Development of electron-transporting conjugated oligomers based on fluorination reactions and their application to organic field-effect transistors

Abstract

Organic field-effect transistors (OFETs) based on π-conjugated systems have been a great interest in recent years as they are indispensable components in organic electronics. In this context, a novel synthetic route to electronegative units: hexafluorocyclopenta[c]thiophene, 4,4-difluoro-4H- cyclopenta[2,1-b:3,4-b']dithiophene, 6,6,12,12-tetrafluoroindeno[3,2-b]fluorene, difluorodioxocyclopenta[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 electronegative oligothiophenes exhibited n-type semiconducting behavior with high field-effect electron mobilities.