Structure Property Relationships:  Asymmetric Oligofluorene−Thiophene Molecules for Organic TFTs

Fluorene−thiophene oligomers show great promise as the active material in p-type organic thin film transistors (TFTs) because of their good performance and good stability under ambient conditions. In this study, a series of fluorene−thiophene co-oligomers were asymmetrically substituted with an alkyl group to probe the effect chemical structure has on their thin film properties. The alkyl groups are n-hexyl, n-octyl, and n-dodecyl, respectively. These oligomers were characterized by elemental analysis, mass spectrometry, differential scanning calorimetry, and thermogravimetric analysis, whereas the thin films of these oligomers were characterized by X-ray diffraction, atomic force microscopy, and field-effect transistor measurements. We found that the performance of these asymmetric molecules is similar to their symmetric counterparts. Mobilities as high as 0.16 cm2 V-1 s-1 were found for the n-dodecyl-substituted oligomer.