Hannover 2010 – scientific programme

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MO: Fachverband Molekülphysik

MO 12: Photochemistry I

MO 12.1: Invited Talk

Wednesday, March 10, 2010, 10:30–11:00, F 142

Ultrafast photochemistry of fulgides: Tuning the ring-opening reaction by vibrational excess energy — •Simone Draxler, Thomas Brust, Markus Braun, and Wolfgang Zinth — Lehrstuhl für BioMolekulare Optik, LMU München

Fulgides are molecular switches that can undergo reversible structural changes upon illumination. The ring-closure is a barrierless reaction on the sub-picosecond time-scale. The ring-opening reaction proceeds via two barriers in the excited state. Its dynamics and efficiency can be altered significantly by vibrational excess energy. It was found [1] that reaction times of the ring-opening decrease and quantum yields increase with rising temperature. The reaction also becomes more efficient by introducing optical excess energy [2]. These properties are used to guide the reaction path. Therefore we investigate the ring-opening reaction in a non-equilibrium state, where the closed form is generated in a preceding ring-closure reaction. We found, that the ring-opening reaction is accelerated when the delay time to the preceding reaction is decreased. In addition a more than threefold improvement of the reaction efficiency can be achieved. We conclude, that some picoseconds after ring-closure the intramolecular vibrational redistribution is not yet completed and that different groups of vibrational modes exist, with strongly different populations. Especially the modes promoting the ring-opening reaction are highly excited and promote the reaction before vibrational relaxation is completed on a time scale of about 5 ps.

[1] S. Draxler et al., Phys. Chem. Chem. Phys. (2009) 11, 5019

[2] T. Brust et al., J. Photochem. Photobiol. A (2009) 207, 209