WO2024170695A1

WO2024170695A1 - Compounds for use in photosensors

Info

Publication number: WO2024170695A1
Application number: PCT/EP2024/053895
Authority: WO
Inventors: Kiran Kamtekar; Connor PATRICK; Nir YAACOBI-GROSS; Michal MACIEJCZYK; Florence BOURCET
Original assignee: Cambridge Display Technology Limited; Sumitomo Chemical Co., Ltd
Priority date: 2023-02-17
Filing date: 2024-02-15
Publication date: 2024-08-22
Also published as: TW202438500A; GB2627286A; GB202302314D0

Abstract

A compound of formula (I) wherein: X¹ is C(R¹)₂, Si(R¹)₂ or Ge(R¹)₂ wherein R¹ in each occurrence is a substituent; Y¹ is O, S or Se; Ar¹ in each occurrence is independently an unsubstituted or substituted monocyclic or polycyclic aryl or heteroaryl group or is absent; B¹ independently in each occurrence is a bridging group; f1 and f2 are each 1; g is at least 1; and A in each occurrence is independently a monovalent electron-accepting group. The compound of formula (I) may be used as an electron-accepting material of an organic photoresponsive device.

Description

COMPOUNDS FOR USE IN PHOTOSENSORS

BACKGROUND

WO2022/129137 discloses compounds of formula each EAG-EDG-EAG wherein EDGis a group of formula (II) and each EAG is independently an electron-accepting group of formula (III):

J V ollbrecht et al, “Design of narrow bandgap non-fullerene acceptors for photovoltaic applications and investigation of non-geminate recombination dynamics”, J. Mater. Chem. C, 2020,8, 15175- 15182 discloses solar cells containing donor polymer PTB7-Th or PBDBT and acceptor CETIC-4F (illustrated below) or COTIC-4F

W02021/079140 discloses a composition comprising an electron acceptor material and an electron donor material wherein the electron-acceptor material is a compound of formula EAG-EDG-EAG wherein each EAG is an electron-accepting group and EDG is a group of formula:

SUMMARY

The present disclosure provides a compound of formula (I):

wherein:

X¹ is C(R¹)₂, Si(R¹)2 or Ge(R¹)2 wherein R¹ in each occurrence is a substituent;

Y¹ is O, S or Se;

Ar¹ in each occurrence is independently an unsubstituted or substituted monocyclic or polycyclic aryl or heteroaryl group or is absent;

B¹ independently in each occurrence is a bridging group; fl and f2 are each independently 1 ; g is at least 1; and

A in each occurrence is independently a monovalent electron-accepting group.

Optionally, at least one A is an electron-accepting group of formula (II):

wherein:

G is C=0, C=S SO, SO2, NR³³ or C(R³³)2 wherein R³³ is CN or COOR⁴⁰ wherein R⁴⁰ in each occurrence is H or a substituent;

R³ is H or a substituent;

Z are each independently CN, CF3 or COOR⁴⁰ wherein R⁴⁰ in each occurrence is H or a substituent; and

Ar² is an unsubstituted or substituted monocyclic or polycyclic aromatic or heteroaromatic ring.

Optionally, Ar² is selected from: benzene substituted with at least one CN substituent; and an unsubstituted or substituted monocyclic or polycyclic heteroaromatic group.

Optionally, the group of formula (II) has formula (Ila):

wherein each X⁷-X¹⁰ is independently CR¹² or N wherein R¹² in each occurrence is H or a substituent selected from Ci-2ohydrocarbyl and an electron withdrawing group, with the proviso that when each of X⁷-X¹⁰ is CR¹² then at least one R¹² is CN.

Optionally, the group of formula (II) has formula (lib):

wherein Ar³ is an unsubstituted or substituted monocyclic or polycyclic aromatic or heteroaromatic group.

Optionally, Ar² is unsubstituted or substituted benzene.

Optionally, B¹ is selected from unsubstituted or substituted furan; unsubstituted or substituted thiophene; or a fused analogue thereof.

Optionally, B¹ is a group of formula (III):

wherein Y² is O, S or Se; and Ar⁴ is an unsubstituted or substituted monocyclic or polycyclic aromatic or heteroaromatic group.

Optionally, Ar³ is a group of formula (Illa):

wherein R⁸ in each occurrence is H or a substituent.

The present disclosure provides a composition comprising a compound as described herein and an electron-donating material.

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 an organic photoresponsive device comprising an anode, a cathode and a photoactive layer disposed between the anode and the cathode wherein the photoactive layer comprises a composition as described herein.

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 1000 nm.

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.

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.

Donor Group D

The compound of formula (I) comprises an electron-donating group D:

X¹ is C(R¹)2, Si(R¹)2 or Ge(R¹)2 wherein R¹ in each occurrence is a substituent.

Y¹ is O, S or Se.

