JP2013531100A - Organic light emitting device and method - Google Patents

Abstract

  A composition that may be useful in an organic light emitting diode, comprising a fluorescent light emitting polymer comprising a light emitting repeat unit and a triplet acceptor unit attached to the light emitting polymer.

Description

  This application is based on British Patent Application No. 1010741.5 filed on June 25, 2010, British Patent Application No. 1010742.3 filed on June 25, 2010, and British Patent Application No. 1010745 filed on June 25, 2010. No. 6, British Patent Application No. 1010743.1 filed on June 25, 2010 and British Patent Application No. 1101642.5 filed on January 31, 2011. The contents of each of the applications forming the aforementioned priority are hereby incorporated by reference in their entirety.

  The present invention relates to an organic light emitting composition, a device containing the organic light emitting composition, and a method for producing the device.

  Electronic devices containing active organic materials for use in devices such as organic light emitting diodes, organic photovoltaic devices, organic photodetectors, organic transistors and memory array devices are gaining increasing attention. Devices comprising organic materials offer benefits such as low weight, low power consumption and flexibility.

  Furthermore, the use of soluble organic materials allows the use of solution processing, such as ink jet printing or spin coating, in the manufacture of devices.

  Common organic light emitting devices (“OLEDs”) are fabricated on glass or plastic substrates that are coated with a transparent anode such as indium tin oxide (“ITO”). A thin film layer of at least one electroluminescent organic material is disposed on the first electrode. Finally, a cathode is disposed on the layer of electroluminescent organic material. A charge transport layer, charge injection layer or charge blocking layer can be disposed between the anode and the electroluminescent layer and / or between the cathode and the electroluminescent layer.

  During operation, holes are injected into the device through the anode and electrons are injected into the device through the cathode. Holes and electrons combine in the organic electroluminescent layer to form excitons, which then emit radiation that decays.

In WO90 / 13148, the organic light emitting material is a conjugated polymer such as poly (phenylene vinylene). In US Pat. No. 4,539,507, organic light emitting materials are a class of materials known as low molecular weight materials such as tris- (8-hydroxyquinoline) aluminum (“Alq ₃ ”).

  These materials produce electroluminescence due to radiative decay of singlet excitons (fluorescence), but according to spin statistics, up to 75% of excitons are non-radiatively decayed triplet excitons, ie fluorescent It has been determined that for OLEDs, the quantum efficiency can be as low as 25%. For example, Chem. Phys. Lett. 1993, 210, 61, Nature (London), 2001, 409, 494, Synth. Met. 2002, 125, 55 and references thereof.

  The presence of triplet excitons that can have relatively long-lived triplet excited states can be detrimental to the lifetime of OLEDs as a result of triplet-triplet or triplet-singlet interaction. ("Lifetime", as used herein in the context of OLED, means the length of time it takes for the brightness of the OLED at a constant current to drop by 50% from its initial brightness value. “Lifetime” means the half-life of a triplet exciton as used herein in the context of the lifetime of a triplet excited state).

  WO 2005/043640 discloses that in organic light emitting devices, the lifetime of the device can be slightly extended by blending perylene derivatives with organic light emitting materials. However, higher concentrations of perylene derivatives improve lifetime and at the same time cause a significant red shift in the emission spectrum.

  US Patent Application No. 2007/145886 discloses an OLED comprising a triplet quenching material to prevent or reduce triplet and triplet or triplet and singlet interactions.

  US Patent Application No. 2005/095456 describes an OLED having a light-emitting layer comprising a host material, a dye or pigment, and an additive that exhibits an absorption edge at an energy level higher than the energy level of the absorption edge of the dye or pigment. Disclosure.

  OLEDs have great potential for display and lighting applications. However, there is still a need to improve the performance of these devices.

  In a first aspect, the present invention provides a composition comprising a fluorescent polymer and a triplet accepting unit.

  In an optional variation, the triplet acceptor unit is a triplet acceptor compound mixed with the light emitting polymer and any other component or components of the composition.

  In another optional variation, the triplet accepting unit is attached to the light emitting polymer or any other component or components of the composition.

  Optionally, the composition comprises at least one of a hole transport material and an electron transport material, and the triplet accepting unit is bound to at least one of the hole transport material, the electron transport material and the light emitting polymer.

  Optionally, the triplet accepting unit is attached to the light emitting polymer.

  Optionally, the light emitting polymer comprises a light emitting repeat unit, and at least one of a repeat unit that provides electron transport and a repeat unit that provides hole transport, and the triplet acceptor material comprises a light emitting repeat unit, a repeat unit that provides electron transport. And at least one repeating unit that provides hole transport.

  Optionally, the triplet accepting unit is a repeating unit in the main chain of the light emitting polymer, or a side chain group or end group of the light emitting polymer.

  Optionally, the triplet accepting unit is substituted with one or more solubilizing groups.

  Optionally, the solubilizing group is selected from alkyl and alkoxy.

  Optionally, the light emitting polymer comprises arylamine repeat units.

  Optionally, the arylamine repeat unit is a unit of formula (V).

In which Ar ¹ and Ar ² are optionally substituted aryl or heteroaryl groups, n is 1 or more, preferably 1 or 2, and R is H or a substituent.

  Optionally, the polymer comprises aryl or heteroaryl repeat units.

  Optionally, the polymer comprises a repeating unit of formula (IV).

In the formula, R ¹ and R ² are independently H or a substituent, and R ¹ and R ² can be linked to form a ring.

  Optionally, the triplet receptive material is present in an amount of at least 0.1 mol%.

  Optionally, the composition has a photoluminescent emission peak wavelength in the range of 400-500 nm.

  Optionally, the triplet accepting unit does not comprise perylene.

  In a second aspect, the present invention provides a formulation comprising a solvent and the composition of the first aspect.

  In a third aspect, the present invention provides an organic light emitting device comprising an anode, a cathode, and a light emitting layer comprising the composition of the first aspect between the anode and the cathode.

  In a fourth aspect, the present invention provides a method of forming the organic light emitting device of the third aspect, comprising depositing the formulation of the second aspect and evaporating the solvent.

  In a fifth aspect, the present invention provides the use of a unit for accepting triplet excitons generated by a light emitting polymer in a composition comprising a triplet accepting unit and a light emitting polymer.

  The triplet accepting unit and the light emitting polymer may be as described for the first aspect of the invention.

  Optionally, according to the fifth aspect, the triplet accepting unit is physically mixed with the light emitting polymer.

  Optionally, according to the fifth aspect, the triplet accepting unit is chemically bonded to the light emitting polymer.

