Synthesis, solubility, and field-effect mobility of elongated and oxa-substituted α,ω-dialkyl thiophene oligomers.: Extension of "polar intermediate" synthetic strategy and solution deposition on transistor substrates

Our investigation of thiophene oligomers as organic thin film transistor (TFT) semiconductors is extended to the hexamer with dodecyl and octadecyl end-substituents and with side chains containing ethereal oxygens. Two thiophene tetramers are studied as well. All of the new compounds are prepared via polar, monosubstituted half-oligomers that are purified, further elaborated, and dimerized. Properties are reported in comparison with the previously reported dihexyl compounds. All of the compounds form ordered films with orientation perpendicular to the substrate. For the hexamers, the longer chains decrease the TFT mobility of evaporated films, while the oxygens have very little electronic effect, even though the oxygen does cause an approximate doubling of the solubility. A tetramer with an ether side chain has a mobility below 0.01 cm(2)/Vs. Films were also cast from dilute solution and showed mobilities at or above 0.01, cm(2)/Vs in several cases. This casting process may be useful in devising all-liquid-phase fabrication protocols for organic-based electronic circuits.