Bandgap engineering through controlled oxidation of polythiophenes.

The use of Rozen's reagent (HOFCH3CN) to convert polythiophenes to polymers containing thiophene-1,1-dioxide (TDO) is described. The oxidation of polythiophenes can be controlled with this potent, yet orthogonal reagent under mild conditions. The oxidation of poly(3-alkylthiophenes) proceeds at room temperature in a matter of minutes, introducing up to 60% TDO moieties in the polymer backbone. The resulting polymers have a markedly low-lying lowest unoccupied molecular orbital (LUMO), consequently exhibiting a small bandgap. This approach demonstrates that modulating the backbone electronic structure of well-defined polymers, rather than varying the monomers, is an efficient means of tuning the electronic properties of conjugated polymers.