ESR of protonated “emeraldine”: Insulator to metal transition

Abstract The temperature dependence of the X-band electron spin resonance for the emeraldine oxidation state of polyaniline is investigated under different protonation levels ranging from the unprotonated insulating emeraldine base to the metallic emeraldine hydrochloride. For all the samples studied, the signal is composed of two lines, one Lorentzian and the other Gaussian and broader. The different temperature dependences of the intensity of the Lorentzian and Gaussian signals for each sample allows one to distinguish between localized and mobile spins. Moreover the study of the linewidth of the Lorentzian signal as a function of the temperature and of the protonation level leads to a discussion on the nature of the conduction mechanism in polyaniline.