Erlangen 2018 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 4: Photochemistry
MO 4.1: Vortrag
Montag, 5. März 2018, 14:00–14:15, PA 1.150
Impact of kilobar Pressures on Ultrafast Photoisomerization Dynamics of a Triazene and of a Thiacyanine System — •Lena Grimmelsmann1, Vitor Schuabb2, Beritan Tekin1, Roland Winter2, and Patrick Nuernberger1 — 1Physikalische Chemie II, Ruhr-Universität Bochum, 44780 Bochum — 2Physikalische Chemie I, Technische Universität Dortmund, 44227 Dortmund
Mechanisms of cis-trans photoisomerization can remarkably differ, depending on the actual molecular system and its environment. Previous liquid-phase studies at 1 bar have shown that the triazene compound berenil isomerizes via a volume-conserving bicycle-pedal motion, whereas for the thiacyanine NK88 a rotation mechanism with two competing excited-state pathways occurs. For disclosing the associated dynamics, systematic variation of the viscosity of the environment can be highly beneficial. However, if this is done by employing different solvents, the polarity of the solute’s surrounding is modified as well to a significant degree. An alternative for adjusting the viscosity is pressurizing the system, thus keeping polarity changes low. In this study, we apply femtosecond fluorescence upconversion to berenil and NK88 dissolved in 2-propanol or water under pressures of 1 to 1500 bar. For berenil, a negligible impact of the viscosity on the fluorescence dynamics is found, in agreement with the bicycle-pedal motion. By contrast, the two fluorescence lifetimes of NK88 exhibit a prolongation scaling linearly with the viscosity, and their relative amplitudes indicate a pressure-dependent branching ratio for the two accessible photoisomerization pathways.