Excitation transfer, theory

Single molecule data measured at room temperature indicated that a distri bution of excitation transfer rate constants could be observed [18], while Basche and co-workers [19] showed, studying linewidths at low temperature, that the observed rates are larger than expected from classical Forster excitation transfer theory and suggested that in these systems through-bond interaction might play a role. 

We have established an important principle in electron transfer theory that is not present in conventional one-dimensional models. The reaction coordinate is always localizing and corresponds to coordinate Aj. The coordinate X2 corresponds to the direction in which the matrix element between ground and excited states is switched on. If this coordinate has zero length then the branching space becomes one dimensional and an adiabatic reaction path does not exist. We now consider two examples. 

Many of the features of electron transfer reactions involving excited states can be understood based on electron transfer theory. 

Wong KF, Bagchi B, Rossky PJ (2004) Distance and orientation dependence of excitation transfer rates in conjugated systems beyond the Forster theory. J Phys Chem A 108 5752-5763... 

One would still like to examine the effect of ethidium on the torsional rigidity and dynamics at high binding ratios. One would also like to test the Forster theory for excitation transfer between bound ethidium molecules, since it has been questioned/65- This is possible in principle by deconvoluting the effects of depolarization by excitation transfer on the FPA, as will be shown subsequently. DLS also provides crucial information on this same question. 

Radiationless excitation transfer occurs only when (D + A) initial state is in or near resonance with (D +A ) final state and there is a suitable donor-acceptor interaction between them. The rate of transfer, kt> a. is given by the time-dependent perturbation theory,... 

The Pgl process can be complicated by other processes—for example, excitation transfer reactions. The available theory of Pgl cannot describe these complications but is rather restricted to a class of simple systems. The conditions that such simple systems must fulfill are summarized as follows ... 

Muenter, Gilman, Lenhard, and Penner (279) have reinterpreted Hailstone s results along these lines. They showed that a plot of activation energies versus Lenhard s reversible potentials for the dyes that inject electrons from their initially excited states could be fit to the form predicted by the electron transfer theory of Marcus and Levich ... 

The 1977 review of Martynov et al. [12] discusses existing mechanisms of ESPT, excited-state intramolecular proton transfer (ESIPT) and excited-state double-proton transfer (ESDPT). Various models that have been proposed to account for the kinetics of proton-transfer reactions in general. They include that of association-proton-transfer-dissociation model of Eigen [13], Marcus adaptation of electron-transfer theory [14], and the intersecting state model by Varandas and Formosinho [15,16], Gutman and Nachliel s [17] review in 1990 offers a framework of general conclusions about the mechanism and dynamics of proton-transfer processes. 

A question that arises in consideration of the annihilation pathways is why the reactions between radical ions lead preferentially to the formation of excited state species rather than directly forming products in the ground state. The phenomenon can be explained in the context of electron transfer theory [34-38], Since electron transfer occurs on the Franck-Condon time scale, the reactants have to achieve a structural configuration that is along the path to product formation. The transition state of the electron transfer corresponds to the area of intersection of the reactant and product potential energy surfaces in a multidimensional configuration space. Electron transfer rates are then proportional to the nuclear frequency and probability that a pair of reactants reaches the energy in which they have a common conformation with the products and electron transfer can occur. The electron transfer rate constant can then be expressed as... 

Among the recent attempts to develop the theory of chemical carcinogenesis one encounters a number of speculations on the possible role in tumor formation of different factors which may be generally termed as physical or sterical. We have recently discussed in detail on a few occasions the theories involving the physical factors, among them the electron or excitation transfer mechanisms.27 32 26 24 In this communication, we should like to discuss, at least in part, some of the propositions concerning the role of steric effects in carcinogenesis by polycyclic aromatic hydrocarbons. 

Excited state potentials can also be estimated from kinetic studies of electron transfer quenching reactions involving a series of acceptors and/or donors with varying potentials. By applying electron transfer theory to the quenching step, in conjunction with the predicted dependence of the quenching rate constant on AG° for the electron transfer reaction, estimates for the redox potentials may be obtained (2 ). These approaches have been used successfully in the evaluation of the redox properties of several metal complexes,... 

Several theories have been developed to explain how energy absorbed by one molecule is transferred to a second acceptor molecule of the same or a different species. At first sight exciton theory,20 66 which accounts for excitation transfer in molecular aggregates or crystals and the Davydov splitting effects connected with it, appears to bear little relationship to the treatment of long-range resonance transfer as developed, for example, by Forster.81-32 However, these theories can be shown to arise from the same general considerations treated at different well-defined mathematical limits.33-79... 

Determination of macromolecules conformations is one of the basic problems of science about polymers. Simultaneously with development of theory [4-6] the perfection and enrichment of experimental methods of determination of macromolecules conformations in various phase and aggregate states occurs. However the method of neutron scattering was almost the only one method allowing reliable determination of polymer chains conformation in solid amorphous state until now [7], Not long ago they begun to use with this aim also the method based on measurement of rate of electron excitement transfer between molecules of chromophores covalent bonded with polymer chain [8],... 

Picosecond infrared studies (144-146) of the dynamics of [(NC)5-RuIICNRu11I(NH3)5]1 following MMCT photolysis permitted observation of the formation and decay of the MMCT excited state and the evaluation of vibronic coupling and energy-transfer dynamics. The experimental results were in agreement with recent electron-transfer theories that have been used to predict excited vibrational populations resulting from back electron transfer in the Marcus inverted region (146). 

Kenkre VM, Knox RS. Generalized master-equation theory of excitation transfer. Phys. Rev. B. 1974 9 5279-5290. 

The lifetime of the MLCT excited state of [Ru(bipy)3] has been measured in several solvents and at different temperatures. Among the- conclusions drawn are that k, is only slightly solvent-dependent, that k , agrees quantitatively with predictions of energy gap law for radiationless transitions, and that the solvent dependence of kinetic parameters for MLCT —> d, dctransitions can be considered in the context of electron-transfer theory. These results may have implications for the use of [Ru(bipy)3] as sensitizer. The solvent dependence of the MLCT transitions of [Ru(bipy)3], [Os(bipy)3], [Os(bipy)2(py)2p, and [Os(bipy)2 l,2-(Ph2P)2CsH4 f has been interpreted in... 

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