Excited state dynamics in the strong coupling regime

Abstract

Strong exciton-photon coupling exhibits the possibility to modify photophysical and photochemical properties of organic molecules without changing their structure. This is due to the formation of hybrid light-matter states, called polaritons, which are created when the strong coupling regime is achieved. The polaritons inherit properties from both parts, light and matter, resulting in unique properties. In this thesis, the excited state dynamics of different strongly coupled systems are presented. The emission lifetime of polaritons were explored by optical spectroscopy. Their emission lifetime showed to be independent of both their excitonic/photonic constitution and the measuring angle. These findings support the theory of the exciton reservoir theory. Furthermore, the impact of strong light-matter interactions on the photoisomerization quantum yield of a photoswitch was examined. The photoisomerization quantum yield showed a dependence whether the system was excited at the lower or upper polariton and on the photonic/excitonic constitution of the polariton. When exciting the upper polariton, the quantum yield was unperturbed whereas it dropped significantly when exciting the lower polariton. Finally, the formation of aggregated states in the strong coupling regime were studied. It was observed that the emission can be controlled by simply altering the photonic and excitonic contribution to the lower polariton. A higher excimer emission was seen for samples, whose lower polariton have a higher excitonic character, whereas a higher photonic contribution resulted in an enhanced polariton emission. The deeper understanding of the excited state dynamics in the strong cou- pling regime might result in higher performances in optical applications such as TTA upconversion or singlet fission. Furthermore, the deepened knowledge can unveil the potential of the arising field of polaritonic chemistry.