GB2520744A

GB2520744A - Organic light-emitting composition, device and method

Info

Publication number: GB2520744A
Application number: GB1321105.7A
Authority: GB
Inventors: Sophie Heidenhain; Jonathan Pillow; Tomoyasu Yoshida
Original assignee: Cambridge Display Technology Ltd; Sumitomo Chemical Co Ltd
Current assignee: Cambridge Display Technology Ltd; Sumitomo Chemical Co Ltd
Priority date: 2013-11-29
Filing date: 2013-11-29
Publication date: 2015-06-03
Also published as: GB201321105D0

Abstract

A polymer comprises a unit of formula (I): wherein R1 and R2 in each occurrence are independently a substituent; and n, m p and q are each independently 0 or a positive integer. Also shown is a composition comprising a fluorescent light-emitting material and a polymer of formula (I). The polymer may be used as a component of a composition that is suitable for use in organic light emitting diodes and other organic electronic devices.

Description

Oranic Li2ht-Emittin Composition, Device and Method

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 photovoltaic devices, 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 a'lows use of solution processing in device manufacture, for example inkjet printing or spin-coating.

A typical organic light-emissive device (OLED") is fabricated on a glass or plastic substrate coated with a transparent anode such as indium-tin-oxide ("ITO"). A thin layer of a film of at least one electroluminescent organic material is provided over the first electrode. Finally, a cathode is provided over the layer of electroluminescent organic material. Charge transporting, charge injecting or charge blocking layers may be provided between the anode and the electroluminescent layer and / or between the cathode and the electroluminescent layer.

In operation. holes are injected into the device through the anode and electrons are injected into the device through the cathode. The holes and electrons combine in the organic electroluminescent layer to form excitons which then undergo radiative decay to give light.

In W090/l3148 the organic light-emissive material is a conjugated pcAymer such as poly(phcnylcncvinylene). In US 4,539,507 the organic light-cniissivc material is of the class known as small molecule materials, such as tris-(8-hydroxyquinoline) aluminium ( "A1q3" ).

These materials electr&uminesce by radiative decay of singlet excitons (fluorescence) however spin statistics dictate that up to 75% of excitons are triplet excitons which undergo non-radiative decay. i. e. quantum efficiency may he as low as 25% for fluorescent OLEDs-see, for example, Chem. Phys. Lett., 1993,210, 61, Nature (London), 2001,409, 494, Synth. Met., 2002,125, 55 and references therein.

It has been postulated that the presence of triplet excitons, which may have relatively long- lived triplet excited states, can be detrimental to OLED performance as a result of triplet-triplet or triplet-singkt interactions.

WO 2005/043640 discloses that blending a perylene derivative with an organic light-emissive material in an organic light-emissive device can give a small increase in the lifetime of the device. However, while higher concentrations of perylene derivative gr e greater improvements in lifetime this results in a significant red-shift in the emission spectrum.

US 2007/145886 discloses an OLED comprising a triplet-quenching material to prevent or reduce triplet-triplet or triplet-singlet interactions.

WO 2012/086670 and W() 2012/086671 disclose a composition ol a light-emitting material and certain polymers.

US 2005/095456 discloses an OLED having a light-emitting layer comprising a host materiaL a dye or pigment and an additive exhibiting an absorption edge of which energy level is higher than that of an absorption edge of the dye or the pigment.

Masood Parvez et al; Acta Cryst. (2001); E57, o346-o348 discloses a preparation of chiral naphthalene systems with C2 symmetry for subsequent use as a chiral catalytic transfer agent.

C UC Sr CH

R

C-

ii) (:11) (1ff) vie H. Me) L (UI) ÷ I lb

-

Nfl Me L 3 Ct\L e k B) tie

-

(fli) (\T)

Summary of the Invention

In a first aspect the invention provides a polymer compnsing a unit of lormula (I): (R')m (I) wherein R1 in each occurrence is independently a substituent; R2 in each occurrence is independenfly a suhstituent; and n, m p and q are each independently 0 or a positive integer.

n and m may each independently be 0. 1. 2 or 3.

In a second aspect the invention provides a composition comprising a fluorescent light-emitting material and a compound comprising a unit of formula (I): / (R1) (R1)m (I) wherein R1 in each occurrence is independently a substituent; R2 in each occurrence is independenfly a suhstituent; and n, m p and q are cach independently 0 or a positive integer.

In a third aspect the invention provides an organic light-emitting device comprising m anode, a cathode and one or more organic semiconducting layers including a light-emitting layer between the anode and the cathode wherein at least one of the organic semiconducting layers comprises a compound comprising a unit of formifia (I): (R2) AR)q (R1)m (I) wherein R1 in each occurrence is independently a substituent; R2 in each occurrence is independently a substituent; and n, m p and q are each independently 0 or a positive integer.

In a fourth aspect the invention provides a formulation comprising a polymer according to the first aspect and at least one solvent.

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

In a sixth aspect the invention provides a method of forming an organic light-emitting device according to the third aspect, the method comprising the steps of forming the one or more organic semiconducting layers over one of the anode and cathode, and forming the other the anode and cathode over the light-emitting layer.

Optionally according to the sixth aspect, the light-emitting layer is formed by depositing the lormulation according to the uifth aspect over one ol the anode and cathode and evaporating the at least one solvent.

Brief Description of the Drawings

Figure 1 illustrates an organic light-emitting device according to an embodiment of the invention; Figure 2 is a schematic illustration of triplet quenching; Figure 3 is a schematic illustration of a first triplet-triplet annihilation mechanism; and Figure 4 is a schematic illustration ol a second triplet-triplet annihilation mechanism: Figure 5 is a graph of external quantum efficiency vs. voltage for a device according to an embodiment of the invention and a comparative device; and Figure 6 is a graph of brightness vs. time for a device according to an embodiment of the invention and a comparative device.

