WO2022129137A1

WO2022129137A1 - Compound

Info

Publication number: WO2022129137A1
Application number: PCT/EP2021/085841
Authority: WO
Inventors: Kiran Kamtekar; Sophie Ann JONES; Nir YAACOBI-GROSS
Original assignee: Cambridge Display Technology Ltd.; Sumitomo Chemical Co., Ltd.
Priority date: 2020-12-15
Filing date: 2021-12-15
Publication date: 2022-06-23
Also published as: EP4263551A1; JP2023522874A; TW202231707A; GB202019810D0; GB2602025A; CN116670139A

Abstract

A compound of formula (I): EAG – EDG – EAG (I) wherein EDG is an electron-donating group of formula (II) each EAG is independently an electron accepting group of formula (III) (II) (III) each X is independently O or S; each Y is independently O, S, Se, NR⁸ or C(R⁹)₂ wherein R⁸ and R⁹ independently in each occurrence are selected from H or a substituent; Ar³ and Ar⁴ independently in each occurrence is a monocyclic or polycyclic aromatic or heteroaromatic group; R¹ and R² independently in each occurrence is a substituent; R3 - R6 are each independently H or a substituent; Z¹ is a direct bond or Z¹ together with the substituent R⁴ forms Ar¹ wherein Ar¹ is a monocyclic or polycyclic aromatic or heteroaromatic group; Z² is a direct bond or Z² together with the substituent R⁵ forms Ar² wherein Ar² is a monocyclic or polycyclic aromatic or heteroaromatic group; p is 0, 1, 2 or 3; q is 0, 1, 2 or 3; R¹⁰ in each occurrence is H or a substituent; ---- represents a linking position to EDG; and R⁷ in each occurrence is H or a substituent with the proviso that at least one R⁷ is CN. The compound of formula (I) may be used as an electron acceptor in a bulk heterojunction layer of an organic photoresponsive device.

Description

COMPOUND

BACKGROUND

Embodiments of the present disclosure relate to organic compounds for use in organic photoresponsive devices, in particular electron-accepting compounds for use in organic photodetectors.

A range of organic electronic devices comprising organic semiconductor materials are known, including organic light-emitting devices, organic field effect transistors, organic photovoltaic devices and organic photodetectors (OPDs).

WO 2018/065352 discloses an OPD having a photoactive layer that contains a small molecule acceptor which does not contain a fullerene moiety and a conjugated copolymer electron donor having donor and acceptor units.

WO 2018/065356 discloses an OPD having a photoactive layer that contains a small molecule acceptor which does not contain a fullerene moiety and a conjugated copolymer electron donor having randomly distributed donor and acceptor units. Yao et al, “Design, Synthesis, and Photovoltaic Characterization of a Small Molecular Acceptor with an Ultra-Narrow Band Gap”, Angew Chem Int Ed Engl. 2017 Mar 6;56(11):3045-3049 discloses a non-fullerene acceptor with a band gap of 1.24 eV.

Li et al, “Fused Tri s(thi enothiophene) -Based Electron Acceptor with Strong NearInfrared Absorption for High-Performance As-Cast Solar Cells”, Advanced Materials, Vol. 30(10), 2018 discloses a fused octacyclic electron acceptor (FOIC) for solar cells.

Gao et al, “A New Non-fullerene Acceptor with Near Infrared Absorption for High Performance Ternary-Blend Organic Solar Cells with Efficiency over 13%” Advanced Science, Vol. 5(6), June 2018 discloses a solar cell containing an acceptor-donor-acceptor (A-D-A) type non-fullerene acceptor 3TT-FIC which has three fused thieno[3,2- b]thiophene as the central core and difluoro substituted indanone as the end groups.

Wang et al, “Fused Hexacyclic Non-fullerene Acceptor with Strong Near-Infrared Absorption for Semitransparent Organic Solar Cells with 9.77% Efficiency” discloses solar cells containing acceptor IHIC, based on electron-donating group dithienocyclopentathieno[3,2-Z>]thiophene flanked by electron-withdrawing group 1,1- dicyanom ethylene-3 -indanone.

SUMMARY In some embodiments, the present disclosure provides a compound of formula (I):

EAG - EDG - EAG

(I) wherein EDG is an electron-donating group of formula (II) each EAG is independently an electron accepting group of formula (III):

each X is independently O or S; each Y is independently O, S, Se, NR⁸ or C(R⁹)2 wherein R⁸ and R⁹ independently in each occurrence are selected from H or a substituent;

Ar³ and Ar⁴ independently in each occurrence is a monocyclic or polycyclic aromatic or heteroaromatic group; R¹ and R² independently in each occurrence is a substituent;

R³ - R⁶ are each independently H or a substituent;

Z¹ is a direct bond or Z¹ together with the substituent R⁴ forms Ar¹ wherein Ar¹ is a monocyclic or polycyclic aromatic or heteroaromatic group;

Z² is a direct bond or Z² together with the substituent R⁵ forms Ar² wherein Ar² is a monocyclic or polycyclic aromatic or heteroaromatic group; p is 0, 1, 2 or 3; q is 0, 1, 2 or 3;

R¹⁰ in each occurrence is H or a substituent;

— represents a linking position to EDG; and R⁷ in each occurrence is H or a substituent with the proviso that at least one R⁷ is CN.

Optionally, Ar³ and Ar⁴ are each independently selected from thiophene, furan, thi enothiophene, furofuran, thi enofuran benzothiophene and benzofuran.

Optionally, p and q are each 1.

