Stuttgart 2012 – scientific programme

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MO: Fachverband Molekülphysik

MO 13: Poster 1: Cold Molecules, Femtosecond Spectroscopy, Molecular Dynamics

MO 13.15: Poster

Tuesday, March 13, 2012, 16:30–19:00, Poster.IV

Accessing higher-lying Reaction Pathways of a Molecular Switch by Femtosecond Pump–Repump–Probe Spectroscopy — •Stefan Ruetzel, Martin Kullmann, Johannes Buback, Patrick Nuernberger, and Tobias Brixner — Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

Many photochromic compounds and their ultrafast dynamics after photoexcitation have been studied in recent years by means of femtosecond spectroscopy such as transient absorption measurements. However, the role of higher-lying excited states in these photoreactions has not been explored for many of these systems. By exploiting spectrally resolved pump–repump–probe transient absorption spectroscopy we are able to resolve the kinetics that happen after excitation to higher-lying electronic states.

Here we present pump–repump–probe data of the molecular switch 6,8-dinitro-1’,3’,3’-trimethylspiro[2H-1-benzopyran-2,2’-indoline], a photochromic system present in two ring-open isomers in solution which differ in a cis/trans configuration of a double bond. The pump pulse excites the molecule to its first electronically excited state, the second pulse is resonant with excited-state absorption, and the whitelight probe pulse allows the observation of many possible product absorptions. Our data suggests the formation of new absorbing species triggered by optical repumping of the main isomer. A detailed data analysis as well as a discussion of possible photoproducts to be formed after repumping is presented.