Sodium Sulfide-Promoted Thiophene-Annulations - American

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Sodium Sulfide-Promoted Thiophene-Annulations: Powerful Tools for Elaborating Organic Semiconducting Materials Masahiro Nakano, and Kazuo Takimiya Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b03413 • Publication Date (Web): 24 Oct 2016 Downloaded from http://pubs.acs.org on October 24, 2016

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Chemistry of Materials

Sodium Sulfide-Promoted Thiophene-Annulations: Powerful Tools for Elaborating Organic Semiconducting Materials Masahiro Nakano* and Kazuo Takimiya* Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science (CEMS), 2-1, Hirosawa, Wako, Saitama, 351-0198, Japan.

ABSTRACT: We describe herein facile thiophene annulation reactions promoted by sodium sulfide hydrate (Na 2S•9H2O) for the synthesis of acene(di)thiophenes that can be further utilized as organic semiconductors or building blocks for the elaboration of semiconducting oligomers and polymers. Sodium sulfide hydrate is an efficient source of sulfur for both the aromatic nucleophilic substitution (SNAr) reaction and the nucleophilic hydrogen substitution (SNH) reaction to give a range of electron-donating acene(di)thiophenes and an electron-deficient naphtho[2,3-b:6,7-b']dithiophene diimide (NDTI), respectively. We also describe organic semiconducting materials on the basis of these acene(di)thiophenes and their use in organic devices, such as organic field-effect transistors and organic photovoltaics, and demonstrate that synthetic evolution is one of the keys to promoting the field of organic semiconducting materials.

1. INTRODUCTION Acenes, which are linear cata-condensed polycyclic aromatic hydrocarbons represented by tetracene and pentacene (Figure 1a, n = 3 and 4), are the most well studied organic semiconductors for organic field-effect transistors that show promising hole mobility.1 The high mobility is due to the large intermolecular orbital overlap in the solid state, which originates in the planar and rigid molecular structures with a largely -extended electronic structure.2 On the other hand, oligo- and polythiophenes are representative organic semiconductors with a largely extended -conjugation, in which the coplanar thiophene-thiophene junction through the -positions of the thiophene rings plays an important role. Compared to a biphenyl substructure, a 2,2'-bithiophene substructure has good coplanarity owing to the small steric hindrance between the two aromatic rings.3 Thus, thiophene-based compounds have been regarded as promising organic semiconductors and/or building blocks for the elaboration of semiconducting oligomers and polymers with largely extended -conjugation structures. Another advantage of thiophene-based compounds is their capability to achieve selective functionalization; distinct reactivity is observed between the thiophene - and -positions in a range of chemical transformations, which in turn affords the opportunity to design new elaborated semiconducting systems in combination with facile-conjugation through the coplanar thiophene-thiophene junction. Acene(di)thiophenes, in which an acene core and thiophene ring(s) are fused to construct a large polycyclic system, have been known since the 1960s and recently attracted attention in the field of organic semiconductors as they possess the advantages of both acenes and thiophene-based compounds.4 Representative examples of acenedithiophene-based organic semiconductors include 5,11-bis(triethylsilylethynyl)anthra[2,3-b:6,7-b']dithiophene (TES-ADT),5,6 a p-type organic semiconductor for solution-processed organic field-effect transistors (OFETs), and poly({4,8-bis[(2-

Figure 1. Chemical structure of acenes and acene(di)thiophenes (a) and acene(di)thiophene-based semiconducting materials (b). ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7),7,8 a p-type polymer for organic photovoltaics (OPVs) combined with fullerene-based n-type organic semiconductors. With interest in organic semiconductors and their applications in optoelectronic devices becoming widespread, the synthesis and characterization of acene(di)thiophene-based materials have been intensively studied in the last decade.9 From the viewpoint of synthetic chemistry, only a few useful methods for the synthesis of acene(di)thiophene structures have been developed; representative examples include the synthesis of benzo[1,2-b:4,5-b']dithiophene (BDT)10 and anthra[2,3-b:6,7b']dithiophene (ADT)11 derivatives from thiophene-based starting compounds through the corresponding dione intermediates (Scheme 1). These well-established reactions have served as the “workhorse” in the synthesis of a wide range of BDT and ADT derivatives, some of which have been incorporated into the conjugated backbone in semiconducting polymers. In contrast,

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the synthesis of naphthodithiophenes (NDTs) is much more difficult than that of BDT and ADT derivatives12 because the construction of the fused-naphthalene moiety between two thiophenes requires a well-designed strategy. Cheng et al. have reported sophisticated methods for the synthesis of a series of alkylated angular-shaped NDTs (Scheme 2a).13 Another straightforward synthesis of alkyloxy-NDTs has been developed by Facchetti et al.14,15 These new NDT derivatives have been incorporated into semiconducting oligomers and polymers for OFET and OPV applications,16 demonstrating that the development of new synthetic chemistry will broaden the horizon of organic optoelectronic materials. We have been also interested in the synthesis and characterization of thiophene-based fused aromatic compounds, often called as thienoacenes, as small-molecule organic semiconductors for OFET application.17 For organic semiconductors in OFET devices, it is critical to realize two-dimensional (2D)

Scheme 1. Synthesis of benzo[1,2-b:4,5-b']dithiophene (BDT) and anthra[2,3-b:6,7(7,6)-b']dithiophene (ADT) derivatives through dione intermediates.

Scheme 2. Synthesis of naphthodithiophenes with alkyl- (a) and alkyloxy- groups (b).

