

Any of Ar , Ar and Ar may independently be substituted with one or more substituents. Preferred substituents are selected from the group R consisting of:

alkyl, for example C _1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with O, S, substituted N, C=0 and -COO- and one or more H atoms of the alkyl group may be replaced with F or aryl or heteroaryl optionally substituted with one or more groups R ⁴ ,

aryl or heteroaryl optionally substituted with one or more groups R ⁴ ,

NR ⁵ 2, OR ⁵ , SR ⁵ ,

fluorine, nitro and cyano;

wherein each R ⁴ is independently alkyl, for example C _1-20 alkyl, in which one or more non-adjacent C atoms may be replaced with O, S, substituted N, C=0 and -COO- and one or more H atoms of the alkyl group may be replaced with F, and each R ⁵ is independently selected from the group consisting of alkyl and aryl or heteroaryl optionally substituted with one or more alkyl groups.

Where present, substituted N or substituted C of R ³ , R ⁴ or of the divalent linking group may independently in each occurrence be NR ⁶ or CR ⁶ ₂ respectively wherein R ⁶ is alkyl or optionally substituted aryl or heteroaryl. Optional substituents for aryl or heteroaryl groups R ⁶ may be selected from R ⁴ or R ⁵ .

In one preferred arrangement, R 2 i*s Ar3 and each of Ar 1 , Ar2 and Ar 3 are independently and optionally substituted with one or more C _1-20 alkyl groups.

In another preferred arrangement, aryl or heteroaryl groups of formula (III) are phenyl, each phenyl group being optionally substituted with one or more alkyl groups.

In another preferred arrangement, Ar ¹ , Ar ² and Ar ³ are phenyl, each of which may be substituted with one or more C _1-20 alkyl groups, and r, x and y are each 1.

In another preferred arrangement, Ar ¹ and Ar ² are phenyl, each of which may be substituted with one or more C _1-20 alkyl groups, and R is 3,5-diphenylbenzene wherein each phenyl may be substituted with one or more alkyl groups. In yet another preferred arrangement, Ar 1 , Ar2 and Ar 3 are phenyl, each of which may be

1 2

substituted with one or more C _1-20 alkyl groups, r = 1 and Ar and Ar are linked by an O or S atom, for example carbazole substituted by one or more alkyl groups.

In yet another preferred arrangement, Ar ¹ and Ar ² are phenyl, each of which may be substituted with one or more C _1-20 alkyl groups, R ² is C _1-20 alkyl or phenyl substituted by

1 2

one or more C _1-20 alkyl groups; m, r, x and y are each 1 , and Ar and Ar are linked by a direct bond, for example carbazole substituted by one or more alkyl groups.

Exemplary charge-transporting amines include the following:

wherein * represents the linkage point of the charge-transporting group to the polymer backbone or to Sp and R is as described above. In the case where no * is shown, the charge transporting group may be linked through any aromatic ring atom of the charge- transporting group.

A spacer group may be bound to any atom of the aforementioned charge transporting groups, for example to an aromatic C atom or to the N atom of the group of formula (III).

Following deposition from solution, the side chains of the polymer may undergo pi-pi stacking, which may serve to increase the hole mobility of the hole transporting layer.

Spacer groups

The spacer groups Sp, Sp ¹ , Sp ² and Sp ³ may increase solubility of the polymer as compared to a polymer in which the spacer group is absent. Moreover, the spacer may contain non-conjugating atoms to separate the conjugated charge transporting group from, and prevent conjugation with, any unsaturated groups, such as aromatic groups, that may be present in the backbone or another part of the side chain. The spacer may contain a flexible chain in which the chain atoms do not form part of a ring, such as an alkyl group wherein the carbon atoms of the alkyl group are not part of a ring, to provide sufficient flexibility for the charge-transporting and crosslinking groups.

Exemplary spacer groups comprise:

a linear or branched alkyl group, for example a C4-20 alkyl chain in the case of Sp and a C _1-20 alkyl chain in the case of Sp ¹ , Sp ² or Sp ³ ; and

an ether or polyether group, for example a group of formula

wherein n is at least 1.

