Compound

Abstract

A compound of formula (I) or (II): A2-(B1)x1-(D1)y1-(B1)x2-A3 (I) A2-(B2)z1-(D2)y2-(B3)x3-A1-(B3)x4-(D3)y3-(B2)z2-A3 (II) A1 is a divalent heteroaromatic electron-accepting group; A2 and A3 are each independently a monovalent electron-accepting group; D1, D2 and D3 are each independently an electron-donating group; B1, B2, and B3 are each independently a bridging group; x1–x4 are each independently 0, 1, 2 or 3; y1, y2 and y3 are each independently at least 1; z1 and z2 are each independently 0, 1, 2 or 3; and at least one occurrence of D1 of formula (I) or at least one occurrence of at least one of D2 and D3 of formula (II) is a group of formula (III): (III) wherein each X is independently O, S or Se; each R1 is independently H or a substituent; each R2 is independently H or a substituent with the proviso that at least one R2 is C5 heteroaryl or phenyl substituted with at least one R5 group wherein each R5 is independently C1-20 alkyl wherein one or more non-adjacent C atoms of the C1-20 alkyl may be replaced with O, S, NR3, COO, CONR3, or Si(R4)2 wherein each R3 is H or a substituent and each R4 is a substituent.

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 5 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). WO 2021 / 174532 discloses compounds having the following formulae: CN110818725 discloses: Xiaoling Ma, et al, ACS Appl. Mater. Interfaces 2021, 13, 48, 57684-57692 "Over 17% 15 Efficiency of Ternary Organic Photovoltaics Employing Two Acceptors with an Acceptor- Donor-Acceptor Configuration" discloses Ternary organic photovoltaics (OPVs) were constructed with one wide-band-gap donor PM6 and two A-D-A-type acceptors (M-series M36 and MQ5) with similar chemical structures. Chen, Z., Ma, SS., Zhang, K. et al. "A Near-infrared Non-fullerene Acceptor with Thienopyrrole-expanded Benzo[l,2-6:4,5-6']dithiophene Core for Polymer Solar Cells. Chin J Polym Sci 39, 35-42 (2021) discloses a near-infrared non-fullerene acceptor (NFA) BDTIC, based on thienopyrrole-expanded benzo[l,2-6:4,5-6f]dithiophene unit (heptacyclic 5, / V-heteroacene) as core. SUMMARY The present disclosure provides a compound of formula (I) or (II): A2 - (B^x1 - (D^y1 - (B1)x2 - A3 (I) A2 - (62)71 - (D2)y2 - (B3)x3- A1 - (B3)x4 - (D3)y3 - (B2)z2 - A3 (II) wherein: A1 is a divalent heteroaromatic electron-accepting group; A2 and A3 independently in each occurrence is a monovalent 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 and x2 are each independently 0, 1, 2 or 3; x3 and x4 are each independently 0, 1, 2 or 3; y1, y2 and y3 are each independently at least 1; z1 and z2 are each independently 0, 1, 2 or 3; and wherein at least one occurrence of D1 of formula (I) or at least one occurrence of at least one of D2 and D3 of formula (II) is a group of formula (III): (HI) wherein: each X is independently selected from is O, S and Se; R1 in each occurrence is independently H or a substituent; and R2 in each occurrence is independently H or a substituent with the proviso that at least one R2 is Cs heteroaryl or phenyl substituted with at least one R5 group wherein R5 in each occurrence is independently selected from C1-20 alkyl wherein one or more non-adjacent C atoms of the C1-20 alkyl may be replaced with O, S, NR3, COO, CONR3, or Si(R4)? wherein R3 in each occurrence is H or a substituent and R4 in each occurrence is a substituent. R2 is preferably thienyl or phenyl substituted with at least one R5 group. Optionally, at least one R2 is phenyl substituted with at least one R5 group. Optionally, R2 is phenyl substituted with at least two R5 groups. Optionally, R5 independently in each occurrence is a C1-12 alkyl group. Optionally, R1 is selected from H; C1-20 alkyl wherein one or more non-adjacent C atoms of the C1-20 alkyl may be replaced with 0, S, NR3, COO, CONR3, or Si(R4)2 wherein R3 in each occurrence is H or a substituent and R4 in each occurrence is a substituent; optionally substituted Ce-2oaryl, preferably phenyl; and optionally substituted heteroaryl, preferably thienyl. Optionally, least one R1 is a Ci 19 alkoxy group. Optionally, each R1 independently is a C1-19 alkoxy group Optionally, A2 and A3 are each independently selected from groups of formulae (IXa)-(IXq): wherein: U is a 5- or 6-membered ring which is unsubstituted or substituted with one or more substituents and which may be fused to one or more further rings; R10 is H or a substituent; G is C=O, C=S SO, SO2, NR33 or C(R33)2 wherein R33 is CN or COOR40 and R40 is H or a substituent; J is C=O, C=S, NR11 or CR12R13 wherein R11 is CN or COOR40 and R40 is H or a substituent 5 and R12 and R13 are each independently CN, CF3 or COOR40; R13 in each occurrence is a substituent; R15 in each occurrence is independently H or a substituent; R16 is a substituent; Ar6 is a 5-membered heteroaromatic