Tuning the optoelectronic properties of nonfullerene electron acceptors.

CHEMPHYSCHEM ARTICLES DOI: 10.1002/cphc.201402568

Tuning the Optoelectronic Properties of Nonfullerene Electron Acceptors Yuan Fang,[a] Ajay K. Pandey,[a] Dani M. Lyons,[a] Paul E. Shaw,[a] Scott E. Watkins,[b] Paul L. Burn,*[a] Shih-Chun Lo,[a] and Paul Meredith*[a] Broad spectral coverage over the solar spectrum is necessary for photovoltaic technologies and is a focus for organic solar cells. We report a series of small-molecule, nonfullerene electron acceptors containing the [(benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile unit as a high electron affinity component. The optoelectronic properties of these molecules were fine-tuned with the objective of attaining strong absorption at longer wavelengths by changing the low-ionization-potential moiety. The electron-accepting function of these materials was

investigated with poly(3-n-hexylthiophene) (P3HT) as a standard electron donor. Significant photocurrent generation in the near infrared region, with an external quantum yield reaching as high as 22 % at 700 nm and an onset > 800 nm was achieved. The results support efficient hole transfer to P3HT taking place after light absorption by the acceptor molecules. A Channel IIdominated power conversion efficiency of up to 1.5 % was, thus, achieved.

1. Introduction n-Type organic materials are rarer than their p-type counterparts, but are just as vital for efficient organic optoelectronic devices.[1] For example, in the case of organic light-emitting diodes, n-type materials play an important role in electron injection and hole blocking to ensure that exciton formation occurs in the emitting layer.[2] In the case of bulk heterojunction organic solar cells (OSCs), the role of the n-type component is somewhat more complex. In general, fullerene-based molecules have dominated the n-type landscape in OSCs, with considerable effort focused on the development of donor materials to extend the junction absorption into the near infrared (NIR) region.[3] In this regard, donor materials have been considered the primary light-absorbing component of the cell— the process of current generation involving photoinduced electron transfer (or PET) from the donor material to an acceptor material with suitable electron affinity. We have termed this process the Channel I mechanism for simplicity of nomenclature.[4] Consequently, donor materials have been designed to absorb light of longer wavelengths, while still working with the traditional acceptor materials, namely fullerenes.[5] However, there is a second mechanism possible for charge generation in OSCs. The Channel II mechanism involves the excitation of [a] Dr. Y. Fang, Dr. A. K. Pandey, Dr. D. M. Lyons, Dr. P. E. Shaw, Prof. P. L. Burn, Dr. S.-C. Lo, Prof. P. Meredith Centre for Organic Photonics & Electronics The University of Queensland, Brisbane QLD 4072 (Australia) E-mail: [email protected] [email protected]

the acceptor material followed by hole transfer [photoinduced hole transfer (PHT)] to the donor material.[6] Although the Channel II mechanism is clearly at play in bulk heterojunction solar cells that include fullerene acceptors,[7] particularly when the ratio of donor to acceptor is low, as is the case for many narrow optical gap (so-called low-band-gap) polymers,[8] there have been few acceptors specifically designed to have a narrow optical gap for exploitation of the Channel II mechanism.[4, 9] Only a small number of different types of nonfullerene acceptor materials for use in OSCs have been reported.[10] Notable amongst these materials are the perylenes and vinazenes, although again these have been designed with narrow optical gap donors in mind.[11] In contrast, we have been working on developing small-molecule acceptors that are solution processable and have narrow optical gaps with the specific aim of studying the Channel II mechanism for charge generation in bulk heterojunction solar cells. In our previous work, we have shown that by replacing the fluorenyl moiety of 2-[(7-{9,9-di-npropyl-9H-fluoren-2-yl}benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile[12] (1; Figure 1) with a dithienosilolyl group to give 2-[{7-(4,4-di-n-propyl-4H-silolo[3,2-b:4,5-b’]dithien-2yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile[4] (2; Figure 1), it was possible to unequivocally identify that the

[b] Dr. S. E. Watkins CSIRO Materials Science and Engineering, VIC 3169 (Australia) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201402568. An invited contribution to a Special Issue on Organic Electronics

2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Figure 1. Chemical structures of previously reported acceptors.[4, 12]

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CHEMPHYSCHEM ARTICLES Channel II mechanism was operating, as well as determine the contribution of 2 to the photocurrent at longer wavelengths. Here, we describe the synthesis of a series of small-molecule (< 600 Daltons) electron-acceptor materials and compare them to those previously reported. We show that the optoelectronic properties can be engineered at the molecular level and then discuss how the structural changes lead to charge generation by the Channel II mechanism in bulk heterojunction solar cells with poly(3-n-hexylthiophene) (P3HT) as the donor material. The molecules all contain the [(benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile high-electron-affinity component with the properties being tuned by changing the low-ionization-potential moiety.

2. Results and Discussion 2.1. Synthesis and Physical Properties The syntheses of the four new compounds are outlined in Scheme 1. The synthesis of the advanced intermediate 7-

www.chemphyschem.org bromobenzo[c][1,2,5]thiadiazole-4-carbaldehyde (4) has been previously reported (see the Experimental Section) in the preparation of 1 and 2 and this work follows the same general strategy with the two key reactions being the coupling of the low-ionization-potential chromophore with 4 and the subsequent condensation reaction to install the dicyanovinyl moiety. For the N-2-ethylhexylcarbazole derivative 6, the first reaction involved the coupling of the carbazole boronic acid 3 with 4 to give 5. Under palladium-catalyzed conditions, 5 was formed in a 78 % yield. Condensation of 5 with malononitrile gave 6 in a 76 % yield. The replacement of the carbazole unit with a dithienopyrrole unit in narrow-optical-gap polymers has been shown to extend the absorption to longer wavelengths.[13] Therefore, in the first iteration of tuning the properties, we exchanged the N-2-ethylhexylcarbazole moiety for the equivalent N-2-ethylhexyldithienopyrrole unit. The first step in this case was to metalate N-2-ethylhexyldithienopyrrole unit (7) at the 2-position before conversion into the tri-n-butylstannane derivative 8; this was then used immediately without purification in a Stille coupling with 4 to give aldehyde 9 in an overall yield

Scheme 1. Synthesis routes to the acceptors.



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CHEMPHYSCHEM ARTICLES of 66 % for the two steps. 9 was then condensed with malononitrile to form 10, which was isolated in a 92 % yield. It is well known that the nature of the alkyl or alkoxy substituents can affect the thermal properties and film structure; hence, in the case of the dithienopyrrole derivative we also prepared the nhexyl version.[14] The n-hexyl version 14 was formed in an identical manner as 10, with 11 converted into stannane 12, which was coupled with 4 to give aldehyde 13 in a 73 % yield for the two steps. Finally, 14 was formed by the reaction of 13 and malononitrile in an 89 % yield. In a final structural variation, we took compound 2, which performed better than compound 1 in bulk heterojunction solar cells,[4] and added a 4-fluorophenyl unit to fine-tune the dipole and determine how it affected the optoelectronic properties of the material. It has been reported that fluorine substituents can provide subtle variations to the properties of macromolecular materials. The synthesis of 15 has been previously reported for the preparation of 2.[4] In this work, 15 was brominated in the 6-position under mild conditions to give 16 in a 95 % yield. A Suzuki coupling with commercially available 4-fluorophenylboronic acid furnished aldehyde 17 (65 % yield), which was then reacted with malononitrile to give 18 in an excellent yield of 94 %. As might be expected for small molecules, the materials all had good solubility in polar aprotic organic solvents. In the first part of the analysis we determined the thermal characteristics of the materials using differential scanning calorimetry (DSC). For microcrystalline samples of 2, 6, 10, and 14 (from recrystallization), the first heating scan only showed the melting of the compounds. When the samples were then subsequently cooled at a rate of 10 8C min 1, the DSC traces for 2, 10, and 14 did not show a thermal transition corresponding to crystallization (see Figure 2 for 14 and the Supporting Information for 2 and 10). However, under the same conditions 6

