Fluorine Reagent Supercharges Thiophene For Organic Electronics

Thiophene-based materials have emerged as important organic semiconductors for making electronic devices such as solar cells, field-effect transistors, and light-emitting diodes. In the quest to better regulate the electronic properties and improve the stability of the oligomeric thiophene chains, chemists have set out to partially or completely oxidize thiophene’s sulfur. Adding oxygen to sulfur is quite the trick, however, because few reagents are powerful enough for the job. Shlomo Rozen of Tel Aviv University, in Israel, has come up with one such approach as part of his group’s effort to develop “offspring” reagents of elemental fluorine. Fluorine is one of the strongest oxidizing reagents known, but its extreme reactivity is hard to control. To tame fluorine for oxygen-transfer reactions, Rozen developed HOF•CH₃CN, which is made by bubbling nitrogen-diluted F₂ through aqueous acetonitrile. Rozen’s group used HOF•CH₃CN to prepare oligothiophenes containing both oxygenated and nonoxygenated thiophene units. The researchers transferred oxygen atoms to dibromothiophenes (shown) and then cross-coupled them with unoxidized thiophenes. The resulting partially oxidized oligothiophenes can be fully oxidized by further treatment with HOF•CH₃CN (Chem. Eur. J., DOI: 10.1002/chem.201203936). The new oligothiophenes have narrower electronic band gaps and higher oxidation and reduction potentials compared with other oligothiophenes, Rozen said, which should help tune the electronic properties of organic semiconductors.