Berlin 2005 – scientific programme

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MO: Molekülphysik

MO 43: Ultrafast Processes

MO 43.8: Talk

Tuesday, March 8, 2005, 18:15–18:30, HU 2091

Ultrafast Infrared Spectroscopy of the Ring Opening Reaction of CN-Dihydroazulene — •Tobias Schrader, Uli Schmidhammer, Wolfgang Schreier, Florian Koller, Arne Sieg, and Eberhard Riedle — LS für BioMolekulare Optik, Ludwig-Maximilians-Universität München

Ultrafast molecular switches offer a large potential in the field of opto-electronics. A promising candidate is the photochromic compound 1,1-dicyano-2-(4-cyanophenyl)-1,8a-dihydroazulene (CN-DHA). Upon excitation with UV light it undergoes a ring opening reaction to its vinylheptafulvene (CN-VHF) isomer. We report on the first UV pump, mid IR probe experiments of the ultrafast reaction dynamics and compare it to existing UV pump, visible probe data [1]. The IR experiments were performed in acetonitrile-d3 at probe wavelengths between 1400 cm⁻¹ and 1570 cm⁻¹ with a time resolution of 200 fs. We observe strong excited state absorption (ESA) that shows some variations at early times which are indicative of the previously concluded excited state ring opening [1]. The ESA decays with a time constant of 13 ps that corresponds to the return to the electronic ground state. Slower contributions to the signal are likely linked to the cis-trans isomerisation of VHF. The results are interpreted with the help of high level quantum chemical calculations.

[1] V. De Waele, M. Beutter, U. Schmidhammer, E. Riedle and J. Daub, Chem. Phys. Lett. 390 (2004) 328.