Dexter exchange

One can see tliat tlie Dexter exchange mechanism is exponentially dependent on tlie distance between tlie donor and acceptor, and as such it begins to play a visible role only at very short distances when tlie electron clouds begin to... 

Figure 23. Two principal mechanisms of excitation energy transfer (EET). (a) The Forster dipole-dipole mechanism, in which the active electrons, one and two, remain, respectively, on D and A throughout the process, (b) In the (Dexter) exchange mechanism, electrons one and two exchange locations.

Fig. 6. Schematic representation of Dexter (exchange, left) and Forster (dipole-dipole, right) mechanisms for energy...

The energy transfer from Tb + to Eu + ion in the [Eu/Tb(tfa)3(tppo)2] pure chelate and the in situ chelate doped in gel glass indicates that the Dexter exchange mechanism is operative in the energy transfer process between ions" . Pettinari and coworkers" showed terbium 4-acylpyrazol-5-onate and its derivatives are luminescent materials, also pointing to the importance of properties such as hydrophobicity, solubility in non-polar solvents and large size of the molecule. 

The approaches to heterometaUic systems outlined above all rely upon coordination chemistry, whether to a metal ion or a nanoparticle surface. Supramolecular interactions can also play a role in assembling heterometaUic systems. For instance, Sambrook et al. prepared a pseudo-rotaxane (18) templated around a chloride ion (Fig. 9) in which lanthanide ions are bound to the thread while a luminescent rhenium complex is bound to the macrocycle component [49]. Thus there is no direct link between the donor chromophore and the lanthanide ion, and Dexter exchange is not viable in the absence of bonds enforcing Forster energy transfer. This extreme of behaviour helps to rationalize the behaviour of more conventionaUy... 

The rate constant for the Dexter exchange mechanism is given by ... 

The Dexter Exchange Mechanism involves a direct contact between the donor and the acceptor atoms or molecules. The exchange interaction between the donor D and acceptor A involves a transition state with a D- A distance that is close to the sum of the gas-kinetic collision radii of D and A, respectively. Therefore, information about the energy transfer mechanism can be gained by structural studies of the system under consideration. If the D- A distance is short (normally < 5 A) then the exchange mechanism is the more likely, but if the D-A distance is long ( 5 A) then the resonance mechanism would be more likely. 

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