Control of Excited State Dynamics of Ru(II) Complexes for Dual Activity

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In this project, funded by the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Claudia Turro of the Department of Chemistry and Biochemistry at Ohio State University, in collaboration with Kim Dunbar at Texas A&M University and Jeremy Kodanko at Wayne State University, aims at understanding the steps that take place after a transition metal complex absorbs a photon of light at very early times--in the femtosecond to picosecond domain. Applications of these metal complexes include solar energy conversion and the delivery of drugs for photodynamic therapy. The project will also focus on the design of new complexes that release a wider range of ligands, especially those that coordinate strongly, through irradiation with low energy visible to near-infrared light. One major goal is the investigation of complexes that exhibit dual-reactivity. The basic knowledge gained regarding photoinduced ligand exchange will aid in the design of complexes that require the ligand exchange process to be eliminated in order to increase the lifetime of the triplet metal-to-ligand charge transfer (3MLCT) state, a factor important in solar energy conversion. This collaborative team is also well positioned to provide the highest level of education and training for students underrepresented in science. The major goal of this project is to understand the basic principles governing photophysical processes in Ru(II) complexes at early times. Focus is on the factors that control efficient photosubstitution, as well as dual-activity compounds. These substances generate cytotoxic singlet oxygen and also undergo ligand exchange. The mechanism by which two different photoactive states are populated in these complexes remains unknown and is counter to the rules of photochemistry developed for organic molecules. In addition, photoinduced drug release using Ru(II) complexes is highly dependent on the identity of both the leaving and ancillary ligands, a point that will be investigated. It is hypothesized that fast population of the metal-centered triplet ligand field (3LF) state is required for ligand exchange to take place, but it is yet unknown if ligand exchange also occurs directly from the lowest-energy 3MLCT (triplet metal-to-ligand charge transfer) state. The basic knowledge gained regarding photoinduced ligand exchange will aid in the design or complexes that require the ligand exchange process to be eliminated in order to increase the lifetime of the 3MLCT state, a factor important in solar energy conversion. The proposed research includes electronic and vibrational ultrafast spectroscopic studies, as well as the synthesis of new complexes for improved ligand dissociation and for dual action.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.