Design of New Ru(II) Complexes to Control Excited State Reactivity

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In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Claudia Turro of the Department of Chemistry and Biochemistry at The Ohio State University works in collaboration with Professor Kim Dunbar (Texas A&M University) and Professor Jeremy Kodanko (Wayne State University) investigate fundamental processes in inorganic photochemistry. This project seeks to understand the fundamental steps that take place on ultrafast (femtosecond to picosecond) time scales after a transition metal complex absorbs a photon of light. New ruthenium complexes are designed, synthesized and studied to determine how their excited state processes and photochemistry depend on variation in structure. Transition metal complexes studied in this research are important in applications that range from solar energy conversion to the delivery of drugs for phototherapy. This collaborative team is also well positioned to provide the highest level of education and training for students underrepresented in science.The central goal of this project is to understand the basic principles that govern the photophysical processes in ruthenium II complexes at early times, including the factors that control efficient photosubstitution and dual-activity compounds. New ruthenium complexes are designed, synthesized and studied to test theories about how variation in structure affects photochemistry and photophysics. The mechanism by which two different photoactive states are populated in these ruthenium complexes remains unknown and is counter to the rules of photochemistry developed for organic molecules. Photoinduced ligand release using ruthenium II complexes is highly dependent on the identity of both the leaving and ancillary ligands. One hypothesis being tested to explain this structural dependence is that fast population of the metal-centered ligand field state is required for ligand exchange to take place. It is yet unknown if this occurs through direct intersystem crossing from the singlet manifold or from a vibrationally hot triplet state. The basic knowledge gained regarding photoinduced ligand exchange also aids in the design of complexes that eliminate the exchange process in order to increase the lifetime of the metal-to-ligand charge transfer state. This is an important factor in solar energy conversion. The project also focuses on the design and synthesis of new complexes that release a wider range of ligands through irradiation with visible or low energy near-infrared light. Transition metal complexes studied in this research have potential applications that include solar energy conversion and phototherapy. This collaborative research provides students with training in diverse research skills.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.