Chemically robust conjugated polymer platform for thin-film sensors

To examine chemically robust thin conjugated polymer films for use as optical and conductometric sensors, we graft polythiophene and two alkyl-based derivatives to optically transparent substrates. Though structurally contrasting to other film deposition techniques, grafted polythiophene films preserve their documented absorption, luminescence and electrical properties. Photoluminescence intensities are sensitive to trace amounts of iron and iodine in solution with reasonable Stern–Volmer constants and downward sloping Stern–Volmer plots characteristic to thin-film sensors. Rising conductivities indicate chemical doping is responsible for photoluminescence quenching. We vary reaction times and solvents to optimize desired properties and produce robust polythiophene films, verified by X-ray photoemission spectroscopy, that are uniform across the substrate with thicknesses ranging from 20 to 200 nm and controllable levels of surface roughness. Due to steric effects, polythiophene and poly(3-methylthiophene) films exhibit the highest conductivities while poly(3-hexylthiophene) films exhibit greater photoluminescence efficiencies. These platforms show promise as thin films for in-solution sensing.