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Definitions

• the present invention is directed to the provision of Light Emitting Electrochemical Cells (LEECs) and luminescent emitter compounds for use in LEECs, in particular to Thermally Activated Delayed Fluorescence (TADF) compounds for use in LEECs or other light emitting devices.
• LEECs Light Emitting Electrochemical Cells
• TADF Thermally Activated Delayed Fluorescence
• OLEDs Organic Light Emitting Diodes
• OLEDs have come to the fore as the state-of-the-art technology for visual displays and lighting.
• OLEDs are desirable as they are light weight, flexible, provide better contrast and possess large viewing angle.
• OLEDs are also more power efficient than traditional lighting sources and thus their wide adoption can alleviate significantly the strain on current energy demand because lighting alone constitutes about 20% of energy consumption worldwide.
• the "first generation” OLEDs were based on organic fluorescent emitters whose efficiency was intrinsically capped at 25% due to only being able to recruit singlet excitons.
• the “second generation” OLEDs employed organometallic phosphorescent emitters, which harvest both singlet and triplet excitons for emission due to the enhanced intersystem crossing (ISC) mediated by the large spin-orbit coupling of heavy metals such as iridium (III) and platinum(ll).
• ISC intersystem crossing
• heavy metals such as iridium (III) and platinum(ll).
• TADF-based OLEDs address the key detracting features endemic to "second generation” OLEDs while retaining their advantages (Reference 2).
• the principle of TADF relies on a small energy gap between the lowest singlet and triplet excited states ( ⁇ 3 ⁇ ).
• the electrons in the triplet state can return to the singlet state by reverse intersystem crossing (RISC) using thermal energy, followed by radiative fluorescence (Reference 1 a).
• RISC reverse intersystem crossing
• the small AE S T IS realized by spatial separation between HOMO and LUMO to minimize the electronic repulsion between these orbitals.
• a large number of organic TADF emitters have been reported to date. They can make use of donor and acceptor moieties of various types within the molecule to achieve the desired small energy gap between the lowest singlet and triplet excited states ( ⁇ 3 ⁇ ). The majority of these molecules are based on a twisted intramolecular charge transfer (TICT) design in which the donor and acceptor moieties are designed to be nearly orthogonal to each other (References 1 a, 1 c and 3).
• LEECs Single-layer solid-state light-emitting electrochemical cells
• the emitters in LEECs are frequently ionic transition metal complexes, the most popular and highest performing class of which are cationic iridium(lll) complexes.
• the present invention provides a light-emitting electrochemical cell (LEEC) comprising: a charged organic thermally activated delayed fluorescence (TADF) species and sufficient counter ions to balance the charge on the charged organic thermally activated delayed fluorescence (TADF) species; or mixtures thereof, as emitter material.
• LEC light-emitting electrochemical cell
• the electroluminescent material of the LEEC may comprise, consists of, or consist essentially of the charged organic thermally activated delayed fluorescence (TADF) species and sufficient counter ions to balance the charge on the TADF species.
• TADF charged organic thermally activated delayed fluorescence
• organic salts organic charged TADF species and counter ions
• LEECs electroluminescent devices
• OLEDs organic charged TADF species and counter ions
• They may also be employed in applications using their photoluminescence properties.
• the salts and their other uses also constitute further aspects of the invention.
• Mixtures of charged TADF species and/or counter ions may be employed.
• Other emitter materials may additionally be employed.
• More than one TADF chromophore may be employed in the charged TADF species, for example one two or three TADF chromophores of the known types may be bonded together in a molecule and provided with charge and corresponding counter ions.
• the present invention also provides a method of producing light, the method comprising:
• TADF charged organic thermally activated delayed fluorescence
• TADF charged organic thermally activated delayed fluorescence
• an electroluminescent device including the charged organic TADF species and sufficient counter ions to balance the charge on the charged organic TADF species; or mixtures thereof as emitter material;
• the electroluminescent device may be an OLED or a LEEC for example.
• TADF species may be derived from the discrete uncharged TADF molecules that are well known in the art, for example those described in patent documents describing options for TADF chromophores: CN103694992, CN1038194423, EP02733761 , US2014/01224762, US2013/0306945, US2014/0103329, US2014/0138669, WO2012133188, WO2013180261 , WO2014013947, WO2014024446, WO201424447, WO2014034092, WO2014038417, WO2014042006, WO2014083785, WO014092083, WO2014104346, WO2014122895, WO2013092313, EP251 1360, EP2733762, US8847218, US20120241732, US2014138870, WO201 1070963, WO2013081088, WO
• the charged organic thermally activated delayed fluorescence (TADF) species does not contain a metal, although the counter ions may be metal cations if the TADF species is negatively charged. For example alkali metal cations.
