This award will support the construction of a pulse-accelerated flow spectrophotometer for use in the study of rapid light-induced electron transfer reactions. This type of instrumentation allows the recording of spectra for species with lifetimes as short as 1/100,000-th of a second and the measurement of rates of reactions which occur over such a short time span, but is not yet commercially available. Nearly all light-driven energy conversion processes rely at some point on electron transfer reactions, including photosynthesis. One of the most promising schemes for the use of synthetic substances for light-driven energy conversion involves the use of molecules containing two metals. The absorption of light causes an electron to be transferred between the metal atoms to create a high energy molecule from which electrical or chemical energy may be extracted as the electron returns to its preferred location. Two new approaches are being used in this project for the direct assessment of thermal intramolecular electron transfer rates. The first of these makes use of preferential solvation to interconvert mixed-valence redox isomers of unsymmetrical binuclear metal complexes. Pulse accelerated flow spectrophotometry is being used to time-resolve the redox isomerization process. The second approach is based on light-induced (pulsed laser) metal-to-metal charge transfer in the near IR to create high energy isomers, again in mixed-valence complexes. Relaxation by electron transfer to create low energy isomers can be followed in the visible by transient absorbance spectroscopy. This project is supported in part by a Presidential Young Investigator award.
