Tuning the Semiconducting Properties of Sexithiophene by alpha,omega-Substitution-alpha,omega-Diperfluorohexylsexithiophene: The First n-Type Sexithiophene for Thin-Film Transistors We thank DARPA (N00421-98-1187) and the NSF-MRSEC program through the Northwestern Materials Research Center (DMR-9632472) for support of this research. H.S. thanks the Royal Society for a University Research Fellowship (URF).