• This absence of metal in the organic TADF species provides benefits in terms of cost and can avoid toxicity caused by the presence of heavy metals.
• the TADF species can provide the benefits in terms of high efficiencies found with OLED devices but in use in a LEEC, by virtue of the charge and corresponding counter ions.
• the charged organic thermally activated delayed fluorescence (TADF) species and its accompanying counter ions can present the advantage of good solubility allowing solution processing, for example inkjet type printing when fabricating display devices, especially when fabricating large displays.
• the benefits of solution processing can be employed when fabricating OLEDs or LEECs.
• Other benefits of LEECs can be realised, such as the ability to fabricate the device in air and the ability to use air stable electrodes.
• the emitter material of the light-emitting electrochemical cell may comprise, consist of, or consist essentially of a TADF species that includes a charged substituent or charged substituents.
• the charged substituents may be an integral part of the TADF species i.e. the charged substituent may exhibit or contribute to either acceptor or donor behaviour that provides the TADF effect.
• cyanobenzene moieties are used as acceptor moieties to complement carbazole moieties as donor moieties for TADF (e.g. reference 1 a)
• alternatives to cyano substituents to achieve acceptor behaviour can include carboxylate (-C0 2 " ), sulfonate (-S0 3 " ) phosphate (-P0 4 ⁇ ), quaternary ammonium (- NR 3 + ) or phosphonium (-PR 3 + ) as discussed in more detail and with reference to a particular embodiment hereafter.
• the substituents R on the nitrogen or phosphorus may be independently for each occurrence selected from H, alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10).
• An electron withdrawing group of the acceptor portion of the molecule is charged, allowing the option of using the emitter material in a LEEC.
• charged substituents may be provided as part of a donor portion of a TADF molecule.
• alkoxide -RO " or thiolate (-RS ).
• the groups R connecting to the rest of the TADF species may be selected from hydrocarbylene chains, for example C1 to C30 or even C1 to C10, that may be substituted or unsubstituted hydrocarbylene or unsaturated hydrocarbylene.
• the hydrocarbylene chain can include substituted or unsubstituted saturated, unsaturated or aromatic rings.
• the charged species may be distinct from the TADF effect but supplied as charged substituents bonding to the TADF species without contributing to or contributing substantially to the TADF effect of the chromophore.
• the emitter material of the light-emitting electrochemical cell may comprise, consist of, or consist essentially of a compound according to formula I:
• TADF is an organic thermally activated delayed fluorescence moiety
• Y is a metal free charged species bonded to the TADF moiety
• n is at least 1 ;
• A is a counter ion
• the counter ion A is oppositely charged with respect to the metal free charged species Y to balance charge.
• the charged species Y may be bonded directly to the TADF moiety.
• the charged species Y includes a charged group and a linking group that bonds the charged group to the TADF moiety.
• Use of a linking group provides a modular route to functionalization of TADF chromophores for applications in LEECs.
• a linking group or groups with an attached charged group allows the potential to use any of the wide range of TADF moieties that are already known, for example in the documents discussed above.
• metal free charged species Y is a non-metal charged group Z and optional linking group L;
• the linking group L is optional for each occurrence of groups Z. Conveniently where linking groups L are employed, one is used for each group Z. Where present the linking group L may, independently for each occurrence, comprise or consist of a hydrocarbylene chain, for example C1 to C30 or even C1 to C10, that may be substituted or unsubstituted, hydrocarbylene or unsaturated hydrocarbylene.
• the hydrocarbylene chain can include substituted or unsubstituted saturated, unsaturated or aromatic rings.
• the hydrocarbylene chain may include or consist of substituted or unsubstituted cyclopentane-1 ,3-diyl, cyclohexane-1 ,4-diyl, 1 ,4- phenylene or 4,4'-biphenylene moieties.
• Aromatic rings where present may be aryl or heteroaryl.
• linking group L may be independently substituted for each occurrence. For example once, twice, or three times, e.g. once, i.e. formally replacing one or more hydrogen atoms of the hydrocarbylene chain.
