The new polymer detailed in a the Chemical Communications journal under the title “Highly sensitive mechano-controlled luminescence in polymer films modified by dynamic CuI-based cross-linkers” consists of polybutylacrylate integrating copper complexes (where copper atoms are linked to organic molecules). The paper reports that the copper complexes are acting as a mechanophore within the polymer. When the polymer is
stretched under ultraviolet light, the copper complexes glow at a greater intensity than without the mechanical stress.
What the researchers observed, is that the copper complexes changed shape continuously, but as the complexes increased in size, they became less flexible and gave off a brighter glow. The team surmised that the larger, less flexible complexes were able to release light more efficiently because their motion was restricted, causing them to lose less energy than the smaller, more freely moving complexes. They then exploited this relationship between flexibility and brightness to create a stress-detecting polymer.
“When the copper complexes are incorporated into the polymer as cross-links, the act of stretching the polymer also reduces the flexibility of the molecules,” researcher Ayumu Karimata said. “This causes the copper complexes to luminesce more efficiently with greater intensity.”
The copper mechanophores developed by the OIST team are sensitive to smaller stresses than mechanophores made from organic compounds, which change colour or emit light when mechanical stress breaks a weak chemical bond.