Neutral soliton formation and disorder in pernigraniline base

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Abstract
A new long-lived photoinduced absorption near 1.8 eV is reported for pernigraniline base, the Peierls degenerate ground state form of polyaniline. The absence of associated infrared active vibrational modes and the results of light-induced ESR experiments identify the photoexcited defects as disorder confined neutral soliton pairs with a temperature dependent antiferromagnetic exchange interaction. The optical transitions across the Peierls gap are suggested to be broadened by static and quantum fluctuations. The results are in very good agreement with recent predictions of Su and Epstein and Mckenzie and Wilkins.