Excited-State Electron Exchange

It is interesting to compare the ground and excited-state electron-exchange reactions in terms of orbital occupancy. For the Ru complex140, whose excited state is MLCT, the exchange between Ru(bpy)3+ and Ru(bpy)3+ [Eq. (91)]... 

Photoinduced Electron-Transfer Reactions 13.4.2. Excited-State Electron Exchange... 

The nonadiabatic (nonsecular) contributions T, and T34 to the coherence decay are caused by inelastic 7 ,-type processes. Equation (41b) shows that these inelastic scattering processes are induced by anharmonic-ity (k ) in the ground state and a combination of anharmonicity and electron-phonon coupling (Vg ) in the excited state. Here describes the decay (creation) of the pseudolocalized phonon into (from) two band phonons. The relevant part of is in (39) the last term, which describes in the excited state the exchange of a pseudolocalized phonon with a band phonon. At low temperature (/c7 phonon scattering processes in the ground and excited state. 

HELIUM, SINGLET AND TRIPLET EXCITED STATES, ELECTRON SPIN AND THE ROLE OF THE EXCHANGE INTEGRAL... 

The rate constant of these bimolecular processes is controlled by several factors. To elucidate these factors, a detailed reaction mechanism must be considered. Since both electron transfer and exchange energy transfer are collisional processes, the same kinetic formalism may be used in both cases [10]. Using an oxidative excited-state electron-transfer reaction as an example (equation (21)), the reaction rate can be discussed on the basis... 

From the fundamental chemistry point of view photoredox reactions of polypyridyl complexes have contributed substantially to our understanding of thermal and light-induced electron transfer reactions. Extension of Marcus and Rehm-Weller theories to excited state electron transfer of metal complexes is now on a firm basis. Quantitative analyses have allowed estimation of self-exchange rate constants for a number of quenchers and/ or identification of possible low-lying excited states of the quenchers. Table 16 presents a collection of self-exchange rate constants determined in this manner. 

Figure Al.6.24. Schematic representation of a photon echo in an isolated, multilevel molecule, (a) The initial pulse prepares a superposition of ground- and excited-state amplitude, (b) The subsequent motion on the ground and excited electronic states. The ground-state amplitude is shown as stationary (which in general it will not be for strong pulses), while the excited-state amplitude is non-stationary. (c) The second pulse exchanges ground- and excited-state amplitude, (d) Subsequent evolution of the wavepackets on the ground and excited electronic states. Wlien they overlap, an echo occurs (after [40]).

According to Eq. (A.4), if < 0, the ground state will be the in-phase combination, and the out-of-phase one, an excited state. On the other hand, if > 0, the ground state will be the out-of-phase combination, while the in-phase one is an excited state. This conclusion is far reaching, since it means that the electronic wave function of the ground state is nonsymmetric in this case, in contrast with common chemical intuition. We show that when an even number of electron pairs is exchanged, this is indeed the case, so that the transition state is the out-of-phase combination. 

In a regime of strong interaction between the chains no optical coupling between the ground slate and the lowest excited state occurs. The absence of coupling, however, has a different origin. Indeed, below 7 A, the LCAO coefficients start to delocalize over the two chains and the wavefunclions become entirely symmetric below 5 A due to an efficient exchange of electrons between the chains. This delocalization of the wavcfunclion is not taken into account in the molecular exciton model, which therefore becomes unreliable at short chain separations. Analysis of the one-electron structure of the complexes indicates that the... 

The decomposition of dioxetanone may involve the chemically initiated electron-exchange luminescence (CIEEL) mechanism (McCapra, 1977 Koo et al., 1978). In the CIEEL mechanism, the singlet excited state amide anion is formed upon charge annihilation of the two radical species that are produced by the decomposition of dioxetanone. According to McCapra (1997), however, the mechanism has various shortfalls if it is applied to bioluminescence reactions. It should also be pointed out that the amide anion of coelenteramide can take various resonance structures involving the N-C-N-C-O linkage, even if it is not specifically mentioned. 

Schuster, G. B. (1979). Chemiluminescence of organic peroxides. Conversion of ground-state reactants to excited-state products by chemically initiated electron-exchange luminescence mechanism. Acc. Chem. Res. 12 366-373. 

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