We report the synthesis and characterization of a novel donor-acceptor semiconducting polymer bearing naphthobisthiadiazole (NTz), a doubly benzothiadiazole (BTz)-fused ring, and its applications to organic field-effect transistors and bulk heterojunction solar cells. With NTz's highly π-extended structure and strong electron affinity, the NTz-based polymer (PNTz4T) affords a smaller bandgap and a deeper HOMO level than the BTz-based polymer (PBTz4T). PNTz4T exhibits not only high field-effect mobilities of ~0.56 cm(2)/(V s) but also high photovoltaic properties with power conversion efficiencies of ~6.3%, both of which are significantly high compared to those for PBTz4T. This is most likely due to the more suitable electronic properties and, importantly, the more highly ordered structure of PNTz4T in the thin film than that of PBTz4T, which might originate in the different symmetry between the cores. NTz, with centrosymmetry, can lead to a more linear backbone in the present polymer system than BTz with axisymmetry, which might be favorable for better molecular ordering. These results demonstrate great promise for using NTz as a bulding unit for high-performance semiconducting polymers for both transistors and solar cells.

We report the synthesis, characterization, and OFET and OPV properties of a series of novel naphthodithiophene (NDT3)-based donor− acceptor semiconducting polymers. A striking feature of the present polymers is the very close π−π stacking of 3.5 Å, most likely as a result of the large π system and the D−A system in the polymer backbone. PNDT3NTz-DT, in particular, is found to be one of the few examples of versatile polymers that exhibit both the field-effect mobility of ∼0.5 cm 2 /(V s) and the PCE of ∼5%. These results indicate that NDT3 is a promising versatile core unit for semiconducting polymers and that the use of highly π-extended heteroarenes as both the donor and the acceptor unit is a promising design strategy to develop high performance polymers.

Single crystal X-ray analysis of NTz2T-Me and BTz2T-Me.Single crystals of NTz2T-Me and BTz2T-Me for X-ray structural analysis were obtained by sublimation and recrystallization from ethyl acetate, respectively. The X-ray crystal structural analysis was performed on a Rigaku CCD Mercury (Mo Ka radiation, l = 0.71070 Å, graphite monochromator, T = 293 K, 2q max = 55.0º). The structure was solved by the direct method using SHELXS-97. S1 Non-hydrogen atoms were refined anisotropically, and all hydrogen atoms were included in the calculations but not refined. All calculations were performed using the crystallographic software of SHELXL-97. S1

A new class of oligothienoquinoidal derivatives with newly employed (acyl)cyanomethylene termini are reported. For the synthesis of (acyl)cyanomethylene-substituted thienoquinoidals, similar methods successfully employed for the synthesis of related dicyanomethylene-or ((alkyloxy)carbonyl)cyanomethylene-substituted thienoquinoidals were not applicable, and thus a new synthetic route was developed. The introduced (acyl)cyanomethylene terminal groups act both as a solublizing group to facilitate solution processability and an electron-withdrawing group to keep the LUMO energy levels sufficiently low for n-channel organic semiconductors. The LUMO energy levels estimated from their reduction potential are ∼4.2 eV below the vacuum level, which just falls in between those for the corresponding dicyanomethylene-and ((alkyloxy)carbonyl)cyanomethylene-substituted thienoquinoidals. This qualitatively agrees with the electron-withdrawing nature of the terminal groups; the order of the electron withdrawing nature is cyano-> acyl-> (alkyloxy)carbonyl-groups. Spin-coating chloroform solutions of (acyl)cyanomethylene-substituted thienoquinoidals gave homogeneous thin films on the Si/SiO 2 substrates, and the thin films based on the terthienoquinoidal derivatives became highly crystalline upon thermal annealing. The annealed film acted as the active semiconducting channel in the FET devices under ambient conditions, and the electron mobilities extracted from the saturation regime were ∼0.06 cm 2 V -1 s -1 . These n-channel FET characteristics are nearly the same or slightly better than those of the FETs based on the related ((alkyloxy)carbonyl)cyanomethylene-terminated terthienoquinoidal, indicating that the (acyl)cyanomethylene moiety is a useful terminal group on the thienoquinoidals for the development of soluble n-channel organic semiconductors.

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