Compound

Abstract

[Refer to original abstract doc for image] Disclosed are compounds of formulae (I) and (II): Al - (B l )x l - (D I )y 1 - (B l )x 2 - Al Al - (B2 )x 5 - (D 2 )y 2 - (B3 )x 3 - A2 - (B 3 )x4 - (D 3 )y

Description

BACKGROUND Embodiments of the present disclosure relate to electron-accepting compounds and more specifically compounds suitable for use as an electron-accepting material in a photoresponsive device. An organic photodetector may contain a photoactive layer of a blend of an electrondonating material and an electron-accepting material between an anode and a cathode. Known electron-accepting materials include fullerenes and non-fullerene acceptors (NFAs). CN116425768 discloses compounds of formula (I): WO2024 / 094804 discloses compounds containing an electron-accepting group of formula (HI): (HI) wherein: each R1 is independently a substituent; R2 and each R3 is H or a substituent; J is C=O, C=S, S=O, SO2, NR11 or CR12R13 wherein R11 is CN or COOR40 and R40 is H or a substituent and R12 and R13 are each independently CN, CF3 or COOR40; and either each Z1 is N and each Z2 is CR4, or each Z1 is CR4 and each Z2 is N wherein each R4 is independently H or a substituent. Tengfei Li et al, "Sensitive photodetection below silicon bandgap using quinoid-capped organic semiconductors", Science Advances, vol. 9 issue 13, 2023 discloses quinoid-terminated compounds for near-infrared photodetectors. Yi Zhang et al, "Sensitive SWIR Organic Photodetectors with Spectral Response Reaching 1.5 pm", Advanced Materials, https: / / doi.org / 10.1002 / adma.202406950 discloses an organic photodetector containing NFA "Y-QC4F" having a difluoro-substituted quinoid terminal group (QC-2F). SUMMARY The present inventors have found that providing a non-fullerene acceptor (NFA) with certain electron-accepting end-groups having an N-containing electron-withdrawing heteroaromatic group can deepen the HOMO of such an NFA as compared to compounds in which such a heteroaromatic group is not present. This may improve compatibility of the NFA with an electron-donor having a deep-lying HOMO, thereby improving photoinduced hole transfer from the NFA to the electron donor. The present inventors have also found that such an N-containing electron-withdrawing heteroaromatic group may increase the absorption wavelength of such an NFA as compared to compounds in which such a heteroaromatic group is not present. Accordingly, in a first aspect the present disclosure provides compounds of formula (I) or (II): A1 - (B1)x1 - (D1)y1 - (B1)x2 - A1 (I) A1 - (B2)x5 - (D2)y2 - (B3)x3- A2 - (B3)x4 - (D3)y3 - (B2)x6 - A1 (II) wherein: A2 is a divalent heteroaromatic electron-accepting group; D1, D2 and D3 independently in each occurrence is an electron-donating group; B1, B2, and B3 independently in each occurrence is a bridging group; x1 - x6 are each independently 0, 1, 2 or 3; y1, y2 and y3 are each independently at least 1; each A1 is an electron-accepting group and at least one A1 is a group of formula (III), (IV) or (V): (HI) (IV) (V) wherein: each R1 is independently a substituent; R2 is H or a substituent; Ar1 is selected from benzene; 1,2,3-triazole; 1,25-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N and Ar1 is unsubstituted or substituted with one or more substituents; -- represents a point of attachment of A1; Z^Z6 independently in each occurrence is selected from N and CR4 wherein R4 in each occurrence is H or a substituent; if Ar1 is benzene and A1 is the group of formula (III) then at least one of Z1 and Z2 is N; if Ar1 is benzene and A1 is the group of formula (IV) then at least one of Z3 and Z4 is N; and if Ar1 is benzene and A1 is the group of formula (V) then at least one of Z5 and Z6 is N. Optionally, Ar1 is benzene. In the case where Ar1 is benzene, optionally: if A1 is a group of formula (III) then Z1 and Z2are each N; if A1 is a group of formula (IV) then Z3 and Z4are each N; and if A1 is a group of formula (V) then Z5and Z6are each N. Optionally, Ar1 is 1,4-diazine and: if A1 is a group of formula (III) then Z1 and Z2are each CR4; if A1 is a group of formula (IV) then Z3 and Z4 are each CR4; if A1 is a group of formula (V) then Z5 and Z6 are each CR4; Optionally, at least one A1 is a group of formula (III). Optionally, each A1 is a group of formula (III), (IV) or (V). Optionally, each A1 is the same. Optionally, each R1 is independently selected fromCN, CF3 and COOR40 wherein R40in each occurrence is H or a substituent. Optionally, Ar1 is substituted with at least one electron-withdrawing group. Optionally, the at least one electron-withdrawing group is selected from Br, Cl, F, CN, C1-12fluoroalkyl and COOR15 wherein R15 is a C1-20 hydrocarbyl group. Optionally, each R4 is independently selected from H or an electron-withdrawing group. The present disclosure provides a composition comprising an electron-donating material and an electron-accepting material wherein the electron accepting material is a compound as described herein. The present disclosure provides an organic electronic device comprising an active layer comprising a compound or composition as described herein. Optionally, the organic electronic device is an organic photoresponsive device comprising a bulk heterojunction layer disposed between an anode and a cathode and wherein the bulk heterojunction layer comprises a composition as described herein. Optionally, the organic photoresponsive device is an organic photodetector. The present disclosure provides a photosensor comprising a light source and an organic photodetector as described herein wherein the organic photodetector is configured to detect light emitted from the light source. Optionally, the light source emits light having a peak wavelength of greater than 900 nm. The present disclosure provides a formulation comprising a compound or composition as described herein dissolved or dispersed in one or more solvents. The present disclosure provides a method of forming an organic electronic device as described herein wherein formation of the active layer comprises deposition of a formulation as described herein onto a surface and evaporation of the one or more solvents. DESCRIPTION OF DRAWINGS The disclosed technology and accompanying figures describe some implementations of the disclosed technology. Figure 1 illustrates an organic photoresponsive device according to some embodiments. The drawings are not drawn to scale and have various viewpoints and perspectives. The drawings are some implementations and examples. Additionally, some components and / or operations may be separated into different blocks or combined into a single block for the purposes of discussion of some of the embodiments of the disclosed technology. Moreover, while the technology is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the technology to the particular implementations described. On the contrary, the technology is intended to cover all modifications, equivalents, and alternatives falling within the scope of the technology as defined by the appended claims. DETAILED DESCRIPTION Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. References to a layer "over" another layer when used in this application