Hannover 2016 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 7: Femtosecond Spectroscopy 2
MO 7.5: Vortrag
Dienstag, 1. März 2016, 12:15–12:30, f102
Quantum chemical studies of pyrene: long known molecule, new insights — •Matthias K. Roos, Teresa Küblböck, Sebastian Reiter, and Regina de Vivie-Riedle — Department Chemie, Ludwig-Maximilians-Universität München
Pyrene, an intensively studied molecule especially known for its excimers, is used today as a fluorescence marker. Yet, the microscopic mechanism accounting for its photophysics is still rather unclear. It is experimentally known that after excitation to the S2 (La) ultrafast relaxation to the S1 (Lb) occurs followed by fluorescence or excimer formation.
We studied pyrene with quantum chemical methods including TD-DFT and CASSCF in the gas phase and in solution (PCM). With this, we optimized minima for the La and Lb state and simulated absorption spectra that are in excellent agreement with the experimental ones. We also located a conical intersection between the S2 and S1 near the excited states minima enabling the ultrafast relaxation. In addition, an explanation is presented for the difference in oscillator strength between La and Lb without considering the symmetry of the molecule.
Furthermore, we investigated possible structures for the pyrene excimer. Minima are located on the S1 and S2 surface that differ in the rotation angle between the pyrene moities. Hirayama’s rule is confirmed that excimers for bridged pyrenes should exist especially for a propyl bridge. For the first time, we can present optimized structures for such bridged excimers already suggested in the literature.