Synthesis, solid-state, and charge-transport properties of conjugated polythiophene-S,S-dioxides

An alkylated semiconducting polymer comprising alternating bithiophene-[all]-S,S-dioxide and aromatic monothiophene units in the polymer backbone was synthesized with the intent of modifying the energy gap and lowest unoccupied molecular orbital for use as a stable n-type semiconductor. Films spun from this semiconducting polymer were characterized utilizing X-ray scattering, near edge X-ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, and thin-film field effect transistors to determine how oxidation of the thiophene ring systems impacts the structural and electronic properties of the polymer. The thiophene-S,S-dioxide polymers have lower optical and electrical band gaps than corresponding thiophene polymers. X-ray scattering results indicate that the polymers are well ordered with the π-π stacking distances increased by 0.4 Å relative to analogous thiophene polymers. The electrical stability of these polymers is poor in transistors with a drop in the field effect mobility by approximately one order of magnitude upon addition of just 5% of the thiophene-S,S-dioxide unit in a copolymer with thiophene.