posters 5th Asia-Pacific NMR Symposium 2013

Solid state NMR investigations of nanostructured aniline oxidation products (#237)

Zoran Zujovic 1 , Michel Nieuwoudt 2 , Graham A Bowmaker 1 , Paul A Kilmartin 1
  1. Polymer Electronic Research Centre, School of Chemical Sciences, The University of Auckland, Auckland, New Zealand
  2. School of Chemical Sciences, The University of Auckland, Auckland, New Zealand

Compared with data obtained by techniques such as elemental analysis, FTIR and Uv-Vis spectroscopy,1 it has been observed that the imine nitrogens in nanostructured materials2-4 obtained by the oxidative polymerization of aniline are often significantly underestimated in 15N spectra. In order to critically analyze the applicability of solid state NMR to these materials, double labeled (15N, 13C) single (NH4OH, SD) and double (NH4OH+LiOH, DD) dedoped samples have been investigated. Various solid state NMR experiments were carried out: 1H-15N and 1H-13C CP (cross-polarization), 15N Direct Polarization (DP), and T1H(H) and T1ρH(C) relaxation experiments.5 Single dedoping with NH4OH does not remove all the positive charges. This is seen in the 15N spectrum, where CP MAS failed to reveal the imine nitrogens at a significant level. Subsequent dedoping with LiOH removed most of the positive charges (confirmed by electron paramagnetic resonance, EPR) which resulted in an increase in intensity of the imine peak in the 15N CP MAS spectra. A substantial shoulder in the range 100-150 ppm which originates mainly from positive charges is significantly reduced in the DD sample. At the same time the spectrum exhibits a more intense imine peak compared with that in the spectrum of the SD sample. DP experiments confirmed that the imine part of the structure has been more exposed to the effects of polarons. Also, these experiments confirmed that CP MAS experiments are more sensitive to the presence of polarons. This is checked with the T1ρH(C) experiment wherebecause of paramagnetic effects the SD sample has more protons with shorter TH (650 µs) which relax faster and cannot contribute to the transfer of polarization to 15N nuclei, especially to the imine nitrogens.

  1. Ciric-Marjanovic, G. In Nanostructured Conductive Polymers; Eftekhari, A., Ed.; Wiley: London, 2010, p 19.
  2. Zujovic, Z. D.; Laslau, C.; Bowmaker, G. A.; Kilmartin, P. A.; Webber, A. L.; Brown, S. P.; Travas-Sejdic, J. Macromolecules 2010, 43, 662.
  3. Zujovic, Z. D.; Zhang, L.; Bowmaker, G. A.; Kilmartin, P. A.; Travas-Sejdic, J. Macromolecules 2008, 41, 3125.
  4. Hopkins, A. R.; Lipeles, R. A.; Hwang, S.-J. Synth. Met. 2008, 158, 594.
  5. Zujovic, Z. D.; Wang, Y.; Bowmaker, G. A.; Kaner, R. B. Macromolecules 2011, 44, 2735.