A diagram showing the nature of the 'popping' effect in some crystals under UV light

Turning light into motion

Singaporean researchers have described a chemical reaction in solid materials that enables microscopic crystals to spring in the air when exposed to ultraviolet light.

The achievement opens up new possibilities for research into converting light into mechanical energy, known as the photosalient effect, and could possibly result in development of innovative applications for harvesting solar energy.

“Our work validates that the so called ‘bad’ UV light from sources such as the Sun can be utilised to convert chemical reactions to drive mechanical motions with practical uses,” said Professor Jagadese J Vittal of the Department of Chemistry at the National University of Singapore who led the research.

“Knowledge and application of such behaviour is very important towards addressing the global energy crisis.”

The experiment of Professor Vittal and his team presents the first instance of the photosalient effect driven by a photochemical reaction being observed in a solid material. The team examined a series of new compounds to better understand the mechanism and tried to enhance the efficiency of the photosalient effect.

“Photoactuated movements are induced by the application of light to certain type of crystals, but they are observed to be less efficient than the biomechanical motions of plant and animal tissues,” Professor Vittal said. “In our work, we observed that the conversion of energy in the crystals may be able to mimic the motility of biological systems and provide a new way to transfer light energy into mechanical motion.”

The crystals, exposed to the UV light, spring in the air, reaching heights hundreds of times greater than their own size, virtually bursting like pop-corn exposed to heat.

The experiment found that even very weak UV light can trigger the reaction in some crystals.

Working together with their colleagues from the New York University Abu Dhabi and the Max Plank Institute for Solid State Research in Germany, the scientists discovered that the popping and disintegration of the crystals was caused by the strain generated during the photochemical reaction.

The sudden expansion during this reaction results in the release of pressure in the form of ballistic events.

The research was featured on the cover of the latest issue of the English version of German scientific journal Angewandte Chemie.

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