LIGHT EMITTING COMPOSITION AND DEVICE

Abstract

An organic light-emitting device comprising an anode; a cathode; and a first light-emitting layer between the anode and the cathode, wherein the first light-emitting layer comprises a fluorescent light-emitting material of formula (I): (Formula (I)) wherein Ar1 and Ar2 each independently in each occurrence is a substituted or unsubstituted aryl or heteroaryl group; n and m independently in each occurrence is 1, 2 or 3; R independently in each occurrence is a substituent; and Ar1 and Ar2 linked directly to the same N atom may be linked by a direct bond or a linking unit to form a ring; and wherein a first phosphorescent light-emitting material is provided in the first light-emitting layer or in a second light-emitting layer adjacent to the first light-emitting layer.

Description

BACKGROUND

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 light-emitting device (OLED) may comprise a substrate carrying an anode, a cathode and an organic light-emitting layer between the anode and cathode comprising a light-emitting material. Further layers may be provided between the anode and the cathode, for example one or more charge-injection or charge-transport layers.

During operation of the device, holes are injected into the device through the anode and electrons are injected through the cathode. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of the light-emitting material combine in the light-emitting layer 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.

The light emitting layer may contain a semiconducting host material and a light-emitting dopant wherein energy is transferred from the host material to the light-emitting dopant. For example, J. Appl. Phys. 65, 3610, 1989 discloses a host material doped with a fluorescent light-emitting dopant (that is, a light-emitting material in which light is emitted via decay of a singlet exciton) and Appl. Phys. Lett., 2000, 77, 904 discloses a host material doped with a phosphorescent light emitting dopant (that is, a light-emitting material in which light is emitted via decay of a triplet exciton).

Hosts for luminescent dopants include “small molecule” materials such as tris-(8-hydroxyquinoline)aluminium (“Alq3”) and non-conjugated polymers such as polyvinylcarbazole (“PVK”).

In order to function effectively as a host it is necessary for the relevant excited state energy level of the host material to be sufficiently high to allow transfer of excitons from an excited state energy level of the host to an excited state energy level of a luminescent dopant (for example, transfer to the singlet excited state energy level S₁ for a fluorescent emitter and the triplet excited state energy level T₁ for a phosphorescent emitter).

It may be desirable to provide multiple light-emitting materials in the same light-emitting layer or in adjacent layers, for example to obtain white light, however singlet and/or triplet excitons may transfer to the material or materials with the lowest excited state energy, resulting in quenching of emission from one or more materials with a higher excited state energy.

Schwartz et al, “Triplet Harvesting in Hybrid White Organic Light-Emitting Diodes”, Adv. Funct. Mater. 2009, 19, 1319-1333, discloses use of a blue fluorophor with red and green phosphors in both separate fluorescent and phosphorescent layer and in a “triple blend” layer containing the blue fluorescent emitter and the green and red phosphorescent emitters. In the case of the “triple blend” layer device, doping of the green phosphorescent emitter Ir(ppy)₃ into fluorescent blue emitter 4P-NPD is reported to result in a complete lack of green emission, which is attributed to triplet exciton transfer from the green phosphorescent emitter to the blue emitter.

It is an object of the invention to provide a device containing both fluorescent and phosphorescent emitters wherein quenching of phosphorescent emission is limited or avoided. It is a further object of the invention to provide a device containing both fluorescent and phosphorescent light-emitting materials, in particular fluorescent blue and phosphorescent green light-emitting materials, wherein these two emitters are provided in the same layer or in adjacent layers and wherein quenching of phosphorescence is limited or avoided.

SUMMARY OF THE INVENTION

In a first aspect the invention provides an organic light-emitting device comprising an anode; a cathode; and a first light-emitting layer between the anode and the cathode, wherein the first light-emitting layer comprises a fluorescent light-emitting material of formula (I):

wherein Ar¹ and Ar² each independently in each occurrence is a substituted or unsubstituted aryl or heteroaryl group; n and m independently in each occurrence is 1, 2 or 3; R independently in each occurrence is a substituent; and Ar¹ and Ar² linked directly to the same N atom may be linked by a direct bond or a linking unit to form a ring; and wherein a first phosphorescent light-emitting material is provided in the first light-emitting layer or in a second light-emitting layer adjacent to the first light-emitting layer.

Optionally, each Ar¹ and Ar² is an aryl, preferably phenyl.

Optionally, each m is 2.

Optionally, each R is a substituted or unsubstituted aryl or heteroaryl, optionally a substituted or unsubstituted phenyl.

Optionally, Ar¹ and Ar² groups linked directly to the same N atom are linked by a direct bond or linking unit to form a ring.

Optionally, the linked Ar¹ and Ar² groups are linked by an O or S atom.

Optionally, the fluorescent light-emitting material is a substituted or unsubstituted compound of formula (Ia):

wherein x in each occurrence is independently 0 or 1.

Optionally, the fluorescent light-emitting material has a photoluminescent peak of less than 490 nm and optionally greater than 400 nm.

Optionally, the first phosphorescent light-emitting material has a photoluminescent peak in the range of 490-580 nm.

Optionally, the first phosphorescent light-emitting material is a metal complex.

Optionally, the first phosphorescent light-emitting material is a complex of iridium, rhodium, platinum, palladium, rhenium or osmium.

Optionally, the light-emitting layer comprising the first phosphorescent light-emitting material further comprises a host material.

Optionally, the host material is a polymer.

Optionally, the fluorescent light-emitting material is provided in the first light-emitting layer in an amount in the range 1-20 mol, preferably 5-10 mol %.

Optionally, the first phosphorescent light-emitting material is provided in the first or second light-emitting layer in an amount in the range 0.5-5 mol %.

Optionally, the first phosphorescent light-emitting material is provided in the first light-emitting layer

Optionally, substantially all light emitted from the device is emitted from the first light-emitting layer.

Optionally, the fluorescent light-emitting material of formula (I): phosphorescent light-emitting material ratio is less than 20:1.

Optionally, the first phosphorescent light-emitting material is provided in a second light-emitting layer adjacent to the first light-emitting layer.

Optionally, the device comprises a second phosphorescent light-emitting material in a light-emitting layer of the device.

Optionally, the second phosphorescent light-emitting material is provided in the first or second light-emitting layer.

Optionally, the second phosphorescent light-emitting material is provided in the first or second light-emitting layer in an amount in the range 0.1-1 mol %.

Optionally, the second phosphorescent light-emitting material has a photoluminescent peak of greater than 580 nm.

Optionally, the fluorescent light-emitting material of formula (I) is bound to a polymer.

Optionally, the device emits white light.

In a second aspect, the invention provides a light-emitting composition comprising a fluorescent light-emitting material of formula (I) and a first phosphorescent light-emitting material:

wherein Ar¹, Ar², n, m and R are as described in the first aspect.