Optionally, Z¹ and Z² are each a direct bond. Optionally, the group of formula (III) has formula (Illa):

Optionally, R¹ and R² in each occurrence is selected from the group consisting of: linear, branched or cyclic C1.20 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced by O, S, NR¹², CO or COO wherein R¹² 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-(Ar⁶)v wherein Ak is a C1.14 alkylene chain in which one or more C atoms may be replaced with O, S, CO or COO; u is 0 or 1; Ar⁶ 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, at least one of R¹ and R² is phenyl which is unsubstituted or substituted with one or more substituents selected from C1.20 alkyl wherein one or more non-adjacent, nonterminal C atoms may be replaced by O, S, NR¹², CO or COO and one or more H atoms of the Ci -20 alkyl may be replaced with F. Optionally, each R³-R⁶ is independently selected from:

H;

C1.21 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with

O, S, COO or CO; and an aromatic or heteroaromatic group Ar⁶ which is unsubstituted or substituted with one or more substituents. In some embodiments, the present disclosure provides a composition comprising an electron donor and an electron acceptor wherein the electron acceptor is a compound according to any one of the preceding claims.

Optionally, the composition comprises at least one further electron acceptor. Optionally, the the composition comprises a fullerene further electron acceptor.

In some embodiments, the present disclosure provides a formulation comprising a compound or composition as described herein dissolved or dispersed in a solvent.

In some embodiments, the present disclosure provides an organic photoresponsive device comprising an anode, a cathode and a photoresponsive layer disposed between the anode and cathode wherein the photoresponsive layer comprises an electron acceptor and an electron donor wherein the electron-accepting material is a compound as described herein.

Optionally, the organic photoresponsive is an organic photodetector.

In some embodiments, the present disclosure provides a method of forming an organic photoresponsive device as described herein comprising formation of the photoresponsive organic layer over one of the anode and cathode and formation of the other of the anode and cathode over the photoresponsive organic layer.

Optionally, formation of the photoresponsive organic layer comprises deposition of the formulation as described herein. In some embodiments, the present disclosure provides a photosensor comprising a light source and an organic photodetector according as described herein configured to detect light emitted from the light source.

Optionally, the light source emits light having a peak wavelength greater than 750 nm.

Optionally, the photosensor is configured to receive a sample in a light path between the organic photodetector and the light source.

In some embodiments, the present disclosure provides a method of determining the presence and / or concentration of a target material in a sample, the method comprising illuminating the sample and measuring a response of a photodetector as described herein configured to receive light emitted from the sample upon illumination.

Optionally, the organic photodetector is the organic photodetector of a photosensor as described herein. DESCRIPTION OF DRAWINGS

The disclosed technology and accompanying figures describe some implementations of the disclosed technology.

Figure 1 illustrates an organic photodetector according to an embodiment of the invention; Figure 2 shows solution and film absorption spectra for Compound Example 1 according to some embodiments of the present disclosure;

Figure 3 shows a film absorption spectrum for Compound Example 2 according to some embodiments of the present disclosure

Figure 4A shows the external quantum efficiencies of an organic photodetector according to some embodiments of the present disclosure and a comparative photodetector containing a comparative electron acceptor;

Figure 4B shows the dark current of the devices of Figure 3 A;

Figure 5 shows external quantum efficiencies of photodetectors according to some embodiments of the present disclosure having differing electron donor : electron acceptor ratios;

Figure 6A is a graph of current densities vs wavelength for organic photodetectors containing Compound Example 2;

Figure 6B is a graph of external quantum efficiencies vs wavelength for organic photodetectors containing Compound Example 2; and Figure 7 is a graph of external quantum efficiencies vs wavelength for organic photodetectors containing Compound Example 1 and a fullerene.

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." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof. 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 an element include all isotopes of that element unless stated otherwise.

The teachings of the technology provided herein can be applied to other systems, not necessarily only 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. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. 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. For example, while some aspect of the technology may be recited as a computer-readable medium claim, other aspects may likewise be embodied as a computer-readable medium claim, or in other forms, such as being embodied in a means-plus-function claim.

In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

The present disclosure provides compounds of formula (I): EAG - EDG - EAG

(I) wherein EDG is an electron-donating group of formula (II) and each EAG is an electron accepting group of formula (III). Formula (II) is:

wherein: each X is independently O or S; each Y is independently O, S, Se, NR⁸ or C(R⁹)2 wherein R⁸ and R⁹ independently in each occurrence are selected from H or a substituent;

Ar³ and Ar⁴ independently in each occurrence is a monocyclic or polycyclic aromatic or heteroaromatic group;

R¹ and R² independently in each occurrence is a substituent; R³ - R⁶ are each independently H or a substituent;

Z² is a direct bond or Z² together with the substituent R⁵ forms Ar² wherein Ar² is a monocyclic or polycyclic aromatic or heteroaromatic group; p is 0, 1, 2 or 3; and q is 0, 1, 2 or 3.

Optionally, R¹ and R² independently in each occurrence are selected from the group consisting of: linear, branched or cyclic C1.20 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced by O, S, NR¹², CO or COO wherein R¹² 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-(Ar⁶)v wherein Ak is a Ci-14 alkylene chain in which one or more C atoms may be replaced with O, S, CO or COO; u is 0 or 1; Ar⁶ 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.

Ci-i4 hydrocarbyl may be Ci-14 alkyl; unsubstituted phenyl; and phenyl substituted with one or more Ci-6 alkyl groups.

Ar⁶ is preferably phenyl. Where present, substituents of Ar⁶ may be a substituent R¹⁶ wherein R¹⁶ in each occurrence is independently selected from F, C1.20 alkyl wherein one or more non- adjacent, non-terminal C atoms may be replaced by O, S, NR¹², CO or COO and one or more H atoms of the C1.20 alkyl may be replaced with F.

If v is 3 or more then -(Ar⁶)v may be a linear or branched chain of Ar⁶ groups. A linear chain of Ar⁶ groups as described herein has only on monovalent terminal Ar⁶ group whereas a branched chain of Ar⁶ groups has at least two monovalent terminal Ar⁶ groups.

Optionally, at least one of R¹ and R² in each occurrence is phenyl which is unsubstituted or substituted with one or more substituents selected from R¹⁶ as described above.

Optionally, each R³-R⁶ is independently selected from: H; F:

Ci-2i alkyl linear or branched wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO; and an aromatic or heteroaromatic group Ar⁶ which is unsubstituted or substituted with one or more substituents.