• substituents are halo (e.g. fluoro, chloro, bromo and iodo),-SF 5 , -CF 3 , -OMe,
• substituent is amino it may be NH 2 , NHR or NR 2 , where the substituents R on the nitrogen may be alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10).
• substituents R on the nitrogen may be alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10).
• similar options for substitution may be employed for other groups or substituents that may be substituted or unsubstituted as described herein.
• groups that may be substituted may be, for example, substituted once, twice, or three times, e.g. once, i.e. formally replacing one or more hydrogen atoms of the group. Examples of such substituents are halo (e.g.
• substituent is amino it may be NH 2 , NHR or NR 2 , where the substituents R on the nitrogen may be alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10).
• aryl is meant herein a radical formed formally by abstraction of a hydrogen atom from an aromatic compound.
• heteroaryl moieties are a subset of aryl moieties that comprise one or more heteroatoms, typically O, N or S, in place of one or more carbon atoms and any hydrogen atoms attached thereto.
• exemplary aryl substituents for example, include phenyl or naphthyl that may be substituted.
• Exemplary heteroaryl substituents for example, include pyridinyl, furanyl, pyrrolyl and pyrimidinyl.
• heteroaromatic rings include pyridazinyl (in which 2 nitrogen atoms are adjacent in an aromatic 6-membered ring); pyrazinyl (in which 2 nitrogens are 1 ,4-disposed in a 6-membered aromatic ring); pyrimidinyl (in which 2 nitrogen atoms are 1 ,3-disposed in a 6-membered aromatic ring); or 1 ,3,5-triazinyl (in which 3 nitrogen atoms are 1 ,3,5-disposed in a 6-membered aromatic ring).
• the linking group includes one or more rings they may be cycloalkyi they may be for example cyclohexyl or cyclopentyl rings.
• a linking group L may also include heteroatoms in a hydrocarbylene chain, for example by substituting one or more carbon atoms in the chain e.g. one, two, or three carbon atoms with any one of O, N, or S for example.
• Examples of unsubstituted hydrocarbylene chains for group L include:
• Non-metal charged groups Z may be, independently for each occurrence, positively or negatively charged. Counter ions A will have the opposite charge. For example where charged groups Z are singly charged and counter ions A are also singly charged then compounds of formula II may take either the form of formula III or of formula IV:
• groups Z are positively charged they may be, independently for each occurrence, selected from the group consisting of quaternary nitrogen cations, and quaternary phosphorus cations. Conveniently all groups Z will be the same.
• groups Z are negatively charged they may be provided with anionic substituents such as carboxylate, sulfonate, sulfinate, phosphonate, cyanide and thiocyanate.
• quaternary nitrogen groups Z include:
• R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are, independently for each occurrence, selected from the group consisting of -H, substituted or unsubstituted primary , secondary or tertiary alkyl, that may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4); substituted or unsubstituted aryl or heteroaryl, -CF 3 , - OMe, -SF 5 , -NO 2 , halo (e.g.
• the quaternary nitrogen is pyridynyl as in structure 3
• the attachment to linking group L or directly to a TADF moiety may be to a carbon rather than to the nitrogen
• the quaternary nitrogen group Z may take the form of structure 5:
• R 8 , R 9 , R 10 and R 11 bonds to a linking group L or directly to a TADF moiety and the others of R 8 , R 9 , R 10 and R 11 , independently for each occurrence selected from the group consisting of -H, substituted or unsubstituted primary , secondary or tertiary alkyl, that may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4); substituted or unsubstituted aryl or heteroaryl, -CF 3 , -OMe, - SF 5 , -N0 2 , halo (e.g.
• R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are aryl, heteroaryl or cycloalkyl and are substituted, they may be substituted with substituted or unsubstituted primary , secondary or tertiary alkyl, that may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4); substituted or unsubstituted aryl or heteroaryl, -CF 3 , -OMe, -SF 5 , -N0 2 , halo (e.g.
• quaternary nitrogen groups Z include:
• quaternary phosphorus groups Z include:
• R 1 , R 2 and R 3 have the same meaning as for the corresponding quaternary nitrogen group 1 discussed above and wherein -L indicates the position of bonding to a linking group L or directly to a TADF moiety.
• quaternary phosphorus groups Z include:
• TADF indicates the position of bonding to a linking group L or directly to a TADF moiety.
