When gold turns invisible: Bioimaging and security inks applications

A gold compound shifts from a visible fluorescence to emitting infrared when ground -- a big shift with potential applications in bioimaging and security inks.

Some materials luminesce, changing their color and intensity when under mechanical forces such as grinding or rubbing. These luminescent "mechanochromic" materials can produce various emission colors in the visible light spectrum, from blue to red. Their color-shifts under force are well documented, and are caused by changes to the molecules' crystal structures.

Recently, a big shift from the visible spectrum to the infrared has been identified and described in the Journal of the American Chemical Society. Such a large change is unprecedented and is exciting because of its potential applications for bioimaging and invisible inks.

In an attempt to develop new mechanochromic compounds, a research group at Hokkaido University in Japan found a gold compound called 9-anthryl gold(I) isocyanide complex has a unique feature. In its original form, the substance produced a visible blue fluorescence with a wavelength of 448 nanometres (nm). After being ground up into a fine powder, the substance produced infrared emissions (phospholescence) with a wavelength of 900 nm. The infrared emissions are invisible to the naked eye.

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