The structure and amounts of the fluorescent light-emitting material of formula (I) and the first phosphorescent light-emitting material in the composition of the second aspect may be as described in the first aspect.

Optionally according to the second aspect, the composition further comprises a host material. Optionally according to the second aspect, the composition further comprises a second phosphorescent light-emitting material. Where present, the structure and amounts of the host material and second phosphorescent material in the composition of the second aspect may be as described in the first aspect.

In a third aspect the invention provides a formulation comprising a composition according to the second aspect and at least one solvent.

In a fourth aspect the invention provides a method of forming an OLED according to the first aspect, the method comprising the steps of forming the first and, if present, the second light-emitting layer over the anode; and forming a cathode over the first and second light-emitting layers, wherein the light-emitting layers may be deposited in any order in the case where the second light-emitting layer is present.

Optionally according to the fourth aspect, each of the first light-emitting layer and, if present, the second light-emitting layer are formed by depositing, respectively, a first solution comprising the fluorescent light-emitting material and at least one solvent followed by evaporation of the at least one solvent and a second solution comprising the phosphorescent light-emitting material and at least one solvent followed by evaporation of the at least one solvent.

Optionally according to the fourth aspect, the first light-emitting layer is formed by depositing a formulation according to the third aspect and evaporating the solvent.

DESCRIPTION OF THE DRAWINGS

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

FIG. 1A illustrates an OLED according to an embodiment of the invention;

FIG. 1B illustrates an OLED according to another embodiment of the invention;

FIG. 2 shows electroluminescent spectra of devices having a single emissive layer according to embodiments of the invention;

FIG. 3 is a graph of external quantum efficiency vs. voltage for devices having a single emissive layer according to embodiments of the invention;

FIG. 4 shows electroluminescent spectra of devices having two emissive layers according to embodiments of the invention; and

FIG. 5 is a graph of external quantum efficiency vs. voltage for devices having two emissive layers according to embodiments of the invention;

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates an OLED according to an embodiment of the invention. The OLED 100 has an anode 101, a cathode 105 and a light-emitting layer 103 between the anode and the cathode formed on a substrate 107. Further layers may be provided between the anode and the cathode including one or more of a hole injection layer, a hole transporting layer and an electron blocking layer between the anode and the light-emitting layer, and one or more of a hole-blocking layer and an electron-transporting layer between the cathode and the light-emitting layer.

Exemplary OLED structures including one or more further layers include the following:

Anode/Hole-injection layer/Light-emitting layer/Cathode

Anode/Hole transporting layer/Light-emitting layer/Cathode

Anode/Hole-injection layer/Hole-transporting layer/Light-emitting layer/Cathode

Anode/Hole-injection layer/Hole-transporting layer/Light-emitting layer/Electron-transporting layer/Cathode.

Preferably, at least one of a hole-transporting layer and hole injection layer is present.

Preferably, both a hole injection layer and hole-transporting layer are present.

A fluorescent light-emitting material of formula (I) and a first phosphorescent light-emitting material are provided in light-emitting layer 103. The fluorescent light-emitting material of formula (I) may be a blue fluorescent light-emitting material and the first phosphorescent light-emitting material may be a green phosphorescent light-emitting material. The layer 103 may contain one or more further light-emitting materials, and in the case of a white light-emitting OLED the layer 103 may contain a second, red phosphorescent light-emitting material.

The fluorescent emitter may be provided in an amount in the range of 5-20 mol %. The first phosphorescent light-emitting material may be provided in an amount in the range of 1-5 mol %

Where two or more phosphorescent materials having different colours are present in light-emitting layer 103, for example a red phosphorescent material and a green phosphorescent material, the concentration of the phosphorescent material having the longest peak photoluminescent wavelength (lowest triplet energy level) may be provided in the light-emitting layer an amount in the range of 0.1-2 mol %.

The light-emitting layer may further contain a host material. The host material may have a singlet energy level sufficient for transfer of singlet excitons to the fluorescent light-emitting material of formula (I) and/or sufficient for transfer of triplet excitons to the phosphorescent light-emitting material.

A blue light-emitting material as described herein may have a photoluminescence spectrum with a peak of less than 490 nm and optionally greater than 400 nm.

A green light-emitting material as described herein may have a photoluminescence spectrum with a peak in the range of 490-580 nm.

A red light-emitting material as described herein may have a photoluminescence spectrum with a peak greater than 580 nm, optionally 580-700 nm.

FIG. 1B illustrates an OLED according to a further embodiment of the invention. The device is as described with reference to FIG. 1A, except that the device has two light-emitting layers 103a and 103b between the anode and the cathode. Further layers may be provided between the anode and the cathode, as described with reference to FIG. 1A.

The fluorescent light-emitting material of formula (I), the first phosphorescent material and, if present, the second phosphorescent material and any other light-emitting materials may independently be provided in one of layers 103a and 103b, with the proviso that each of layers 103a and 103b contains at least one light-emitting material.

In the case of a white light-emitting OLED, the light emitted may have CIE x coordinate equivalent to that emitted by a black body at a temperature in the range of 2500-9000K and a CIE y coordinate within 0.05 or 0.025 of the CIE y co-ordinate of said light emitted by a black body, optionally a CIE x coordinate equivalent to that emitted by a black body at a temperature in the range of 2700-4500K.

Fluorescent Light-Emitting Material

Exemplary fluorescent light-emitting materials of formula (I) include the following, each of which may optionally be substituted with one or more substituents:

Each Ar¹ and Ar² of materials of Formula (I) may independently be unsubstituted or substituted with one or more substituents. R may be an aliphatic group, for example C_1-20 alkyl, or an aromatic or heteroaromatic group Ar³ that may be unsubstituted or substituted with one or more substituents.

Preferably, each Ar¹ and Ar² is phenyl. Preferably, each R is Ar³. Preferably, each Ar³ is phenyl.

Ar¹, Ar² and Ar³ may each independently be unsubstituted or substituted with one or more substituents. Exemplary substituents for Ar¹, Ar² and Ar³ may be selected from substituents R², and each R² may independently be selected from the group consisting of:

• • substituted or unsubstituted alkyl, optionally C_1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C═O or —COO— and one or more H atoms may be replaced with F;
  • substituted or unsubstituted aryl or heteroaryl group, or a linear or branched chain of aryl or heteroaryl, preferably phenyl, each of which may independently be substituted, for example a group of formula —(Ar⁴)_r wherein Ar⁴ in each occurrence independently is a substituted or unsubstituted aryl or heteroaryl, preferably phenyl, and r is at least 1, optionally 1, 2 or 3;

In the case where R² comprises one or more aryl or heteroaryl groups Ar⁴, each Ar⁴ may independently be substituted with one or more substituents selected from the group 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═O and —COO— and one or more H atoms of the alkyl group may be replaced with F.

