Organic field-effect transistors (OFETs) based on ir-conjugated systems have been a great interest in recent years as they are indispensable components in organic electronics. In this con-text, a novel synthetic route to electronegative units: hexafluorocyclopenta [c] thiophene, 4, 4-diflu-oro-4H-cyclopenta [2, 1-b:3, 4-b'] dithiophene, 6, 6, 12, 12-tetrafluoroindeno [3, 2-b] fluorene, difluoro-dioxocyclopenta [c] thiophene, and difluorodioxocyclopenta [b] thiophene have been accomplished by the use of fluorination reactions as a key step. The oligomers containing these units also have been synthesized to elucidate the precise structure-property-FET characteristics relationships. The annelation of the electron-withdrawing groups effectively lowers the LUMO energy levels without disrupting the effective conjugation of the backbones, which was unambiguously clarified by spectroscopic and electrochemical measurements as well as X-ray analyses. These electroneg-ative oligothiophenes exhibited n-type semiconducting behavior with high field-effect electron mobilities.