Reversible Photoionization in Liquid Solutions

Abstract

The Stern-Volmer constant of fluorescence quenching by reversible intermolecular charge transfer is obtained by means of integral encounter theory. The latter provides the first non-Markovian description of the phenomenon which accounts for the reversibility of excited-state ionization. The forward and backward electron transfers (bimolecular and geminate) are specified by the position-dependent rates of ionization and recombination. Assuming that the conventional free energy gap law is inherent to all of them, a reasonable explanation is given for the famous Rehm and Weller free energy dependence of the Stern-Volmer constant. It requires the production of ions in excited states when forward electron transfer is highly exergonic and implies that the charge recombination occurs not only to the ground but also to the excited triplet state. It is assumed that spin conversion in the radical ion pairs is faster than the geminate recombination.

Corrections to the law of mass action and properties of the asymptotic t=∞ state for reversible diffusion-limited reactions

“…In particular, the question of the corrections to the LMA may be addressed for other types of reaction schemes, including, e.g., reactions between excited molecules, in which case particles possess an intrinsic life-time. As well, one may expect that the effects observed here will become more pronounced for photochemical, ionization and electrochemical reactions [47].…”

Ultrafast Excited State Dynamics of the Perylene Radical Cation Generated upon Bimolecular Photoinduced Electron Transfer Reaction

“…If this is not the case, this simple exponential model is no longer valid and more sophisticated models have to be used. 53,54 In principle, the sum k sep + k CR should also be accessible from the time profile of the transient ion absorption. Indeed, if the quenching is sufficiently fast, such profiles exhibit a decay that can be well reproduced with an exponential function decaying to a constant value different from zero.…”

Fluorescence Quenching by Reversible Charge Separation Followed by Ions Recombination and Their Separation Suppressed by Coulomb Attraction

“…The latter phenomena disappears when the fluorescence is registered stationary. It was shown in [6] that the stationary detected quantum yield obeys the usual Stern-Volmer law but its constant is different:…”

“…Their recombination to the ground state remains the single channel of their annihilation. But unlike the similar equation (37) in [6] the last one is valid for solvents of any polarity because the electrostatic ion attraction is accounted for by the Coulombic term C in the definition of K, given in (24). The Markovian analog of the latter result was obtained even in the pioneering work of Rehm and Weller [2], who neglected ion separation from the very beginning, assuming that the final product of ionization is the bounded ion pair Advances in Physical Chemistry 5 (an exciplex) that cannot dissociate at all.…”

“…The Markovian analog of the latter result was obtained even in the pioneering work of Rehm and Weller [2], who neglected ion separation from the very beginning, assuming that the final product of ionization is the bounded ion pair Advances in Physical Chemistry 5 (an exciplex) that cannot dissociate at all. As a result they got by the simplest rate calculations that [2,6] …”