Electron-Transporting Oligothiophenes Containing Dicyanomethylene-Substituted Cyclopenta[b]thiophene: Chemical Tuning for Air Stability in OFETs

We have synthesized new electron-transporting oligothiophenes containing dicyanomethylene-substituted cyclopenta[b]thiophene as an active material for the fabrication of solution-processable n-type organic field-effect transistors (OFETs). The influence of the number of dicyanomethylene groups as well as the position of hexyl groups was investigated in detail by performing photophysical and electrochemical measurements. Results revealed that the optical energy gaps and the lowest unoccupied molecular orbital (LUMO) energy levels can be controlled by changing the number of dicyanomethylene groups. In contrast, the position of hexyl groups has little influence on molecular electronic properties. X-ray diffraction and atomic force microscopy measurements revealed that spin-coated thin films of the new compounds had a crystalline structure. OFETs based on these compounds were evaluated in vacuum and air-exposed conditions, and the electron mobility of up to 0.016 cm(2) V-1 s(-1) was achieved. Furthermore, we demonstrated that the air stability of the OFETs depends on the LUMO energy level of the compounds.