Stuttgart 2012 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 12: Femtosecond Spectroscopy III
MO 12.6: Vortrag
Dienstag, 13. März 2012, 15:30–15:45, V38.03
Internal conversion vs. ultrafast intersystem crossing: A benchmark study on substituted cyclopenten-2-ones — •Oliver Schalk1,2, Peter Lang1, Guorong Wu2, Michael S. Schuurman2, Albert Stolow2, and Eberhard Riedle1 — 1BioMolekulare Optik, LMU, München — 2SIMS, Ottawa, Canada
Carbonyl groups are one of the most common functional groups in organic molecules. So far no systematic study exists to address their influence on excited state dynamics. Here we provide first insight using time-resolved photoelectron and transient absorption spectroscopy, as well as ab initio calculations to study the photodynamics of various substituted cyclopenten-2-ones in dependence on the solvent. We excite the molecules to the lowest ππ∗-state. Within 100 fs they reach a energetically lower nπ∗-state where the wavepacket bifurcates. Several channels are open for a rapid return to the ground state, provided by conical intersections which are similar to those found in simple polyenes, including [1,2]-hydrogen migration, pyramidalization and ring opening [1]. However, experiments show that the vast majority of molecules instead perform intersystem crossing to the triplet manifold within 1-5 ps. A likely explanation for this behavior is a tilt in the conical intersection geometry induced by the carbonyl group which makes internal conversion hardly accessible for a change of potential energy surfaces. The rate for intersystem crossing is then determined by both, the relative energetic positions of the triplet and the nπ∗-state and spin orbit couplings which depend on solvent and substitution.
[1] O. Schalk et al., J. Am. Chem. Soc. 131, 16451, (2011).