The spacer groups Sp, Sp ¹ , Sp ² and Sp ³ may independently comprise ring atoms, for example benzene, spacing the charge-transporting group from the polymer backbone. For example, the benzene group of a styrene monomer may form part of the spacer group. However Sp, and optionally Sp ¹ , Sp ² and Sp ³ , contain at least 4 non-ring atoms spacing the charge-transporting group from the polymer backbone. In one arrangement, the total number of non-ring atoms of Sp and Spl spacing the charge-transporting group and the crosslinkable group respectively from the polymer backbone may be less than or equal to 10. In another arrangement, Sp and / or Spl may have no more than 8 non-ring atoms spacing the charge-transporting group and the crosslinkable group respectively from the polymer backbone. For example, Sp may contain 6 non-ring atoms and Spl may contain 4 non-ring atoms. A maximum of 10 non-ring spacer atoms may provide good polymer solubility without adversely affecting the semiconducting properties of the polymer by the presence of long, non-semiconducting spacer groups. The non-ring atoms of Sp and / or Spl are preferably provided in a continuous chain, preferably a saturated chain.

Polymer repeat units and compositions

In one arrangement, the polymer may be a polymer containing only repeat units of formulae (I) and (II); a polymer containing only repeat units of formula (X); or a polymer containing only repeat units of formula (X) and formula (II). In another arrangement, the polymer may contain one or more further repeat units, for example repeat units with side chains different from sidechains of units (I) and (II) such as a spacing co-repeat unit. The further repeat units may be selected to modify the properties of the polymer, for example its electronic or physical properties (e.g. solubility of the polymer).

The polymer may contain more than one charge transporting repeat unit. For example, the polymer may comprise a repeat unit of formula (I) or a repeat unit of formula (X), and one or more further repeat units containing different charge-transporting repeat units. These further repeat units may provide different energy levels allowing for stepped charge transport between an electrode and the light-emitting layer. For example, a polymer may comprise a hole-transporting repeat unit of formula (X) and a further hole transporting repeat unit having a different hole-transporting unit providing a different HOMO level to the repeat unit of formula (X), for example a repeat unit of formula (I) as described above wherein CT is not a phenoxazine. The polymer may also comprise two different repeat units of formula (X) wherein the different repeat units differ at least in the HOMO level of the POZ groups of the respective repeat units due to different substituents on the POZ groups. The polymer may be any form of polymer, including a random, block or regioregular polymer, and the polymerization method used may be selected accordingly.

Where present, the crosslinkable repeat units may be provided in an amount of up to 20 mol % in the polymer, optionally in the range of 0.5-20 mol %, optionally in the range of 1-15 mol %.

Exemplary polymers may include one or more charge-transporting repeat units, one or more crosslinkable repeat units and one or more further repeat units selected from the following:

Charge transporting repeat units:

22







 WO 2012/175975

Further repeat units that do not provide any charge transporting or crosslinking functionalit are illustrated below:

wherein f is 1 -5, optionally 1 -3.

Crosslinked charge transporting polymer:

wherein n + m represent a molar percentage of a repeat unit in the polymer, and n + m = 100. In other arrangements, further repeat units may be present in which case n + m is less than 100.

35



wherein n + m + p represent a molar percentage of a repeat unit in the polymer, and n + m + p = 100. In other arrangements, further repeat units may be present in which case n + m + p is less than 100.

The above exemplary polymers are not limiting, and it will be appreciated that the skilled person will be aware of combinations of one or more charge transporting repeat units and crosslinkable repeat units as described herein. For example, any of the benzocyclobutane crosslinkable repeat units illustrated above may be replaced with another crosslinkable repeat unit comprising a crosslinkable group XL described above. Each of the charge transporting repeat units, crosslinkable repeat units and further repeat units may be substituted with one or more substituents R , for example one or more alkyl groups.

The presence of two different charge-transporting groups with different energy levels in the polymer may allow for stepped charge injection from an electrode into the light- emitting layer of an OLED via a charge-transporting layer containing the polymer between the electrode and the light-emitting layer.

Figure 1 illustrates schematically an OLED according to an embodiment of the invention.

