Mainz 2017 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 10: Highly Excited Molecules and Clusters

MO 10.7: Vortrag

Mittwoch, 8. März 2017, 16:15–16:30, N 6

Time-resolved Photoionisation of the S2 (ππ*) State of Xanthone — •Marco Flock, Hans-Christian Schmitt, and Ingo Fischer — Julius-Maximilians University of Würzburg, Institute of Physical and Theoretical Chemistry, Am Hubland, 97074 Würzburg, Germany

Previous studies on Fluorenone, NDCA and Naphthalimide showed, that relaxation processes in such aromatic heterocycles are determined by a competition between internal conversion (IC) and intersystem crossing (ISC). Which relaxation pathway is preferred depends strongly on the vibrational levels of the excited states. As a further representative of the group of aromatic heterocycles, we investigated the excited state dynamics of the S2 (ππ*) state of Xanthon. In a jet-cooled photoionization experiment, we resolved the vibronic properties of this state and found a defined structure with well-resolved vibronic bands. In time-resolved experiments, we found a depopulation of the S2 state with two time constants τ(1) < 1 ps and τ2 = 24 ps followed by a constant signal offset, which occurs from the population of the long-lived T1 (nπ*) state. Thus, two relaxation pathways can be mentioned. In a first model, IC to the S1 (nπ*) state followed by an ISC process to the T1 (nπ*) state could take place. In another model, the first time constant belongs to a fast ISC process to the T2 (ππ*) state, whereas the slower time constant represents a following IC process to the long-lived T1 (nπ*) state. In both models, El-Sayed forbidden ISC processes may take place.