Internal reorganization energy

It should, however, be emphasized that the relaxation from (X ) -l-i to X (+) does not always require a negligible energy. Counterexamples where the homolytic cleavage of an ion radical appears to be endowed with a sizable internal reorganization energy can be found in the electrochemical reduction of perbenzoates,60 where the observation of a transition between a concerted and a stepwise mechanism fits with an exothermic cleavage of the anion radicals. 

The forward and backward activation free energies and the corresponding rate constants thus depend on an extrinsic factor, the standard free energy of the reaction, AG° = E — E°, and an intrinsic factor, the standard activation free energy, that reflects the solvent and internal reorganization energy, Aq and A [equation (1.31)]. 

FIGURE 1.21. Reduction of aliphatic 1,2-diones in acetonitrile59 Correlation between the experimental activation free energies and values of the internal reorganization energies... 

There is no such simple expression for the internal reorganization energy Aj, which must be given as a sum of terms related to the vibrational states of the reactants and products... 

A second point of interest is that the A values inferred for high spin Fe(III) complexes (eg Hb) are much larger than those seen for low spin systems (eg cytc). The slow reactions seen for high spin Fe heme proteins likely reflect a large internal reorganization energy associated with the reaction from 5 coordinate Fe(II) to 6 coordinate Fe(III). 

In summary, the comparatively small internal reorganization energy of C o, together with its excellent redox properties, should make the Cgo chromophore a valuable electron acceptor component in molecular photovoltaic devices. 

Solvent reorganization energy Internal reorganization energy Photoexcited triplet state of metalloporphyrin Nuclear frequency factor... 

I. Place, A. Farran, K. Deshayes, P. Piotrowiak, Triplet energy transfer through the walls of hemicarcerands temperature dependence and the role of internal reorganization energy, J. Am. Chem. Soc, 1998, 120, 12626-12633. 

The reorganization pertains to the neighborhood of die transferred electron (i.e., to the solvent molecules, but also to the donors and acceptors diemselves). This is why the reorganization energy, in the first approximation consists of die internal reorganization energy (A, ) that... 

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