Consecutive thiophene-annulation approach to π-extended thienoacene-based organic semiconductors with [1]benzothieno[3,2-b][1]benzothiophene (BTBT) substructure.

We describe a new synthetic route to the [1]benzothieno[3,2-b][1]benzothiophene (BTBT) substructure featuring two consecutive thiophene-annulation reactions from o-ethynyl-thioanisole substrates and arylsulfenyl chloride reagents that can be easily derived from arylthiols. The method is particularly suitable for the synthesis of unsymmetrical derivatives, e.g., [1]benzothieno[3,2-b]naphtho[2,3-b]thiophene, [1]benzothieno[3,2-b]anthra[2,3-b]thiophene, and naphtho[3,2-b]thieno[3,2-b]anthra[2,3-b]thiophene, a selenium-containing derivative, [1]benzothieno[3,2-b][1]benzoselenophene. It also allows us to access largely π-extended derivatives with two BTBT substructures, e.g., bis[1]benzothieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene and bis[1]benzothieno[2,3-d:2',3'-d']naphtho[2,3-b:6,7-b']dithiophene (BBTNDT). It should be emphasized that these new BTBT derivatives are otherwise difficult to be synthesized. In addition, since various substrates and reagents, o-ethynyl-thioanisoles and arylthiols, respectively, can be combined, the method can be regarded as a versatile tool for the development of thienoacene-based organic semiconductors in this class. Among the newly synthesized materials, highly π-extended BBTNDT afforded very high mobility (>5 cm(2) V(-1) s(-1)) in its vapor-deposited organic field-effect transistors (OFETs), which is among the highest for unsubstituted acene- or thienoacenes-based organic semiconductors. In fact, the structural analyses of BBTNDT both in the single crystal and thin-film state indicated that an interactive two-dimensional molecular array is realized in the solid state, which rationalize the higher carrier mobility in the BBTNDT-based OFETs.

Synthesis, characterization, and transistor and solar cell applications of a naphthobisthiadiazole-based semiconducting polymer.

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.