means that the layers may be in direct contact or one or more intervening layers may be present. References to a layer "on" another layer when used in this application means that the layers are in direct contact. References to a specific chemical element include any isotope of that chemical element unless specifically stated otherwise. The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements. These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims. To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details. The present disclosure provides compounds of formulae (I) and (II): A1 - (B1)x1 - (D1)y1 - (B^x2 - A1 (I) A1 - (B2)x5 - (D2)y2 - (B3)x3- A2 - (B3)x4 - (D3)y3 - (B2)x6 - A1 (II) A1 is a monovalent electron-accepting group. A2 is a divalent heteroaromatic electron-accepting group. D1, D2 and D3 independently in each occurrence is an electron-donating group. B1, B2, and B3 independently in each occurrence is a bridging group. x1 - x6 are each independently 0, 1, 2 or 3, preferably 0 or 1. In some embodiments, x1 and x2 are the same and are preferably both 0 or both 1. In some embodiments, one of x1 and x2 is 0 and the other of xl and x2 is 1. x3 and x4 are preferably the same and are preferably both 0 or both 1, more preferably both 0. x5 and x6 are preferably the same and are preferably both 0 or both 1. y1, y2 and y3 are each independently at least 1, preferably 1, 2 or 3. y2 and y3 are preferably the same. Each of the electron-accepting groups A1 and A2 as a lowest unoccupied molecular orbital (LUMO) level that is deeper (i.e., further from vacuum) than the LUMO of (D^y1 in the case of formula (I), and deeper than both of (D2)y2 and (D3)y3 in the case of formula (II), preferably at least 1 eV deeper. The LUMO levels of electron-accepting groups and electron-donating groups may be as determined by modelling the LUMO level of these groups, in which each bond to adjacent group is replaced with a bond to a hydrogen atom. Modelling may be performed using Gaussian09 software available from Gaussian using Gaussian09 with B3LYP (functional) and 6-31G(D)* (Basis set). In some embodiments, the compound of formula (I) or (II) has an absorption peak greater than 900 nm, optionally greater than 1100 nm, optionally greater than 1250 nm. The absorption peak is suitably less than 1500 nm. At least one A1, preferably each A1, is a group of formula (III), (IV) or (V): (HI) (IV) (V) Each R1 is independently a substituent. Preferably, each R1 is independently selected from CN; Ci-6 fluoroalkyl, preferably CF3; and COOR40 wherein R40 in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. CN is preferred. A C1-20 hydrocarbyl group as described anywhere herein may be selected from phenyl which may be unsubstituted or substituted with one or more substituents selected from C1-12 alkyl and a linear, branched or cyclic C1-20alkyl. R2 is H or a substituent. Preferably, R2 is H, F, Cl, CN, NO2, C1-20 alkyl or C1-20 alkoxy wherein one or more H atoms of the C1-20 alkyl or C1-20 alkoxy may be replaced with F. — represents a point of attachment of A1 to a donor group D or, if present, to a bridging group B. Ar1 is selected from benzene; 1,2,3-triazole; 1,2,5-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N. Ar1 may be selected from: wherein R5 independently in each occurrence is H or a substituent and R6 is H or a substituent. R5 independently in each occurrence is preferably H; C1-20 alkyl wherein one or more non-adjacent C atoms of C2-20 alkyl may be replaced with O, S or NR6; and an electronwithdrawing group, more preferably H or an electron-withdrawing group. Preferred electron-withdrawing groups are F, Cl, Br, CN, C1-12 fluoroalkyl and COOR15 wherein R15 is a C1-20 hydrocarbyl group. Optionally, each R6 of any NR6 or PR6 described anywhere herein is independently selected from H; C1-20 alkyl wherein one or more non-adjacent C atoms other than the C atom bound to N or P may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; and phenyl which is unsubstituted or substituted with one or more substituents, optionally one or more C1-12 alkyl groups wherein one or more non-adjacent C atoms of the alkyl may be replaced with 0, S, COO or CO and one or more H atoms of the alkyl may be replaced with F. Preferably, R6 is H, C1-20 alkyl, and phenyl which may be unsubstituted or substituted with one or more C1-6 alkyl groups. In the case where A1 is a group of formula (III), Z1 and Z2 are each independently selected from CR4 and N wherein R4 is H or a substituent with the proviso that at least one of Z1 and Z2 is N if Ar1 is benzene. In some embodiments, Z1 and Z2 are CR4 and Ar1 is selected from 1,2,3-triazole; 1,2,5-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N. In some embodiments, one of Z1 and Z2 is N and the other of Z1 and Z2 is CR4 or both Z1 and Z2 are N, and Ar1 is selected from benzene; 1,2,3-triazole; 1,2,5-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N. In the case where A1 is a group of formula (IV), Z3 and Z4 are each independently selected from CR4 and N wherein R4 is H or a substituent with the proviso that at least one of Z3 and Z4 is N if Ar1 is benzene. In some embodiments, Z3 and Z4 are CR4 and Ar1 is selected from 1,2,3-triazole; 1,2,5-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N. In some embodiments, one of Z3 and Z4 is N and the other of Z3 and Z4 is CR4 or both Z3 and Z4 are N, and Ar1 is selected from benzene; 1,2,3-triazole; 1,2,5-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N. In the case where A1 is a group of formula (V), Z5 and Z6 are each independently selected from CR4 and N wherein R4 is H or a substituent with the proviso that at least one of Z5 and Z6 is N if Ari is benzene. In some embodiments, Z5 and Z6 are CR4 and Ar1 is selected from 1,2,3-triazole; 1,2,5-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N. In some embodiments, one of Z5 and Z6 is N and the other of Z3 and Z4 is CR4 or both Z5 and Z6 are N, and Ar1 is selected from benzene; 1,2,3-triazole; 1,2,5-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N. Each R4 is independently H or a substituent, optionally H or a substituent selected from H, Ci-20 alkyl wherein one or more non-adjacent, non-terminal C atoms of C2-20 alkyl may be replaced with O, S, NR6, CO or COO; and an electron-withdrawing group. Preferred electron-withdrawing groups are F, Cl, Br, CN, C1-12 fluoroalkyl and COOR15 wherein R15 is a C1-20hydrocarbyl group. Preferably, R4 is H. By "non-terminal C atom" of an alkyl group as used anywhere herein means a C atom other than the C atom of the methyl group at the end of an n-alkyl chain or the C atoms of the methyl groups at the ends of a branched alkyl chain. If a C atom of an alkyl group as described anywhere herein is replaced with another atom or group, the replaced C atom may be a terminal C atom of the alkyl group or a nonterminal C-atom. If a terminal C atom of a group as described anywhere herein is replaced then the resulting group may be an anionic group comprising a countercation, e.g., an ammonium or metal countercation, preferably an ammonium or alkali metal cation. A C atom of an alkyl substituent group which is replaced with another atom or group as