Theoretical studies of physicochemical properties of aniline oligomers: analysis of counterion influence

We present some semiempirical quantum chemistry calculations, geometric structures, charge distribution, gap energy, and enthalpy of formation (H _f ) for aniline oligomers in the different oxidation states using the AM1 method. A linear relationship between calculated optical transition values and the experimental reported ones was found. The effect of the interaction between the chloride counterion and these molecules was analyzed and indicates a decrease both in H _f of the aniline oligomers in the radical cation state and in E(SOMO-LUMO). The withdrawal of one electron from the reduced aniline tetramer to form a radical cation in the presence of chloride (Cl^–) yields to the radical cation band, similar to the polaron band in the polyaniline case. Contrary to the expected results, our calculations show that Cl^– was able to transfer about 80% of its charge to the oligomers.