On the Coherent Description of Diffusion‐Influenced Fluorescence Quenching Experiments

Abstract

The fluorescence quenching by electron transfer of a fluorophore, 2,5-bis(dimethylamino)-1,3-benzenedicarbonitrile, to 1,3-dimethyl-2-nitrobenzene, has been studied by means of time-resolved and steady-state experiments at different viscosities and up to large quencher concentrations. Differential Encounter Theory (DET) has been used to rationalize the results, in combination with electron transfer modelled by the Marcus theory. Additionally, the solvent structure and the hydrodynamic effect on the diffusion coefficient have been taken into account. Any simpler model failed to simultaneously fit all the results. The large number of quencher concentrations used is crucial to unambiguously extract the electron transfer parameters.

Influence of the excitation light intensity on the rate of fluorescence quenching reactions: pulsed experiments

“…2 Experimental scrutiny of these theories is only now being performed. [3][4][5][6][7] It has been shown how the viscosity and the magnetic field modulate reactions. For example, it has been observed that recombination efficiency depends on the viscosity of the medium non-monotonically as a combined effect of the molecular transport and the spatial characteristics of the electron transfer reactions.…”

Contact and Distant Luminescence Quenching in Solutions

“…This program was successfully realized in a very recent paper [96]. The lack of information was filled in by relating the Stern-Volmer constant κ(c) to the DET rate constant, k A (t):…”

“…The obtained relationships between diffusion and viscosity, D(η), for the models (128) were shown to be very close to the StokesEinstein models for the stick and slip friction coefficient. Specifying D in this way, the authors of [96] …”

“…In fact, the authors of [96] tested 6 different models of k A (t) calculations (with and without accounting for g (r) and D(r)) and selected only two of them which account simultaneously for the liquid structure and the space dependence of D(r) (one or another). 150 experimental data points for κ(c, D) were obtained from the fluorescence quantum yield studied in the 8 solvents of different compositions (viscosities).…”

“…Besides, the hydrodynamic effect is taken into account, which results in the space dependence of the diffusion coefficient at short distances between reactants. This dependence is represented by the simple expressions taken from either the Northrup and Hynes or Deutch and Felderhof models [96]:…”