Development of Molybdenum and Tungsten Cluster Complexes for Singlet Oxygen Generation and Biological Implications

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Due to their intrinsic photophysical properties, metal iodide complexes containing [{M6I8}L6]2- clusters with M = Mo, W and six terminal ligands (L) have attracted considerable interest for their prospective applications as light-emitting devices, dye-sensitized solar cells, optical oxygen sensors, and sensitizers. Studies of our joint German-Russian consortium within this project will involve the preparation and modification of cluster compounds based on the octahedral [M6I8] cluster core with M = Mo, W, including the development of new tungsten iodide clusters, such as [M5I8] square pyramidal cluster core, [M5M´I8] mixed metal clusters, and [M5I8C] clusters with a capping non-metal atom (C). Ligand (L) substitution reactions are well-established in our research groups for octahedral [{M6I8}I6]2- clusters, to yield compounds with [{M6I8}L6]2- clusters including deviates with mixed ligands. Compounds are prepared and studied photochemically to get a deeper understanding regarding the properties of these materials emphasizing photoluminescence, and luminescence quenching under formation of singlet oxygen. The development of stable Mo and W clusters compounds, capable for singlet oxygen generation in solid state and in solution is considered important because it involves a distinguished potential of compounds under consideration, useful in biological implications but also for other benefit. The properties of cluster compounds, with in part high chemical stability (depending on the type of ligand) and their verifiable potential of exceptional high quantum yields for luminescence and singlet oxygen generation is exceptional and thus a challenge not only in preparative chemistry but also in some fields of spectroscopy, physics, and biology. The establishment of such compounds may be unique for future applications in hygiene, due to their capability of singlet oxygen generation under visuals light irradiation condition in various media (solid, solution, and in matrices). For this goal and for a deeper theoretical understanding of such compounds we develop and optimize cluster compounds and tune their properties related to several criteria, such as solubility and chemical stability in different media, photochemical stability and singlet oxygen quantum yields. We will prepare water soluble clusters, immobilized into, or on the surface of matrices, study photophysical properties, and investigate their activity in biological environments, meaning that an immobilization of cluster compounds on biocompatible matrices is important. In course of these studies we will determine, analyze and learn about external preconditions of cluster compounds, related to the (cluster to O2) energy transfer conditions for high singlet oxygen generation.