Excited-State Coordination Chemistry; A Different Quenching Encounter

Cuny Queens College, Flushing NY

Investigators

Abstract

This award in the Inorganic, Bioinorganic and Organometallic program supports research on the acid-base properties of excited-state transition metal complexes by Professor Harry Gafney of the Department of Chemistry at Queens College of the City University of New York. The work will delineate the factors which result in the formation of bimetallic complexes from monomeric components or in the formation of a dissociative excited state from a bimetallic complex that relaxes to reform the original compound. These are the factors that produce excited state acid-base chemistry rather than the more usual energy or electron-transfer reactions. The photoinduced formation and dissociation of various complexes of Ru(II) containing the bipyridyl and other ligands with trivalent Rh, Ir and Co will be examined by means of excited-state and time-resolved methods. Transient absorbtions will be identified through their spectral and kinetic characteristics, while quenching and photochemical reactivity will be correlated with excited-state energies, redox potentials and acid dissociation constants to identify the reaction mechanisms. The goal of this research is to determine how the acidic and basic properties of transition metal complexes, specifically of ruthenium, change when illuminated by light and converted into their excited states. Most of the known net photochemistry of molecules of all types involves the transfer of either energy or electrons rather than protons. The development of excited-state acid-base chemistry will open new avenues for its utilization in a variety of areas. There are potential near-term medical applications which include photodynamic therapy and radioisotope cancer treatment by means of a chemically-loaded endoscope. Both graduate and undergraduate students will be involved in this project and will learn a breath of skills in both synthetic and photochemical methods which will leave them well-prepared to pursue a variety of industrial, medical or industrial career paths.