Absorption and refractive index changes of poly (3-octylthiophene) under NO2 gas exposure

Optical characterization of spin coated regioregular head-to-tail head-to-tail poly (3-octylthiophene) (P3OT) thin films under 5, 10 and 3000 ppm of NO2 with N2 balance is reported. Undoped and doped states mechanisms under gas flux and gas pressure are discussed based on changes in optical absorption and refractive index. Two energy levels at 0.65 and 1.60 eV as the polarons and bipolarons under a 3000 ppm NO2 doped state were observed and the origin discussed. A doped saturation and partial recovery levels were analyzed. A refractive index change from 1.6951 to 1.5346 at 633 nm for undoped and doped samples was obtained. Potential applications for optical sensors based on absorption and refractive index change are discussed.