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Fakultät für Physik

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(c) 2002 BMO

Mechanisms of Complex Photoreactions
(Femtochemistry - Femtobiology)

Light absorption can induce large molecular re-arrangments that often result in products difficult to access by thermal chemistry. A drastic example is the re-arrangment of the N-oxide depicted in the picture to an imidazolone which we are currently studying. Such photoreactions usually include serveral elementary processes many of them representing fundamental reaction types in organic chemistry. By triggering these reactions with femtosecond pulses these reactions can be monitored in real time. Applying femtosecond vibrational spectroscopy (IR and Raman) allows us to determine molecular structures of intermediates and thereby obtain a great wealth of mechanistic information.
In this spirit we have recently studied the photo-transformation of ortho-nitrobenzaldehyde to nitroso benzoic acid (see scheme). This reaction is prototypical for a class of photoreactions that find widespread application in protecting group chemistry. Applying various femtosecond techniques we have deviced an "evidence based" mechanism for that reaction. For instance, we could clearly identify the first intermediate of the reaction - a ketene which is formed in an ultrafast (400 fs) hydrogen transfer process. The formation of the ketene can almost literally "be seen" by an emerging IR band at 2100 cm-1 (see contour plot). The band is due to the highly characteristic stretch vibration of ketene function. The fate of this ketene and of ensueing intermediates has been studied by means of Raman and IR spectroscopy. More details can be found in a recent article in "Angewandte Chemie".


Previous coworkers:  Wolfgang Schreier
Tobias Schrader
Gerald Ryseck
Nadja Regner
Bjoern Heinz
Peter Gilch
Thorben Cordes


Publications:  "Dynamics of ultraviolet-induced DNA lesions: Dewar formation guided by pre-tension induced by the backbone"
B. P. Fingerhut, T. T. Herzog, G. Ryseck, K. Haiser, F. F. Graupner, K. Heil, P. Gilch, W. J. Schreier, T. Carell, R. de Vivie-Riedle and W. Zinth
New J. Phys. 14, 065006 (2012)
Details

"Impact of Vibrational Excitation on the Kinetics of a Nascent Ketene"
Thomas Schmierer, Wolfgang J. Schreier, Florian O. Koller, Tobias E. Schrader, Peter Gilch
Phys. Chem. Chem. Phys. 11 (2009) 11596
Details

"Excited State Processes of Nitrobenzaldehydes Probed by Ultrafast Fluorescence and Absorption Spectroscopy"
B. Heinz, T. Schmierer, S. Laimgruber, P. Gilch
J. Photochem. Photobiol. A: Chemistry, 199 (2008), 274-281
Details

"On the Mechanism of Intramolecular Sensitization of Photocleavage of the 2-(2-Nitrophenyl)propoxycarbonyl (NPPOC) Protecting Group"
Dominik Wöll, Stefan Laimgruber, Marina Galetskaya, Julia Smirnova, Wolfgang Pfleiderer, Björn Heinz, Peter Gilch, Ulrich E. Steiner
J. Am. Chem. Soc. 129 (2007) 12148
Details

"The Photochemistry of o-Nitrobenzaldehyde as Seen by Femtosecond Vibrational Spectroscopy"
Stefan Laimgruber, Wolfgang J. Schreier, Tobias Schrader, Florian Koller, Wolfgang Zinth, and
Angew. Chem. Int. Ed. 44 (2005) 7901-7904
Details

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Letzte Änderung: 2024-06-17 19:32