Optical dispersion and electronic transition characterizations of spin coated polyaniline thin films

Optical properties of polyaniline, PANI thin films of different thicknesses ranged from 200 to 310 nm prepared by spin coating were characterized by using spectrophotometric measurements of transmittance and reflectance in the spectral range of 200-2500 nm. The optical constants namely refractive index (n) and the absorption index (k) were calculated by using a special computer program. The absorption spectra in the UV-vis region were analyzed in terms of both molecular orbital and band theories. The region shows two absorption bands, namely the Q-band and the Soret (B) band. Some of the important spectral parameters, namely the optical absorption coefficient (α), molar extinction coefficient (ɛmolar), oscillator strength (f) and electric dipole strength (q2) were evaluated. The analysis of the spectral behavior of the absorption coefficient α in the absorption region revealed two direct allowed transitions corresponding to the onset and the fundamental energy gaps. The refractive index n showed an anomalous dispersion in the absorption region as well as normal dispersion in the transparent region. The dispersion of the refractive index in PANI films was analyzed using the concept of the single oscillator. Within this concept the oscillator energy (E0), the dispersion energy (Ed), the high frequency and the dielectric constant (ɛ∞) as well as the lattice dielectric constant (ɛL) were evaluated. Discussion of the obtained results and their comparison with the previously published data were also given.