In the case where any of R³-R⁶ is Ar⁶, Ar⁶ is preferably an aromatic group, more preferably phenyl.

The one or more substituents of Ar⁶, if present, may be selected from Ci-i4 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO. By “non-terminal” C atom of an alkyl group as used herein is meant a C atom of the alkyl other than the methyl C atom of a linear (n-alkyl) chain or the methyl C atoms of a branched alkyl chain.

Preferably, R⁸ is selected from H and a Cl-30 hydrocarbyl group. The C1.30 hydrocarbyl group is optionally selected from be C1.30 alkyl; unsubstituted phenyl; and phenyl substituted with one or more C1.12 alkyl groups.

Preferably, R⁹ in each occurrence is independently selected from a substituent as described with respect to R¹.

Optionally, Ar³ and Ar⁴ are each independently selected from thiophene, furan, thi enothiophene, furofuran, thienofuran, benzothiophene and benzofuran. Ar³ and Ar⁴ are each independently unsubstituted or substituted with one or more substituents. Preferred substituents of Ar³ and Ar⁴, if present, are selected from groups R³-R⁶ described above other than H, preferably C1.20 alkyl wherein one or more non- adjacent, non-terminal C atoms are replaced with O, S, CO or COO.

Preferably, each R³-R⁶ is H; C1.20 alkyl; or C1.20 alkoxy. In some embodiments at least one of, optionally both of, R⁴ and R⁵ is not H, and each R³ and R⁶ is H. Preferably, p is 0 or 1, more preferably 1.

Preferably q is 0 or 1, more preferably 1.

Y in each occurrence is preferably O or S.

Preferably, Z¹ and Z² are each a direct bond. In some embodiments, Z¹ is linked to R⁴ to form a monocyclic aromatic or heteroaromatic group and / or Z² is linked to R⁵ to form a monocyclic aromatic or heteroaromatic group.

Optionally, Z¹ is linked to R⁴ to form a thiophene ring or furan ring and / or Z² is linked to R⁵ to form a thiophene ring or furan ring.

Each EAG is a group of formula (III):

wherein:

R¹⁰ is H or a substituent;

Optionally, each R⁷ is independently selected from H; C1.12 alkyl; and CN with the proviso that at least one R⁷ is CN.

R¹⁰ is preferably H. Substituents R¹⁰ are preferably selected from the group consisting of 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; and an aromatic group Ar⁹, 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, non-terminal C atoms may be replaced with O, S, COO or CO.

Exemplary groups of formula (III) are:

The groups of formula (III) may be the same or different. Preferably, they are the same. Optionally, the compound of formula (I) has a LUMO level of more than 4.00 eV from vacuum level, optionally at least 4.10 eV from vacuum level. Unless stated otherwise, HOMO and LUMO levels of a material as given herein are values measured by square wave voltammetry of a film of the material.

Exemplary compounds of formula (I) are:

Additional electron acceptors

In some embodiments, the compound of formula (I) is the only electron acceptor of a composition comprising the compound of formula (I) and an electron donor. In some embodiments, the composition may comprise one or more further electron acceptors. The one or more further acceptors may be selected from fullerenes and non-fullerene acceptors (NF As).

The compound of formula (I) : further acceptor(s) 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.

The fullerene may be a Ceo, C70, C76, C78 or Cs4 fullerene or a derivative thereof including, without limitation, PCBM-type fullerene derivatives (including phenyl-C61 -butyric acid methyl ester (CeoPCBM) and phenyl -C 71 -butyric acid methyl ester (C70PCBM)), TCBM- type fullerene derivatives (e.g. tolyl-C61 -butyric acid methyl ester (CeoTCBM)), and ThCBM-type fullerene derivatives (e.g. thienyl-C61 -butyric acid methyl ester (CeoThCBM)

Where present, a fullerene acceptor may have formula (VIII):

(VIII) 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 (Villa), (Vlllb) and (VIIIc):

(Villa) (Vlllb) (Vine) wherein R³⁰-R⁴² are each independently H or a substituent. Substituents R³⁰-R⁴² 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 nonadj acent, non-terminal C atoms may be replaced with O, S, CO or COO and one or more H atoms may be replaced with F.

Substituents of aryl or heteroaryl groups R³⁰-R⁴², where present, are optionally selected from C1.12 alkyl wherein one or more non-adj acent, non-terminal C atoms may be replaced with O, S, CO or COO and one or more H atoms may be replaced with F.

Electron donor

The donor (p-type) compound is not particularly limited and may be appropriately selected from electron donating materials that are known to the person skilled in the art, including organic polymers and non-polymeric organic molecules. The p-type compound has a HOMO deeper (further from vacuum) than a LUMO of the compound of formula (I). Optionally, the gap between the HOMO level of the p-type donor and the LUMO level of the n-type acceptor compound of formula (I) is less than 1.4 eV. Suitably, the donor and acceptor materials form a type II interface. In a preferred embodiment the p-type donor compound is an organic conjugated polymer, which can be a homopolymer or copolymer including alternating, random or block copolymers. Preferred are non-crystalline or semi- crystalline conjugated organic polymers. Further preferably the p-type organic semiconductor is a conjugated organic polymer with a low band gap, typically between 2.5 eV and 1.5 eV, preferably between 2.3 eV and 1.8 eV. As exemplary p-type donor 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, polybenzofl ,2-b:4,5-b'jdithiophene, 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 p-type donors 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. It is understood that the p-type donor may also consist of a mixture of a plurality of electron donating materials.

Optionally, the donor polymer comprises a repeat unit of formula (X):

wherein R⁵⁰ and R⁵¹ independently in each occurrence is H or a substituent.

Substituents R⁵⁰ and R⁵¹ may be selected from groups other than H described with respect to R³.

Preferably, each R⁵⁰ is a substituent. In a preferred embodiment, the R⁵⁰ groups are linked to form a group of formula -Y¹-C(R⁵²)2- wherein Y¹ is O, |S, NR⁵³, or C(R⁵²)2; R⁵² in each occurrence is H or a substituent, preferably a substituent as described with reference to R¹, most preferably a C1.30 hydrocarbyl group; and R⁵³ is H or a substituent, preferably H or a Ci .30 hydrocarbyl group.

