Hannover 2013 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 6: SYED: Electronic 2D Spectroscopy from Small to Large Systems II
MO 6.2: Hauptvortrag
Montag, 18. März 2013, 14:30–15:00, E 415
Ultrabroad 2D-UV spectroscopy: from coherent internal conversion in pyrene towards exciton dynamics in DNA — •Igor Pugliesi, Nils Krebs, and Eberhard Riedle — BioMolekulare Optik, LMU München
The congested absorption spectra of proteins and DNA strands pose a major limitation in the investigation of their photochemistry through pump-probe experiments. This limitation is hoped to be overcome with 2D-UV spectroscopy, which resolves both the excitation and detection frequency. In contrast to 2D-Vis, where a bandwidth up to 150 nm can be reached, experimental realizations in the UV are so far limited to about 5 nm. Here we present 2D-UV results on pyrene, a model system for photophysical relaxation, obtained with our new setup comprising 25 nm broad UV pump pulses and a super-continuum probe covering 250 - 720 nm. The pulses are wide enough to cover two vibronic bands of the S2 1B2u ← S0 electronic transition at 312 nm and clearly resolve the off-diagonal peaks between the vibronic bands. The ultrabroad supercontinuum probe visualizes the excitation dependent ultrafast 100 fs S2-S1 internal conversion and the S1 vibrational relaxation. The coherent excitation of vibrational states survives the internal conversion to the S1 state and results in wavepackets in the S1 state - as seen directly in the excited state absorption. 2D-UV is now ready for the investigation of UV absorbing chromophores ubiquitous in organic chemistry and biochemistry. In conjunction with achromatic second harmonic generation producing up to 100 nm broad UV pulses the full potential of 2D-UV spectroscopy can be reached.