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Changing colours of light

In a phenomenon known as mechanochromism, certain solid and liquid crystalline materials change their photoluminescence properties upon mechanical stimulation, such as grinding, ball-milling and crushing. Although such compounds have attracted much attention with hopes of various applications, it has heretofore been thought difficult to synthesize mechanochromic compounds with desired emission properties and behaviours as each molecule emits different colours.

A team of scientists at Hokkaido University in Japan synthesized 48 organic compounds containing gold atoms, or gold(I) isocyanide complexes—28 of which were found to be mechanochromic, emitting changing colours such as blue, green, yellow and orange upon stimulation.

With the aim of unraveling the mechanism behind the colour changes, the researchers conducted detailed analyses of the crystal structures of almost all the molecules in the studied compounds. They found various formations of molecular arrangements, which, they concluded, is key to understanding the changes in their photoluminescence properties.

Their findings could be applied to develop a sensor for detecting minute forces that occur in a several-nanometre segment in the cells—currently regarded as a difficult task. "If such a sensor is developed, it will contribute to identifying the mechanism for cellular movements and such," said the research paper's co-author Hajime Ito.

The research results were published in May in the Journal of the American Chemical Society and included in "JACS Spotlights." The article was also selected as part of the "ACS Editors' Choice" program.