described anywhere herein is preferably a non-terminal C atom, and the resultant substituent group is preferably non-ionic. Exemplary groups of formula (III) include, without limitation: Each of which may be unsubstituted or substituted with one or more substituents. Exemplary groups of formula (IV) include, without limitation: Exemplary groups of formula (V) include, without limitation: The A1 groups of a compound of formula (I) or the A1 groups of a compound of formula (II) may be the same or different, preferably the same. Acceptor Unit A2 A2 of compounds of formula (II) is preferably a fused heteroaromatic group comprising at least 2 fused rings, preferably at least 3 fused rings. In some embodiments, A2 of formula (II) is a group of formula (VIII): (VIII) wherein: Ar2 is an aromatic or heteroaromatic group; and Y is O, S, NR6 or R7-C=C-R7 wherein R7 in each occurrence is independently H or a substituent wherein two substituents R7 may be linked to form a monocyclic or polycyclic ring; and R6 is H or a substituent. In the case where A2 is a group of formula (VIII), Ar2 may be a monocyclic or polycyclic heteroaromatic group which is unsubstituted or substituted with one or more R9 groups wherein R9 in each occurrence is independently a substituent. Preferred R9 groups are selected from F; CN; N02; C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR17 wherein R17 is a C1-12 hydrocarbyl, COO or CO and one or more H atoms of the alkyl may be replaced with F; an aromatic or heteroaromatic group, preferably phenyl, which is unsubstituted or substituted with one or more substituents; and a group selected from W40 wherein Z40, Z41, Z42 and Z43 are each independently CR13 or N wherein R13 in each occurrence is H or a substituent, preferably a C1-20 hydrocarbyl group; Y40 and Y41 are each independently O, S, NX71 wherein X71 is CN or COOR40; or CX60X61 wherein X60 and X61 is independently CN, CF3 or COOR40; W40 and W41 are each independently 0, S, NX71 or Cx60X61 wherein X60 and X61 is independently CN, CF3 or COOR40; and R40 in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. Exemplary substituents of an aromatic or heteroaromatic group R9 are F, CN, NO2, and C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR7, COO or CO and one or more H atoms of the alkyl may be replaced with F. R17as described anywhere herein may be, for example, C1-12 alkyl, unsubstituted phenyl; or phenyl substituted with one or more C1-6 alkyl groups. Exemplary monocyclic heteroaromatic groups Ar2 are oxadiazole, thiadiazole, triazole and 1,4-diazine which is unsubstituted or substituted with one or more substituents. Thiadiazole is particularly preferred. Exemplary polycyclic heteroaromatic groups Ar2 are groups of formula (V): (V) X1 and X2, are each independently selected from N and CR10 wherein R10 is H or a substituent, optionally H or a substituent R9 as described above. X3, X4, X5 and X6 are each independently selected from N and CR10 with the proviso that at least one of X3, X4, X5 and X6 is CR10. Z is selected from O, S, SO2, NR6, PR6, C(R10)2, Si(R10)2 C=0, C=S and C=C(R5)2 wherein R10 is as described above; R6 is H ora substituent; and R5in each occurrence is an electronwithdrawing group. Preferably, each R5 is CN, COOR40; or CX60X61 wherein X60and X61is independently CN, CF3 or COOR40 and R40 in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. A2 groups of formula (VIII) are preferably selected from groups of formulae (Villa) and (VUIb): For compounds of formula (VUIb), the two R7 groups may or may not be linked. Preferably, when the two R7 groups are not linked each R7 is independently selected from H; F; CN; NO2; C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR7, CO, COO, NR6, PR6, or Si(R10)2 wherein R10 and R6 are as described above and one or more H atoms may be replaced with F; and aryl or heteroaryl, preferably phenyl, which may be unsubstituted or substituted with one or more substituents. Substituents of the aryl or heteroaryl group may be selected from one or more of F; CN; NO2; and C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, CO, COO and one or more H atoms may be replaced with F. Preferably, when the two R7 groups are linked, the group of formula (VUIb) has formula (VIIIb-1) or (VIIIb-2): (VIIIb-1) (VIIIb-2) Ar3 is an aromatic or heteroaromatic group, preferably benzene, which is unsubstituted or substituted with one or more substituents. Ar3 may be unsubstituted or substituted with one or more substituents R9 as described above. X is selected from O, S, SO2, NR6, PR6, C(R10)2, Si(R10)2 C=0, C=S and C=C(R7)2 wherein R10, R6 and R7 are as described above. Exemplary electron-accepting groups of formula (VIII) include, without limitation: wherein Ak1 is a C1-20alkyl group Divalent electron-accepting groups A2 other than formula (VIII) are optionally selected from formulae (IVa)-(IVj) (IVa) (IVb) (IVc) (IVd) (IVi) YA1 is 0 or S, preferably S. R23 in each occurrence is a substituent, optionally C1-12 alkyl wherein one or more non-adjacent C atoms other than the C atom attached to Z3 may be replaced with O, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F. R25 in each occurrence is independently H; F; CN; NO2; C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F; an aromatic group, optionally phenyl, which is unsubstituted or substituted with one or more substituents selected from F and C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR6, COO or CO; or w40 wherein Z40, Z41, Z42 and Z43 are each independently CR13 or N wherein R13 in each occurrence is H or a substituent, preferably a C1-20 hydrocarbyl group; Y40 and Y41 are each independently O, S, NX71 wherein X71 is CN or COOR40; or CX60X61 wherein X60 and X61 is independently CN, CF3 or COOR40; W40 and W41 are each independently 0, S, NX71 wherein X71 is CN or COOR40; or CX60X61 wherein X60and X61 is independently CN, CF3 or COOR40; and R40in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. Z3 is N or P. T1, T2 and T3 each independently represent an aryl or a heteroaryl ring, optionally benzene, which may be fused to one or more further rings. Substituents of T1, T2 and T3, where present, are optionally selected from non-H groups of R25. In a preferred embodiment, T3 is benzothiadiazole. R12 in each occurrence is a substituent, preferably a C1-20 hydrocarbyl group. Ar5 is an arylene or heteroarylene group, optionally thiophene, fluorene or phenylene, which may be unsubstituted or substituted with one or more substituents, optionally one or more non-H groups selected from R25. Bridging units Bridging units B1, B2 and B3 are preferably each selected from vinylene, arylene, heteroarylene, arylenevinylene and heteroarylenevinylene wherein the arylene and heteroarylene groups are monocyclic or bicyclic groups, each of which may be unsubstituted or substituted with one or more substituents. Optionally, B1, B2 and B3 are selected from vinylene and arylene or heteroarylene units of formulae (Via) - (Vin): wherein R6 is H or a substituent; R8 in each occurrence is independently H or a substituent, preferably H or a substituent selected from F; CN; NO2; C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR6, COO or CO and