Donor-Bridge-Acceptor systems tunneling

As a rule, however, the distance between the donor and the acceptor in such binuclear bridge metallocomplexes is not large. Only a few molecules of this type are known in which the electron transfer occurs over considerable distances, comparable with those for electron transfer between randomly arranged centres in vitreous matrices. Consider the results of research on electron tunneling over large distances in bridge systems. 

A density matrix approach makes it possible to examine more general models for systems like this [38,39]. For instance, unlike superexchange theory, this approach admits models that include strong couplings between the closely associated species in the intercalated DNA/donor-acceptor complex. More important, the density matrix description allows a proper treatment of quantum coherences, which is critical in bridging the tunneling and free-conduction regimes of transport. On the one hand,... 

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