Packing in amorphous regions of hydrofluoric-acid-doped polyaniline powder by N-15-F-19 REDOR NMR

Anhydrous N-15-labeled polyaniline powders have been examined by C-13, N-15, and F-19 solid-state NMR as a function of HF doping. Chemical shifts in the F-19 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 Angstrom of the crystalline border, is rendered unobservable by paramagnetic delocalized electrons in the crystalline region. Rotational-echo double-resonance N-15 NMR (with F-19 dephasing) indicates that in the observable amorphous regions the polyaniline chains are tightly packed with an in-plane interchain separation of 10 Angstrom and that fully charged main-chain nitrogens have, on average, one nearest-neighbor fluorine 4 Angstrom away and three next-nearest-neighbor fluorines with an average N-15-F-19 distance of just over 5 Angstrom.