Spectral color

New optical tweezers put pressure to change color

A big stumbling block in the field of photonics is that of color control. Until now, to control the color, i.e. the wavelength of light emission, researchers had to change the chemical structure of the emitter or the concentration of the solvent, all of which require direct contact. , which considerably limits their application.

“Such conditions make it impossible to quickly change color, to use it as a light source in microscopic spaces like a cell, or in closed systems where exchange is not an option,” explains Yasuyuki Tsuboi and professor at the Department of Chemistry of Osaka City University. . Using “optical tweezers”, a technology he developed in previous research, Professor Tsuboi led a team of researchers to show that it was possible to control the color of luminescence from a distance, using only the effect light pressure.

Their findings were recently published online in the German international journal Angewandte Chemie Intl.

For years, Professor Tsuboi and his colleagues have been researching technology that can capture and manipulate nanoscale and microscale materials with a laser. By exploring this “optical tweezers” technology, they discovered that when a silicon crystal with a special needle-like nanostructure, called black silicon, was immersed in a sample solution, the The optical field of the nanostructure trapped a perylene-modified polymer, causing a local concentration of the solution to increase and polymer aggregate to form.

“As the concentration of perylene increases, it forms an excited dimer complex called an excimer,” says lead author Ryota Takao. These excimers emit fluorescence which changes color depending on the degree of concentration.

This is what the research team investigated in previous trapping experiments that did not use a trapping laser. Here they discovered that as the intensity of the laser beam increased, the light pressure also increased, causing the concentration of the polymer aggregate to densify on the black silicon, and vice versa.

“We observed the color of the fluorescence emitted by the polymer aggregate changing in response to this,” says Professor Tsuboi, “with low intensities producing blue, then changing to green, yellow, yellow green, to orange as the intensity increases.” As the intensity of the laser is controlled, the color change is fully reversible and can be done remotely.

Although the research is still in its infancy, it relies on excited complexes and excitation energy transfer, which means potential applications in the ultraviolet and near-infrared regions, in addition to the visible area. The research team is currently encouraging further research in the direction of encapsulating the perylene-modified polymer solution for use as a light source in micromachine components and intracellular bioimaging.

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Materials provided by Osaka City University. Note: Content may be edited for style and length.