The OLED comprises a substrate 1 , an anode 2, for injection of holes into the device, a hole transporting layer 3 comprising a polymer according to the invention over the anode; a light-emitting layer 4 over the hole-transporting layer; and a cathode 5 over the light- emitting layer for injection of electrons into the device. Additional charge transporting, charge blocking and / or charge injecting layers may be provided between the anode and the cathode.

If light is to be emitted through the anode and the substrate then the substrate may be formed from a transparent material, for example glass or transparent plastic, and the anode may be formed from a transparent conductive material. The substrate and / or anode may be opaque if cathode 5 is transparent.

Anode

The anode 1 may be formed from any material suitable for injection of holes. Suitable materials include metals, metal alloys and conductive metal oxides. An exemplary transparent anode material is indium tin oxide. The surface of the anode may be modified by a self-assembled monolayer, for example a fluorinated phosphonic acid.

Hole injection layers

A conductive hole injection layer, which may be formed from a conductive organic or inorganic material, may be provided between the anode 2 and the hole -transporting layer 3. Examples of doped organic hole injection materials include optionally substituted, doped poly(ethylene dioxythiophene) (PEDT), in particular PEDT doped with a charge- balancing polyacid such as polystyrene sulfonate (PSS) as disclosed in EP 0901176 and EP 0947123, polyacrylic acid or a fiuorinated sulfonic acid, for example Nafion ®;

polyaniline as disclosed in US 5723873 and US 5798170; and optionally substituted polythiophene or poly(thienothiophene). Examples of conductive inorganic materials include transition metal oxides such as VOx MoOx and RuOx as disclosed in Journal of Physics D: Applied Physics (1996), 29(11), 2750-2753.

Charge transporting layers

A further hole transporting layer may be provided between the anode 2 and the light- emitting layer 4. Likewise, an electron transporting layer may be provided between the cathode 5 and the light-emitting layer 4.

Similarly, an electron blocking layer may be provided between the anode 2 and the light- emitting layer 4 and a hole blocking layer may be provided between the cathode 5 and the light-emitting layer 4. Transporting and blocking layers may be used in combination. Depending on its HOMO and LUMO levels, a single layer may both transport one of holes and electrons and block the other of holes and electrons.

Light emitting layer

Suitable light-emitting materials for use in the light-emitting layer include small molecule, polymeric and dendrimeric materials, and compositions thereof. Suitable light-emitting polymers include conjugated polymers, for example optionally substituted poly(arylene vinylenes) such as poly(p-phenylene vinylenes) and optionally substituted polyarylenes such as: polyfluorenes, particularly 2,7-linked 9,9 dialkyl polyfiuorenes or 2,7-linked 9,9 diaryl polyfluorenes; polyspirofluorenes, particularly 2,7-linked poly-9,9- spirofiuorene; polyindenofluorenes, particularly 2,7-linked polyindenofluorenes; polyphenylenes, particularly alkyl or alkoxy substituted poly-l ,4-phenylene. Such polymers as disclosed in, for example, Adv. Mater. 2000 12(23) 1737-1750 and references therein.

Polymers for use as light-emitting materials in devices according to the present invention may comprise a repeat unit selected from optionally substituted amine repeat units and / or optionally substituted arylene or heteroarylene repeat units.

Exemplary amine repeat units have formula (IV):

(IV)

wherein Ar 1 and Ar2 i·n each occurrence are independently selected from optionally substituted aryl or heteroaryl groups, m is greater than or equal to 1 , preferably 1 or 2, R is H or a substituent, preferably a substituent, and x and y are each independently 1 , 2 or 3.

R ² is preferably alkyl, for example C _1-20 alkyl, Ar ³ , or a branched or linear chain of Ar ³ groups, for example -(Ar 3 ) _r , wherein Ar 3 in each occurrence is independently selected from aryl or heteroaryl and r is at least 1, optionally 1, 2 or 3.

