Combined experimental and theoretical investigation of optical and structural properties of poly aniline derivatives

The structure of poly aniline (PANI), poly para phenylenediamine (PpPDA), and poly benzidine (PBz) is strongly dependent on the synthesis conditions and procedure. For this reason there is an ambiguity in the proposed structure of the polymers in the literature. A density functional theory (DFT) calculation were performed to establish the structure of synthesized PANI, PpPDA, and PBz. Different structures were considered for each polymer and fully optimized. Then their electrical and optical properties were calculated. Experimental band gaps of studied polymers were obtained using cyclic voltammetry technique and compared with those calculated by DFT. Optical band gap was also obtained from UV–visible spectrum of each polymer dissolved in DMSO solvent. Optical band gap value obtained for aniline is 1.90 eV which is close to the experimental band gap value reported for emeraldine form of poly aniline. Comparing calculated and experimental HOMO–LUMO gaps decline the formation of benzoid (PPDA-a) and phenenzine (PPDA-b) structures during synthesis of PpPDA. However, the exact structure of PpPDA was recognized through comparing experimental and simulated optical properties. Calculated electronic and optical band gaps of phenanzine structure of synthesized benzidine (PBz-c) are close to those of experimental ones and are confirmed by the spectroscopic results. Obtained results show that theoretical calculations play an important role in the detection of complex polymer structures.