Photoinduced electron transfer reorganization energy

Recently, photochemical and photoelectrochemical properties of fullerene (Cto) have been widely studied [60]. Photoinduced electron-transfer reactions of donor-Qo linked molecules have also been reported [61-63]. In a series of donor-Cfio linked systems, some of the compounds show novel properties, which accelerate photoinduced charge separation and decelerate charge recombination [61, 62]. These properties have been explained by the remarkably small reorganization energy in their electron-transfer reactions. The porphyrin-Qo linked compounds, where the porphyrin moieties act as both donors and sensitizers, have been extensively studied [61, 62]. 

As demonstrated in this review, photoinduced electron-transfer reactions are finely controlled by the proper choice of the redox potentials and reorganization energies of electron donors and acceptors, which can be modulated depending... 

Since most organic compounds, in particular n acceptors, have small reorganization energies, the change of redox potentials by the interaction of the corresponding radical anions with M may be the main factor to accelerate the rates of photoinduced electron transfer. Thus, any material M that can stabilize the radical anions by complexation may act as an efficient... 

Photoinduced electron transfer from dilferent electron donors to the triplet excited states of Ceo and C70 occurs efficiently and is typically associated with a small reorganization energy [18, 19, 21-27]. Consequently, the occurrence of fast electron-transfer events involving the fullerene excited states has been well established as giving rise to small intrinsic barriers. In contrast with the fast electron-transfer reactions of the triplet excited state of Ceo, an extremely slow electron-transfer reaction has been reported for the reaction of Ceo in its ground state with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to produce Ceo in benzonitrile. The latter can be followed even by conventional Vis-NIR spectroscopy [28]. In this instance, however, it is not clear whether the generation of Ceo is directly related to electron transfer from DBU to Ceo, or if Ceo evolves from the produet of a secondary reaction. 

The rates of photoinduced electron transfer (ET) reactions in a series of iridium (spacer)pyridinium complexes, [Ir(/r-dmpz)(CO)(Ph2PO-CH2-CH2-py+)]2 and [Ir( -dmpz)(CO)(Ph2PO-C6H4(CH2) -py+)]2 ( = 0 - 3), have been studied in acetonitrile solution at room temperature (99). The nuclear reorganization energies and electronic couplings in these systems have been evaluated. 

The mechanism of quenching had previously been established by observing the formation of free radical ions using flash photolysis.345 Rehm and Weller proposed the empirical Equation 5.5 to fit the data, where AetG° is the free energy of photoinduced electron transfer in the contact pair (Equation 5.1), AG is the free energy of activation that accounts for the structural and solvent reorganization required for the transfer of an electron, kd and k d are the rate constants for the formation and separation of the encounter complex, respectively, Kd = kd/k d is the equilibrium constant of complex formation and Z is the bimolecular collision frequency in an encounter complex, Z 1011 s 346 A value of kd/(ZKd) = 0.25 was used. 

Andres, G. O., Martinez Junza, V., Crovetto, L., Braslavsky, S. E., Photoinduced Electron Transfer from Tetrasulfonated Porphyrin to Benzoquinone Revisited. The Structural Volume normalized Entropy Change Correlates with Marcus Reorganization Energy, J. Phys. Chem. A 2006, 110, 10185 10190. 

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