Gold That Goes Invisible When Ground

This gold compound shifts its emission profile by an unprecedented 452 nm when ground, changing from fluorescent blue to infrared.

AsianScientist (Jun. 13, 2017) – Researchers have developed a gold-based compound that can dramatically change its color from fluorescent blue to invisible infrared when ground. These findings, published in Journal of the American Chemical Society, could be used in bioimaging and invisible 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.

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 that 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. Infrared emissions are invisible to the naked eye.

“This is the first time a material has been reported to make such a dramatic shift—a change of 452 nm—that also reaches into the infrared part of the light spectrum,” said Dr. Tomohiro Seki, the lead and corresponding author of the paper.

The research group’s X-ray crystallographic analyses revealed that the large shift is based on a crystalline-to-amorphous phase transition which should create strong intermolecular interactions between the gold ions.

“The development of infrared emissive materials is generally difficult, and appropriate design strategies remain limited. However, in this case, simple grinding can afford an infrared emissive material,” said Professor Hajime Ito, the corresponding author. “Infrared is invisible to the naked eye but detectable using a spectrometer. So, our material has a great potential for bioimaging and security inks.”



The article can be found at: Seki et al. (2017) Luminescent Mechanochromic 9-Anthryl Gold(I) Isocyanide Complex with an Emission Maximum at 900 nm after Mechanical Stimulation.

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Source: Hokkaido University.
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