Meet crystals that explode in light

Professor Anna Gudmundsdottir is studying photo-explosive crystals in her lab. It’s a topic that hasn’t gotten much attention from researchers, so her students are on the frontiers of discovery with every new and surprising reaction they observe.

“We’re studying what makes crystals behave when exposed to light. We can make them jump, explode or dance. They do all kinds of weird things,” Gudmundsdottir said.

She received a $550,000 grant from the National Science Foundation to examine the properties of organic azido and benzoyl peroxide crystals. Students “grow” them from organic solvents. The crystals react to light in different ways depending on the way the molecules are packed inside them.

Identifying this molecular arrangement is known as crystallography.

“It fascinates me that the same molecules can create different crystals,” UC doctoral student Fiona Wasson said.

When irradiated with light, some crystals bend at either end with the strength to lift objects hundreds of times their size. Others twist into a helix of more than 360 degrees. Others practically hop off the microscopic slide like a tiny jumping bean.

“I’m amazed by what the students have been able to do with these crystals,” Gudmundsdottir said. “We don’t yet understand a lot of it. We’re the first ones to experiment with the gas release, so the discovery makes it a lot of fun for the students.”

What causes this reaction?

Gudmundsdottir said the light prompts the crystals to expel atmospheric nitrogen trapped when the crystals form.

For his undergraduate research fellowship, UC student Ben Miller spent a semester in a lab darkroom Gudmundsdottir built for the express purpose of documenting photo-explosive reactions in crystals. Students use adjustable red lights to focus the microscope’s cameras on the tiny crystals before hitting them with a variety of LED lights.

Miller learned that the crystals that bend from light can also be manipulated with mechanical force using tiny needles and tweezers. Experimenting with them was a lot of fun, he said.

“What’s cool about it is it bends and when it snaps back, there’s no damage to the surface or anything. That’s pretty unique for crystals.” he said. “I learned a lot. Sometimes I think, ‘I know something about science that nobody else knows.’ And that’s very interesting.”

Typically, the crystals UC students grow in the lab only put on a show once before their nitrogen escapes. But other crystals can perform their bending or twisting show again and again, raising the possibility of creating light-powered muscle fibers or sensor actuators, Gudmundsdottir said.

She sees even more potential for crystals that release oxygen when activated with light. These could be used to create a safer, lightweight oxygen system for airplanes that suffer a loss of cabin pressure at altitude, she said.

Or even some day for space exploration, Wasson said.

“There is lots of light in space,” Wasson said. “It’s exciting to study this. We’re just in the first few years of exploring it.”

Featured image at top: UC doctoral student Fiona Wasson works with photoexplosive crystals in a chemistry lab. Photo/Andrew Higley/UC Marketing + Brand