AN ESR STUDY ON POLYANILINE IN NONAQUEOUS ELECTROLYTE

ESR measurements were performed for polyaniline (PANI) at various doping levels electrochemically controlled in aprotic conditions, LiBF4/PC-DME and LiAsF6/PC-DME. Spin density and linewidth in the ESR spectrum of LiBF4-doped PANI (PANI/BF4-) change dramatically at c. 3.2 V versus Li/Li+ indicating the formation of bipolarons. On the contrary, the variation of the ESR spectrum of LiAsF6-doped PANI (PANI/AsF6-) in the same potential range is less clear. This corresponds to the fact that the change in spectrum and electrical conductivity of PANI/AsF6- is much slower up to highly positive potentials, which is explained in terms of high stability of the polaronic state. Effects of O2 and H2O on the ESR signal of PANI/BF4- are significant; linewidth of the signal changes reversibly by reactng with O2 and H2O without change in conductivity, suggesting a facile relaxation of the polaronic spins by interacting with paramagnetic spins of O2.