Ar¹ in each occurrence is independently an unsubstituted or substituted monocyclic or polycyclic aryl or heteroaryl group or is absent. g is at least 1, preferably 1, 2 or 3.

Each of the electron-accepting groups A of formula (I) has a lowest unoccupied molecular orbital (LUMO) level that is deeper (i.e., further from vacuum) than the donor group D of formula (I), preferably at least 1 eV deeper. The LUMO levels of electron-accepting groups A and electron-donating groups D 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 LACVP* (Basis set).

Preferably, the compound of formula (I) has a peak absorption wavelength greater than 1000 nm, optionally at least 1200 nm, preferably less than 1800 nm.

Preferably, R¹ in each occurrence is independently selected from:

Ci-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR¹⁷ wherein R¹⁷ is a Ci-nhydrocarbyl, COO or CO and one or more H atoms of the alkyl may be replaced with F; and an aromatic or heteroaromatic group, preferably a C6-20 aryl, more preferably phenyl, which is unsubstituted or substituted with one or more substituents.

Where present, substitutents of an aromatic or heteroaromatic group R¹ are preferably selected from substituents R¹¹ wherein R¹¹ in each occurrence is independently selected from F, Cl, Br, CN, NO2, and Ci -20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR¹⁷ wherein R¹⁷ is a Ci-nhydrocarbyl, COO or CO and one or more H atoms of the alkyl may be replaced with F.

R¹⁷ is optionally a C1-12 alkyl or phenyl which is unsubstituted or substituted with one or more C1-6 alkyl groups.

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 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. Each Ar¹ independently may or may not be present. In embodiments where neither Ari is present the group D has formula D-l :

wherein R² in each occurrence is independently H or a substituent, optionally H or a substituent R¹¹ as described above. Preferably, each R² is H.

Optionally, only one Ar¹ group is present.

Optionally, both Ar¹ groups are present in which case the Ar¹ groups are the same or different. Preferably, Ar¹ in each occurrence is independently selected from furan; thiophene; furofuran; thienothiophene; and furothiophene. Substituents of Ar¹, if present, are optionally selected from substituents R¹¹ as described above.

Bridging units

Bridging units B¹ are preferably each selected from vinylene, arylene and heteroarylene. The arylene and heteroarylene groups are preferably monocyclic or bicyclic groups, each of which may be unsubstituted or substituted with one or more substituents.

Preferably, each B¹ contains at least one arylene or heteroarylene group, more preferably at least one heteroarylene group.

Exemplary monocyclic aromatic and heteroaromatic groups B¹ are benzene, thiophene and furan, each of which may be unsubstituted or substituted with one or more substituents, optionally one or more substituents R⁸ as described below.

Exemplary bicyclic groups B¹ are selected from formulae (III) and (IV):

(Ill) (IV) wherein Ar⁴ is an unsubstituted or substituted monocyclic aromatic or heteroaromatic group, preferably benzene; thiophene; furan; pyridine; pyrazine; or piperidine, each of which may be unsubstituted or substituted with one or more substituents, optionally one or more substituents R⁸ as described below.

Optionally heteroarylene groups B¹ are selected from units of formulae (Via) - (VIo):

(Vim) (VIn) (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; 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.

Substituents of a phenyl group R⁸, where present, may be selected from substituents R¹¹ as described above.

R⁶ is H or a substituent, preferably H or 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 C1-12 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; 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.

R⁸ is preferably H, C1-20 alkyl or C1-19 alkoxy.

R⁸ groups of formulae (Via), (VIb) and (Vic) may be linked to form an optionally substituted bicyclic ring.

Electron- Accepting Groups A

The monovalent acceptor groups A may each independently be selected from any such units known to the skilled person. The A groups of the compound of formula (I) 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. G is preferably C=O or SO2, more preferably C=O.

The N atom of formula (IXe) may be unsubstituted or substituted.

R³ is H or a substituent, preferably H or a substituent selected from the group consisting of Ci- 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; and 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.

Most preferably, R³ is H.

J is O or S, preferably O.

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 in each occurrence is independently H; F; 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 a group selected from:

R¹⁶ is H or a substituent, preferably a substituent selected from:

-(Ar⁵)_w wherein Ar⁵ in each occurrence is independently an unsubstituted or substituted aryl or heteroaryl group, preferably thiophene, and w is 1, 2 or 3;

and

Ci-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.

Ar⁶ is a 5 -membered heteroaromatic group, preferably thiophene or furan, which is unsubstituted or substituted with one or more substituents.

Substituents of Ar⁵ and Ar⁶, where present, are optionally 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.

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 benzothiadi azole.

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 R³, and which is bound to an aromatic C atom of B¹ or B² and to a boron substituent of B¹ or B². Preferred groups A are groups having a non-aromatic carbon-carbon bond which is bound directly to B¹.

