Electronic coupling charge recombination

Fig. 5.18 Suppression of charge recombination in coupled Sn02/CdSe system. The photogenerated electrons in CdSe quickly migrate to the lower lying conduction band of SnOa. As a result, they escape recombination with photogenerated holes in CdSe and are collected in greater number at the back contact OTE producing a larger photocurrent. (Reproduced from [333])...

Since the values of i/ depend on several factors noted above, in the absence of additional data such as the temperature dependence of the electron transfer rate constants for i-2 it is difficult to analyze the apparent difference between i/ for the charge separation reaction and that of the radical ion pair recombination reaction. However, the difference between these two values of u is not unreasonable given that the charge separation involves oxidation of an excited state of the donor, while radical ion pair recombination involves two ground state radicals. Small changes in the nuclear coordinates of the donor and acceptor for these two reactions should be sufficient to produce the observed difference in i/. The electronic coupling factor between ZnTPP and AQ should be different than that between ZnTPP " and AQ". 

Fig. 1. Rise of the perylene cation absorption, which reflects the electron injection dynamics, after excitation of the first singlet state with a 15 fs pump pulse. Variation of the electronic coupling via a change in the anchor group as well as the insertion of one or two -CH2- groups leads to a systematic change in the time scale of both electron injection and charge recombination.

Apart from zinc(II) (na)phthalocyanines, the ruthenium(II) analogs have also been used to complex with pyridyl fullerenes. Arrays 33-35 show electronic coupling between the two electroactive components in the ground state as shown by UV-Vis spectroscopy and electrochemical measurements [45], The use of ruthe-nium(II) instead of zinc(II) phthalocyanines reduces the undesired charge recombination, increasing the lifetime of the radical ion pair state (on the order of hundreds of nanoseconds). 

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