one or more H atoms of the alkyl may be replaced with F; and phenyl which is unsubstituted or substituted with one or more substituents. R8 groups of formulae (Via), (VIb) and (Vic) may be linked to form a bicyclic ring, for example thienopyrazine. R8 is preferably H, C1-20alkyl or C1-19alkoxy. Electron-Donating Groups D1, D2 and D3 Electron-donating groups preferably are fused aromatic or heteroaromatic groups, more preferably fused heteroaromatic groups containing three or more rings. Particularly preferred electron-donating groups comprise fused thiophene or furan rings, optionally fused rings containing thiophene or furan rings and one or more rings selected from benzene, cyclopentadiene, tetrahydropyran, tetrahydrothiopyran and piperidine rings, each of said rings being unsubstituted or substituted with one or more substituents. Exemplary electron-donating groups D1, D2 (Vllt): and D3 include groups of formulae (Vlla)- (Viif) (vug) (Vllh) (VIII) (Vllk) (VIII) (VII m) R6 (VIIo) (VHq) (Viit) wherein YA in each occurrence is independently O, S or NR.55, YA1 in each occurrence is independently 0 or S; XA is C or Si; ZA in each occurrence is 0, CO, S, NR55 or C(R54)2; R51, R52 R54 and R55 independently in each occurrence is H or a substituent; R53 independently in each occurrence is a substituent; and Ar4 is an optionally substituted monocyclic or fused heteroaromatic group. Optionally, R51 and R52 independently in each occurrence are selected from H; F; C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR7, COO or CO and one or more H atoms of the alkyl may be replaced with F; and an aromatic or heteroaromatic group Ar3 which is unsubstituted or substituted with one or more substituents. In some embodiments, Ar3 may be an aromatic group, e.g., phenyl. Ar4 is preferably selected from optionally substituted oxadiazole, thiadiazole, triazole, and 1,4-diazine. In the case where Ar4 is 1,4-diazine, the 1,4-diazine may be fused to a further heterocyclic group, optionally a group selected from optionally substituted oxadiazole, thiadiazole, triazole, 1,4-diazine and succinimide. The one or more substituents of Ar3, if present, may be selected from C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR7, COO or CO and one or more H atoms of the alkyl may be replaced with F. Preferably, each R54 is selected from the group consisting of: H; F; linear, branched or cyclic C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced by O, S, NR7, CO or COO wherein R17 is a C1-12 hydrocarbyl and one or more H atoms of the C1-20 alkyl may be replaced with F; and a group of formula (Ak)u-(Ar7)v wherein Ak is a C1-20 alkylene chain in which one or more non-adjacent C atoms may be replaced with 0, S, NR7, CO or COO; u is 0 or 1; Ar7 in each occurrence is independently an aromatic or heteroaromatic group which is unsubstituted or substituted with one or more substituents; and v is at least 1, optionally 1, 2 or 3. Substituents of Ar7, if present, are preferably selected from F; Cl; NO2; CN; and C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR7, CO or COO and one or more H atoms may be replaced with F. Preferably, Ar7 is phenyl. Preferably, each R51 is H. Optionally, R53 independently in each occurrence is selected from C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR7, COO or CO and one or more H atoms of the alkyl may be replaced with F; and phenyl which is unsubstituted or substituted with one or more substituents, optionally one or more C1-12 alkyl groups wherein one or more non-adjacent C atoms may be replaced with 0, S, NR7, COO or CO and one or more H atoms of the alkyl may be replaced with F. Preferably, R55 as described anywhere herein is H or C1-30 hydrocarbyl group. In a preferred embodiment, D1, D2 and D3 are each independently a group of formula (Vila). Exemplary groups of formula (Vila) include, without limitation: wherein He in each occurrence is independently a C1-20hydrocarbyl group, e.g., C1-20alkyl, unsubstituted aryl, or aryl substituted with one or more C1-12 alkyl groups. The aryl group is preferably phenyl. In some embodiments, y1 of formula (I) is 1. In some embodiments, y2 and y3 of formula (II) are each 1. In some embodiments, y1 of formula (I) or at least one of y2 and y3 of formula (II) is greater than 1. In these embodiments, the chain of D1, D2 or D3 groups, respectively, may be linked in any orientation. For example, in the case where D1 is a group of formula (Vila) and y1 is 2, -[D^yi- may be selected from any of: Exemplary compounds of formula (I) include, without limitation: CeHi3 CeHi3 Cl Electron-donating material A bulk heterojunction layer as described herein comprises an electron-donating material and a compound of formula (I) or (II) as described herein. Exemplary donor materials are disclosed in, for example, WO2013 / 051676, the contents of which are incorporated herein by reference. The electron-donating material may be a non-polymeric or polymeric material. In a preferred embodiment the electron-donating material is an organic conjugated polymer, which can be a homopolymer or copolymer including alternating, random or block copolymers. The conjugated polymer is preferably a donor-acceptor polymer comprising alternating electron-donating repeat units and electron-accepting repeat units. Preferred are non-crystalline or semi- crystalline conjugated organic polymers. Further preferably the electron-donating polymer is a conjugated organic polymer with a low bandgap, typically between 2.5 eV and 1.5 eV, preferably between 2.3 eV and 1.8 eV. Optionally, the electron-donating polymer has a HOMO level no more than 5.5 eV from vacuum level. Optionally, the electron-donating polymer has a HOMO level at least 4.1 eV from vacuum level. As exemplary electron-donating polymers, polymers selected from conjugated hydrocarbon or heterocyclic polymers including polyacene, polyaniline, polyazulene, polybenzofuran, polyfluorene, polyfuran, polyindenofluorene, polyindole, polyphenylene, polypyrazoline, polypyrene, polypyridazine, polypyridine, polytriarylamine, poly(phenylene vinylene), poly(3-substituted thiophene), poly(3,4-bisubstituted thiophene), polyselenophene, poly(3-substituted selenophene), poly(3,4-bisubstituted selenophene), poly(bisthiophene), poly(terthiophene), poly(bisselenophene), poly(terselenophene), polythieno[2,3-b]thiophene, polythieno[3,2-b]thiophene, polybenzothiophene, polybenzo[l,2-b:4,5-b']dithiophene. polyisothianaphthene, poly(monosubstituted pyrrole), poly(3,4-bisubstituted pyrrole), poly-1,3,4-oxadiazoles, polyisothianaphthene, derivatives and co-polymers thereof may be mentioned. Preferred examples of donor polymers are copolymers of polyfluorenes and polythiophenes, each of which may be substituted, and polymers comprising benzothiadiazole-based and thiophene-based repeating units, each of which may be substituted. A particularly preferred donor polymer comprises donor unit (Vila) provided as a repeat unit of the polymer, most preferably with an electron-accepting repeat unit, for example divalent electron-accepting units A1 as described herein provided as polymeric repeat units. Another particularly preferred donor polymer comprises repeat units of