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electronic structures in the solid state for high thin-film mobility. Such 2D electronic structures are generally obtained from the herringbone packing in the solid state, as exemplified by acenes, such as tetracene and pentacene, in which the lack of substituents at the peri-position is the key. However, acene(di)thiophenes without peri-substituents cannot be readily synthesized by the developed methods. This served as our initial motivation to develop a simple and general method for the synthesis of parent or rather simple acene(di)thiophenes, and as a result, we came across the simple sodium sulfide (Na2S)-promoted thiophene annulation reaction on acene cores. It turned out that the method has generality and is easy to carry out and reproducible for the synthesis of a wide range of simple acene(di)thiophenes. In addition, we recently found that the same reagent also induces a similar but mechanistically different annulation reaction on 1,4,5,8-naphthalene tetracarboxylic diimide (NDI) to produce a new electron-deficient acenedithiophene analog. We here describe two distinct reactions using the same reagent, sodium sulfide hydrate (Na2S•9H2O), and the utility of a range of acene(di)thiophenes for the elaboration of various organic semiconducting materials. 2. SODIUM SULFIDE-PROMOTED THIOPHENE ANNULATION FOR SIMPLE ACENE(DI)THIOPHENE SYNTHSIS It is apparently easy to synthesize simple, acene(di)thiophenes having few substituents. In reality, however, the synthesis of parent (unsubstituted) acene(di)thiophene often requires multiple steps and a less effective protocol.18 This is likely due to the need to control the direction of the annulation reaction by introducing substituents and to protect the highly reactive thiophene -position under the reaction conditions. We thus sought a general method for the synthesis of parent acene(di)thiophene from a simple precursor, which is desirable for the further development of organic semiconducting materials. One of the simplest synthetic routes to parent benzo[b]thiophene (BT) is the Sashida reaction,19 in which 1-bromo-2-[2(trimethylsilyl)ethynyl]benzene is first treated with tBuLi to in situ generate an anion intermediate via a lithium-bromine exchange reaction, and the anion intermediate reacts with elemental sulfur to give a thiolate intermediate. The thiolate intermediate is spontaneously converted into BT via the intramolecular thiophene annulation reaction (Scheme 3a). As tBuLi is an intractable and flammable reagent, we sought an alternative reaction to produce the thiolate intermediate, which would enable us to develop a general and effective method for the synthesis of BT and its related compounds. A similar thiophene annulation reaction on the anthraquinone moiety was reported by Shvartsberg and coworkers, in which 2alkynyl-1-chloro- or 1-alkynyl-2-chloro-anthraquinone and Na2S•9H2O were employed as the substrate and the sulfur source, respectively, to afford corresponding anthra[1,2-b]thiophene-6,11-dione or anthra[2,1-b]thiophene-6,11-dione, respectively.20 Obviously, the electron-withdrawing anthraquinone moiety played a critical role in promoting the initial aromatic nucleophilic substitution (SNAr) reaction by the sulfide anion. It is known that the SNAr reactions of sulfide and related

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sulfur nucleophiles can be accelerated in polar aprotic solvents at high temperature.21 With these considerations in mind, we tested the reaction of 1-bromo-2-[2-(trimethylsilyl)ethynyl]benzene with Na2S•9H2O in several polar aprotic solvents and found that the reaction in N-methyl-2-pyrrodidone (NMP) at a high temperature (180 oC) reproducibly afforded BT in good yield (Scheme 3b). The reaction proceeded in a similar manner with a substituent at the acetylene moiety; both the alkyl or phenyl derivatives of BT can be readily obtained from the corresponding o-bromo-ethynylbenzene derivatives in good yields.22 In order to reveal the scope and limitation of this sodium sulfide-promoted thiophene annulation reaction, we tested a range of substrates: benzene derivatives with two- or threefold reaction sites (Table 1, entries 1 and 2 respectively), naphthalene derivatives (entries 3–7),23-25 and anthracene-based ones (entries 8 and 9). All these reactions except entry 9, in which the twofold thiophene annulation on the anthracene core was postulated, gave the desired thiophene-annulated products in good to excellent yields, even for the threefold reaction on the benzene core. It should be noted that a series of naphthodithiophenes (entries 4–7) with different symmetries and thiophene placement can be selectively synthesized by this method, which had hitherto been very difficult to synthesize by other methods. Although anthra[2,3-b]thiophene (entry 8)25 was isolated in excellent yield, anthra[2,3-b:6,7-b']dithiophene (ADT, entry 9) was obtained in a trace yield, and the reaction afforded a black insoluble mixture instead.26 The twofold thiophene annulation on the anthracene failed because of the further reaction of ADT produced by the reaction at its reactive 5- and 11-positions with the reagent. In fact, pure ADT synthesized by an alternative method reacted with Na2S•9H2O to produce a similar unidentified solid under identical conditions. This is thus the limitation of the Na2S-promoted thiophene annulation reaction; owing to its relatively harsh reaction conditions and high temperature, a substrate or product like ADT that is susceptible to such conditions is not applicable. In this regard, it should be pointed out that even for the synthesis of large molecules with five rings, i.e., dithieno[2,3-b:7,6-b']fluorene, dithieno[3,2-b:6,7-b']fluorene,27 dithieno[2,3-b:7,6-b']carbazole,28 and dibenzo[6,7:10,11]tetraceno[2,3-b]thiophene,29 the method

Scheme 3. Synthesis of benzo[b]thiophene (BT); (a) Sashida’s method and (b) sodium sulfide-promoted thiophene annulation.

