Theoretical study of the structure and electronic spectra of fully protonated emeraldine oligomers

摘要

Polyaniline (PANI) is one of the most studied conducting polymers. Obtained in its conducting form (known as '' emeraldine salt '') by chemical or electrochemical oxidation of aniline in aqueous acidic medium, this polymer manifests an array of attractive properties. Nevertheless, these properties still need to be described at the molecular level. Intense theoretical investigations during the past few years aim at explaining the chain organization, conductivity mechanism, and other structural and spectral characteristics. Most studies adopt simplified models in which hydration effect is underestimated., since all simulations are performed either in vacuum or in the presence of a limited number of water molecules. The present computational study sheds tight on the molecular organization of a number of model PANI hydrated clusters with different alignment and multiplicity, which can explain the experimentally recorded UV/VIS spectra. The influence of hydration and interaction with adjacent oligomers is estimated. Short-chain doubly protonated emeraldine oligomers are used as model systems. The calculations are performed at the semi-empirical (AM1) and/or molecular mechanics (AMBER96) level. Proper configurations of the clusters are selected using Monte Carlo simulations. Electron correlation (CIS) is accounted for upon evaluation of the absorption spectra of the clusters. The relative strength of the interchain coupling is estimated by simulation of PANI clusters consisting of two PANI tetramers in water. Comparison to experimental results is made. (c) 2006 Wiley Periodicals, Inc.