Thermally, Operationally, and Environmentally Stable Organic Thin-Film Transistors Based on Bis[1]benzothieno[2,3- d :2′,3′- d ′]naphtho[2,3- b :6,7- b ′]dithiophene Derivatives: Effective Synthesis, Electronic Structures, and Structure–Property Relationship

By developing an efficient synthetic route to the bis[1]benzothieno[2,3-d;2′,3′-d′]naphtho[2,3-b;6,7-b′]dithiophene (BBTNDT) framework, we have successfully synthesized new BBTNDT derivatives with phenyl (DPh-BBTNDT) or n-hexyl groups (C6-BBTNDT) at the 2 and 10 positions. Characterization of their vapor-deposited thin films revealed that, depending on the substituents introduced, their HOMO energy levels were slightly altered, and DPh-BBTNDT with the HOMO energy level of ca. 5.3 eV was supposed to be a stable organic semiconductor under ambient conditions. In fact, the DPh-BBTNDT-based OTFTs showed not only high mobility of up to 7.0 cm2 V–1 s–1 under ambient conditions but also excellent operational and thermal stabilities up to 300 °C, whereas the parent and the hexyl derivative were less stable against the thermal treatments at high temperatures. The high mobility observed for the DPh-BBTNDT-based OTFTs can be correlated to the interactive packing structure in the bulk single crystal and thin film state of DPh-BBTNDT, which corroborates the existence of the well-balanced two-dimensional electronic structure in the solid state. With these excellent device characteristics, it can be concluded that DPh-BBTNDT is a promising and practical vapor-processable organic semiconductor, which can afford thermally, operationally, and environmentally stable OTFTs as well as high mobility.