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The University of Tsukuba successfully synthesizes a helical conductive polymer with circular polarization activity in response to magnetic fields


A research group consisting of Graduate Student Kyoka Komaba and Associate Professor Hiromasa Goto from the Institute of Pure and Applied Sciences at the University of Tsukuba, and Professor Reiji Kumai from the Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK) announced that they have synthesized a helical, magnetically active conductive polymer with exceptionally high optical activity using immunosuppressant cyclosporin A as a helix-inducing agent. This conductive polymer exhibited distinct absorption of circularly polarized light in the same or in the opposite direction of the magnetic field. The results were published in The Journal of Physical Chemistry on February 20.

Molecular structure of the organic conductive polymers obtained in the study.
(a) Fingerprint patterns characteristic of helical conductive polymers imprinted from cholesteric liquid crystals, confirmed by polarizing optical microscopy.
(b) Molecular structure imprinted from synchrotron XRD results.
Provided by Hiromasa Goto, the University of Tsukuba

In the field of semiconductors, expectations are rising for spintronics as a technology for expediting communication. Specifically, spintronics is a technology that manipulates electronic devices by controlling spin (electron rotation) which produces magnetic field. The research group has succeeded to date in synthesizing various conductive polymers that copy the structure of materials with helical spin arrangement. The selection of the substance that induces the helical structure was known to be important in the design of these molecules.

In these developments, the research group investigated the synthesis of conductive polymers using cyclosporin A, which is known as an immunosuppressant with a helical structure. It is composed of amino acids but can also be dissolved in organic solvents. A small amount of cyclosporin A is dissolved in 5CB (a major liquid crystal material used in liquid crystal displays, etc.). Cholesteric liquid crystals are optically active substances with chirality that exhibit light reflection (selective reflection) due to their helical structure. A conductive polymer film was electrochemically synthesized using this liquid crystal as a reaction solvent and 2,7-di(2-furyl)fluorene as a monomer. A helical structure with twisting biased in one direction was formed, resulting in an optically active conductive polymer that polarizes light in a specific direction. Synthesis using ordinary organic solvents results in an optically inactive conductive polymer with molecular chains extending in random directions.

The microstructure of this conductive polymer was investigated by X-ray diffraction using synchrotron radiation at the Photon Factory of the High Energy Accelerator Research Organization (KEK). Results showed that the polymer has the same structure as the helical liquid crystal used as the reaction solvent. Although this conductive polymer is not a liquid crystal, it was found that it has the molecular arrangement of a liquid crystal. Furthermore, circularly polarized photoelectron resonance was measured to investigate its properties as a magnetic material.

Anisotropy in microwave absorption was observed when the material was irradiated with circularly polarized microwaves from different directions while applying a magnetic field in one direction. Differences in microwave absorption relative to the magnetic field were observed in a conductive polymer for the first time. There have been no reports of conductive polymers in the spintronics field, and this is the first step toward polymer spintronics. In the future, the research group plans to combine conductive polymers and magnetically active organic polymers with chirality to develop spintronic plastic materials that can be used in applications different from those of semiconductors and metals.

Goto said, "Conductive polymers are evolving into photoactive materials that use optical activity and luminescence. This research is the result of exploring new perspectives on magnetically active polymers and may lead the way to polymer spintronics. In the future, we will further study the magnetism of polymers, which will lead to the development of polymer spintronic devices."

Journal Information
Publication: The Journal of Physical Chemistry
Title: Optically Electroactive Polymer Synthesized in a Liquid Crystal with Cyclosporin A─Circularly Polarized Electron Spin Resonance
DOI: 10.1021/acs.jpcb.3c07375

This article has been translated by JST with permission from The Science News Ltd. ( Unauthorized reproduction of the article and photographs is prohibited.

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