Vibrational spectroscopic study of iodine-doped poly(isothianaphthene)

Far-infrared, mid-infrared, and Raman spectroscopy were used to characterize iodine-doped poly(isothianaphthene) (PITN) films and powders. The far-infrared and mid-infrared results show changes from absorption mode to reflective mode as the doping level increases, consistent with the iodine-doped PITN becoming more metallic and more conductive at higher doping levels. The far-IR and Raman (514.5-nm laser excitation) results show that 13 is dominant in iodine-doped PITN. The Raman spectral changes observed using 1064-nm excitation are different from those measured using 514.5-nm excitation. The spectra recorded with 514.5-nm excitation show features due to the undoped parts of the polymer, and these indicate that the effective conjugated chain length decreases with increased doping. The Raman spectra obtained by using 1064-nm excitation show features due to polaron and bipolaron states in the doped polymer.