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MO: Fachverband Molekülphysik

MO 4: Femtosekundenspektroskopie II

MO 4.10: Talk

Monday, March 10, 2008, 18:45–19:00, 3G

Ultrafast Electronic and Vibrational Spectroscopy of LOV1C57S Mutant — •Alexander Weigel and Luis Perez Lustres — Institute for Chemistry, Brook-Taylor-Str. 2, 12489 Berlin

The photoactivation of Phot proteins involves two LOV-domains binding flavin mononucleotide as a chromophore. We utilized femtosecond transient absorption spectroscopy to identify the earliest events succeeding the excitation of the C57S mutant of Chlamydomonas reinhardtii LOV1 domain. In accordance with literature the excitated S₁ state was found to decay with a lifetime of ∼2 ns accompanied by a rise of the triplet state spectrum. Several additional features were observed on the shorter timescale. Directly after excitation spectral hole burning reveals the vibrational structure of the transient spectra. Rearrangement of the active site and intramolecular vibrational redistribution lead to a subsequent broadening with time constants of 100 fs and 1 ps. The time traces show pronounced oscillatory behaviour, at least six frequencies between 41 cm⁻¹ and 420 cm⁻¹ could be extracted. Two types of oscillations may be distinguished. One part bears a varying phase over the spectral bands and is clearly attributed to vibrational wavepacket motion. The rest exhibits constant phase behaviour and could stem from vibronic coupling to a nπ^* state in the vicinity of S₁. In accordance with this model an evolution with a time constant of 190 ps and a similar spectral distribution is observed. It is intended to use femtosecond stimulated resonance Raman spectroscopy to further clarify the origin of the oscillations and gain additional insight into structural rearrangements. Preliminary results are presented.