Charged States in Conducting Polymers as studied by in situ ESR UV/Vis NIR Spectroelectrochemistry

COPE Seminar Series

A review is given on recent studies of charged states in conducting polymers using ESR/UV/Vis NIR spectroelectrochemistry. It is demonstrated that this method is a prerequisite to study the charged states formed at oligomers and polymers [1],[2]. This in situ ESR/UV/Vis NIR spectroelectrochemical method is applied to aniline and its reactions of dimers and other oligomers. [3], to α,α´-bis(diphenylamino)-capped oligothiophenes [4] and to the reactivity of thiophene oligomers with changing substitution pattern [5]. The chain length dependence of dimerisation reactions and the stabilisa¬tion of charged states are studied for fluorantheno-pyracylenes where the equilibrium of their σ-dimers in solution and the stabilisation of the radical ions for longer oligomers are followed [6]. The growing of the chain length makes any dimerisation negligible in the temperature range under study.

Furthermore, by the extension of oligomeric structures conducting polymers in their spectroelectrochemical behaviour are one of the main subjects as a detailed analysis of both the ESR and the absorption spectra makes a differentiation of the charged states in polymers available [7]. Like for the analysis of polyaniline [8] it is demonstrated for polypyrrole how the formation and equilibria of both polarons and bipolarons can be described experimentally [9]. For polythiophene it is shown that the copolymerisation of different 3-substituted monomers changes the charged state of the copolymer markedly by stabilizing other species [10]. Thus a change from bipolarons to polaron pairs can be followed which is preferably detected by the described in situ triple spectroelectrochemical technique as demonstrated for polyazulene [11]. Furthermore this spectroelectrochemical technique opens the way to study of interactions of paramagnetic metal ions with spin states at organic ligands. This is demonstrated for polysalenes [12]. An outlook is given on future developments of the method.

Literature:

[1] L. Dunsch, A. Petr, Ber. Bunsenges. Phys. Chem. 1993, 97, 436; A. Petr, L. Dunsch , A. Neudeck, J. Electroanal. Chem. 1996, 412, 153
[2] P. Rapta and L. Dunsch, J. Electroanal. Chem. 2001, 506, 22
[3] A. Petr und L. Dunsch, J. Electroanal. Chem. 1996, 419, 55
[4] D. Rohde, L. Dunsch, A. Tabet, H. Hartmann, J. Fabian, J. Phys. Chem. B 2006, 110, 8223
[5] P. Rapta, O. Zeika, D. Rohde, H. Hartmann, L. Dunsch, ChemPhysChem 2006 7, 863; P. Rapta, D. Rohde, H. Hartmann, L. Dunsch, Tetrahedron Lett. 2006, 47, 7587
[6] L. Dunsch, P. Rapta, N. Schulte, A. D. Schlüter, Angew. Chem. 2002, 114, 2187
[7] A. Neudeck, A. Petr, und L. Dunsch, J. Phys. Chem. B 1999, 103, 912
[8] A. Neudeck, A. Petr, L. Dunsch, Synth. Met. 1999, 107, 143
[9] P. Rapta, A. Neudeck, A. Petr und L. Dunsch, J. Chem. Soc., Faraday Trans. 1998, 94, 3625
[10] J. Tarábek, P. Rapta, E. Jähne, D. Ferse, H.-J. Adler, M. Maumy and L. Dunsch, Electrochim. Acta 2005, 50, 1643
[11] A. Österholm, A. Petr, C. Kvarnström, A. Ivaska and L. Dunsch, J. Phys. Chem. B 2008, 112, 14149-14157
[12] J. Tarábek, P. Rapta, M. Kalbáč and L. Dunsch, Anal. Chem. 2004, 76, 5918

For more information contact Prof. Art Janata (404-894-4828).