formula (X): (X) wherein R18 and R19 are each independently selected from H; F; C1-12 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO and one or more H atoms of the alkyl may be replaced with F; or an aromatic or heteroaromatic group Ar6 which is unsubstituted or substituted with one or more substituents selected from F and C1-12 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with 0, S, COO or CO. The donor polymer is preferably a donor-acceptor (DA) copolymer comprising a donor repeat unit, for example a repeat unit of formula (Vila) or (X), and an acceptor repeat unit. Organic Electronic Device A compound of formula (I) or (II) may be provided as an active layer of an organic electronic device. In a preferred embodiment, a bulk heterojunction layer of an organic photoresponsive device, more preferably an organic photodetector, comprises a composition as described herein. The bulk heterojunction layer comprises or consists of an electron-donating material and an electron-accepting compound of formula (I) or (II) as described herein. In some embodiments, the bulk heterojunction layer contains two or more accepting materials and I or two or more electron-accepting materials. In some embodiments, the weight of the electron-donating material(s) to the electronaccepting material(s) is from about 1:0.5 to about 1:2, preferably about 1:1.1 to about 1:2. Preferably, the electron-donating material has a type II interface with the electronaccepting material, i.e. the electron-donating material has a shallower HOMO and LUMO that the corresponding HOMO and LUMO levels of the electron-accepting material. Preferably, the compound of formula (I) or (II) has a HOMO level that is at least 0.05 eV deeper, optionally at least 0.10 eV deeper, than the HOMO of the electron-donating material. Optionally, the gap between the HOMO level of the electron-donating material and the LUMO level of the electron-accepting compound of formula (I) or (II) is less than 1.4 eV. Unless stated otherwise, HOMO and LUMO levels of materials as described herein are as measured by square wave voltammetry (SWV). Figure 1 illustrates an organic photoresponsive device according to some embodiments of the present disclosure. The organic photoresponsive device comprises a cathode 103, an anode 107 and a bulk heterojunction layer 105 disposed between the anode and the cathode. The organic photoresponsive device may be supported on a substrate 101, optionally a glass or plastic substrate. Each of the anode and cathode may independently be a single conductive layer or may comprise a plurality of layers. At least one of the anode and cathode is transparent so that light incident on the device may reach the bulk heterojunction layer. In some embodiments, both of the anode and cathode are transparent. The transmittance of a transparent electrode may be selected according to an emission wavelength of a light source for use with the organic photodetector. Figure 1 illustrates an arrangement in which the cathode is disposed between the substrate and the anode. In other embodiments, the anode may be disposed between the cathode and the substrate. The organic photoresponsive device may comprise layers other than the anode, cathode and bulk heterojunction layer shown in Figure 1. In some embodiments, a holetransporting layer is disposed between the anode and the bulk heterojunction layer. In some embodiments, an electron-transporting layer is disposed between the cathode and the bulk heterojunction layer. In some embodiments, a work function modification layer is disposed between the bulk heterojunction layer and the anode, and / or between the bulk heterojunction layer and the cathode. The area of the OPD may be less than about 3 cm2, less than about 2 cm2, less than about 1 cm2, less than about 0.75 cm2, less than about 0.5 cm2 or less than about 0.25 cm2. Optionally, each OPD may be part of an OPD array wherein each OPD is a pixel of the array having an area as described herein, optionally an area of less than 1 mm2, optionally in the range of 0.5 micron2 - 900 micron2. The substrate may be, without limitation, a glass or plastic substrate. The substrate can be an inorganic semiconductor. In some embodiments, the substrate may be silicon. For example, the substrate can be a wafer of silicon. The substrate is transparent if, in use, incident light is to be transmitted through the substrate and the electrode supported by the substrate. The bulk heterojunction layer contains a compound of formula (I) or (II) as described herein and an electron-donating compound. The bulk heterojunction layer may consist of these materials or may comprise one or more further materials, for example one or more further electron-donating materials and I or one or more further electron-accepting compounds. Fullerene In some embodiments, a compound of formula (I) or (II) is the only electron-accepting material of a bulk heterojunction layer as described herein. In some embodiments, a bulk heterojunction layer contains a compound of formula (I) or (II) and one or more further electron-accepting materials. Preferred further electronaccepting materials are fullerenes. The present inventors have surprisingly found that a combination of a compound of formula (I) or (II) and a fullerene may enhance external quantum efficiency of an OPD with little or no increase in dark current. The compound of formula (I) or (II) : fullerene acceptor weight ratio may be in the range of about 1:0.1-1: 1, preferably in the range of about 1:0.1-1: 0.5. Fullerenes may be selected from, without limitation, Ceo, C70, C76, C78 and Cs4 fullerenes or a derivative thereof, including, without limitation, PCBM-type fullerene derivatives including phenyl- Cei-butyric acid methyl ester (CsoPCBM), TCBM-type fullerene derivatives (e.g. tolyl-Csi-butyric acid methyl ester (CeoTCBM)), and ThCBM-type fullerene derivatives (e.g. thienyl-Cei-butyric acid methyl ester (CeoThCBM). Fullerene derivatives may have formula (VI): (VI) wherein A, together with the C-C group of the fullerene, forms a monocyclic or fused ring group which may be unsubstituted or substituted with one or more substituents. Exemplary fullerene derivatives include formulae (Via), (VIb) and (Vic): (VIb) wherein R20-R32 are each independently H or a substituent. Substituents R20-R32are optionally and independently in each occurrence selected from the group consisting of aryl or heteroaryl, optionally phenyl, which may be unsubstituted or substituted with one or more substituents; and C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR7, CO or COO and one or more H atoms may be replaced with F. Substituents of aryl or heteroaryl, where present, are optionally selected from C1-12 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR7, CO or COO and one or more H atoms may be replaced with F. Formulations The bulk heterojunction layer may be formed by any process including, without limitation, thermal evaporation and solution deposition methods. Preferably, the bulk heterojunction layer is formed by depositing a formulation comprising the electron-donating material(s), the electron-accepting material(s) and any other components of the bulk heterojunction