Detailed Description of the Invention

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

The OLED 100 comprises an anode 101, a cathode 105 and a fluorescent light-emitting layer 103 between the anode and the cathode. The device is supported on a substrate 107, for example g'ass or plastic.

One or more further layers may be provided between the anode 101 and cathode 105, for example hole-transporting layers, electron transporting layers, hole blocking layers and electron blocking layers. The device may contain more than one light-emitting layer. A further light-emitting layer. if present, may he a fluorescent or phosphorescent Ught-emitting material.

Exemplary device structures include: 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 ayer / 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..

Suitable fluorescent light-emitting materials of fluorescent light-emitting layer 103 include red, een and blue light-emitting materials.

A blue emitting material may have a photcAuminescent spectrum with a peak in the range of 400-490 nm. optionally 420-490 nm.

A green emitting material may have a photolurninescent spectrum with a peak in the range of more than 490nm up to 580 nm, optionally more than 490 nm up to 540 nm.

A red emitting material may optionally have a peak in its photoluminescent spectrum of more than 580 nm up to 630 nm. optionally 585-625 nm.

The fluorescent light-emitting layer 103 contains a compound comprising a unit of formula (I) and a fluorescent light-emitting material. The compound comprising a unit of formula (I) may be covalently bound to the fluorescent light-emitting material or may be a separate material mixed with the tluorescent light-emitting material. Light-emitting layer 103 may consist of the compound comprising a unit of formula (1) and a fluorescent light-emitting material, or may comprise these materials in combination with one or more further materials, for example hole and I or electron transporting materials.

In operation, holes and electrons are injected into the device to form singlet and triplet excitons. Singlet excitons on the fluorescent light-emitting material may undergo radiative decay to produce fluorescence. Preferably. the compound comprising a unit of formula (I) is a triplet-accepting material. Triplet excitons may he formed on or transferred to the triplet-accepting polymer and removed by either non-radiative triplet exciton quenching or by delayed fluorescence arising from triplet-triplet annihilation.

Each of these mechanisms is described below in turn.

The triplet-accepting material reduces the triplet exciton population of the fluorescent light-emitting material. The effect of a material on (he triplet exciton population of a light-emitting material may be measured by quasi-continuous wave excited state absorption.

It will be appreciated that triplet-accepting materials will reduce the density of triplet excitons in a light-enritting layer. which may be by triplet cxciton quenching or TTA, and a triplet-accepting material having a lowest triplet excited state lower than that of the emitting material is present if a reduction in triplet exciton population is observed when that material is used in combination with a light-emitting material as compared to the measured triplet exciton population on a light-emitting material athnc.

Probes of triplet population may be performed as described in King. S., Rothe. C. & Monkman. A. "Triplet build in and decay of isolated polyspirohifluorene chains in dilute solution" J. Chein. Pkvs. 121, 10803-10808 (2004), and Rothe, C.. King, SM.. Dias. F. & Monkman, A.P. "Triplet exciton state and related phenomena in the beta-phase of poly(9.9-dioctyl)fiuorene" Physical Review B 70, (2004). which describe probes of polyfluorene triplet population performed at 780nm. The skilled person will understand how to modify this probe for other light-emitting materials based on the excited state absorption features of those materials.

Triplet quenching Figure 2 illustrates a first energy transfer mechanism!èr an exemplary OLED. For the avoidance of any doubt energy level diagrams herein, including Figure 2, are not drawn to any scale.

Figure 2 iflustrates energy transfer for an OLED provided with a light emitting material having a singlet excited state energy level S and a singlet ground state energy level Sob.

Singlet excitons having energy SE decay by emission of fluorescent light hv, illustrated by the solid arrow between SIB and 50E in Figure 1. Triplet-triplet exciton interactions or triplet-singlet exciton interactions may create "super-excited" states on the light-emitting material.

Without wishing to be bound by any theory, it is believed that formation of these highly energetic "super-excited" states on the light emitting material may be detrimental to operational lifetime of the device. However, by providing a compound comprising a unit of formula (I) having an excited triplet state energy level T1A that is lower than T1, it is possible for triplet excitons to be transfelTed for quenching to the triplet accepting polymer. the alternative of i-adiative decay fi-om Tm to 5o. illustrated by a dotted line in Figure 1, being a spin-forbidden process.

51 and T1 levels of a material can be measured from its fluorescence am! gated low-temperature phosphorescence spectra respectively.

The trplet accepting compound has a lowest singlet excited state energy level SIA that is higher than the lowest singlet excited state energy level SIB. This is to substantially or completely prevent transfer of singlet excitons from 51E to 5lA Preferably, 51A is at least kT higher in energy than Si F in order to prevent any substantial back-transfer of excitons and fluorescence from thc triplet-accepting compound. Likewise, TIE is prefcrably at least kT higher in energy than TIA. Although it may be preferable for energy level SIA to be greater than Slu. it wifl he appreciated that this is iiot essential in order for triplet absorption to occur.

Some light emission from the triplet-accepting compound may he observed. Optionally. light emitted from a composition of a fluorescent emitter and a triplet-accepting material comprising a unit of foimula (I) has a peak wavelength that is the same as or no more than 10 nm longer than the peak wavelength of light emitted from the fluorescent emitter alone.

Triplet-triplet annihilation Figure 3 illustrates a second energy transfer mechanism for an exemplary OLED.

According to this embodiment, triplet-triplet annihilation (TTA). caused by an interaction between two triplet-accepting units, results in a triplet-triplet annihilated singlet exciton having energy of up to 2 x LA, wherein TIA represents the triplet excited state energy level of the triplet-accepting compound. This singlet exciton, formed on a first of the two triplet-accepting units, has energy kvel 5nA that is higher in energy than 51A and 51E and so it may transfer to SIA and then to S1 from which Ught hv may be emitted as delayed fluorescence.

