Polaron-like hopping model

The electronic band structure of a neutral polyacetylene is characterized by an empty band gap, like in other intrinsic semiconductors. Defect sites (solitons, polarons, bipolarons) can be regarded as electronic states within the band gap. The conduction in low-doped poly acetylene is attributed mainly to the transport of solitons within and between chains, as described by the intersoliton-hopping model (IHM) . Polarons and bipolarons are important charge carriers at higher doping levels and with polymers other than polyacetylene. 

In a second possibility, the polaron-like hopping model, a structural distortion of the DNA stabilizes and delocalizes the radical cation over several bases. Migration of the charge occurs by thermal motions of the DNA and its environment when bases are added to or removed from the polaron [23]. 

The hole-resting-site and polaron-like hopping models can be distinguished by the distance and sequence behavior of radical cation migration. Analysis of the hole-resting-site model leads to the prediction that the efficiency of radical cation migration will drop ca. ten-fold for each A/T base pair that separates the G resting sites [33]. 

The phonon-assisted polaron-like hopping model is unique because it is built upon an understanding of the dynamical nature of DNA in solution. The fundamental assumption of this model is that the introduction of a base radical cation into DNA will be accompanied by a consequent structural change that lowers the energy for the system. 

Liu C-S, Schuster GB (2003) Base sequence effects in radical cation migration in duplex DNA support for the polaron-like hopping model. J Am Chem Soc 125 6098-6102 Llano J, Eriksson LA (2004) First principles electrochemical study of redox events in DNA bases and chemical repair in aqueous solution. Phys Chem Chem Phys 6 2426-2433... 

Detailed analysis [175,209] based on a diffusion model of polarons [187] implies that an average hopping distance of the polarons is comparable to the separation between the centers of the nearest-neighbor molecules [22]. This means that the hopping motion very likely takes place between the fiill molecules. 

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