Dresden 2011 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 34: Photochemistry
MO 34.3: Vortrag
Freitag, 18. März 2011, 11:00–11:15, TOE 317
Ultrafast photochemical bond cleavage of diphenylmethylphosphonium cations — •Sebastian Thallmair1,2, Christian Sailer2, Benjamin Phillip Fingerhut1, Eberhard Riedle2, and Regina de Vivie-Riedle1 — 1Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstraße 11, D-81377 München, Germany — 2Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität München, Oettingenstr. 67, D-80538 München, Germany
Diphenylmethylphosphonium cations (DPM–PR3+ ) are known as one of the most effective precursors for photo-produced benzhydryl cations, which are cationic key intermediates in SN1 reactions. With a combined theoretical and experimental investigation we elucidate the mechanism of the initial ultrafast bond cleavage process of DPM–PPh3+. The calculations are performed for a model system with only two phenyl rings. It is designed to preserve the main properties of the full system, still allowing the use of highly correlated quantum chemical methods. The mechanism of the optical excitation and subsequent charge exchange which finally leads to bond cleavage of the C-P bond will be discussed.
Ultrafast broadband transient absorption measurements of DPM–PPh3+ and DPM–PMePh2+ show similar dynamics, supporting an identical mechanism. This legitimates the transfer of the theoretical results of the model system to DPM–PPh3+. The rise of the cation signal after 10 – 20 ps indicates the expected bond cleavage. The theoretically predicted initial radical formation on the sub-picosecond timescale is not confirmed yet due to the overlay of several transient signals.