successfully afforded the desired compounds (Table 1, entries 10–13). Despite the limitation discussed above, its wide applicability to the synthesis of a range of parent acene(di)thiophenes is obviously an advantage of the Na2S-promoted thiophene annulation reaction. This feature would complement various methods for the synthesis of substituted acene(di)thiophenes with alkyl or alkyloxy groups at certain positions (Schemes 1 and 2). Another merit of this method would be its scalability; in our case, BDT and NDT can be prepared in multi-gram scale. In such a large-scale preparation, controlling the reaction conditions, particularly temperature, is critical. As the reagent is a nonahydrate (Na2S•9H2O), it liberates water in the NMP solution, which makes it difficult to raise the reaction temperature to 180 oC. Thus, it is advisable to remove water by using the Dean-Stark condenser prior to the addition of substrate (see Experimental). In regard to the hydrated water in the reagent, we also tested sodium sulfide anhydrate and pentahydrate as the reagent in the same annulation reaction. Sodium sulfide reagents other than the nonahydrate always gave low yields of the desired product, although the reasons for the poor results were unclear. 3. SODIUM SULFIDE-PROMOTED THIOPHENE ANNULATION ON NAPHTHALENE DIIMIDE The acene(di)thiophenes discussed above are generally used as p-type semiconducting materials or electron-donating building blocks as the energy level of their highest occupied molecular orbital (EHOMO: –5.76 ~ –5.05 eV, determined by cyclic voltammetry) is suitable for facile hole injection from the metal electrodes. On the other hand, in the field of organic semiconductors, n-type semiconducting materials with low-lying lowest unoccupied molecular orbital (LUMO) are also required. One of the prototypical n-type semiconducting materials is naphthalene 1,4,5,8-tetracarboxylic diimide (NDI), which consists of a naphthalene core and strong electron-withdrawing imide moieties.30 Following the development of the synthesis of acene(di)thiophenes as p-type organic semiconductors, we designed a thiophene-annulated NDI, namely, naphtho[2,3-b:6,7b']dithiophene-4,5,9,10-tetracarboxylic diimide (NDTI, Scheme 4), as a potential n-type semiconducting core structure with low-lying LUMO energy level (ELUMO) and chemical flexibility that allows effective extension of -conjugation through the its thiophene -positions. The question then was how to construct the NDTI structure. With the straightforward Na2Spromoted thiophene annulation reactions on the acene cores available, we envisioned a possible synthetic route from the corresponding 2,6-dibromo-3,7-diethynyl-NDI derivative to NDTI (Scheme 4a). However, all attempts to synthesize the key precursor met with failure. Instead of the thiophene annulation reaction from the o-halo-ethynylbenzene moiety, treatment of 2,6-diethynyl-NDI derivative,31 which has no reactive handle at the sulfurization site, with sodium sulfide was examined as a similar thiophene annulation reaction was reported for the synthesis of anthra[2,1-b]thiophene-6,11-dione from 1-ethynylated anthraquinone.32 To our surprise, the reaction of N,N'-dioctyl-2,6-(2-trimethylsilylethynyl)-NDI with Na2S•9H2O in ethanol gave a trace

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Table 1. Synthesis of acene(di)thiophenes and related compounds via Na2S-promoted thiophene annulation. Entry

Substrate

product

Yield / %

reference

1

R = TMS (H): 88 R = C8H17: 68 R = Ph: 57

22

2

R = TMS (H): 62 R = C8H17: 62 R = Ph: 75

22

3

70

25

4

R = TMS (H): 85 R = C8H17: 78 R = Ph: 86

24

5

6

R = TMS (H): 68 R = C8H17: 95 R = Ph: 71 R = TMS (H): 90 R = C8H17: 89 R = Ph: 60

24

23

7

R = TMS (H): 60 R = C8H17: 67 R = Ph: 56

24

8

84

25

9

trace

26

10

50

27

11

50

27

12

68

28

13

40

29

7


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Scheme 4. (a) NDTI and its retrosynthetic scheme, (b) synthesis of NDTI using Na2S reagent, and (c) the possible reaction mechanism. amount of the desired NDTI, which was finally isolated as N,N'dioctyl-NDTI (C8-NDTI) after a desilylation reaction induced by treatment with tetrabutylammonium fluoride.33 After optimization of the reaction conditions (solvent, additive, temperature, and reaction time), the desired NDTI derivatives were obtained in moderate yields (Scheme 4b). Note that this reaction can be formally viewed as a nucleophilic hydrogen substitution (SNH) reaction. A plausible reaction pathway of this annulation reaction is speculated as follows (Scheme 4c). Sulfide anions are first added to the acetylene moieties, and the resulting vinylthiolate intermediate acts as a nucleophile in the intramolecular Michael-type addition reaction to promote the formation of a sulfur-containing five-membered ring, which was then aromatized to form fused thiophene rings. The final step of this reaction is thought to be oxidation, and in fact, exposure of the reaction mixture to air before quenching is necessary in the actual annulation reaction. As expected, ELUMO of C8-NDTI was determined to be –4.0 eV by cyclic voltammetry, which is sufficiently low for n-type organic semiconducting materials for OFET devices realizing stable electron transport under ambient conditions.34 In fact, C8NDTI-based devices showed typical n-type characteristics in top-gate bottom-contact transistors under ambient conditions. Although the electron mobility of the devices is not impressively high (electron ~ 0.02 cm2/Vs), devices with much higher electron mobility can be obtained by chemical modifications at the thiophene -positions of the NDTI structure (vide infra). Moreover, the NDTI structure has another modification site at the imide nitrogen atoms; the introduction of large branched alkyl groups, such as 2-decyltetradecyl groups, greatly enhances solubility, enabling the incorporation of the NDTI core into the main chain of semiconducting polymers with electron transporting nature (vide infra).

