A scientist from the Faculty of Pure and Applied Sciences at Tsukuba University developed a method for producing electrically conductive polymers that assume a helical configuration. Using a liquid crystal as a template, he was able to produce optically active polymers that can convert light into a circular polarization. This approach can help reduce the cost of smart screens.
Going into an electronics store these days can be an overwhelming experience if you walk down the aisle of the TV. TV sizes have expanded significantly in recent years, while prices have dropped. This is mainly due to the adoption of organic light emitting devices (OLEDs), which are carbon-based polymers that can shine at adjustable optical wavelengths. These conjugated polymers, which have alternating single and double bonds, are electrically conductive and have colors that can be controlled by chemical doping with other molecules. Its oxidation state can also be changed quickly by an electrical voltage, which affects its coloration. However, future advances may require new materials that can take advantage of other types of optical properties, such as circular polarization.
Now, a researcher at Tsukuba University has introduced a technique for creating blocked polymers in a helical configuration, using a sacrificial liquid crystal template. “Polymers that have optical activity and luminescent function can emit circularly polarized light,” says author Hiromasa Goto. For this process, the liquid crystal molecules were originally in a straight configuration. The addition of monomer molecules caused the liquid crystals to twist into a helical configuration. This imprints a “chirality” or handedness on the structure, making it clockwise or counterclockwise. An electrical voltage was applied which caused the monomers to polymerize. The liquid crystal template was then removed, leaving a frozen polymer helically shaped. By breaking the symmetry of the mirror, the polymer has the ability to convert linearly polarized light into a circular polarization. Polymer furan rings not only contribute to the electrical conductivity, but also help to stabilize the helical structure. “Pine stacking interactions between the rings allow the polymer to aggregate into a highly ordered chiral system,” says Professor Goto. The resulting polymer was tested by circular dichroism absorption spectroscopy and found to have strong optical activity at visible wavelengths. Future applications of this process may include cheaper and more energy efficient electronic displays.
This work was supported by the Japan Society for the Advancement of Science (JSPS), grants for scientific research (magnetic properties of magnetoptically active helical polymers, No. 20K05626).
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