Preferably, each R⁵¹ is H. The donor polymer may comprise a repeat unit selected from one or more of formulae

(XX) - (XXXII)

R²³ in each occurrence is a substituent, optionally Ci-2oalkyl wherein one or more nonadj acent, 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. R²⁵ in each occurrence is independently H; F; CN; NO2; C1-20 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 group Ar⁷, optionally phenyl, which is unsubstituted or substituted with one or more substituents selected from F and Ci -12 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO: or

wherein Z⁴⁰, Z⁴¹, Z⁴² and Z⁴³ are each independently CR¹⁴ or N wherein R¹⁴ in each occurrence is H or a substituent, preferably a C 1-20 hydrocarb yl group; Y⁴⁰ and Y⁴¹ are each independently O, S, NX⁷¹ wherein X⁷¹ is CN or COOR⁴⁰; or CX⁶⁰X⁶¹ wherein X⁶⁰ and X⁶¹ are each independently selected from CN, CF3 or COOR⁴⁰;

W⁴⁰ and W⁴¹ are each independently O, S, NX⁷¹ wherein X⁷¹ is CN or COOR⁴⁰; or CX⁶⁰X⁶¹ wherein X⁶⁰ and X⁶¹ is independently CN, CF3 or COOR⁴⁰; and

R⁴⁰ in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group. ZHs 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.

R¹¹ in each occurrence is a substituent, preferably a C1-20 hydrocarbyl group. Ar⁸ is an arylene or heteroarylene group, optionally thiophene, fluorene or phenylene, which may be unsubstituted or substituted with one or more substituents, optionally one or more non-H groups selected from R²⁵. Preferably, the donor polymer is a donor-acceptor polymer comprising an electrondonating repeat unit, preferably a repeat unit of formula (X), and an electron-accepting repeat unit, preferably a repeat unit selected from formulae (XX)-(XXXI).

Exemplary donor materials are disclosed in, for example, WO2013/051676, the contents of which are incorporated herein by reference.

Optionally, the p-type donor has a HOMO level no more than 5.5 eV from vacuum level. Optionally, the p-type donor has a HOMO level at least 4.1 eV from vacuum level.

Preferably, the donor material (or at least one of the donor materials if more than one donor is present) and compound of formula (I) form a type (II) heterojunction. Preferably, the compound of formula (I) has a HOMO level that is at least 0.05 eV deeper, optionally at least 0.10 eV deeper, than the HOMO of the donor material.

Optionally, the donor material, or at least one of the donor materials if more than one donor is present, has a H0M0-LUM0 band gap of less than 2.00 eV.

Optionally, the donor material, or at least one of the donor materials if more than one donor is present, has an absorption peak of at least 900 nm. Unless stated otherwise, absorption spectra as described herein are as measured in solution using a Cary 5000 UV- vis-IR spectrometer.

Unless stated otherwise, HOMO and LUMO levels of a material as described herein are as measured from a film of the compound using square wave voltammetry. In some embodiments, the weight of the donor compound(s) to the acceptor compound(s) is from about 1 :0.5 to about 1 :2.

Preferably, the electron donor(s) : electron acceptor(s) weight ratio is in the range of about 1 : 0.5 - 1 : 2, preferably 1 : 0.7 - 1 : 1.7. In a preferred embodiment, the weight of the electron acceptor(s) is greater than the weight of the electron donor(s). Organic photodetector

A compound of formula (I) as described herein may be provided as an electron acceptor in a bulk heterojunction layer of a photoresponsive device, preferably an OPD. Figure 1 illustrates an OPD according to some embodiments of the present disclosure. The OPD comprises a cathode 103, an anode 107 and a bulk heterojunction layer 105 disposed between the anode and the cathode. The OPD may be supported on a substrate 101. 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 bulk heterojunction layer comprises a mixture of an electron acceptor and an electron donor. In some embodiments, the bulk heterojunction layer consists of the electron acceptor and the electron donor. In some embodiments, the bulk heterojunction layer comprises a further electron acceptor other than the electron acceptor of formula (I). Optionally, the further electron acceptor is a fullerene.

Optionally, the bulk heterojunction layer has a thickness in the range of 100-1000 nm.

Each of the anode and cathode may independently be a single conductive layer or may comprise a plurality of layers.

The OPD may comprise layers other than the anode, cathode and bulk shown in Figure 1. In some embodiments, a hole-transporting layer is disposed between the anode and the bulk heterojunction layer. In some embodiments, an electron-transporting layer is disposed between the cathode and the bulk heterojunction layer. In some embodiments, a work function modification layer is disposed between the bulk heterojunction layer and the anode, and / or between the bulk heterojunction layer and the cathode.

Apparatus comprising the photodetector may further comprise a voltage source for applying a reverse bias to the photodetector and / or a device configured to measure photocurrent. The voltage applied to the photodetector may be variable. In some embodiments, the photodetector may be continuously biased when in use.

In some embodiments, a photodetector system comprises a plurality of photodetectors as described herein, such as an image sensor of a camera. In some embodiments, a sensor may comprise an OPD as described herein and a light source wherein the OPD is configured to receive light emitted from the light source.

In some embodiments, the light from the light source may or may not be changed before reaching the OPD. For example, the light may be filtered, down-converted or up- converted before it reaches the OPD.

In some embodiments, the light source has a peak wavelength of greater than 750 nm, optionally less than 1500 nm, optionally in the range of 1300-1400 nm.

At least one of the first and second electrodes is transparent so that light incident on the device may reach the bulk heterojunction layer. In some embodiments, both of the first and second electrodes are transparent.

Each transparent electrode preferably has a transmittance of at least 70 %, optionally at least 80 %, to wavelengths in the range of 850-1500 nm.

In some embodiments, one electrode is transparent and the other electrode is reflective.

