Packing in Amorphous Regions of Hydrofluoric-Acid-Doped Polyaniline Powder by 15N−19F REDOR NMR

Anhydrous 15 N-labeled polyaniline powders have been examined by 13 C, 15 N, and 19 F solid-state NMR as a function of HF doping. Chemical shifts in the 19 F NMR spectra of doped polyaniline reveal three distinct types of charged environments. Carbon, nitrogen, and fluorine spin counts show that only about one-third of all the chains in fully HF-doped polyaniline are detected. This observation is consistent with the assumption that the entire crystalline region, and amorphous regions within 50 Å of the crystalline border, is rendered unobservable by paramagnetic delocalized electrons in the crystalline region. Rotational-echo double-resonance 15 N NMR (with 19 F dephasing) indicates that in the observable amorphous regions the polyaniline chains are tightly packed with an in-plane interchain separation of 10 Å and that fully charged main-chain nitrogens have, on average, one nearest-neighbor fluorine 4 Å away and three next-nearest-neighbor fluorines with an average 15 N− 19 F distance of just over 5 Å.