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K: Fachverband Kurzzeit- und angewandte Laserphysik

K 7: Laser Applications II

K 7.4: Vortrag

Mittwoch, 20. März 2019, 15:00–15:20, HS 3

Transient Phototransformation of Chromone Molecules — •Katrin Oberhofer¹, Yana Fomicheva², Andrey Sergeev², Christian Brunner¹, Konstantin Levchenko³, Vadim Kiyko², Reinhard Kienberger¹, Hristo Iglev¹, and Sergey Gagarskiy² — ¹Physics-Department, Technical University of Munich, 85748 Garching, Germany — ²ITMO University, St. Petersburg, 197101 Russia — ³TsNITI Tekhnomash, Moscow, 121108 Russia

Broadband transient absorption spectroscopy is utilized to examine the photochemical transformation dynamics of chromone molecules. When exposed to UV light the studied chromone derivative transforms irreversibly from a non-luminescent form to a stable fluorescent form via a short-lived intermediate state. This process comprises breaking and subsequent new forming of chemical bonds. Fs-pump-probe spectroscopy reveals two exited state absorption bands in the visible range. Fitting the data according to a rate-equation model shows a two-step decay process for the higher energy band which can explain the proposed dynamics of the phototransformation. A first decay constant of 5 ps correlates with the typical time expected for the break of a bond. The subsequent electron relaxation into a new minimum is associated with a red-shift in the transient spectra. Further, atomic nuclei reorientation and relaxation in the excited state according to a second decay constant of 1.5 ns describe the subsequent transformation to the fluorescent final form of the molecule. These examinations are essential in consideration of applying the studied molecules in optical information recording.