  Optionally, according to the fifth aspect, the triplet accepting unit quenches triplet excitons generated by the light emitting polymer.

  Optionally, according to the fifth aspect, the triplet accepting unit mediates the triplet-triplet annihilation of the triplet exciton transferred from the light emitting polymer to the triplet accepting unit.

In a first aspect of the invention, it will be appreciated that the invention relates to a composition in which the triplet accepting unit is substantially non-luminescent. Energy level of the excited singlet state of the light-emitting polymer (S ₁₎ is prevented from any substantial movement of singlet excitons from S ₁ energy level of the light emitting polymer to S ₁ level of the triplet receiving material Therefore, it is lower than the energy level of the corresponding triplet accepting unit, and preferably lower than this energy level.

A “triplet accepting unit” as used herein means a unit capable of receiving triplet excitons from a light emitting polymer. In order to function efficiently, the triplet accepting unit has an energy level T ₁ in the triplet excited state that is lower in energy than the energy level in the triplet excited state of the light emitting unit.

3 is a schematic diagram of a triplet quench. FIG. It is the schematic of a 1st triplet-triplet annihilation mechanism. It is a figure which shows a 2nd triplet-triplet annihilation mechanism. 1 is a diagram illustrating an organic light emitting device according to an embodiment of the present invention. FIG. 6 is a graph of external quantum efficiency versus voltage for an exemplary device and a comparative device. 2 is a graph showing the triplet density of an exemplary device and a comparative device. It is a graph of time-resolved electroluminescence. FIG. 6 is a graph of external quantum efficiency versus time for an exemplary device and a comparative device.

  The inventors have identified several pathways that can cause triplet exciton decay in order to reduce or eliminate decay due to pathways that cause a shortened lifetime of the device. This includes a path where the triplet exciton decays non-radiatively by the quench process, and the triplet exciton annihilates triplet-triplet, providing better device efficiency compared to the non-radiative quenching path. Pathways that provide delayed fluorescence that can be included are included.

Triplet Quench FIG. 1 shows a first energy transfer mechanism of an exemplary OLED. In order to avoid suspicion, the scale of energy levels including FIG. 1 is not described in this specification. FIG. 1 shows the energy transfer of an OLED having a light emitting polymer with a singlet excited state energy level S _1E and a singlet ground state energy level S _0E . Singlet excitons having energy S _1E are attenuated by the fluorescence emission hv indicated by the solid line arrow between S _1E and S _0E in FIG. Triplet and triplet exciton interactions or triplet and singlet exciton interactions can create "superexcited" states on the light-emitting polymer. Without being bound by any theory, it is believed that the formation of these high energy “superexcited” states on the light emitting polymer can be detrimental to the operational lifetime of the polymer. However, providing a triplet acceptor unit having an excited triplet state energy level T _1A lower than T _1E allows the triplet exciton to be transferred to the triplet acceptor unit for quenching, This is an alternative to the radiation decay from T _1E to S _0E , which is the spin forbidden process indicated by the dotted line in FIG. The S ₁ and T ₁ levels can be measured from the fluorescence and phosphorescence spectra, respectively.

The triplet accepting unit of this example has a singlet excitation higher than the energy level S _{1E in the} singlet excited state in order to substantially or completely prevent singlet exciton migration from S _1E to S _1A . It has a state energy level S _1A . Preferably, S _1A is at an energy at least kT higher than S _1E to prevent any substantial reverse movement of excitons. Similarly, T _1E is preferably at an energy at least kT higher than T _1A . While it is preferred that the energy level S _1A is higher than S _1E , it will be understood that this is not essential for triplet absorption to occur.

Triplet-triplet annihilation FIG. 2 shows a second energy transfer mechanism of an exemplary OLED.

According to this embodiment, the triplet-triplet annihilation (TTA) caused by the interaction between two triplet accepting units is a maximum of 2 × T _1A (T _1A is the triplet excited state of the triplet acceptor material). Resulting in a triplet-triplet annihilation type singlet exciton having an energy of 1). This singlet exciton formed on the first triplet accepting unit of the two triplet accepting units has an energy level _SnA that is at a higher energy than S _1A and S _1E , and therefore This singlet exciton can move to S _1A and then to S _1E , from which light hv can be emitted as delayed fluorescence. Triplet excitons on the second triplet accepting unit of the two triplet accepting units can decay to the ground state T _0A .

Initially, the triplet exciton formed at T _1E moves to T _1A . By providing a triplet acceptor material having an energy level T _1A lower than T _1E , rapid exciton transfer from T _1E to T _1A can occur. This movement is relatively rapid compared to the decay rate of triplet excitons from T _1E to S _0E , which is the spin forbidden process indicated by the dotted arrows in FIG. The energy gap between T _1E and T _1A is preferably greater than kT to avoid reverse exciton migration from T _1A to T _1E . Similarly, the energy gap between S _1A and S _1E is preferably greater than kT to avoid reverse exciton migration from S _1E to S _1A .

The decay path of triplet excitons on T _1A competing with triplet-triplet annihilation is the non-radiative (quenching) path to S _0A previously described with respect to FIG. Several measures can be taken to maximize the potential for TTA rather than attenuation to _SOA . In particular,
i) The triplet absorbing material can be selected such that the triplet excitons on T _1A have a relatively long lifetime τ _TA . The relatively long life, but also means that the rate of reduction of the S _0A is relatively slow, the probability of TTA is meant that relatively high.
ii) The concentration of the triplet absorbing material in the light emitting layer may be relatively high, for example in the range of more than 1 mol%, for example 1-10 mol%.
iii) Two or more triplet receptive materials can be placed in close proximity, eg as described below for units of formula (II).

  Each of these measures can be used alone or in combination.

  FIG. 3 shows a third energy transfer mechanism of an exemplary OLED.

In this case, triplet-triplet annihilation occurs between triplet excitons with energy T _1A located on the triplet accepting unit and triplet excitons with energy T _1E located on the light emitting polymer. It will be understood that this results in a triplet-triplet annihilation singlet exciton (TTAS) having an energy of maximum T _1E + T _1A . The energy level S _nA of singlet excitons is higher than S _1E, energy level S _nA therefore, moves the energy to the S _1A, it can be moved from S _1A to S _1E, the light therefrom hv can be emitted as delayed fluorescence.

2 and 3, the energy level S _1A is preferably higher than S _1E , but it will be understood that this is not essential for triplet absorption to occur.