The triplet exciton on the second of the two triplet-accepting units may decay to the ground state TOA.

Initially, the triplet exciton formed at TiE is transferred to T1A. By providing a triplet-accepting compound having energy level T1A that is lower than TiE, rapid transfer of excitons from T1 Fl to T1 A may occur. This transfer is relatively rapid compared to the rate of decay of triplet exeitons from Tin to Son, illustrated by a dotted arrow in Figure 1, which is a spin-forbidden process. The energy gap between T1 and LA is preferably greater than kT in order to avoid hack-transfer of excitons from T1A to TiE. Likewise, the energy gap between 5iA and Sib is preferably greater than kT in order to avoid hack-transfer of excitons from Si to S1K It will be appreciated that, unlike phosphorescent dopants, the triplet-accepting materia' does not provide an energetically favourable pathway for tnplets to undergo radiative decay to produce phosphorescence, and as a result substantially none of the energy of the triplet exciton absorbed by the triplet-accepting material is lost from the triplet-accepting polymer in the form of phosphorescent light emission from the triplet-accepting polymer.

Figure 4 illustrates a third energy transfer mechanism for an exemplary OLED.

In this case, triplet-triplet annihilation occurs between the triplet exciton of energy LA located on the triplet accepting unit and the triplet exciton of energy TIE located on the light-emitting polymer. It will be appreciated that this results in a triplet-triplet annihilated singlet exciton (TTAS) having an energy of up to TiF + LA. This singlet exciton's energy level of SnA is higher in than that of p and so it may transfer its energy to S A and from there to S in from which light hv may be emitted as delayed fluorescence.

In Figures 2 and 3, although it may be preferable for energy level S IA to be greater than S, it will be appreciated that this is not essential in order for triplet absorption to occur.

Without wishing to he hound by any theory, it is believed that avoiding formation of super-excited states on the light-emitting material formed during OLED driving may improve device lifetime. Moreover, by utilising a triplet accepting unit to generate TTA to produce stable delayed fluorescence it is possible to improve efficiency as compared to a device in which triplet excitons are quenched (as illustrated in Figure 2) or as compared to a device in which there is no triplet accepting material wherein intensity of delayed fluorescence may drop sharply following initial OLED driving.

it will be appreciated that it is possible for two or all three of (he triplet-quenching mechanisms and the two TTA mechanisms described above to occur within the same device, and that the amount of delayed fluorescence from each of the TTA two mechanisms will depend on factors such as the concentration of light emitting material, the concentration of triplet accepting units and the excited state lifetime of triplet excitons on the light emitting unit and the triplet accepting unit.

The present inventors have found that TTA occurs in systems containing compounds comprising units of formula (I) as the triplet accepting material. Without wishing to he bound by any theory, it is believed that triplet excitons on T1A of compounds comprising a repeat unit of formula (I) have a relatively long lifetime T-FA. A relatively long lifetime not only means that the rate of decay to 50A is relatively slow but also that the likelihood of TTA is relatively high.

The lifetime of excited state triplets residing on units of formula (I) is optionally at least I microsecond, optionally at least 10 microseconds, optionally at least 100 microseconds. The lifetime of a triplet exciton is its half-life, which may be measured by flash photolysis to measure monomolecular triplet lifetime as described in Handbook of Phoochemistry. 21 Edition, Steven L Murov, Ian Carmichael and Gordon L Hug and references therein, the contents of which are incorporated herein by relerence.

The rate constant for transfer of triplet excitons from the light-emitting material to the triplet-accepting material may he selected so as to he greater than the rate constant br quenching of triplet cxcitons.

Light emitted from light-emitting compositions ob the invention inc'udes delayed fluorescence as described above, as well as fluorescence arising directly from radiative decay of singlet excitons formed by recombination of holes and electrons on the light-emitting material ("prompt fluorescence").

The skilled person will be aware of methods to determine the presence of delayed fluorescence in light emitted from a light-emitting composition. as distinct from prompt fluorescence, for example by measuring light emission from a light-emitting composition following prompt Iluorescence.

In the case of an OLED comprising the light-emitting composition, the delayed fluorescence can originate either from a TTA process, or from recombination of trapped charges with relatively long lifetimes. The TTA process can he distinguished from the trapped charge recombination process by applying a short spike of negative bias whilst measuring the intensity of the delayed fluorescence as described in detail by Popovic, Z.D. & Aziz, H. Delayed electroluminescence in smafl molecule based organic light emitting diodes: evidence for triplet-triplet annihilation and recombination centre mediated light generation mechanism.

J. AppI. Phy. 98, 0135 10-5 (2005). If the negative bias has no lasting effect on the intensity of the delayed fluorescence. TTA is indicated (as opposed to non-prompt fluorescence arising from reeomhination ol trapped charges where the delayed fluorescence is reduced after removal of the bias).

Triplet-accepting material The triplet-accepting material comprises a unit of formula (I). The triplet-accepting material may he a non-polymeric material, or may he a polymer comprising a unit of formu'a (1). In the ease of a polymeric material, the unit ol lormula (I) may he provided as a repeating unit in a backbone of the polymer; a substituent pendant from a repeating unit in the polymer backbone; or an end-capping group at an end of the polymer backbone.

The triplet-accepting material may he mixed with the fluorescent light-emitting material or may he bound thereto. In the case where the triplet accepting material is a polymer compnsing units of formula U). the polymer may comprise both units of formula U) and fluorescent light-emitting repeat units, or the triplet-accepting polymer may be mixed with a separate fluorescent light-emitting material.

The polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography of a polymer comprising units of formula (I) maybe in the range of about 1x103 to 1x108, and preferably 1x104 to 5x106. The polystyrene-equivalent weight-average molecular weight (Mw) of the polymers described herein may be 1x103 to 1x108, and preferably 1x104 to 1x107.

Polymers comprising units of formula (I) are suitably amorphous polymers.

If the unit ol formula (I) is a repeating unit in a polymer backbone then (he unit of lormula (I) maybe a repeating unit of lormula (Ia): (__I _______ (R') (R5m (I a) The repeat unit of formula (Ia) may he directly linked on one or both sides to an aromatic carbon atom of an aromatic or heteroaromatic co-repeat unit of (lie pcñymer. The linking positions of the repeating unit of formula (Ta) may be selected to control the extent of conjugation across the repeat unit of formula (Ia). k an embodiment, the extent of conjugation between repeat units adjacent to a unit of formula (Ia) maybe limited by linking the repeat unit as shown in formula (th): / -(Ib) In the case where n and! or m is a positive integer. RI maybe a Cl -40 hydrocarhyl group.

Optionally, one or both of n and mis 0.

Optionally, one or both of p and q is a positive integer.

Optionally, each R2, where present. is a ClAn hydrocarhyl group.

Exemplary hydrocarbyl groups Ri and R2 (where present) niay be selected froni branched, linear or cyclic C 1-20 ailcyl; unsubstituted aryl; aryl substituted with one or more Ci- alkyl groups; and a branched or linear chain of aryl groups, for example 3,5-diphenylbenzene, wherein each aryl is independently unsubstituted or substituted with one or more substituents. An exemplary aryl is phenyL Exemplary repeat units of formula (lh) include the following: H2g1515 Optionally, the polymer comprises a repeating unit comprising units of formula (I) and one or more further repeat units.

The one or more further repeat units may include triplet-accepting repeat units to provide the polymer with a T1 energy level that is low enough to allow transfer of triplet excitons froni the fluorescent light-emitting material and a Si energy level that is high enough to avoid suhstantia transfer of singlet excitons from the fluorescent light-emitting material to the triplet-accepting polymer.

The one or more further repeat units may include a polycychc aromatic co-repeat unit that may be unsubstituted or substituted with one or more substituents. "Polycyclic aromatic hydrocarbon" as used herein means a hydrocarbon structure of two or more fused rings wherein all atoms of the fused rings are sp2 hybridised. Optionally, the polycyclic aromatic hydrocarbon contains no more than 4 fused benzene rings.

For example. the polycyclic aromatic co-repeat unit may be selected from anthracene and pyrene. each of which may be unsubstituted or substituted with one or more substituents, such as repeat units of formulae (II) and (Ill): (R)a (R4) 104\ a I 4\ k Ic (II) (Ill) wherein R4 in each occurrence is independently a substituent; each a is independently 0. 1 or 2; each his independently 0, 1 or 2; and each c isO, 1, 2, 3 or 4.

The repeat unit of formula (II) may have formifia (ha): 1 \ )=\ (R4t (ha) Optionally, one a awl! or at least one b is at least 1, awl each R4 is independently selected from ClAD hydrocarhyl.

Optionally at least one a and/or at least one b is at least 1 and each R4 is independently selected from C 1-20 aIky wherein non-adjacent C atoms of the C 1-20 aWyl may he replaced by 0, S. C=O, COO orNR whcrcin R" is a substitucnt, for example a Cihydrocarbyl group.

If the fluorescent material and triplet accepting material are mixed then the fluorescent light-emitting material: triplet accepting material weight ratio may he at kast 99.5: 0.5 up to about 70: 30 and may he in the range of about 99: I up to about 80: 20. A higher concentration of the tnplct-acccpting polymer increases the probability of TTA.

In the case where the polymer is a copolymer comprising units of formula (I) and one or more further co-repeat units, the copolymer may contain at least 0.5-50 mol % of repeat units of formula (I), optionally 10-40 mol % repeat units of formula (I).

The triplet-accepting polymer may contain 30-50 mol % of triplet-accepting rcpcat units.

Exemplary further co-repeat units, other than triplet-accepting co-repeat units, include phenylene, fluorene and dihydrophenanthrenc repeat units, each of which may he unsubstituted or substituted with one or more substituents. The further co-repeat units may form 0.5 -50 mol % of the repeat units of the polymer, optionally 5-40 mol %.

Optionally, the triplet-accepting polymer contains triplet accepting repeat units separated from one another by a further unit. Optionally. the polymer contains an alternating AB repeat unit structure wherein A is a triplet-accepting repeat unit and B is a repeat unit of formula (I) or a further co-repeat unit. Polymers of this type may he prepared by Suzuki poymerisation.

One preferred class of co-repeat units have formula (VI): (R3)q (VI) wherein q in each occurrence is independently 0, 1. 2, 3 or 4, optionally I or 2; n is 1, 2 or 3; and R3 independently in each occurrence is a substituent.

Where present, each R3 may independently be selected from the group consisting of: -alkyl, optionally C120 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, 0. S. substituted N. C=O or -COO-, and one or more H atoms may be replaced with F; -aryl and heteroaryl groups that may be unsubstituted or substituted with one or more substituents, preferably phenyl suhstitued with one or more C120 alkyl groups; -a linear or branched chain of aryl or heteroaryl groups, each of which groups may independently be substituted, for example a group of formula -(Ar3) wherein each Ar3 is independently an aryl or heteroaryl group and r is at least 2, preferably a branched or linear chain of phenyl groups each of which may he unsuhstituted or substituted with one or more C 1-20 alkyl groups; and -a crosslinkable-group. for example a group comprising a double bond such and a vinyl or acrylate group, or a benzocyclobutane group.

