Hannover 2013 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 3: SYED: Electronic 2D Spectroscopy from Small to Large Systems I

MO 3.4: Hauptvortrag

Montag, 18. März 2013, 12:30–13:00, E 415

Coherent Two-Dimensional Electronic Spectroscopy With Triggered Exchange — •Patrick Nuernberger, Stefan Ruetzel, Martin Kullmann, Johannes Buback, and Tobias Brixner — Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

We demonstrate how diverse femtosecond spectroscopy approaches coalesce to a comprehensive understanding of the photochemical reaction pathways of a molecule. Two ring-open forms of 6,8-dinitro-1’,3’,3’-trimethylspiro[2H-1-benzopyran-2,2’-indoline] coexist in solution, differing by a cis/trans configuration of a double bond. Pump–probe transient absorption spectroscopy shows that both isomers may undergo a photo-induced ring closure, whereas coherent two-dimensional (2D) electronic spectra directly visualize that cis/trans isomerization among the isomers is a negligible reaction channel.

Via pump–repump–probe spectroscopy, the photodynamics accessible by further excitation are explored and the formation of a radical cation species is identified. By combining the benefits of pump–repump–probe with coherent 2D spectroscopy, we then introduce coherent triggered-exchange 2D (TE2D) electronic spectroscopy, so that reactants can be connected with products formed by the repump pulse after the pump sequence but before the probe event. This approach unveils that only one of the isomers is the reactant from which the radical cation is formed. TE2D electronic spectroscopy thus is a versatile tool for analyzing excited states and associated reaction pathways, with the information from where the reaction started intrinsically preserved.