Exemplary linear aryl chain substituents include biphenyl and terphenyl. An exemplary branched aryl chain substituent is 3,5-diphenylbenzene.

Preferred substituents include C_1-40 hydrocarbyl, for example C_1-20 alkyl, and phenyl which may be unsubstituted or substituted with one or more C_1-20 alkyl groups.

Preferably, Ar¹ groups at an end of the material of formula (I) are substituted. Preferably, R is Ar³ and Ar³ is substituted. Preferably, Ar² is unsubstituted.

Exemplary substituted materials include the following:

wherein R¹ in each occurrence independently represents H or a substituent R². Preferred substituents are C_1-20 alkyl.

The fluorescent light-emitting material may be a distinct unsubstituted or substituted compound of formula (I), or it may be covalently bound to a polymer as a repeat unit in the polymer backbone, a side-group pendant from the polymer backbone or an end-group of the polymer, preferably as a polymer side group.

Where present as a side-group, the fluorescent light-emitting material may be bound directly to a repeat unit in the polymer backbone, or spaced apart therefrom by a spacer group. Exemplary spacer groups are hydrocarbyl groups, optionally C_1-30 hydrocarbyl groups, for example C_1-20 alkyl and phenyl-C_1-20 alkyl. One or more non-adjacent C atoms of an alkyl group of a spacer chain may be replaced with O, S, NR¹⁵, C═O and —COO—, wherein R¹⁵ is a substituent, preferably C_1-10 hydrocarbyl.

Exemplary polymers that the fluorescent light-emitting material may be bound to include conjugated and non-conjugated polymers. The fluorescent material of formula (I) may be bound as a side-group of a repeat unit of a host polymer. Exemplary host polymers are described in more detail below. The compound of formula (I) may be bound to a polymer through any of Ar¹, Ar² and R.

The triplet energy level of the fluorescent light-emitting material is preferably at least 2.0 eV, preferably at least 2.5 eV.

The triplet energy level of the fluorescent light-emitting material is preferably no more than 0.1 eV lower than that of the first phosphorescent material, and is preferably the same as or higher than that of the first phosphorescent material.

Triplet energy levels may be measured from the energy onset of the phosphorescence spectrum measured by low temperature phosphorescence spectroscopy (Y. V. Romaovskii et al, Physical Review Letters, 2000, 85 (5), p 1027, A. van Dijken et al, Journal of the American Chemical Society, 2004, 126, p 7718).

Phosphorescent Light-Emitting Materials

Exemplary phosphorescent light-emitting materials include metal complexes comprising substituted or unsubstituted complexes of formula (II):

ML¹_qL²_rL³_s  (II)

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.

Heavy elements M induce strong spin-orbit coupling to allow rapid intersystem crossing and emission from triplet or higher states. 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 is particularly preferred.

Exemplary ligands L¹, L² and L³ include carbon or nitrogen donors such as porphyrin or bidentate ligands of formula (III):

wherein Ar⁵ and Ar⁶ may be the same or different and are independently selected from substituted or unsubstituted aryl or heteroaryl; X¹ and Y¹ may be the same or different and are independently selected from carbon or nitrogen; and Ar⁵ and Ar⁶ may be fused together. Ligands wherein X¹ is carbon and Y¹ is nitrogen are preferred, in particular ligands in which Ar⁵ is a single ring or fused heteroaromatic of N and C atoms only, for example pyridyl or isoquinoline, and Ar⁶ is a single ring or fused aromatic, for example phenyl or naphthyl.

Examples of bidentate ligands are illustrated below:

Each of Ar⁵ and Ar⁶ 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.

Exemplary substituents include groups R² as described above with reference to Formula (I). Particularly preferred substituents include fluorine or trifluoromethyl which may be used to blue-shift the emission of the complex, for example as disclosed in WO 02/45466, WO 02/44189, US 2002-117662 and US 2002-182441; alkyl or alkoxy groups, for example C_1-20 alkyl or C_1-20 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 (IV)

wherein BP represents a branching point for attachment to a core and G₁ represents first generation branching groups.

The dendron may be a first, second, third or higher generation dendron. G₁ may be substituted with two or more second generation branching groups G₂, and so on, as in optionally substituted formula (IVa):

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 G₁, G₂ and G₃ represent first, second and third generation dendron branching groups. In one preferred embodiment, each of BP and G₁, G₂ . . . G_n is phenyl, and each phenyl BP, G₁, G₂ . . . G_n-1 is a 3,5-linked phenyl.

Preferred dendrons include substituted or unsubstituted dendrons of formula (IVb) and (IVc):

wherein * represents an attachment point of the dendron to a core.

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.

The first phosphorescent light-emitting material and, where present, one or more further phosphorescent light-emitting materials 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. Where further phosphorescent light-emitting materials having a longer wavelength than the first phosphorescent material are present, the concentration of the further phosphorescent materials may be lower than that of the first phosphorescent material in order to minimize downconversion of phosphorescence from the first phosphorescent material Optionally, the one or more further phosphorescent materials are provided in an amount of 0.25-1 mol %.

The first, and if present further, phosphorescent light-emitting materials may each independently be physically mixed with a host material or may be chemically bound to a host material. In the case of a polymeric host, the phosphorescent material(s) may be provided in a side-chain, main chain or end-group of a polymer. Where a phosphorescent material is provided in a polymer side-chain, the phosphorescent material may be directly bound to the backbone of the polymer or spaced apart therefrom by a spacer group, for example a C_1-20 alkyl spacer group in which one or more non-adjacent C atoms may be replaced by COO, CO, O or S.

The first phosphorescent light-emitting material may be a green phosphorescent emitter. A green phosphorescent emitter may have a peak in its photoluminescence spectrum in the range of more than 490 nm to less than 580 nm.

Exemplary phosphorescent green emitters include fac-tris(2-phenylpyridine)iridium(III), which may be substituted with one or more substituents, for example as described above with reference to Formula (II).

Exemplary further phosphorescent light-emitting materials, where present, include materials having a peak in their photoluminescence spectrum at a longer wavelength than that of the first phosphorescent light-emitting material. Exemplary further phosphorescent light-emitting materials include red and yellow phosphorescent emitters. Red emitters may have a peak wavelength of at least 580 nm, optionally in the range 580-700 nm. Exemplary phosphorescent red emitters include fac-tris(1-phenylisoquinoline)iridium(III), which may be substituted with one or more substituents, for example as described above with reference to Formula (II).

