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

Abstract

The effect of multiple light excitation events on bimolecular photo-induced electron transfer reactions in liquid solution is studied experimentally. It is found that the decay of fluorescence can be up to 25% faster if a second photon is absorbed after a first cycle of quenching and recombination. A theoretical model is presented which ascribes this effect to the enrichment of the concentration of quenchers in the immediate vicinity of fluorophores that have been previously excited. Despite its simplicity, the model delivers a qualitative agreement with the observed experimental trends. The original theory by Burshtein and Igoshin (J. Chem. Phys., 2000, 112, 10930-10940) was created for continuous light excitation though. A qualitative extrapolation from the here presented pulse experiments to the continuous excitation conditions lead us to conclude that in the latter the order of magnitude of the increase of the quenching efficiency upon increasing the light intensity of excitation, must also be on the order of tens of percent. These results mean that the rate constant for photo-induced bimolecular reactions depends not only on the usual known factors, such as temperature, viscosity and other properties of the medium, but also on the intensity of the excitation light.

Radiation Models for Computational Fluid Dynamics Simulations of Photocatalytic Reactors

“…The models used in the simulations can affect the results obtained. So, the selection of the models is critical in the computational design or numerical studies of photocatalytic reactors [9].…”

“…If the medium is homogeneous regarding light absorption and refraction index, the flow field will have no impact on radiation. The latter is generally not the case in chemical reactors where the concentration distribution of chemical species evolves in space or time 9, 73. The final step is the simulation of mass balance, which requires all the previous steps.…”

Steady‐State Fluorescence Intensity of Diffusion‐Influenced Reversible Excited Acid–Base Reactions

“…When the intensity of excitation light is kept constant over time, the concentrations of the excited species approach their steady-state values. When the intensity is not very high, the linear response theory could be applicable (see the literatures for the effect of intense excitation light [1][2][3][4][5] ) and the intensity of steady-state fluorescence is given by the time-integral of survival probability:…”

“…One may try to describe the effects of diffusion for the steady-state kinetics in terms of a binary theory of diffusionlimited reactions where the association and dissociation rate constants in Eqs. (5) and (6) are replaced, respectively, with. 8…”

“…When the intensity of excitation light is kept constant over time, the concentrations of the excited species approach their steady‐state values. When the intensity is not very high, the linear response theory could be applicable (see the literatures for the effect of intense excitation light) and the intensity of steady‐state fluorescence is given by the time‐integral of survival probability: where the survival probabilities and are the concentrations of the excited acid and base at a time t , respectively, normalized by the initial concentration of the acid.…”