Berlin 2001 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 10: Ultrafast Spectroscopy

CPP 10.1: Vortrag

Donnerstag, 5. April 2001, 15:45–16:05, 110

The mechanism of excited state intramolecular proton transfer revealed by 30 fs spectroscopy — •S. Lochbrunner, A. J. Wurzer, V. de Waele, K. Stock, J. Piel, and E. Riedle — LS BioMolekulare Optik, Sektion Physik, Ludwig-Maximilians-Universitaet Muenchen

A broad class of molecules that contain an H-chelate ring exhibits intramolecular proton transfer in the electronically excited state (ESIPT). This leads to an extremely fast and large Stokes shift, making these molecules attractive laser dyes and UV-protectors. To investigate the ESIPT process pump probe spectroscopy with an ultrahigh time resolution of 30 fs was applied to a number of proton transfer systems. It allows to observe reactive processes and the associated motions of the nuclei in real time and thereby to reveal the reaction mechanism. We found in general experimental evidence that the ESIPT proceeds as a ballistic wavepacket motion on a time scale of 50 fs independent on the molecule. Despite the reactive energy surface and the influence of the solvent the wavepacket stays quite localized leading to a strong excitation of only a restricted number of degrees of freedom. This coherent excitation causes a No-dqringingNo-dq in vibrational eigenmodes of the ESIPT product and thereby to pronounced oscillations in the signal traces. By means of their frequencies we were able to identify the skeletal modes which are involved in the ESIPT of the various systems and to deduce that characteristic deformations of the chelate ring lead to a concerted shift of the electrons and a persistent change in the electronic configuration.