This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Applying pressure to luminescent organic crystals usually brings molecules closer together and weakens their fluorescence. Materials that instead brighten and undergo a large color change are rare, and clear design principles for achieving both responses in simple, rigid aromatic hydrocarbons have been lacking.
Researchers at the University of Osaka and collaborators have now found that crystals of a uniformly slender aromatic hydrocarbon become brighter under pressure while changing their fluorescence from light blue to yellow. Its emission-wavelength sensitivity was the highest reported for a molecular material to date. The work is published in the Journal of Materials Chemistry C.
The team synthesized two anthracene-substituted phenacene derivatives, a broad chrysene-based molecule and a slender phenanthrene-based molecule. Their crystals were compressed in a diamond anvil cell and examined using fluorescence spectroscopy, Raman spectroscopy and synchrotron X-ray diffraction at SPring-8, a large-scale synchrotron radiation facility. Between 0.4 and 1.4 GPa, the slender crystal became 1.7 times brighter.
By 3.5 GPa, its emission peak had shifted by 131 nm, from 458 to 589 nm, giving a sensitivity of 37.4 nm/GPa. The spectrum recovered after pressure was released, and the response was reproduced over three compression-decompression cycles. Synchrotron measurements showed that the crystal contracted by only about 3% along the molecule's long axis but by more than 10% between molecular layers.
The researchers attribute the color shift to pressure-assisted excimer-like emission between neighboring molecules. Increased packing rigidity may also suppress the nonradiative processes that normally weaken fluorescence. In contrast, the broader chrysene-based crystal simply dimmed under the same pressure range, with only a modest color shift—confirming that the molecule's slenderness, not its size, drives the enhanced and highly sensitive response.
"By choosing a slender molecule, we obtained a crystal whose brightness and color respond strongly to pressure," says corresponding author Ryusei Oketani of the University of Osaka. "We hope this work will lead to materials that make invisible forces visible through color." The findings suggest that a long, uniformly narrow molecular shape could provide a design principle for pressure-responsive light-emitting materials. With further development, such reversible color changes could help visualize forces in mechanical components and structural materials and support high-pressure gauges and anti-counterfeiting technologies.
Extract — continue reading at the source.