Host Materials

The light-emitting layer containing the fluorescent light-emitting material of formula (I) may contain a host material blended with or bound to the material of formula (I). The host material may have a singlet energy level no more than 0.1 eV lower than that of the fluorescent light-emitting material of formula (I), preferably the same as or higher than the material of formula (I). If this light-emitting layer further contains one or more phosphorescent materials then the triplet energy level of the host may also be no more than 0.1 eV lower than, preferably the same as or higher than, the triplet energy level of the one or more phosphorescent materials.

Devices according to embodiments of the invention may include a light-emitting layer in which the only emissive material or materials are phosphorescent materials. In this case, the triplet energy level of the host may also be no more than 0.1 eV lower than, preferably the same as or higher than, the triplet energy level of the one or more phosphorescent materials.

Host materials include small molecule and polymeric hosts. Polymeric hosts include polymers with a non-conjugated backbone and polymers with an at least partially conjugated backbone. Partially conjugated polymers may contain conjugating repeat units in which the conjugating repeat units provide a conjugation path between the repeat units adjacent to the conjugating repeat units, wherein the extent of conjugation along the polymer backbone is limited in order to maintain a relatively high singlet and/or triplet energy level.

Exemplary conjugating repeat units of a partially conjugated polymer include arylene or heteroarylene repeat units, for example phenylene repeat units, fluorene repeat units and indenofluorene repeat units. Arylene or heteroarylene repeat units may be unsubstituted or substituted with one or more substituents. A host polymer may include one, two or more different arylene repeat units.

The extent of conjugation that is provided by a conjugating repeat unit may depend on the positions through which the conjugating repeat unit is linked to adjacent repeat units, and may depend on location and nature of substituents on the conjugating repeat unit.

For example, a high degree of conjugation may be provided by 1,4-linked phenylene repeat units, as illustrated by a chain of phenylene repeat units A-B-C wherein unit B provides a conjugation path between adjacent repeat units A and C on either side of unit B:

Likewise, a high degree of conjugation may be provided by 2,7-linked fluorene repeat units and 2,8-linked indenofluorene repeat units.

A lower degree of conjugation may be provided by 1,2- or 1,3-linked phenylene repeat units and 3- and/or 6-linked fluorene repeat units.

The nature and location of substituents may affect the degree of conjugation of a conjugating repeat unit. A substituent located adjacent to a linking position of a repeat unit may create steric hindrance with an adjacent repeat unit, causing a twist between the two repeat units and reducing the extent of pi orbital overlap between the two repeat units as compared to the case where that substituent is absent. Exemplary substituents for creating steric hindrance between adjacent trepeat units are C_1-30 hydrocarbyl groups, for example C_1-20 alkyl groups and C_1-30 arylalkyl groups.

Exemplary fluorene repeat units have formula (V):

wherein R⁵ in each occurrence is the same or different and is H or a substituent, and wherein the two groups R⁵ may be linked to form a ring.

Each R⁵ is preferably a substituent, and each R⁵ may independently be selected from the group consisting of:

• • substituted or unsubstituted alkyl, optionally C_1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C═O or —COO— and one or more H atoms may be replaced with F;
  • substituted or unsubstituted aryl or heteroaryl group, or a linear or branched chain of aryl or heteroaryl, each of which may independently be substituted, for example a group of formula —(Ar⁴)_r wherein Ar⁴ in each occurrence independently is a substituted or unsubstituted aryl or heteroaryl and r is at least 1, optionally 1, 2 or 3;
  • a crosslinkable group attached directly to the fluorene unit or spaced apart therefrom by a spacer group, for example a group comprising a double bond such and a vinyl or acrylate group, or a benzocyclobutane group

In the case where R⁵ comprises one or more aryl or heteroaryl groups Ar⁴, each Ar⁴ may independently be substituted with one or more substituents R⁶ selected from the group 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═O 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 R⁷,
  • aryl or heteroaryl optionally substituted with one or more groups R⁷,
  • NR⁸₂, OR⁸, SR⁸, and
  • fluorine, nitro and cyano;
    wherein each R⁷ 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═O and —COO— and one or more H atoms of the alkyl group may be replaced with F or D; and each R⁸ is independently selected from the group consisting of alkyl, for example C_1-20 alkyl, and aryl or heteroaryl optionally substituted with one or more alkyl groups, for example phenyl that is unsubstituted or substituted with one or more C_1-20 alkyl groups.

Optional substituents for the aromatic carbon atoms of the fluorene unit, i.e. other than substituents R⁵, are preferably selected from the group consisting of alkyl, for example C_1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with O, S, NH or substituted N, C═O and —COO—, optionally substituted aryl, optionally substituted heteroaryl, alkoxy, alkylthio, fluorine, cyano and arylalkyl. Particularly preferred substituents include C_1-20 alkyl and substituted or unsubstituted aryl, for example phenyl. Optional substituents for the aryl include one or more C_1-20 alkyl groups.

Where present, substituted N may independently in each occurrence be NR⁹ wherein R⁹ is alkyl, optionally C_1-20 alkyl, or optionally substituted aryl or heteroaryl. Optional substituents for aryl or heteroaryl R⁹ may be selected from R⁷ or R⁸, for example C_1-10 alkyl.

Preferably, each R⁵ is selected from the group consisting of C_1-20 alkyl and —(Ar⁴)_r wherein Ar⁴ in each occurrence is substituted or unsubstituted substituted phenyl. Optional substituents for phenyl include one or more C_1-20 alkyl groups.

The repeat unit of formula (V) may be a 2,7-linked repeat unit of formula (Va):

Optionally, the repeat unit of formula (Va) is not substituted in a position adjacent to the 2- or 7-positions.

The extent of conjugation of repeat units of formula (V) to adjacent repeat units may be limited by (a) linking the repeat unit through the 3- and/or 6-positions to limit the extent of conjugation across the repeat unit, and/or (b) substituting the repeat unit with one or more further substituents R⁵ in or more positions adjacent to the linking positions in order to create a twist with the adjacent repeat unit or units, for example a 2,7-linked fluorene carrying a C_1-20 alkyl substituent in one or both of the 3- and 6-positions.

Exemplary conjugating phenylene repeat units have formula (VI):

wherein p is 0, 1, 2, 3 or 4, optionally 1 or 2; q is 1, 2 or 3; and R¹° independently in each occurrence is a substituent, optionally a substituent R⁵ as described above with reference to formula (V), for example C_1-20 alkyl, and phenyl that is unsubstituted or substituted with one or more C_1-20 alkyl groups.

In the case where q=1, the repeat unit of formula (VI) may be 1,4-linked, 1,2-linked or 1,3-linked.

If the repeat unit of formula (VI) is 1,4-linked and if p is 0 then the extent of conjugation of repeat unit of formula (VI) to one or both adjacent repeat units may be relatively high.

