Certain polymers and glasses are known to change shape when exposed to light. This is called a piezoelectric effect, and means that piezoelectric crystals, when subjected to an externally applied voltage, can change shape by a small amount, about 0.1% of the original dimension.

Researchers in Japan have discovered organic crystals that change shape when illuminated with ultraviolet light and then return to their original form under visible light.

For this, they used a tiny rod made from the crystal that flings a far-heavier gold sphere when stimulated with light.

The crystals can go back and forth between the two different shapes up to 100 times before cracking.

The researchers, led by Masahiro Irie, a chemistry professor at Kyushu University, in Fukuoka, alternately shine ultraviolet and visible light on a rectangular crystal to make it contract and then extend back to its original length. When it bends, the rod can push a gold microparticle, which is 90 times heavier than the crystal, through a distance of 30 micrometers.

Previously, Irie invented a type of organic molecule that changes color in response to light; he first described it in the mid-1980s. While studying single crystals of these molecules, his research team found that the crystals also change shape. "We were excited to see the photo-induced shape change for the first time," Irie says.

Crystals that respond to light have advantages over those that respond to electricity, Warner adds. "Electric fields can be difficult to use in a vacuum, or with conducting materials around," he says, adding that the new materials could provide a useful alternative.

As practical applications, the crystals could be incorporated into microfluidics chips to push tiny volumes of liquid through narrow channels, instead of using voltage or pressure from external pumps.

They could also be used in next-generation switches in fiber-optic communication systems. In these systems, packets of data traveling from one point to the other go through multiple hubs where they are switched to the correct route, and are currently using light pulses converted into electrical signals for switching.

Instead, they could use microscopic mirrors to reflect the light from one optical fiber onto another, and the crystals could be used to move the mirrors.