• TADF molecules are known for proposed use as emitter material in OLED devices.
• Reference 6 describes TADF materials and includes discussion of wide range of metal free TADF molecules.
• Such TADF molecules can find use as TADF core structures (chromophores) in the TADF species of compounds employed in the LEECs of the present invention.
• the TADF species will have a small difference in energy gap between singlet and triplet (Si and T ⁇ exited states that is ⁇ l OOmeV ( ⁇ 3 ⁇ ⁇ l OOmEv).
• TADF core structures are described in the references where carbazoyl dicyanobenzene (CDCB) TADF emitter molecules are described.
• carbazole (or derivative) acts as electron donor and dicyanobenzene (or derivative) as electron acceptor.
• the HOMO on the donor and the LUMO on the acceptor are localised, having minimal overlap due to distortion of carbazole out of the plane of the dicyanobenzene caused by steric hindrance. This provides a desirable small ⁇ 3 ⁇ - More generally TADF structures have an electron donor linked to an electron acceptor, typically via a conjugative linker.
• the TADF moiety in a compound used as emitter material of the invention may include more than one TADF chromophore, for example one to three TADF chromophores, such as carbazoyl dicyanobenzene (CDCB) chromophores, bonded together.
• TADF chromophore may be employed to provide the TADF effect.
• D is a donor moiety of the form
• each of A 1 , A 2 , and A 3 are acceptor groups that may be same or different and are independently selected from the group consisting of -CN, -C0 2 " , -C0 2 R * , -S0 3 " , - PO 4 -NFV -PFV, halogen (F, CI, Br, I), wherein R * and the substituents R on -NR 3 + and -PR 3 + , may be independently for each occurrence selected from H, alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10); and - CO 2 -L-Z wherein L is an optional linking group and Z a charged group, each L if present and each Z having, independently for each occurrence, the same meanings as discussed above for compounds of formulas II, III or IV;
• R 11 , R 12 , R 13 , R 14 , R 15 and R 16 represents the bonding position, either directly or via a linking group L, to a charged group Z, each L if present and each Z having, independently for each occurrence, the same meanings as discussed above for compounds of formulas II, III or IV;
• each group R 11 , R 12 , R 13 , R 14 , R 15 and R 16 not involved in bonding to an organic charged group Z is, independently for each occurrence, selected from the group consisting of -H, substituted or unsubstituted primary , secondary or tertiary alkyl, that may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4); substituted or unsubstituted aryl or heteroaryl, -CF 3 , -OMe, -SF 5 , -N0 2 , halo (e.g.
• the group is amino it may be -NH 2 , -NHR or -NR 2 , where the substituents R on the nitrogen may be alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10).
• the group is phosphine oxide or phosphine sulphide it may be selected from the group consisting of: R where the substituents R on the phosphorus may be substituted or unsubstituted alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10).
• the phosphine oxide or phosphine sulphide substituent may be para to the nitrogen of the carbazole structure i.e. one or both of R 15 may be a phosphine oxide or phosphine sulphide substituent. Conveniently where both R 15 are a phosphine oxide or phosphine sulphide substituent they may be the same.
• the phosphine oxide or phosphine sulphide substituent may have phenyl or substituted phenyl groups R on the phosphorus.
• Phosphine oxide or phosphine sulphide may be used as acceptor moieties, or part of acceptor moieties (substituents on acceptor moieties) in the structure of a TADF molecule, such as the TADF compounds described herein.
• phosphine oxide or phosphine sulphide acts to moderate the character of the donor and can therefore alter the photo physical behaviour of a TADF compound, for example resulting in a change in colour and or intensity of emission.
• Phosphine oxide and phosphine sulphide substituents may be introduced, for example, in accordance with the Scheme below which illustrates substitution on carbazole, a typical donor moiety:
• a 1 and A 2 may be the same and A 3 different, as the synthetic route is generally less complex.
• a 1 and A 2 may both be -CN and A 3 may be -F.
• moieties D may also be selected from:
• n ( ) indicates the optional presence of saturated -CH 2 - groups in the rings annelated to the benzene ring, wherein n is independently for each occurrence, 0, 1 , or 2; and optionally at least one charged group Z, optionally via a linking group L, is
• At least one charged group Z is provided on -Ar or ( ⁇ — when not provided elsewhere on the charged organic thermally activated delayed fluorescence (TADF) species.
