Charge Carrier Transport and Optical Properties of Poly[N-methyl(aniline)

Abstract

Simultaneous electron spin resonance (ESR) and UV−vis−NIR measurements have been carried out during oxidation of a poly[N-methyl(aniline)] (PNMA) film, which was prepared electrochemically in aqueous solutions containing 1 M trifluoroacetic acid. In situ conductance measurements were also performed during the electrochemical doping of PNMA. The combination of the different experimental techniques allows a simultaneous elucidation of optical and electrochemical properties of the conducting polymer film. Although there are a lot of predictions and discussions on the free charge carriers of poly(aniline) (PANI) and its derivatives, there is no direct evidence of the correlation between polarons and conductance for PANI and its derivatives during doping. This article provides the correlation between the spin and spinless species and the conductance of PNMA during the electrochemical doping in acidic aqueous solutions. PNMA differs from other conjugated polymers (e.g. polypyrrole) in that the results from ESR and in situ conductance are consistent. At higher doping (oxidation) levels, the conductance decreases with the decrease in the ESR signal, indicating that there is no spinless bipolaronic conducting state in PNMA. Polaron pairs are supposed to be responsible for these decreases.