Scheme 5. N,N' -alkylation and -arylation of N,N'-unsubstituted NDTI. In the syntheses of NDTI derivatives via the Na2S-promoted SNH reaction described above (Scheme 4b), the substrates already carry certain alkyl groups on the imide nitrogen atoms, which means that the synthesis of new NDTI derivatives with different alkyl groups always starts from scratch. To circumvent this inconvenience in the synthesis of NDTI derivatives, we have developed an improved and versatile method that employs N,N'-unsubstituted-2,7-bis(triethylsilyl)-NDTI (Scheme 5) as the key and common intermediate. From the key intermediate, a range of N-alkyl- and N-phenyl-substituted NDTI derivatives were efficiently synthesized by the Mitsunobu reaction and the copper-catalyzed coupling reaction with phenylboronic acid, respectively (Scheme 5). Another merit of this protocol is that the key NDTI intermediate can be readily synthesized in a multi-gram scale (> 10 g) without tedious workup and purification operations. 35 We be-

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lieve that this method can pave the way to wide-ranging applications of the NDTI structure in various semiconducting materials in the future. 4. APPLICATION OF ACENE(DI)THIOPHENES In this section, we summarize recent developments of semiconducting materials based on acene(di)thiophenes that can be synthesized by Na2S-promoted reactions, together with their properties in organic devices, such as OFETs and OPVs. First, we describe briefly the synthesis of such semiconducting materials; for most small-molecule semiconductors, the annulation reaction is the final step in the synthesis. On the other hand, for such materials as semiconducting oligomers and polymers, further synthetic reactions, which are mostly palladium-catalyzed coupling reactions, are employed for the completion of material synthesis. In such coupling reactions, the halogen functionality, specifically bromide, and the trialkylstannyl group, which are the key organometallic species in the Stille coupling reactions, are often required. For conventional acene(di)thiophenes, these functionalities are easily introduced at the thiophene -positions (Scheme 6a). In the case of NDTI, however, the reactivity of the thiophene -positions is quite low, likely owing to the strong electron-withdrawing nature of the imide moieties. To our surprise, neither metalation reaction with LDA and nBuLi nor electrophilic halogenation proceeded, which impressed on us the fact that the thiophene -positions in NDTI are the least reactive among the related compounds we have treated. However, such inactivity was found to be circumvented by the func-

Scheme 6. Bromination and stannylation of acene(di)thiophenes (a) and NDTI (b). Polymerization reaction via brominated/stannylated compounds (c).

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tional group conversion from trialkylsilyl to bromide. The corresponding dibrominated NDTI can be then converted into the corresponding stannylated NDTI (Scheme 6b). Using the brominated and stannylated derivatives, the acenedithiophenes were incorporated into semiconducting oligomers and polymers. Semiconducting polymers were synthesized by the -wave-assisted Stille coupling reactions between an ,'dibrominated or -stannylated derivative and a co-polymerized -unit with distannyl or dibromo groups (Scheme 6c). Depending on the nature of the acenedithiophene and the combined units, EHOMO and ELUMO of the resulting semiconducting oligomers and polymers were finely tuned36 and as a result, p-, n-, or ambipolar materials can be designed and synthesized (vide infra). With facile annulation chemistry as well as chemical modification at the thiophene -positions, a range of small molecules, oligomers, and polymers based on the acenedithiophenes were developed as depicted in Figure 2 for representative materials. Among the small-molecule semiconductors, '-diphenyl acenedithiophenes, which were directly prepared by the Na2Spromoted annulation from the corresponding o-bromo-phenylethynyl precursors, are known to have good film-forming property by vacuum deposition. In fact, thin-film transistors made of derivatives with linear37 and large acenedithiophene cores, naphtho[2,3-b:6,7-b']dithiophene (Figure 2a, 2),24 gave OFET devices with very high hole mobility (hole) of up to 1.5 cm2 V–1s–1 (Table 2). With the electron-deficient acenedithiophene, NDTI, n-type organic semiconductors were developed. In sharp contrast to the superior performance based on the '-diphenyl acenedithiophenes as p-type organic semiconductors, the electron mobility of the '-diphenyl derivative of NDTI (4) was not improved; rather, it decreased compared with that of -unsubstituted C8-NDTI (3). On the other hand, the introduction of a chlorine group at the -position was effective to improve the

Figure 2. Small molecule (a) and polymer (b) semiconducting materials based on acene(di)thiophenes.

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Table 2. Estimated HOMO/LUMO energy levels and device performances of the thiophene-fused acene-based semiconducting materials. Compound

