Intra- und Intermolekulare Dynamik pi-konjugierter Moleküle und ihrer Dimere
Zusammenfassung der Projektergebnisse
In this project we investigated the photochemistry and photophysics of isolated π-conjugated molecules that are of interest for material science and the intermolecular dynamics between such molecules. The results of this project are relevant for understanding energy- and charge-transfer processes in supramolecular assemblies considered to be building blocks for materials in light harvesting and optoelectronics. The studies were carried out on cold molecules in the gas phase to understand the intrinsic molecular processes without perturbations by solvent molecules or a crystal lattice. A distinguishing feature of the project was the close cooperation with theoretical chemistry, more specifically nonadiabatic dynamics simulations. As the experimental method we employed time-resolved photoionization, using a picosecond laser with a time resolution of around 4 ps. An imaging detector was added to the existing setup, which permits to (a) complement the mass information from ion detection in the probe step by information on the kinetic energy of the ions and (b) to record photoelectron spectra, which contributes additional information on the dynamics. For several molecules, we unraveled (1) the time scale on which energy deposited in the molecule by photoexcitation was redistributed, (2) which electronic state the energy flow ended up and (3) on what time scale the photochemical processes between two chromophores, in particular the formation of excimers, took place. Excimers are dimers that are weakly bound in the ground state, but rather strongly in the electronically excited state. The investigation of the dimers of pyrene and tetracene was in the center of the project. Pyrene is still the most important model for excimer formation, a process that might influence the properties in organic semiconductor materials, but can also be employed for sensor applications. We performed a study on isolated pyrene dimers that yielded detailed insight into the mechanism of excimer formation. The tetracene dimer on the other hand is (beside pentacene) the model to understand singlet fission, a process that is thought to increase the efficiency of light harvesting in solar cells. Our work outlines the role that excimer formation plays in singlet fission and shows that it can act as a trap for electronic excitation. In conclusion, the work has resulted in new insights in the excited-state dynamics of dimers of polycylic aromatic hydrocarbons.
Projektbezogene Publikationen (Auswahl)
-
Dynamics of Isolated 1,8-Naphthalimide and N-Methyl-1,8-naphthalimide: An Experimental and Computational Study, J. Phys. Chem. A 120, 2089 (2016)
T. Gerbich, H.-C. Schmitt, I. Fischer, R. Mitrić, J. Petersen
-
The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer, Phys. Chem. Chem. Phys. 19, 25002 (2017)
J. Hoche, H.-C. Schmitt, A. Humeniuk, I. Fischer, R. Mitric, M.I.S. Röhr
-
The excited-state structure and photophysics of isolated acenaphthylene, Chem. Phys. 515, 744 (2018)
M. Flock, M.-P. Herbert, I. Fischer
-
A time-resolved photoelectron imaging study on isolated tolane: observation of the biradicalic 1Au state, Phys. Chem. Chem. Phys. 21, 13157 (2019)
M. Flock, L. Bosse, D. Kaiser, B. Engels, I. Fischer
-
Isolated 2- hydroxypyrene and its dimer: a frequency- and time-resolved spectroscopic study, New. J. Chem. 2021
H.-C. Schmitt, I. Fischer, L. Ji, J. Merz, T. B. Marder, J. Hoche, M. I. S. Röhr, R. Mitric
