Effects of oxidation state on the measured g value in polyaniline

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Abstract
Samples of polyaniline (PANi) have been prepared electrochemically and oxidised to various oxidation states. These 'as-prepared' samples were investigated using ESR spectroscopy. It was found that both linewidth and g value are dependent on oxidation level. In the reduced form of PANi the spin species are ascribed to neutral pi -radical defects, indicative of spins trapped at chemical defect sites along the polymer chain. On oxidation to the 'emeraldine' form of PANi the g value is seen to shift. Such shifts in g imply that the spins which are injected during electrochemical oxidation reside on the nitrogen sites along the PANi chain. These spin species are different from those which are seen in the reduced form. Further oxidation of the emeraldine form cause a loss of nitrogen site spins, although at the highest oxidation levels studied (0.8 V against a saturated calomel reference (SCE)) such spins are seen to return. This could either be due to further spin injection on nitrogen sites during oxidation or the creation of spins at chain degradation sites, which are associated with nitrogen atoms, i.e. due to chain cleavage at ring-nitrogen bonds during hydrolysis.