![]() 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. 3–7 It has been shown how the viscosity and the magnetic field modulate reactions. 2 Experimental scrutiny of these theories is only now being performed. In the past 20 to 30 years, a number of theoretical approaches have enlightened us with a deep physical understanding of these reactions, to the point where the notion of the rate coefficient was abandoned and instead substituted by the concept of reaction kernels able to account for magnetic field effects, internal states of the reactants and reversibility. Furthermore, this time dependent distribution coupled with subsequent processes, like recombination of products in the geminate stage, can only be understood in terms of non-markovian ( i.e. This is caused by the change over time of the ensemble-averaged quencher concentration surrounding the fluorophore as the reaction proceeds. ![]() It has been known since the seminal work of Smoluchowski 1 that, in the case of bimolecular photo-induced processes, the rate coefficients are not constant but rather change with time as a result of the mutual diffusion of the reactants. The present work attempts to elucidate this question. However, for photo-induced reactions it has never been explored experimentally if the rate of the bimolecular reactions depends itself on the intensity of the triggering light. Introduction Chemical reactions in solution develop at rates that depend on a number of factors: temperature, pressure, electric and magnetic fields, driving force and solvent characteristics such as the refractive index, the dielectric constant and the viscosity. 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. 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. Phys., 2000, 112, 10930–10940) was created for continuous light excitation though. The original theory by Burshtein and Igoshin ( J. ![]() Despite its simplicity, the model delivers a qualitative agreement with the observed experimental trends. 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. 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. The effect of multiple light excitation events on bimolecular photo-induced electron transfer reactions in liquid solution is studied experimentally. Pasteura 5, 02-093 Warsaw, Poland d Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany e Fakultät für Physik, Ludwig-Maximilians-Universität München, Am Coulombwall 1, D-85748 Garching, Germany f Institute of Physical and Theoretical Chemistry, Graz University of Technology, StremayrgaGraz, Austria E-mail: Fax: +48 22 343 33 33 Tel: +48 22 343 20 86 b Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK c Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Phys., 2017, 19, 6274-6285 Influence of the excitation light intensity on the rate of fluorescence quenching reactions: pulsed experimentsį a Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, 01-224 Warsaw, Poland.
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