ELUMO / eV

EHOMO / eV

electron / cm2 V-1s-1 c

hole / cm2 V-1s-1 c

PCE / %

Reference

a

1 2

-

-5.4 -5.2 a

-

0.08 1.5

-

37 24

3 4 5

-4.0 b -4.0 b -4.1 b

-6.1 b -5.8 b -

2.0×10-2 9.7×10-3 0.73

3.0×10-4 -

-

33 38 38

6 7 8

-4.1 b -4.2 b -

-5.9 b -5.8 b -5.0 a

0.17 0.16 -

4.0×10-2 0.14 0.77

-

40 40 41

9 10 11

–4.1 b -4.2 b

- 5.3 a - 5.6 b

0.27 0.21

0.1 0.10 -

8.2 d 2.7 e -

43 33 44

-

12 -4.0 b - 5.6 b 2.6×10-3 3.3×10-4 3.5 e 46 a b Determined by a photoelectron yield spectroscopy in air (PESA, a Riken AC-2 model). Determined by cyclic voltammetry. V vs. Ag/AgCl in benzonitrile containing tetrabutylammonium hexafluorophosphate (Bu 4NPF6, 0.1 M) as supporting electrolyte at a scan rate of 100 mV/s. Counter and working electrodes were made of Pt. All the potentials were calibrated with the Fc/Fc + (E1/2 = +0.46 V measured under identical conditions). c Top-contact bottom-gate OFET deveices based on deposited or spin-coated thin-films. d The device structure is ITO/PEDOT:PSS/9:PC71BM/LiF/Al. e The device structure is ITO/PEDOT:PSS/PTB7:10 or 12/Ca/Al. performance of n-type OFETs; in this case, the chlorine group acted as not only an electron-withdrawing group to lower ELUMO but also a functional group that alters the packing structure in the solid state from the one-dimensional columnar structure to the 2D brick wall structure,38 which is believed to be the key to enhancing electron mobility in the thin-film state (4, electron ~ 0.73 cm2 V–1s–1).39 This result encouraged us to further use the NDTI structure as a building block for n-type organic semiconductors. It is interesting to note that although the electron mobility is low, the '-diphenyl NDTI afforded ambipolar OFET devices in which both hole and electron are injected from the electrode and both carriers are active depending on the device operation conditions. Attaching electron-donating acenethiophenes, such as benzo[b]thiophene (6) or naphtho[2,3-b]thiophene (7), to the -positions of NDTI enhanced the ambipolar nature. In particular, 7-based devices showed well-balanced hole and electron mobilities higher than 0.1 cm2 V–1s–1.40 Representative semiconducting polymers based on the present acenedithiophenes are depicted in Figure 2b, and their device performances are also summarized in Table 2. The simple copolymer with NDT and bithiophene (8) worked as a p-type semiconductor for solution-processed OFET devices, and relatively high hole mobility (hole ~ 0.77 cm2 V-1s-1) was recorded.41 On the other hand, the combination of an alkylated NDT unit42 and an electron-deficient co-monomer unit, naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole (NTz), gave a superior ptype polymer (9) for OPV applications; OPV devices with a bulk heterojunction active layer consisting of the polymer and PC71BM achieved high power conversion efficiency (PCE) of 8.2% under irradiation by AM 1.5 solar simulator.43

NDTI-based polymers occupy an interesting position in semiconducting polymers as the electronic nature can be easily tuned by a co-polymerized unit combined with NDTI in the main chain.44 For example, electron-donating bithiophene unit (10) afforded ambipolar polymers with balanced hole and electron mobilities (hole ~ 0.10 cm2 V-1s-1, electron ~ 0.27 cm2 V-1s1 ), whereas the combination with electron-deficient NTz unit afforded n-type unipolar polymer (11, electron ~ 0.21 cm2 V-1s-1). Interestingly, the donor-acceptor nature of the former polymer shifted the absorption band to the near-infrared region (NIR, ~ 950 nm), and the polymer could act as the NIR absorber with sufficient n-type nature for OPV application. Although PCE was not very high (compound 12, ~ 3.5%), the combination with PTB7 as the donor polymer gave all-polymer OPVs covering a wide solar spectrum from visible to the NIR region.45,46 5. SUMMARY We focused on sodium sulfide-promoted thiophene annulation reactions to prepare acene(di)thiophenes that could be utilized to elaborate various organic semiconducting materials. It should be emphasized that with the same sodium sulfide reagent, two types of thiophene annulation reactions with different mechanisms would take place to afford electron-rich and electron-deficient acene(di)thiophenes. The method offers several advantages, including availability of reagent (commercially available and inexpensive), easy operation of the experimental protocol, wide applicability to many substrates, high yields in many cases, and scalability. We do not insist that the present method is unique for the synthesis of electron-rich acenedithio-

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phenes; in fact, for the synthesis of derivatives with such substituents as alkyl and alkyloxy groups, straightforward methods have been reported. Furthermore, during the preparation of this manuscript, Itami et al. reported an amazingly simple method for the synthesis of a wide range of thiophene-fused -systems with aryl groups at the thiophene -position from corresponding diarylacetylenes and elemental sulfur.47 Thus, it can be said that the unique feature of the present method is its capability to afford parent systems or rather simple, less-substituted compounds. Furthermore, the method is applied to the synthesis of various thiophene-fused extended -systems with vacant thiophene -positions. In this context, the method likely complements existing methods for the synthesis of acene(di)thiophenes and other thiophene-fused -extended derivatives. On the other hand, we can say that the sodium sulfide-promoted thiophene annulation reaction for the synthesis of NDTI is quite unique and has mechanistically characteristic features.48 This finding is critical for the development of NDTI-based ntype and ambipolar materials, and emphasizes that synthetic evolution leads to a new class of promising materials for organic electronics. Both electron-rich and electron-deficient acene(di)thiophenes can be prepared in large scale by the reaction, indicating that the materials described here can be further utilized in many applications, including the further elaboration of materials via chemical modifications and/or polymerization and application in optoelectronic devices. We hope that this paper would motivate researchers to apply the reactions and the present acene(di)thiophenes for future evolution in their research fields. 6. EXPERIMENTAL General All chemicals and solvents are of reagent grade unless otherwise indicated. N-Methylpyrrolidone (NMP) and toluene were purified with a standard procedure prior to use. Precursors with o-halo-ethynyl or ethynyl substructure were synthesized as reported.22-26,33,37 General procedure for Na2S-promoted thiophene annulation for acene(di)thiophene synthesis. A suspension of sodium sulfide hydrate (Na2S·9H2O, 2~4 equivalents to 1 ethynyl group) in NMP was stirred for 15 min at room temperature. The mixture was added the corresponding precursor with o-halo-ethynyl substructure(s) (< 1.0 mmol scale), and heating was carried out at 185 oC. After the mixture was stirred for 12 h at the same temperature, the resulting mixture was added into saturated aqueous ammonium chloride solution. The resulting precipitate was collected by filtration and washed with water and methanol. The residue was purified by column chromatography or vacuum sublimation to give acene(di)thiophene derivatives. Large-scale synthesis of BDT Na2S·9H2O (43.1 g, 0.18 mol) and NMP (0.95 L) were added into a reaction vessel equipped with a Dean-Stark trap, and the

