Ultrafast reaction dynamics of the complete photo cycle of an indolylfulgimide studied by absorption, fluorescence and vibrational spectroscopy

• Published in: Journal of molecular liquids 2008-06, Vol.141 (3), p.130-136
• Main Authors: Draxler, Simone, Brust, Thomas, Malkmus, Stephan, Koller, Florian O., Heinz, Björn, Laimgruber, Stefan, Schulz, Christine, Dietrich, Steffen, Rück-Braun, Karola, Zinth, Wolfgang, Braun, Markus
• Format: Article
• Language: English
• Subjects: Fulgide; Molecular switch; Photochromism; Ultrafast dynamics
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2008.02.001

The reaction dynamics of the complete photo cycle, ring-opening (C → E) and ring-closure (E → C), of 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 broad-band spectroscopy with a Kerr-gate setup. For the C → E ring-opening reaction induced by light at ~ 550 nm, a time constant of ~ 3 ps was found for the S 1 decay and the S 0 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 → 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 reactions 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.