In the case where R3 comprises an aryl or heteroary group. or a hnear or branched chain of aryl or hetcroaryl groups. the or each aryl or heteroaryl group may be substituted with one or more substituents R7 selected from the group consisting of: alkyl, for example C120 alkyl, wherein one or more non-adjacent C atoms may he replaced with 0, S, substituted N, C=O and -COO-and one or more H atoms of the alkyl group may be replaced with F; NR92. OR9. SR9. SiR93 and fluorine, nitro and cyano; wherein each R9 is independently selected from the group consisting of alkyl, preferably Cu20 alkyl; and aryl or heteroaryl. preferably phenyl, optionally substituted with one or more C120 alkyl groups.

Substituted N, where present. may be -NR9-wherein R9 is as described above.

Preferably, each R3, where present, is independently selected from CIAO hydrocarhyl, and is more preferably selected from C120 alkyl; unusubstituted phenyl; phenyl substituted with one or more C120 alkyl groups; a linear or branched chain of phenyl groups, wherein each phenyl may be unsubstituted or substituted with one or more substituents; and a crosslinkable group.

If n is 1 then exemplary repeat units of formula (VI) include the following: (R3)q (R)q A particularly preferred repeat unit of formula (VI) has formula (VIa): (VIa) Substituents R3 of formula (VIa) are adjacent to linking positions of the repeat unit, which may cause steric hindrance between the repeat unit of formula (VIa) and adjacent repeat units, resulting in the repeat unit of formula (VIa) twisting out of plane relative to one or both adjacent repeat units.

Exemplary repeat units where n is 2 or 3 include the following: (R3)q (R3)q (R3)q (R3)q (R3)q A preferred repeat unit has formula (Vib): (VIb) The two R3 groups of formula (VIb) may cause steric hindrance between the phenyl rings they are bound to, resulting in twisting of the two phenyl rings relative to one another.

A further class of co-repeat units is optionally substituted fluorene repeat units.,sueh as repeat units of formula (VII): (R8)d R3 R3 (VII) wherein R3 in each occurrence is the same or different and is a substituent as described with reference to formula (VI), and wherein the two groups may he Unked to form an unsubstituted or substituted ring; R8 is a substituent; and d is 0, 1, 2 or 3.

The aromatic carbon atoms of the fluorene repeat unit may he unsubstituted, or may be substituted with one or more substituents R8. Exemplary substituents R8 are alkyl, for example Cu20 alkyl, wherein one or more non-adjacent C atoms niay be replaced with 0, 5, NH or substituted N, C=O and -COO-, optionally substituted aryl, optionally substituted heteroaryl, alkoxy. alkylthio, fluorine, cyano and arylalkyl. Particularly prefelTed substituents include C120 alicyl and substituted or unsubstituted aryl, for example phenyl.

Optional substituents for the aryl include one or more C120 alkyl groups.

Substituted N, where present, may be -NR5-wherein R5 is -20 alkyl; unsubstituted phenyl; or phenyl substituted with one or more C120 ailcyl groups.

The extent of conjugation of repeat units of formula (VII) to aryl or heteroaryl groups of adjacent repeat units may be controlled 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 (h) substituting the repeat unit with one or more substituents R8 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 C120 alkyl substituent in one or both of the 3-and 6-positions.

The repeat unit of formula VII) may be an optionally substituted 2,7-linked repeat unit of formula (VIla): R3 R3 (VITa) Optionally, the repeat unit ol lormula (Vita) is not substituted in a position adjacent to the 2-or 7-position. Linkage through the 2-and 7-positions and absence of substituents adjacent to these linking positions provides a repeat unit that is capable of providing a relatively high degree of conjugation across the repeat unit.

The repeat unit of formula (VII) may he an optionally substituted 3,6-linked repeat unit of formula (VIIb) R3 R3 (Vllb) The extent of conjugation across a repeat unit of formula (VIIb) niay be relatively low as compared to a repeat unit of formula (VITa).

Another exemplary co-repeat unit has formula (VIII): (R8)d (R8)d R3R3 (V Ill) wherein R3. R8 and d are as described with reference to formulae WI) and (VII) above. Any 3. 3 of the R groups may be hnked to any other of the R groups to form a nng. The ring so formed may he unsuhstituted or may he substituted with one or more suhstituents, optionally one or more C120 alkyl groups.

Repeat units of formula (VIII) may have formula (Villa) or (VIITh): (R8) (R8) R3R3 R3R3 (Villa) (VIllb) An exemplary repeat unit of formula (VIII) has the following structure, wherein aromatic carbon atoms may each independently be unsubstituted or substituted with a substituent R8.

and wherein the cyclopentyl groups may each independently he unsubstituted or substituted with one or more substituents. for example one or more C120 alkyl groups: Light emitting material The light-emitting material may be any form of organic fluorescent material including, without limitation, small molecules, dendrirneric and polymeric fluorescent materials.

A light-emitting polymer may he a light-emitting homop&ymer comprising Ught-emitting repeat units, or it may be a copolymer comprising light-eniltting repeat units and further repeat units such as hole transporting and / or electron transporting repeat units as disclosed in, for example, WO 00/55927. Each repeat unit may be provided in a main chain or side chain of the polymer.

A light-emitting polymer may contain repeat units in the polymer backbone that are conjugated together.

Light-emitting polymers may contain arylamine repeat units, for example repeat units of formula (IX): ( (Ar8) ( tN9)d \R13 \ g (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.

R', which may be the same or different in each occurrence when g> 1, is preferably selected from the group consisting of ailcyl. for example C120 ailcyl. Ar'°, a branched or linear chain of Ar'° 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 Ar'° in each occurrence is independently optionally substituted aryl or heteroaryl. Exemplary spacer groups are Ci2o alkyl, phenyl and phenyl-C120 alkyl.