Figure 2. DSC scans of 14 with heating and cooling rates of 10 8C min 1.

showed an exothermic transition corresponding to crystallization at around 130 8C (Figure 3 a). If a cooling rate of 300 8C min 1 was used, then no crystallization thermal transition was observed for 6 (Figure 3 b). Therefore, for 2, 10, 14, and fast-cooled 6, the material formed after melting is essentially amorphous. On heating, the amorphous forms of the ma 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Figure 3. DSC scans of 6 with a) slow cooling at a rate of 10 8C min 1, b) fast cooling (first heating at 100 8C min 1, first cooling at 300 8C min 1, and second heating at 200 8C min 1).

terials were all found to undergo a glass transition (Tg) in the range 50–60 8C, and a subsequent crystallization before a remelting step (this process is illustrated for 14 in Figure 2 with the remaining graphs shown in the Supporting Information). Finally, the melting point of 18 (277–279 8C) was outside the temperature range we could probe with our DSC. The DSC trace of the as-formed material showed no thermal transitions up to 250 8C (see the Supporting Information). However, when a sample was heated above the melting point on a hot plate and then cooled rapidly, on the subsequent heating, a Tg at 84 8C was observed with crystallization processes occurring at 97 8C and 134 8C. Once crystallization had occurred, the next heating cycle showed no features within the temperature limit of the experiment. In preparing films from solutions of a small molecule acceptor with a polymer donor, the evaporation of the solvent would be like the fast cooling in the DSC experiments, and hence, the acceptor could be considered to be “amorphous” in the blend with the polymer. Therefore, as described in more detail in Section 2.3, the solution processed films were heated to a temperature above the Tg of the respective acceptor to instigate the crystallization process. Furthermore, the rich thermal characteristics of such compounds provides a method for tuning and studying the role of aggregation in the optoelectronic properties of bulk heterojunction films comprised of nonfullerene acceptors. ChemPhysChem 0000, 00, 1 – 11

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2.2. Optoelectronic Properties We determined the electronic properties of the materials by using a combination of electrochemistry and photoelectron spectroscopy in air (PESA). Cyclic voltammetry measurements showed that all the compounds underwent a chemically reversible reduction (the E1/2 values are summarized in Table 1). The

Table 1. Optical and electronic properties of the acceptors. Acceptor

ls,maxabs [nm][a]

lf,maxabs [nm][b]

2 6 10 14 18

575, 463, 603, 602, 604,

578, 467, 589, 600, 625,

364 331 383 380 384

373 332 396 398 406

E1/2 reduction [V][c] 1.1 1.2 1.2 1.2 1.1

Electron affinity [eV][d]

IP [eV][e]

3.7 3.6 3.6 3.6 3.7

5.8 5.9 5.7 5.7 5.7

[a] Absorption peaks measured in dichloromethane solution. [b] Absorption peaks measured from films spin cast from chloroform solutions onto fused silica substrates. [c] Quoted against the ferrocenium/ferrocene couple. [d] Electron affinity determined in solution by cyclic voltammetry. [e] IP determined in the solid state by PESA.

E1/2 values are reported against the ferrocenium/ferrocene couple and were used to calculate electron affinity (Table 1) by reference to the ionization potential (IP) of ferrocene.[15] Within experimental error, all the reduction potentials are the same, which is consistent with the fact that it is the [(benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile component that is primarily responsible for the electron affinity of the molecule. The IPs of thin films of the materials were measured by PESA (Table 1). For 1, the IP was outside the PESA window (> 6.2 eV). By replacing the fluorenyl unit with the more easily oxidized carbazole unit the IP becomes measurable; 6 has an IP of 5.9 eV. The replacement of the phenyl rings of the carbazole with thiophenes would be expected to decrease the IP further and this was observed; 10 and 14 have IPs of around 5.7 eV. In previous reports, compounds comprised of dithienopyrrole moieties have had lower IPs than their silole counterparts,[16] and this can be seen in the comparison of the IPs of 10 and 14 with 2. Finally, the IP of 18 is also around 5.7 eV, which is a little surprising given the extension of the conjugation length that occurs with the addition of the 4-fluorophenyl group. Given the reduction potentials are similar and the differences in the IP measured by PESA, we might expect a trend in the absorption maxima of 1 < 6 < 2 < 10 14 18. This trend is, in fact, generally followed in the solution spectra (Figure 4), with the following peak maxima being observed: 1 at 450 nm, 6 at 463 nm, 2 at 575 nm, and 10, 14, and 18 at 604 nm. In moving from solution to the solid state all the compounds displayed a substantial red tail. For 1, this red tail is due to aggregation,[12] and given the similarity between the compound structures it would be reasonable to assign the observed shoulders to the same phenomenon in the new materials. The photoluminescence (PL) spectra of all the compounds in solution featured a single broad peak with no apparent vibronic 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Figure 4. Solution (solid lines) and film (dashed lines) absorption and photoluminescence spectra of 2, 6, 10, 14, and 18.

structure. In the solid state, the emission from the compounds with the exception of 6 shifted to longer wavelengths and were broadened, which is consistent with aggregation in the solid state. The unexpected behavior of 6 may be the result of a reduced number of conformations in the solid state relative to the solution. Furthermore, the emission from 14 featured a peak at 675 nm in addition to the dominant peak at 957 nm, which was not observed for the other compounds. The origin of this additional PL feature is unknown, but its absence from the solution measurements indicates it is probably the result of intermolecular interactions. 2.3. Solar Cell Device Characterization and Performance In the final part of the study, we prepared bulk heterojunction solar cells with the following structure, ITO/PEDOT:PSS/ P3HT:acceptor/Sm/Al [ITO = indium tin oxide, PEDOT:PSS = poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)], with the aim of determining whether the acceptor materials generated current through the Channel II mechanism. Details of the device fabrication are provided in the Experimental Section. In a previous report, it was found that a weight ratio of 1.5:1 of 2:P3HT gave optimal performance, and hence, device optimization in this work focused around that ratio.[4] During the device fabrication process, the bulk heterojunction layers were heated at 70 8C for 10 min to remove the solvent before the cathode deposition. For 6, 10, and 14, this is above their Tg ChemPhysChem 0000, 00, 1 – 11

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Table 2. Photovoltaic (PV) parameters of compounds 6, 10, 14, and 18 in bulk heterojunction solar cells with P3HT. Changes to open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF), and PCE are measured after thermal treatment close to Tg, with the best performance being obtained after pre-annealing of the 18:P3HT blend at 140 8C. Over three different fabrication cycles the standard deviation in each PV parameter was within 10 %. Active layer

Solvent

Ratio

Annealing

VOC [V]

JSC [mA cm 2]

FF

PCE [%]

6:P3HT

DCB DCB DCB DCB DCB DCB DCB DCB

1.5:1 1.5:1 1.5:1 1.5:1 1.5:1 1.5:1 1.5:1 1.5:1

as-prepared post annealed at 85 8C as-prepared post annealed at 110 8C as-prepared post annealed at 110 8C as-prepared[a] as-prepared at 140 8C

0.54 0.42 0.52 0.48 0.50 0.58 0.54 0.54

1.06 0.99 2.07 2.30 0.87 1.41 3.2 5.88

0.40 0.35 0.39 0.36 0.42 0.40 0.43 0.46

0.2 0.1 0.4 0.4 0.2 0.3 0.8 1.5

10:P3HT 14:P3HT 18:P3HT

[a] As-prepared procedure uses a solvent-removal annealing step at 70 8C for 10 min.

