Düsseldorf 2007 – scientific programme

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MO: Fachverband Molekülphysik

MO 24: Femtosecond Spectroscopy III

MO 24.1: Talk

Tuesday, March 20, 2007, 14:30–14:45, 6C

Transient states and kinetics in the photochromic reaction of spironaphtoxazine — •Uwe Megerle, Uli Schmidhammer, Stefan Lochbrunner, and Eberhard Riedle — Lehrstuhl für BioMolekulare Optik, LMU München

We investigated the primary photoproducts of the photochromic molecular switch spironaphtoxazine (SNO) dissolved in DMSO. The experiments were performed by UV-excitation (345 nm) transient absorption spectroscopy with a time resolution of about 100 fs. The broad spectrum of the probe-continuum (350-750 nm) allowed observing the spectral characteristics of all intermediate states. By measuring kinetic curves at numerous wavelengths we determined precise rate constants for the different steps of the photoreaction. This was supported by examining the time dependence of the absorption shift as well as the temporal increase of the transition dipole moment. The relatively high viscosity and slow relaxation times of DMSO decelerate the isomerisation step in the ring opening reaction compared to other solvents and therefore facilitate the assignment of the observed decay times. Thus the sequence of processes on both potential energy surfaces becomes much clearer than in cyclohexane and acetonitrile solutions that were investigated for comparison and can be directly compared to recent calculations [1].

[1] F. Maurel, J. Aubard, P. Millie, J.P. Dognon, M. Rajzmann, R. Guglielmetti and A. Samat, J. Phys. Chem. 110 (2006), 4759.