Berlin 2001 – scientific programme
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MO: Molekülphysik
MO 3: Reactive and Energy Transfer Processes
MO 3.2: Talk
Monday, April 2, 2001, 16:00–16:15, H1058
Excited State Intramolecular Proton Transfer mechanism in 2,-(2’-hydroxy)benzothiazol (HBT) — •V. de Waele1, L. Kurtz2, R. de Vivie-Riedle2, and E. Riedle1 — 1LS BioMolekulare Optik, Sektion Physik, Ludwig-Maximilians-Universitaet Muenchen — 2Max-Planck-Institut fuer Quantenoptik, Garching
The Excited State Intramolecular Proton Transfer (ESIPT) in HBT was recently investigated in pump-probe experiments with a cross-correlation of 35 fs. Strongly oscillating signals due to vibronic wavepacket motion during and after the proton transfer were observed. The Fourier analysis allowed the identification of 4 low frequency contributions (118, 254, 289 and 529 cm−1) suggesting a proton transfer mechanism governed by skeleton motions of the chelate ring. We present an ab initio study of the structural and vibrational properties of the lowest excited state of HBT. Geometries and normal modes were computed at CIS level and the energy was corrected with the TDDFT method. The resultant energetic level scheme reproduces the experimental data. The analysis of the molecular distortions along the minimum energy path from the S1 enol form to the S1 keto form reveals that the transfer occurs via a contraction of the chelate ring : the distance between the Oxygen and the Nitrogen atoms appears to be the relevant dynamic coordinate of the process. A normal mode analysis along the S1 reaction path shows in the low frequency regime only 5 contributing modes at 116, 258, 288, 514 and 534 cm−1. The excellent agreement with the time resolved study confirms that the observed oscillations are directly connected to the reaction path of the proton transfer.