group which is unsubstituted or substituted with one 10 or more substituents; T1, T2 and T3 each independently represent an aryl or a heteroaryl ring which may be fused to one or more further rings and each of T1, T2 and T3 is independently unsubstituted or substituted with one or more substituents; and Ar8 is a fused heteroaromatic group which is unsubstituted or substituted with one or more 15 substituents and which is bound to an aromatic C atom of B1 or B2 and to a boron substituent of B1 or B2. Optionally, at least one of A2 and A3 is a group of formula (IXa-2) or (IXa-3): (IXa-2) (IXa-3) wherein each X7-X10 is independently CR12 or N wherein R12 in each occurrence is H or a substituent selected from Ci 20 hydrocarbyl and an electron withdrawing group; and each R15 independently is H or a substituent. Optionally, the electron withdrawing group is F, Cl or CN. 5 The present disclosure provides a composition comprising an electron-donating material and an electron-accepting material wherein the electron accepting material is a compound of formula (I) or (II). An organic electronic device comprising an active layer comprising a compound of formula (I) or (II) ora composition as described herein. 10 Optionally, the organic electronic device is an organic photoresponsive device comprising a photoactive layer comprising the compound of formula (I) or (II) or the composition as described herein disposed between the anode and cathode. Optionally, the photoactive layer is a bulk heterojunction layer comprising a composition as described herein. 15 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 photosensor 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 of formula (I) or (II) or a 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 is a schematic illustration of an organic photoresponsive device according to some embodiments; Figure 2 is an absorption spectrum of Compound Example 2 In 1,2,4-trimethylbenzene solution; and Figure 3 is an absorption spectrum of a film of Compound Example 2 cast from 1,2,4-trimethylbenzene solution. 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 atom include any isotope of that atom 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. Organic Electronic Device Figure 1 illustrates an organic photoresponsive device, preferably an organic photodetector, 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. The bulk heterojunction layer comprises a non-fullerene acceptor (NFA) of formula (I) or a NFA of formula (II) and an electron-donating material: A2 - (B^x1 - (D1)y1 - (B1)x2 - A3 (I) A2 - (62)71 - (D2)y2 - (B3)x3- A1 - (B3)x4 - (D3)y3 - (B2)z2 - A3 (II) wherein: A1 is a divalent heteroaromatic electron-accepting group; A2 and A3 independently in each occurrence is a monovalent 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 and x2 are each independently 0, 1, 2 or 3; x3 and x4 are each Independently 0, 1, 2 or 3; y1, y2 and y3 are each independently at least 1; z1 and z2 are each independently 0, 1, 2 or 3. Each of the electron-accepting groups A1 and A2 has a lowest unoccupied molecular orbital (LUMO) level that Is deeper (i.e., further from vacuum) than the LUMO of any of the electron-donating groups D1, D2 or D3, 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 Gausslan09 with B3LYP (functional) and LACVP* (Basis set). For compounds of formula (I), at least one D1 is a group of formula (III). For compounds of formula (II), at least one occurrence of at least one of D2 and D3 is a group of Formula (III). The bulk heterojunction layer may consist of the NFA of formula (I) or (II) and the electrondonating compound or it 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 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, the electron-donating material has a type II interface with the compound of formula (I) or (II), i.e., the electron-donating material has a shallower HOMO and LUMO than the corresponding HOMO and LUMO levels the compound of formula (I) or (II). 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 compound of formula (I) or (II) is less than 1.4 eV. Preferably, compounds of formula (I) and (II) have a peak absorption wavelength as measured in solution of greater than 800 nm, or greater than 900 nm or greater than 1000 nm, optionally less than 1500 nm or 1400 nm. 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 photoresponsive device comprises a bulk heterojunction photoactive layer 105. In other embodiments, the photoactive layer comprises an electron-accepting sub-layer comprising or consisting of a compound of formula (I) or (II) described herein disposed between the anode and cathode; and an electron-donating sub-layer comprising or consisting of one or more electron-donating materials disposed between the anode and the electron-accepting layer and in direct contact with the electron-accepting layer. 