München 2004 – scientific programme

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MO: Molekülphysik

MO 15: Femtosekundenspektroskopie: Photoelektronen + Isomerisierung

MO 15.6: Talk

Tuesday, March 23, 2004, 17:45–18:00, HS 315

Excited state dynamics of trans- and cis-azobenzene after UV excitation in the π π^* band: Isomerization in the S₁ state — •Markus Braun, Christopher Root, and Helmut Satzger — Ludwig-Maximilians-Universität München, Lehrstuhl für BioMolekulare Optik, Oettingenstraße 67, 80538 München

In azobenzene, two benzene rings are connected via two double bonded nitrogen atoms (azo group, N=N). The molecule has two isomers, the thermally stable trans- and the metastable cis-form. They can be interchanged by optical excitation with light at suitable wavelengths with a time constant of the isomerisation reaction in the sub-ps to ps range. Transient absorption measurements on cis- and trans-azobenzene after UV excitation in the π π^*-band are presented and compared to data obtained after VIS excitation in the n π^*-band. The data show a two-step process, where after a fast motion on the S₂ potential energy surface, the molecule relaxes to the S₁-state and in both cases (trans → cis and cis → trans) the isomerization reaction takes place on the S₁ potential energy surface.