Flying colours

Researchers in Japan claim to have developed a new photochromic material that changes colour thousands of times faster than conventional materials when exposed to light.

Jiro Abe and colleagues at Aoyama Gakuin University note that photochromic materials are most familiar as the invisible layers found in the lenses of many high-end sunglasses, which change colour when exposed to sunlight.

For years, researchers have explored the possibility of using these unusual materials for optical data storage in computers and as 'molecular switches' for more controlled drug delivery.

But conventional photochromic materials tend to be relatively slow-acting (tens of seconds to hours) and unstable, which prevents their use in many applications.

The material developed by the Japanese scientists is unique in that it shows instantaneous colouration on exposure to ultraviolet light and its disappearance within tens of milliseconds when the light is turned off.

The decolouration speed is thousands of times faster than conventional materials.