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 the photoactive layer. In some embodiments, a hole-transporting layer and / or an electron-blocking layer is disposed between the anode and the photoactive layer. In some embodiments, an electron-transporting layer and / or a hole-blocking layer is disposed between the cathode and the photoactive layer. In some embodiments, a work function modification layer is disposed between the photoactive layer and the anode, and / or between the photoactive layer and the cathode. 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. Formula (III) At least one occurrence of D1 of formula (I) or at least one occurrence of at least one of D2 and D3 of formula (II) is a group of formula (III): (HI) Each X is independently selected from is O, S and Se, preferably S. R1 in each occurrence is independently H or a substituent. Preferably, R1 is selected from H; Ci-20 alkyl wherein one or more non-adjacent C atoms of the C1-20 alkyl may be replaced with 0, S, NR3, COO, CONR3, or Si(R4)2 wherein R3 in each occurrence is H or a substituent and R4 in each occurrence is a substituent; optionally substituted Ce-2oaryl, preferably phenyl; and optionally substituted heteroaryl, preferably thienyl. Substituents of an aryl or heteroaryl group R1 may be selected from F, Cl, CN, NO2 and Ci-12 alkyl wherein one or more non-adjacent C atoms may be replaced with 0, S, NR3, COO CONR3 or CO and one or more H atoms of the alkyl may be replaced with F. Preferred substituents of an aryl or heteroaryl group R1 are C1-12 alkyl and Ci-n alkoxy. R3 is preferably H or a C1-20 hydrocarbyl group. R4 is preferably a C1-20 hydrocarbyl group. A Ci 20 hydrocarbyl group as described anywhere herein may be selected from C1-20 alkyl; unsubstituted phenyl; and phenyl substituted with one or more C1-12alkyl groups. Preferably, at least one R1 and more preferably each R1 is independently a C1-19 alkoxy group. R2 in each occurrence is independently H or a substituent with the proviso that at least one R2 is phenyl substituted with at least one R5 group wherein R5 in each occurrence is independently selected from C1-20 alkyl wherein one or more non-adjacent C atoms of the C1-20 alkyl may be replaced with O, S, NR3, COO, CONR3, or Si(R4)2 wherein R3 in each occurrence is H or a substituent and R4 in each occurrence is a substituent. Preferably, R5 independently in each occurrence is a C1-12 alkyl group. Preferably, each R2 is phenyl substituted with at least one R5 group. 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 units of formulae (Via) - (VIo): wherein R55 is H or a substituent, optionally H or a C1-20 hydrocarbyl group; and R8 in each occurrence is Independently H or a substituent, preferably H or a substituent selected from F; CN; NO2; Ci 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; 5 phenyl which is unsubstituted or substituted with one or more substituents; and -B(R14)2 wherein R14 in each occurrence is a substituent, optionally a C1-20 hydrocarbyl group. Re as described anywhere herein is H or a substituent, preferably H or a C1-20 hydrocarbyl group, more preferably H; C1-20 alkyl; or phenyl which is unsubstituted or substituted with one or more Ci-12 alkyl groups. R8 groups of formulae (Via), (VIb) and (Vic) may be linked to form a bicyclic ring which may be substituted with one or more substituents, optionally one or more substituents 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. R8 is preferably H, C1-20 alkyl or C1-19alkoxy. R8 groups of formulae (Via), (VIb) and (Vic) may be linked to form an optionally substituted bicyclic ring. In compounds of formula (I), each x1 is preferably 0 or 1. In compounds of formula (II), x3 and x4 are each preferably 0 and z1 and z2 are each preferably 0 or 1. Electron-Accepting Groups A2 and A3 The monovalent acceptor groups A2 and A3 may each independently be selected from any such units known to the skilled person. The A2 and A3 groups of the compound of formula (I) or (II) may be the same or different, preferably the same. Exemplary monovalent acceptor groups Include, without limitation, groups of formulae (IXa)-(IXq) U is a 5- or 6-membered ring which is unsubstituted or substituted with one or more substituents and which may be fused to one or more further rings. G is C=O, C=S SO, SO2, NR33 or C(R33)2 wherein R33 is CN or COOR40 and R40 is H or a substituent, optionally H or a Ci 20 hydrocarbyl. G is preferably C=O or SO2, more 5 preferably C=O. The N atom of formula (IXe) may be unsubstituted or substituted. R10 is H or a substituent, preferably a substituent selected from the group consisting of Ci-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; and an aromatic 10 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. Preferably, R10 is H. J is 