This research award in the Inorganic, Bioinorganic and Organometallic Chemistry program at NSF supports work by Professor Jeffrey Rack at Ohio University to investigate a new class of transition metal complexes that change structure and color when exposed to solar radiation (light). The emphasis of the study is the synthesis and complete characterization of photochromic ruthenium and osmium complexes, whose mode of action is associated with sulfur-to-oxygen and oxygen-to-sulfur isomerization of sulfoxide ligands bound to the metal in these chromophoric complexes. These studies will focus on discovering the kinetic and thermodynamic parameters for the action of this unique family of chromophores that utilize light to break and make bonds on a very fast timescale. Members of this new class of transition metal complexes will be employed in the fabrication of solar-driven nanoscale devices for information storage applications. Thus, both fundamental and applied aspects of this chemistry will be explored. Students associated with this project will be involved in a variety of outreach programs that engage male and female students from local area schools in chronically economically depressed Appalachia (Athens, OH).
The development of light-activated compounds and materials is important for both laboratory and industrial settings. The transduction of light energy to other forms of energy is of intrinsic interest and relevance in biology, chemistry, physics, and engineering. These molecules and these studies will reveal new strategies for the conversion of light energy into other forms of energy.
Photochromic compounds or materials are those that change color when exposed to or irradiated with light. A commonplace example are the Transitions(c) lenses that one can have in their eyeglasses for corrective vision. There is a chemical material on the lens that undergoes a chemical reaction when exposed to light, leading to a new compound that absorbs more light and appears dark. The objective of this proposal was to investigate a new class of photochromic materials and to prepare new individual samples for this class. We met these goals of the project by preparing and studying 12 new compounds. By employing laser techniques, we were able to measure how fast the reaction occurs and how the material changes color. In one paper, we described the fastest color-changing reaction by this class of materials: 85 picoseconds. Pico represents one-trillionth of a second. This represents a major advance for this project. When we started, the compounds were greater than 1000 times slower. We also discovered some very-slow and completely inactive photochromic compounds and noticed some details that allow us to identify whether or not a compound will be photochromic prior to light exposure. We are using this information to make new, more efficient and fast acting photochromic compounds. We also discovered a new and rare effect of conversion of light energy to mechanical energy. In simple terms, we have discovered materials that change shape when irradiated with light. Including this example, there are only three classes of compounds known that show this effect. Importantly, these results were employed to secure a renewal grant where we will continue these studies and make new findings. Students associated with this project have all found gainful employment or have proceeded onto their next stages of professional development. A Ph.D. student is now a postdoctoral scholar at Lawrence Berkeley National Laboratory. The other graduate students are continuing on the renewal grant. Undergraduate researchers working on this project are now either attending graduate school in chemistry (Tulane University, Indiana University, Michigan State University, Caltech, and Johns Hopkins University) or medical school (North East Ohio College of Medicine) or in pharmacology school (The Ohio State University). These students learned much about data collection and interpretation, developed presentation skills (both oral and poster) in a scientific environment, and made contacts with other professionals at local, regional and national scientific meetings. Half of the students on this project have been women, including the Ph.D. graduate. Almost all students on this project have come from Appalachian Ohio, a chronically, economically-depressed region of the United States. All of the students in my lab are first generation college students, meaning they are the first in their family to go to college. The graduate students on this project are similarly the first to obtain advanced degrees in their family.
