Berlin 2001 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 10: Ultrafast Spectroscopy
CPP 10.4: Talk
Thursday, April 5, 2001, 16:45–17:05, 110
The primary dynamics of the photochromic switch Dihydroazulene — •U. Schmidhammer1, M. Beutter1, V. de Waele1, E. Riedle1, Th. Mrozek2, and J. Daub2 — 1LS BioMolekulare Optik, Sektion Physik, Ludwig-Maximilians-Universitaet — 2Institut fuer Organische Chemie, Universitaet Regensburg
We investigated the primary dynamics of the photochromic switching process from dihydroazulenes (DHA) to vinylheptafulvenes (VHF) with 40 fs temporal resolution. For 2-(4-cyanophenyl)-1,1(8aH)-azulenedicarbonitrile we found that this process takes place in three steps. It starts with an extremely fast (70-200 fs) first process that we ascribe to charge transfer in the excited DHA. Within 1-2 ps the weak bond in the five-membered ring of the azulene moiety is broken to form s-cis-VHF*. Finally the molecule relaxes within 10-15 ps to the electronic ground state and simultaneously isomerizes to s-trans-VHF. The return to the ground state was clearly identified by probing with a pulse in the near infrared. Measurements were also performed with a DHA made configurational rigid by extra bridging and with a biphotochromic DHA that allows reversible multifold switching. Pronounced oscillations on all signals are due to vibrational wavepacket dynamics which characterize the molecular modes involved in the skeletal motions during the beginning of the switching process. The analysis of all these data will lead to a detailed microscopic understanding of the underlying reaction mechanism.