Preferably at least one A, preferably both groups A, are a group of formula (II):

wherein:

G is as described above and is preferably C=O or SO2, more preferably C=O;

R³ is as described above;

Ar² 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 each Z is independently CN, CF3 or COOR⁴⁰ wherein R⁴⁰ in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. Preferably, each Z is the same. Preferably, each Z is CN.

Ar² may be unsubstituted or substituted with one or more substituents. Substituents of Ar² are preferably selected from groups R¹¹ as described above.

Optionally, the group of formula (II) has formula (Ila):

each X⁷-X¹⁰ is independently CR¹² or N wherein R¹² in each occurrence is H or a substituent selected from Ci-2o hydrocarbyl and an electron withdrawing group. Preferably, the electron withdrawing group is F, Cl, Br or CN, more preferably F, Cl or CN; and most preferably CN.

The Ci -20 hydrocarbyl group R¹² may be selected from C1-20 alkyl; unsubstituted phenyl; and phenyl substituted with one or more C 1-12 alkyl groups.

In a particularly preferred embodiment, each of X⁷-X¹⁰ 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.

Optionally, the group of formula (II) has formula (lib):

wherein Ar³ is an unsubstituted or substituted monocyclic or polycyclic aromatic or heteroaromatic group. Preferably, Ar³ is benzene which is unsubstituted or substituted with one or more substituents. Substituents of Ar³ may be selected from R¹¹ as described above, more preferably R¹² as described above.

Exemplary groups of formula (IXd) include:

Exemplary groups of formula (IXe) include:

An exemplary group of formula (IXq) is:

An exemplary group of formula (IXg) is:

An exemplary group of formula (IXj) is:

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 R³.

Exemplary groups of formula (IXm) are:

An exemplary group of formula (IXn) is:

Groups of formula (IXo) are bound directly to a bridging group B¹ or B² substituted with a group of formula -B(R¹⁴)2 wherein R¹⁴ in each occurrence is a substituent, optionally a C1-20 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 C1-12 alkyl groups. 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:

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 or consists of the compound of formula (I) and an electron-donating compound. The bulk heterojuction layer comprise one or more further materials, for example one or more further electron-donating materials and / or one or more further electron-accepting materials.

In some embodiments, the weight of the electron-donating material(s) to the electron-accepting material(s) is from about 1:0.5 to about 1:2, preferably about 1:1.1 to about 1:2.

Preferably the, or each, electron-donating material has a type II interface with the, or each, electron-accepting material, i.e. the or each electron-donating material has a shallower HOMO and LUMO that the corresponding HOMO and LUMO levels of the or each electronaccepting material. Preferably, the compound of formula (I) has 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) is less than 1.4 eV. 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 the compound of formula (I) 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 electronblocking 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.

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 poly acene, poly aniline, 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, poly benzo [1,2- b:4,5-b']dithiophene, polyisothianaphthene, poly(monosubstituted pyrrole), poly(3,4- bisubstituted pyrrole), poly-l,3,4-oxadiazoles, polyisothianaphthene, derivatives and copolymers 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.

The donor polymer is preferably a donor-acceptor (DA) copolymer comprising a donor repeat unit and an acceptor repeat unit.

Preferred donor units are selected from thiophene which is optionally substituted with one or more substituents R¹¹ as described above; and repeat units of formulae (X), (XII) and (XII):

wherein:

Y^A in each occurrence is independently O, S or NR⁵⁵; Z^A in each occurrence is O, CO, S, NR⁵⁵ or C(R⁵⁴)2; and R⁵¹, R⁵⁴ and R⁵⁵ independently in each occurrence is H or a substituent.

Optionally, R⁵¹ independently in each occurrence is selected fromH; F; C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR², 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. 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 R⁵¹ is H.

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 Ci -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 O, 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 O, S, NR⁶, CO or COO and one or more H atoms may be replaced with F. Preferably, Ar⁷ is phenyl.

Preferably, R⁵⁵ is H or Ci-2ohydrocarbyl group.

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, optionally phenyl or a 5 -membered heteroaromatic group, which is unsubstituted or substituted with one or more substituents selected from F and C1-12 alkyl wherein one or more non-adjacent, nonterminal C atoms may be replaced with O, S, COO or CO.

wherein Y³ is O, S or Se, preferably S; R⁵ in each occurrence is H or a substituent, more preferably H or a substituent R¹¹ as described above, most preferably H; and Q is C(R²¹)2 or Si(R²¹)2 wherein R²¹ in each occurrence is a substituent, preferably a substituent selected from: C1-20 alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, NR¹⁷ wherein R¹⁷ is a Ci-nhydrocarbyl, COO or CO and one or more H atoms of the alkyl may be replaced with F; and an aromatic or heteroaromatic group, preferably a C6-20 aryl, more preferably phenyl, which is unsubstituted or substituted with one or more substituents. Substituents of an aromatic or heteroaromatic group R²¹ may be selected from R¹¹ as described above.

