XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Conducting Polyaniline - Polaronic vs. Bipolaronic Forms
Jasmina Petrova, Julia Romanova, Galia Madjarova, Anela Ivanova, Alia Tadjer
University of Sofia, Faculty of Chemistry, 1 James Bourchier Ave., 1164 Sofia, Bulgaria
Polyaniline (PANI) exists in several oxidation states, which allow a wide range of electric, magnetic and optical characteristics. Major attention receive the investigations searching for correlation between molecular geometry and electronic structure of the ground and excited states.
Our study is focused on the so-called emeraldine salt (ES) – the doped semioxidized form of PANI. Experimental data [1, 2] indicate that ES can exist both in spin-silent and in spin-active states. The electronic structure of ES is rationalized in terms of its bipolaron (diamagnetic) and polaron (paramagnetic) forms [3]. For describing these forms we constructed a series of fully HCl-protonated oligomers (octamer to hexadecamer). The forms differ also in the position of the counterions (Cl-). All calculations include implicit aqueous environment.
The molecular features affected most prominently by the protonation, namely, structure, energetics, electron and spin density partitioning, are analyzed. The results show unequivocally that the studied molecular characteristics are essentially size-independent. The bipolarons and polarons are dissimilar both in geometry and in electron density distribution. Particularly, the negative ions are responsible for the localization of spin density at the nitrogens they screen, resulting in dissimilar spin lattices in the two fully polaronic forms [4].
Electronic spectra in aqueous medium are calculated. The simulated spectra are compared to the available experimental data.

[1] V. Prigodin, A. Samukhin, A. Epstein Synth. Metals 2004, 141, 155.
[2] P. K. Kahol, A. Raghunathan, B. J. McCormick Synth. Metals 2004, 140, 261.
[3] S. Stafström, J. L. Brédas, A. J. Epstein, H. S. Woo, D. B. Tanner, W. S. Huang, A. G. MacDiarmid Phys. Rev. Lett. 1987, 59, 1464.
[4] J. N. Petrova, J. R. Romanova, G. K. Madjarova, A. N. Ivanova, A. V. Tadjer. J. Phys. Chem. B 2011, 115, 3765.


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