Berlin 2001 – scientific programme

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MO: Molekülphysik

MO 3: Reactive and Energy Transfer Processes

MO 3.4: Talk

Monday, April 2, 2001, 16:30–16:45, H1058

The interplay of the electronic states in excited state proton transfer systems — •T. Bizjak, K. Stock, S. Lochbrunner, and E. Riedle — LS BioMolekulare Optik, Sektion Physik, Ludwig-Maximilians-Universitaet Muenchen

Molecules exhibiting ultrafast proton transfer in the electronically excited state (ESIPT) show a strong Stokes shift which is established within typically 100 fs after excitation. This makes them attractive candidates for laser media, UV-protectors, etc.. Though the initial part of the dynamics seems to be quite similar in the various systems, the excited state life time varies within three orders of magnitude. This is thought to be the manifestation of a delicate interplay between two electronically excited states. The electronic contributions to the full ESIPT process are investigated on the model system o-hydroxybenzaldehyde. Pump probe spectroscopy with a time resolution of 30 fs was used to characterize the wavepacket motion associated with the very fast initial process. The substance solvated in cyclohexane was excited at 340 nm and changes of the sample transmission were observed at various wavelengths between 480 and 560 nm. We found a transfer time of 50 fs and signal oscillations due to coherent vibrations in skeletal modes. To identify long living signal contributions we measured the absolute fluorescence yield and its dependence on the excitation wavelength. An excited state life time of 55 ps was found which decreases with increasing excitation wavelength. The results are compared to recent experiments in the gas phase.