0 or S, preferably 0. R13 in each occurrence is a substituent, optionally C1-12 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. R15 is H or a substituent. Preferably, R15 in each occurrence is independently H; F; Cl; Ci-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; aromatic group Ar2, 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 a group selected from: R16 is H or a substituent, preferably a substituent selected from: -(Ar3)w wherein Ar3 in each occurrence is independently an unsubstituted or substituted aryl or heteroaryl group, preferably thiophene, and w is 1, 2 or 3; and 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. Ar6 is a 5-membered heteroaromatic group, preferably thiophene or furan, which is unsubstituted or substituted with one or more substituents. Substituents of Ar3 and Ar6, where present, are optionally selected from 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. 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. Z1 is N or P. Ar8 is a fused heteroaromatic group which Is unsubstituted or substituted with one or more substituents, optionally one or more non-H substituents R10, and which is bound to an aromatic C atom of B1 or B2 and to a boron substituent of B1 or B2. Preferred groups A2 and A3 are groups having a non-aromatic carbon-carbon bond which is bound directly to D1 of formula (I) or D2 or D3 of formula (II) or, if present to B1 of formula (I) or B2 of formula (II). Preferably at least one of A2 and A3, preferably both of A2 and A3, are a group of formula (IXa-1): (IXa-1) wherein: G is as described above and is preferably C=O or SO2, more preferably C=O; R10 is as described above and is preferably H; Ar9 is an unsubstituted or substituted monocyclic or fused aromatic or heteroaromatic group, preferably benzene or a monocyclic or bicyclic heteroaromatic group having C or N ring atoms only; and X60 are each independently CN, CFs or COOR40 wherein R40 in each occurrence is H or a substituent, preferably H or a Ci 20 hydrocarbyl group. Preferably, each X60 is CN. Ar9 may be unsubstituted or substituted with one or more substituents. Substituents of Ar9 are preferably selected from groups R12 as described below. Optionally, the group of formula (IXa-1) has formula (IXa-2) or (IXa-3): each X7-X10 is independently CR12 or N wherein R12 in each occurrence is H or a substituent 5 selected from C1-20 hydrocarbyl and an electron withdrawing group; and R15 is independently H or a substituent as described herein. Preferably, the electron withdrawing group is F, Cl, Br or CN, more preferably F, Cl or CN; and for example, F or CN. The Ci 20 hydrocarbyl group R12 may be selected from C1-20 alkyl; unsubstituted phenyl; and phenyl substituted with one or more C1-12 alkyl groups. 10 In a particularly preferred embodiment, each of X7-X10 of formula (IXa-3) is CR12 and each R12 is independently selected from H or an electron-withdrawing group, preferably H, F or CN. According to his embodiment, R12 of X8 and X9 is an electron-withdrawing group, preferably F or CN. Exemplary groups of formula (IXd) include: Exemplary groups of formula (IXe) include: An exemplary group of formula (IXq) is: CN An exemplary group of formula (IXg) is: CN An exemplary group of formula (IXj) is: 10 wherein Ak is a C1-12 alkylene chain In which one or more C atoms may be replaced with O, S, NR6, CO or COO; An is an anion, optionally -SOs-; and each benzene ring is independently unsubstituted or substituted with one or more substituents selected from substituents described with reference to R10. Exemplary groups of formula (IXm) are: Groups of formula (IXo) are bound directly to a bridging group B1 or B2 substituted with a 5 group of formula -B(R14)2 wherein R14 in each occurrence is a substituent, optionally a Ci- 20 hydrocarbyl group; is a bond to the boron atom -B(R14)2; and — is a C-C bond between formula (IXo) and the bridging group. Optionally, R14 is selected from C1-12 alkyl; unsubstituted phenyl; and phenyl substituted with one or more C1-12alkyl groups. 10 The group of formula (IXo), the B1 or B2 group and the B(R14)2 substituent of B1 or B2 may be linked together to form a 5- or 6-membered ring. Optionally groups of formula (IXo) are selected from: Acceptor Unit A1 A1 is preferably a fused heteroaromatic group comprising at least 2 fused rings, preferably at least 3 fused rings. 5 In some embodiments, A1 of formula (II) is a group of formula (VIII): wherein: Ar1 is an aromatic or heteroaromatic group; and 10 Y is 0, 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), Ar1 may be a monocyclic or polycyclic heteroaromatic group which is unsubstituted or substituted with one or more R9 groups 15 wherein R9 in each occurrence is independently a substituent. Preferred R9 groups are selected from F; CN; NO2; Ci-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, 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 y40 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 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. 