Solar photochemistry

INOR 354

J. L. Dempsey, qjillian@caltech.edu, Jay R. Winkler, and H. B. Gray, hbgray@caltech.edu. Beckman Institute, California Institute of Technology, Pasadena, CA 91125
Many research groups have taken up the 21st century grand challenge of finding efficient and economical ways of storing solar energy in chemical bonds. A major goal is to extract protons and electrons from water using solar driven molecular machines that work as well or better than natural photosystems. Lessons learned about the control of electron tunneling and hopping through proteins and other molecules are aiding the design of sensitizer-modified molecular assemblies that incorporate binding sites for catalysts that can generate hydrogen fuel from sunlight and water. Cobalt(II) macrocycles capable of catalyzing the evolution of dihydrogen are being investigated as part of this program. In work thus far, we have found that photochemically generated cobalt(I) likely adds a proton to give a cobalt(III) hydride that can react further to produce dihydrogen. We are employing laser flash-quench methods coupled with time-resolved spectroscopic monitoring to map out the key steps in these and related redox catalytic cycles.