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reaction vessel was placed in an oil bath set at 195 oC. After stirring for 4 h, distilled water was removed from the DeanStark trap, and the temperature of the heated solution in the reaction vessel reached approximately 190 oC. Then, a solution of 1,4-dibromo-2,5-bis(trimethylsilylethynyl)benzene (19.1 g, 0.044 mmol) in NMP (50 mL) was slowly added dropwise while keeping the temperature constant. After stirring at the same temperature for 1 day, the resulting mixture was added into saturated aqueous ammonium chloride solution (1.0 L). The resulting precipitate was collected by filtration, washed with water and methanol, dissolved in dichloromethane, and purified by column chromatography on silica gel eluted with hexane to give benzo[1,2-b:4,5-b']dithiophene (5.64 g, 66%). Large-scale synthesis of NDT Na2S·9H2O (52.8 g, 0.22 mol) and NMP (0.90 L) were added into a reaction vessel equipped with a Dean-Stark trap, and the reaction vessel was placed in an oil bath set at 195 oC. After stirring for 4 h, an azeotropic mixture containing water was collected from the Dean-Stark trap, and the temperature of the solution in the reaction vessel reached approximately 190 oC. Then, a solution of 1,5-dichloro-2,6-bis(trimethylsilylethynyl)naphthalene (18.0 g, 0.046 mmol) in NMP (90 mL) was added slowly while keeping the temperature constant. After stirring at the same temperature for 24 h, the resulting mixture was added into saturated aqueous ammonium chloride solution (0.9 L). The resulting precipitate was collected by filtration, washed with water, methanol, and hexane, dissolved in dichloromethane, and purified by column chromatography on silica gel eluted with hexane to give naphtho[1,2-b:5,6-b']dithiophene (9.31 g, 84%). General procedure for thiophene-annulation of N, N'-alkyl2,6-bis(trimethylsilylethynyl)-NDIs Under argon atmosphere, Na2S·9H2O (3.1 equivalents to 1 ethynyl group) was added to a stirred suspension of 2,6-bis(trimethylsilylethynyl)-NDI derivative in 2-methoxyethanol and acetic acid (50/1, v/v) at 0 oC. After stirring for 12 h at 60 oC, the mixture was cooled to room temperature and stirred for 3 h under atmospheric condition. Then, the mixture was diluted with water. The resulting precipitate was collected by filtration and washed with methanol. After drying, the crude product was purified by column chromatography (SiO2, CH2Cl2/hexane = 1/2) to afford NDTI with trimethylsilyl groups. Large-scale synthesis of N,N'-unsubstituted NDTI Under argon atmosphere, Na2S·9H2O (18.0 g, 0.075 mol) was added to a stirred suspension of N,N'-unsubstituted 2,6bis(triethylsilyl)-NDI (20.9 g, 0.034 mol) in 2-methoxyethanol (1.1 L) and acetic acid (38 mL) at 0 oC. After stirring for 12 h at rt, the mixture was stirred for 2 days under atmospheric condition. Then, the mixture was diluted with water (ca. 1.5 L). The resulting precipitate was collected by filtration and washed with methanol. After drying, hot chloroform (~60 oC, ca. 1.2 L) was added and the insoluble residue was removed by filtration. Then,

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the filtrate was concentrated in vacuo. Recrystallization from chloroform-methanol gave N,N'-unsubstituted NDTI as a maroon solid (10.75 g, 46%).

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected], [email protected]

Author Contributions All authors have given approval to the final version of the manuscript.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by JSPS KAKENHI Grant Numbers 15H02196 and 16K05900.

REFERENCES (1) Anthony, J. E., The Larger Acenes: Versatile Organic Semiconductors. Angew. Chem. Int. Ed. 2008, 47, 452–483. (2) Brédas, J.-L.; Beljonne, D.; Coropceanu, V.; Cornil, J., ChargeTransfer and Energy-Transfer Processes in -Conjugated Oligomers and Polymers: A Molecular Picture. Chem. Rev. 2004, 104, 4971–5004. (3) McCullough, R. D., The Chemistry of Conducting Polythiophenes. Adv. Mater. 1998, 10, 93–116. (4) Anthony, J. E., Functionalized Acenes and Heteroacenes for Organic Electronics. Chem. Rev. 2006, 106, 5028–5048. (5) Payne, M. M.; Parkin, S. R.; Anthony, J. E.; Kuo, C. C.; Jackson, T. N., Organic Field-Effect Transistors from Solution-Deposited Functionalized Acenes with Mobilities as High as 1 cm2 /V s. J. Am. Chem. Soc. 2005, 127, 4986–4987. (6) Gundlach, D. J.; Royer, J. E.; Park, S. K.; Subramanian, S.; Jurchescu, O. D.; Hamadani, B. H.; Moad, A. J.; Kline, R. J.; Teague, L. C.; Kirillov, O.; Richter, C. A.; Kushmerick, J. G.; Richter, L. J.; Parkin, S. R.; Jackson, T. N.; Anthony, J. E.; Contact-induced crystallinity for high-performance soluble acene-based transistors and circuits. Nat. Mater. 2008, 6, 216–221. (7) Lu, L.; Yu, L., Understanding Low Bandgap Polymer PTB7 and Optimizing Polymer Solar Cells Based on It. Adv. Mater. 2014, 26, 4413–4430. (8) Zhang, S.; Ye, L.; Zhao, W.; Liu, D.; Yao, H.; Hou, J., Side Chain Selection for Designing Highly Efficient Photovoltaic Polymers with 2D-Conjugated Structure. Macromolecules 2014, 47, 4653−4659. (9) Wang, C.; Dong, H.; Hu, W.; Liu, Y.; Zhu, D., Semiconducting -Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics. Chem. Rev. 2012, 112, 2208– 2267. (10) Beimling, P.; Koßmehl, G., Synthesis of benzo[1,2-b:4,5-b']dithiophene and its 4,8-Dimethoxy and 4,8-dimethyl derivatives. Chem. Ber. 1986, 119, 3198–3203. (11) Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J., Synthesis, Morphology, and Field-Effect Mobility of Anthradithiophenes. J. Am. Chem. Soc. 1998, 120, 664–672. (12) Takimiya, K.; Osaka, I., Naphthodithiophenes: Emerging Building Blocks for Organic Electronics. Chem. Rec. 2015, 15, 75–188.

