Resonance transfer mechanism

The other point is that if one is going to see resonance transfer as Libby suggested, one would investigate the Tr-to-ir-system, the first case being db low spin which has a hole in the 7r-orbital level. There probably wouldn t be any hold up in resonance transfer mechanism in ruthenium (111) complexes. 

The energy transfer process in the antenna system is generally considered to take place according to a resonance transfer mechanism first proposed by Forster (see below). The antenna system increases the effective cross-section of photon absorption by increasing the number of pigments associated... 

Organic Bridging Groups—In most of the systems to be mentioned here, the point of discussion is the distinction between chemical transfer and resonance transfer mechanisms. In the former, an intermediate occurs in which the electron (or a positive hole) is temporarily trapped by the ligand, which may thus be considered a free radical in the latter, there is no such intermediate, or, more strictly, if there is an intermediate its lifetime is comparable with the lifetimes of the transition states which separate it from reactants and products. 

Meanwhile, it was found by Asai and colleagues [48] that tetraphenylphosphonium salts having such anions as Cl, Br , and Bp4 work as photoinitiators for radical polymerization. Based on the initiation effects of changing counteranions, they proposed that a one-electron transfer mechanism is reasonable in these initiation reactions. However, in the case of tetraphenylphosphonium tetrafluoroborate, it cannot be ruled out that direct homolysis of the p-phenyl bond gives the phenyl radical as the initiating species since BF4 is not an easily pho-tooxidizable anion [49]. Therefore, it was assumed that a similar photoexcitable moiety exists in both tetraphenyl phosphonium salts and triphenylphosphonium ylide, which can be written as the following resonance hybrid [17] (Scheme 21) ... 

The occurrence of energy transfer requires electronic interactions and therefore its rate decreases with increasing distance. Depending on the interaction mechanism, the distance dependence may follow a 1/r (resonance (Forster) mechanism) or e (exchange (Dexter) mechanisms) [ 1 ]. In both cases, energy transfer is favored by overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor. 

The most important mechanism for singlet energy transfer is the Forster resonance transfer ... 

All of the examples of singlet energy transfer we have considered take place via the long-range resonance mechanism. When the oscillator strength of the acceptor is very small (for example, n-> n transitions) so that the Fdrster critical distance R0 approaches or is less than the collision diameter of the donor-acceptor pair, then all evidence indicates that the transfer takes place at a diffusion-controlled rate. Consequently, the transfer mechanism should involve exchange as well as Coulomb interaction. Good examples of this type of transfer have been provided by Dubois and co-workers.(47-49)... 

A general theory of the aromatic hydrocarbon radical cation and anion annihilation reactions has been forwarded by G. J. Hoytink 210> which in particular deals with a resonance or a non-resonance electron transfer mechanism leading to excited singlet or triplet states. The radical ion chemiluminescence reactions of naphthalene, anthracene, and tetracene are used as examples. 

The key distinguishing feature of charge-transfer (CT) complexation is that the partial admixture of ionic D+A character in the resonance hybrid (5.72) confers a tendency toward association that is absent in the purely covalent D- A limit, i.e., in the absence of covalent-ionic resonance. The mechanism of CT binding is... 

More convincing proof for a particle-enhanced energy transfer mechanism comes from a study of the concentration dependence of the transfer. Bulk Forster transfer leads to a linear dependence on acceptor concentration with constant donor-to-acceptor ratio. The resonance mechanism would be expected to saturate at (relatively) high concentrations and fall off linearly at very low concentrations. 

This is called a chemical, radical or stepwise mechanism. Or was it (ii) by the action of the bridging group to increase the probability of electron transfer by tunneling, termed resonance transfer 56,9i... 

The chemical mechanism was supported for M = Co and Cr, whereas a resonance transfer was favored by Ru(III) and these differences were rationalized. As important as these... 

Electron-pair donor (or Lewis base), NUCLEOPHILE ELECTRON SINK ELECTRON SPIN RESONANCE ELECTRON TRANSEER MARCUS EQUATION ELECTRODE KINETICS Electron transfer mechanism,... 

Finally—and I think the subject is becoming ripe for development on this level —let us turn to the question of the mechanisms by which electron transfer takes place. One important distinction is whether the electron transfers by a resonance mechanism or by a chemical one. Different observations can be made depending on this difference in mechanism. Perhaps one of the most significant is based on the fact that if there is resonance transfer, preparation for receiving the electron will be made at the Co(III) center, but if the electron transfers to the ligand, this kind of preparation at the metal ion center is not required. An experimental approach to distinguish between the two cases may be this when Co (111) receives the electron directly, there may be a strong discrimination between the isotopes of... 

Harry Gray Two points in Prof. Taube s paper quoted as experiments in progress haven t been mentioned. Both are concerned with the mechanism of electron transfer, because the transmission in the ligand, wherever the attack is, is through the 7r-system, and in cobalt(III) in the detectable radical ion intermediate, because of the improbability of resonance transfer from tt to electron resonance experiment in which one tries the reduction by chromous and looks for the ESR signal of the radical ion. 

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