Strong exciton-photon and exciton-exciton coupling and its effects on molecular photophysics

Abstract

The energy of molecular states and their transition dynamics form the key properties to understand the photophysics of organic molecules. Strong exciton-photon and exciton-exciton couplings enable the possibility to manipulate these properties without changing the chemical structures. This is due to the formation of new energy states. Furthermore, the transition dynamics between the new-generated and original molecular states need to be considered. This dissertation describes the preparation, characterization and simulation of strongly coupled systems and their use for studying molecular photophysical properties. An energy-inverted singlet-triplet system was achieved by strong exciton-photon coupling. This opens up a new pathway to allow a barrier-free reverse intersystem crossing in organic dyes. In addition, the manipulation of excimer emission by strong exciton-photon coupling was analyzed. It was found that the ratio of the intensity of polaritonic and excimer emission depended on the detuning between the molecular and photonic contributions of the hybrid light-matter state, as well as the energy position of that state. Finally, a strongly exciton-exciton coupled system was realized through the formation of J-aggregates. In the aggregates, the exciton delocalization counteracted the energy gap law and led to an innovative strategy for generating highly emissive dyes in the near-infrared regime. The research results and analysis in this thesis contribute to a deeper understanding of the fundamental molecular photophysics in the strong exciton-photon and exciton-exciton coupling regimes. This paves the way for many potential future applications, such as light emitting devices and photothermal therapies.