Any of Ar2, Ar9 and, if present, Ar'° in the repeat unit of Formula (TX) may he linked by a direct bond or a divalent linking atom or group to another of Ar8, Ar9 and Ar'°. Preferred divalent linking atoms and groups include 0. S; substituted N; and substituted C. Any of Ar8, Ar9 and, if present, ArW may be substituted with one or more substituents.

Exemplary substituents are substituents R'°. wherein each R1° may independently be selected from the group consisting of: -substituted or unsubstituted ailcyl, optionally -20 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl. 0, S. substituted N, C=0 or -COO-and one or more H atoms may be replaced with F; and -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 henzocyclohutane group Preferred repeat units of formula (IX) have formulae 1-3: ( Ar8,,Ar) ( Aç7Ar9) ( Aç7Ar9) N-Ar9-N I Ar10 Ar1° Ar10 Ar10 1 2 3 The polymer may contain one, two or more different repeat units of formula (IX).

in one optional arrangement, central Ar9 group linked to two N atoms, for example as in formula 1. is phenylene that may be unsubstituted or substituted with one or more In another optional arrangement, the central Ar9 group of formula 1 is a polycyclie aromatic that may he unsubstituted or substituted with one or more substituents R'°. Exemp'ary polyeyelie aromatic groups are naphthaene, peryene, anthracene, fluorene and dihydrophenanthrene. Each of these polycyclic aromatic groups may be substituted with one or more substituents R'°. Two substituents R'° may be linked to form a substituted or Optionally, Ar8 is phenyl that may be unsubstituted or substituted with one or more suhstituents R10.

Optionally, Ar9 groups linked to only one N atom of the repeat unit of formula (IX) are phenyl that maybe unsubstituted or substituted with one or more substituents R10.

R' of formula (IXa) is preferably a hydrocarbyl, preferably C120 alkyl. phenyl that is unsubstituted or substituted with one or more C 1-20 alkyl groups, or a branched or linear chain of phenyl groups wherein each said phenyl group is unsubstituted or substituted with one or more C120 alkyl groups.

Optionally. R13 is Ar'°, for example phenyl, or is -(Ar'0) wherein r is at least 2 and wherein the group -(Ar'°)r forms a linear or branched chain of aromatic or heteroaromatic groups, for example 3.5-diphenylbeniene wherein each phenyl may he substituted with one or more substituents Rio, for example one or more C120 alkyl groups.

Optionally, c, d and g are each I and Ar2 and Ar9 are phenyl hnkcd by an oxygen atom to form a phenoxazine ring.

Amine repeat units may provide hole-transporting and / or light-emitting functionality.

Exemplary light-emitting amine repeat units include a blue light-emitting repeat unit of formula (IXa) and a green light-emitting repeat unit formula (IXb): ObO (IXa) (IXh) The repeat units of formula (IXa) and (IXb) may be unsubstituted or one or more of the rings of the repeat unit of form&a (lXh) may he substituted with one or more suhstituents R'5, preferably one or more Ci -20 alkyl groups.

Amine repeat units may he provided in a copolymer with one or more co-repeat units, and may form 0.5 mol % up to about 50 mol % of the repeat units of the Ught-emitting copolymer. optionally about 1-25 mol %. optionally about 1-10 mol %.

Exemplary co-repeat units include, without limitation, fluorene, phenylene. indenofluorene, dihydrophenanthrene repeat units. Co-repeat units of the light-emitting polymer may include one or more of the co-repeat units (VI). (VII) and (VIII) described above with reference to the triplet-accepting polymer; phenanthrene repeat units; naphthalene repeat units; anthracene repeat units; and perylene repeat units. Each of these 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-naphthalcnc; 2,6-naphthalene; 2,7-phenanthrene; and 2,5-perylene. Each of these repeat units may be substituted or unsubstituted, for example substituted with one or more C1A0 hydrocarbyl groups.

Polymer synthesis PrefelTed methods for preparation of conjugaled light-emitting polymers comprise a "metal insertion" wherein the metal atom of a metal comp'ex 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. I. Yamamoto, Electrically Conducting And Thermally Stable it -Conjugated Poly(arylene)s Prepared by Organometallic Processes", Progress in Polymer Science 1993, 17, 1153-1205. In the case of Yamarnoto polyrnerisation, a nickel complex catalyst is used; in the case of Suzuki polyrnerisation, 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 he appreciated that repeat units illustrated throughout this application may he derived from a monomer carrying suitalie leaving groups. Likewise, an end group or side group may be bound to the polymer by reaction of a suitable leaving group.

Suzuki polymerisation may be used to prepare regioregular, block and random copolymers.

In particular. hornopolyrners or random copolymers may be prepared when one reactive group is a halogen and the other reactive group is a boron derivative group. Alternativdy.

block or regioregular. in particular AB, copolyrners 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 groups include tosylate, mesylate awl Inflate.

Charge transporting and charge blocking layers In the case of an OLED. a ho'e transporting layer may he provided between the anode and the light-emitting layer or layers. Likewise, an dectron transporting ayer may he provided between the cathode and the light-emitting layer or layers.

Similarly, an electron blocking layer may he 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 Mock the other of holes and electrons.

A charge-transporting layer or charge-blocking layer may be cross-linked, particularly if a layer overlying that charge-transporting or charge-blocking layer is deposited from a solution.

The cross Unkable group used for this cross linking may he a cross linkable group comprising a reactive double bond such and a vinyl or acrylate group, or a benzocyclobutane group.