Any of Ar ¹ , Ar ² and Ar ³ may independently be substituted with one or more substituents. Preferred substituents are selected from the group R ³ consisting of:

alkyl, for example C _1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with O, S, substituted N, C=0 and -COO- and one or more H atoms of the alkyl group may be replaced with F or aryl or heteroaryl optionally substituted with one or more groups R ⁴ ,

aryl or heteroaryl optionally substituted with one or more groups R ⁴ ,

NR ⁵ 2, OR ⁵ , SR ⁵ , and

fluorine, nitro and cyano;

wherein each R ⁴ is independently alkyl, for example C _1-20 alkyl, in which one or more non-adjacent C atoms may be replaced with O, S, substituted N, C=0 and -COO- and one or more H atoms of the alkyl group may be replaced with F, and each R ⁵ is independently selected from the group consisting of alkyl and aryl or heteroaryl optionally substituted with one or more alkyl groups.

Any of the aryl or heteroaryl groups in the repeat unit of Formula (IV) may be linked by a direct bond or a divalent linking atom or group. Preferred divalent linking atoms and groups include O, S; substituted N; and substituted C. Where present, substituted N or substituted C of R , R or of the divalent linking group may independently in each occurrence be NR ⁶ or CR ⁶ ₂ respectively wherein R ⁶ is alkyl or optionally substituted aryl or heteroaryl. Optional substituents for aryl or heteroaryl groups R ⁶ may be selected from R ⁴ or R ⁵ .

In one preferred arrangement, R ² is Ar ³ and each of Ar ¹ , Ar ² and Ar ³ are independently and optionally substituted with one or more C _1-20 alkyl groups.

Particularly preferred units satisfying Formula (IV) include units of Formulae 1 -3:

1 2 · 3

wherein Ar and Ar are as defined above; and Ar is optionally substituted aryl or heteroaryl. Where present, preferred substituents for Ar ³ include substituents as described forAr ¹ and Ar ² , in particular alkyl and alkoxy groups.

Ar ¹ , Ar ² and Ar ³ are preferably phenyl, each of which may independently be substituted with one or more substituents as described above.

In another preferred arrangement, aryl or heteroaryl groups of formula (IV) are phenyl, each phenyl group being optionally substituted with one or more alkyl groups.

In another preferred arrangement, Ar ¹ , Ar ² and Ar ³ are phenyl, each of which may be substituted with one or more C _1-20 alkyl groups, and r = 1.

In another preferred arrangement, Ar ¹ and Ar ² are phenyl, each of which may be substituted with one or more C _1-20 alkyl groups, and R is 3,5-diphenylbenzene wherein each phenyl may be substituted with one or more alkyl groups.

Exemplary (hetero)arylene repeat units include optionally substituted fiuorene, phenylene and / or indenofiuorene repeat units. Exemplary fiuorene repeat units include repeat units of formula (V):

(V)

wherein R ⁶ and R ⁷ are independently H or a substituent and wherein R ⁶ and R ⁷ may be linked to form a ring.

R ⁶ and R ⁷ are optionally selected from the group consisting of hydrogen; optionally substituted Ar ³ or a linear or branched chain of Ar ³ groups, wherein Ar ³ is as described above; and optionally substituted alkyl, for example C _1-20 alkyl, wherein one or more non- adjacent C atoms of the alkyl group may be replaced with O, S, substituted N, C=0 and - COO-.

In the case where R ⁶ or R ⁷ comprises alkyl, optional substituents of the alkyl group include F, CN, nitro, and aryl or heteroaryl optionally substituted with one or more groups R ⁴ wherein R ⁴ is as described above.

In the case where R ⁶ or R ⁷ comprises aryl or heteroaryl, each aryl or heteroaryl group may independently be substituted. Preferred optional substituents for the aryl or heteroaryl groups include one or more substituents R ³ .

Optional substituents for the fiuorene unit, other than substituents R ⁶ and R ⁷ , are preferably selected from the group consisting of alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, substituted N, C=0 and -COO-, optionally substituted aryl, optionally substituted heteroaryl, fluorine, cyano and nitro.

In one preferred arrangement, at least one of R ⁶ and R ⁷ comprises an optionally substituted C1-C20 alkyl or an optionally substituted aryl group, in particular phenyl substituted with one or more C _1-20 alkyl groups.

The repeat units of formula (V) may be 2,7-linked.