If p is at least 1, and/or the repeat unit is 1,2- or 1,3 linked, then the extent of conjugation of repeat unit of formula (VI) to one or both adjacent repeat units may be relatively low. In one optional arrangement, q=1, the repeat unit of formula (VI) is 1,3-linked and p is 0, 1, 2 or 3. In another optional arrangement, the repeat unit of formula (VI) has formula (VIa):

Another exemplary arylene repeat unit has formula (VII):

wherein R⁵ is as described with reference to formula (V) above. Each of the R⁵ groups may be linked to any other of the R⁵ groups to form a substituted or unsubstituted ring, for example a ring substituted with one or more C_1-20 alkyl groups.

Further arylene co-repeat units include: phenanthrene repeat units; naphthalene repeat units; anthracene repeat units; and perylene repeat units. Each of these arylene repeat units may be linked to adjacent repeat units through any two of the aromatic carbon atoms of these units. Specific exemplary linkages include 9,10-anthracene; 2,6-anthracene; 1,4-naphthalene; 2,6-naphthalene; 2,7-phenanthrene; and 2,5-perylene.

The polymer may contain non-conjugating repeat units that block any conjugation path between repeat units adjacent to the non-conjugating repeat unit. Exemplary non-conjugating repeat units have formula (VIII):

—(Ar⁷-Sp¹-Ar⁷)—  (VIII)

wherein each Ar⁷ independently represents a substituted or unsubstituted aryl or heteroaryl group; and Sp¹ represents a spacer group that does not provide any conjugation path between the two groups Ar⁷.

Preferably, Ar⁷ is phenyl which may be substituted with one or more substituents R⁵ as described above with respect to formula (V). Preferred substituents are one or more C_1-20 alkyl groups.

Sp¹ may contain a single non-conjugating atom only between the two groups Ar⁷, or Sp¹ may contain non-conjugating chain of at least 2 atoms separating the two groups Ar⁷.

A non-conjugating atom may be, for example, —O—, —S—, —CR¹¹₂— or —SiR¹¹₂— or wherein R¹¹ in each occurrence is H or a substituent, optionally C_1-20 alkyl.

A spacer chain Sp¹ may contain two or more atoms separating the two groups Ar⁷, for example a C_1-20 alkyl chain wherein one or more non-adjacent C atoms of the chain may be replaced with O or S.

Examples of cyclic non-conjugating spacers are optionally substituted cyclohexane or adamantane repeat units that may have the structures illustrated below:

Exemplary substituents for cyclic conjugation repeat units include C_1-20 alkyl and C_1-20 alkoxy. Exemplary non-conjugating repeat units include the following:

wherein R¹² in each occurrence is independently H or a substituent, optionally H or C_1-20 alkyl.

The polymer may contain amine repeat units in particular amines of formula (IX):

wherein Ar⁸ and Ar⁹ in each occurrence are independently selected from substituted or unsubstituted aryl or heteroaryl, g is greater than or equal to 1, preferably 1 or 2, R¹³ is H or a substituent, preferably a substituent, and c and d are each independently 1, 2 or 3.

Preferably, polymers comprising repeat units of formula (IX) are copolymers comprising one or more arylene repeat units as described above, for example one or more repeat units selected from formulae (V), (VI) and (VII), and one or more repeat units of formula (IX).

R¹³, which may be the same or different in each occurrence when g>1, is preferably selected from the group consisting of alkyl, for example C_1-20 alkyl, Ar¹⁰, a branched or linear chain of Ar¹⁰ groups, or a crosslinkable unit that is bound directly to the N atom of formula (IX) or spaced apart therefrom by a spacer group, wherein Ar¹⁰ in each occurrence is independently optionally substituted aryl or heteroaryl. Exemplary spacer groups are C_1-20 alkyl, phenyl and phenyl-C_1-20 alkyl.

Any of Ar⁸, Ar⁹ and, if present, Ar¹⁰ in the repeat unit of Formula (IX) may be linked by a direct bond or a divalent linking atom or group to another of Ar⁸, Ar⁹ and Ar¹⁰. Preferred divalent linking atoms and groups include O, S; substituted N; and substituted C.

Any of Ar⁸, Ar⁹ and, if present, Ar¹⁰ may be substituted with one or more substituents. Exemplary substituents are substituents R¹⁴, wherein each R¹⁴ may independently be selected from the group consisting of:

• • substituted or unsubstituted alkyl, optionally C_1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C═O or —COO— and one or more H atoms may be replaced with F; and
  • a crosslinkable group attached directly to the aryl or heteroaryl group or spaced apart therefrom by a spacer group, for example a group comprising a double bond such and a vinyl or acrylate group, or a benzocyclobutane group.

Substituted N, where present, may be N substituted with a hydrocarbyl group, for example a C_1-10 alkyl, unsubstituted phenyl or phenyl substituted with one or more C_1-10 alkyl groups.

Preferred repeat units of formula (IX) have formulae 1-3:

In one preferred arrangement, R¹³ is Ar¹⁰ and each of Ar⁸, Ar⁹ and Ar¹⁰ are independently and optionally substituted with one or more C_1-20 alkyl groups.

Ar⁸, Ar⁹ and Ar¹⁰ are preferably phenyl, each of which may independently be substituted with one or more substituents as described above.

In another preferred arrangement, Ar⁸ and Ar⁹ are phenyl, each of which may be substituted with one or more C_1-20 alkyl groups, and R¹³ is 3,5-diphenylbenzene wherein each phenyl may be substituted with one or more C_1-20 alkyl groups.

In another preferred arrangement, c, d and g are each 1 and Ar⁸ and Ar⁹ are phenyl linked by an oxygen atom to form a phenoxazine ring.

Amine repeat units may be provided in a molar amount in the range of about 0.5 mol % up to about 50 mol %, optionally about 1-25 mol %, optionally about 1-10 mol %.

The host polymer may contain repeat units of formula (X):

wherein Ar⁸, Ar⁹ and Ar¹⁰ are as described with reference to formula (IX) above, and may each independently be substituted with one or more substituents described with reference to Ar⁸, Ar⁹ and Ar¹⁰, and z in each occurrence is independently at least 1, optionally 1, 2 or 3, preferably 1, and Y is N or CR¹⁴, wherein R¹⁴ is H or a substituent, preferably H or C_1-10 alkyl. Preferably, Ar⁸, Ar⁹ and Ar¹⁰ of formula (X) are each phenyl, each phenyl being optionally and independently substituted with one or more C_1-20 alkyl groups.

In one preferred embodiment, all 3 groups Y are N.

If all 3 groups Y are CR¹⁴ then at least one of Ar⁸, Ar⁹ and Ar¹⁰ is preferably a heteroaromatic group comprising N.

