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MO: Fachverband Molekülphysik
MO 1: Biomoleküle
MO 1.1: Hauptvortrag
Montag, 10. März 2008, 14:00–14:30, 3F
Ultrafast Dynamics of Non-Radiative Processes in Electronically Excited DNA Building Blocks — •Friedrich Temps and Nina K. Schwalb — Institut für Physikalische Chemie, Universität Kiel, D-24098 Kiel
In a thrust to shed light on the mechanisms responsible for the high UV photostability of DNA, we study the electronic relaxation dynamics of free nucleobases, selected hydrogen-bonded base pairs, and short single- and double-stranded oligonucleotides using femtosecond fluorescence spectroscopy. Recent new results concern the modified base N6N6-dimethyladenine, which shows so-called “dual fluorescence”. Time-resolved measurements after excitation at different wavelength, starting just above the electronic origin, showed that the observed red-shifted emission previously ascribed to an intramolecular charge transfer state arises virtually without time delay. By comparison with adenine, it is suggested that the optically excited state undergoes a transformation through a conical intersection to a relaxed excited state, which is responsible for the red fluorescence and may be related to the ππ∗(Lb) or the nπ∗ state. In addition, time-resolved fluorescence decay data will be reported for guanosine-cytidine (G·C) Watson-Crick base pairs in solution. The results demonstrate a strong acceleration of the radiationless electronic relaxation in G·C compared to the free monomers. Excitation wavelength and solvent dependent measurements resolved the gas vs. solution phase puzzle, where apparently different behaviors were observed. Eventually, an outlook is given on experiments on short DNA chains with different sequences.