• Substituents on -Ar and where present can include phosphine phosphine sulphide, to moderate the donor properties.
• mpound of formula V may also be selected from:
• R 11 , R 12 , R 13 , R 14 , R 15 and R 16 represents the bonding position, either directly or via a linking group L, to a charged group Z, each L if present and each Z having, independently for each occurrence, the same meanings as discussed above for compounds of formula III or IV;
• each group R 11 , R 12 , R 13 , R 14 , R 15 and R 16 not involved in bonding to an organic charged group Z is, independently for each occurrence, selected from the group consisting of -H, substituted or unsubstituted primary , secondary or tertiary alkyl, that may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4); substituted or unsubstituted aryl or heteroaryl, -CF 3 , -OMe, -SF 5 , -N0 2 , halo (e.g.
• the TADF moieties according to formula Va or formula VI bond to a charged group Z via at least one of the positions R 15 (para to the carbazole nitrogen).
• both carbazole structures in the TADF moieties of formula VI have the same substitution pattern.
• LEECs may include compounds using TADF species of formula III or formula IV that may for example take the form of formulas VII, VIII or Villa:
• R 11 , R 12 , R 13 , R 14 , R 15 and R 16 take the same meaning as discussed above, whennot involved in bonding to an organic group Z; linking group L may be present or absent and if present may take the form discussed above with respect to formula II; Z is a monocationic metal free charged group such as described herein.
• Counter ions A as described herein are provided to counter charges Z, for example mono anionic species A " such as described herein. More generally structures such as formulas VII and VIII are also contemplated where groups Z include more than one charge and/or are anionic. Counter ions A are provided to carry counter charges to those on groups Z and be provided to achieve charge balance as for general formula I. Thus counter ions A may carry more than one charge e.g.
• anionic counter ions A in compounds of the invention may be, independently for each occurrence selected from the group consisting of halide (chloride fluoride, bromide or iodide), PF 6 “ , BF 4 " , BR 4 " , OTf “ , OTs “ , SbX 6 " , NTf 2 " N0 3 " ,and C0 3 2” .
• X is halide (fluoride, chloride, bromide or iodide) and R is an aryl group, for example phenyl. Where A is halide it may conveniently be P.
• Anionic counter ions A employed may be mixed, for example a mixture of fluoride and chloride maybe employed.
• cationic counter ions A in compounds of the invention may be, independently for each occurrence selected from the group consisting of cations of first and second group elements in the periodic table and quaternary ammonium cations.
• Cationic counter ions A employed may be mixed, for example a mixture of lithium and sodium ions maybe employed.
• cationic counter ions A may be selected from Li + , K + , Na + Mg 2+ , Ca 2+ and NR 4 + .
• the groups R of the quaternary ammonium salt may be, independently for each occurrence selected from the group consisting of -H, alkyl (primary secondary or tertiary), aryl and heteroaryl.
• Alkyl, aryl or heteroaryl substituents may be saturated or unsaturated, and substituted or unsubstituted.
• Primary , secondary or tertiary alkyl may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4).
• the present invention provides a charged organic thermally activated delayed fluorescence (TADF) species and sufficient counter ions to balance the charge on the charged organic thermally activated delayed fluorescence (TADF) species as described herein.
• TADF charged organic thermally activated delayed fluorescence
• These organic salts can find use as emitter material in a light-emitting electrochemical cell (LEEC). These organic salts may be in accordance with formula I and the various other options described herein. These organic salts may be employed as or as part of the light emitting material in other devices, such as OLEDs for example.
• the charged organic thermally activated delayed fluorescence (TADF) species is metal free but may have metal counter ions as described herein.
• Examples of compounds of formulas VII and VIII include compounds of formulas IX and X:
• L is absent or is independently selected from the group consisting of :
• n is from 0 to 10 or even from 0 to 7;
• Z is independently selected from the group consisting of:
• Counter ions A may be independently for each occurrence selected from the group consisting of PF 6 " , BF 4 " and F " .
• Other counter ions a may be used as described herein. Conveniently in compounds of formula X, where there are two occurrences of L, Z, and A: both groups L are absent or are the same; both groups Z are the same; and both anions A are the same.
• Examples of such compounds include compounds of formulas XI and XII:
• cyano groups are used as substituents on cyanobenzene acceptor moieties in TADF species, typically with carbazole or related nitrogen containing species as donors.