  Without being bound by any theory, it is believed that the lifetime of the device can be improved by avoiding the formation of superexcited states on the light emitting polymer formed during OLED driving. In addition, by utilizing a triplet acceptor unit that generates a TTA that produces stable delayed fluorescence, as compared to a device where triplet excitons are quenched (as shown in FIG. 1) or the intensity of delayed fluorescence. May improve efficiency compared to devices that lack the triplet accepting unit, which may drop sharply after the initial OLED drive.

  The mechanism for quenching the triplet and two or all three of the aforementioned two TTA mechanisms occur within the same device, and the amount of delayed fluorescence from each of the two mechanisms of TTA depends on the concentration of the luminescent material, the triplet. It will be appreciated that it depends on factors such as the concentration of the accepting unit, and the lifetime of the excited state of the triplet exciton on the luminescent and triplet accepting units. The measures described above with respect to FIG. 2 can be used to increase the likelihood of TTA.

  The rate constant of triplet exciton transfer from the luminescent material to the triplet acceptor material can be selected to exceed the rate constant of quenching of the triplet exciton.

  Luminescence from the luminescent composition of the present invention can include the aforementioned delayed fluorescence, as well as fluorescence that results directly from recombination of holes and electrons on the luminescent material (“prompt fluorescence”).

  One skilled in the art will recognize how to determine the presence of delayed fluorescence in the light emitted from the luminescent composition, for example, by measuring the luminescence from the luminescent composition after prompt fluorescence.

  In the case of an OLED comprising a luminescent composition, delayed fluorescence can result from a TTA process or from a relatively long-lived trap charge recombination. The TTA process is described in Popovic, Z. et al. D. & Aziz, H .; Delayed electroluminescence in small molecule based organic light emitting diodes: evidence for triplication and recombination and recombination. J. et al. Appl. Phy. 98, 013510-5 (2005) can be distinguished from the trap charge recombination process by applying a short negative bias spike and simultaneously measuring the intensity of delayed fluorescence. If the negative bias has no lasting effect on the intensity of delayed fluorescence, TTA is suggested (as opposed to non-prompt fluorescence resulting from trap charge recombination, where delayed fluorescence decreases after the bias is removed) .

Triplet Accepting Unit The triplet accepting unit used may be a compound that is not chemically bonded to the light emitting polymer and any other component of the light emitting composition but is physically mixed. Alternatively, the triplet accepting unit can be bound to a component of the composition, either directly or via a spacer group, and in particular can be covalently bound.

  When triplet accepting units are blended with a light emitting polymer, the units are preferably substituted with solubilizing groups.

Exemplary triplet acceptor compounds include aromatic or heteroaromatic compounds that include one or more monocyclic or polycyclic rings, and optionally include one or more alkenyl or alkynyl groups, such as Polycyclic aromatic hydrocarbons such as anthracene and ananthrene and derivatives thereof; mono- or distyrylaryl and derivatives thereof such as distyrylbenzene, distyrylbiphenyl, stilbene, fulvene, dibenzofulvene, cyclic such as cyclooctatetraene Linear polyenes including polyenes (2-6 alkenes), as well as Handbook of Photochemistry, 2nd edition, Steven L Murov, Ian Carmichael and Gordon L Hug, the entire contents of which are incorporated herein by reference. Contained additional materials of the mounting is. Each said compound may be optionally substituted, for example substituted with an alkyl group. In one embodiment, the triplet accepting unit does not comprise a polycyclic aromatic hydrocarbon unit comprising more than 12 sp ² hybridized carbon atoms.

  Exemplary mono- and di-styrylaryl compounds include:

  Exemplary anthanthrene compounds include the following:

Wherein, Ak is alkyl, in particular branched or C ₁ ~ ₁₀ alkyl straight. Particularly preferred alkyl groups are n-butyl, t-butyl, n-hexyl and n-octyl.

  The triplet accepting unit may be a compound that is physically mixed with the luminescent polymer and any other component that may be present in the composition, or of the luminescent composition or, if present, these other components. Can be combined into one. The other component or components can be one or more charge transport materials such as, for example, hole transport materials or electron transport materials. When the triplet accepting unit is attached to a light emitting polymer, the triplet accepting unit is provided as a repeating unit in the polymer backbone, one or more side groups that are pendant from the polymer backbone, or a polymer end group Can be done.

Triplet accepting units emit light by polymerizing monomers containing triplet accepting repeat units that are substituted with at least two polymerizable groups such as leaving groups that can participate in metal-catalyzed cross-coupling reactions. It will be understood that polymerisation of monomers containing three or more leaving groups will produce branch points in the polymer when three or more of the leaving groups are capable of binding to the polymer backbone. ). For this purpose, substitution of leaving groups on the sp ² carbon atom of the triplet acceptor unit can be used. Exemplary leaving groups include halogen groups and boronic acid groups or boronic ester groups for use in the Suzuki or Yamamoto polymerization reaction described in more detail below. The triplet accepting unit can be bonded to any repeating unit of the light emitting polymer described below, for example, can be bonded to the light emitting repeating unit, the electron transport repeating unit and / or the hole transport repeating unit. In one embodiment, the polymer comprises a triplet-accepting repeat unit and an arylene comonomer repeat unit, such as a repeat unit of formula (IV) below.

  Exemplary repeat units include the following:

Wherein ^*, linked repeating units indicates the point of attachment to the polymer chain, Ak is alkyl, in particular branched or C ₁ ~ ₁₀ alkyl straight. Particularly preferred alkyl groups are n-butyl, t-butyl, n-hexyl and n-octyl. R is H or a substituent, optionally alkyl, or optionally substituted aryl or heteroaryl, for example phenyl substituted with one or more alkyl groups.

  A triplet accepting unit is a compound on a polymer that is substituted with one polymerizable group, such as a leaving group that can participate in a metal-catalyzed cross-coupling reaction such as a halogen or a boronic acid or boronic ester. By reacting with the leaving group, it can be arranged as a side chain group or a terminal group of the light emitting polymer.

  Exemplary end group units include:

Alternatively, the side chain groups can be incorporated into the light emitting polymer by providing the side chain groups as monomer substituents, as shown below.
PG-polymerizable unit-PG
｜
In the triplet absorption unit formula, PG represents a polymerizable group such as the aforementioned leaving group or a polymerizable double bond.

  Exemplary side group monomers include the following.

Wherein ^*, linked repeating units indicates the point of attachment to the polymer chain, R represents an alkyl, in particular branched or C ₁ ~ ₁₀ alkyl straight, heteroaryl or aryl (optionally alkyl, With aryl or heteroaryl substituents).