but below their crystallization temperature. Nevertheless, the 70 8C thermal anneal was expected to induce some initial crystallization, in the same manner as was observed for 1.[12b] For 18, a further short anneal above its Tg and crystallization temperatures was undertaken before completion of the device. The as-prepared device that contained the N-2-ethylhexyl derivative 6 was found to have a power conversion efficiency (PCE) of 0.2 %, with annealing not improving the performance (see Table 2). The plot of external quantum efficiency (EQE) versus wavelength in Figure 5 shows peaks at around 340 nm and 440 nm with an onset to photocurrent generation near 650 nm. To gain an understanding of the contribution of each of the component absorptions to the total photocurrent, we compared the EQE with the absorption spectra of the neat (6 and P3HT) and blended films as shown in Figure 6 (similar comparisons for the other compounds are presented in the Supporting Information). This simple analysis does not take into account the cavity optics effects that are present in such thin-film solar cells, but to first order this analysis can be used to understand the origin of the photocurrent. For the 6:P3HT blend, the absorption spectrum is similar to that of P3HT. However, the EQE appears to be more weighted in shape to that of the absorption of acceptor 6. Irrespective of any additional cavity interference effects, the fact that photocurrent is generated at 650 nm demonstrates that the Channel I mechanism is in play and corresponds to the absorption edge of P3HT (see the Supporting Information, and note, 6 does not absorb at this wavelength). However, the shape of the EQE at shorter wavelengths suggests that the light absorption by 6 contributes to the photocurrent. Given that there is some overlap between the absorption of P3HT and the emission of 6, it is difficult to determine whether photocurrent generation is due to energy transfer from 6 to P3HT followed by charge generation by the Channel I mechanism or whether the Channel II process is in play. That being said, based on previous reports of both fullerene and nonfullerene acceptors, it is likely that both pathways are operating in these devices.[4, 17] The performance of 10 was similar to that of 6 (Table 2), but in this case there was clear evidence for photocurrent generation occurring from hole transfer from the P3HT to the narrow 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

optical gap acceptor 10. For 10, there is no overlap of its PL spectrum with the absorption spectrum of P3HT, meaning that the photocurrent generated beyond 650 nm arises solely from the Channel II mechanism. Furthermore, the structure of the EQE at shorter wavelengths is reminiscent of the shape of the absorption spectrum of 10; this suggests that absorption of the acceptor, even at shorter wavelengths, is a significant pathway to photocurrent gener-

Figure 5. a) EQE spectra of compounds 6, 10, 14, and 18 with P3HT in typical as-prepared devices. b) Post-device-fabrication annealing-induced changes to the EQE spectra of (a); the most prominent improvement in photocurrent yield comes from compound 18.

ation. Given the similarity in the structure of 10 and 14 (they only differ by the type of alkyl chain) it might be expected that the overall efficiency would be similar, and this is in fact what is observed after annealing. It should be noted, comChemPhysChem 0000, 00, 1 – 11

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www.chemphyschem.org 3. Conclusions

Figure 6. Thin-film absorption spectra on glass of neat films of 6, and P3HT as compared with the absorption spectrum of 6:P3HT (1.5:1 by wt.).

We have developed a range of small molecule acceptor materials designed to possess different absorption profiles and optical gaps. The molecules all contained a [(benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile unit as the high electron affinity component and were varied in the low-ionization-potential moiety. By adding a 6-(4-fluorophenyl)-4,4-di-npropyl-4H-silolo[3,2-b:4,5-b’]dithien-2-yl] unit to the high-electron-affinity component it was possible to engineer an electron acceptor with an onset to absorption of > 800 nm, and that generated photocurrent by the Channel II mechanism. Optimization of the processing conditions led to a PCE of up to 1.5 %, which is excellent for a device comprised of a nonfullerene acceptor that operates by the Channel II mechanism.

Experimental Section pound 10 has been recently reported as a donor material in blends with PCBM.[18] For 18, there is clear photocurrent generation beyond the absorption edge of P3HT (the onset is 850 nm), which can only come from absorption of the acceptor followed by hole transfer to the polymer (the Channel II mechanism). Compared to 6, 10, and 14, a significantly higher EQE was measured for 18. The optimum annealing temperature for 18 was slightly higher than that for the other compounds; it was found to be in the range of 120–140 8C. Figure 7 shows a typical J–V curve of an 18:P3HT solar cell. The photocurrent density of 6 mA cm 2 is consistent with the broad photocurrent EQE response with an onset at 850 nm. Although significant changes to photocurrent density at short circuit were observed across the various acceptors, the optimized devices of compounds 6, 10, 14, and 18 all had VOC values in the range of 0.50–0.58 V. The small variation in VOC is in good agreement with the electrochemistry and PESA measurements.

Organic Solar Cell Device Fabrication and Testing At least 24 devices comprised of each material combination were fabricated and tested to ensure reliable statistics. Cells were fabricated on precleaned indium tin oxide (ITO) substrates using standard procedures. The ITO substrates were cleaned in a warm Alconox detergent bath at 70 8C followed by sequential cleaning in deionized water, acetone, and 2-propanol in an ultrasonic bath. In the first step, a 30 nm thick layer of PEDOT:PSS (H. C. Stark) was spin coated on top of the clean ITO substrates in air. The PEDOT:PSS-coated substrates were then annealed at 170 8C for 15 min before transferring to a nitrogen-filled glove box with oxygen and moisture levels < 0.1 ppm. The photoactive layer of compounds 6, 10, 14, or 18 blended with P3HT was spin coated at 1000 rpm. The resulting thickness, in each case, measured with a Dektak 150 profilometer, was found to be in the range of 80– 90 nm. For excess solvent removal before device completion, the freshly coated photoactive layers comprised of compounds 6, 10, and 14 were baked at 70 8C for 10 min. Due to the limited solubility of 18 in dichlorobenzene (DCB) the blend solution of 18:P3HT was first heated at 80 8C before spin coating. Also, for 18 two different preannealing steps were used, 70 8C for 10 min or 140 8C for 2 min. The metal deposition (1 nm Sm/80 nm Al) was performed in a vacuum evaporator at a base pressure of 2 10 6 mbar with thermal sources. The devices had an active area of 0.2 cm2. All as-prepared devices were immediately characterized for their photovoltaic performance inside a nitrogen filled glove box. Post-fabrication thermal annealing of devices with compounds 6, 10, and 14 was achieved by directly placing complete devices on top of a hotplate operating at 85 8C or 110 8C for 2 min. No post-fabrication annealing was performed on devices formed with preannealed blends of compound 18 (see Table 2). An AM 1.5 solar simulator (Abet Technologies) operating at standard illumination of ~ 100 mW cm 2 was used for J–V measurements. The EQE measurements were performed at a chopping frequency of 120 Hz by using a QEX7 set up from PV Technologies, Inc. The integrated EQE current agreed with the white-light short-circuit current density (without masking) to within 10 %.

Spectroscopy Figure 7. Typical current density–voltage (J–V) characteristics of a solar cell composed of 18:P3HT in the dark, and under AM 1.5G standard illumination at ~ 100 mW cm 2.


The UV/Vis absorption spectra were recorded on a Varian Cary 5000 UV/Vis spectrophotometer. Solutions were prepared in specChemPhysChem 0000, 00, 1 – 11

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CHEMPHYSCHEM ARTICLES troscopic grade dichloromethane and thin films were prepared by spin coating from chloroform onto fused silica substrates. The PL spectra of the compounds in solution were obtained on a Horiba Jobin–Yvon Fluoromax-4 fluorometer by exciting at 550 nm for 6, and 580 nm for 2, 10, 14, and 18. The film PL spectra were obtained by exciting the films with the 442 nm output of a HeCd laser and measuring the emission with a silicon photodiode coupled to a monochromator. A lock-in detector was used to increase the signal-to-noise ratio. The films were stored under vacuum for the duration of the measurement to minimize photo-oxidation. The measured PL spectra were corrected for the wavelength-dependent response of the instrument.