• charged groups such as carboxylate (-C0 2 " ), sulfonate (-S0 3 " ) phosphate (-P0 4 ⁇ ), quaternary ammonium (-NR 3 + ) or phosphonium (-PR 3 + ) may be employed. This allows the charged substituents that facilitate use in a LEEC to be an integral part of the TADF species. It is also possible to have charged groups on both the acceptor and on the donor moieties of a TADF species. Suitable counter ions are used as appropriate.
• charged groups may be provided by use of a carboxylic ester function -C0 2 -L-Z on acceptor moieties.
• the carboxylic ester function provides acceptor behaviour to the acceptor moieties, L represents an optional linking group and Z a charged group. Both L and Z have the same meaning as discussed herein with respect to formulas II, III and IV.
• each of A 1 , A 2 , A 3 R 11 , R 12 and D has, independently for each occurrence the same meaning as discussed above with respect to compounds of formula V may be employed together with sufficient suitable counter ions A to balance charge.
• a further example of charged compounds in accordance with the invention is provided by charged derivatives of the compound XVI, where sulphone (-S0 2 -) provides acceptor behaviour,
• donor moieties D independently for each occurrence take the same meaning as discussed above with respect to compounds of formula V; R 17 and R 18 independently for each occurrence take the same meaning as discussed above as substituents R 11 and R 12 in compounds of formula V; and at least one charged group Z is provided: each group Z being provided either directly or via a linking group L at one of the occurrences of R 17 and R 18 or attached to a donor moiety D; wherein each L if present and each Z has, independently for each occurrence, the same meanings as discussed above for compounds of formulas II, III or IV.
• Examples of charged derivatives of formula XVI include charged derivatives of formula XVIa or XVIb
• R 13 , R 14 , R 15 , R 16 , R 17 and R 18 represents the bonding position, either directly or via a linking group L, to a charged group Z, each L if present and each Z having, independently for each occurrence, the same meanings as discussed above for compounds of formula III or IV;
• each group of R 13 , R 14 , R 15 , R 16 ' R 17 and R 18 not involved in bonding to an organic charged group Z is, independently for each occurrence, selected from the group consisting of -H, substituted or unsubstituted primary , secondary or tertiary alkyl, that may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4); substituted or unsubstituted aryl or heteroaryl, -CF 3 , -OMe, -SF 5 , -N0 2 , halo (e.g.
• the TADF moieties according to formula XVIa or formula XVIb bond to a charged group Z, via at least one of the positions R 15 (para to the carbazole or diphenylamine nitrogen).
• both carbazole or diphenylamine structures in the TADF moieties of formula XVIa or of formula XVIb have the same substitution pattern.
• the charged TADF moieties of formula XVIa or of formula XVIb may be according to formula XVIc or formula XVId:
• groups Z are the charged groups bonded to the rest of the molecule by optional linkages L as described herein and each group of R 13 , R 14 , R 15 , R 16 ⁇ R 17 and R 18 depicted is not involved in bonding to an organic charged group Z.
• Examples of compounds of formula XVI include compounds of formula XVII and of formula XX:
• cationic counter ion or counter ions A used to balance the charges.
• cationic counter ion or counter ions For example potassium ions.
• Synthesis of charged organic thermally activated delayed fluorescence (TADF) species and sufficient counter ions to balance the charge on the charged organic thermally activated delayed fluorescence (TADF) species can be carried out by a skilled person. These salts may be made by modification of the TADF species to provide charged species and the desired counter ion or counter ions used in the synthetic route to the charged species or introduced by suitable ion exchange procedures.
• the cyano groups on dicyanobenzene acceptor moieties of TADF molecules may be modified to provide carboxylate, carboxylic acid, or carboxylic ester groups.
• carbazole or similar donor moieties of TADF molecules may be modified before and/or after synthesis of the TADF molecule to provide a charged group or groups.
• Examples of compounds of the invention therefore include compounds of formulas XVIII, XIX, XXI, XXII and XXIII:
• the light-emitting electrochemical cell (LEEC) of the invention uses a charged organic thermally activated delayed fluorescence (TADF) species and sufficient counter ions to balance the charge on the charged organic thermally activated delayed fluorescence (TADF) species as emitter material.