Exemplary phenylene repeat units include repeat units of formula (VI):

(VI)

wherein R ⁶ is as described above with reference to formula (V) and p is 1 , 2, 3 or 4, optionally 1 or 2. In one arrangement, the repeat unit is a 1 ,4-phenylene repeat unit.

The repeat unit of formula (VI) may have formula (Via):

(Via)

The light-emitting layer may consist of a light-emitting material alone, or may comprise this material in combination with one or more further materials. In particular, the light- emitting material may be blended with hole and / or electron transporting materials or alternatively may be covalently bound to hole and / or electron transporting materials as disclosed in for example, WO 99/48160.

Light-emitting copolymers may comprise a light-emitting region and at least one of a hole transporting region and an electron transporting region as disclosed in, for example, WO 00/55927 and US 6353083. 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 - for example, an amine unit of formula (IV) as described above may provide both hole transport and light-emission functionality. A light-emitting copolymer comprising light-emitting repeat units and one or both of a hole transporting repeat units and electron transporting repeat units may provide said units in a polymer main-chain, as per US 6353083, or in polymer side- groups pendant from the polymer backbone.

Suitable light-emitting materials may emit in the UV, visible and / or infra-red region of the electromagnetic spectrum. The OLED may contain one or more of red, green and blue light-emitting materials. A blue light-emitting material may have photoluminescent spectrum with a peak wavelength in the range of less than or equal to 480 nm, such as in the range of 400-480 nm.

A green light-emitting material may have photoluminescent spectrum with a peak wavelength in the range of above 480 nm - 560 nm.

A red light-emitting material may have photoluminescent spectrum with a peak wavelength in the range of above 560 nm - 630 nm.

More than one light-emitting material may be used. For example, red, green and blue light-emitting material may be used to obtain white light emission.

The light emitting layer may comprise a host material and at least one light-emitting dopant. The host material may be a material as described above that would, in the absence of a dopant, emit light itself. When a host material and dopant are used in a device, the dopant alone may emit light. Alternatively, the host material and one or more dopants may emit light. White light may be generated by emission from multiple light sources, such as emission from both the host and one or more dopants or emission from multiple dopants.

In the case of a fluorescent light-emitting dopant the singlet excited state energy level (Si) of the host material should be higher than that of the fluorescent light-emitting dopant in order that singlet excitons may be transferred from the host material to the fluorescent light-emitting dopant. Likewise, in the case of a phosphorescent light- emitting dopant the triplet excited state energy level (Ti) of the host material should be higher than that of the phosphorescent light-emitting dopant in order that triplet excitons may be transferred from the host material to the fluorescent light-emitting dopant.

Exemplary phosphorescent light-emitting dopants include metal complexes comprising optionally substituted complexes of formula (VII):

(VII)

wherein M is a metal; each of L , L and L 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

1 2

sites on L , b is the number of coordination sites on L and c is the number of

coordination sites on L ³ .

Heavy elements M induce strong spin-orbit coupling to allow rapid intersystem crossing and emission from triplet or higher states (phosphorescence). Suitable heavy metals M include 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, palladium, rhenium, osmium, iridium, platinum and gold. Iridium are particularly preferred.

Exemplary ligands L ¹ , L ² and L ³ include carbon or nitrogen donors such as porphyrin or bidentate ligands of formula (VIII):

(VIII)

wherein Ar ⁴ and Ar ⁵ may be the same or different and are independently selected from optionally substituted aryl or heteroaryl; X ¹ and Y ¹ may be the same or different and are independently selected from carbon or nitrogen; and Ar ⁴ and Ar ⁵ may be fused together. Ligands wherein X ¹ is carbon and Y ¹ is nitrogen are particularly preferred.

Examples of bidentate ligands are illustrated below:

Each of Ar ⁴ and Ar ⁵ may carry one or more substituents. Two or more of these substituents may be linked to form a ring, for example an aromatic ring.