(13) Cheng, S.-W.; Chiou, D.-Y.; Lai, Y.-Y.; Yu, R.-H.; Lee, C.-H.; Cheng, Y.-J., Synthesis and Molecular Properties of Four Isomeric Dialkylated Angular-Shaped Naphthodithiophenes. Org. Lett. 2013, 15, 5338–5341. (14) Loser, S.; Bruns, C. J.; Miyauchi, H.; Ortiz, R. P.; Facchetti, A.; Stupp, S. I.; Marks, T. J., A Naphthodithiophene-Diketopyrrolopyrrole Donor Molecule for Efficient Solution-Processed Solar Cells. J. Am. Chem. Soc. 2011, 133, 8142–8145. (15) Loser, S.; Miyauchi, H.; Hennek, J. W.; Smith, J.; Huang, C.; Facchetti, A.; Marks, T. J., A "zig-zag" naphthodithiophene core for increased efficiency in solution-processed small molecule solar cells. Chem. Commun. 2012, 48, 8511–8513. (16) Cheng, S.-W.; Chiou, D.-Y.; Tsai, C.-E.; Liang, W.-W.; Lai, Y.Y.; Hsu, J.-Y.; Hsu, C.-S.; Osaka, I.; Takimiya, K.; Cheng, Y.-J., Angular-Shaped 4,9-Dialkyl α- and β-Naphthodithiophene-Based Donor–Acceptor Copolymers: Investigation of Isomeric Structural Effects on Molecular Properties and Performance of FieldEffect Transistors and Photovoltaics. Adv. Funct. Mater. 2015, 25, 6131–6143. (17) Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E., Thienoacene-Based Organic Semiconductors. Adv. Mater. 2011, 23, 4347–4370. (18) Laquindanum, J. G.; Katz, H. E.; Benzodithiophene Rings as Semiconductor Building Blocks. Adv. Mater. 1997, 9, 36–39. (19) Sashida, H.; Sadamori, K.; Tsuchiya, T., A Convenient One-Pot Preparation of Benzo[b]-tellurophenes, -selenophenes, and -thiophenes from o-Bromoethynylbenzenes. Synth. Commun. 1998, 28, 713–727. (20) Ivanchikova, I. D.; Lebedeva, N. I.; Shvartsberg, M. S., A Simple Synthesis of Angular Anthrathiophenediones via Acetylenic Derivatives of Anthraquinone. Synthesis 2004, 13, 2131–2134. (21) Cogolli, P.; Maiolo, F.; Testaferri, L.; Tingoli, M.; Tiecco, M., Nucleophilic aromatic substitution reactions of unactivated aryl halides with thiolate ions in hexamethylphosphoramide. J. Org. Chem. 1979, 44, 2642–2646. (22) Kashiki, T.; Shinamura, S.; Kohara, M.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H., One-pot Synthesis of Benzo[b]thiophenes and Benzo[b]selenophenes from o-Halo-Substituted Ethynylbenzenes: Convenient Approach to Mono-, Bis-, and TrisChalcogenophene-Annulated Benzenes. Org. Lett. 2009, 11, 2473–2475. (23) Shinamura, S.; Miyazaki, E.; Takimiya, K., Synthesis, Properties, Crystal Structures, and Semiconductor Characteristics of Naphtho[1,2-b:5,6-b']dithiophene and -diselenophene Derivatives. J. Org. Chem. 2010, 75, 1228–1234. (24) Shinamura, S.; Osaka, I.; Miyazaki, E.; Nakao, A.; Yamagishi, M.; Takeya, J.; Takimiya, K., Linear- and Angular-Shaped Naphthodithiophenes: Selective Synthesis, Properties, and Application to Organic Field-Effect Transistors. J. Am. Chem. Soc. 2011, 133, 5024–5035. (25) Niimi, K.; Miyazaki, E.; Osaka, I.; Takimiya, K., Facile Syntheses of Anthra[2,3-b]chalcogenophenes. Synthesis 2012, 44, 2102– 2106. (26) Nakano, M.; Niimi, K.; Miyazaki, E.; Osaka, I.; Takimiya, K., Isomerically Pure Anthra[2,3-b:6,7-b']-difuran (anti-ADF), -dithiophene (anti-ADT), and -diselenophene (anti-ADS): Selective Synthesis, Electronic Structures, and Application to Organic Field-Effect Transistors. J. Org. Chem. 2012, 77, 8099–8111. (27) Cheng, S.-W.; Chiou, D.-Y.; Lai, Y.-Y.; Yu, R.-H.; Lee, C.-H.; Cheng, Y.-J., Synthesis and Molecular Properties of Four Isomeric Dialkylated Angular-Shaped Naphthodithiophenes. Org. Lett. 2013, 15, 5338–5341. (28) Chen, Y.; Tian, H.; Yan, D.; Geng, Y.; Wang, F.; Conjugated Polymers Based on a S- and N-Containing Heteroarene: Synthesis, Characterization, and Semiconducting Properties. Macromolecules 2011, 44, 5187–5185.

