Self-assembly, Physicochemical, and Field-effect Transistor Properties of Solution-crystallized Organic Semiconductors Based on π-Extended Dithieno[3,2-b:2′,3′-d]thiophenes

Abstract

Thienoacene-based π-conjugated oligomers, DTT-NP8 and DTT-BT8, were designed and synthesized. Their strong intermolecular interactions originating from S£S contacts enable the fabrication of single-crystal microribbons via solution processing. Organic single-crystal transistors exhibited fieldeffect mobilities as high as 0.54 cm 2 V ¹1 s ¹1 and on/off current ratio of ca. 10 6 . π-Conjugated oligomers with rigid, fused-ring structures are of particular interest for applications in organic field-effect transistors (OFETs).1 Among π-conjugated organic materials, pentacene and its derivatives have been considered the benchmark materials for OFETs because of their excellent semiconducting behavior, 1d,2 which is comparable to that of hydrogenated amorphous silicon (a-Si:H). However, pentacene and its functionalized derivatives still suffer from degradation under ambient conditions due to photoinduced oxidative decomposition and/or the formation of dimeric adducts.3 Recent developments by several groups in synthesizing new organic semiconductors and optimizing device fabrication have resulted in improved environmental stability and electrical performance. 4Fused thiophene-based materials have emerged as one of the most promising alternatives, and indeed led to high chargecarrier mobilities exceeding 1 cm 2 V ¹1 s ¹1, together with excellent stability and processability. 4 The high polarizability of sulfur atoms and their ability to engage in strong S£S and S£π intermolecular interactions are believed to contribute to high mobilities of those thiophene-based materials.1a,5 Consequently, rational molecular design for solution-processable organic semiconductors to offer optimum molecular ordering from nano to macroscopic scales, which enables efficient charge transport, is a significant challenge for future OFET technology.In our earlier work, 6 we fabricated one-dimensional (1D) charge-transport superstructures based on 2,6-bis(4-octylphenyl)thieno[3,2-b:2¤,3¤-d]thiophene , and successfully demonstrated OFETs with a high hole mobility of 10.2 cm 2 V ¹1 s ¹1 by employing its single-crystal microribbons selfassembled via solution processing. Motivated by this result, we became interested in introducing multiple S£S interactions to π-conjugated oligomers to render an alternative charge-transport pathway other than ππ interactions.6 The 2-naphthyl-and 2-benzothienyl-functionalized dithieno[3,2-b:2¤,3¤-d]thiophene derivatives DTT-NP8 and DTT-BT8 (Scheme 1), which are π-expanded analogues of DTT-8, have been designed in the present study. Herein, we report self-assembly, optical, and single-crystal OFET properties of these materials. Single-crystal OFETs offer the opportunity to explore their intrinsic chargetransport properties, as the influence of grain boundaries, molecular disorder, and charge traps can be minimized. 4,6,7 Scheme 1 illustrates the synthetic approach to the new semiconducting molecules based on the annulated dithieno[3,2-b:2¤,3¤-d]thiophene core. The SuzukiMiyaura coupling reaction of 1 with 2 in the pre...

High‐Mobility Regioisomeric Thieno[f,f′]bis[1]benzothiophenes: Remarkable Effect of Syn/Anti Thiophene Configuration on Optoelectronic Properties, Self‐Organization, and Charge‐Transport Functions in Organic Transistors

“…To the best of our knowledge, the μ values measured for the syn ‐TBBT‐8 thin films (up to 7.4 cm 2 V −1 s −1 ) are the highest reported to date for thin‐film OFETs fabricated by facile dip‐coating processes. [20c,22] In marked contrast to the results for the syn ‐isomer, the anti ‐TBBT‐8 isomer exhibited lower charge‐transport properties ( µ max = 1.4 × 10 −3 cm 2 V −1 s −1 and I on / I off ≈10 3 ) with negligible anisotropy (see Table ). The lower crystallinity and surface coverage can explain the inferior performance of thin‐film OFET devices based on the anti ‐TBBT‐8 isomer.…”

“…To examine the intrinsic charge‐transport properties and the regioisomeric effect of the syn ‐ and anti ‐TBBT‐8 isomers, single‐crystal OFETs, as illustrated in Figure a, were fabricated in a top‐contact, bottom‐gate configuration. Well‐organized single‐crystal microribbons consisting of each pure isomer were grown by drop‐casting from anisole solutions (1–2 g L −1 ) onto octyltrichlorosilane (OTS)‐treated SiO 2 /Si substrates followed by drying under nitrogen atmosphere, according to the procedures reported in our previous work[4e,20] (see the Experimental Section). The overall length of the microribbons extended to several hundreds of micrometers or even longer, with a typical width of 1–20 µm and a thickness of less than 100 nm.…”

“…In order to prepare large‐area crystalline thin films of the syn ‐ and anti ‐TBBT‐8 isomers, we employed a dip‐coating method,[20c,23] in which precleansed bare SiO 2 /Si substrates (15 mm × 15 mm in size) were dipped into their toluene solutions (1.5 g L −1 ) and lifted out at a constant rate (1 µm s −1 ). Uniformly grown continuous thin films with a thickness of typically 30–50 nm covering the entire substrate area dipped into the solution could be obtained for the syn ‐TBBT‐8 isomer under optimized conditions ( Figure a).…”

An Effective Route to Dithieno[3,2-b:2′,3′-d]thiophene-Based Hexaheteroacenes

“…Over the past two decades a large number of thiophene-based photo-and electroactive compounds has been developed and utilized to fabricate photonic and electronic devices. 1,2 In this context, dithieno[3,2-b:2',3'-d]thiophene (DTT), due to rigid planar scaffold structure with high π-conjugation as well as ability to create effective intermolecular S…S interactions, has found a wide application in the design of p-type semiconductors, including (hetero)aryl-linked DTT molecules [3][4][5][6][7][8][9][10][11] as well as ringfused molecules with DTT core, [12][13][14][15][16][17][18] for organic field-effect transistors (OFET). In addition, DTT subunit has been also used for the construction of light-harvesting materials for organic photovoltaics, [19][20][21][22][23][24][25][26][27] electrochromic [28][29][30][31] and photochromic [32][33][34] materials.…”

“…1,2 In this context, because of its rigid planar scaffold and its high degree of -conjugation, as well as its ability to undergo effective intermolecular S-S interactions, dithieno[3,2-b:2′,3′d]thiophene (DTT), as well as analogous (het)aryl-linked DTT molecules [3][4][5][6][7][8][9][10][11] and ring-fused molecules with DTT a core, [12][13][14][15][16][17][18] have found widespread application in the design of p-type semiconductors for organic field-effect transistors (OFETs). The DTT subunit has been also used in the construction of light-harvesting materials for organic photovoltaics, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] as well as in electrochromic [28][29][30][31] and photochromic materials. [32][33][34] For instance, two examples of semiconductor materials based on benzo-fused DTT frameworks, P-BTDT 12 and C6-DBTDT,…”