Phonon-assisted hopping

Henderson P T, Jones D, Hampikian G, Kan Y Z and Schuster G B 1999 Long-distance charge transport in dupiex DNA the phonon-assisted poiaron-iike hopping mechanism Proc. Natl Acad. Sc/., USA 96 8353-8... 

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. 

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... 

The soliton conductivity model for rrans-(CH) was put forward by Kivelson [115]. It was shown that at low temperature phonon assisted electron hopping between soliton-bound states may be the dominant conduction process in a lightly doped one - dimensional Peierls system such as polyacetylene. The presence of disorder, as represented by a spatially random distribution of charged dopant molecules causes the hopping conduction pathway to be essentially three dimensional. At the photoexitation stage, mainly neutral solitons have to be formed. These solitons maintain the soliton bands. The transport processes have to be hopping ones with a highly expressed dispersive... 

An X-ray photoelectron spectroscopic study of Ni(DPG)2I showed no evidence of trapped valence or any appreciable change in the charge on the metal upon oxidation.97 The site of partial oxidation and hence the electron transport mechanism is still unclear but one explanation of the relatively low conductivity is that the conduction pathway is metal centred and that the M—M distances are too long for effective orbital overlap. Electron transport could be via a phonon-assisted hopping mechanism or, in the Epstein—Conwell description, involve weakly localized electronic states, a band gap (2A) and an activated carrier concentration.101... 

A small [Ni(CN)4]2 impurity concentration selectively quenches the Elc polarized emission. The temperature behavior of the quenching properties is explained by a phonon-assisted hopping from localized states of the chain to the [Ni(CN)4]2-quencher90-92. ... 

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

The diffusion coefficient is Da = (1 /xa)R2, where l/xa is the phonon-assisted fracton-hopping time and R is the mean hopping distance for fracton modes with frequency near CD,. The rate of phonon-assisted fracton hopping is calculated with Eqs. (34) and (35) specifically for the cases where one fracton decays into another fracton and a phonon, as well as for the reverse process. 

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