Multi-Exciton Dynamics in Molecular Nano-Hybrid Systems

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It is of ongoing interest to uncover details of energy transfer processes in molecular systems. The technological importance of electronic excitation energy transfer in photovoltaic cells or light emitting diodes represents one reason for this tendency. Novel phenomena like multiple exciton generation, exciton fission and fusion as well as hybrid state formation with plasmon excitations of metal nano-structures or microcavity photons constitutes another reason. In order to explore such novel phenomena the particular regime of stronger optical excitation where different molecules are excited simultaneously will be in the focus of theoretical project work.Therefore, we will utilize and further develop a many-electron theory to study the photoinduced response of a single molecule or a molecular dimer. Different wave function based methods shall be applied. Turning to larger molecular complexes a multi-exciton approach will be introduced and nonlinear kinetic equations will be derived. With that ultrafast photoinduced processes of excitation energy transfer shall be studied where higher excited molecular electronic states become populated (mainly in systems of perylen or para-sexiphenyl molecules). A microscopic description of a multitude of nonlinear and partially coherent energy transfer processes shall be achieved, in particular in their dependence on intensity and duration of optical excitation and beyond the regime of standard exciton-exciton annihilation. Concerning the molecular dimer the benchmark computations within the many-electron approach are used to validate the importance of those results obtained with the multi-exciton description for the same system. Further-on, energies and coupling matrix elements needed for the multi-exciton theory are offered. To bridge the gap between the formal derivation of kinetic equations and spectroscopic experiments we will calculate, for example, emission and transient absorption spectra.Besides the study of isolated molecular complexes we will also account for effects of plasmon excitations of metal nano-particles placed in the vicinity of the molecules. A particular control of the multi-exciton dynamics shall be demonstrated. A step into a novel research area will be the consideration of molecular systems placed in a microcavity. Following suggestions from literature we will investigate the formation of new regimes of cavity photon assisted excitation energy transfer among the molecules.