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, NR6, 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, Ci 12 alkyl, unsubstituted phenyl; or phenyl substituted with one or more Ci 6 alkyl groups. 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. 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 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 oralkali 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 monocyclic heteroaromatic groups Ar1 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 Ar1 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=O, C=S and C=C(R5)2 wherein R10 is as described above; R6 is H or a substituent; and R5 in each occurrence is an electronwithdrawing group. Preferably, each R5 is CN, COOR40; or CX60X61 wherein X60and X61is independently CN, CFs or COOR40 and R40 in each occurrence is H or a substituent, preferably H or a Ci 2o hydrocarbyl group. A1 groups of formula (VIII) are preferably selected from groups of formulae (Villa) and (VUIb): (Villa) 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 5 H; F; CN; NO2; Ci-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR6, 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; 10 NO2; and C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, 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): 15 (VIIIb-1) (VIIIb-2) Ar2 is an aromatic or heteroaromatic group, preferably benzene, which is unsubstituted or substituted with one or more substituents. Ar2 may be unsubstituted or substituted with one or more substituents selected from H, F, Cl, CN, NO2, C116 alkyl or Ci ie alkoxy wherein one or more H atoms of the Ci is alkyl or C1-16 alkoxy may be replaced with F. X is selected from O, S, SO2, NR6, PR6, C(R10)2, Si(R10)2 C=0, C=S and C=C(R=)z wherein R10, R6 and R5 are as described above. 5 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) (IVb) (IVd) (IVf) (IVi) (IVk) YA1 is O 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 0, 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 O, 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 O, S, NR6, COO or CO; or wherein Z40, Z41, Z42 and Z43 are each independently CR13 or N wherein R13 in each occurrence is H or a substituent, preferably a Ci-20 hydrocarbyl group; Y40 and Y41 are each independently 0, S, NX71 wherein X71 is CN or COOR40; or CX60X61 wherein X60and X61is independently CN, CF3 or COOR40; W40 and W41 are each independently 0, S, NX71 wherein X71 Is CN or COOR40; or CX60X61 wherein X60and X61is 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 Ci 20 hydrocarbyl group. Ar5 is an arylene or heteroarylene group, optionally thiophene, fluorene or phenylene, 5 which may be unsubstituted or substituted with one or more substituents, optionally one or more non-H groups selected from R25. Electron-Donating Groups D1, D2 and D3 In some embodiments the, or each, D1 of formula (I) is a group of formula (III). In some embodiments the, or each, D2 and D3 of formula (II) is a group of formula (III). 10 In the case of formula (I) wherein y1 is at least 2 then at least one D1 is a group of formula (III) and the one or more other groups D1 may be a donor group other than Formula (III). In the case of formula (II) then at least one of D2 and D3 is optionally a donor group other than formula (III). Exemplary electron-donating groups D1, D2 and D3 other than formula (III) include groups 15 of formulae (VIIa)-(VHp): (Vile) (Viig) (Vllh) (VII m) wherein YA in each occurrence is independently 0, S or NR6 wherein R6 is H or a substituent as described above, preferably 0 or S; YA1 in each occurrence is independently 0 or S; ZA in each occurrence is O, CO, S, NR55 or C(R54)?; R51, R52 R54and 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 O, S, NR6, 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 O, S, NR6, 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, NR17, 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, NR6, 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, NR6, 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 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, optionally one or more Ci 12 alkyl groups 5 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. Preferably, R55 as described anywhere herein is H or C1-30 hydrocarbyl group. In a preferred embodiment, D1, D2 and D3 are each a group of formula (Vile). In some preferred embodiments, y1 of formula (I) is 1. 