Each of Ar⁸, Ar⁹ and Ar¹⁰ may independently be substituted with one or more substituents. In one arrangement, Ar⁸, Ar⁹ and Ar¹⁰ are phenyl in each occurrence. Exemplary substituents include R⁵ as described above with reference to formula (V), for example C_1-20 alkyl or alkoxy.

Ar¹⁰ of formula (X) is preferably phenyl, and is optionally substituted with one or more C_1-20 alkyl groups or a crosslinkable unit. The crosslinkable unit may be bound directly to Ar¹⁰ or spaced apart from Ar¹⁰ by a spacer group.

Preferably, z is 1 and each of Ar⁸, Ar⁹ and Ar¹⁰ is unsubstituted phenyl or phenyl substituted with one or more C_1-20 alkyl groups.

A particularly preferred repeat unit of formula (X) has formula (Xa), which may be unsubstituted or substituted with or more substituents R⁵, preferably one or more C_1-20 alkyl groups:

Preferably, polymers comprising repeat units of formula (X) are copolymers comprising one or more arylene repeat units as described above, for example one or more repeat units selected from formulae (V), (VI) and (VII), and one or more repeat units of formula (X).

A fluorescent material of formula (I) and/or one or more phosphorescent light-emitting materials may be bound directly to the host material. In the case of a polymeric host, the fluorescent material may be provided in a side-chain of a repeat unit of the host polymer.

Polymer Synthesis

Preferred methods for preparation of conjugated polymers, such as host polymers or charge transporting polymers for use in a charge transporting layer, comprise a “metal insertion” wherein the metal atom of a metal complex catalyst is inserted between an aryl or heteroaryl group and a leaving group of a monomer. Exemplary metal insertion methods are Suzuki polymerisation as described in, for example, WO 00/53656 and Yamamoto polymerisation as described in, for example, T. Yamamoto, “Electrically Conducting And Thermally Stable pi-Conjugated Poly(arylene)s Prepared by Organometallic Processes”, Progress in Polymer Science 1993, 17, 1153-1205. In the case of Yamamoto polymerisation, a nickel complex catalyst is used; in the case of Suzuki polymerisation, a palladium complex catalyst is used.

For 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.

It will therefore be appreciated that repeat units illustrated throughout this application may be derived from a monomer carrying suitable leaving groups. Likewise, an end-capping group or side group carrying only one reactive leaving group may be bound to the polymer by reaction of a leaving group at the polymer chain end or side respectively.

Suzuki 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 copolymers may be prepared when both reactive groups of a first monomer are boron and both reactive groups of a second monomer are halogen.

As alternatives to halides, other leaving groups capable of participating in metal insertion include sulfonic acids and sulfonic acid esters such as tosylate, mesylate and triflate.

Charge Transporting and Charge Blocking Layers

A hole transporting layer may be provided between the anode and the light-emitting layer or layers. Likewise, an electron transporting layer may be provided between the cathode and the light-emitting layer or layers.

Similarly, an electron blocking layer may be provided between the anode and the light-emitting layer and a hole blocking layer may be provided between the cathode and the light-emitting layer. 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.

If present, a hole transporting layer located between the anode and the light-emitting layers preferably has a HOMO level of less than or equal to 5.5 eV, more preferably around 4.8-5.5 eV or 5.1-5.3 eV as measured by cyclic voltammetry. The HOMO level of the hole transport layer may be selected so as to be within 0.2 eV, optionally within 0.1 eV, of an adjacent layer (such as a light-emitting layer) in order to provide a small barrier to hole transport between these layers.

If present, an electron transporting layer located between the light-emitting layers and cathode preferably has a LUMO level of around 3-3.5 eV as measured by cyclic voltammetry. For example, a layer of a silicon monoxide or silicon dioxide or other thin dielectric layer having thickness in the range of 0.2-2 nm may be provided between the light-emitting layer nearest the cathode and the cathode. HOMO and LUMO levels may be measured using cyclic voltammetry.

A hole transporting layer may contain a homopolymer or copolymer comprising amine repeat units of formula (IX) as described above, preferably a copolymer comprising repeat units of formula (IX) and arylene repeat units, for example arylene repeat units selected from one or more repeat units of formulae (V), (VI) or (VII).

An electron transporting layer may contain a polymer comprising a chain of optionally substituted arylene repeat units, such as a chain of fluorene repeat units.

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 and the light-emitting layer or layers of an OLED to improve hole injection from the anode into the layer or layers of semiconducting polymer. 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 fluorinated sulfonic acid, for example Nafion®; polyaniline as disclosed in U.S. Pat. No. 5,723,873 and U.S. Pat. No. 5,798,170; 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.

Cathode

The cathode is selected from materials that have a workfunction allowing injection of electrons into the light-emitting layer. Other factors influence the selection of the cathode such as the possibility of adverse interactions between the cathode and the light-emitting 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 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 between the organic layers and one or more layers of conductive material, for example one or more metal layers, 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(11), 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 comprises 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.

Encapsulation

Organic optoelectronic 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 one or more plastic layers, for example a substrate of alternating plastic and dielectric barrier layers or a laminate of thin glass and plastic.

The device may be 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 silicon dioxide, silicon monoxide, silicon nitride or alternating stacks of polymer and dielectric or an airtight container. In the case of a transparent cathode device, a transparent encapsulating layer such as silicon monoxide or silicon dioxide may be deposited to micron levels of thickness, although in one preferred embodiment the thickness of such a layer is in the range of 20-300 nm. 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.

Solution Processing

Common organic solvents, including mono- or poly-alkylbenzenes such as toluene and xylene, may be used to deposit materials used to form charge-transporting or light-emitting layers of an OLED. The materials may form a formulation for deposition with one or more solvents, and the formulation may be a solution or dispersion containing the materials to be deposited. A single solvent or mixture of two or more solvents may be used.

Particularly preferred solution deposition techniques including printing and coating techniques such spin-coating and inkjet printing. Other solution deposition techniques include dip-coating, roll printing and screen printing.

During OLED formation, a layer of the device may be crosslinked to prevent it from partially or completely dissolving in the solvent or solvents used to deposit an overlying layer. Layers that may be crosslinked include a hole-transporting layer prior to formation by solution processing of an overlying light-emitting layer, or crosslinking of one light-emitting layer prior to formation by solution processing of another, overlying light-emitting layer.

Suitable crosslinkable groups include groups comprising a reactive double bond such and a vinyl or acrylate group, or a benzocyclobutane group. Where a layer to be crosslinked contains a polymer, the crosslinkable groups may be provided as substituents of repeat units of the polymer.

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

Printing methods such as inkjet printing are 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.