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(29) Lv, Bo.; Shen, X.; Xiao, J.; Duan, J.; Wang, Xuefei,; Yi, Y., Chem. Asian J. 2015, 10, 2677–2682. (30) Guo, X.; Facchetti, A.; Marks, T. J., Imide- and Amide-Functionalized Polymer Semiconductors. Chem. Rev. 2014, 114, 8943– 9021. (31) Buckland, D.; Bhosale, S. V.; Langford, S. J., A chemodosimer based on a core-substituted naphthalene diimide for fluoride ion detection. Tetrahedron Lett. 2011, 52, 1990–1992. (32) Baranov, D. S.; Gold, B.; Vasilevsky, S. F.; Alabugin, I. V. Divergent Cyclizations of 1-R-Ethynyl-9,10-anthraquinones: Use of Thiourea as a “S2-“ Equivalent in an “Anchor-Relay” Addition Mediated by Formal C-H Activation. J. Org. Chem. 2013, 78, 2074–2082. (33) Fukutomi, Y.; Nakano, M.; Hu, J.-Y.; Osaka, I.; Takimiya, K. Naphthodithiophenediimide (NDTI): Synthesis, Structure, and Applications. J. Am. Chem. Soc. 2013, 135, 11445–11448. (34) Jones, B. A.; Facchetti, A.; Wasielewski, M. R.; Marks, T. J., Tuning Orbital Energetics in Arylene Diimide Semiconductors. Materials Design for Ambient Stability of n-Type Charge Transport. J. Am. Chem. Soc. 2007, 129, 15259–15278. (35) Nakano, M.; Sawamoto, M.; Yuki, M.; Takimiya, K., N,N'-Unsubstituted Naphthodithiophene Diimide: Synthesis and Derivatization via N-Alkylation and -Arylation. Org. Lett. 2016, 18, 3770–3773. (36) Takimiya, K.; Osaka, I.; Nakano, M., -Building Blocks for Organic Electronics: Revaluation of "Inductive" and "Resonance" Effects of -Electron Deficient Units. Chem. Mater. 2014, 26, 587–593. (37) Takimiya, K.; Kunugi, Y.; Konda, Y.; Niihara, N.; Otsubo, T., 2,6-Diphenylbenzo[1,2-b:4,5-b']dichalcogenophenes: A New Class Of High-Performance Semiconductors for Organic FieldEffect Transistors. J. Am. Chem. Soc. 2004, 126, 5084–5085. (38) Nakano, M.; Osaka, I.; Hashizume, D.; Takimiya, K., -Modified Naphthodithiophene Diimides-Molecular Design Strategy for Air-Stable n-Channel Organic Semiconductors. Chem. Mater. 2015, 27, 6418–6425. (39) Takimiya, K.; Nakano, M.; Sugino, H.; Osaka, I., Design and elaboration of organic molecules for high field-effect-mobility semiconductors. Synth. Met. 2016, 217, 68–78. (40) Hu, J.-Y.; Nakano, M.; Osaka, I.; Takimiya, K., Naphthodithiophenediimide (NDTI)-based triads for high-performance air-stable, solution-processed ambipolar organic field-effect transistors. J. Mater. Chem. C 2015, 3, 4244–4249. (41) Osaka, I.; Abe, T.; Shinamura, S.; Miyazaki, E.; Takimiya, K., High-Mobility Semiconducting Naphthodithiophene Copolymers. J. Am. Chem. Soc. 2010, 132, 5000–5001. (42) Shinamura, S.; Sugimoto, R.; Yanai, N.; Takemura, N.; Kashiki, T.; Osaka, I.; Miyazaki, E.; Takimiya, K., Orthogonally Functionalized Naphthodithiophenes: Selective Protection and Borylation. Org. Lett. 2012, 14, 4718–4721. (43) Osaka, I.; Kakara, T.; Takemura, N.; Koganezawa, T.; Takimiya, K., Naphthodithiophene-Naphthobisthiadiazole Copolymers for Solar Cells: Alkylation Drives the Polymer Backbone Flat and Promotes Efficiency. J. Am. Chem. Soc. 2013, 135, 8834–8837. (44) Nakano, M.; Osaka, I.; Takimiya, K., Naphthodithiophene Diimide (NDTI)-Based Semiconducting Copolymers: From Ambipolar to Unipolar n-Type Polymers. Macromolecules 2015, 48, 576–584. (45) Zhou, E.; Nakano, M.; Izawa, S.; Cong, J.; Osaka, I.; Takimiya, K.; Tajima, K., All-Polymer Solar Cell with High Near-Infrared Response Based on a Naphthodithiophene Diimide (NDTI) Copolymer. ACS Macro Lett. 2014, 3, 872–875. (46) Nakano, K.; Nakano, M.; Xiao, B.; Zhou, E.; Suzuki, K.; Osaka, I.; Takimiya, K.; Tajima, K., Naphthodithiophene Diimide-Based

Page 10 of 11

Copolymers: Ambipolar Semiconductors in Field-Effect Transistors and Electron Acceptors with Near-Infrared Response in Polymer Blend Solar Cells. Macromolecules 2016, 49, 1752−1760. (47) Meng, L.; Fujikawa, T.; Kuwayama, M.; Segawa, Y.; Itami, K., Thiophene-Fused -Systems from Diarylacetylenes and Ele-mental Sulfur. J. Am. Chem. Soc. 2016, 138, 10351−10355. (48) Recently mono-thiophene-fused NDI, naphtho[2,3-b]thiophene diimide was reported: see, Chen, W.; Nakano, M.; Kim, J.-H.; Takimiya, K.; Zhang, Q., Naphtho[2,3-b]thiophene diimide (NTI): a mono-functionalisable core-extended naphthalene diimide for electron-deficient architectures. J. Mater. Chem. C 2016, 4, 8879−8883.

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Sodium Sulfide-Promoted Thiophene-Annulations - American

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