Darmstadt 2008 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 4: Femtosekundenspektroskopie II

MO 4.5: Vortrag

Montag, 10. März 2008, 17:30–17:45, 3G

Femtosecond Dynamics of Electron Transfer in a Neutral Organic Mixed-Valence Compound — •Markus Margraf¹, Juliane Köhler¹, Raman Maksimenka^1,2, Alexander Heckmann¹, Christoph Lambert¹, and Ingo Fischer¹ — ¹University of Würzburg, Department of Chemistry, 97074 Würzburg — ²Laboratoire Francis Perrin, CEA Saclay, F-91191 Gif-sur-Yvette Cedex

A neutral organic mixed valence compound was studied by femtosecond time-resolved transient absorption spectroscopy with the aim to gain insight into its charge-transfer dynamics upon optical excitation. The back electron transfer was investigated in five different solvents: n-hexane, toluene, dibutyl ether, methyl-tert-butyl ether (MTBE) and benzonitrile. In the pump step, the molecule was excited at 760 nm and 850 nm into the intervalence charge-transfer band. The resulting transients can be described by two time-constants. We assign one time-constant to the rearrangement of solvent molecules in the charge transfer state and the second time-constant to back-electron transfer to the electronic ground state. On the one hand we investigated the influence of the solvent polarity on the rate of back electron transfer, on the other hand the dependence on orientation of polarisation between pump- and probepulse. Back electron transfer rates range from 1.5 · 10¹² s⁻¹ in benzonitrile through 8 · 10¹¹ s⁻¹ in MTBE, around 1.6 · 10¹¹ s⁻¹ in dibutylether and toluene and to 3.8 · 10⁹ s⁻¹ in n-hexane.