Phonon-assisted polaron hopping

The anthraquinone derivatives may oxidize DNA when they are randomly bound to the DNA or attached to it covalently at particular locations. Radical cations introduced in the DNA by the excited anthraquinone cause damage both within the binding pocket and locally separated from the anthraquinone binding site. A mechanism has been proposed for long-range charge transport in DNA which depends on the spontaneous distortion of the DNA structure and which is called phonon-assisted polaron hopping [243-245]. 

Hopping Models Hole-Resting-Site and Phonon-Assisted Polaron Transport... 

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. 

Henderson PT, Jones D, Hampikian G, Kan Y, Schuster GB (1999) Long-distance charge transport in duplex DNA the phonon-assisted polaron-like hopping mechanism. Proc Natl Acad Sci USA... 

Scheme 3. Phonon-assisted polaron-like hole hopping. Reprinted with permission from ref. 161c. Copyright 1999 American Chemical Society.

In discussing low temperature-dependent mobility, we should mention charge transport by polarons, an intermolecular phonon-assisted hopping process 24>25>. Polarons (charge carriers trapped in their polarization field) arise from a strong electron-phonon interaction where there is a weak overlap of wave functions of... 

Shortly after Holstein published his work on polarons in molecular crystals. Miller and Abrahams introduced a very useful description of hopping conduction in terms of a phonon-assisted electron tunneling process [38]. Miller-Abrahams theory does not include the polaronic effect. Nevertheless it... 

Moreover, Eq. (5.1) assumes that conduction in each energy shell can be treated separately. This is a doubtful procedure when charge motion involves exchange of energy with the lattice as in the case in phonon assisted hopping and polaron conduction. 

Semiconductivity in oxide glasses involves polarons. An electron in a localized state distorts its surroundings to some extent, and this combination of the electron plus its distortion is called a polaron. As the electron moves, the distortion moves with it through the lattice. In oxide glasses the polarons are very localized, because of substantial electrostatic interactions between the electrons and the lattice. Conduction is assisted by electron-phonon coupling, ie, the lattice vibrations help transfer the charge carriers from one site to another. The polarons are said to "hop" between sites. 

In Ae small polaron picture, on the other hand, the electron-phonon interaction, compounded by the localization effects introduced by the disorder, leads to the formation of small polarons. The polaron binding energy is then the largest energy in the problem, and charge transport involves multiphonon-assisted hopping of small polarons (Emin, 1984). 

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