As mentioned above, multiple triplet accepting units can be placed in close proximity to increase the possibility of TTA and delayed fluorescence. For example, such two units can be provided in an optionally substituted unit having the general formula (II).
TAU-Spacer-TAU
(II)
In the formula, “TAU” represents the triplet accepting unit of formula (I), and the spacer is a conjugated or non-conjugated spacer group. The spacer group separates the two triplet accepting TAU groups and preferably separates their electronic characteristics (eg HOMO and LUMO). Depending on the exact nature of the conjugation and orbital overlap, Sp can optionally include one or more arylene or heteroarylene groups such as substituted phenyl, biphenyl or fluorene. Alternatively, Sp can optionally include an unconjugated linking group, such as alkyl, or the linking of another molecule that does not provide a conjugation pathway between the TAU group and the TAU group.

  The unit of formula (II) may be a separate compound physically mixed with the light emitting polymer or may be bound to the light emitting polymer. When the light emitting polymer is a polymer, the unit of the formula (II) can be bonded as a repeating unit, a side chain group or a terminal group of the main chain as described above.

Alternatively or additionally, the triplet accepting unit may be an oligomer or polymer comprising a repeating structure of formula (IIb), or a component of the oligomer or polymer.
(TAU-spacer) _m
(IIb)
In the formula, m is at least 2. This oligomer or polymer can be mixed with the light-emitting polymer or placed in the polymer backbone.

  Although the coupling of the triplet accepting unit and the light emitting polymer has been described above, it will be understood that the triplet accepting unit can also be coupled to any other component of the composition, if present. The concentration of the triplet accepting unit is optionally in the range of at least 0.1 mol%, or at least 1 mol%, for example 0.1-10 mol% or 1-10 mol%, relative to the luminescent material. The higher the triplet receptive material concentration, the greater the potential for TTA.

  To increase the likelihood of TTA, the lifetime of the excited triplet present on the triplet acceptor material is optionally at least 1 microsecond, optionally at least 10 microseconds, optionally at least 100 microseconds. It is. The lifetime of a triplet exciton is its half-life, which is described in Handbook of Photochemistry, 2nd edition, Steven L Murov, Ian Carmichael and Gordon L Hug and its references, the contents of which are incorporated herein by reference. As described, it can be measured by flash photolysis to measure the lifetime of single molecule triplets.

  Triplet acceptor materials, unlike phosphorescent dopants, do not provide an energetically prone route for absorbed triplets to radiatively decay, resulting in triplet excitons absorbed by the triplet acceptor material. It will be appreciated that no energy is substantially lost from the triplet acceptor material in the form of phosphorescence from the triplet acceptor material.

  The density of triplet excitons on a luminescent material, for example on the polymer backbone of a conjugated luminescent polymer, can be measured using absorption in a quasi-continuous oscillation (quasi-cw) excited state, as described in more detail below. it can.

  FIG. 4 shows the structure of an OLED according to an embodiment of the present invention. The OLED includes a transparent glass or plastic substrate 1, an anode 2, a cathode 4, and a light emitting layer 3 provided between the anode 2 and the cathode 4. Additional layers (not shown) such as a charge transport layer, charge injection layer or charge blocking layer can be located between the anode 2 and the cathode.

Luminescent polymer The luminescent polymer may be a luminescent homopolymer comprising a luminescent repeat unit or may comprise a luminescent repeat unit and further repeat units such as hole transport and / or electron transport repeat units as disclosed, for example, in WO 00/55927. It may be a copolymer containing. Each repeating unit is located in the main chain or side chain of the polymer.

  Light emitting polymers suitable for use in layer 3 include poly (arylene vinylenes) such as poly (p-phenylene vinylene), and polyfluorenes, particularly 2,7-linked 9,9 dialkyl polyfluorenes or 2,7-linked 9 , 9 polyarylenes such as diarylpolyfluorenes; polyspirofluorenes, especially 2,7-linked poly-9,9-spirofluorenes; polyindenofluorenes, especially 2,7-linked polyindenofluorenes; polyphenylenes, especially alkyl or Poly-1,4-phenylene substituted with alkoxy is included. Such polymers are described, for example, in Adv. Mater. 2000, 12 (23) 1737-1750 and references therein.

  The light-emitting polymer is preferably, for example, Adv. Mater. 2000, 12 (23) pp. 1737-1750 and references therein, containing repeat units selected from arylene repeat units.

Exemplary first repeat units include J.I. Appl. Phys. 1996, 79, 934; 1,4-phenylene repeating unit; fluorene repeating unit disclosed in European Patent No. 0842208; for example, Macromolecules 2000, 33 (6), indenofluorene disclosed on pages 2016-2020 Repeat units; and spirofluorene repeat units disclosed, for example, in EP 0707020. Each of these repeating units is optionally substituted. Examples of the substituents, C ₁ ~ ₂₀ alkyl or solubilizing groups such as alkoxy; include substituents to increase and the glass transition temperature of the polymer (Tg); fluorine, nitro or electron-withdrawing group such as cyano. The arylene repeat unit or chain thereof can provide electron transport functionality. For example, polyfluorene chains can provide electron transport functionality to the polymer.

  Particularly preferred polymers comprise optionally substituted 2,7-linked fluorene, most preferably repeating units of formula IV.

In the formula, R ¹ and R ² are independently H or a substituent, and R ¹ and R ² can be linked to form a ring. R ¹ and R ² are preferably hydrogen; optionally substituted alkyl (one or more non-adjacent C atoms are replaced by O, S, N, C═O and —COO— An optionally substituted aryl or heteroaryl; and an optionally substituted arylalkyl or heteroarylalkyl. More preferably, at least one of R ¹ and R ² comprises an optionally substituted alkyl, such as a C ₁ -C ₂₀ alkyl or aryl group.

  “Aryl” and “heteroaryl” as used herein include both fused and unfused aryl and heteroaryl groups, respectively.

  Optionally, the fluorene repeat unit is present in an amount of at least 50 mol%.

When R ¹ or R ² is aryl or heteroaryl, the preferred aryl or heteroaryl group is phenyl, and preferred optional substituents include alkyl groups (one or more non-adjacent C atoms may be replaced by O, S, N, C═O and —COO—.

Optional substituents of the fluorene unit other than the substituents R ¹ and R ² are preferably alkyl (one or more non-adjacent C atoms are O, S, N, C═O and —COO— Optionally substituted aryl, optionally substituted heteroaryl, alkoxy, alkylthio, fluorine, cyano and arylalkyl.

  Preferably, the polymer comprises the aforementioned arylene repeat units and arylamine repeat units, especially repeat unit V.