If present, a hole transporting layer located between the anode and the light-emitting layers preferably has a I-IOMO level of less than or equal to 5.5 cv, more preferably around 4.8-5.5 eV or 5.1-5.3 eV as measured by cyclic voltanirnetry. The HOMO level of the hole transport layer may he selected so as to he within 0.2 cv, optionally within 0.1 cv, 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 Thcated between the light-emitting layers and cathode preferably has a LUMO level of around 2.5-3.5 cv 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 O.2-2nm 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 ayer may contain a homopolynier or copolymer comprising a repeat unit of formifia (IX) as described above, for example a copoymer comprising one or more amine repeat units of formula (IX) and one or more arylene repeat units, for example one or more arylene repeat units selected from formulae (VI), (VII) and (VIII).

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

If a hole-or electron-transporting layer is adjacent a light-emitting layer containing a phosphorescent material then the T1 energy level of the material or materials of that layer are preferably higher than that of the phosphorescent emitter in the adjacent light-emitting layer.

Hole injection layers A conductive hole injection layer, which may be lormed from a conductive organic or inorganic material, may he provided between the anode 101 and the light-emitting layer 103 of an OLED as illustrated in Figure 1 to assist 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 US 5723873 and US 5798170; and optionally substituted polythiophene or poly(thienothiophene). Exampks 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 105 is selected from materials that have a workfunction allowing injection of electrons into the light-emitting layer of the OLED. 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 conductive materials such as metals, for example a hilayer of a low work function material and a high work function material such as calcium and aluminium, for cxanipe as disdosed in WO 98/10621. The cathode may comprise elemental barium, for example as disclosed in WO 98/57381, AppI. Phys. Lett. 2002, 81(4), 634 and WO 02/84759. The cathode may comprise a thin layer of metal compound, in particular an oxide or fluoride of an alkali or alkali earth metal, between the organic layers of the device and one or more conductive cathode 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 work function of less than 3.5 eV, more preferably less than 3.2 cv, most preferably less than 3 cv. 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 ernissive pixels.

A transparent cathode comprises a layer of an electron injecting material that is sufficiently thin to he transparent. Typically, the lateral conductivity of this layer will he 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 hottom-cmitting devices may he replaccd or supplcmented 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 examp'e a substrate ol alternating plastic and dielectric harrier 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 harrier properties such as silicon dioxide, silicon monoxide, sihcon nitride or alternating stacks of polymer and didectric or an airtight container. In the case of a transparcnt 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.

Formulation proces sing A formulation suitable for forming a light-emitting layer may he formed from the composition of the invention and one or more suitable solvents.

The formulation may be a solution of the composition in the one or more solvents, or may be a dispersion in the one or more solvents in which one or more components are not dissolved.

Preferably, the foimulation is a solution.

Solvents suitable for dissolving compositions of the invention, particularly compositions containing polymers comprising alkyl substituents. include benzenes substituted with one or more C110 alkyl or C110 alkoxy groups, for example toluene, xylenes and methylanisoles.

Particularly prefeiTed solution deposition techniques include printing and coating techniques such as spin-coating and inkjet. printing.

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.

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 photorcsist 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 maybe closed or open at the channel ends.

Other solution deposition techniques include dip-coating, roll printing and screen printing.

Examples

Monomer Example 1

Monomer Example 1 was prepared according to the following reaction scheme: o a Me0OC-4CO0Me NaOMe, MeOH

LJ

Acenaphthenequinone AcOH C14H29PPh3Br H20 C14WR _____ %*__.

KOt-Bu 13 27., 13 27 C14H214H29 HCOONH4, Pd/C Chemical Formula: C46H70 Chemical Formula: C46H74 Exact Mass: 622.55 Exact Mass: 626.58 Molecular Weight: 623.05 Molecular Weight: 627.08 c5 o [ir(OMe)(cod)]2, DTBPY Dioxane °B à1 Chemical Formula: C55H96B204 Exact Mass: 878.75 Molecular Weight: 879.02

Polymer Example 1

Polymer Example 1 was prepared by Suzuki polymerisation as described in WO 00/53656 of the foBowin monomers: C14H29 C14H2 l5mol% 35mo1% Br \/ \/ Br SOmol % Comparative Polymer 1 Comparative Polymer 1 was prepared by Suzuki polymerisation as described in WO 00/53656 of the following monomers: Br \/ \/ C9H19 -Br mol % 50 mol %

Device Example 1

A blue organic light-emitting device having the following structure was prepared: ITO / HIL (35 nm) / HTL (22 nni) I LE (65 nrn) I Cathode, wherein ITO is an indium-tin oxide anode; HIL is a hole-injecting layer; HTL is a hole-transporting layer; LE is a hght-emitting layer; and the cathode comprises a layer of metal fluoride in contact with the light-emitting layer and a layer of silver and a layer of aluminium.

To form the device, 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. The hole transporting layer was formed to a thickness of 21 nm by spin-coating a Hole Transporting Polymer 1 and crosslinking the polymer by heating. The light-emitting layer was formed by spin-coating a mixture of Blue Polymer 1: Polymer Example 1 (5:1 w/w) . The cathode was formed by evaporation of a first layer of a metal fluonde to a thickness of about 2 nm, a second layer of aluminium to a thickness of about 100 nm and a third layer of silver to a thickness of about 100 nm.

Blue Polymer 1 was prepared by Suzuki polymerisation as dcscr bed in WO 00/53656 of the following monomers: B\B Br-\Br n-C6H13 n-C3H13 omol% i8moI% Br-O1. Br 3m&% 25m&% Br Br tBu tBu 4m0l% Hole-Transporting Polymer 1 was formed by Suzuki polymerisation as described in WO OO'/53656 of the lollowing monomers: B 77 C4H9 C4H9 mol% 40 mol% Br -\/Br Br Br 5m&% 5mol% Comparative Device I For the purpose of comparison, a device was prepared as described for Device Example 1 except that the light-emitting layer was lormed by spin-coating a mixture of Blue Polymer I Comparative Polymer 1 (6:1 w/w).

