Hopping mechanism

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... 

Strictly speaking, the process of J-diffusion described by the above equation is not diffusion at all. The very first collision restores equilibrium in the whole J-space. In this sense, strong collisions represent the hopping mechanism of J-relaxation, which is the only alternative to the diffusion mechanism [20, 24, 25, 36]. Since the term J-diffusion is so pervasive, we do not like to reject it. However, it should be understood in a wider sense and used to denote J-migration . Then it remains valid for both weak and strong collisions. Still, it should be remembered that there is a considerable difference between these limits. For strong collision we obtain from Eq. (1.30)... 

For strong collisions (y = 0), is still equal to //to, but qj does not exist and the diffusion mechanism of rotational relaxation is replaced by a hopping mechanism. 

Solid mixed ionic-electronic conductors (MIECs) exhibit both ionic and electronic (electron-hole) conductivity. Naturally, in any material there are in principle nonzero electronic and ionic conductivities (a i, a,). It is customary to limit the use of the term MIEC to those materials in which a, and 0, 1 do not differ by more than two orders of magnitude. It is also customary to use the term MIEC if a, and Ogi are not too low (o, a i 10 S/cm). Obviously, there are no strict rules. There are processes where the minority carriers play an important role despite the fact that 0,70 1 exceeds those limits and a, aj,i< 10 S/cm. In MIECs, ion transport normally occurs via interstitial sites or by hopping into a vacant site or a more complex combination based on interstitial and vacant sites, and electronic (electron/hole) conductivity occurs via delocalized states in the conduction/valence band or via localized states by a thermally assisted hopping mechanism. With respect to their properties, MIECs have found wide applications in solid oxide fuel cells, batteries, smart windows, selective membranes, sensors, catalysis, and so on. 

The localization of the HOMO is also important for another reason. Since it describes the distribution of a hole in a radical cation, it relates to the hindrance that a positive charge will encounter as it propagates along the chain. There is indeed experimental evidence (9) that the hole states of the polysilane chain are localized and that they move by a hopping mechanism. 

Keywords Charge injection Charge transfer Hopping mechanism Mismatches... 

The activated hopping mechanism that also involves adenines as charge carriers is validated by experiments in which we directly injected the positive charge into an adenine [19]. We have shown that photolysis of injection system 18 oxidizes the adenine base, maybe by through-bond charge transfer (19—>20). Therefore, incorporation of 18 into DNA duplexes makes it possible to inject the hole directly into an adenine base in the middle of an... 

Fig. 14 Reaction profile diagram for the hole transfer from a guanine radical cation (G +) to a distant GGG sequence via the activated hopping mechanism, which also involves adenines (A) as charge carriers...

A multistep hopping mechanism explains not only the long distance hole transfer through DNA, it can also rationalize the electron transfer through reduced DNA as T. Carell and M.D. Sevilla demonstrate in this volume. 

Giese B (2004) Hole Injection and Hole Transfer through DNA The Hopping Mechanism. 236 27-44... 

The results of Wegner and Riihe (1989) clearly show that electronic conduction in conducting polymers such as polythiophene and polypyrrole occurs via a hopping mechanism that is dominated by interchain rather than intrachain hopping. 

The conductance of the perylenebisimide (PBI) 15 was measured by the STM-BJ technique as 1 nS [73]. Note that the thiophenol handles are not conjugated to the central core, contributing to the small value. Electron transport was temperature-independent, indicating a tunneling mechanism. However, when a gate electrode reduced the core to its radical anion, the conductance became thermally activated, indicating that electron transport then follows a hopping mechanism into and out of the core. 

Tran E, Cohen A, Murray R, Rampi MA, Whitesides GM (2009) Redox site-mediated charge transport in a Hg-SAM//Ru(NH3)63+/2+//SAM-Hg junction with a dynamic interelectrode separation compatibility with redox cycling and electron hopping mechanisms. J Am Chem Soc 131 2141-2150... 

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