Optionally, the transparent electrode comprises or consists of a layer of transparent conducting oxide, preferably indium tin oxide or indium zinc oxide. In preferred embodiments, the electrode may comprise poly 3, 4-ethylenedi oxythiophene (PEDOT). In other preferred embodiments, the electrode may comprise a mixture of PEDOT and polystyrene sulfonate (PSS). The electrode may consist of a layer of PEDOT:PSS.

Optionally, the reflective electrode may comprise a layer of a reflective metal. The layer of reflective material may be aluminium or silver or gold. In some embodiments, a bilayer electrode may be used. For example, the electrode may be an indium tin oxide (ITO)/silver bi-layer, an ITO/aluminium bi-layer or an ITO/gold bi-layer.

The device may be formed by forming the bulk heterojunction layer over one of the anode and cathode supported by a substrate and depositing the other of the anode or cathode over the bulk heterojunction layer.

The area of the OPD may be less than about 3 cm², less than about 2 cm², less than about 1 cm², less than about 0.75 cm², less than about 0.5 cm² or less than about 0.25 cm². Optionally, each OPD may be part of an OPD array wherein each OPD is a pixel of the array having an area as described herein, optionally an area of less than 1 mm², optionally in the range of 0.5 micron² - 900 micron².

The substrate may be, without limitation, a glass or plastic substrate. The substrate can be described as an inorganic semiconductor. In some embodiments, the substrate may be silicon. For example, the substrate can be a wafer of silicon. The substrate is transparent if, in use, incident light is to be transmitted through the substrate and the electrode supported by the substrate.

The substrate supporting one of the anode and cathode may or may not be transparent if, in use, incident light is to be transmitted through the other of the anode and cathode.

The bulk heterojunction layer may be formed by any process including, without limitation, thermal evaporation and solution deposition methods.

Preferably, the bulk heterojunction layer is formed by depositing a formulation comprising the acceptor material and the electron donor material dissolved or dispersed in a solvent or a mixture of two or more solvents. The formulation may be deposited by any coating or printing method including, without limitation, spin-coating, dip-coating, roll-coating, spray coating, doctor blade coating, wire bar coating, slit coating, ink jet printing, screen printing, gravure printing and flexographic printing.

The one or more solvents of the formulation may optionally comprise or consist of benzene 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-io alkyl benzoate, benzyl benzoate or dimethoxybenzene. In preferred embodiments, a mixture of trimethylbenzene and benzyl benzoate is used as the solvent. In other preferred embodiments, a mixture of trimethylbenzene and dimethoxybenzene is used as the solvent.

The formulation may comprise further components in addition to the electron acceptor, the electron donor 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 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 and / or emission of light from a target material in a sample disposed in a light path between the light source and the organic photodetector. The sample may be a non-biological sample, e.g. a water sample, or a biological sample taken from a human or animal subject. The sensor may be, without limitation, a gas sensor, a biosensor, an X-ray imaging device, an image sensor such as a camera image sensor, a motion sensor (for example for use in security applications) a proximity sensor or a fingerprint sensor. A ID or 2D photosensor array may comprise a plurality of photodetectors as described herein in an image sensor. The photodetector may be configured to detect light emitted from a target analyte which emits light upon irradiation by the light source or which is bound to a luminescent tag which emits light upon irradiation by the light source. The photodetector may be configured to detect a wavelength of light emitted by the target analyte or a luminescent tag bound thereto.

EXAMPLES

Compound Example 1

Compound Example 1 may be prepared according to Scheme 1

Scheme 1 Intermediate 2:

//-Butyl lithium (97.4 ml, 1.6M, 0.16 mol) was added to a solution of thieno[3,2- b]thiophene (1) (10 g, 0.07 mol) in THF (100 ml) at -78 °C and the mixture stirred at 25 °C for an hour. After coolingto -78 °C trimethyltin chloride (35.5 g, 0.18 mol) in THF (100 ml) was added and the mixture stirred at 25 °C for 16 hours. It was then quenched with water (200 ml) at 0 °C, extracted with hexane (200 ml), the organic layer was washed with brine and dried over anhydrous sodium sulphate and concentrated. The curde solid was dissolved in chloroform (50 ml), methanol (250 ml) was added and the mixture stirred at 0 °C for 2 hours. The resulting slurry was filtered, washed with methanol (100 ml) and dried under vacuum to give Intermediate 2 as a white solid (20 g, 60 % yield).

HPLC: 98.45 %.

'H-NMR (400 MHz, DMSO-d₆): 8 [ppm] 0.362 (s, 18H), 7.38 (s, 2H).

Intermediate 4:

Intermediate 3 can be synthesised as described in Journal of Materials Chemistry A: Materials for Energy and Sustainability (2020), 8, (10), 5163-5170, the contents of which are incorporated herein by reference.

Bis(triphenylphosphine)palladium (II) dichloride (144 mg, 0.2 mmol) was added to a mixture of Intermediate 2 (4.8 g, 0.01 mol) and methyl 2-bromothiophene-3-carboxylate (3) (4.77 g, 0.02 mmol) in degassed toluene (100 ml) and the mixture heated at 80 °C for 16 hours. After cooling, the resulting slurry was filtered, washed with toluene (20 ml) and dried under vacuum to give Intermediate 4 as a yellow solid (4.5 g).

HPLC: 95.7 %.

'H-NMR (400 MHz, CDCh): 6 [ppm] 1.57 (s, 4H), 3.88 (s, 6H), 7.28 (s, 2H), 7.54 (d, J = 5.40 Hz, 2H), 7.69 (s, 2H). Intermediate 6:

//-butyl lithium (2.5M in hexane, 17.1 ml, 0.04 mol) was added to a solution of 1-bromo- 4-hexylbenzene (5) (12.0 g, 0.05 mol) in THF (60 ml) at -100 °C and the mixture stirred for 2.5 hours. Intermediate 4 (3 g, 0.01 mol) was added as a solid andthe mixture was allowed to warm to 25 °C and stirred for 16 hours. After cooling to 0°C it was quenched with NH4CI solution (20 % aqueous, 30 ml), extracted with ethyl acetate (2 x 20 ml), washed with brine (30 ml), dried over anhydrous sodium sulphate and concentrated under reduced pressure. The residue was purified silica column chromatography (2 % EtOAc in hexane as elunt) to give Intermediate 6 (4.5 g, 63 % yield).