Wherein Ar ¹ and Ar ² are optionally substituted aryl or heteroaryl groups, n is 1 or more, preferably 1 or 2, and R is H or a substituent, A substituent is preferred. R is preferably alkyl or aryl or heteroaryl, most preferably aryl or heteroaryl. Either the aryl or heteroaryl group of the unit of Formula 1 may be substituted, including where R is aryl or heteroaryl, and in one embodiment Ar ¹ , Ar ² and R are each optionally Is substituted by phenyl. Preferred substituents are alkyl (one or more non-adjacent C atoms may be replaced by O, S, N, C═O and —COO—), optionally substituted aryl, Selected from optionally substituted heteroaryl, alkoxy, alkylthio, fluorine, cyano and arylalkyl. Preferred substituents include alkyl groups and alkoxy groups. Either the aryl group or heteroaryl group of the repeating unit of Formula 1 may be linked by a direct bond or a divalent linking atom or linking group. Preferred divalent linking atoms and linking groups include O, S, substituted N, and substituted C.

  Particularly preferred units that satisfy Formula 1 include units of Formulas 1-3.

Wherein Ar ¹ and Ar ² are as defined above and Ar ³ is an optionally substituted aryl or heteroaryl. When present, preferred substituents for Ar ³ include alkyl groups and alkoxy groups.

  The arylamine repeat unit is preferably present in an amount of up to 30 mol%, preferably up to 20 mol%. These percentages apply to the total number of arylamine units present in the polymer when more than one type of repeat unit of formula V is used. The repeating unit of formula (V) can provide one or more of hole transport functionality and light emission functionality.

  The polymer can include heteroarylene repeat units for charge transport or emission.

  The coupling of a triplet accepting unit and a light-emitting polymer can result in an intramolecular triplet accepting pathway that is not available in the corresponding mixed system, so it is more efficient than mixing a triplet acceptor material with a light-emitting polymer. Triplet acceptance can be provided.

  Further, the coupling can be beneficial for processing reasons. For example, if the triplet acceptor unit is poorly soluble, binding the triplet acceptor unit to a soluble light-emitting polymer causes the triplet acceptor unit to be incorporated into the solution by the light-emitting polymer, and the device can be fabricated using solution processing techniques. Can be manufactured. Furthermore, if the triplet accepting unit is a relatively volatile material such as stilbene or a derivative thereof, the risk of evaporation of the triplet accepting material during device manufacture is eliminated. This means that the emissive layer formed by solution deposition is generally heated as part of the device fabrication process (eg, to evaporate the solvent), thereby evaporating the volatile triplet accepting units. This is particularly problematic in the case of OLEDs formed using solution processing methods. Finally, combining triplet accepting units with a light emitting polymer can prevent phase separation effects in solution processed devices that can be detrimental to device performance.

Conjugation of triplet accepting units to the polymer backbone when the light emitting polymer is a conjugated polymer comprising a light emitting repeat unit and further repeat units, for example a light emitting amine repeat unit of formula (V) and a fluorene repeat unit of formula (IV) (Eg, due to conjugation with a fluorene repeat unit) reduces the T ₁ energy level of the triplet accepting unit, and thus tends to cause energy to move triplet excitons from the emitter unit to the triplet accepting unit. This reduction in the T ₁ energy level of the triplet acceptor unit allows the triplet acceptor unit to be used in combination with a light-emitting polymer having a T ₁ level that is too low to be used with such unconjugated triplet acceptor units. It becomes possible.

  A preferred method of preparing conjugated luminescent polymers involves “metal insertion” in which the metal atom of the metal complex catalyst is inserted between the aryl or heteroaryl group of the monomer and the leaving group. Exemplary metal insertion methods include, for example, Suzuki polymerisation as described in WO 00/53656, and T.W. Yamamoto, “Electrically Conducting And Thermally Stable π-Conjugated Poly (arylene) s Prepared by Organic Processes, 3rd page, 115th” In the case of Yamamoto polymerization, a nickel complex catalyst is used, and in the case of Suzuki polymerization, a palladium complex catalyst is used.

  For example, in the synthesis of a linear polymer by Yamamoto polymerization, 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.

  Thus, it will be appreciated that the repeat units shown throughout this application can be derived from monomers bearing appropriate leaving groups. Similarly, end groups or side groups can be attached to the polymer by reaction of a suitable leaving group.

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

  As an alternative to halides, other leaving groups that can participate in metal insertion include groups including tosylate, mesylate and triflate.

  The light-emitting layer 3 can consist only of the light-emitting polymer and the triplet accepting unit, or can comprise these materials in combination with one or more further materials. In particular, the light-emitting polymer can be blended with a hole and / or electron transport material, or can be covalently bonded to the hole and / or electron transport material, for example as disclosed in WO 99/48160.

  The light emitting copolymer can comprise a light emitting region and at least one of a hole transport region and an electron transport region, as disclosed, for example, in WO 00/55927 and US Pat. No. 6,353083. If only one of the hole transport region and the electron transport region is provided, the electroluminescent region can also provide the other of the hole transport functionality and the electron transport functionality, for example, the aforementioned amine unit can be Both hole transport and light emission functionality can be provided. A luminescent copolymer comprising a luminescent repeat unit and one or both of a hole transport repeat unit and an electron transport repeat unit can provide the unit in the polymer backbone, as in US Pat. The unit can be provided from the chain to a polymer side group in a pendant state.

The light emitting polymer can emit any color, provided that its S ₁ and T ₁ energy levels relative to the triplet accepting unit are as described above, but the light emitting polymer is preferably a blue light emitting polymer. In particular, it is a material having a photoluminescent emission with a peak wavelength in the range of 400 to 500 nm, preferably 430 to 500 nm.

  The light emitting layer 3 may be patterned or may not be patterned. A device comprising an unpatterned layer can be used, for example, as an illumination light source. White light emitting devices are particularly suitable for this purpose. The device comprising the patterned layer can be, for example, an active matrix display or a passive matrix display. In the case of an active matrix display, a patterned electroluminescent layer is generally used in combination with a patterned anode layer and an unpatterned cathode. In the case of a passive matrix display, the anode layer is formed from parallel stripes of anode material and parallel stripes of electroluminescent and cathode materials arranged perpendicular to the anode material, the electroluminescent and cathode materials The stripes are generally separated by stripes of insulating material (“cathode separator”) formed by photolithography.

Hole injection layer A conductive hole injection layer, which can be formed from a conductive organic or inorganic material, is provided between the anode 2 and the electroluminescent layer 3 from the anode to one or more of the semiconducting polymers. It can be useful for injecting holes into the layer.