Other ligands suitable for use with d-block elements include diketonates, in particular acetylacetonate (acac); triarylphosphines and pyridine, each of which may be substituted. 3 3

Exemplary substituents include groups R groups R as described above with reference to Formula (IV). Particularly preferred substituents include fluorine or trifiuoro methyl which may be used to blue-shift the emission of the complex, for example as disclosed in WO 02/45466, WO 02/44189, US 2002-1 17662 and US 2002-182441 ; alkyl or alkoxy groups, for example C _1-20 alkyl or alkoxy, which may be as disclosed in JP 2002-324679; carbazole which may be used to assist hole transport to the complex when used as an emissive material, for example as disclosed in WO 02/81448; bromine, chlorine or iodine which can serve to functionalise the ligand for attachment of further groups, for example as disclosed in WO 02/68435 and EP 1245659; and dendrons which may be used to obtain or enhance solution processability of the metal complex, for example as disclosed in WO 02/66552.

A light-emitting dendrimer typically comprises a light-emitting core bound to one or more dendrons, wherein each dendron comprises a branching point and two or more dendritic branches. Preferably, the dendron is at least partially conjugated, and at least one of the branching points and dendritic branches comprises an aryl or heteroaryl group, for example a phenyl group. In one arrangement, the branching point group and the branching groups are all phenyl, and each phenyl may independently be substituted with one or more substituents, for example alkyl or alkoxy.

A dendron may have optionally substituted formula (IX)

wherein BP represents a branching point for attachment to a core and Gi represents first generation branching groups.

The dendron may be a first, second, third or higher generation dendron. Gi may be substituted with two or more second generation branching groups G ₂ , and so on, as in optionally substituted formula (IXa):

(IXa)

wherein u is 0 or 1 ; v is 0 if u is 0 or may be 0 or 1 if u is 1 ; BP represents a branching point for attachment to a core and Gi, G ₂ and G ₃ represent first, second and third generation dendron branching groups.

BP and / or any group G may be substituted with one or more substituents, for example one or more C _1-20 alkyl or alkoxy groups.

Where used, a light-emitting dopant may be present in an amount of about 0.05 mol % up to about 20 mol %, optionally about 0.1 -10 mol % relative to their host material.

The light-emitting dopant may be physically mixed with the host material or it may be chemically bound to the host material in the same manner described above with respect to binding of the light-emitting dopant to the charge transporting material.

The light-emitting layer may be patterned or unpatterned. A device comprising an unpatterned layer may be used an illumination source, for example. A white light emitting device is particularly suitable for this purpose. A device comprising a patterned layer may be, for example, an active matrix display or a passive matrix display. In the case of an active matrix display, a patterned electroluminescent layer is typically used in combination with a patterned anode layer and an unpatterned cathode. In the case of a passive matrix display, the anode layer is formed of parallel stripes of anode material, and parallel stripes of electroluminescent material and cathode material arranged perpendicular to the anode material wherein the stripes of electroluminescent material and cathode material are typically separated by stripes of insulating material ("cathode separators") formed by photolithography.

The light-emitting layer may comprise a polymer comprising a repeat unit of formula (X) as described above. The polymer comprising the repeat unit of formula (X) may comprise a light-emitting repeat unit. Alternatively, the polymer may be a host blended with a fluorescent or phosphorescent dopant, for example a metal complex as described above.

Cathode

Cathode 5 is selected from materials that have a workfunction allowing injection of electrons into the light-emitting layer 4. Other factors influence the selection of the cathode such as the possibility of adverse interactions between the cathode and the materials of the light-emitting layer. 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 a low workfunction material and a high workfunction material such as calcium and aluminium as disclosed in WO 98/10621 ; elemental barium as disclosed in WO 98/57381, Appl. Phys. Lett. 2002, 81(4), 634 and WO 02/84759; or a thin layer of metal compound, in particular an oxide or fluoride of an alkali or alkali earth metal, to assist electron injection, for example lithium fluoride as disclosed in WO 00/48258; barium fluoride as disclosed in Appl. Phys. Lett. 2001 , 79(5), 2001; and barium oxide. 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. Work functions of metals can be found in, for example, Michaelson, J. Appl. Phys. 48(1 1), 4729, 1977.

