The research will be presented at the 228th American Chemical Society National Meeting in Philadelphia August 22-26, 2004
Supramolecular complexes created by Karen Brewer's group at Virginia Tech convert light energy (solar energy) into a fuel that can be transported, stored, and dispensed, such as hydrogen gas.
The process has been called artificial photosynthesis, says Brewer, associate professor of chemistry. "Light energy is converted to chemical energy. Solar light is of sufficient energy to split water into hydrogen and oxygen gas, but this does not happen on its own; we need a catalysts to make this reaction occur."
One major challenge is to use light to bring together the multiple electrons needed for fuel production reactions. Electrons are the negatively charged particles that surround an atom's nucleus, allowing atoms to react and form bonds.
Previous research has focused on collecting electrons using light energy. The Brewer group has gone the next step and created molecular machines that use light to bring electrons together (photoinitiated electron collection) then deliver the electrons to the fuel precursor, in this case, water, to produce hydrogen.
The researchers create a large molecular assembly called a supramolecular complex. Light signals this molecular assembly or machine to collect electrons and make them available for delivery to substrates.
Water is readily available and cheap, says Brewer, "but, so far, our compound is expensive. The goal is to make it catalytic and to couple it to oxygen production. We are working to build a supramolecular complex that will initiate the collection and movement of electrons and bonding of atoms without being destroyed in the process, so we don't have to build another molecular machine every time we want to convert water to hydrogen." Our systems do functioning catalytically but the efficiency needs to be enhanced.
Mark Elvington, a graduate student in chemistry, will present the research, "Photochemical reactivity of mixed-metal supramolecular complexes: Applications as photochemical molecular devices," at 9:30 a.m., Wednesday, Aug. 25, at Pennsylvania Convention Center room113A. Co-authors are Brewer, Elvington, and Ran Miao, also a Ph.D. student in chemistry at Virginia Tech from Fudan University.
The research is supported by the American Chemical Society Petroleum Research Fund. Learn more at http://www.
Photochemical reactivity of mixed-metal supramolecular complexes: Applications as photochemical molecular devices
Karen J. Brewer, Mark Elvington, and Ran Miao. Department of Chemistry, Virginia Tech, Blacksburg, VA 24061-0212
Mixed-metal supramolecular complexes are a promising structural motif for the construction of a wide assortment of photochemical molecular devices. Triads of the form LA-BL-Rh(III)-BL-LA can be designed to possess low lying metal to metal charge transfer (MMCT) states and function as molecular devices for photoinitiated electron collection (LA = Ru(II) or Os(II) polypyridine light absorber, BL = polyazine bridging ligand). Electrons collected in these systems localize on the central Rh core making them more easily available for delivery to substrates. Aspects of the photochemical reactivity of these complexes will be presented.