layer dissolved or dispersed in a solvent or a mixture of two or more solvents. The formulation may be deposited by any coating or printing method including, without limitation, spin-coating, dip-coating, roll-coating, spray coating, doctor blade coating, wire bar coating, slit coating, ink jet printing, screen printing, gravure printing and flexographic printing. The one or more solvents of the formulation may optionally comprise or consist of benzene or naphthalene substituted with one or more substituents selected from fluorine, chlorine, Ci-10 alkyl and C110 alkoxy wherein two or more substituents may be linked to form a ring which may be unsubstituted or substituted with one or more C1-6 alkyl groups, optionally toluene, xylenes, trimethylbenzenes, tetramethylbenzenes, anisole, indane and its alkylsubstituted derivatives, and tetralin and its alkyl-substituted derivatives. The formulation may comprise a mixture of two or more solvents, preferably a mixture comprising at least one benzene substituted with one or more substituents as described above and one or more further solvents. The one or more further solvents may be selected from esters, optionally alkyl or aryl esters of alkyl or aryl carboxylic acids, optionally a Ci-10 alkyl benzoate, benzyl benzoate or dimethoxybenzene. In preferred embodiments, a mixture of trimethylbenzene and benzyl benzoate is used as the solvent. In other preferred embodiments, a mixture of trimethylbenzene and dimethoxybenzene is used as the solvent. The formulation may comprise further components in addition to the electron-accepting material, the electron-donating material and the one or more solvents. As examples of such components, adhesive agents, defoaming agents, deaerators, viscosity enhancers, diluents, auxiliaries, flow improvers colourants, dyes or pigments, sensitizers, stabilizers, nanoparticles, surface-active compounds, lubricating agents, wetting agents, dispersing agents and inhibitors may be mentioned. Applications A circuit may comprise the OPD connected to a voltage source for applying a reverse bias to the device and / or a device configured to measure photocurrent. The voltage applied to the photodetector may be variable. In some embodiments, the photodetector may be continuously biased when in use. In some embodiments, a photodetector system comprises a plurality of photodetectors as described herein, such as an image sensor of a camera. In some embodiments, a sensor may comprise an OPD as described herein and a light source wherein the OPD is configured to receive light emitted from the light source. In some embodiments, the light source has a peak wavelength of at least 900 nm or at least 1000 nm, optionally in the range of 900-1500 nm. In some embodiments, the light from the light source may or may not be changed before reaching the OPD. For example, the light may be reflected, filtered, down-converted or up-converted before it reaches the OPD. The organic photoresponsive device as described herein may be an organic photovoltaic device or an organic photodetector. An organic photodetector as described herein may be used in a wide range of applications including, without limitation, detecting the presence and I or brightness of ambient light and in a sensor comprising the organic photodetector and a light source. The photodetector may be configured such that light emitted from the light source is incident on the photodetector and changes in wavelength and / or brightness of the light may be detected, e.g., due to absorption by, reflection by and / or emission of light from an object, e.g. a target material in a sample disposed in a light path between the light source and the organic photodetector. The sample may be a non-biological sample, e.g. a water sample, or a biological sample taken from a human or animal subject. The sensor may be, without limitation, a gas sensor, a biosensor, an X-ray imaging device, an image sensor such as a camera image sensor, a motion sensor (for example for use in security applications) a proximity sensor or a fingerprint sensor. A ID or 2D photosensor array may comprise a plurality of photodetectors as described herein in an image sensor. The photodetector may be configured to detect light emitted from a target analyte which emits light upon irradiation by the light source or which is bound to a luminescent tag which emits light upon irradiation by the light source. The photodetector may be configured to detect a wavelength of light emitted by the target analyte or a luminescent tag bound thereto. EXAMPLES Acceptor Unit 1 Acceptor Unit 1 may be prepared according to the foliowing scheme: o-chloranil Et2O NBS AcOH H2O Malonitrile TiCI4 (1 M) Pyridine Cone. H2SO4 Cone. HNO3 Compound Example 1 Compound Example 1 may be prepared according to the foilowing scheme: 1) n-BuLi 2) Bu3SnCI Cl Compound Example 2 Compound Example 2 may be prepared according to the following scheme: NBS THF / Acetone Pd2(dba)3 [CBU)3PH]BF4 k3po4 n-BuLi 'PrOBpin P(o-tol)3 Pd2(dba)3 Modelling data The HOMO and LUMO energy levels of compounds of formula (I) and (II) and comparative compounds were modelled using Gaussian09 software available from Gaussian using Gaussian09 with B3LYP (functional) and 6-31G(D) (Basis set). Alkyl groups of model compounds were restricted to methyl to simplify modelling. Results are set out in Tables 1-7 in which in which Slf corresponds to oscillator strength of the transition from SI (predicting absorption intensity). As shown in these results, an increase in Xmax wavelength can be achieved by use of acceptor groups A1 as described herein. Tables 1A and IB provide modelling data for compounds of formula (I) in which each A1 is a group of formula (III) and -(D^yi- is a group of formula: In Table 1A no bridging groups are present. In Table IB, x1 and x2 are each 1 and B1 is an alkoxy-substituted thiophene bridge B1. Table 1A Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm Q 0 vO cn s s J J” s\Zv\Z-x NC O^° O 0 Comparative -5.20 -3.88 945 1.61 959 CN S S J JT NC Comparative -5.12 -3.74 895 1.86 924 Cl y=\ / = / CN / / C / sk ZS / J 2T / = s / Zv / ZZ nc jp3 nn r t CI^X-ssJ ' x Cl Comparative -5.29 -3.95 928 1.92 950 F v / / V: / =7 M M V-Cj cm / X' / 'i NC 2T / = $ / / 7 / 1 / nc / ¥% O / 7 JT / ^7 F'-’Xysss' F Comparative -5.24 -3.88 916 1.85 939 CN . 