Inverted region in intramolecular electron

Closs, G. L., Calcaterra, L. T., Green, N. J., Miller, J. R., and Penfield, K. W., 1986, Distance, Stereoelectronic Effects, and the Marcus Inverted Region in Intramolecular Electron-Transfer in Organic Radical-Anions J. Phys. Chem. 90 3673n3683. 

Gloss GL, Calcaterra LT, Green NJ, Penfield KW, Miller JR. (1986) Distance, stereoelectronic effects, and the Marcus inverted region in intramolecular electron transfer in organic radical anions. J Phys Chem 90 3673-3683. 

Phys. 74 6746 (1981) b) G. L. Gloss, L. T. Calcaterra, N. J. Green, K. W. Penfield, and J. R. Miller, Distance, stereoelectronic effects, and the Marcus inverted region in intramolecular electron transfer in organic radical anions, J. Phys. Chem. 90 3673 (1986). a) S. Larsson, Electron transfer in chemical and biological systems. Orbital rules for nonadiabatic transfer, J. Am. Chem. Soc. 103 4034 (1981) b) S. Larsson, n Systems as bridges for electron transfer between transition metal ions, Chem. Phys. Lett. 90 136 (1982) c) S. Larsson, Electron transfer in proteins, J. Chem. Soc., Faraday Trans. 2 79 1375 (1983) d) S. Larsson, Electron-exchange reaction in aqueous solution, J. Phys. Chem. 88 1321 (1984) e) S. Larsson,... 

Jiang, H. Xu, H. Ye, J. Synthesis and cation-mediated electron transfer in intramolecular fluorescence quenching of donor-acceptor podands observation of Marcus inverted region in forward electron transfer reactions. 

Figure 2.3 Evidence for the Marcus inverted region from intramolecular electron rate constants as a function of AG° in methyltetrahydrofuran solution at 206 K. Reprinted with permission from G.L. Closs, L.T. Calcaterra, H.J. Green, K.W. Penfield and J.R. Miller, ]. Phys. Chem., 90,3673 (1986). Copyright (1986) American Chemical Society...

The imbedded nature of the potential curves in Figure 6 for electron transfer in the inverted region is a feature shared with the nonradiative decay of molecular excited states. In fact, in the inverted region another channel for the transition between states is by emission, D,A -> D+,A + hv, which can be observed, for example, from organic exciplexes,74 chemiluminescent reactions,75 or from intramolecular charge transfer excited states, e.g. (bipy)2Rum(bipyT)2+ - (bipy)2Run(bipy)2+ + hv. 

Scott JR, Willie A, MacLean M, et al. Intramolecular electron transfer in cytochrome b5 labeled with ruthenium(II) polypyridine complexes rate measurements in the Marcus inverted region. J Am Chem Soc 1993 115 6820-4. 

Intramolecular electron transfer rate constants k (s-1) as a function of the free energy difference for the reaction Biphenyl( )-androstane-/4 —> Biphenyl-androstane-v4( ), estimated from the electrochemical reduction potentials in 2-methyltetra-hydrofuran the inverted region for electron transfer rates is prominent. Redrawn from Miller et al. [10]. 

Excited state lifetime tq is another important parameter to be controlled, especially if the photoactive complex is intended for bimolecular photochemical electron transfer. MLCT excited states of most polypyridine complexes decay both radia-tively and non-radiatively, with the respective rate constants and k r. The inherent excited state lifetime is defined as tq = l/( r + nr)- The non-radiative decay pathway in most cases prevails k r K. Hence To = 1 /km- Non-radiative decay of MLCT excited states can be treated as intramolecular electron transfer in the Marcus inverted region ... 

Clear-cut experimental evidence for the existence of an inverted region was provided in 1984 by the work Miller et al.352 on long-distance intramolecular electron transfer in the rigidly linked bichromophoric radical anions 9 (Figure 5.4), which were generated by pulsed electron injection. The electrons are initially captured with nearly equal probability by either the donor chromophore biphenyl or the acceptor chromophore mounted on the other side of the saturated 5a-androstane spacer. Electron transfer rates to attain equilibrium were determined by time-resolved observation of the ensuing absorbance changes. 

We have demonstrated in two independent studies that electrolyte effects can have a strong influence on the energetics of a charge-separated species and on the dynamics of intramolecular electron transfer in moderately polar media. In the case of weakly exoergic ET, the ion dynamics can effectively control the transfer rate. The developed spectroscopic probes indicate that association with ions can stabilize a photoinduced charge-separated species by as much as 1 eV. Further investigation of electrolyte effects in photoinduced electron transfer, particularly in the "inverted region, is needed. 

An important contribution from the field of intramolecular organic electron-transfer is the discovery of some reactions that clearly show the inverted region indicated by the Marcus formalism [23]. As we noted earlier (Section 9.1.2.6), the Marcus model predicts that, in... 

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