LCMS: 96.5 %.

'H-NMR (400 MHz, CDCh): 6 [ppm] 0.91 (t, J = 6.64 Hz, 12H), 1.33-1.37 (m, 24H), 1.59-1.64 (m, 8H), 2.62 (t, J= 7.88 Hz, 8H), 3.26(bs, 2H), 6.47 (d, J= 5.36 Hz, 2H), 6.66 (s, 2H), 7.11-7.17 (m, 18H). Intermediate 7:

Boron trifluoride diethyl etherate (2.74 ml, 0.02 mol) was added dropwise to a solution of Intermediate (6) (4.5 g, 0.004 mol) in dry DCM (60 ml) under nitrogen at 0 °C. After stirring at 26 °C for 16 hours the mixture was quenched with ice-water (30 ml), diluted with di chloromethane (50 ml), the organic layer was washed with water (30 ml), dried over anhydrous sodium sulphate and concentrated under reduced pressure. The residue was purified by -silica column chromatography (2 to 5 % DCM in hexane as eluent) to give Intermediate 7 as a red-orange solid (2 g, 46 % yield).

HPLC: 98.1 %.

'H-NMR (400 MHz, CDCh): 8 [ppm] 0.88 (t, J = 6.84 Hz, 12H), 1.29-1.37 (m, 24H), 1.55-1.63 (m, 8H), 2.56 (t, J= 7.92 Hz, 8H), 7.08-7.10 (m, 10H), 7.16-7.18 (m, 10H).

Intermediate 8:

//-butyl lithium (2.5M in hexane, 16.5 ml, 0.04 mol) was added to a solution of Intermediate 7 (10 g, 0.01 mol) in dry THF (150 ml) at-78 °C. After 1 hour, tributyl tin chloride (16.9 g, 0.05 mol) in THF (20 ml) was slowly added and the mixture allowed to warm to room temperature and stirred for 16 hours. The solvent was removed under reduced pressure and crude residue triturated with methanol and filtered to give Intermediate 8 as yellow solid (4 g, ~75 % desired product by LCMS).

Intermediate 10: Tri(o-tolyl)phosphine (147 mg, 0.48 mmol) and tris(dibenzylideneacetone) - dipalladium(O) (117 mg, 0.13 mmol) was added to a degassed solution of Intermediate 8 (2.5 g, 1.61 mmol) and 5-bromo-4-[(2-ethylhexyl) oxy]thiophene-2-carbaldehyde (1.28 g, 4.02 mmol) in toluene (150 ml) and the mixture heated to 80 °C for 16 hours. The mixture was concentrated and the crude product purified by silica column chromatography (0 to 50 % DCM in hexanes as eluent) to give Intermediate 10 (1.1 g with 81% LCMS purity and 0.3 g with 86% LCMS purity).

Compound Example 1 : A degassed solution of Intermediate 10 (550 mg, 0.38 mmol), Intermediate 11 (461 mg, 1.89 mmol) and para-toluene sulfonic acid (540 mg, 2.84 mmol) in ethanol (25 ml) was stirred at 65 °C for 18 hours and the mixture concentrated. A further 550 mg of intermediate 10 was also converted to Compound Example 1 The crude products were combined and purified twice by silica column chromatography (hexane:dichloromethane (1 : 1) as eluent). Fractions containing the desired product were combined and further triturated with ethanol and filtered to give Compound Example 1 (500 mg).

HPLC: 93.79 %.

'H-NMR (400 MHz, CDCh): 8 [ppm] 0.87-0.90 (m, 12H), 0.93-0.97 (m, 6H), 0.99-1.04 (m, 6H), 1.29-1.34 (m, 12H), 1.26-1.41 (m, 12H), 1.56-1.67 (m, 24H), 1.85-1.90 (m, 2H), 2.61 (t, J= 7.6 Hz, 8H), 4.17 (d, J= 4.8 Hz, 4H), 7.15-7.20 (m, 18H), 7.78 (s, 2H), 8.12

(s, 2H), 8.75 (br, s, 2H), 8.98 (s, 2H).

Intermediate 11 was formed according to Scheme 2:

1) t-Butyl acetoacetate

Malononitrile

NaH

THF, 0°C to RT

Scheme 2

Intermediate 13

A mixture of l,2-Dibromo-4,5-dimethylbenzene (100 g, 0.38 mol), potassium hydroxide (105 g, 1.89 mol) and potassium permanganate (298 g, 1.89 mol) in water (2 L) was heated at 115 °C for 24 hours. After cooling to room temperature, sodium bisulphite was added, the pH was adjusted to 8 using 10 % potassium hydroxide solution and the mixture was filtered through a celite pad and washed with water (2 x 50 ml). The aqueous layer was acidified to a pH of 1 with concentrated HCI to give a white precipitation which was filtered, washed with water (2 x 250 ml) and triturated with methanol. The resulting solid was filtered and dried under vacuum to give Intermediate 13 (46 g, 38 % yield).

'H-NMR (400 MHz, DMSO-d6): 8 [ppm] 8.18 (s, 2H).

Intermediate 14: Intermediate 13 (200 g, 618 mmol) in acetic anhydride (I L) was heated at 130 °C for 4 hours. After cooling to room temperature, the crude solid was filtered, washed with toluene (200 ml) and dried under vacuum to give Intermediate 14 (200 g).

