Hamburg 2009 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 13: Molekülphysik Poster 1

MO 13.7: Poster

Dienstag, 3. März 2009, 16:30–19:00, VMP 8 Foyer

Competing ultrafast photo-induced ring closure and E-Z isomerization of a photochromic furylfulgide — •Ron Siewertsen, Falk Renth, and Friedrich Temps — Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, D-24098 Kiel

Fulgides and their derivates are thermally irreversible photochromic switches with high application potential. Their photochromism is based on the photo-reversible interconversion between the open (E)- and the closed (C)-isomer. The photo-induced E→C ring closure and the competing E→Z isomerization reactions of the (E)-isomer of the furylfulgide 1-[1-(2,5-dimethyl-3-furyl)-ethylidene]-2-isopropylidene succinic anhydride in n-hexane have been studied using femtosecond time-resolved spectroscopy. Transient absorption measurements after excitation at λ=335 nm provide clear evidence for an ultrafast branching into the two reaction channels within 250 fs with a (C) : (Z) product ratio of about 2 : 1. Two observed time constants for the product formation of (C) and (Z) (0.10 and 0.25 ps) suggest that both reactions proceed via distinct conical intersections. Oscillations of the transient absorption with frequencies of 64 and 114 cm⁻¹ are interpreted as excited-state vibrations during the E→Z isomerization reaction. Time-dependent DFT geometry optimizations were performed to gain insight into the involved reaction coordinates. Our results are of interest for the understanding of competing ultrafast reactions in polyatmic molecules and the ability to influence the branching by coherent control techniques.