Electron Delocalization in One-Electron Oxidized Aniline Oligomers, Paradigms for Polyaniline. A Study by Paramagnetic Resonance in Fluid Solution

How far is an electron delocalized in organic conducting polymers? Insights into this aspect are presented by analyzing the spin distribution in radical cations of seven differently substituted aniline oligomers. The paramagnetic stages of dimers, tetramers, and hexamers were studied by EPR/ENDOR spectroscopy in fluid solution and DFT calculations. The EPR isotropic hyperfine coupling constants are compared with calculated counterparts for two model systems. In all derivatives, the main portion of the spin and the charge are confined to the central phenylenediamine moiety; i.e., only a very limited electron delocalization into the adjacent phenyl substituents exists. These experimentally established results point to a substantial contribution of interchain hole transfer in conducting polyanilines.