Intermediate 15:

Tert-butyl aceto acetate (103 g, 654 mmol) was added to a mixture of Intermediate 14 (200 g, 654 mmol), acetic anhydride (1 L) and triethyl amine (600 ml) and the reaction mixture stirred at 25 °C for 16 hours. After quenching with a mixture of (10 M HC1, 1 L) and ice (1 kg) while maintaining the temperature below 50 °C, the mixture was heated to 75 °C for 2 hours and cooled to room temperature. The solid was filtered and dried to give Intermediate 15 as a brown solid (132 g, 68 % yield). LCMS: 96.8 %.

'H-NMR (400 MHz, DMSO-d6): 8 [ppm] 3.28 (s, 2H), 8.25 (s, 2H).

Intermediate 16:

A solution of Intermediate 15 (120 g, 394 mmol), ethylene glycol (244 g, 3.9 mol) and para-toluenesulfonic acid (6.78 g, 39.4 mmol) in toluene (1.5 L) was heated at 125 °C for 40 hours. After cooling to room temperature, the reaction mixture was added to water

(500 ml), the organic layer was separated and concentrated under vacuum. The crude residue was suspended in hexane (1 L), stirred for 30 minutes and filtered to give Intermediate 16 (91 g 59 % yield).

'H-NMR (400 MHz, CDC13): 8 [ppm] 2.56 (s, 2H), 4.09 - 4.12 (m, 4H), 4.20 - 4.24 (m, 4H), 7.65 (s, 2H).

Intermediate 17:

Potassium ferrocyanide (48.6 g, 132 mmol), 1-butyl imidazole (42.9 g, 383 mmol) and Copper (I) iodide (12.5 g, 65.6 mmol) were added in three portions to a solution of Intermediate 16 (65 g, 165 mmol) in o-xylene (2.5 L). After heating at 140 °C for 44 hours, the reaction mixture was cooled to room temperature, filtered through a Florisil plug, and washed with toluene followed by ethyl acetate. The filtrate was concentrated under reduced pressure to 1 L and stirred at 25 °C for 16 hours. The resulting solid was filtered, washed with hexanes and purified by silica column chromatography (hexanes: ethyl acetate (2:8) as eluent). Fractions containing the desired product were concentrated under reduced pressure, hexane (1 L) was added to the residue, and the resulting solid was filtered and dried under vacuum to give Intermediate 17 (30 g, 64 % yield). HPLC: 98.9 %.

'H-NMR (400 MHz, CDC13): 8 [ppm] 2.62 (s, 2H), 4.15 - 4.21 (m, 4H), 4.24 - 4.28 (m, 4H), 7.83 (s, 2H).

Intermediate 18:

Hydrogen chloride in diethyl ether (2 M, 500 ml, 1.0 mol) and water (5ml) were added to a solution of Intermediate 17 (90 g, 316 mmol) in tert-butyl methyl ether (1 L). After stirring at 25 °C for 48 hours, the mixture was filtered, the resulting solid washed with diethyl ether (100 ml x 3) and stirred 3 times with acetone (500 ml) for 1 hour and filtered. The resulting solid was dried under vacuum to give Intermediate 18 (61 g, 80% yield). HPLC: 95 %. 1H-NMR (400 MHz, CDC13): 8 [ppm] 3.07 (s, 2H), 4.20 - 4.36 (m, 4H), 8.11 (s, 1H), 8.16 (s, 1H).

Intermediate 11

A solution of malononitrile (5.49 g, 83.2 mmol) in THF (200 ml) was added to a suspension of sodium hydride (3.31 g, 83.2 mmol) in THF (200 ml) at 25 °C and stirred at 25 °C for an hour. The resulting mixture was added to a suspension of Intermediate 18 (20 g, 83.2 mmol) in THF (600 mL) at 0 °C, and the reaction mixture stirred at 25 °C for 16 hours. The resulting mixture was concentrated under vacuum to give a crude dark purple solid. This procedure was repeated on another 40g of intermediate 18. The crude material was combined and purified by silica column chromatography (10 to 20 % MeOH in DCM as elunt). Fractions containing the desired product were combined, concentrated under reduced pressure and the residue stirred in a mixture of dichloromethane and acetonitrile to give Intermediate 11 (20.2 g, 33% yield).

LCMS: 96.35 % purity.

'H-NMR (400 MHz, CD3OD): 8 [ppm] 3.61 (s, 2H), 5.55 (s, 1H), 7.73 (s, 1H), 8.29 (s, 1H).

Compound Example 2

Compound Example 2 may be prepared according to Scheme 3 :

Scheme 3

Intermediate 20 can be synthesised as described in Adv. Sci. 2018, 5, 1800307, the contents of which are incorporated herein by reference. HOMO and LUMP measurements

HOMO and LUMO values of Compound Example 1 were measured by square wave voltammetry.

In square wave voltammetry, 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 comprised 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 was 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 was dissolved in Toluene (3mg/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 were calculated from 3 freshly spun film samples for both the HOMO and LUMO data. Table 1

Comparative Compound 1 As shown in Table 1, Compound Example 1 has a significantly smaller band gap and significantly deeper LUMO than Comparative Compound 1.

Absorption measurements

Figure 2 shows absorption spectra of Compound Example 1 in film, cast from a 15 mg/ml solution, and in a 15 mg / ml solution. Figure 3 shows an absorption spectrum of Compound Example 2 in film, cast from a 15 mg/ml solution

Absorption spectra were in solution and in film using a Cary 5000 UV-vis-IR spectrometer. As shown in Figure 2, Compound Example 1 shows absorption in film at wavelengths of up to about 1500 nm. Device Example 1

A device having the following structure was prepared: Cathode / Donor : Acceptor layer / Anode

A glass substrate coated with a layer of indium-tin oxide (ITO) was treated with polyethyleneimine (PEIE) to modify the work function of the ITO.

A formulation containing a mixture of a donor polymer and Compound Example 1 (acceptor) in a donor : acceptor mas ratio of 1 : 1.5 was deposited over the modified ITO layer by bar coating from a 15 mg / ml solution in 1,2,4 Trimethylbenzene; 1,2- Dimethoxybenzene 95:5 v/v solvent mixture. The film was dried at 80°C to form a ca. 500 nm thick bulk heterojunction layer.

