Electronic coupling distance dependence

Composilion has a marked effect on p. Dilution can cause (i to drop by orders of magnitude. The functional dependence is often expressed in terms of an exponential dependence on intersite distance R=at m as suggested by the homogeneous lattice gas model, p c)exponential distance dependence of intersite coupling precludes observing a percolation threshold for transport. 

Eng MP, Albinsson B (2006) Non-exponential distance dependence of bridge-mediated electronic coupling. Angew Chem Int Ed 45 5626—5629... 

Figure 6. Distance dependence of the interactions between two equivalent jt-type orbitals. The magnitude of the interaction, A (jt), at any given distance is approximately equal to twice the electronic coupling, Vci, for hole transfer between the two orbitals, (a) Through-space (TS) coupling. (b) Through-bond (TB) coupling. Using HF/ 3-21G theory, j8 3.0 A"1, for TS interactions, and 0.8 per bond for TB interactions in the diene series 1(n).

An important question remains to be answered although the phenomenological P value appears to be fairly insensitive to the nature of the hydrocarbon bridge, does it necessarily follow that Pei, for the distance dependence of the electronic coupling, Vd, should likewise display a similar insensitivity Extracting Vd values, and hence 3d, from experimental ET rate data is presently fraught with difficulties and uncertainties. An alternative approach to this problem is to calculate the couplings. A par-... 

We have assumed here that J can be treated as a constant. In some types of calculation, the explicit distance-dependence of the electron coupling integral must be taken into account. Little is yet known of the appropriate form of such a dependence. ... 

Fig.6 The distance dependence of electron-transfer rates in DNA hairpins [51]. The acceptor is a photoexcited derivatized stilbene (SA) or phenanthrene (PA) the electron donor is guanine (G), deazaguanine (Z), or inosine (I). The decay is much more rapid in the Z-PA couple compared to the G-SA couple because the tunneling energy is further from the bridge states in the case of Z-PA...

To estimate the consequences of such a bridge modification in a quantitative fashion one needs to treat an extended system where donor and acceptor sites are separated by intervening WCPs. We used the effective Hamiltonian approach described in Sect. 2.7 to clarify the distance dependence of the electronic coupling in DNA and the effect of bridge modifications [50]. 

The distance dependence of electron transfer has been studied extensively for the homogeneous case. An approximately exponential decay of the electronic coupling has been found with the number of saturated bonds in the spacer unit (see for example [6,7]). The results presented here suggest that an exponential dependence fits also our data for heterogeneous electron transfer in ultra-high vacuum. A different result has been reported for electron transfer from Re complexes to anatase where a local triplet state can play a role [8]. 

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