The cathode may be opaque or transparent. Transparent cathodes are particularly advantageous for active matrix devices because emission through a transparent anode in such devices is at least partially blocked by drive circuitry located underneath the emissive pixels. A transparent cathode will comprise a layer of an electron injecting material that is sufficiently thin to be transparent. Typically, the lateral conductivity of this layer will be low as a result of its thinness. In this case, the layer of electron injecting material is used in combination with a thicker layer of transparent conducting material such as indium tin oxide.

It will be appreciated that a transparent cathode device need not have a transparent anode (unless, of course, a fully transparent device is desired), and so the transparent anode used for bottom-emitting devices may be replaced or supplemented with a layer of reflective material such as a layer of aluminium. Examples of transparent cathode devices are disclosed in, for example, GB 2348316.

Solution processing

The polymers are preferably soluble in order to allow their deposition from a composition comprising a solvent solution. The polymers are preferably soluble in common organic solvents and can be included in compositions comprising for example alkylated benzenes (such as xylene and toluene) and chlorinated solvents such as chloroform. Exemplary deposition methods include spin-coating, dip-coating, blade-coating, inkjet printing, roll printing and screen printing.

Exemplary solvents for the polymers of the invention include organic solvents, for example mono- or poly-alkylbenzenes such as toluene and xylene and chlorinated solvents.

The light-emitting layer may be deposited by any process, including vacuum evaporation and deposition from a solution in a solvent.

Coating, such as spin-coating is particularly suitable for devices wherein patterning of the light-emitting layer is unnecessary - for example for lighting applications or simple monochrome segmented displays.

Printing, such as inkjet printing, is particularly suitable for high information content displays, in particular full colour displays. A device may be inkjet printed by providing a patterned layer over the first electrode and defining wells for printing of one colour (in the case of a monochrome device) or multiple colours (in the case of a multicolour, in particular full colour device). The patterned layer is typically a layer of photoresist that is patterned to define wells as described in, for example, EP 0880303. The hole transporting layer, the light-emitting layer and, if present, a hole injection layer may be printed into a single well.

As an alternative to wells, the ink may be printed into channels defined within a patterned layer. In particular, the photoresist may be patterned to form channels which, unlike wells, extend over a plurality of pixels and which may be closed or open at the channel ends.

Examples

Charge transport and cross-linking monomers may be prepared via methods known to those skilled in the art. The following examples illustrate certain features of the present invention. They are intended to be illustrative of the invention but not limiting.

Intermediate (I)

To a solution of bromostyrene (5g, 0.03mol) in THF (100ml) at -78°C under nitrogen, was added n-butyllithium (1 1 ml, 1 .Oeq, 2,5M in hexanes) dropwise. After stirring at this temperature for lhr, l -4,dibromobutane (58g, 0.3mol) was added rapidly and the reaction mixture allowed to warm to ambient temperature overnight. Water ( 100ml) was then added and the solvent removed under reduced pressure. The organic phase was extracted with DCM (3x50ml), washed with water, dried (MgSC^) and concentrated in vaco. The resulting yellow oil was treated with 3 ,5 -di-t-butyl-catechol (1 %) and excess

dibromobutane removed via distillation (99°C, -l Ombar pressure). The orange residue was filtered through a silica plug, (100% hexane to 3%EtOAc) and the filtrate evaporated to give the 4-(4-bromo-butyl)-styrene as a clear oil (3.6g, 65%).

1H-NMR (400MHz, CDC1 ₃ ) δ in ppm: 7.34 (2H, d, ArH), 7.14 (2H, d, ArH), 6.38 (1H, dd, =CH2), 5.71 (1Η, d, CH=), 5.20 (1Η, d), 3.42 (2Η, t, ArCH ₂ ), 2.64 (2Η, t, Br-CH ₂ ), 1.89 (2Η, m, CH ₂ CH ₂ ), 1.78 (2H, m, CH ₂ CH ₂ ); MS: M ⁺ 238 ( 100%).