Synthesis Methods and Characterization All reagents were purchased from commercial sources and used without further purification unless otherwise stated. Anhydrous tetrahydrofuran was distilled from sodium/benzophenone, and anhydrous toluene was distilled from sodium. 1H and 13C NMR spectra were recorded in d-chloroform with a Bruker 300, 400, or 500 spectrometer, and chemical shifts were referenced to 7.26 ppm and 77.0 ppm for the proton and carbon spectra, respectively. BtH = protons on benzothiadiazol rings, ThH = protons on thienyl rings, PhH = protons on phenyl rings, CarH = protons on carbazolyl rings. Coupling constants are reported to the nearest 0.5 Hz. Melting points were measured on a BUCHI Melting Point B-545 and were corrected. Infrared spectra were recorded on a PerkinElmer Spectrum 100 FTIR spectrometer with an attenuated total reflectance (ATR) attachment. DSC was performed with a PerkinElmer Diamond DSC under a nitrogen atmosphere. Mass spectra were recorded on an Applied Biosystems Voyager matrix-assisted laser desorption/ ionization time-of-flight (MALDI-TOF) mass spectrometer in positive reflection mode, and the matrix used was 1,8,9-anthracenetriol. Elemental analyses were carried out in School of Chemistry and Molecular Biosciences, The University of Queensland. Cyclic voltammetry measurements were carried out on a BAS Epsilon voltammetric analyzer at room temperature in an electrolyte solution of 0.1 m tetra-n-butylammonium perchlorate (TBAP) in argon-purged anhydrous tetrahydrofuran at a scan rate of 100 mV s 1. Anhydrous tetrahydrofuran was doubly distilled, first from sodium/benzophenone and then lithium aluminium hydride prior to use. Glassy carbon working, platinum counter, and silver/silver nitrate in acetonitrile reference electrodes were used, and the E1/2 values are quoted against the ferrocenium/ferrocene couple.[15] PESA measurements were recorded with a Riken Keiki AC-2 PESA spectrometer with a power setting of 5–10 nW and a power number of 0.5.

7-[9-(2-Ethylhexyl)-9 H-carbazol-2-yl]benzo[c][1,2,5]thiadiazole-4-carbaldehyde (5) A mixture of [9-(2-ethylhexyl)-9 H-carbazol-2-yl)]boronic acid 3[19] (50 mg, 0.15 mmol), 7-bromobenzo[c][1,2,5]thiadiazole-4-carbaldehyde[20] (4, 31 mg, 0.13 mmol), tert-butanol (0.5 mL), aqueous sodium carbonate (0.5 mL, 2 m) and toluene (1.5 mL) was deoxygenated five times by placing under vacuum (100 mBar) and backfilling with argon. After tetrakis(triphenylphosphine)palladium(0) (4.5 mg, 0.004 mmol) was added, the mixture was deoxygenated a further five times, and then heated at reflux for 20 h. After cooling to room temperature, the organic layer was separated and the aqueous layer was extracted with dichloromethane (3 5 mL). The organic layer and the dichloromethane extracts were combined, dried over anhydrous magnesium sulfate, and filtered. The solvent was removed under reduced pressure and the residue was purified 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemphyschem.org by column chromatography over silica using a dichloromethane/nhexane (80: 20) mixture as the eluent to give 5 as an orange gum (45 mg, 78 %). 1H NMR (500 MHz, CDCl3): d = 10.81 (1 H, s, CHO), 8.35 (1 H, d, J = 7.5 Hz, BtH), 8.25 (1 H, d, J = 8.0 Hz, CarH), 8.18 (1 H, d, J = 1.5 Hz, CarH), 8.16 (1 H, d, J = 7.5 Hz, CarH), 8.02 (1 H, d, J = 7.5 Hz, BtH), 7.81 (1 H, dd, J = 8.0, 1.5 Hz, CarH), 7.52 (1 H, ddd, J = 1.0 Hz, J = 7.0 Hz, J = 8.0 Hz, CarH), 7.45 (1 H, d, J = 8.0 Hz, CarH), 7.29–7.26 (1 H, m, CarH), 4.29–4.22 (2 H, m, NCH2), 2.19–2.12 (1 H, m, CH), 1.48–1.25 (8 H, m, CH2), 0.94 (3 H, t, J = 7.5 Hz, CH3), 0.85 ppm (3 H, t, J = 7.0 Hz, CH3); 13C NMR (100 MHz, CDCl3): d = 189.0, 154.2, 153.9, 141.9, 141.5, 141.0, 133.4, 132.8, 127.1, 126.4, 126.0, 123.9, 122.3, 120.7, 120.5, 120.2, 119.2, 110.9, 109.2, 47.5, 39.5, 31.1, 28.9, 24.5, 23.0, 14.0, 11.0 ppm; IR: nmax = 1687 cm 1 (C= O); UV/Vis (CH2Cl2) lmax = 413 (4.36), 323 sh (4.44), 305 (4.50), 264 (4.56), 237 nm (4.63 dm3 mol 1 cm 1); MS (MALDI-TOF): m/z (%): calcd for C27H27N3OS: 441.2 (100), 442.2 (32), 443.2 (10); found: 441.2 (100), 442.2 (95), 443.2 (26); elemental analysis calcd (%) for C27H27N3OS: C 73.4, H 6.2, N 9.5, S 7.3; found: C 73.1, H 6.1, N 9.4, S 7.0.

2-[(7-{9-(2-Ethylhexyl)-9 H-carbazol-2-yl}benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile (6) A solution of 5 (135 mg, 0.31 mmol), malononitrile (202 mg, 3.1 mmol), and pyridine (0.5 mL) in chloroform (13 mL) was deoxygenated five times by placing under vacuum (100 mBar) and backfilling with argon, and then heated at reflux for 24 h. After cooling to room temperature, the solvent was removed under reduced pressure and the residue was purified by column chromatography over silica using a dichloromethane/n-hexane mixture (6:4) as the eluent to give 6 as an orange solid (115 mg, 76 %). M.p.: 174– 175 8C; 1H NMR (500 MHz, CDCl3): d 8.84 (1 H, s, CHC(CN)2), 8.81 (1 H, d, J = 7.5 Hz, BtH), 8.22 (1 H, d, J = 8.0 Hz, CarH), 8.20 (1 H, s, CarH), 8.15 (1 H, d, J = 8.0 Hz, CarH), 8.02 (1 H, d, J = 7.5 Hz, BtH), 7.82 (1 H, dd, J = 8.0, 1.5 Hz, CarH), 7.55–7.52 (1 H, m, CarH), 7.45 (1 H, d, J = 8.0 Hz, CarH), 7.29 (1 H, dd, J = 7.5 Hz, J = 7.5 Hz, CarH), 4.26–4.21 (2 H, m, NCH2), 2.17–2.11 (1 H, m, CH), 1.47–1.26 (8 H, m, CH2), 0.95 (3 H, t, J = 7.5 Hz, CH3), 0.85 ppm (3 H, t, J = 7.5 Hz, CH3); 13 C NMR (100 MHz, CDCl3): d = 154.4, 152.9, 152.5, 141.9, 141.1, 140.8, 132.8, 130.4, 127.3, 126.8, 124.1, 122.1, 121.9, 120.8, 120.3, 120.1, 119.4, 113.8, 113.0, 110.9, 109.3, 82.4, 47.4, 39.5, 31.1, 28.9, 24.5, 23.0, 14.1, 11.0 ppm; IR nmax = 2223 cm 1 (CN); UV/Vis (CH2Cl2) (4.49), 331 (4.41), 265 (4.61), 242 nm lmax = 460 (4.63 dm3 mol 1 cm 1); MS (MALDI-TOF) m/z (%): calcd for C30H27N5S requires 489.2 (100), 490.2 (36), 491.2 (11); found: 489.3 (100), 490.3 (37), 491.3 (24); elemental analysis calcd for C30H27N5S: C 73.6, H 5.6, N 14.3, S 6.55; found: C 73.7, H 5.5, N 14.1, S 6.5.