• TADF charged organic thermally activated delayed fluorescence
• TADF charged organic thermally activated delayed fluorescence
• a typical LEEC of the invention may comprise two electrodes with a layer comprising the charged organic thermally activated delayed fluorescence (TADF) species and sufficient counter ions to balance the charge as the organic semiconductor layer that exhibits electroluminescence.
• the luminescent layer may consist of or consist essentially of the charged organic thermally activated delayed fluorescence (TADF) species and counter ions.
• TADF charged organic thermally activated delayed fluorescence
• ionic liquids such as 1 -butyl- 3-methylimidazolium hexafluorophosphate [Bmim][PF 6 ] may be employed to provide further ions.
• Other options include a host guest system where the electroluminescent material is dispersed in a matrix. For example a matrix of a charged organic material.
• D, R 11 , R 12 , A 1 , A 2 , and A 3 have the same meaning as discussed above, and with suitable counter ions to balance the charges on group(s) Z. and/or groups A 1 , A 2 , and A 3 if they carry charges.
• the compound of formula V may be provided without charged groups Z and corresponding counter ions (and optional linking groups L), even if none of A 1 , A 2 , and A 3 . are charged.
• compounds of formula V are TADF molecules they may be used in light emitting devices such as OLEDs, when charged or when not charged.
• the invention includes a light emitting device for example an Organic Light Emitting Diode, comprising a compound of formula V.
• a light emitting device for example an Organic Light Emitting Diode, comprising a compound of formula V.
• the invention provides a compound according to formula XIV: wherein each group R 11 , R 12 , R 13 , R 14 , R 15 and R 16 is, independently for each occurrence, selected from the group consisting of -H, substituted or unsubstituted primary , secondary or tertiary alkyl, that may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4); substituted or unsubstituted aryl or heteroaryl, -CF 3 , - OMe, -SF 5 , -N0 2 , halo (e.g.
• Compounds of formula XIV exhibit good TADF behaviour and can be used for devices such as OLEDs.
• the invention also includes a light emitting device for example an Organic Light Emitting Diode, comprising a compound of formula XIV.
• the present invention provides a compound of formula Xlllc:
• R * of acceptor groups, -C0 2 R * are independently for each occurrence selected from H, alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 - C20 or even C1 -C10); and -C0 2 -L-Z wherein L is an optional linking group and Z a charged group, each L if present and each Z having, independently for each occurrence, the same meanings as discussed above for compounds of formulas II, III or IV; and
• R 11 , R 12 and D have, independently for each occurrence the same meaning as discussed above with respect to compounds of formula V, whether charged or uncharged.
• R * may be alkyl or H.
• the compound according to formula Xlllc When at least one charged group Z is present the compound according to formula Xlllc has suitable counter ions to balance the charges. Alternatively the compound according to formula Xlllc may be uncharged.
• compounds of formula Xlllc are TADF molecules they may be used in light emitting devices such as OLEDs, when charged or when not charged.
• the invention includes a light emitting device for example an Organic Light Emitting Diode, comprising a compound of formula Xlllc.
• R * of acceptor groups, -C0 2 R * are independently for each occurrence selected from -H, alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 - C20 or even C1 -C10) and -C0 2 -L-Z wherein L is an optional linking group and Z a charged group, each L if present and each Z having, independently for each occurrence, the same meanings as discussed above for compounds of formulas II, III or IV; and the donor moieties are carbazole derivatives as described above with respect to formula VI.
• none of the substituents R * , R 11 , R 12 , R 13 , R 14 , R 15 and R 16 may carry a charged group Z.
• R * is selected from the group consisting of -H, alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 - C20 or even C1 -C10); and each R 11 , R 12 , R 13 , R 14 , R 15 and R 16 may be selected from the group consisting of: of -H, substituted or unsubstituted primary , secondary or tertiary alkyl, that may be cyclic and may be unsaturated (for example C1 -C10 or even C1 -C4); substituted or unsubstituted aryl or heteroaryl, -CF 3 , -OMe, -SF 5 , -N0 2 , halo (e.g.
• substituent is amino it may be NH 2 , NHR or NR 2 , where the substituents R on the nitrogen may be alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10).
• R on the nitrogen may be alkyl, aryl or heteroaryl (for example substituted or unsubstituted C1 -C20 or even C1 -C10).
