Berlin 2014 – scientific programme

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MO: Fachverband Molekülphysik

MO 5: Posters 1: Electronic Spectroscopy, Photochemistry, Femtosecond Spectroscopy

MO 5.14: Poster

Monday, March 17, 2014, 16:30–18:30, Spree-Palais

The role of excess energy in the ultrafast Wolff rearrangement and subsequent reactions of 5-diazo Meldrum’s acid — Andreas Steinbacher, •Sebastian Roeding, Tobias Brixner, and Patrick Nuernberger — Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg

5-Diazo Meldrum’s Acid (DMA), an α-diazocarbonyl used in photolithography, is known to show a rich wavelength-selective photochemistry upon UV irradiation [1,2]. Transient-absorption studies in the liquid phase revealed an ultrafast intramolecular Wolff rearrangement to a ketene after 267 nm excitation. For DMA in the gas phase, pyrolysis studies [3] postulate a proceeding reaction of the product ketene via a second Wolff rearrangement.

We compare the time-resolved photofragment ion signals of DMA in the gas phase for 267 nm and 200 nm pump wavelength. The probe step is performed by multiphoton ionization with an 800 nm pulse. A global fit of the ion transients with a sequential model allows us to discriminate the dynamics of the reaction intermediates. Our data identify the timescales for ketene formation and indicate a subsequent Wolff rearrangement of the ketene product for higher pump energies.
A. Bogdanova, and V. Popik, JACS 125 (2003)
P. Rudolf, J. Buback, J. Aulbach, P. Nuernberger, and T. Brixner, JACS 132 (2010).
S. L. Kammula, H. L. Tracer, P. B. Shevlin, and M. Jones, J. Org. Chem. 42 (1977).