Optical electron transfer energy

Reorganisation energies of optical electron transfer processes. R. D. Cannon, Adv. Inorg. Chem. Radiochem., 1978, 21 179-230 (155). 

Reorganization Energies of Optical Electron Transfer Processes R. D. Cannon... 

REORGANIZATION ENERGIES OF OPTICAL ELECTRON TRANSFER PROCESSES... 

Moreover, from the data in Table 2 it is possible to estimate the fi ee energy of activation of the reaction studied. In order to do this we must assume, above all, that the optical electron transfer, to which the band correspond, is the same as the themud electron transfer, to which the k values correspond. However, the data in Table 3 cannot be used directly for estimating the activation free energy of the thermal electron transfer reaction. The first obvious reason comes from the fact that the band corresponds to the (Co(NH3)4(pzC02)] -[Ru(CN) ion-pair instead of to the [Co(NH3)4(pzC02)] -[Fe(CN) J "... 

Table 3.- Activation free energies estimated for the optical electron transfer within the [Co(NH3)4(pzC02)] -[Fe(CN)J ion-pair (see the text). T=298.2 K.

In optical electron transfer, the photon energy helps to balance the electronic mismatch associated with vertical excitation from equilibrium, where, as noted... 

The FCWD expressions for thermal ET (e.g., Eq. 32 or its low-temperature quantal counterpart) may be adjusted to accommodate optical electron transfer if AG° is replaced with AG° + liv (emission) or AG° - kv (absorption), where tiv is the optical transition energy [96]. The relationship between thermal and optical coupling elements is discussed in Section 1.4.2 of this chapter. 

As we have seen above, CT interactions introduce low-energy excited states responsible for the absorption bands in the visible region (Figure 11). Light excitation in these CT absorption bands formally leads to the transfer of an electron from the donor to the acceptor component (optical electron transfer). As a consequence— particularly when this process leads to formation of charges of the same sign in the two components—one can expect destabilization of the pseudorotaxane structure followed by dethreading. In practice, however, this simple approach does not work because the back electron transfer process is much faster than the separation of the molecular components—a process which requires extended nuclear motions and... 

Similarly, the energy for the optical-electron transfer, E, is given by ... 

Fig. 5. Energy profiles and parameters relevant to optical electron transfer.

The energy of an optical electron transfer transition, E p, is correlated according to Hush theory [24,25] to the energy gradient between the minima of the A.B and curves, AE, and to the reorganizational energy, X (eq 2). Detailed expressions for the calculation of 1 in terms of... 

The optical electron transfer band is expected to be Gaussian-shaped, with a halfwidth, AVj 2> is directly related to the reorganiza-tional energy by eq 3 [24,25]. 

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