Research Communications

Chemical chameleons 

Color-changing molecules could be used for sunglasses, military applications

February 8, 2009

jeffrackIn a third-floor lab in Ohio University’s Clippinger Laboratories, chemistry isn’t black and white. It’s purple, red, yellow, orange and — depending on the type of laser — even peach. 
With the support of a $315,000 grant from the National Science Foundation, an Ohio University research team is studying the ability of certain molecules to absorb light and change color at heightened speeds.

“The idea is to design molecules and materials that respond to light in specific and predictable ways,” said Associate Professor of Chemistry Jeffrey Rack, who had the idea for the research as a graduate student and started working on it in earnest when he came to the university in 2001.

To measure a molecule’s ability to absorb light, Rack and chemistry graduate student Beth Anne McClure use laser spectroscopy. After placing a sample in front of a lamp, the team excites the molecules — or raises their energy level — by hitting the sample with a laser beam. The result of the photochemical reaction is a different compound with a different color, Rack said.

“The notion of initiating substantial changes in molecules with light is very compelling,” said Rack. “Plus, things that change color are cool.”

The research focuses on a particular family of chromophores, molecules that absorb light, which Rack said could improve the effectiveness of a fashion accessory seen widely around campus —sunglasses.

Currently, the photochromic material in sunglasses — the material that absorbs the light — is also thermochromic, which means that it reacts to heat. This causes sunglasses to “fatigue,” or to stay dark, he said.

“The problem with the thermochromic effect is that if you’re sitting in a very hot room, the sunglasses would start to change color regardless of how much light is there. This would be very annoying to the person wearing them,” Rack said.

The molecule the team is investigating is not thermochromic and grows lighter in color when in darker environments to enhance visibility. This molecule could potentially be used as a next generation photochromic material, he said. The research also could have industrial and military applications for pilots who need increased visibility under certain conditions, he noted.

Where do these intriguing molecules come from? The team synthesizes, or essentially creates, the molecules in its experiments by modifying the ligands on a given atom, said McClure. Ligands are molecules that bind to a specific site on an atom.

By modifying ligands, McClure recently created a molecule that can change to one color and then back to its original color when hit with two separate beams of light.

Another molecule the team has tested can transform from a shade of peach to a shade of purple in a matter of minutes, McClure said. She added that the change in color indicates to what degree the molecule has absorbed the laser’s light.

The team has experimented with a variety of molecules capable of absorbing light roughly 200 million times faster than the flickering of a television screen, Rack said.

By Emily Hubbell

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