Preferred acceptor units include benzothiadiazole which is optionally substituted with one or more substituents R¹¹; and repeat units of formula (XIII):

wherein R² is H or a substituent; and Y⁴ is O, S or Se, preferably S.

R² is preferably H; C1-12 alkyl wherein one or more C atoms of the C1-12 alkyl other than a terminal C atom or the C atom bound to N of NR² may be replaced with O, S, CO or COO; or an aromatic or heteroaromatic group, preferably a C6-12 aryl group, more preferably phenyl, which may be unsubstituted or substituted with one or more substituents.

Where present, substituents of an aromatic or heteroaromatic group R² are preferably selected from R¹¹ as described above.

Fullerene

In some embodiments, the compound of formula (I) 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) and one or more further electron-accepting materials. Preferred further electron-accepting materials are fullerenes. The compound of formula (I) : 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):

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-R³² are 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 C1-12 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) 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, rollcoating, spray coating, doctor blade coating, wire bar coating, slit coating, ink jet printing, screen printing, gravure printing and flexographic printing.

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 C1-10 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 dimethoxy benzene 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 1000 nm or at least 1200 nm, optionally in the range of 1000-1500 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/AgCl 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/AgCl using cyclic voltammetry (CV).

The sample is dissolved in toluene (3 mg / 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 toluene solution.

Synthesis

Compounds of Formula (I) having a donor group D-l in which no Ar¹ group is present as described above may be prepared according to the following General Scheme 1 in which R’ is a Ci- 12 alkyl:

General Scheme 1

Donor groups D in which at least one Ar¹ is present may be prepared according to General Scheme 2, following general approaches set out in JP2015/183032 and W02021/079140, the contents of which are incorporated herein by reference, or General Scheme 3 for which the publications referred to within the Scheme are incorporated herein by reference:

General Scheme 2

General Scheme 3

Compound Example 1 was prepared according to the following reaction scheme:

