Stuttgart 2012 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 8: Photochemistry
MO 8.6: Vortrag
Dienstag, 13. März 2012, 11:45–12:00, V38.02
Photosensitized generation of diphenylmethyl cations — •Sebastian Thallmair1,2, Christian F. Sailer1, Johannes Ammer2, Eberhard Riedle1, and Regina de Vivie-Riedle2 — 1LS für BioMolekulare Optik, Ludwig-Maximilians-Universität München — 2Department Chemie, Ludwig-Maximilians-Universität München
Carbocations are omnipresent intermediates in organic chemistry as well as in biochemistry. Photoinduced bond cleavage of diphenylmethylphosphonium cations offers a convenient and very effective way to generate diphenylmethyl cations in both polar and moderately polar solvents. An alternative route to the direct photoexcitation is to use a photosensitizer to induce the bond cleavage. We looked at anthracene as a possible candidate.
Its low energy absorption band (λ ≈ 360 nm) is well separated energetically from the absorption bands of the precursor molecule (λ ≈ 280 nm) and therefore gives the possibility to excite anthracene selectively in the presence of diphenylmethylphosphonium cations. Ultrafast broadband transient absorption measurements deliver insight into the evolution of the photoproducts from the femto- to the microsecond timescale. We can show that carbocations are generated from the S1 state of anthracene. In contrast, the anthracene triplet seems to be unreactive.
Based on quantum chemical calculations performed for a phosphonium model system the mechanism of photosensitization will be discussed.