[Editors] MIT chemist studies how electrons behave

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT chemist studies how electrons behave

--Work could improve lights, other devices
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For Immediate Release
TUESDAY, NOV. 28, 2006
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

PHOTO, IMAGES AVAILABLE

CAMBRIDGE, Mass.--Troy Van Voorhis likes to watch how things work. 
This natural curiosity led to his current research on the behavior of 
electrons and how they function in various molecular systems, 
including artificial photosynthesis. The theories and simulations he 
and his team create may help lead to improvements in devices such as 
electronics, solar cells and lighting.

Now the MIT assistant professor of chemistry will have more 
opportunities to explore new simulations. Van Voorhis is one of 20 
promising researchers recently awarded the 2006 David and Lucile 
Packard Foundation fellowship. He will receive an unrestricted 
research grant of $625,000 over five years.

"This frees me long-term to develop methods to make reliable 
predictions about the transfer of electrons, which is the most basic 
chemical reaction," said Van Voorhis, 30. "It is difficult to 
simulate the changes in electronic structure that accompany electron 
transfer, because a reaction pushes the electrons out of equilibrium, 
and current techniques for describing this are not adequate."

Van Voorhis and his team are developing methods and computer software 
that can simulate what happens when a dot in a light-emitting diode 
(LED) of a computer display turns on. In the case of an optical LED, 
positive and negative charges are strongly attracted to one another 
and become trapped. The unusual rules of quantum physics dictate that 
the charges can only recombine to emit light if they are spinning in 
opposite directions. As a result, typically only 25 percent of the 
trapped charges produce light; the other 75 percent of the charges 
spin in the same direction and are essentially wasted.

Van Voorhis and his colleagues have developed a computer program that 
simulates how these coupled spinning charges are nudged to react and 
thus emit light. The simulations indicate that the emission will 
increase if some of the charges spinning in one direction can be 
turned into charges spinning in the opposite direction and then form 
stable pairs.

"This situation could be selectively created in optical LEDs to 
improve the efficiency of a device such as a display," he said.

There are also potential applications of these visualization 
techniques to electronic devices, pharmaceuticals, energy and other 
fields, but they still are far off in the future.

Another big challenge being tackled by the Van Voorhis group is 
understanding and simulating the process of photosynthesis. In plant 
photosynthesis, light reacts with carbon dioxide and water to produce 
sugar and oxygen, which humans can later burn to produce energy. The 
knowledge of how to artificially mimic a process like photosynthesis 
could help scientists figure out a way to efficiently store solar 
energy in molecules that last for long periods.

The challenge is that the bonds being broken in any photosynthetic 
process are very strong. By breaking these strong bonds and forming 
weaker ones, molecules with higher energy are created. These 
molecules store the energy harvested from sunlight, and this energy 
is later released when the high-energy molecules are burned. However, 
current methods for artificial photosynthesis waste too much energy 
in breaking the strong bonds. Van Voorhis hopes to understand how to 
break bonds more efficiently so that a larger portion of the valuable 
energy is stored in the product molecules.

"We only have a partial knowledge of what is going on in 
photosynthesis," Van Voorhis said. "If you don't know exactly how 
something works, you don't know how to improve it."

To improve this state of affairs, his lab has been studying how 
electrons create and destroy chemical bonds. The new funding from the 
Packard Fellowship will allow him to move to the next step and start 
researching how to get light to turn into energy that won't escape as 
heat.

http://web.mit.edu/newsoffice/2006/vanvoorhis.html

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