Lewis Acid Doped Polyaniline. Part II: Spectroscopic Studies of Emeraldine Base and Emeraldine Hydrochloride Complexation with FeCl₃

Abstract

It is demonstrated that Lewis acid doping of polyaniline in the oxidation state of emeraldine can be conveniently monitored by 57Fe Mössbauer spectroscopy if FeCl3 is used as the dopant. The spectrum of doped polyaniline consists of two doublets with distinctly different Mössbauer parameters which can be unequivocally ascribed to two types of complexing sites (amine and imine nitrogens). From the temperature dependence of the isomer shift and the recoil free absorption, we have calculated Mössbauer lattice temperature ϑm‘ as probed by both complexing sites, which were 83 K for the amine and 126 K for the imine sites. These low values of ϑm‘ imply significant mobility of the dopant at temperatures close to room temperature, which is typical of small molecules inserted into polymer matrices. FeCl3-doped polyaniline is soluble in nitromethane, and acetonitrile and films cast from these solvents show conductivity of 0.2 S/cm. FeCl3-doped polyaniline is also a strong near-infrared absorber.