Molecular Origami

Dr. Jeffrey Rack and apprentice Jason Malizia shape photochemical molecules

12 October 2012
By Rachel Grimm
Illustration by Paula Welling

Photochemistry, for Dr. Jeffrey Rack, is as simple as a sunflower turning its yellow head to face the eastern sun. When a morning glory unfurls its flowers at dawn or when the pupil of the human eye adjusts like a camera aperture, the absorption of light triggers a chemical reaction, resulting in a change in molecular shape and structure. These light-induced chemical reactions, though microscopic, have a profound role in nature. Everything from basic photosynthesis to the synthesis of vitamin D in the human body depends on light.

Although scientists have long understood the crucial role of these chemical reactions in nature, Rack is interested in pushing the boundaries of this natural phenomenon. This summer, he and Jason Malizia, a junior studying chemistry, tried to synthetically mimic and manipulate naturally occurring photochemical reactions. “It’s kind of [like] fooling nature. You gotta be good. That’s why so many chemists have egos,” Rack said.

But for all his talk of ego, Rack hardly seems to have one. Humble in his academic and professional successes—he was awarded the prestigious University Professor award for the 2012-2013 school year—Rack exudes enthusiasm. He talks with his hands to explain his summer research project, and he even takes down the molecular model hanging from his ceiling to provide a patient demonstration.
“When you shine light on it,” Rack explained, “the connectivity of the molecule itself changes.” In other words, the molecule has two configurations, or isomers, and scientists can flip back and forth between these two isomers by shining light of a specific wavelength on the molecule. This process is known as isomerization.

Isomerization is both “rapid and efficient,” and takes place in just a fraction of a second—mere picoseconds, to be precise. To measure this rapid reaction, Jason uses a laser spectrometer. This $500,000 instrument, one of only six in North America, functions like a time microscope, allowing Jason to observe and measure reactions that occur in extremely small units of time. Jason is curious to measure just how fast the chemical reaction occurs when light is shined on the molecule.

When isomerization occurs, Rack further explained, the molecule changes both shape and color. When enough molecules are present, this change in color is visible to the naked eye, and it can be used to identify isomers. When one molecule has two identifiable isomers, they can be used to store information.

“One of the isomers can represent the 0 state in binary information code; the other isomer can represent the 1 state . . . this is exactly how computers work,” Rack said. And while computers store information digitally, these isomers can store information molecularly.

Working under the supervision of Rack, Jason synthesizes these light-sensitive molecules and analyzes, or characterizes, their photochemical properties. Jason’s lab is red like a photographer’s dark room to limit unwanted light exposure. Jason has been working for the most part on the level of single molecules, but he hopes to eventually synthesize symmetrical molecules that can then be assembled into polymers—long strings of molecules bonded together. This summer, Jason worked to create a polymer that, like its molecular building blocks, will change shape when it interacts with light. It’s origami on the molecular level.

The more we know about light-induced chemical reactions, the more we can exploit their potential, said Rack. And for him, the possibilities are as diverse as nature itself.