10 In some preferred embodiments, y1 of formula (I) is 2 or 3 and D1 in each occurrence is the same. Preferably, y2 and y3 of formula (II) are each 1. In the case where y1 of formula (I) is greater than 1, e.g., 2 or 3, or at least one of y2 and y3 of formula (II) is greater than 1, e.g., 2 or 3, the chain of D1, D2 or D3 groups, 15 respectively, may be linked in any orientation. Exemplary compounds of formula (I) include: NC> CN NC> ,CN NC CN Electron-donating material Exemplary electron-donating materials of a photoactive layer as described herein 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 a repeat unit of formula (X): (X) wherein YA, ZA, R51 and R54 are as described above. Another particularly preferred donor polymer comprises repeat units of formula (XI): (XI) wherein R18 and R19 are each independently selected from H; F; Ci 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 O, 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 (X) or (XI), and an acceptor repeat unit, for example divalent electron-accepting units A2 as described herein provided as polymeric repeat units. Fullerene In some embodiments, the compound of formula (I) or (II) is the only electron-accepting material of an electron-accepting sub-layer or a bulk heterojunction layer as described herein. In some embodiments, an electron-accepting layer or a bulk heterojunction layer contains a compound of formula (I) or (II) and one or more further electron-accepting materials. Preferred further electron-accepting materials are fullerenes. The combined weight of 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 (CeoPCBM), TCBM-type fullerene derivatives (e.g., tolyl-Cei-butyric acid methyl ester (CeoTCBM)), and ThCBM-type fullerene derivatives (e.g., thienyl-Cei-butyric acid methyl ester (CeoThCBM). Fullerene derivatives may have formula (V): (V) 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 (Va), (Vb) and (Vc): (Va) (Vb) (Vc) 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, NR6, 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 C112 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR6, CO or COO and one or more H atoms may be replaced with F. Formulations The photoactive layer may be formed by any process including, without limitation, thermal evaporation and solution deposition methods. Preferably, an electron-accepting sub-layer or a bulk heterojunction layer is formed by depositing a formulation comprising the compound of formula (I) or (II) and any other components of the layer, including one or more electron-donating materials in the case of a bulk heterojunction layer, dissolved or dispersed in a solvent or a mixture of two or more solvents followed by evaporation of the one 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, inkjet printing, screen printing, gravure printing and flexographic printing. The one or more solvents of the formulation may optionally comprise or consist of benzene substituted with one or more substituents selected from chlorine, Ci-io alkyl and Ci-io alkoxy wherein two or more substituents may be linked to form a ring which may be unsubstituted or substituted with one or more Ci 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-lo alkyl benzoate, benzyl benzoate or dimethoxybenzene. In preferred embodiments, a mixture of trlmethylbenzene and benzyl benzoate is used as the solvent. In other preferred embodiments, a mixture of trlmethylbenzene and dlmethoxybenzene 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. The photoactive layer is formed over one of the anode and cathode of the organic photoresponsive device and the other of the anode and cathode is formed over the photoactive layer. Applications A circuit may comprise the OPD connected to one or more of a voltage source for applying a reverse bias to the device; a device configured to measure photocurrent; and an amplifier configured to amplify an output signal of the OPD. 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 / 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. The detection surface area of an OPD as described herein may be selected according to the desired application. Optionally, an OPD as described herein has a detection surface area of 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. Examples Measurements Unless stated otherwise, HOMO and LUMO levels of materials as described herein are as measured by square wave voltammetry (SWV). In SWV, the current at a working electrode is measured while the potential between the working electrode and a reference electrode is swept linearly in time. The difference current between a forward and reverse pulse is plotted as a function of potential to yield a voltammogram. Measurement may be with a CHI 660D Potentiostat. The apparatus to measure HOMO or LUMO energy levels by SWV may comprise a cell containing 0.1 M tertiary butyl ammonium hexafluorophosphate in acetonitrile; a 3 mm diameter glassy carbon working electrode; a platinum counter electrode and a leak free Ag / AgCI reference