In SituElectron Spin Resonance Measurements of Electrochemically Dopedn-Type Polythiophene

The electrochemical, optical and magnetic properties in polythiophene during electrochemical n -type doping have been investigated by cyclic voltammetry, optical absorption spectrum and ESR measurements. The spin susceptibility increases by about one order of magnitude from 1.7×10 -7 to 5.1×10 -6 emu/mol up to dopant concentration of about 8 mol%. With further increasing dopant concentration up to about 20 mol%, the spin susceptibility decreases, followed by the slight increase of spin susceptibility again. The ESR linewidth decreases by doping from about 7.0 G to about 2.0 G and then again increases slightly with increasing dopant concentration. The g value of 2.0039 at the reduced state shifts upon doping to smaller value of 2.0027 which corresponds to the nearly free electron g value. The evolution of ESR spectrum in electrochemically doped n -type polythiophene is essentially the same behaviour as that of p -type doping. These results were discussed in terms of polaron and bi-polaron models.