7-[4-(2-Ethylhexyl)-4 H-dithieno[3,2-b:2’,3’-d]pyrrol-2yl]benzo[c][1,2,5]thiadiazole-4-carbaldehyde (9) n-Butyl lithium (1.6 m in hexane, 3.28 mmol, 2 mL) was added over a period of 30 min to a stirred solution of 4-(2-ethylhexyl)-4H-dithieno[3,2-b:2’,3’-d]pyrrole 7[21] (735 mg, 2.52 mmol) in anhydrous tetrahydrofuran (50 mL) that had been cooled in an acetone/dry ice bath under argon. The reaction mixture was stirred with acetone/dry ice bath cooling for 3 h, and then tri(n-butyl)tin chloride (1.15 g, 3.53 mmol) was added dropwise over a period of 30 min. The reaction mixture was stirred with acetone/dry ice bath cooling for an additional 1 h, and then allowed to warm to room temperature, and stirred overnight. After the solvent was removed, the residue was dissolved in ethyl acetate (100 mL). Aqueous sodium fluoride (1.2 m, 50 mL) was added and the mixture stirred for 1 h at ChemPhysChem 0000, 00, 1 – 11

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CHEMPHYSCHEM ARTICLES room temperature. The organic phase was separated, washed with water (3 50 mL), dried over magnesium sulfate, filtered and the solvent removed to leave crude 4-(2-ethylhexyl)-2-[tri(n-butyl)stannyl]-4H-dithieno[3,2-b:2’,3’-d]pyrrole 8, which was used without further purification. Bis(triphenylphosphine)palladium dichloride (42 mg, 0.06 mmol) was added to a stirred solution of 7-bromobenzo[c][1,2,5]thiadiazole-4-carbaldehyde (455 mg, 1.87 mmol) and 4-(2-ethylhexyl)-2-(tri(n-butyl)stannyl)-4H-dithieno[3,2-b:2’,3’-d]pyrrole in anhydrous tetrahydrofuran (25 mL). The mixture was deoxygenated five times by placing under vacuum (300 mBar) and backfilling with argon, and then heated at reflux for 16 h. After cooling to room temperature, the solvent was removed and the residue was purified by column chromatography over silica with dichloromethane as the eluent to give a black-red solid of 9 (750 mg, 66 %). M.p.: 134–135 8C; 1H NMR (300 MHz, CDCl3): d = 10.63 (1 H, s, CHO), 8.52 (1 H, s, C3-ThH), 8.18 (1 H, d, J = 7.5 Hz, BtH), 7.93 (1 H, d, J = 7.5 Hz, BtH), 7.28 (1 H, d, J = 5.5 Hz, C6-ThH), 7.00 (1 H, d, J = 5.5 Hz, C5-ThH), 4.22–4.07 (2 H, m, NCH2), 2.05–1.96 (1 H, m, CH), 1.48–1.24 (8 H, m, CH2), 0.96–0.87 (6 H, m, CH3); 13C NMR (100 MHz, CDCl3): d = 188.3, 153.8, 152.1, 147.4, 146.4, 135.5, 134.5, 133.1, 126.1, 124.4, 122.3, 118.2, 115.3, 114.9, 111.1, 51.2, 40.5, 30.6, 28.6, 24.1, 23.0, 14.1, 10.7 ppm; IR: nmax = 1673 cm 1 (C=O); UV/Vis (CH2Cl2): lmax = 530 (4.47), 338 (4.38), 301 sh (4.08), 257 nm (4.05 dm3 mol 1 cm 1); MS (MALDI-TOF): m/z (%): calcd for C23H23N3OS3 requires 453.1 (100), 454.1 (29), 455.1 (18), 456.1 (4); found: 453.3 (100), 454.2 (47), 455.3 (32), 456.2 (5); elemental analysis calcd (%) for C23H23N3OS3 : C 60.9, H 5.1, N 9.3, S 21.2, found: C 60.8, H 5.1, N 9.05, S 21.4.

2-[(7-{4-[2-Ethylhexyl]-4 H-dithieno[3,2-b:2’,3’-d]pyrrol-2yl}benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile (10)[18] A mixture of 9 (450 mg, 1.0 mmol), malononitrile (1.3 g, 20 mmol) and pyridine (0.5 mL) in anhydrous toluene (20 mL) was deoxygenated five times by placing under vacuum (100 mBar) and backfilling with argon, and then heated at 70 8C for 16 h. After cooling to room temperature, the solvent was removed and the residue was purified by column chromatography over silica with a dichloromethane/n-hexane mixture (7:3) as the eluent to give 10 as a black solid (460 mg, 92 %). M.p.: 180–181 8C. 1H NMR (300 MHz, CDCl3): d = 8.72 (1 H, s, CHC(CN)2), 8.71 (1 H, d, J = 8.5 Hz, BtH), 8.50 (1 H, s, C3-ThH), 7.91 (1 H, d, J = 8.5 Hz, BtH), 7.32 (1 H, d, J = 5.5 Hz, C6ThH), 7.00 (1 H, d, J = 5.5 Hz, C5-ThH), 4.22–4.08 (2 H, m, NCH2), 2.05–1.98 (1 H, m, CH), 1.45–1.26 (8 H, m, CH2), 0.95 (3 H, t, J = 7.5 Hz), 0.89 ppm (3 H, t, J = 7.0 Hz); 13C NMR (100 MHz, CDCl3): d = 154.5, 151.3, 150.7, 148.3, 146.6, 135.6, 134.4, 130.4, 127.5, 122.4, 120.1, 119.5, 115.5, 115.0, 114.4, 113.6, 111.1, 79.6, 51.3, 40.5, 30.6, 28.6, 24.1, 23.0, 14.1, 10.7 ppm; IR: nmax = 2220 cm 1 (CN); UV/Vis (CH2Cl2) lmax = 604 (4.62), 382 (4.13), 349 (4.21), 336 sh (4.10), 295 (4.17), 264 nm (4.10 dm3 mol 1 cm 1); MS (MALDI-TOF) m/z (%): calcd for C26H23N5S3 : 501.1 (100), 502.1 (33), 503.1 (19), 504.1 (5); found: 501.3 (100), 502.3 (54), 503.3 (33), 504.3 (19); elemental analysis: calcd (%) for C26H23N5S3 : C 62.25, H 4.6, N 14.0, S 19.2; found: C 62.1, H 4.6, N 14.0, S 18.9.

