München 2004 – scientific programme

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MO: Molekülphysik

MO 4: Femtosekundenspektroskopie: Elektrontransfer

MO 4.2: Talk

Monday, March 22, 2004, 11:15–11:30, HS 315

The ultrafast photodynamics of indole — •Tanja Bizjak¹, Prem B. Bisht², Stefan Lochbrunner¹, and Eberhard Riedle¹ — ¹Lehrstuhl für BioMolekulare Optik, Sektion Physik, Ludwig-Maximilians-Universität München — ²Physics Department, Indian Institute of Technology Madras, Chennai, India

Indole is a chromophore of many nitrogen heterocyclic biomolecules, like the essential amino acid tryptophan. We have performed femtosecond UV-visible broadband absorption studies of the photodynamics of indole in different solvents and compared the results with steady state measurements. In the nonpolar solvent cyclohexane we observe population transfer from the optically excited L_a state to the L_b state within 7 ps. In the polar solvent ethanol ultrafast state reversal is found followed by population transfer from the L_b to the L_a state within 6 ps. In water efficient photoionization is observed in addition to fluorescence. Presolvated electrons are formed together with indole radicals within our time resolution of 60 fs and are solvated further in about 350 fs. We propose an ultrafast branching between the ionization and fluorescence channel immediately after the optical excitation. Contrary to the case of solvated electrons in pure water, electrons stemming from indole do neither exhibit dielectric relaxation in the range of 1 - 2 ps nor recombination on the 100 ps time scale.