Compound Example 1

Intermediate 2 Compound 1 Intermediate 1 (1.55 g, 2.32 mmol) was dissolved in anhydrous THF (30 mL), then cooled in an ice/salt bath to -10 °C. The mixture was sparged with N₂ for 15 minutes. N- bromosuccinimide (0.866 g, 4.87 mmol) was added portion-wise to maintain a temperature of -10°C. After complete addition, the reaction vessel was wrapped in aluminium foil and stirred for 2 hours under N2. Na2S2O3 (20 mL) was added to quench any remaining NBS, then the mixture was diluted with n-heptane (30 mL). The organic phase was washed with saturated water (2 × 40 mL), then brine (40 mL) and dried over MgSO4.The solid was removed by filtration and the solvent was removed under reduced pressure to yield Compound 1 Intermediate 2 (1.91 g, 99%). The product used directly in the next step without any further purification; HPLC purity = 99.18%. ¹H NMR (600 MHz, CDCl3): δ [ppm] 6.96 (s, 2H), 6.86 (t, J = 1.2 Hz, 2H), 6.71 (d, J = 1.2 Hz, 2H), 2.47 (t, J = 7.6 Hz, 8H), 1.51 (septet, J = 7.6 Hz, 8H), 1.30-1.24 (m, 24H), 0.89-0.85 (m, 12H). LCMS m/z 825.2799 [M+H]⁺. Intermediate 4 A solution of bromothiophene 3 (10.0 g, 19.3 mmol) in anhydrous THF (160 mL) was cooled to -78 °C, then sparged with N₂ for 15 minutes. n-Butyllithium (2.5 M in hexane, 8.47 mL, 21.2 mmol) was added dropwise to the mixture, ensuring that the internal temperature did not exceed -72 °C. The reaction was stirred at -78 °C for 2 hours before dropwise addition of neat 2-Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (4.70 mL, 23.1 mmol), ensuring that the internal temperature did not exceed -72 °C. The reaction was stirred at -78°C for a further 1 hour, then allowed to warm to room temperature and stirred for a further 16 hours. The reaction was cooled to 0 °C and quenched by the dropwise addition of aqueous 1 M HCl solution (~50 mL) so as to maintain an internal temperature of <2 °C. After complete quenching, the mixture was warmed up to room temperature. Water (150 mL) and n-heptane (200 mL) was added, the organic phase was separated, washed with water (2 × 150 mL), then brine (150 mL). The organic layer was dried over MgSO₄, filtered and the solvent was evaporated under reduced pressure to yield Compound 1 Intermediate 4 (10.94 g, containing residual solvent and protonated thiophene) as a pale orange oil. NMR purity = 84%. ¹H NMR (600 MHz, CDCl3): δ [ppm] 6.94 (s, 1H), 5.55 (s, 1H), 3.93 (d, J = 5.93 Hz, 2H), 3.75 (d, J = 10.9 Hz, 2H), 3.62 (d, J = 10.9 Hz, 2H), 1.80-1.74 (m, 1H), 1.50-1.44 (m, 2H), 1.34- 1.26 (m, 42H), 0.91 (t, J = 6.9 Hz, 8H), 0.81 (s, 3H). LCMS m/z 656.4246 [M+H]⁺. Intermediate 5 Compound 1 Intermediate 2 (1.90 g, 2.30 mmol) and Compound 1 Intermediate 4 (3.24 g, 5.75 mmol) were dissolved in THF (75 mL) and sparged with N2 for 30 minutes. At the same time, a solution of K₃PO₄ in water (3 M, 7.66 mL, 23 mmol) was prepared and sparged with N2 for a minimum of 30 minutes. Tris(dibenzylideneacetone) dipalladium(0) (105 mg, 115 μmol) and tri-tert-butylphosphonium tetrafluoroborate (66.7 mg, 230 μmol) were added to the THF solution, which was then sparged with N2 for a further 10 min. The degassed K3PO4 solution was charged to the flask, then the mixture was placed into a pre-heated oil bath at 65 °C and stirred for 1 hour. Once complete, the reaction was cooled and toluene (120 mL) was added. The organic layer was washed with water (2 × 60 mL), then brine (120 mL). The combined organic extracts were dried over MgSO₄ and the solvent removed under reduced pressure to yield Compound 1 Intermediate 5 (6.03 g) as a waxy red solid. Due to stability of the acetal group, the material was used directly in the next step without further purification. HPLC purity = 92.50%. LCMS m/z 1541.1460 [M+H]⁺. Intermediate 6 Compound 1 Intermediate 5 (3.56 g, 2.31 mmol) was dissolved in THF (165 mL). Water (32 mL) was added before dropwise addition of trifluoroacetic acid (7.04 mL, 92.2 mmol). The reaction was warmed to 55 °C and stirred under N2 for 1 hour. The reaction was cooled to room temperature and then poured onto ice (150 g). A mixture of THF/n-heptane (4:1, 200 mL) was added before portion wise addition of saturated NaHCO3 solution (~100 mL, until the aqueous layer reached pH = 7). The organic layer was separated and washed with water (2 × 150 mL), then brine (150 mL). The combined organic extracts were dried over MgSO4 and the solvent removed under reduced pressure to yield a bright red oil. The crude material was purified by silica chromatography (heptane/toluene, gradient elution from 0 to 90%), then dried under vacuum for 18 h to yield Compound 1 Intermediate 6 (3.16 g, containing residual solvent) as a bright red viscous oil; HPLC purity = 95.94%. ¹H NMR (600 MHz, CDCl₃): δ [ppm] 9.73 (s, 2H), 7.44 (s, 2H), 7.30 (s, 2H), 6.86 (s, 2H), 6.81 (s, 4H), 4.06 (d, J = 5.4 Hz, 4H), 2.47 (t, J = 7.9 Hz, 8H), 1.88 (septet, J = 6.1 Hz, 2H), 1.59- 1.43 (m, 18H), 1.38-1.33 (m, 8H), 1.30-1.22 (m, 60H), 0.88-0.82 (m, 26H). LCMS m/z 1367.9843 [M]⁺. Compound Example 1 IC-2CN was prepared as described in WO2022/129137, the contents of which are incorporated herein by reference. Compound 1 Intermediate 6 (500 mg, 365 μmol), IC-2CN (444 mg, 1.82 mmol) and p- toluenesulfonic acid (471 mg, 2.74 mmol) were dissolved anhydrous toluene (18 mL) and anhydrous ethanol (36 mL). The mixture was sparged with N2 for 10 minutes, before warming to 65 °C and allowed to stir under N₂ for 60 minutes. The reaction was allowed to cool to room temperature, then was concentrated under reduced pressure (leaving ~5 mL of residual solvent). Toluene (100 mL) was added and the material was passed through a short silica plug (toluene/EtOAc, 95:5). The solvent was removed under reduced pressure and the resulting crude material was purified by silica chromatography (heptane/dichloromethane, gradient elution from 33 to 100%). The purified material was dissolved in minimal dichloromethane (~5 mL) and precipitated into n-pentane (~75 mL). The solid was collected by filtration and dried in a vacuum oven for 18 hours (50 °C, 0.1 mbar) to yield Compound Example 1 (450 mg, 68%) as a deep blue solid; HPLC purity = 90.63%. ¹H NMR (600 MHz, CDCl3): δ [ppm] 9.00 (s, 2H), 8.77 (s, 2H), 8.12 (s, 2H), 7.67 (s, 2H), 7.50 (br s, 2H), 6.94 (s, 2H), 6.81 (s, 4H), 4.16 (d, J = 4.9 Hz, 4H), 2.51 (t, J = 7.9 Hz, 8H), 1.94 (septet, J = 5.8 Hz, 2H), 1.62-1.48 (m, 18H), 1.42-1.36 (m, 8H), 1.34-1.22 (m, 60H), 0.90-0.79 (m, 26H). LCMS m/z 1820.9302 [M+H]⁺. UV-vis (1,2,4-trimethylbenzene) λmax (ε) 951 (212000), 847 (101000), 310 (47300) nm. SWV (solution, toluene) HOMO = −5.30 eV; LUMO = −4.13 eV; E_g = 1.17 eV. SWV (film, toluene) HOMO = -5.37 eV; LUMO = -4.28 eV; E_g = 1.19 eV.