7-(4-n-Hexyl-4 H-dithieno[3,2-b:2’,3’-d]pyrrol-2-yl)benzo[c][1,2,5]thiadiazole-4-carbaldehyde (13) n-Butyl lithium (1.6 m in hexane; 1.88 mmol, 1.2 mL) was added over a period of 30 min to a stirred solution of 4-n-hexyl-4H-dithieno[3,2-b:2’,3’-d]pyrrole 11[22] (380 mg, 1.44 mmol) in anhydrous tet 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemphyschem.org rahydrofuran (40 mL) that had been cooled in an acetone/dry ice bath under argon. The reaction mixture was stirred with acetone/ dry ice bath cooling for 3 h, and then tri(n-butyl)tin chloride (657 mg, 2.0 mmol) was added dropwise over a period of 30 min. The reaction mixture was stirred with acetone/dry ice bath cooling for an additional 3 h, and then allowed to warm to room temperature, and stirred overnight. The solvent was removed, and the residue was dissolved in ethyl acetate (60 mL). Aqueous sodium fluoride (1.2 m, 20 mL) was added and the mixture stirred for 1 h at room temperature. The organic phase was separated, washed with water (3 30 mL), dried over magnesium sulfate, filtered, and the solvent removed to leave crude 4-n-hexyl-2-(tri-n-butylstannyl)-4Hdithieno[3,2-b:2’,3’-d]pyrrole 12, which was used without further purification. Bis(triphenylphosphine)palladium dichloride (26.0 mg, 0.04 mmol) was added to a stirred solution of 7-bromo-benzo[c][1,2,5]thiadiazole-4-carbaldehyde (298 mg, 1.23 mmol) and 4-nhexyl-2-(tri-n-butylstannyl)-4H-dithieno[3,2-b:2’,3’-d]pyrrole in anhydrous tetrahydrofuran (20 mL). The mixture was deoxygenated five times by placing under vacuum (300 mBar) and backfilling with argon, and then heated at reflux for 16 h. After cooling to room temperature, the solvent was removed and the residue was purified by column chromatography over silica with dichloromethane as the eluent to give 13 as a black-red solid (450 mg, 73 %). M.p.: 124–125 8C. 1H NMR (300 MHz, CDCl3): d = 10.62 (1 H, s, CHO), 8.51 (1 H, s, C3-ThH), 8.17 (1 H, d, J = 7.5 Hz, BtH), 7.93 (1 H, d, J = 7.5 Hz, BtH), 7.28 (1 H, d, J = 5.5 Hz, C6-ThH), 7.02 (1 H, d, J = 5.5 Hz, C5ThH), 4.28 (2 H, t, J = 7.0 Hz, NCH2), 1.98–1.88 (2 H, m, CH2), 1.45– 1.22 (6 H, m, CH2), 0.87 ppm (3 H, t, J = 7.0 Hz, CH3); 13C NMR (100 MHz, CDCl3): d = 188.3, 153.8, 152.0, 147.1, 145.9, 135.5, 134.3, 133.0, 126.1, 124.3, 122.2, 118.3, 115.0, 114.9, 110.9, 47.3, 31.4, 30.3, 26.6, 22.5, 14.0 ppm. IR: nmax = 1671 cm 1 (C=O); UV/Vis (CH2Cl2): lmax : 531 (4.45), 352 sh (4.27), 337 (4.35), 304 sh (4.03), 257 nm (4.02 dm3 mol 1 cm 1); MS (MALDI-TOF): m/z (%): calcd for C21H19N3OS3 : 425.1 (100), 426.1 (27), 427.1 (17); found 425.3 (100), 426.3 (79), 427.3 (36); elemental analysis calcd (%) for C21H19N3OS3 : C 59.3, H 4.5, N 9.9, S 22.6; found: C 59.1; H 4.4, N 10.0, S 22.25.

2-[(7-{4-n-Hexyl-4 H-dithieno[3,2-b:2’,3’-d]pyrrol-2yl}benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile (14) A solution of 13 (400 mg, 0.94 mmol), malononitrile (620 mg, 9.4 mmol), and pyridine (1 mL) in anhydrous toluene (20 mL) was deoxygenated five times by placing under vacuum (200 mBar) and backfilling with argon, and then heated at 75 8C for 20 h. After cooling to room temperature, the solvent was removed and the residue was purified by column chromatography over silica with a dichloromethane:n-hexane mixture (7:3) as the eluent to give a black solid of 14 (395 mg, 89 %). M.p.: 194–195 8C; 1H NMR (300 MHz, CDCl3): d = 8.65 (1 H, s, CHC(CN)2), 8.65 (1 H, d, J = 8.5 Hz, BtH), 8.45 (1 H, s, C3-ThH), 7.85 (1 H, d, J = 8.0 Hz, BtH), 7.33 (1 H, d, J = 5.5 Hz, C6-ThH), 7.02 (1 H, d, J = 5.5 Hz, C5-ThH), 4.27 (2 H, t, J = 7 Hz, NCH2), 1.96–1.89 (2 H, m, CH2), 1.45–1.25 (6 H, m, CH2), 0.88 ppm (3 H, t, J = 7.0 Hz, CH3); 13C NMR (100 MHz, CDCl3): d = 154.6, 151.6, 150.9, 148.0, 146.3, 135.7, 134.7, 130.6, 127.4, 122.6, 120.3, 119.8, 115.5, 115.2, 114.4, 113.6, 111.0, 80.0, 47.5, 31.4, 30.3, 26.6, 22.5, 14.0 ppm; IR: nmax = 2221 cm 1 (CN); UV/Vis (CH2Cl2): lmax = 604 (4.60), 382 (4.11), 349 (4.19), 336 sh (4.08), 297 (4.08), 261 nm (4.04 dm3 mol 1 cm 1); MS (MALDI-TOF): m/z (%): calcd for C24H19N5S3 : 473.1 (100), 474.1 (31), 475.1 (18); found: 473.2 (100), 474.1 (51), 475.2 (18); elemental analysis: calcd for C24H19N5S3 : C 60.9, H 4.0, N 14.8, S 20.3; found: C 60.7, H 4.0, N 15.0, S 20.0. ChemPhysChem 0000, 00, 1 – 11

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CHEMPHYSCHEM ARTICLES 7-(6-Bromo-4,4-di-n-propyl-4 H-silolo[3,2-b:4,5-b’]dithien-2yl)benzo[c][1,2,5]thiadiazol-4-carbaldehyde (16) A Schlenk tube equipped with a magnetic stirrer bar was charged with 7-(4,4-di-n-propyl-4 H-silolo[3,2-b:4,5-b’]dithien-2-yl)benzo[c][1,2,5]thiadiazol-4-carbaldehyde[4] (15; 400 mg, 0.91 mmol) and N,N’-dimethylformamide (25 mL). The solution was placed in an ice bath and stirred under nitrogen for 10 min in the dark. A solution of N-bromosuccinimide (178 mg 1.0 mmol) in N,N’-dimethylformamide (5 mL) was added dropwise to the solution. The reaction mixture was then stirred with ice bath cooling for 1.5 h and then at room temperature for 2 h. Dichloromethane (100 mL) was then added to the solution. The obtained mixture was washed with water (3 70 mL), dried over anhydrous magnesium sulfate, and filtered. The solvent was removed and the residue was purified by column chromatography over silica with dichloromethane as the eluent to give 16 as a black solid (450 mg, 95 %). M.p.: 162–163 8C; 1 H NMR (300 MHz, CDCl3): d = 10.71 (1 H, s, CHO), 8.28 (1 H, s, C3ThH), 8.22 (1 H, d, J = 7.5 Hz, BtH), 7.98 (1 H, d, J = 7.5 Hz, BtH), 7.09 (1 H, s, C5-ThH), 1.52–1.39 (4 H, m, SiCH2), 1.01–0.94 ppm (10 H, m, CH2 and CH3); 13C NMR (100 MHz, CDCl3): d = 188.5, 153.8, 153.2, 152.2, 149.1, 144.0, 142.4, 139.5, 133.5, 132.9, 132.8, 132.6, 124.9, 123.1, 113.5, 17.9, 17.7, 14.3 ppm; IR: nmax = 1676 cm 1 (C=O); UV/ Vis (CH2Cl2): lmax = 509 (4.36), 363 (4.00), 334 sh (4.00), 323 (4.04), 312 sh (4.04), 247 nm (4.11 dm3 mol 1 cm 1); MS (MALDI-TOF): m/z (%): calcd for C21H19BrN2OS3Si: 518.0 (84), 519.0 (27), 520.0 (100), 521.0 (31), 522.0 (19); found: 518.1 (73), 519.1 (82), 520.0 (100), 521.0 (94), 522.0 (35); elemental analysis calcd for C21H19BrN2OS3Si: C 48.5, H 3.7, N 5.4, S 18.5; found: C 48.2, H 3.4, N 5.4, S 19.5.