  Examples of doped organic hole injection materials include optionally substituted doped poly (ethylenedioxythiophene) (PEDT), particularly as disclosed in EP 0901176 and EP 0947123. PEDT doped with charge balancing polyacids such as polystyrene sulfonate (PSS), polyacrylic acid or fluorinated sulfonic acids such as Nafion®; polyaniline disclosed in US Pat. No. 5,723,873 and US Pat. No. 5,798,170; As well as optionally substituted polythiophene or poly (thienothiophene). Examples of conductive inorganic materials include transition metal oxides such as VOx MoOx and RuOx, such as those disclosed in Journal of Physics D: Applied Physics (1996), 29 (11), pages 2750-2754. included.

Charge Transport Layer A hole transport layer can be provided between the anode and the electroluminescent layer. Similarly, an electron transport layer can be provided between the cathode and the electroluminescent layer.

  Similarly, an electron blocking layer can be provided between the anode and the electroluminescent layer, and a hole blocking layer can be provided between the cathode and the electroluminescent layer. The transport layer and blocking layer can be used in combination. Depending on its HOMO and LUMO levels, a single layer can transport one of holes and electrons and block the other of holes and electrons.

  When present, the hole transport layer located between the anode 2 and the electroluminescent layer 3 preferably has a HOMO level of 5.5 eV or less, more preferably about 4.8 to 5.5 eV. The HOMO level can be measured, for example, by cyclic voltammetry.

  When present, the electron transport layer located between the electroluminescent layer 3 and the cathode 4 preferably has a LUMO level of about 3 to 3.5 eV. For example, a layer of silicon monoxide or silicon dioxide or other thin dielectric layer having a thickness in the range of 0.2-2 nm is provided between the electroluminescent layer 3 and the layer 4.

  Polymers for use as charge transport materials can include arylene units such as the fluorene unit of formula (IV) and other units described above.

  The hole transport polymer may comprise a repeat unit of formula (V), such as an arylamine repeat unit, in particular the repeat unit of formulas 1-3 described above. The polymer may be a homopolymer or a copolymer comprising arylene repeat units in an amount up to 95 mol%, preferably up to 70 mol%. These percentages apply to the total number of arylamine units present in the polymer when two or more repeating units of formula (V) are used.

  The charge transport unit can be provided on the polymer main chain or the polymer side chain.

Cathode The cathode 4 is selected from materials having a work function capable of injecting electrons into the electroluminescent layer. Other factors, such as the possibility of deleterious interactions between the cathode and the electroluminescent material, also affect cathode selection. The cathode can be made of a single material such as an aluminum layer.

  Alternatively, the cathode can comprise a plurality of metals, for example, a bilayer of a low work function material and a high work function material, such as calcium and aluminum disclosed in WO 98/10621; WO 98/57381, Appl. Phys. Lett. Elemental barium disclosed in 2002, 81 (4), 634 and WO02 / 84759; or metal compounds, particularly alkali metal or alkaline earth metal oxides, as disclosed in WO00 / 48258, to aid electron injection Or a thin layer of fluoride, such as lithium fluoride; Appl. Phys. Lett. 2001, 79 (5), 2001, barium fluoride; as well as barium oxide. In order to efficiently inject electrons into the device, the cathode preferably has a work function of less than 3.5 eV, more preferably less than 3.2 eV, and most preferably less than 3 eV. Metal work functions are described, for example, in Michaelson, J. et al. Appl. Phys. 48 (11), 4729, 1977.

  The cathode can be opaque or transparent. Transparent cathodes are particularly advantageous in active matrix devices, as light passing through the transparent anode in the active matrix device is at least partially blocked by a drive circuit located under the luminescent pixel. The transparent cathode includes a layer of electron injection material that is sufficiently thin and transparent. In general, the lateral conductivity of this layer is 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 conductive material such as indium tin oxide.

  Transparent cathode devices do not require a transparent anode (unless of course a completely transparent device is desired), and therefore transparent anodes used in bottom light emitting devices are layers of reflective material such as an aluminum layer. It will be understood that can be replaced or supplemented with. An example of a transparent cathode device is disclosed, for example, in GB 2348316.

Sealing optical devices tend to be sensitive to moisture and oxygen. Thus, the substrate preferably has good barrier properties to prevent moisture and oxygen from entering the device. The substrate is typically glass, but alternative substrates can be used, particularly where device flexibility is desired. For example, the substrate may be a plastic such as in US Pat. No. 6,268,695 which discloses a substrate with alternating plastic and barrier layers, or a thin glass and plastic laminate disclosed in EP 0949850. Can be included.

  The device is preferably sealed with an encapsulant (not shown) to prevent moisture and oxygen ingress. Suitable encapsulants include glass sheets, films with suitable barrier properties such as silicon dioxide, silicon monoxide, silicon nitride, or alternately stacked with polymers and dielectrics as disclosed, for example, in WO01 / 81649 Or hermetic containers disclosed, for example, in WO 01/19142. For transparent cathode devices, a transparent sealing layer such as silicon monoxide or silicon dioxide can be deposited to a micron level thickness, but in a preferred embodiment, the thickness of such layer is 20-300 nm. It is a range. Any atmospheric moisture and / or oxygen getter material that can penetrate the substrate or encapsulant can be deposited between the substrate and encapsulant.

Solution Treatment The light emitting layer 3 can be deposited by any method including vacuum evaporation and deposition from a solution in a solvent. When the emissive layer includes polyarylene such as polyfluorene, suitable solvents for solution deposition include mono- or poly-alkylbenzenes such as toluene and xylene. Particularly preferred solution deposition techniques include printing and coating techniques, preferably spin coating and ink jet printing.

  Spin coating is particularly suitable for devices that do not require patterning of electroluminescent materials, such as lighting applications or simple monochrome segment displays.

  Inkjet printing is particularly suitable for displays with a large amount of information, in particular full color displays. The device prints by providing a patterned layer on the first electrode and defining wells for single color (for monochrome devices) or multiple colors (for multicolor, especially for full color devices) printing Can be inkjet. The layer to be patterned is generally a photoresist layer that is patterned to define wells, for example as described in EP 0880303.

  As an alternative to wells, ink can be printed in channels defined in the patterned layer. In particular, a photoresist can be patterned to form a channel, which, unlike a well, extends over a plurality of pixels and may be closed or open at the end of the channel.