Qx-2C1

Step 1:

Qx-2C1 Intermediate 1 (250g, 1.06 mol) was dissolved in 2.5 L of dichloroethane. N- Bromosuccinimide (754g, 4.24 mol), was added to reaction mixture portion wise and it was heated at 75 °C for 16 hours. Solid impurities were filtered off and washed with heptane. Filtrate was concentrated under vacuum to get 255g of crude material. Product Qx-2C1 Intermediate 2 was used in the next step without further purification.

Step 2:

Qx-2C1 Intermediate 2 (99.9 g, 434 mmol) and Qx-2C1 Intermediate 3 (55g, 310 mmol) were dissolved in IL of ethanol, p-toluene sulfonic acid (4.69g, 24.7 mmol) was added to the reaction mixture and it was heated at 68 °C for 3 hours. Then, the reaction was concentrated under vacuum to give 105g of crude product which was purified by column chromatography with dichloromethane to give 80g of the desired product.

Step 3:

Qx-2C1 Intermediate 4 (50 g, 134 mmol) was dissolved in 500 mL of methanol. Lithium hydroxide monohydride (12.9 g, 308 mmol) was added to the reaction mixture, and it was stirred at room temperature for 16 hours. The reaction mixture was filtered and the obtained solid was stirred in diluted hydrochloric acid for 3 hours. The solid was filtered to obtain 30g of the desired product Qx-2C1 Intermediate 5.

Step 4:

Qx-2C1 Intermediate 5 (30 g, 104 mmol) and acetic anhydride (600 mL) were combined in the flask. The reaction mixture was heated at 130 °C for 6 hours. After this time, it was cooled down and concentrated under reduced pressure to obtain 30g of crude product Qx-2C1 Intermediate 6 which was used directly in the next step without further purification.

Step 5

To stirred solution of Qx-2C1 Intermediate 6 (30 g, l llmmol) in acetic anhydride (240 mL) was added tri ethylamine (11.2 g, 111 mmol). To this tert-butyl acetoacetate (18.3 g, 116 mmol) was added dropwise. The reaction mixture was stirred at room temperature for 16 hours and then poured slowly into another flask containing 1.5 N hydrochloric acid (400 mL) and 400 mL of ice water. This was then stirred for 48 hours at room temperature. The obtained solid was isolated by filtration to give 15 g of the desired product Qx-2C1 Intermediate 7 as a black solid which was used in the next step without further purification.

Step 6

Qx-2C1 Intermediate 7 (5 g, 18.7 mmol) was dissolved in pyridine (90 ml). To this malononitrile (3.08 g, 46.7 mmol) was added and the mixture was stirred for 2 hours at room temperature. The reaction was concentrated under reduced pressure to give 9g of crude material which was purified by neutral alumina column chromatography using di chloromethane and 1% tri-ethylamine in methanol. The obtained product was triturated with hexane / dichloromethane and filtered off to give 2.013 g of pure Qx-2C1 product (98.81% by HPLC) as triethylamine salt. Compound Example 2

Intermediate 6 (360 mg, 263 pmol), Qx-2C1 (412 mg, 1.31 mmol) and p-toluenesulfonic acid (339 mg, 1.97 mmol) were dissolved anhydrous toluene (13 mL) and anhydrous ethanol (26 mL). The mixture was sparged with N2 for 10 minutes, before warming to 65 °C and allowed to stir under N2 for 90 minutes. Once complete, the hot reaction mixture was filtered, then the remaining solid washed with hot MeOH (2 x 20 mL), hot EtOH (2 x 20 mL) and pentane (2 x 20 mL). The solid was dried on the filter paper under an N2 shower. The solid was purified by silica chromatography (heptane/di chloromethane, gradient elution from 33 to 100%). The purified material was dissolved in minimal di chloromethane (~5 mL) and precipitated into MeOH (~75 mL). The solid was collected by filtration and dried in a vacuum oven for 18 hours (50 °C, 0.1 mbar) to yield Compound Example 2 (324 mg, 63%) as a deep blue solid; HPLC purity = 97.19%. ¹H NMR (600 MHz, CDCl3): δ [ppm] 8.82 (br s, 2H), 8.47 (s, 2H), 8.39 (s, 2H), 7.70 (s, 2H), 6.95 (s, 2H), 6.81 (s, 4H), 4.19 (d, J = 4.3 Hz, 4H), 2.53 (t, J = 7.9 Hz, 8H), 1.96 (septet, J = 6.1 Hz, 2H), 1.63-1.48 (m, 18H), 1.43-1.36 (m, 8H), 1.36-1.20 (m, 58H), 0.90-0.80 (m, 24H). Note: Not all resonances observed due to overlapping signals. LCMS m/z 1961.9491 [M]⁻, 1977.9491 [M+NH₄]⁺. UV-vis (1,2,4-trimethylbenzene) λmax (ε) 978 (233000), 873 (94700), 779 (30600) nm. SWV (solution, toluene) HOMO = −5.33 eV; LUMO = −4.24 eV; Eg = 1.09 eV. SWV (film, toluene) HOMO = −5.53 eV; LUMO = −4.22 eV; E_g = 1.31 eV. Compound Example 3