7 / *SX-CN V\ / = / a / M M VkJ CN 77 / / / 8^ SK J ncA^x jfX V> V> T^'y-cN 7C i^s s / Zv / / nc Jr^o flXA J T T^7 NC^Xys^ ' x NC Comparative -5.56 -4.31 989 1.85 996 °Y<N CN V S S J nc T / = S' / / NC J Y^O OO Q^N / = / M. -5.23 -3.90 936 1.79 944 V 7 N^\ \=\ / = / J / / / \ / \ A\^n M W °vXj CM 7X / 7Sx / x A J NcA^^'yXXX5--^^r CN sCZxZZ nc n4Ao 0Q 11 1 / — —\ \;SN -5.26 -3.93 932 1.80 946 Cl V°\ / ^ M W VO CN s _ / Sk\ J CM klJT * / \ NC J 7^0 <^\ V"S CI-^VO Cl -5.38 -4.09 967 1.83 969 Cl . . N«k,CI \=\ / = / 1 II r> / \ / ^\^n M M Vv CN \X / A, S j ncA^^ / OV-VO^^Vn JT s s\Zv\ZI nc n0A qq CI"V^N Cl -5.41 -4.13 970 1.83 978 ll. 7^^ z "V V z VOO ¢ / \ x=Z m0] / 0” ro i0« z° gJ^X O A U z z==< -5.38 -4.08 961 1.77 968 CN . , N^^CN V=\ / =- / J « / \ / \ / ^kN M M °vAJ FN .Q / QXs-. / k JL. j J" 7s SO2XZZ nc 4 / ^° o N"\<O V. / \^J J 1 / -\ NC-^VjsN NC -5.66 -4.45 1027 1.74 1022 N-S J CN \ / s _x-S\0CH ' ncA^^^-o-qo-^^ Ok S' / \ NC A J^° S-N -5.44 -4.06 896 2.02 902 N-nZ Xn T CN J / S XS UTj / * Z\ NC A j"° ^Jr zN-N -5.25 -3.83 873 1.97 892 Table IB Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Am ax / nm o z ry / o r v Y) / O’ jot la* « -J ° j / / T\^ z \^J o z -4.76 -3.76 1243 2.23 1204 z / =2^ j XJ u-^. J n— 2 / V^ / ^o r w kJ] xxX / 0° jOA / Y / O-^ w J o j JMj Cr » \s=y Z -4.70 -3.63 1168 2.41 1171 Cl ci^ / ^i r'X / ^\ / \k W VZ °y^ NC\ \j^s^jrOrOr^^ 'Z^3 sXZJX1Z cn o v s r 7 \ v / \=y \= / ^Z'ci Cl -4.84 -3.82 1224 2.52 1205 z -n r w °D<? N_~ “O kJ? U>v / A zo^ J °\— / 4rvo —° 31 \-5s / Z -4.79 -3.76 1203 2.45 1189 NC / \ / ^X / VX W W °\_. Nt 'x^° _XZSsx / sxX-K^^r"CN ^S S\Z / vZ 0<^A- CN o A- / / =X \=\ W^CN CN -5.07 -4.14 1334 2.54 1266 O^n Q 0 °C ni tt AA O zsx nc^ z y. ? S's smX7Z o^x tl cn 0 N~\> / \= / \= / -4.78 -3.77 1235 2.38 1197 An 'Ox / «JL \J\J x NS y Xo5 Axsx xsx aOcn nc^^^'V 's s\Zy*CZ X CN o X) 1^ 5 / \= / \=Z N^z -4.81 -3.80 1235 2.41 1201 Cl Cl / ^X / \\ V / / \\ / ) O NC V >C ^sk zsx_X Kzv CN Nfx s nroxPsooN nc / ^y ? 's s___ oz\ 11 In x ftn TL / n= / \= / o^ci Cl -4.91 -3.94 1288 2.46 1230 a CI^On / a I » L \ / / y / °x nc v O° -X. zss_-< CN NC-O^\( o \ \Y CN 0 \\ T1 X / / = / \s=< Nsy^CI Cl -4.94 -3.98 1296 2.49 1240 F f-^5^ r \ / ^x / VAn U U °y^ NC\ « Xz-0 X, zsx zSxOO-^A'CN NC-Q-^^ # s sOXL_, <y \ 11 CN 0 N \ >-. I '^A. “==0"F F -4.87 -3.89 1271 2.40 1216 F f-^ / ^n r \ / n / \\ I <7 V / Z °\ NC N-^ / 55^ x—\ )—■ / \—a L y zk^-0 JK Ax. zsO KzF-'tT'CN Nc~O~--''y sZ X" \ V \ \ Z—( \—n~> / -N CN 0 \\ C / X. / >= / \=A N^XF F -4.91 -3.94 1280 2.42 1225 NC NC^O A \ / A J \JyJ ‘V NCv V Xz.0 2<C zSx zSxOOxzAA'CN niXs NC^X^^X^ l / "S S\ZX2Z O^V \L CN 0 \ N \ / XX \X X^CN CN -5.14 -4.25 1399 2.36 1290 Tables 2A and 2B Tables 2A and 2B provide modelling data for compounds of formula (I) in which each A1 is a group of formula (III) and -(D^yi- is a group of formula: In Table 2A no bridging groups are present. In Table 2B, x1 and x2 are each 1 and B1 is an alkoxy-substituted thiophene bridge B1. Table 2A Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm ] / S ~' / z\ NC G'0 qq Comparative -5.44 -3.90 806 1.27 867 Table 2B Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm __ NC nc^ / x( 3 / X7 ¢ / / ) cn ° o O Comparative -4.92 -3.78 1086 1.83 1113 Ci , / \ Z\ / v / / / O_ NC nX / n?rWv<X / CN \ / ¾ # s^y V CN / ° / X X NYi >= / \===\ XX^ci ' Cl -5.09 -3.99 1124 2.03 1141 Cl . O O Z nX VM °\ NC( vx° cn / ° r> XX / = / \=\ N^ / ^CI Z Cl -5.11 -4.01 1126 2.06 1145 Tables 3A and 3B provide modelling data for compounds of formula (I) in which each A1 is a group of formula (III) and -(D^yi- is a group of formula: In Table 3A no bridging groups are present. In Table 3B, x1 and x2 are each 1 and B1 is an alkoxy-substituted thiophene bridge B1. Table 3A Table 3B Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm / 0 NC CN CN 0 / Comparative -4.79 -3.82 1278 2.15 1159 Cl O NC \ / Y-a 1 " xs^ Ji Nyj.s_ryry#^s^yN f 0 nJS CN / ° V^CI Cl -4.97 -4.02 1317 2.35 1179 Cl CI^^N / \ 0 NC N ~W^° ^OLzS^ / yXy.# s nc^^vK^3 y ° CN 0 i / NY^CI Cl -5.00 -4.06 1323 2.38 1189 Tables 4A and 4B provide modelling data for compounds of formula (I) in which each A1 is a group of formula (III) and -(D^yi- is a group of formula: In Table 4A no bridging groups are present. In Table 4B, x1 and x2 are each 1 and B1 is an alkoxy-substituted thiophene bridge B1. Table 4A Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm CN NC Comparative -5.70 -4.14 795 1.17 809 CN \Z NC NC^.^ N^s^k N J / T o o \ W CI^V-^ Cl Cl -5.91 -4.37 804 1.41 805 CN NC NC^s^^ W / / -¾ ^^^CN N^k^ N II 1 AW CI^XysN N^AGi Cl Cl -5.95 -4.40 802 1.38 812 Table 4B Tables 5A and 5B provide modelling data for compounds in which each A1 is a group of formula (Ill)and -(D^yi- is a group of formula: In Table 5A no bridging groups are present. In Table 5B, x1 and x2 are each 1 and B1 is an alkoxy-substituted thiophene bridge B1. Table 5A Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm / -0 cn f \ CN NC'^VY’^8 ° iu Comparative -5.62 -4.15 846 1.03 869 o \ z / =\ ° Q^J=Z\>§ o w / Xs. o W J ° W M o— / )=z Vo )= / a z o z -5.83 -4.38 858 1.21 869 z P Z / ° / \ -°A / =\ / / -° o^z ,= / ° [ w o z^Y w ^== / o Vo o z=< z \_ o -5.87 -4.42 857 1.19 876 Table 5B Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm p-\ jy-CC NC- / 0 0 V-CN CN 1 ' NC Comparative -4.96 -3.92 1190 1.73 1131 Cl | Cl VtVV NC— / 0 O VCN CN NC -5.14 -4.13 1225 1.95 1149 Table 6 provides modelling data for compounds in which each A1 is a group of formula (III), no bridging groups are present and -(D^yi- is a group of formula: Table 6 Table 7 provides modelling data for compounds of formula (I) in which each A1 is a group of formula (IV). Table 7 Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm z o [ —z 1 co J °K TA o z -5.40 -4.06 931 1.18 941 z o U) 1 w w w o z -5.33 -4.00 938 1.48 979 Table 8 provides modelling data for compounds of formula (II) in which each A1 is a group of formula (III). Table 8 Structure / ID HOMO / eV LUMO / eV Eg / nm Slf Amax / nm Xa . xX CN J'-'-r'K A NC J |[ c NN Il V AX1'' b \ JC / \ / VJL / b [| I r^Y\ «» / Y^ 1 II nc^y juX yn XXX YU CN \= / CN Comparative -5.03 -4.09 1320 2.34 1432 ,cn O XY YX W N\ nc< YyJ s XXX XX \= / 'o s'^OUnX / Uv'^ 0 <'N 7<xx Comparative -4.62 -3.82 1558 2.58 1571 CN C # Y / X nc- / ^ YxXy __ / / CN M- / -WlQx N* ' / 5^--^ / 11^—S“N Az y^ s-^x [>^5 M / VULxs W 1H. ci—f / =n ° s^vJLy—\_ / —V-L / ^8 0 N\ yci c|- jOf5 X rvCk ~CI -4.74 -3.96 1601 2.95 1589 o X f if Z ,z xu z T T yXo r~( / =C\j C\ \_ / W. W *zJy*z wZ / --K \ zKv H W\ X J\V Z 1 j TXl z z X T ° -4.76 -3.99 1609 2.99 1596 Oxy XiP FN -s~ nc Nc-Qw-i VN sXWJX W ° \JL?\ / OC / Ji JJ (Vvj ""l 1 nc JUX %-N X T j X ON V? CN Comparative -5.22 -4.08 1091 1.87 1237 / cn J* Jx vJ ncv NC-'JJUJ ^-CN .—(A—n',S''n J—< rtx^yi s m sx / sxr) ^= / o ypvv / XUJy 0 N's'N nXX Comparative -4.81 -3.82 1255 2.07 1371 % o 1 1 z / / / jJW x x-X ,z*Pv^ co ,co z’^’yAz A^co "U / <5 PW V v o -5.15 -3.85 958 1.22 1062 ,cn J ij-x^ X^i ncx NC-CN «—\V-^jlS—i n"s"n i-AjrvuJ— n \ s-^x v^s yy s-^-P Y"^ y-e >-N C|—f )=7 0 J >—? J )==7 o '=( Xci )=N r^UU W N=\ ci rtn" ,n j yy ci s r\ -4.95 -3.99 1305 2.35 1411 \ / A \ CN N\ / N / NX^\ NC NcXXs^VT / XiATAs'^ x>° / N w °=\A Xj nvn Ol NCryX y^JN CN CN Comparative -5.30 -4.37 1328 1.93 1348 Comparative -4.73 -3.99 1688 1.89 1503 CN NC NC- / \ ✓ zS. \ \“CN °'—\ / n ° , ° n \ / a )=7 N. ,N ' =( Cl s Cl -4.89 -4.16 1711 2.20 1508 CN NC NC“Z \ y xSx \ VcN 7"^ Nf \N z-< ■ / xS y || Q ) { c |f (' \ । ci—( )= o y-o ^=( )-ci )=N ' N, ,N ' N=( Cl s Cl -4.92 -4.19 1715 2.23 1511 NQ CN NC^ PN V7 O NC M j\= / CN 'll ° ° ir' NC X, CN < O N'"N e > QjOlRtF / T H 7\ ' N. „N ' S Comparative -5.63 -4.57 1173 1.60 1209 O fl yyo °*=ri NC. J. X ..A'., J^ / CN nc it # \ cn ^\IL#—\ / —\JL / ^ x / / X ' Nx N ' s Comparative -5.02 -4.15 1436 1.71 1341 Cl Cl CIX^X J^ZCI Xa Xj Il'N N”ll NV^x^o NC.^t X m'A'm k. X>xCN nc L)vs\ XX / S^XX CN ^\iLz / —\ / —NxJL / ^ nX ^ / x ' Nx ,N ' S -5.18 -4.32 1451 1.98 1346 Cl Cl Ck J. A / CI Jl xN Nz T i fl x^Xj^o NC. A X -Am V nc it XX A~^XX CN —\ / — X )rA x ' N, ,N ' S -5.21 -4.35 1453 2.00 1349