An anode stack of MoO3 (lOnm) and ITO (50nm) was formed over the bulk heterojunction by thermal evaporation (MoOs) and sputtering (ITO).

The donor polymer is a donor-acceptor polymer having a band gap of 1.86 eV and a donor repeat unit of formula (X) wherein R⁵⁰ groups are linked to form a group of formula -O- C(R⁵²)₂-. The donor polymer forms a type II interface with Compound Example 1.

Comparative Device 1

A device was prepared as described for Device Example 1 except that Compound

Example 1 was replaced with Comparative Compound 1.

Comparative Compound 1

With reference to Figure 4A, much higher external quantum efficiency is achieved in the range of about 1100-1500 nm, although this is accompanied by an increase in dark current as shown in Figure 4B. Device Examples 2-4

Device Examples 2-4 were prepared as described for Device Example 1 except that the Donor Polymer 1 : Compound Example 1 weight ratio was changed as shown in Table 2.

Table 2

With reference to Figure 5, external quantum efficiency is highest for Device Example 4, containing the lowest amount of Compound Example 1.

Device Example 5

Two devices (5-1 and 5-2) were prepared as described for Device Example 4 except that Compound Example 2 was used in place of Compound Example 1.

Plots of current density vs voltage and external quantum efficiency vs. wavelength are shown in Figures 6A and 6B, respectively.

Device Example 6

A number of devices were prepared as described for Device Example 1 except that the formulation deposited onto the modified ITO layer contained fullerene CeoPCBM in addition to the donor polymer and Compound Example 1 in a ratio of donor polymer 1.0 : Compound Example 1 0.8 : CeoPCBM 0.2.

As shown in Figures 6A and 6B, some variability in device performance is observed between devices 5-1 and 5-2 which do not contain fullerene. The present inventors have found that such variations may be reduced or eliminated by providing an electronaccepting fullerene in the bulk heterojunction layer, as shown in Figure 7.

Further, inclusion of a fullerene may results in an increase in external quantum efficiency as compared to a device in which a compound of formula (I) is the only electron acceptor. Modelling data

Energy levels of Model Compound Examples 1 and 2 and Model Comparative Compound 1 were modelled using Gaussian09 software available from Gaussian using Gaussian09 with B3LYP (functional). As set out in Table 4, Model Compound Examples 1 and 2 each have a deeper LUMO and smaller band gap than Model Comparative Compound 1.

Table 4

Claims

CLAIMS ) A compound of formula (I):

EAG - EDG - EAG

each X is independently O or S; each Y is independently O, S, Se, NR⁸ or C(R⁹)2 wherein R⁸ and R⁹ independently in each occurrence are selected from H or a substituent; - 43 -

R¹⁰ in each occurrence is H or a substituent;

— represents a linking position to EDG; and

R⁷ in each occurrence is H or a substituent with the proviso that at least one R⁷ is CN.

2) The compound according to claim 1 wherein Ar³ and Ar⁴ are each independently selected from thiophene, furan, thi enothiophene, furofuran, thienofuran, benzothiophene and benzofuran.

3) The compound according to claim 1 or 2 wherein p and q are each 1. 4) The compound according to any one of the preceding claims wherein Z¹ and Z² are each a direct bond.

5) The compound according to any one of the preceding claims wherein the group of formula (III) has formula (Illa): - 44 -

) The compound according to any one of the preceding claims wherein R¹ and R² in each occurrence is selected from the group consisting of: linear, branched or cyclic C1.20 alkyl wherein one or more non-adjacent, nonterminal C atoms may be replaced by O, S, NR¹², CO or COO wherein R¹² 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-(Ar⁶)v wherein Ak is a C1.14 alkylene chain in which one or more C atoms may be replaced with O, S, CO or COO; u is 0 or 1; Ar⁶ 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. ) The compound according to claim 6 wherein at least one of R¹ and R² is phenyl which is unsubstituted or substituted with one or more substituents selected from C1.20 alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced by O, S, NR¹², CO or COO and one or more H atoms of the C1.20 alkyl may be replaced with F. ) The compound according to any one of the preceding claims wherein each R³-R⁶ is independently selected from: H; Ci-2i alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, S, COO or CO; and an aromatic or heteroaromatic group Ar⁶ which is unsubstituted or substituted with one or more substituents. 9) A composition comprising an electron donor and an electron acceptor wherein the electron acceptor is a compound according to any one of the preceding claims.

10) The composition according to claim 9 wherein the composition comprises at least one further electron acceptor.

11) The composition according to claim 10 wherein the composition comprises a fullerene further electron acceptor.

12) A formulation comprising a compound or composition according to any one of the preceding claims dissolved or dispersed in a solvent.

13) An organic photoresponsive device comprising an anode, a cathode and a photoresponsive layer disposed between the anode and cathode wherein the photoresponsive layer comprises an electron acceptor and an electron donor wherein the electron-accepting material is a compound according to any one of claims 1-8.

14) An organic photoresponsive device according to claim 13 wherein the organic photoresponsive device is an organic photodetector. 15) A method of forming an organic photoresponsive device according to claim 13 or

14 comprising formation of the photoresponsive organic layer over one of the anode and cathode and formation of the other of the anode and cathode over the photoresponsive organic layer.

16) A method according to claim 15 wherein formation of the photoresponsive organic layer comprises deposition of the formulation according to claim 10.

17) A photosensor comprising a light source and an organic photodetector according to claim 14 configured to detect light emitted from the light source. 18) A photosensor according to claim 17 wherein the light source emits light having a peak wavelength greater than 750 nm.

19) A photosensor according to claim 16 or 17 configured to receive a sample in a light path between the organic photodetector and the light source. 20) A method of determining the presence and / or concentration of a target material in a sample, the method comprising illuminating the sample and measuring a response of a photodetector according to claim 14 configured to receive light emitted from the sample upon illumination.

21) A method according to claim 20 wherein the organic photodetector is the organic photodetector of a photosensor according to any one of claims 17-19