Professor Claudia Turro, Ohio State University.  "Excited States of Transition Metal Complexes for Applications in Solar Energy Conversion and Medicine."  

Harvard/MIT Inorganic Chemistry Seminar.

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Abstract:  Molecules that absorb visible light may use this energy provided photons to access reactions not possible from their ground electronic states. These excited state molecules can then be used for a number of applications, including sensors, energy conversion schemes, and photomedicine. The use of light to activate the action of a drug has become important as mode of cancer therapy because it is significantly less invasive and poses low levels of systemic toxicity to the patient, thus reducing undesirable side effects. Photoinduced ligand exchange has been used to release drugs with spatiotemporal control which, together with the production of ¹O₂, represent important reactions initiated by light with potential applications in photochemotherapy (PCT). These photoinduced reactions of Ru(II) and Rh₂(II,II) complexes will be presented, along with their activity towards biological targets and cancer cells. Importantly, Ru(II) complexes were recently discovered to undergo multiple photochemical pathways following activation with light, and this property was used to design new dual-action compounds. These new complexes are able to both release a medically relevant compound and to produce ¹O₂ and were shown to exhibit significant enhancement of activity stemming from their ability to induce cell death through two different, independent pathways. These new dual-action complexes provide a new platform for drug delivery and enhanced therapeutic activity upon excitation with low energy light. Our work with dirhodium(II,II) complexes for photochemotherapy and the extension to their use in photocatalysis for solar energy conversion will be discussed.

The search for renewable, clean sources of energy is critical for the future of the planet. The use of abundant sunlight to generate electricity or to efficiently and catalytically transform inexpensive simple molecules into clean fuels, such as hydrogen from water, remains a challenge. Systems for efficient conversion of sunlight into chemical fuels requires strong light absorption that is well-matched to the solar spectrum, catalysts that effect the desired transformation, followed by combining the light absorber (LA) with the catalyst (CAT) into functional LA-CAT architectures. Current LAs used in these applications typically do not absorb the entire solar spectrum efficiently from the ultraviolet, UV, to the near-IR (infrared) range, such that some fraction of photons that make up the solar spectrum are not utilized. We have developed new Rh₂(II,II) complexes that serve as dyes that absorb light strongly throughout the visible region and into the near-IR. These compounds are capable of undergoing excited state redox processes, such as the photoinduced reduction of substrates and semiconductors. In addition, complexes with longer excited state lifetimes are able to act as single-molecule photocatalysts for the production of hydrogen with red light. The role of the molecular structure and metal-metal distance on the excited state properties will be discussed.