Organic Lett. doi: 10.1021/ol801135g (2008

A super-fast colour-changing chemical has been synthesized by Jiro Abe and his colleagues at Aoyama Gakuin University in Sagamihara, Japan. The molecule is a ring system containing naphthalene groups.

When the colourless version of the molecule is zapped by ultraviolet light it changes to its green-coloured form by breaking a carbon–nitrogen bond to leave a molecule in which two electrons are left delocalized in their naphthalene rings as radicals. This change takes a fraction of a second. When the light is turned off the molecule can quickly flip back to its colourless version. This light-induced colour change can happen whether the molecule is a solid or in a solution. Photochromic materials such as this are used in light-sensitive lenses and data-storage devices.