"Ultrafast Reaction Dynamics of the Complete Photo Cycle of an Indolylfulgimide Studied by Absorption, Fluorescence and Vibrational Spectroscopy
"S. Draxler, T. Brust, S. Malkmus, F. O. Koller, B. Heinz, S. Laimgruber, C. Schulz, S. Dietrich, K. Rück-Braun, W. Zinth und M. Braun
Journal of Molecular Liquids 141 (2008) 130-136
The reaction dynamics of the complete photo cycle, ring-opening (C &rarr E) and ringclosure (E &rarr C), of a N-methyl-(6-bromo-1,2-dimethyl-3-indolyl)fulgimide dissolved in acetonitrile are analysed via steady-state and ultrafast spectroscopy using transient absorption in the UV/VIS and mid-IR complemented by ultrafast fluorescence broadband spectroscopy with a Kerr-gate setup. For the C &rarr E ring-opening reaction induced by light at ~550 nm, a time constant of ~3 ps was found for the S1 decay and the S0 repopulation. Non-exponential signatures, which occur in the 10 ps time domain, were observed and are assigned to the cooling of hot molecules in the electronic ground state. The E &rarr C reaction dynamics induced by UV light pulses at 360 nm and 387 nm occur within less than 1 ps and are followed by vibrational cooling on the 10 ps time domain. Thus, both ring-opening and ring-closure reaction are completed within a few picoseconds. From transient IR studies and fluorescence measurements it is concluded that these pericyclic reactions occur from different geometries on the excited state potential energy surface.
BMO authors (in alphabetic order):
Generation of light pulses on the time scale of 5 fs