Polaron Excitations in Fullerenes: Theory as π-Conjugated Systems
- 1 January 1993
- journal article
- Published by Oxford University Press (OUP) in Progress of Theoretical Physics Supplement
- Vol. 113, 229-238
- https://doi.org/10.1143/ptps.113.229
Abstract
We review the recent theoretical treatment of fullerenes as π-conjugated systems. Polaronic properties due to the Jahn-Teller type effects are mainly discussed. (1) A Su-Schrieffer-Heeger type electron-phonon model is is applied to fullerenes: C60 and C70, and is solved within the adiabatic approximation applied to the phonons. When the system (C60 or C70) is doped with one or two electrons (or holes), the additional charges accumulate at twenty carbons almost along an equatorial line of the molecule. The dimerization becomes the weakest along the same line. Two energy levels, the occupied state and the empty state, intrude largely in the gap. The intrusion is larger in C70 than in C60. These are “polarons” in doped fullerenes. It is also found that C60 and C70 are related mutually with respect to electronical structures as well as lattice geometries. (2) We apply the model to the fullerene epoxide C60O. It has the polaron-type lattice distortion around the oxygen, and also shows the energy level intrusion in the gap. (3) Optical properties of C60 are calculated and discussed. In the absorption of the doped molecule, a new peak structure is present owing to the polaronic distortion. In the luminescence of the neutral C60, the spacing between Hg(8)-phonon side-band peaks and the relative intensities agree well with experiments. In the dispersion of the third harmonic generation, the magnitudes of ∣χ(3)∣ agree with those of experiments at the resonance of the lowest allowed transition as well as the region away from the resonance.Keywords
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