Thermodynamics electron transfer quenching

Under thermodynamically favourable PET reactions (AGet < 0) the radical ions are formed either as contact ion pair (CIP) or solvent-separated ion pair (SSIP). A closely related question is whether the primary intermediate is a SSIP or CIP. Gould and Farid [8] in their recent study have suggested that in polar solvents, such as acetonitrile, electron transfer quenching results in the formation of SSIP directly and in these solvents the fully solvated ions (SSIP) can separate to form free radical ions (FRI). Therefore, under these conditions the... 

Finally, the CuCo.l0 + catenate does not luminesce under any condition, showing that the potentially luminescent MLCT level of the Cu-complexed moiety is quenched by the Co-based one. A possible quenching mechanism is energy transfer, since the d Co + metal ion has low-energy d-d levels (<10 000 cm ) [65], but also electron transfer is thermodynamically allowed (AG = -0.54 eV). 

The thermodynamic feasibility of the electron-transfer quenching process can be assessed by means of the well known Weller equation ... 

A.J. Bard, University of Texas The fact that one can generate chemiluminescence in polymer films containing Ru-(bpy)3 2 implies that the excited state may not be quenched completely by electron transfer reactions. Are the photoreactions you describe thermodynamically uphill (i.e., with chemical storage or radiant energy) or are they photocatalytic ... 

At present there is a sufficiently complete picture of photoelectrochemical behavior of the most important semiconductor materials. This is not, however, the only merit of photoelectrochemistry of semiconductors. First, photoelectrochemistry of semiconductors has stimulated the study of photoprocesses on materials, which are not conventional for electrochemistry, namely on insulators (Mehl and Hale, 1967 Gerischer and Willig, 1976). The basic concepts and mathematical formalism of electrochemistry and photoelectrochemistry of semiconductors have successfully been used in this study. Second, photoelectrochemistry of semiconductors has provided possibilities, unique in certain cases, of studying thermodynamic and kinetic characteristics of photoexcited particles in the solution and electrode, and also processes of electron transfer with these particles involved. (Note that the processes of quenching of photoexcited reactants often prevent from the performing of such investigations on metal electrodes.) The study of photo-electrochemical processes under the excitation of the electron-hole ensemble of a semiconductor permits the direct experimental verification of the applicability of the Fermi quasilevel concept to the description of electron transitions at an interface. 

Intrinsic limitations of an artificial photosynthetic system include the thermodynamically favoured back electron transfer reactions of the intermediate photoproducts [47, 48]. For an oxidative ET quenching process the destructive back electron reactions are given by Eq. (9) and (10). The fraction of usable photo-... 

The thermodynamics of electron transfer can influence CT quenching only inasmuch as electron transfer contributes to the excited CT complex(exdplex). In valence bond terms, the value of lc2 describes the percentage of electron... 

What is actually observed, however, is that [Rh(phi)2(phen)]3+ intercalated into DNA quenches the intensity of [Ru(phen)2(dppz)]2+ much more effectively than it quenches the two lifetimes, as summarized in Table II. This effect is most pronounced when the DNA helix is a short oligonucleotide. The direct comparison of quenching in the absence of DNA cannot be accomplished because the ruthenium(II) complex does not luminesce in aqueous solution however, electron transfer from [Ru(phen)3]2+ to [Rh(phi)2(phen)]3+ in buffered solution provides a control with the same thermodynamic driving force (40). 

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