7-[6-(4-Fluorophenyl)-4,4-di-n-propyl-4 H-silolo[3,2-b:4,5b’]dithien-2-yl]benzo[c][1,2,5]thiadiazol-4-carbaldehyde (17) A mixture of 4-fluorophenyl boronic acid (136 mg, 0.97 mmol), 16 (420 mg, 0.81 mmol), tert-butanol (3 mL), aqueous sodium carbonate (3 mL, 2 m), and toluene (9 mL) was deoxygenated five times by placing under vacuum (100 mBar) and backfilling with argon. After tetrakis(triphenylphosphine)palladium(0) (28 mg, 0.024 mmol) was added, the mixture was deoxygenated a further five times, and then heated at reflux for 16 h. After cooling to room temperature, toluene (100 mL), and water (50 mL) were added to the mixture. The organic layer was separated, washed with water (3 50 mL), dried over anhydrous magnesium sulfate, and filtered. The solvent was removed and the residue was purified by column chromatography over silica with dichloromethane as the eluent to give 17 as a black red solid (281 mg, 65 %). M.p. : 198–200 8C; 1H NMR (300 MHz, CDCl3): d = 10.70 (1 H, s, CHO), 8.32 (1 H, s, C3-ThH), 8.22 (1 H, d, J = 8.0 Hz, BtH), 7.99 (1 H, d, J = 8.0 Hz, BtH), 7.62–7.57 (2 H, m, PhH), 7.27 (1 H, s, C5-ThH), 7.13–7.06 (2 H, m, PhH), 1.53–1.44 (4 H, m, SiCH2), 1.05–0.96 ppm (10 H, m, CH2 and CH3); 13C NMR (100 MHz, CDCl3): d = 188.4, 162.3 (d, J = 246.5 Hz), 154.0, 153.8, 152.1, 147.8, 146.1, 145.4, 143.1, 139.4, 133.6, 133.1, 132.9, 130.6 (d, J = 3.5 Hz), 127.4 (d, J = 8.0 Hz), 125.9, 124.7, 122.9, 115.9 (d, J = 21.5 Hz), 17.9, 17.8, 14.4 ppm; IR: nmax = 1682 cm 1 (C=O); UV/Vis (CH2Cl2): lmax = 532 (4.51), 382 (4.21), 319 (4.20), 287 (4.17), 253 nm (4.28 dm3 mol 1 cm 1); MS (MALDI-TOF): m/z (%): calcd for C27H23FN2OS3Si: 534.1 (100), 535.1 (38), 536.1 (24), 537.1 (7); found: 534.1 (100), 535.1 (62), 536.1 (35), 537.1 (14); elemental analysis calcd for C27H23FN2OS3Si: C 60.6, H 4.3, N 5.2, S 18.0; found: C 60.7, H 4.2, N 5.2, S 17.9. 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemphyschem.org 2-[(7-{6-(4-Fluorophenyl)-4,4-di-n-propyl-4 H-silolo[3,2-b:4,5b’]dithien-2-yl}benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile (18) A solution of 17 (271 mg, 0.51 mmol), malononitrile (670 mg, 10.1 mmol), and pyridine (0.7 mL) in anhydrous toluene (15 mL) was deoxygenated five times by placing under vacuum (100 mBar) and backfilling with argon. Then the mixture was heated at 70 8C for 20 h. After cooling to room temperature, the solvent was removed and the residue was purified by column chromatography over silica with a dichloromethane/n-hexane mixture (7:3) as the eluent to give 18 as a black solid (280 mg, 94 %). M.p.: 277–279 8C; 1 H NMR (500 MHz, CDCl3): d = 8.76 (1 H, s, CHC(CN)2), 8.74 (1 H, d, J = 8.0 Hz, BtH), 8.34 (1 H, s, ThH), 7.96 (1 H, d, J = 8.0 Hz, BtH), 7.61– 7.58 (2 H, m, PhH), 7.28 (1 H, s, ThH), 7.11–7.08 (2 H, m, PhH), 1.54– 1.46 (4 H, m, SiCH2), 1.04–1.01 (4 H, m, CH2), 0.99 ppm (6 H, t, J = 7.5 Hz, CH3); 13C NMR (100 MHz, CDCl3): d = 162.4 (d, J = 246.5 Hz), 155.4, 154.5, 152.0, 151.0, 147.6, 146.8, 146.3, 143.5, 139.5, 134.0, 133.8, 130.8, 130.4 (d, J = 3.5 Hz), 127.5 (d, J = 8 Hz), 126.0, 123.2, 120.7, 116.0 (d, J = 22.0 Hz), 114.2, 113.5, 80.9, 17.9, 17.8, 14.4 ppm; IR: nmax = 2221 cm 1 (CN); UV/Vis (CH2Cl2): lmax = 602 (4.64), 384 (4.29), 331 (4.12), 291 (4.20), 257 nm (4.37 dm3 mol 1 cm 1); MS (MALDI-TOF): m/z (%): calcd for C30H23FN4S3Si: 582.1 (100), 583.1 (43), 584.1 (25), 585.1 (8); found 582.1 (100), 583.1 (44), 584.0 (35), 585.1 (11); elemental analysis calcd for C30H23FN4S3Si: C 61.8, H 4.0, N 9.6, S 16.5; found: C 61.7, H 3.8, N 9.8, S 16.4.

Acknowledgements Y.F. and A.K.P. are Australian Renewable Energy Agency Research Fellows (Projects 6-F019 and 6-F022). P.E.S. is supported by an Australian Research Council Discovery Early Career Researcher Award (DE120101721). P.L.B. and P.M. are University of Queensland Vice Chancellor’s Senior Research Fellows and P.M. is an Australian Research Council Discovery Outstanding Research Award Fellow. We acknowledge funding from the University of Queensland (Strategic Initiative—Centre for Organic Photonics & Electronics) and the Queensland Government (National and International Research Alliances Program). This program has also been supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). Responsibility for the views, information, or advice expressed herein is not accepted by the Australian Government. This work was performed in part at the Queensland node of the Australian National Fabrication Facility (ANFF), a company established under the National Collaborative Research Infrastructure Strategy to provide nano- and microfabrication facilities for Australia’s researchers. Keywords: energy conversion · materials science · organic electronics · thin films · solar cells [1] a) C. D. Dimitrakopoulos, P. R. L. Malenfant, Adv. Mater. 2002, 14, 99 – 117; b) E. Ahmed, G. Ren, F. S. Kim, E. C. Hollenbeck, S. A. Jenekhe, Chem. Mater. 2011, 23, 4563 – 4577; c) B. P. Karsten, J. C. Bijleveld, R. A. J. Janssen, Macromol. Rapid Commun. 2010, 31, 1554 – 1559. [2] P. K. H. Ho, J.-S. Kim, J. H. Burroughes, H. Becker, S. F. Y. Li, T. M. Brown, F. Cacialli, R. H. Friend, Nature 2000, 404, 481 – 484. [3] a) H. Zhou, L. Yang, W. You, Macromolecules 2012, 45, 607 – 632; b) L. Huo, J. Hou, S. Zhang, H.-Y. Chen, Y. Yang, Angew. Chem. Int. Ed. 2010, 49, 1500 – 1503; Angew. Chem. 2010, 122, 1542 – 1545; c) F. Liu, Y. Gu, C.


