Conformational effects on optical charge transfer in the emeraldine base form of polyaniline from electroabsorption measurements and semiempirical calculations

and the trace of the change in polarizability (Tr Da ↔ ) is 200 Å. Similar values were obtained for the corresponding electronic transition of a five-ring oligomer of EB that is symmetrically terminated with phenyl rings, also in a PMMA matrix. In order to understand the origin of the substantial value of uDmW u measured for these nominally symmetric species, a series of calculations were performed in which the geometries of model oligomers were varied in a systematic fashion and resulting effects on the values of uDmW u were determined. Numerous low-energy conformers were identified by this method having substantial values of uDmW u, suggesting that the large uDmW u measured experimentally results from conformational heterogeneity. Our findings suggest that Stark spectroscopy is a useful probe of structural disorder in this technologically important polymer in the solid state. © 2001 American Institute of Physics. @DOI: 10.1063/1.1388559#