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

Fluorescent Compound 1

Fluorescent Compound 1 was prepared according to the following method:

Fluorescent Compound 2—Synthesis

Fluorescent Compound 2 was prepared according to the following method:

• • Intermediate I: A solution of phenoxazine (156.28 g, 0.85 mol, 1.1 eq)) and 1-bromo-4-tert-butylbenzene (165.26 g, 0.78 mol, 1.0 eq) in toluene (2 L) was degassed by bubbling nitrogen through the reaction mixture for 1 hour. Palladium acetate (3.5 g, 15.5 mmol, 0.02 eq) and tri(o-tolyl)phosphine (4.72 g, 15.5 mmol, 0.02 eq) were added and the solution stirred for a further 30 mins at RT. After this time sodium tert-pentoxide (170.81 g, 1.55 mol, 2.0 eq) was added and stirring continued for an additional 30 mins at ambient temperature before stirring at 130° C. overnight. The reaction mixture was then cooled in an ice-water bath and quenched by the addition of water (500 ml) and filtered though a celite-florisil plug. Concentration under reduced pressure followed by titration (twice with hot MeCN) and drying under vacuum at 40° C., gave the product as a grey solid (149 g, 82%). GCMS: M⁺ 315 (100%).
  • Intermediate II: A solution of Intermediate I (98.56 g, 0.31 mol) in anhydrous DCM (2 L) under N₂, was cooled to −5° C. (internal temperature) using a ice/water bath. 1,3-Dibromo-5,5-dimethyl hydantoin (49.2 g, 0.17 mol) was transferred to a 500 ml round bottom flask and flushed with nitrogen for 15 mins. Anhydrous DMF (100 ml) was then added and the solution transferred via cannular to a dropping funnel. This solution was added dropwise to the reaction mixture, so as to maintain a temperature between 0 and −5° C., and the reaction mixture was allowed to warm to room temperature overnight. The resulting green suspension was filtered through an alumina plug using DCM as eluant. Concentration under reduced pressure followed by titration (twice with MeCN) and drying under vacuum at 40° C., gave the product as a beige solid (84.7 g, 68%). GCMS: GCMS: M⁺394 (96%).
  • Intermediate III: A solution of intermediate II (112.00 g, 0.28 mol, 1.0 eq)) and 4-tert-butylphenylboronic acid (55.61 g, 0.31 mol, 1.1 eq) in toluene (1.5 L) was degassed by bubbling nitrogen through the reaction mixture for 1 hour. Palladium acetate (1.5 g, 28.4 mmol, 0.01 eq) and tris(o-methoxyphenyl)phosphine (4.00 g, 11.4 mmol, 0.04 eq) were added, followed by addition of tetraethyl ammonium hydroxide (500 ml, 20 wt % in water) quickly, over 20 mins. After stifling overnight at 115° C., the solution was cooled to room temperature, the base separated and the reaction mixture filtered through a silica gel plug. Concentration under reduced pressure followed by titration (several times with IPA), filtration and drying under vacuum at 40° C., gave the product as a beige solid (90 g, 93%). GCMS: M⁺448 (94%).
  • Intermediate IV: A solution of Intermediate III (89.9, 0.20 mol) in anhydrous DCM (1.6 L) under N₂, was cooled to −5° C. (internal temperature) using a ice/water bath. 1,3-Dibromo-5,5-dimethyl hydantoin (31.5 g, 0.11 mol) was transferred to a 250 ml round bottom flask and flushed with nitrogen for 15 mins. Anhydrous DMF (80 ml) was then added and the solution transferred via cannular to a dropping funnel. This solution was added dropwise to the reaction mixture, so as to maintain a temperature between 0 and −5° C. and the reaction mixture was allowed to warm to room temperature overnight. The resulting green solution was filtered through an alumina plug using DCM as eluant. Concentration under reduced pressure followed by titration (twice from MeCN) and drying under vacuum at 40° C., gave the product as a beige solid (91 g, 86%). GCMS: M⁺448 (94%).
  • Fluorescent Compound 2: A solution of intermediate IV (10.00 g, 19.0 mmol, 2.1 eq) and 4,4′-diboronic acid pinacol ester triphenylamine (4.48 g, 9.0 mmol, 1.0 eq) in toluene (100 ml) was degassed by bubbling nitrogen through the reaction mixture for hour. Palladium acetate (0.02 g, 0.09 mmol, 0.01 eq) and tris(o-methoxyphenyl)phosphine (0.13 g, 0.37 mmol, 0.04 eq) were added, followed by addition of bis(tetraethylammonium) carbonate (50 ml, 35 wt % in water) quickly over 20 mins. After stirring overnight at 115° C., the solution was cooled to room temperature, the base separated and the reaction mixture filtered through a silica gel-fluorsil plug eluting with DCM. The resulting crude solid was purified by repeated column chromatography (silica-gel, 20% DCM/hexane) and recrystallization from DCM/hexane until the desired purity of >99.6% (HPLC) was achieved. The resulting material was dried under vacuum at 40° C., to give the product as a bright yellow solid.

Light-Emitting Composition 1

A solution for forming a light-emitting composition was formed by dissolving Host Polymer 1 (94 mol %), Fluorescent Compound 1 (5.5 mol %) and Green Phosphorescent Compound 1 (illustrated below, 0.5 mol %) in ortho-xylene.

Green Phosphorescent Compound 1

Host Polymer 1 was prepared by Suzuki polymerization of the following monomers as described in WO 00/53656:

Light-Emitting Composition 2

A solution was prepared as described for Light-Emitting Composition 1, except with 5.65 mol % of Fluorescent Compound 1 and 0.35 mol % of Green Phosphorescent Compound 1.

Light-Emitting Composition 3

A solution was prepared as described for Light-Emitting Composition 1, except with 5.75 mol % of Fluorescent Compound 1 and 0.25 mol % of Green Phosphorescent Compound 1.

Device Example 1

An organic light-emitting device having the following structure was prepared:

ITO/HIL/HTL/LE/Cathode

wherein ITO is an indium-tin oxide anode; HIL is a hole-injecting layer comprising a hole-injecting material, HTL is a hole-transporting layer, and LE is a light-emitting layer.

A substrate carrying ITO was cleaned using UV/Ozone. The hole injection layer was formed by spin-coating an aqueous formulation of a hole-injection material available from Plextronics, Inc. A hole transporting layer was formed to a thickness of 20 nm by spin-coating a hole-transporting polymer and crosslinking the polymer by heating. A light-emitting layer was formed by depositing Light-Emitting Composition 1 to a thickness of 75 nm by spin-coating. A cathode was formed by evaporation of a first layer of a metal fluoride to a thickness of about 2 nm, a second layer of aluminium to a thickness of about 200 nm and an optional third layer of silver.

The hole-transporting polymer was formed by Suzuki polymerization as described in WO 00/53656 of the following monomers:

Device Example 2

An organic light-emitting device was prepared as described in Device Example 1 except that Light-Emitting Composition 2 was used in place of Light-Emitting Composition 1.

