Charge hopping

3 Concepts of Photoinduced Electron and Energy Transfer Processes 

Charge injection from the donor into the bridge occurring with k, . 

Hopping among (ideally) isoenergetic charge-transfer states of adjacent bridge 

Assuming, that charge hopping involving different bridge units is a diffusive process a simple treatment leads to the overall rate constant [33] 

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Scheme 5 Charge injection into adenine (A), and efficiency of charge hopping between adenines...

In practice, the defect structure of the materials LiJCo, M)02 and Lix(Ni, M)02 under oxidizing conditions found at cathodes, is complex. For example, oxidation of Fe3+ substituted lithium nickelate, LL(Ni, Fe)02, under cathodic conditions leads to the formation of Fe4+ and Ni4+. Conductivity can then take place by means of rapid charge hopping between Fe3+, Ni3+, Fe4+, and Ni4+, giving average charges of Fe3+S and Ni3+S. These solids are the subject of ongoing research. 

Once the electrons and holes have been injected, they migrate into ETL and HTL to form excited states referred to as polarons by physicists or radical ions by chemists. These polarons or radical ions move, by means of a so-called charge-hopping mechanism, through the electron and hole transport materials (ETMs and HTMs), which typically possess good charge mobility properties, and eventually into the EML. 

Amino acid residue models such as a tyrosine residue model (p-cresol) lengthen remarkably the charge hopping distance, a phenomenon which can solve i he problem in the electrocatalysis mentioned in the above item 5) and enhance remarkably the catalytic activity. 

Regarding item 6) above on electrocatalysis, the coexistence of tyrosine residue model, p-cresol (p-Crej, enhanced remarkably the catalytic activity of Ru-red confined in a Nafion membrane coated on an electrode (Fig. 19.3).20) This was attributed to the nearly twofold lengthening of the charge hopping distance by p-cresol from 1.28 nm to 2.25nm). 

If, on the other hand, the LUMO of the bridge is energetically accessible from the donor orbitals, electron injection from the donor is promoted and the bridge acts as a real intermediate in transferring the electron to the acceptor. This situation is then termed as charge hopping. 

Fig. 3.6 Charge hopping in a donor-bridge-acceptor system involving a modular bridge...

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