&9&



[4] [5]

[6] [7] [8] [9]

[10]

[11]

[12]

Wang, W. Zhao, D. Chen, A. L. Briseno, T. P. Russell, Adv. Mater. 2012, 24, 3947 – 3951. Y. Fang, A. K. Pandey, A. M. Nardes, N. Kopidakis, P. L. Burn, P. Meredith, Adv. Energy Mater. 2013, 3, 54 – 59. a) S. Beaupr, M. Leclerc, J. Mater. Chem. A 2013, 1, 11097 – 11105; b) M. C. Scharber, D. Mhlbacher, M. Koppe, P. Denk, C. Waldauf, A. J. Heeger, C. J. Brabec, Adv. Mater. 2006, 18, 789 – 794; c) G. Zhao, Y. He, Y. Li, Adv. Mater. 2010, 22, 4355 – 4358. A. A. Bakulin, J. C. Hummelen, M. S. Pshenichnikov, P. H. M. V. Loosdrecht, Adv. Funct. Mater. 2010, 20, 1653 – 1660. Y. He, Y. Li, Phys. Chem. Chem. Phys. 2011, 13, 1970 – 1983. H. Wang, X. Yu, C. Yi, H. Ren, C. Liu, Y. Yang, S. Xiao, J. Zheng, A. Karim, S. Z. D. Cheng, X. Gong, J. Phys. Chem. C 2013, 117, 4358 – 4363. a) M. Zhang, H. Wang, H. Tian, Y. Geng, C. W. Tang, Adv. Mater. 2011, 23, 4960 – 4964; b) Y.-J. Hwang, G. Ren, N. M. Murari, S. A. Jenekhe, Macromolecules 2012, 45, 9056 – 9062; c) J. D. Douglas, M. S. Chen, J. R. Niskala, O. P. Lee, A. T. Yiu, E. P. Young, J. M. J. Frchet, Adv. Mater. 2014, 26, 4313 – 4319. a) C. L. Chochos, N. Tagmatarchisc, V. G. Gregoriouab, RSC Adv. 2013, 3, 7160 – 7181; b) Z. E. Ooi, T. L. Tam, R. Y. C. Shin, Z. K. Chen, T. Kietzke, A. Sellinger, M. Baumgarten, K. Mllen, J. C. deMello, J. Mater. Chem. 2008, 18, 4619 – 4622; c) J. L. Yang, S. Schumann, R. A. Hatton, T. S. Jones, Org. Electron. 2010, 11, 1399 – 1420; d) E. Zhou, J. Cong, M. Zhao, L. Zhang, K. Hashimoto, K. Tajima, Chem. Commun. 2012, 48, 5283 – 5285. a) A. M. Poe, A. M. D. Pelle, A. V. Subrahmanyam, W. White, G. Wantz, S. Thayumanavan, Chem. Commun. 2014, 50, 2913 – 2915; b) W. Jiang, L. Ye, X. Li, C. Xiao, F. Tan, W. Zhao, J. Hou, Z. Wang, Chem. Commun. 2014, 50, 1024 – 1026; c) B. Walker, X. Han, C. Kim, A. Sellinger, T.-Q. Nguyen, ACS Appl. Mater. Interfaces 2012, 4, 244 – 250; d) J. E. Anthony, Chem. Mater. 2011, 23, 583 – 590; e) P. Sonar, J. P. F. Lim, K. L. Chan, Energy Environ. Sci. 2011, 4, 1558 – 1574. a) K. Gui, K. Mutkins, P. E. Schwenn, K. B. Krueger, A. Pivrikas, P. Wolfer, N. S. Stutzmann, P. L. Burn, P. Meredith, J. Mater. Chem. 2012, 22, 1800 – 1806; b) P. E. Schwenn, K. Gui, A. M. Nardes, K. B. Krueger, K. H. Lee, K.



[13]

[14]

[15]

[16]

[17] [18] [19]

[20] [21] [22]

Mutkins, H. Rubinstein-Dunlop, P. E. Shaw, N. Kopidakis, P. L. Burn, P. Meredith, Adv. Energy Mater. 2011, 1, 73 – 81. a) N. Blouin, A. Michaud, M. Leclerc, Adv. Mater. 2007, 19, 2295 – 2300; b) W. Yue, Y. Zhao, S. Shao, H. Tian, Z. Xie, Y. Geng, F. Wang, J. Mater. Chem. 2009, 19, 2199 – 2206. I. Meager, R. S. Ashraf, S. Mollinger, B. C. Schroeder, H. Bronstein, D. Beatrup, M. S. Vezie, T. Kirchartz, A. Salleo, J. Nelson, I. McCulloch, J. Am. Chem. Soc. 2013, 135, 11537 – 11540. D. A. M. Egbe, S. Trk, S. Rathgeber, F. Khnlenz, R. Jadhav, A. Wild, E. Birckner, G. Adam, A. Pivrikas, V. Cimrova, G. Knçr, N. S. Sariciftci, H. Hoppe, Macromolecules 2010, 43, 1261 – 1269. a) H. Usta, G. Lu, A. Facchetti, T. J. Marks, J. Am. Chem. Soc. 2006, 128, 9034; b) Y. Zhang, J. Zou, H.-L. Yip, Y. Sun, J. A. Davies, K.-S. Chen, O. Acton, A. K.-Y. Jen, J. Mater. Chem. 2011, 21, 3895 – 3920; c) L. Huo, J. Hou, H.-Y. Chen, S. Zhang, Y. Jiang, T. L. Chen, Y. Yang, Macromolecules 2009, 42, 6564 – 6571. G. Ren, C. W. Schlenker, E. Ahmed, S. Subramaniyan, S. Olthof, A. Kahn, D. S. Ginger, S. A. Jenekhe, Adv. Funct. Mater. 2013, 23, 1238 – 1249. H.-I. Lu, C.-W. Lu, Y.-C. Lee, H.-W. Lin, L.-Y. Lin, F. Lin, J.-H. Chang, C.-I. Wu, K.-T. Wong, Chem. Mater. 2014, 26, 4361 – 4367. K. C. Moss, K. N. Bourdakos, V. Bhalla, K. T. Kamtekar, M. R. Bryce, M. A. Fox, H. L. Vaughan, F. B. Dias, A. P. Monkman, J. Org. Chem. 2010, 75, 6771 – 6781. J. U. Ju, S. O. Jung, Q. H. Zhao, Y. H. Kim, J. T. Je, S. K. Kwon, Bull. Korean Chem. Soc. 2008, 29, 335 – 338. M.-M. Shi, D. Deng, L. Chen, J. Ling, L. Fu, X.-L. Hu, H.-Z. Chen, J. Polym. Sci. Part A 2011, 49, 1453 – 1461. P. Gao, D. Cho, X. Yang, V. Enkelmann, M. Baumgarten, K. Mllen, Chem. Eur. J. 2010, 16, 5119 – 5128.

Received: August 6, 2014 Published online on && &&, 2014


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ARTICLES New acceptors: A series of small-molecule, nonfullerene electron acceptors containing the [(benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile unit is designed to possess different absorption profiles and optical gaps (see picture). When poly(3-n-hexylthiophene) (P3HT) is used as the standard electron donor, significant photocurrent generation in the near infrared region, with an external quantum yield reaching as high as 22 % at 700 nm and an onset > 800 nm are achieved.


Y. Fang, A. K. Pandey, D. M. Lyons, P. E. Shaw, S. E. Watkins, P. L. Burn,* S.-C. Lo, P. Meredith* && – && Tuning the Optoelectronic Properties of Nonfullerene Electron Acceptors


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