Temperature effects on intramolecular electron transfer kinetics under "normal", "inverted", and "nearly optimal" conditions

Abstract

The temperature dependence of electron transfer over a wide range of driving forces extending from far in the "normal" to deep into the "inverted" region is studied with the aid of a limited number of closely related and fully rigid bridged donor-acceptor systems. The interpretation of temperature-dependent electron-transfer kinetics is shown to be complicated by the relatively large influence of the temperature dependence of the solvent dielectric properties. This problem becomes especially evident if the barrier is small, when it may lead to an overall nullification or even inversion of the temperature effect on the experimental rate. Upon correction for the temperature dependence of the solvent properties, the rate of electron transfer is found to be independent of temperature in the inverted region, where nuclear tunneling becomes dominant, in contradiction to expectations based on the classical Marcus treatment which, however, is shown to be capable of giving a qualitative description of the temperature dependence in the normal region, even under close to "optimal" conditions.

Distance Dependence of Singlet and Triplet Charge Recombination Pathways in a Series of Rigid Bichromophoric Systems

“…An exponential distance dependence was indeed found for both k cs and k cr in 1[n]. 1a-g, [13][14][15][16][17] As already noted above, however, for k cr the situation is complicated. In fact charge recombination can occur Via three distinctly different pathways.…”

Long‐Lived Charge‐Transfer States in Compact Donor–Acceptor Dyads

“…Moreover, the temperature dependence of the rates of electron-transfer processes occurring under inverted-region conditions has in general been found to be small or even absent. [16][17][18][19] These observations can be explained by nuclear tunneling becoming increasingly important in the inverted region. This suggests that under such conditions electron transfer can no longer be adequately described by the curve-crossing model underlying Equation (1).…”

“…Consequently, the rate of photoinduced electron transfer for such dyads is not only solvent- [14,15] but also temperature-dependent, with an activation barrier described by Equation (1). [16] …”

Photoinduced energy transfer from the triplet state of naphthalene moiety in the Tb3+/Eu3+ complexes of a specially designed naphthalene cryptand

“…The ET efficiency and the quenching of naphthalene emission in such systems were found to depend to a large extent on the relative orientation of the lanthanide ion with respect to the naphthalene p plane [11][12][13]. The effect of orientation of the donor with respect to the acceptor on the ET efficiency and ET rates has also been reported in compounds where the donor and the acceptor are linked by spacer group [14][15][16][17][18][19][20][21][22][23][24][25]. Such ET processes could take place through the singlet state [26,27] or the triplet state of an aromatic unit acting as the ligand [28][29][30][31].…”