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: Researchers at Nagoya University have built a graphene nanoribbon that can switch the direction of its twist using a natural solvent. Graphene nanoribbons are thin, ribbon-shaped structures made of fused carbon rings.
Twisted or helical versions of these ribbons show promise for advanced light and electronic devices. However, until now, no graphene nanoribbon could switch its twist on demand. Scientists have worked out how to switch between right-handed and left-handed twists (chirality) by changing the solvent around the ribbon.
The discovery, published in Nature Communications, opens opportunities for new optical switches, chemical sensors and spintronic components that adapt to changing environments. Tomoyuki Ikai, lead author and professor at Nagoya University's Graduate School of Engineering, is a polymer chemist inspired by natural helical structures such as DNA and proteins. Polymers are large molecules built from many small, repeating units linked together in a chain.
Ikai had been working on ladder polymers, in which each repeating unit is locked into place and cannot freely rotate around the bond connecting it to its neighbor, unlike a typical flexible linear polymer. In 2019, Ikai and his collaborators built the first rigid, helix-shaped polymer. In 2021, they perfected a chemical method to fuse these building blocks together without flaws.
This method allowed them to build the new graphene nanoribbon. "We used the same fusion approach already used to make predictable helical ladder polymers. But instead of a stable building block, such as [6]helicene, we used [4]helicene, a four-ring unit written off as too unstable to be useful," Ikai said.
These units are difficult to control on their own because they switch chirality too quickly to hold a single-handedness. The team's method fuses these small, restless units into one long chain. Once joined, they found that a neighbor effect took hold: Each unit's twist began to match its neighbors, and long stretches of the ribbon settled into a single, shared spiral.
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