Hannover 2010 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 15: Photochemistry II
MO 15.3: Vortrag
Mittwoch, 10. März 2010, 14:30–14:45, F 142
Methoxy benzyl alcohol interferes with its own oxidation: an ultrafast transient absorption study of flavin photocatalysis — •Matthias Wenninger1, Uwe Megerle1, Robert Lechner2, Burkhard König2, and Eberhard Riedle1 — 1Lehrstuhl für BioMolekulare Optik, LMU München — 2Institut für Organische Chemie, Universität Regensburg
Flavin is one of the most commonly used cofactors in nature where it acts as redox switch in many metabolic cycles. Flavin shows a strong optical absorption around 450 nm and therefore can be used as a photocatalyst, e.g., for the oxidation of methoxybenzyl alcohol (MBA). Using femtosecond broadband absorption spectroscopy we observe a rapid quenching of the excited singlet state of flavin in MBA via electron transfer (4 ps). By electron back transfer to the MBA (40 ps) the flavin returns to the electronic ground state. The S1 quenching competes with the intersystem crossing to the triplet state, which appears to be the reactive channel for the oxidation of MBA. A fast electron transfer therefore inhibits a high reaction quantum yield.
In acetonitrile solutions with low concentrations of flavine and MBA the quenching is slowed down significantly. The observed kinetics can be well fitted with a diffusion model: it accounts for the higher efficiency of MBA quenchers close to the excited flavin. Now the dynamics proceed on the 100 ps to ns timescale. This leads to a rising triplet formation with decreasing MBA concentration. In this way, understanding the ultrafast dynamics allows to determine the conditions for optimal photocatalysis.