Mainz 2017 – scientific programme
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MO: Fachverband Molekülphysik
MO 8: Fast Intramolecular Dynamics
MO 8.7: Talk
Tuesday, March 7, 2017, 16:15–16:30, N 25
La or Lb, that is the question! – A quantum dynamical study of pyrene — •Matthias K. Roos, Sebastian Reiter, and Regina de Vivie-Riedle — Department Chemie, Ludwig-Maximilians-Universität München
Pyrene, the textbook example for the formation of excimers, is nowadays a widely used fluorescence marker, sensing molecule and building block in organic semiconductors useful for organic lightemitting diodes (OLEDs) or organic photovoltaic cells (OPV). Nonetheless, the basic mechanism behind its exceptional photophysic is not well understood.
Pyrene is excited by UV light to the S2 state, a ππ* state labeled La according to Platt’s notation. Meanwhile, S1 or Lb only has a negligible contribution to the absorption due to cancellation effects. Yet, emission occurs exclusively from the Lb state according to experiments. Therefore, an ultrafast relaxation pathway like a conical intersection between these two states must exist.
We use quantum dynamical methods to simulate this photophysical process on a two dimensional grid, built from displacement vectors between minimum structures. Therefore, we employ the Wilson G-Matrix method for the kinetic energy operator. The quantum chemical potential is dealt with a state of the art post-HF method. Couplings between excited potential energy surfaces result from diabatization. We discuss wave packet evolution, population transfer and distribution. The delay time is compared to experimental results and we talk about the implications of our simulation.