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

In this project funded by the Chemical Mechanism, Function and Properties Program of the Chemistry Division, Professor Claudia Turro of the Department of Chemistry and Biochemistry at The Ohio State University, in collaboration with Professor Jeremy Kodanko at Wayne State University, aims at understanding the steps that take place at very early times (femtosecond to picosecond) after a transition metal complex absorbs a photon of light. These ruthenium complexes are important in applications that include solar energy conversion and the delivery of drugs for phototherapy. The project will also focus on the design of new transition metal complexes that release a wider range of ligands, especially those that coordinate strongly, with visible or low energy near-IR light. These systems can have potential applications in drug delivery. The investigation of complexes that exhibit dual-reactivity will be a major goal of the proposed work. The basic knowledge gained regarding photoinduced ligand exchange will also aid in the design or complexes that require the ligand exchange process to be eliminated in order to increase the lifetime of the 3MLCT (triplet metal-to-ligand charge transfer) state, an important factor 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 focus of this collaborative project is to understand the basic principles that govern the photophysical processes in Ru(II) complexes at early times, including the factors that control efficient photosubstitution. Focus is on dual-activity compounds which generate cytotoxic singlet oxygen and simultaneously 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, the 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 3LF (triplet ligand field) 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 state. The basic knowledge gained regarding photoinduced ligand exchange will also aid in the design of 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 work includes ultrafast studies, electronic and vibrational, 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.