Cifi measurements made using a Minolta CS200 Chromaineter are provided in Table 1.

Table 1

________ CIEx CIEy Comparative Device 1 ___________ 0.137 0.131 Device Example 1 0.137 0.119 The CIE (y) value of Device Example 1 is significantly lower (deeper blue) than that of Comparative Device 1.

With reference to Figure. external quantum efficiencies of Device Example 1 and Comparative Device 1 are very similar.

With reference to Figure time taken for hrightnesses of Device Example I and Comparative Device 1 to fall to 80% of m initial brightness are very similar.

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 he apparent to those skilled in the art without departing from the scope of the invention as set forth in the following claims.

Claims

Claims A polymer comprising a unit of formula U): /-\ (R1) (R')m (1) wherein R' in each occurrence is independently a suhstituent; R2 in each occurrence is independently a substituent; and n, m p and q are each independently 0 or a positive integer.
2. A polymer according to claim 1 wherein the unit of formula U) is provided as a repeating unit in the polymer backbone.
3. A polymer according to claim 2 wherein the unit of formula (1) has formula (Ia): / (__I _______ (R') (R1)m (Ia)
4. A polymer according to claim 3 wherein the repeat unit has the formula (Ib): (R2) I' (Ib)
5. A polymer according to any preceding claim wherein one or both of n and mis 0.
6. A polymer according to any preceding claim wherein one or both of p and q is a positive integer.
7. A polymer according to any preceding claim wherein each R2, where present, is a 4ohydrocarhyl group.
8. A polymer according to any preceding claim wherein the polymer comprises a repeating unit comprising units of formula (1) and one or more further repeat units.
9. A polymer according to any preceding claim wherein the one or more further repeat units include a polycyclic aromatic co-repeat unit that may be unsubstituted or substituted with one or more substituents.
10. A polymer according to claim 9 wherein the polycyclic aromatic co-repeat unit is selected from anthracene and pyrene. each of which may be unsubstituted or substituted with one or more substituents.
11. A polymer according to claim 10 wherein the anthraccne and pyrene repeat units are selected from repeat units of formulae (II) and (III): (R)a (R4) 4 a 4 (R)b (R) (II) (III) wherein R4 in each occunence is independently a substituent; each a is independently 0, 1 or 2; each b is independently 0, 1 or 2; and each c isO, 1, 2, 3 or 4.
12. A polymer according to claim 11 wherein the repeat unit of formula (II) has formula (ha): j , (RI {R4 a (ha)
13. A polymer according to claim 12 wherein at least one a and / or at least one b is at least 1, and each R4 is independently selected from Ciohydrocarhy1.
14. A polymer according to claim II or 12 wherein at least one a and/or at east one his at least 1 and each R4 is independently selected from C 1-20 alkyl wherein non-adjacent C atoms of the C1-20 alkyl may be replaced by 0, S, C=0, COO or MR" wherein R'1
15. A composition comprising a fluorescent light-emitting material and a compound comprising a unit of formula U):-/--\ (R')m (I)wherein R' in each occurrence is independently a suhstituent; R2 in each occurrence is independently a substituent; and a, m p and q are each independently 0 or a positive integer.
16. A composition according to claim 15 wherein the compound comprising a unit of formula (I) is a polymer according to any of claims 1-14.
17. A light-emitting composition according to claim 15 or 16 wherein the fluorescent light-emitting material is a polymer.
18. A light-emitting composition according to claim 17 wherein the fluorescent light-emitting polymer comprises repeat units of formula (IX): ( (Ar8)cf_(Ar9)d \R13 Ig (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, R'3 is H or a substituent, preferably a substituent, and c and d are each independently 1, 2 or 3; and any two of Ar8, Ar9 and R'3 directly bound to the same N atom may be linked by a direct bond or a divalent linking group to form a ring.
19. A light-emitting composition according to claim 17 or 18 wherein the fluorescent light-emitting polymer comprises one or more co-repeat units selected from phenylenc, fluorenc and dihydrophcnanthrcnc repeat units, cach of which maybe unsubstituted or substituted with one or morc substituents.
20. A light-emitting composition according to any of claims 15-19 wherein the fluorescent light-emitting material: compound comprising the unit of formula (1) weight ratio is in the range of about 99.5: 0.5: to about 70: 30.
21. A light-emitting composition consisting essentially of a fluorescent light-emitting material and the compound comprising the unit of fornufla (I).
22. An organic light-emitting device comprising an anode, a cathodc and one or more organic semiconducting layers including a light-emitting layer between the anode and the cathode wherein at least one of the organic semiconducting layers comprises a compound comprising a unit of formula (1): (R2) / (R1)m (1) 1-. . . wherein R in each occurrence is independently a substituent; R-in each occuience is independently a suhstituent; and ii, m p and q are each independenUy 0 or a positive integer.
23. An organic light-emitting device according to claim 22 wherein the light-emitting layer comprises the compound comprising a unit of formula (I).
24. An organic light-emitting device according to claim 23 wherein the light-emitting layer comprises a composition according to claim 15 or 16.
25. An organic light-emitting device according to claim 22, 23 or 24 wherein the compound comprising a unit of formula (1) is a polymer according to any of claims I -14.
26. A formulation comprising a polymer according to any of claims 1-14 and at least onc solvent.
27. A formulation comprising a composition according to claim 15 or 16 and at least one solvent.
28. A method of forming an organic hght-emitting device according to any of claims 22- 25. the method comprising the steps of forming the one or more organic seniiconducting layers over one of the anode and cathode, and forming the othcr thc anode and cathode over the light-emitting layer.
29. A method according to claim 28 wherein the light-emitting layer is formed by depositing the formulation according to claim 27 over one of the anode and cathode and evaporating the at least one solvent.