• An example of a compound of formula XXIV that carries charge at both the carboxylic acceptor groups and the donor moieties is formula XXV:
• Figure 1 shows absorption and emission spectra of TADF compounds
• Figures 2a and 2b show electroluminescent behaviour of light emitting electrochemical cells.
• Compound 4 was obtained by S N 2 reaction of sodium imidazolate with 3 followed by silyl deprotection using sodium hydride in a one-pot fashion.
• the HOMO of XI (-5.93 eV) is slightly lower than that of XII (-5.87 eV) due to the presence of electron-withdrawing fluorine atom.
• the LUMO of XI (-2.92 eV) is slightly higher than that of XII (-2.99 eV), which is due to the increased conjugation imparted by the second carbazole moiety that lowers the LUMO in XII.
• FIG 1 the normalised absorption spectra in aerated acetonitrile for XI (line A) and XII (line B) are shown - at 298K. Also shown are the corresponding emission spectra for XI in deaerated acetonitrile (line A1 ) and thin film (line A2). Also shown are the corresponding emission spectra for XII in deaerated acetonitrile (line B1 ) and thin film (line B2).
• the electrochemical and emission data for XI and XII are summarised in Table 1 below.
• a em is the wavelength of maximum emission
• ⁇ is the photo luminescence quantum yield
• T E is the fluorescence lifetime
• E H OMO and E LU MO are the energy levels obtained from cyclic voltammetry with ⁇ being the difference.
• the emission in MeCN solution and in a thin solid film for both in XI and XII is broad and unstructured, characteristic of CT (charge transfer) emission; the excitation and absorption spectra matched, pointing to a high level of purity.
• the emission spectra in MeCN are red-shifted by about 30-40 nm, respectively, compared to emission in the thin film.
• the thin film was deposited from a solution of acetonitrile in a film without any dopants or other additives present.
• XI and XII are much brighter with ⁇ ⁇ values of 9.1 and 35.5%, respectively, under aerated conditions.
• biexponential decay in the emission lifetimes is now observed, including both a short component and a long microsecond component, a hallmark of TADF emission.
• Diphenylamine 12 is converted to the imidazole derivative 13 by a similar route to that shown for carbazole in Scheme 1 above. Reaction of 13 with bis(4-fluorophenyl) sulphone affords intermediate 14. Methylation with iodomethane and anion metathesis with saturated NH 4 PF 6 solution provides the product XX.
• the compounds of the invention can be utilised in the fabrication of a LEEC.
• LEECs were prepared on top of a patterned indium tin oxide (ITO) coated glass substrate. Prior to the deposition of the emitting layer, a 80nm of PEDOT:PSS was coated in order to increase the reproducibility of the cells.
• ITO indium tin oxide
• the emitting layer (100 nm) was prepared by spin-coating of an acetonitrile solution consisting of the emitting compound alone or with the addition of an ionic liquid (IL) 1 -butyl-3-methylimidazolium hexafluorophosphate [Bmim][PF 6 ] at a molar ratio of 4:1 .
• IL ionic liquid
• the devices were transferred into an inert atmosphere glovebox.
• a layer of 70 nm of aluminium that serves as the top electrode was thermally evaporated in a high vacuum chamber integrated in the inert atmosphere glovebox.
• NS25 In order to determine the performance of the LEECs, the devices were operated using a block-wave pulsed current driving method (1000Hz and 50% of duty cycle) at different average current densities of 10, 25 and 50 Am "2 . This operational mode was selected over constant voltage mode as it decreases the turn-on time and leads to a more sustained behaviour versus time.
• the luminance and average voltage are depicted in Figures 2 for LEECs using XII and XII : [Bmim][PF 6 ] 4:1 mixture as the component(s) for the light-emitting layer.
• Figure 2a shows the luminance over time of the LEEC using XII : [Bmim][PF 6 ] 4:1 mixture as the luminescent layer. The average voltage with time is shown on the insert graph.
• Figure 2b shows similar graphs for the LEEC using XII only as the luminescent layer.
• the table shows luminance (Lum max ), power conversion efficiency (PCE max ), external quantum efficiency (EQE max ) and photo luminescent quantum yield (PLQY) for the two LEECs tested.
• the electroluminescent (EL) spectra for these LEECs are similar to those of the photo luminescent spectra of figure 1 . All cells emitted homogenously from the active area. The spectra feature an unstructured green emission centred at 538 nm (CIE coordinates: 0.35, 0.57 ).

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