Compound Example 3, Intermediate 2

Compound 3, Intermediate 1 (3.05 g, 7.57 mmol) was dissolved in anhydrous THF (120 mL), then cooled to -78 °C. The mixture was sparged with N2 for 15 minutes, n- Butyllithium (2.5 M in hexane, 6.32 mL, 15.8 mmol) was added dropwise to the mixture, ensuring that the internal temperature did not exceed -70 °C. The reaction was stirred at -78 °C for 90 minutes before being slowly warmed to 0 °C and left to stir at this temperature for a further 1 hour. The reaction was cooled back down to -78 °C before dropwise addition of neat tributyltin chloride (6.32 mL, 15.8 mmol), ensuring that the internal temperature did not exceed -70 °C. The reaction was stirred at -78°C for a further 1 hour, then allowed to warm to room temperature and stirred for a further 16 hours. The reaction was cooled to 0 °C and quenched by addition of water (75 mL). The organic layer was extracted with ^-heptane (100 mL), then washed with water (3 x 75 mL) and then saturated brine solution (75 mL). The organic extracts were dried over MgSCL and the solvent removed under reduced pressure to give Compound 3, Intermediate 2 as a pale yellow oil (8.38 g, 112% containing excess BusSnCl). The material was used directly in the next step without further purification; HPLC purity = 34.58% - note that this is complex mixture of tin-containing species.

LCMS m/z 981.5079 [M+H]⁺.

Compound Example 3 Intermediate 4

Compound Example 3, Intermediate 2 (2.62 g, 2.67 mmol) and Compound Example 3, Intermediate 3 (3.03 g, 5.87 mmol) were dissolved in anhydrous toluene (55 mL) and sparged with N2 for 15 minutes. Tris(dibenzylideneacetone) dipalladium(O) (195 mg, 214 pmol) and tris(o-tolyl)phosphine (243 mg, 801 pmol) were charged to the flask and the mixture sparged with N2 for a further 5 minutes. The mixture was heated to 110 °C and stirred under N2 for 1 hour. The cooled reaction mixture was passed through a silica plug, washing initially with n- heptane (this filtrate was discarded), then with w-heptane/dichloromethane (1:1). The solvent was removed under reduced pressure to yield Compound Example 3 Intermediate 4 (6.17 g, 180%, containing excess intermediate 3 and tin-containing species) as a viscous red oil; HPLC purity = 52.54%.

