Photoluminescent sensor can be re-used

Materials World magazine
18 Apr 2017

Okinawa Institute of Science and Technology (OIST) researchers have published an article reporting a new kind of sensor molecule that brightens up when the material they are incorporated into comes under heavy mechanical stress.

These light-based sensing molecules, called photoluminescent mechanophores, are not new, but currently available applications are single-use only. They typically involve a strong force – such as compressing, twisting or stretching – to break a chemical bond between two atoms or irreversibly pull apart two molecular patterns in the sensing molecule, changing the wavelength of the light emitted by the mechanophore. Once these molecules have radically changed their structure in response to this force, it is extremely difficult to return to the initial situation, so they do not work well for repeated exposure to mechanical stress.

To overcome this issue, Dr Georgy Filonenko and Prof Julia Khusnutdinova from OIST’s Coordination Chemistry and Catalysis Unit designed a photoluminescent mechanophore that retains its properties over time and repeated mechanical stress.

The researchers incorporated the stress-sensing molecule into polyurethane, then stretched the resulting material with increasing force, triggering a correspondingly brighter glow under an ultraviolet light. The reaction happens within hundreds of milliseconds, resulting in an up to two-fold increase in luminescence intensity. When the mechanical traction stops, the polymer material and the mechanophore revert to their initial position, decreasing the light readout. This allows for repeated applications of mechanical force.

‘Our material shows how a macroscopic force, as basic as stretching a flexible strand of material, can efficiently trigger microscopic changes all the way down to isolated molecules,’ Dr Filonenko said.