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

  When multiple layers of an OLED are formed by solution processing, those skilled in the art will know, for example, by cross-linking one layer and then depositing subsequent layers or the material that forms the first layer of the adjacent layer. One will recognize techniques for preventing admixing of adjacent layers by selecting the material of the adjacent layers so that they do not dissolve in the solvent used to deposit the second layer.

Monomer Example 1
Monomers to form triplet quenching units were prepared according to the following method.

  This synthesis shows substitution at the 2 and 8 positions. Similar substitutions can be provided at the 6,12 and / or 4,10 positions as shown below.

Composition Example 1
Monomer 1 was polymerized with triarylamine and fluorene comonomers by Suzuki polymerization as described in WO 00/53656 to form a copolymer comprising an amine repeat unit of formula (V) and a fluorene repeat unit of formula (IV).

Composition Example 2
Material 11 to quench the triplet was prepared according to the following method.

i. 4-bromobenzaldehyde, NaO ^t Bu, THF, ii. BuLi, IPB, THF, iii. 3, Pd (PPh ₃ ) ₂ Cl ₂ , Et ₄ NOH, toluene, iv. 1-bromo-4-iodobenzene, Pd (PPh ₃ ) ₄ , Ag ₂ CO ₃ , THF, v. BuLi, H ₂ O, THF

  Compound 11 was mixed with a luminescent polymer comprising a fluorene repeat unit of formula (IV) and a luminescent amine repeat unit of formula (V).

Device Example 1
A device having the following structure was formed.
ITO / HIL / HTL / EL / MF / Al
ITO represents an indium tin oxide anode, HIL is a 35 nm hole injection layer, and HTL is a 15 nm positive of a polymer containing a fluorene repeat unit of formula (IV) and an amine repeat unit of formula (V). A hole transport layer, EL is an electroluminescent layer (70 nm) comprising a luminescent polymer comprising a fluorene repeat unit of formula (IV) and an amine repeat unit of formula (V) blended with a triplet acceptor material; MF is a metal fluoride and the MF / Al bilayer forms the cathode of the device. HIL, HTL and EL layers were deposited by spin coating the composition from solution and evaporating the solvent.

Device Example 2
A device was formed as in Device Example 1. In this device, the HTL comprises 50:50 mol of copolymer F8-TFB (poly- (9,9-dioctylfluorene-N- (4- (2-butyl) phenyl) -diphenylamine)) and EL is triplet Is blended with DPVBi (4,4′-bis (2,2′diphenylvinyl) -1,1′-biphenyl), a quenching additive (1% mol ratio) of 95: 5 mol copolymer F8-PFB (poly -(9,9'-dioctylfluorene-co-bis-N, N '-(4-butylphenyl) -bis-N, N'-phenyl-1,4-phenylenediamine)).

  DPVBi has the triplet energy of the red-green part of the spectrum (Chen, P. et al., White organic light-emitting devices with a bipolar transport. And the physic. 0230505-3 (2007); Schwartz, G., Fehse, K., Pfeiffer, M., Walzer, K. & Leo, K. Highly efficient whitening organics competing compres- e. fluorescent and phosphorescent regions. Applied Physics Letters 89, 083509 (2006); and Romanovskii, YV and others. ).

  DPVBi also has a high singlet energy (3.2 eV) compared to the luminescent polymer, so this molecule accepts the triplet of the polymer without affecting the singlet emission state. This is confirmed by the observation that incorporating this small molecule into the polymer has no effect on the device's photoluminescence intensity or spectrum.

  Singlet and triplet exciton dynamics were studied using time-resolved electroluminescence, and absorption of quasi-cw and time-resolved excited states. Excited state absorption techniques have been described elsewhere (King, S., Rothe, C. & Monkman, A. Triple build in and dehydrated polyspirobifluorine chains in dilute solution. 10808 (2004), and Dhoot, AS, Ginger, DS, Beljonne, D., Shuai, Z. & Greenham, N. C. Triple formation and deci- cation of dehydrated polymer 3 195-201 (2002)), polyfluore Using these techniques, the triplet state is well characterized by the strong excited-state absorption properties having a peak at 780 nm due to the triplet state (King, S., Rothe, C. et al. & Monkman, A. Triple build in and decay of isolated polyspirobifluorine chains in dilute solution.J. Chem. Phys. 121, 10803-10, Ro. & Monkman, AP Triplet exciton state and related phenomena in the beta-phase of poly (9,9-dioc) yl) fluorene.Physical Review B70 (2004 years)). Although the investigation of polyfluorene triplet populations was conducted at 780 nm, those skilled in the art will understand how to adapt this investigation to other emissive materials and based on the excited state absorption properties of those materials.

  FIG. 5 shows the external quantum efficiency (EQE) of device example 2 (diamonds) and the external quantum efficiency (squares) of a comparative device without the triplet quenching additive. Devices containing additives that quench the triplet show a significant decrease in peak EQE of about 20% at high voltage. The loss of efficiency occurs without changing the electroluminescence spectrum of the device. Thus, as can be expected from singlet energy, the additive does not quench singlet excitons and does not participate in the emission of the device. Without being bound by any theory, it is believed that the loss of efficiency is caused by the removal of the TTA component by quenching the triplet from the light emitting polymer.

  The density of triplet excitons on the polymer backbone is measured using quasi-cw excited state absorption as outlined above.

FIG. 6 shows the triplet density both on the polymer backbone with a triplet quencher (diamond) and without the polymer backbone (square), and for devices with additives, the triplet density on the fluorene backbone. Is about 1/10 lower, so the additive is very efficient at quenching triplets from the polymer at all device drive voltages. Literature values for the extinction coefficient of absorption of triplet excited states in conjugated polymers range from 10 ⁻¹⁶ to 10 ⁻¹⁵ cm ² , which gives a typical drive current of 50 mAcm ⁻² for standard devices. The triplet density of 10 ¹⁶ to 10 ¹⁷ cm ^-3 occurs at, and the decay is dominated by the extinction of the triplet of each other's bimolecule that results in the generation of luminescent singlet excitons.

  FIG. 7 shows time-resolved electroluminescence during turn-off of Device Example 2 compared to time-resolved triplet transient absorption and its square. The dotted line has the same slope. Also shown is the effect on electroluminescence turn-off when a reverse bias pulse of -10 v 200 ns duration is applied to the device 250 ns after the device current is switched off.

