Structural control of the electronic coupling between donor and photosensitizer in molecular dyads via modification of a peripheral ligand

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Photoinduced electron transfer is a fundamental process in natural and artificial photosynthesis. Compared to natural photosynthesis, where electron transfer occurs in high yields and leads to the formation of long-lived charge separated states, the synthesis of (supra)molecular structures with specifically controlled electron transfer properties is a challenging and usually iterative process. The targeted synthesis and optimization of molecular donor-acceptor systems with tailor-made properties with respect to of an intramolecular photoinduced electron transfer requires a detailed understanding of the underlying structure-dynamics relationships and in particular the interaction between molecular structure and electronic coupling (|H_DA |^2), reorganization energy (λ) and driving force (〖-∆G〗^*), which are the central parameters for (intramolecular) electron transfer according to the semi-classical Marcus theory. The influence of molecular structure on λ and 〖-∆G〗^* is generally well understood. In contrast, the structural factors determining the electronic coupling |H_DA |^2 between a photosensitizer in the electronically excited state and a donor chemically linked to it are much less intuitive and in general it is challenging to describe the effects of different structural factors on |H_DA |^2 in photoactive transition metal complex dyads in isolation. The aim of this project is to quantitatively determine the electronic coupling |H_DA |^2 for reductive electron transfer from the donor to the photoexcited acceptor for a class of molecular dyads based on a Ru(II)-polypyridine-based photosensitizer (as acceptor) and a covalently linked electron donor. The spectroscopic-theoretical work of this project aims at the systematic deduction of structure-mechanism relationships with respect to the influence of electron transfer by structural modification of the peripheral ligands of the photosensitizers, i.e. the ligands that do not link the photoactive center with the electron donor.