Intermediate (II)

To a suspension of NaH (8.4g, 21 mmol, 60% in mineral oil) in DMF (250ml) at 0°C under nitrogen, was added a solution of phenoxazine (35g, 19mmol) in DMF (50ml) dropwise so as to maintain an internal temperature of <5°C. After stirring for lhr, a solution of the (I) (45.7ml, 19mmol) in DMF (50ml) was added dropwise and the reaction mixture allowed to warm to ambient temperature overnight. Water (100ml) was added to the reaction mixture and the organic phased extracted with toluene (3x50ml), washed with water, dried (MgSO^ and concentrated under reduced pressure. The resulting crude material was dissolved in toluene, filtered (florisil/silica plug), concentrated and the resulting oil recrystalized (IP A/toluene) to give the product as a while solid (53g, 81%)

MS: M ⁺ 341 (100%).

Intermediate (III)

To a suspension of magnesium turnings (1.32g, 55mmol) and an iodine crystal, in THF (26ml) under nitrogen, was added dropwise the first part of a solution of styrene (I) (9.8g, 41mmol) in THF (15ml). The mixture was heated to initiate the reaction and the addition of (I) continued dropwise so as to maintain gentle reflux. After the addition was complete, the reaction mixture was heated to 60°C for lhr 30mins cooled to room temperature and added dropwise to a solution of benzocyclobutyl bromide (BCBBr) (5g, 27mmol), PdCl ₂ (dppf) (1.1 lg, 0.05eq) and dppf (1.51g, 0.1 eq) in THF (50ml) and the resulting mixture heated at 70°C overnight. The mixture was then cooled to room temperature quenched with water (500ml), extracted with toluene (3x50ml) and the organic phase washed with water, dried (MgSO^ and concentrated under reduced pressure. The crude material was purified by column chromatography (Si0 ₂ , hexane) to give the product as a clear oil (l,3g, 18%).

MS: M ⁺ 262 (100%)

Polymer Example 1

Synthesis of a Polymer Example 1 is illustrated below:

Example 1

A suspension of (II) (7.37g, 21mmol) and (III) (0.63g, 2.4mmol) in heptanone 20ml (degassed with nitrogen for 30mins before use) was heated to 40°C.

Azobisisobutyronitrile (AIBN) (35,4mg, 1.0mol%) was added and the reaction mixture heated at 60°C for 24hrs. The reaction mixture was diluted with toluene (30ml) and added dropwise to diethyl ether (500ml) to precipitate the polymer. The resulting polymer was redissolved in toluene (20ml) and reprecipitated into diethyl ether (400ml) to give the product.

Mw 95,000, Mp 85,000, PD 2.01.

Polymer Example 2

A suspension of (II) (8.0g, 23mmol) in heptanone 20ml (degassed with nitrogen for 30mins before use) was heated to 40°C. Azobisisobutyronitrile (AIBN) (38.5mg, 1.0mol%) was added and the reaction mixture heated at 60°C for 24hrs. The reaction mixture was diluted with toluene (30ml) and added dropwise to diethyl ether (500ml) to precipitate the polymer. The resulting polymer was redissolved in toluene (20ml) and reprecipitated into diethyl ether (400ml) to give the homopolymer.

Mw 81,000, Mp 72,000, PD 1.94.

Example 3

Charge transporting polymers containing a spacer of at least 4 carbon atoms between the non-conjugated backbone and the hole transporting unit (Example 2) were found to be soluble in o-xylene, as were their crosslinked counterparts (Example 1). In the absence of a spacer group (Example 3), the polymer was found to be extremely insoluble in o-xylene and showed limited solubility in anisole even after extensive heating. A similar result was observed for PVK. In contrast, the corresponding crosslinked derivative (Example 4), containing a spacer group of 4 carbon atoms between the crosslinking group and polymer backbone, was found to be soluble.

Example 1 Example 2

Device Example 1

A device having the following structure was prepared:

ITO / HIL / HTL / EL / Cathode

wherein ITO is an indium-tin oxide anode; HIL is a hole injection layer comprising a hole injection material available from Plextronics, Inc.; HTL is a hole -transporting layer comprising a hole transporting polymer of Example 1 ; EL is a light-emitting layer comprising a polyfiuorene; and Cathode is a cathode comprising a layer of fluoride, a layer of aluminium and a layer of silver. Although 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 scope of the invention as set forth in the following claims.