LCMS m/z 1275.9453 [M+H]⁺. Compound Example 3 Intermediate 5 Compound Example 3 Intermediate 4 (3.50 g, 2.74 mmol) was dissolved in THF (195 mL). Water (39 mL) was added before dropwise addition of trifluoroacetic acid (3.77 mL, 49.3 mmol). The reaction was warmed to 55 °C and stirred under N2 for 2.5 hours. The reaction was cooled to room temperature and then poured onto ice (200 g). A mixture of THF/n-heptane (4:1, 200 mL) was added before portion wise addition of saturated NaHCO3 solution (~75 mL, until the aqueous layer reached pH = 7). The organic layer was separated and washed with water (2 × 150 mL), then brine (150 mL). The combined organic extracts were dried over MgSO4 and the solvent removed under reduced pressure to yield a bright red oil. The crude material was purified by silica chromatography (heptane/dichloromethane, gradient elution from 0 to 100%) to yield Compound Example 3 Intermediate 5 (1.98 g, 66%) as a bright red viscous oil; HPLC purity = 93.95%. ¹H NMR (600 MHz, CDCl₃): δ [ppm] 9.77 (s, 2H), 7.49 (s, 2H), 7.36 (s, 2H), 4.11 (t, J = 5.2 Hz, 4H), 1.93 (dq, J = 10.4, 5.2 Hz, 6H), 1.65-1.58 (m, 4H), 1.55-1.48 (m, 4H), 1.45- 1.25 (m, 50H), 1.06-0.97 (m, 11H), 0.97-0.87 (m, 23H), 0.73 (t, J = 6.1 Hz, 8H), 0.64 (t, J = 7.2 Hz, 6H). LCMS m/z 1103.7786 [M+H]⁺. Compound Example 3 Compound Example 3 Intermediate 5 (445 mg, 403 μmol), Qx-2Cl (633 mg, 2.01 mmol) and p-toluenesulfonic acid (520 mg, 3.02 mmol) were dissolved anhydrous toluene (40 mL) and anhydrous ethanol (15 mL). The mixture was sparged with N2 for 10 minutes, before warming to 65 °C and allowed to stir under N₂ for 60 minutes. Once complete, the hot reaction mixture was filtered, then the remaining solid washed with hot MeOH (2 × 30 mL), hot EtOH (2 × 30 mL) and pentane (2 × 30 mL). The solid was dried on the filter paper under an N₂ shower. The solid was dried in a vacuum oven for 18 hours (50 °C, 0.1 mbar) to yield Compound Example 3 (592 mg, 87%) as a deep blue solid; HPLC purity = 89.61%. ¹H NMR (600 MHz, toluene-d8): δ [ppm] 8.81 (s, 2H), 8.17 (s, 2H), 8.00 (t, J = 5.3 Hz, 2H), 7.82 (t, J = 11.2 Hz), 7.45 (br s, 2H), 3.81 (s, 4H), 1.99 (dq, J = 11.5, 4.2 Hz, 4H), 1.86-1.77 (m, 2H), 1.68-1.60 (m, 4H), 1.77-1.52 (m, 4H), 1.49-1.36 (m, 39H), 1.21-1.10 (m, 10H), 1.10- 1.01 (m, 12H), 0.99 (dt, J = 5.7, 1.2 Hz, 6H), 0.91 (dt, J = 6.9, 1.3 Hz, 6H), 0.89-0.84 (m, 2H), 0.78 (t, J = 7.4 Hz, 6H). LCMS m/z 1698.6919 [M+H]⁺. UV-vis (1,2,4-trimethylbenzene) λmax (ε) 983 (233000), 880 (92300), 785 (29400). SWV (solution, toluene) HOMO = −5.27 eV; LUMO = −4.25 eV; Eg = 1.02 eV. SWV (film, toluene) HOMO = −5.48 eV; LUMO = −4.23 eV; E_g = 1.25 eV. Model data Energy levels of exemplary compounds were modelled using Gaussian09 software available from Gaussian using Gaussian09 with B3LYP (functional). Results are set out in Table 1 in which in which S1f corresponds to oscillator strength of the transition from S1 (predicting absorption intensity). Table 1 HOMO LUMO E λ_max Structure _g ^S1f

Table 2

Table 2 shows modelling data with variation of acceptor groups A and a donor group D in which X¹ is QR¹^ and no Ar¹ groups are present.

Table 3

Table 3 shows modelling data with variation of acceptor groups A and a donor group D in which X¹ is Si(R¹)2 and no Ar¹ groups are present.

Table 4

Table 4 shows modelling data with variation of acceptor groups A and a donor group D in which X¹ is Ge(R¹)2 and no Ar¹ groups are present.

Table 5

Table 5 shows modelling data for compounds in which each B¹ is a 3, 4-diphenylthi enopyrazine bridging unit.

Claims

1. A compound of formula (I):

wherein:

Y¹ is O, S or Se;

B¹ independently in each occurrence is a bridging group; fl and f2 are each 1 ; g is at least 1 ; and

A in each occurrence is independently a monovalent electron-accepting group.

2. The compound according to claim 1 wherein at least one A is an electron-accepting group of formula (II):

wherein:

R³ is H or a substituent;

3. The compound according to claim 2 wherein Ar² is selected from: benzene substituted with at least one CN substituent; and an unsubstituted or substituted monocyclic or polycyclic heteroaromatic group.

4. The compound according to claim 3 wherein the group of formula (II) has formula (Ila):

5. The compound according to claim 3 wherein the group of formula (II) has formula (lib) :

6. The compound according to claim 3 wherein Ar² is unsubstituted or substituted benzene.

7. The compound according to any one of the preceding claims wherein B¹ is selected from unsubstituted or substituted furan; unsubstituted or substituted thiophene; or a fused analogue thereof.

8. The compound according to claim 7 wherein B¹ is a group of formula (III):

9. The compound according to claim 8 wherein Ar³ is a group of formula (Illa):

wherein R⁸ in each occurrence is H or a substituent.

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

11. A formulation comprising a compound or composition according to any one of the preceding claims dissolved or dispersed in one or more solvents.

12. An organic photoresponsive device comprising an anode, a cathode and a photoactive layer disposed between the anode and the cathode wherein the photoactive layer comprises a composition according to claim 10.

13. A photosensor comprising a light source and an organic photodetector according to claim 12 wherein the organic photodetector is configured to detect light emitted from the light source.

14. The photosensor according to claim 13, wherein the light source emits light having a peak wavelength of greater than 1000 nm.