Chemist Discovers New Class of Materials

Assistant Professor of Chemistry Mark Lee Jr.

Asst. Prof. Mark Lee Jr. discovered that aromatic hydrocarbons will chemically react with polyhedral boranes (green in figure below) to create a new class of highly fluorescent materials.

Jordan Yount
News Source: 
College of Arts & Science
Departments: 
Chemistry

About eight years ago, Assistant Professor of Chemistry Mark Lee Jr. was in the lab trying to make a simple ether compound from a boron-oxygen-hydrogen bond. He injected the mixture he was trying to manipulate into his lab’s new mass spectrometer and found the reaction he was trying to achieve had failed. However, Lee says he saw evidence of a chemical reaction involving boron atoms, which should not have happened because the boron should have been inert and would not usually participate in such chemical reactions. He tucked that observation away in his mind as a curiosity to be explored at some later date.

Then, about three years ago, Lee was teaching one of three sections of a huge general chemistry class—1,500 freshmen, which he calls a high-pressure, 24/7 endeavor.

“So, just to maintain my sanity, I gave myself a small research project that I could do on nights and weekends based on an observation I made eight years ago of some reactivity that should not have occurred,” Lee says. “I started this project not expecting it to turn into something big.”

Instead, his little side project led to the creation of an entirely new class of materials with widespread potential applications.  Lee’s research group focuses mainly on polyhedral boranes—a large family of man-made cluster compounds composed either of boron and hydrogen or carbon, boron, and hydrogen. He says there are hundreds of these types of compounds that do not exist in nature, and they have been around for 60 years. In fact, Lee’s doctoral adviser, Curators’ Distinguished Professor of Chemistry and Radiology M. Frederick Hawthorne discovered some of these boron clusters in 1959, but Lee says there are not many practical uses for these since they are so inert.

What Lee discovered working on his side project is that the polyhedral boranes will react with aromatic hydrocarbons such as benzene or toluene, which he says no boron chemist would have predicted.

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“The result is that these materials are highly fluorescent in solution, and fluorescence has myriad potential applications such as bio-imaging agents for use in medicine or biochemistry, organic light-emitting diodes like those in phone or television screens, sensors, low-cost solar cells, and much more,” Lee says. “My group is now expanding on the scope of this new chemistry. These new materials, which I’m referring to as “polyarylboranes,” are much broader in scope than I imagined, and now my students are expanding the scope using other clusters.”

Fluorescence is measured by quantum yield. Lee explains that materials that fluoresce are excited by a photon of light, and the likelihood that the material emits a photon of light in a fluorescence process is its quantum yield. “It’s the number of emitted photons divided by the number of absorbed photons, and that ratio can never exceed one, so a perfect quantum yield equals one,” Lee says. Some of the materials he’s experimenting with have quantum yields as high as 0.8.

Lee’s work was recently published by one the top chemistry journals in the world, Angewandte Chemie International Edition, and he is the sole author of the paper, which is highly unusual. Lee is working with MU chemistry professor Sylvia Jurisson to use these new materials for a practical application and says those results will be published soon.

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