electrode. Ferrocene is added directly to the existing cell at the end of the experiment for calculation purposes where the potentials are determined for the oxidation and reduction of ferrocene versus Ag / AgCI using cyclic voltammetry (CV). The sample is dissolved in toluene (3 mg I ml) and spun at 3000 rpm directly on to the glassy carbon working electrode. LUMO = 4.8-E ferrocene (peak to peak average) - E reduction of sample (peak maximum). HOMO = 4,8-E ferrocene (peak to peak average) + E oxidation of sample (peak maximum). A typical SWV experiment runs at 15 Hz frequency; 25 mV amplitude and 0.004 V increment steps. Results are calculated from 3 freshly spun film samples for both the HOMO and LUMO data. Unless stated otherwise, absorption spectra were measured using a Cary 5000 UV-VIS-NIR Spectrometer. Measurements were taken from 175 nm to 3300 nm using a PbSmart NIR detector for extended photometric range with variable slit widths (down to 0.01 nm) for optimum control over data resolution. Unless stated otherwise, absorption values are of a solution. Absorption data are obtained by measuring the intensity of transmitted radiation through a solution sample. Absorption intensity is plotted vs. incident wavelength to generate an absorption spectrum. A method for measuring absorption may comprise measuring a 15 mg / ml solution in a quartz cuvette and comparing to a cuvette containing the solvent only. Unless stated otherwise, solution absorption data as provided herein is as measured in a methylated benzene solution, optionally a 1,2,4-trimethylbenzene solution. Data from model compounds was generated using Gaussian09 software available from Gaussian using Gaussian09 with B3LYP (functional) and LACVP* (Basis set). Donor Group 1 Side chains synthesis 5 Compound Example 1 Compound Example 1 was prepared according to the following reaction scheme: CeH-is p-TsOH, Toluene / Ethanol Compound Example 1 Compound Example 2 Compound Example 2 was prepared following the synthesis of Compound Example 1. Cyano-substituted acceptor units were prepared as described in WO2022 / 129137, the contents of which are incorporated herein by reference. Compound Example 2 Compound Examples 1 and 2 are soluble in solvents including alkylated benzenes, for example 1,2,4-trlmethylbenzene and chlorinated benzenes, for example dichlorobenzene. Absorption spectra of Compound Example 2 in 1,2,4-trimethylbenzene solution and in a film cast from 1,2,4-trimethylbenzene solution are shown in Figures 2 and 3, respectively. 10 SWV and absorption data of Compound Example 2 are provided in Table 1. Modelling data is provided in Table 1 for comparison using a model of Compound Example 2 in which all alkyl chains are methyl to simplify calculations. Slf corresponds to oscillator strength of the transition from SI (predicting absorption intensity) Model data Model data of further compounds is set out in Table 2 in which Slf corresponds to oscillator strength of the transition from SI (predicting absorption intensity) and Eopt is the 5 modelled optical gap. Table 2 Structure HOMO / eV LUMO / eV Eg / nm Slf Amax / nm Reference material NticN NC if / *0 NC bN -5.28 -3.84 864 2.95 923 Reference material > vCw o TX / xzsv i XX J n= / i Q x °x NC Tn 1 -5.28 -3.78 829 2.41 914 Reference material A Y / ° \ Q lJL J n= / l MJuHFI / TT0" NC^f-\=O CN / W f lfX ci s' , Cl b -5.14 -3.71 865 2.72 954 Reference material 1«. CN 0 X O J n 0SxA^cn T Js L NC iv ° ” Q x NC CN -5.36 -3.81 802 2.46 881 Reference material VCN > xo , °YYN NcVy0 °x A -5.25 -3.82 866 2.87 947 Reference material '■ / NGk™ / CN N n \ V2 t , yA nc^t Yo * Yv 's Y if o Y\ <. \ N N Y M NC CN -5.48 -3.90 785 3.00 867 Reference material cYa <s / \ Q n't ... iULJ cv=(( s YrYN nc y=° 1 Yn x Y Y -5.14 -3.71 865 2.72 954 Reference material w x °' Q Cl "ci -5.20 -3.72 844 2.80 926 Reference material NC CN / A_,Ss_a) OSS\J^,CN NC iLX 'i <^sZ NC CN -5.44 -4.07 905 2.71 987 Reference material V 4 0 | °\>^CN h s \ xn. / / । CN >' M >-( Vi NC 1 H N \=< JL# V ^sv # NC 1 o^s $ a^a -5.10 -3.74 913 2.89 1001 Reference material \ NX / N > c p __zS-s—Z N 0=vA^ / CN Nc^rXso n y'f / 'sx y / P Q °' NC CN -5.30 -3.78 815 2.43 894 z z °\_S oVtX Z Tf ° 'Ol [tn —.......... 1 >—. Cz-O~ ¢ / J -O. 1 ^0” o IL z vTrn o— / z c> 2 Z -5.30 -3.77 811 2.34 950 NCi cn ° -XX w ___ / o N 0=\ftCN X CN r^S^ Ss V / / L / k\ Ox ' Q XV NcZ CN -5.29 -3.76 812 2.32 893 NC ,CN ft »v k "'AA ,s^.s j A ,sAl «1 VkAAp s k “ V_ / / s kA s opA 'cn > ftO Q NC ™ -5.23 -3.74 831 2.44 916 N? CN \ AT O nc p x y= / JkA- / M. N oAA^CN "i A ™ NC^A / ^0 [ / Ss IT / ft rli °x o, cn w ftJk x NC CN -5.49 -4.04 858 2.27 942 NC FN Jft u (ft <-ft NC CN -5.42 -4.03 890 2.32 982 NC CN Q V Kft °ft AN NIC ft —A-s. XSvft ft AsftTft JUM sft V ff S N S' A CN k\ oK jAA nc o i 0 x ossZ cn o NC CN -5.36 -4.06 955 2.31 1059

