Tailoring of heteroleptic copper based photosensitizers and their photophysical characterization

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The sufficient and environmentally friendly supply of energy is a major challenge in this century. A promising option is given by the increased use of solar energy, which requires the design of efficient, inexpensive and sustainable photosensitizers for light harvesting. In addition, a suitable photosensitizer should possess a strong absorption in the visible, long-lived excited states, a reversible electrochemical behavior and a high stability.So far molecular photosensitizers are most often based on rare and precious metals, like iridium or ruthenium, limiting their large-scale application. The usage of complexes based on earth-abundant metals in this approach is rather unexplored. To bring such non-noble systems into practice that has to be changed. In this respect photoactive copper(I) complexes possess a great potential.Therefore, the proposed project deals with the development of tailored heteroleptic Cu(I) photosensitizers and the detailed investigation of their (triplet) excited states as well as of their charge-transfer processes. For this purpose different design strategies, e.g. the exchange of classic diphosphine ligands by heterobidentate P^N ligands or a direct connection of the diimine and the diphosphine ligand, will be applied to enhance stability and absorptivity. Furthermore, additional electron storage moieties will be introduced, which allow to affect the redox properties specifically as well as the efficiency and time constant of the photoinduced electron transfer.The newly designed Cu(I) complexes will be systematically studied by steady-state as well as time-resolved transient absorption and emission spectroscopy to elucidate the underlying structure-property relationships and to understand the nature of the excited states. This should ultimately result in synthesis guidelines, e.g. in instructions to the right choice of the ligands, the type and position of substituents and the kind of electron storage. Within an iterative process these findings will be used straight away to further improve these Cu(I) photosensitizers.Moreover, these heteroleptic Cu(I) complexes will be applied for photon upconversion processes for the first time. In consequence, the capability of these compounds to transform photons of low energy into high energy photons, which allows to use a broader range of the light in subsequent reactions, will be clarified.All in all, by the combination of synthesis, structural and spectroscopic characterization as well as application of novel photoactive Cu(I) complexes this project will establish heteroleptic copper photosensitizers as a valuable class of substances for the priority program SPP 2102. This will finally contribute to an increased utilization and conversion of sunlight as a promising and clean energy source.