Ultra-fast electron transfer

The relevance of adiabatic electron transfer to the primary charge separation reaction has been the subject of considerable discussion, mainly due to the observation of undamped low-frequency nuclear motions associated with the P state (see Section 5.5). More recently, sub-picosecond time-scale electron transfer has been observed at cryogenic temperatures, driven either by the P state in certain mutant reaction centres (see Section 5.6) or by the monomeric BChls in both wild-type and mutant reaction centres (see Section 5.7). These observations have led to the proposal that such ultra-fast electron transfer reactions require strong electronic coupling between the co-factors and occur on a time-scale in which vibrational relaxation is not complete, which would place these reactions in the adiabatic regime. Finally, as discussed in Section 2.2, evidence has been obtained that electron transfer from QpJ to Qg is limited by nuclear rearrangement, rather than by the driving force for the reaction. 

Solvent Effect on Ultra-fast Electron Transfer in Mixed-Valence Biferrocene Monocation. 

The long effective pathlength and high surface area afforded by these colloidal semiconductor materials allow spectroscopic characterization of interfacial electron transfer in molecular detail that was not previously possible. It is likely that within the next decade photoinduced interfacial electron transfer will be understood in the same detail now found only in homogeneous fluid solution. In many cases the sensitization mechanisms and theory developed for planar electrodes" are not applicable to the sensitized nanocrystalline films. Therefore, new models are necessary to describe the fascinating optical and electronic behavior of these materials. One such behavior is the recent identification of ultra-fast hot injection from molecular excited states. Furthermore, with these sensitized electrodes it is possible to probe ultra-fast processes using simple steady-state photocurrent action spectrum. 

The group also found that electron injection onto the Ti02 conduction band could occur on a fast or ultra fast time scale. The kinetics of electron transfer in the dye-sensitized nanocrystalline Ti02 solar cell is summarized by following equations. Recombination reaction takes place in a hundredth of a nanosecond. Regeneration of the dye cation by the iodide system is faster than the recombination reaction. 

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