Device Example 3

An organic light-emitting device was prepared as described in Device Example 1 except that Light-Emitting Composition 3 was used in place of Light-Emitting Composition 1.

With reference to FIG. 2, the electroluminescent spectra of Devices 1-3 all show blue fluorescent emission with a peak around 410-420 nm (from Fluorescent Compound 1) and green phosphorescent emission with a peak around 510-520 nm (from Phosphorescent Green Compound 1), indicating that the triplet energy level of Fluorescent Compound 1 is high enough to avoid substantial or complete quenching of emission from Phosphorescent Green Compound 1.

FIG. 3 shows variation of external quantum efficiency (EQE) with voltage for Device Examples 1 and 3. The triplet energy level of Fluorescent Compound 1 is less than 0.1 eV lower than that of Green Phosphorescent Compound 1. Without wishing to be bound by any theory, it is believed that the lower EQE for Device Example 3 is due to some quenching of phosphorescence by Fluorescent Compound 1.

Device Example 4

An organic light-emitting device was prepared as described in Device Example 1, except that two light-emitting layers were provided between the hole transporting layer and the cathode.

A first, red and green light-emitting layer was deposited onto the hole-transporting layer by spin-coating a polymer formed by Suzuki polymerization as described in WO 00/53656 of the following monomers, followed by thermal crosslinking of the polymer:

A second, blue light-emitting layer was deposited onto the first light-emitting layer by spin-coating a composition of Host Polymer 1 (94 mol %) and Fluorescent Compound 1 (6 mol %), and the cathode was formed over the second light-emitting layer.

Device Example 5

An organic light-emitting device was prepared as described in Device Example 4, except that the hole transporting layer was not present.

With reference to the electroluminescent spectra of FIG. 4, it can be seen that both Device Example 4 and Device Example 5 produce red, green and blue emission.

FIG. 5 shows variation of external quantum efficiency (EQE) with voltage for Device Examples 4 and 5. The triplet energy level of Fluorescent Compound 1 is less than 0.1 eV lower than that of Green Phosphorescent Compound 1. However, no significant difference in EQE is observed between these devices. Without wishing to be bound by any theory, it is believed that the presence of Fluorescent Compound 1 in a separate layer to Green Phosphorescent Compound 1 reduces the probability of any phosphorescence quenching by Fluorescent Compound 1 as compared to a device in which Fluorescent Compound 1 and Green Phosphorescent Compound 1 are in the same layer.

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.

Claims

1. An organic light-emitting device comprising an anode; a cathode; and a first light-emitting layer between the anode and the cathode, wherein the first light-emitting layer comprises a fluorescent light-emitting material of formula (I):

wherein Ar1 and Ar2 each independently in each occurrence is a substituted or unsubstituted aryl or heteroaryl group; n and m independently in each occurrence is 1, 2 or 3; R independently in each occurrence is a substituent; and Ar1 and Ar2 linked directly to the same N atom may be linked by a direct bond or a linking unit to form a ring; and wherein a first phosphorescent light-emitting material is provided in the first light-emitting layer or in a second light-emitting layer adjacent to the first light-emitting layer.

2. An organic light-emitting device according to claim 1, wherein each Ar1 and Ar2 is an aryl.

3. (canceled)

4. An organic light-emitting device according to claim 1, wherein each m is 2.

5. An organic light-emitting device according to claim 1, wherein each R is a substituted or unsubstituted aryl or heteroaryl.

6. (canceled)

7. An organic light-emitting device according to claim 1, wherein Ar1 and Ar2 groups linked directly to the same N atom are linked by a direct bond or linking unit to form a ring.

8. (canceled)

9. An organic light-emitting device according to claim 1, wherein the fluorescent light-emitting material is a substituted or unsubstituted compound of formula (Ia):

wherein x in each occurrence is independently 0 or 1.

10. An organic light-emitting device according to claim 1, wherein the fluorescent light-emitting material has a photoluminescent peak of less than 490.

11. An organic light-emitting device according to claim 1, where the first phosphorescent light-emitting material has a photoluminescent peak in the range of 490-580 nm.

12.-18. (canceled)

19. An organic light-emitting device according to claim 1, wherein the first phosphorescent light-emitting material is provided in the first light-emitting layer.

20. An organic light-emitting device according to claim 19 wherein substantially all light emitted from the device is emitted from the first light-emitting layer.

21. (canceled)

22. An organic light-emitting device according to claim 1, wherein the first phosphorescent light-emitting material is provided in a second light-emitting layer adjacent to the first light-emitting layer.

23. An organic light-emitting device according to claim 1, wherein the device comprises a second phosphorescent light-emitting material in the first or second light-emitting layer.

24.-25. (canceled)

26. An organic light-emitting device according to claim 23 wherein the second phosphorescent light-emitting material has a photoluminescent peak of greater than 580 nm.

27. (canceled)

28. An organic light-emitting device according to claim 1, wherein the device emits white light.

29. A light-emitting composition comprising a fluorescent light-emitting material of formula (I) and a first phosphorescent light-emitting material:

wherein Ar1 and Ar2 each independently in each occurrence is a substituted or unsubstituted aryl or heteroaryl group; n and m independently in each occurrence is 1, 2 or 3; R independently in each occurrence is a substituent; and Ar1 and Ar2 linked directly to the same N atom may be linked by a direct bond or a linking unit to form a ring.

30. A light-emitting composition according to claim 29, the composition further comprising a host material.

31. A formulation comprising a composition according to claim 29, and at least one solvent.

32. A method of forming an OLED according to claim 1, the method comprising the steps of forming the first and, if present, the second light-emitting layer over the anode; and forming a cathode over the first and second light-emitting layers, wherein the light-emitting layers may be deposited in any order in the case where the second light-emitting layer is present.

33. A method according to claim 32, wherein each of the first light-emitting layer and, if present, the second light-emitting layer are formed by depositing, respectively, a first solution comprising the fluorescent light-emitting material and at least one solvent followed by evaporation of the at least one solvent and a second solution comprising the phosphorescent light-emitting material and at least one solvent followed by evaporation of the at least one solvent.

34. A method according to claim 33, wherein the first light-emitting layer is formed by depositing a formulation comprising a composition comprising a fluorescent light-emitting material of formula (I) and a first phosphorescent light-emitting material:

Ar1 and Ar2 each independently in each occurrence is a substituted or unsubstituted aryl or heteroaryl group; n and m independently in each occurrence is 1, 2 or 3; R independently in each occurrence is a substituent; and Ar1 and Ar2 linked directly to the same N atom may be linked by a direct bond or a linking unit to form a ring and at least one solvent and, evaporating the solvent.