Claims

1. A compound of formula (I) or (II):A1 - (B1)x1 - (D1)y1 - (B1)x2 - A1(I)A1 - (B2)x5 - (D2)y2 - (B3)x3- A2 - (B3)x4 - (D3)y3 - (B2)x6 - A1(II)wherein:A2 is a divalent heteroaromatic electron-accepting group;D1, D2 and D3 independently in each occurrence is an electron-donating group;B1, B2, and B3 independently in each occurrence is a bridging group;x1 - x6 are each independently 0, 1, 2 or 3;y1, y2 and y3 are each independently at least 1;each A1 is an electron-accepting group and at least one A1 is a group of formula (III), (IV) or (V):(HI) (IV) (V)wherein: each R1 is independently a substituent; R2 is H or a substituent;Ar1 is selected from benzene; 1,2,3-triazole; 1,25-thiadiazole; 1,2,3-thiadiazole; and a six-membered heteroaromatic group in which ring atoms are selected from C and N and Ar1 is unsubstituted or substituted with one or more substituents;-- represents a point of attachment of A1;Z^Z6 independently in each occurrence is selected from N and CR4 wherein R4 in each occurrence is H or a substituent;if Ar1 is benzene and A1 is the group of formula (III) then at least one of Z1 and Z2 is N;if Ar1 is benzene and A1 is the group of formula (IV) then at least one of Z3 and Z4 is N; andif Ar1 is benzene and A1 is the group of formula (V) then at least one of Z5 and Z6 is N.

2. The compound according to claim 1 wherein Ar1 is benzene.

3. The compound according to claim 2 wherein:if A1 is a group of formula (III) then Z1 and Z2 are each N;if A1 is a group of formula (IV) then Z3 and Z4are each N; andif A1 is a group of formula (V) then Z5and Z6are each N.

4. The compound according to claim 1 wherein Ar1 is 1,4-diazine and:if A1 is a group of formula (III) then Z1 and Z2 are each CR4;if A1 is a group of formula (IV) then Z3 and Z4are each CR4; andif A1 is a group of formula (V) then Z5 and Z6 are each CR4;5. The compound according to any one of the preceding claims wherein at least one A1 is a group of formula (III).

6. The compound according to any one of the preceding claims wherein each A1 is a group of formula (III), (IV) or (V).

7. The compound according to claim 6 wherein each A1 is the same.

8. The compound according to any one of the preceding claims wherein each R1 is independently selected fromCN, CF3 and COOR40 wherein R40in each occurrence is H or a substituent.

9. The compound according to any one of the preceding claims wherein Ar1 is substituted with at least one electron-withdrawing group.

10. The compound according to claim 9 wherein the at least one electron-withdrawing group is selected from Br, Cl, F, CN, C1-12fluoroalkyl and COOR15 wherein R15 is a Ci-20 hydrocarbyl group.

11. The compound according to any one of the preceding claims wherein each R4 is independently selected from H or an electron-withdrawing group.

12. A composition comprising an electron-donating material and an electron-accepting material wherein the electron accepting material is a compound according to any one of the preceding claims.

13. An organic electronic device comprising an active layer comprising a compound or composition according to any one of the preceding claims.

14. An organic electronic device according to claim 13 wherein the organic electronic device is an organic photoresponsive device comprising a bulk heterojunction layer disposed between an anode and a cathode and wherein the bulk heterojunction layer comprises a composition according to claim 12.

15. An organic electronic device according to claim 14 wherein the organic photoresponsive device is an organic photodetector.

16. A photosensor comprising a light source and an organic photodetector according to claim 15 wherein the organic photodetector is configured to detect light emitted from the light source.

17. The photosensor according to claim 16, wherein the light source emits light having a peak wavelength of greater than 900 nm.

18. A formulation comprising a compound or composition according to any one of claims 1 to 12 dissolved or dispersed in one or more solvents.

19. A method of forming an organic electronic device according to any one of claims 13-15 wherein formation of the active layer comprises deposition of a formulation according to claim 18 onto a surface and evaporation of the one or more solvents.s

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