  After turning off the current, first, there is a rapid decay of brightness on a time scale similar to the RC time constant of the device, followed by an EL residual signal, which is approximately the same as the original total electroluminescence. It accounts for 30% and decays in a few microseconds. In general, slow transient emission of OLEDs is attributed to either deep traps or charge recombination from the interfacial charge layer, or TTA (Kondakov, DY Characteristic of triplet-triplet in organic lighting-emittering. based on anthracene derivatives.J. Appl. from Pristine Polyfluorine Thin Film Devices at Low Temperature. Physical Review Letters 90, 127402 (2003), and Sinha, S., Monkman, AP., Gunner, R. & S. thin films.Appl.Phys.Lett.82, p.4693-4695 (2003)).

  To distinguish the two mechanisms, the same transient electroluminescence trace was measured 100 ns after the device current was turned off, with a 10 v reverse bias pulse applied, which pulse contributes to the luminance decay. The trap charge is removed or at least significantly disturbed. The data shows that due to quenching by the electric field of singlet excitons, the emission is slightly quenched during the reverse bias pulse, but the EL decay after the reverse bias pulse is unchanged compared to the standard decay form It is shown that. Therefore, it can be concluded that the recombination of trapped charges is not a significant cause of the residual luminance signal (Popovic, ZD & Aziz, H. Delayed electroluminescence in small-molecular-lighted organic lighting-emetics: triplet-triplet anihilation and recombination-center-mediated light-generation mechanism. J. Appl. Phys. 98, 013510-5 (2005))). Furthermore, when the shape of the residual luminescence is compared with the triplet density (shown in FIG. 7), two things are observed. First, the triplet decay time scale is similar to the EL decay, but more importantly, the approximate slope of the residual luminance decay is very similar to the slope of the triplet density squared. Yes. This observation is strong evidence that the EL residual decay is due to a bimolecular triplet-triplet annihilation reaction leading to a luminescent singlet exciton. Because triplets are much more stable than singlets with respect to the electric field due to their inherently high exciton binding energies, the density of triplet excitons is determined by applying a reverse bias pulse of 10v. Is not significantly quenched (Rothe, C., King, SM & Monkman, AP Electric-field-induced single and triple olfighting of films. Phys. Rev. B72, 085220 (2005) and Deussen, M., Scheidler, M. & Bassler, H. Electric-Field- nduced Photoluminescence Quenching in Thin-Film Light-Emitting-Diodes Based on Poly (Phenyl-P-Phenylene Vinylene), pp. .Synth.Met.73,123~129 (1995 years)).

  FIG. 8 shows the electroluminescence decay of both the device with the triplet quenching additive (dotted line) and the device without the solid line (solid line), but the effect on lifetime is obvious and T90 is improved about 5 times. And the final device lifetime is improved by more than three times. The lower panel of FIG. 5, which shows the efficiency of the device during the life test, shows that the attenuation of the two devices is remarkably similar since the additional efficiency gain due to the TTA contribution is lost early in the life test. It is clearly stated.

  The cost for extending this lifetime is a 20% reduction in EQE due to complete removal of TTA, and it is much more important to stabilize this initial decay. In a further variation, both high efficiency and long life can be achieved by utilizing a stable TTA as described above.

  Although the invention has been described with reference to specific exemplary embodiments, various modifications, changes and / or combinations of the features disclosed herein can be made from the scope of the invention as set forth in the claims below. It will be understood that it will be apparent to those skilled in the art without departing.

Claims (25)

  A composition comprising a fluorescent polymer comprising a luminescent repeat unit and a triplet acceptor unit attached to the luminescent polymer.   The composition according to claim 1, wherein the triplet accepting unit is present in an amount ranging from 0.1 to 10 mol%.   The composition of claim 1, wherein the triplet accepting unit is a triplet accepting compound mixed with the light emitting polymer and any other component or components of the composition.   The composition of claim 1, wherein the triplet accepting unit is attached to the light emitting polymer or any other component or components of the composition.   5. The composition of claim 4, comprising at least one of a hole transport material and an electron transport material, wherein the triplet accepting unit is bound to at least one of the hole transport material, the electron transport material and the light emitting material. .   5. The composition of claim 4, wherein the triplet accepting unit is attached to the light emitting polymer.   The light emitting polymer includes at least one of a light emitting repeating unit, and a repeating unit that provides electron transport and a repeating unit that provides hole transport, and a triplet accepting material includes a light emitting repeating unit, a repeating unit that provides electron transport, and a hole transport. 7. The composition of claim 6, wherein the composition is bound to at least one of the repeating units that provides   The composition according to claim 4 or 5, wherein the triplet accepting unit is a repeating unit in the main chain of the light emitting polymer, or a side chain group or a terminal group of the light emitting polymer.   9. A composition according to any preceding claim, wherein the triplet accepting unit is substituted with one or more solubilizing groups.   10. A composition according to claim 9, wherein the solubilizing group is selected from alkyl and alkoxy.   11. A composition according to any preceding claim, wherein the light emitting polymer comprises arylamine repeat units. 12. The composition of claim 11, wherein the arylamine repeat unit is a unit of formula (V).
[Wherein Ar ¹ and Ar ² are an optionally substituted aryl group or heteroaryl group, n is 1 or more, preferably 1 or 2, and R is H or a substituent] .   13. A composition according to any preceding claim, wherein the polymer comprises aryl or heteroaryl repeat units. 14. A composition according to claim 13 comprising repeating units of formula (IV).
[Wherein R ¹ and R ² are independently H or a substituent, and R ¹ and R ² can be linked to form a ring].   15. A composition according to any preceding claim, wherein the triplet receptive material is present in an amount of at least 0.1 mol%.   The composition according to claim 1, which has a photoluminescent emission peak wavelength in the range of 400 to 500 nm.   17. A composition according to any of claims 1 to 16, wherein the triplet accepting unit does not comprise perylene.   A formulation comprising a solvent and the composition of any of claims 1-17.   An organic light emitting device comprising an anode, a cathode, and a light emitting layer comprising the composition according to any one of claims 1 to 17 between the anode and the cathode.   20. A method of forming an organic light emitting device according to claim 19 comprising depositing the formulation of claim 14 and evaporating the solvent.   Use of a unit for accepting triplet excitons generated by a light emitting polymer in a composition comprising a triplet accepting unit and a light emitting polymer.   The use according to claim 21, wherein the triplet accepting unit is physically mixed with the light emitting polymer.   23. Use according to claim 22, wherein the triplet accepting unit is chemically bonded to the light emitting polymer.   24. Use according to any of claims 21 to 23, wherein the triplet accepting unit quenches triplet excitons generated by the light emitting polymer.   24. Use according to any of claims 21 to 23, wherein the triplet accepting unit mediates triplet-triplet annihilation of triplet excitons transferred from the light emitting polymer to the triplet accepting unit.