Claims

1. A compound of formula (I) or (II): / \2 _ (Bi)x1 - (D-)y- - (B-)x2 - A3(I)A2 - (62)21 - (D2)y2 - (B3)x3- A1 - (B3)x4 - (D3)y3 - (B2)z2 - A3(II)wherein:A1 is a divalent heteroaromatic electron-accepting group;A2 and A3 independently in each occurrence is a monovalent 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 and x2 are each independently 0, 1, 2 or 3;x3 and x4 are each independently 0, 1, 2 or 3;y1, y2 and y3 are each independently at least 1;z1 and z2 are each independently 0, 1, 2 or 3; andwherein at least one occurrence of D1 of formula (I) or at least one occurrence of at least one of D2 and D3 of formula (II) is a group of formula (HI):(HI)wherein:each X is independently selected from is 0, S and Se;R1 in each occurrence is independently H or a substituent; andR2 in each occurrence is independently H or a substituent with the proviso that at least one R2 is Cs heteroaryl or phenyl substituted with at least one R5 group wherein R5 in each occurrence is independently selected from C1-20 alkyl wherein one or more non-adjacent C atoms of the Ci 20 alkyl may be replaced with O, S, NR3, COO, CONR3, or Si(R4)2 wherein R3 in each occurrence is H or a substituent and R4 in each occurrence is a substituent.

2. The compound according to claim 1 wherein at least one R2 is phenyl substituted with at least one R5 group.

3. The compound according to claim 2 wherein at least one R2 is phenyl substituted with at least two R5 groups.

4. The compound according to claim 1 or either of claims 2 and 3 wherein R5 independently in each occurrence is a C1-12 alkyl group.

5. The compound according to claim 1 or any one of claims 2-5 wherein R1 is selected fromH;C1-20 alkyl wherein one or more non-adjacent C atoms of the C1-20 alkyl may be replaced with 0, S, NR3, COO, CONR3, or Si(R4)2 wherein R3 in each occurrence is H or a substituent and R4 in each occurrence is a substituent;optionally substituted Ce-2oaryl, preferably phenyl; and optionally substituted heteroaryl, preferably thienyl.

6. The compound according to claim 5 wherein at least one R1 is a C1-19 alkoxy group.

7. The compound according to claim 6 wherein each R1 independently is a C1-19 alkoxygroup8. The compound according to claim 1 or any one of claims 2-7 wherein A2 and A3 are each independently selected from groups of formulae (IXa)-(IXq):rio (IXa)A(upwherein:U is a 5- or 6-membered ring which is unsubstituted or substituted with one or more substituents and which may be fused to one or more further rings;R10 is H or a substituent;G is C=O, C=S SO, SO2, NR33 or C(R33)2 wherein R33 is CN or COOR40 and R40 is H or a substituent;J is C=O, C=S, 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;R13 in each occurrence is a substituent;R15 in each occurrence is independently H or a substituent;R16 is a substituent;Ar6 is a 5-membered heteroaromatic group which is unsubstituted or substituted with one or more substituents;T1, T2 and T3 each independently represent an aryl or a heteroaryl ring which may be fused to one or more further rings and each of T1, T2 and T3 is independently unsubstituted or substituted with one or more substituents; andAr8 is a fused heteroaromatic group which is unsubstituted or substituted with one or more substituents and which is bound to an aromatic C atom of B1 or B2 and to a boron substituent of B1 or B2.

9. The compound according to claim 8 wherein at least one of A2 and A3 is a group of formula (IXa-2) or (IXa-3):(IXa-2) (IXa-3)wherein each X7-X10 is independently CR12 or N wherein R12 In each occurrence Is H or a substituent selected from Ci 20 hydrocarbyl and an electron withdrawing group; and each R15 independently is H or a substituent.

10. The compound according to claim 9 wherein the electron withdrawing group is F, Cl or CN.

11. A composition comprising an electron-donating material and an electron-accepting material wherein the electron accepting material is a compound according to claim 1 or any one of claims 2-10.

12. An organic electronic device comprising an active layer comprising a compound according to any one of claims 1-10 or a composition according to claim 11.

13. An organic electronic device according to claim 12 wherein the organic electronic device Is an organic photoresponslve device comprising a photoactive layer comprising the compound according to any one of claims 1-10 or the composition according to claim 11 disposed between the anode and cathode.

14. The organic electronic device according to claim 13 wherein the photoactive layer is a bulk heterojunction layer comprising a composition according to claim 11.

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 photosensor 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 according to any one of claims 1-10 or a composition according to claim 11 dissolved or dispersed in one or more solvents.

19. A method of forming an organic electronic device according to claim 12 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.

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