Direct evidence of a bipolaron charge carrier in conducting polyazines from carbon-13 and nitrogen-15 solid-state NMR spectroscopy: detection of a nitrenium cation by natural abundance 15N solid-state NMR spectroscopy

Natural abundance 13C and l5N solid-state NMR experiments were performed on undoped and doped samples of polyazine, (−N=C(R)-C(R)=N−)x. The topology of the polymer requires that doping-induced charge carriers must be either polarons (radical cations) or bipolarons (dications). Magnetic susceptibility measurements shows that the iodine-doped polymers are diamagnetic, so the charge carriers must be bipolarons. The specific bipolaron charge carrier in polyazines has been identified; the nitrogens bear the charge primarily in the form of a nitrenium cation. This is the first report of a nitrenium cation detected by 15N solid-state NMR spectroscopy. Independent of the substitution of the polyazine, R = H or CH3, the same charge carrier is present.