Switchable graphene nanoribbon flips its twist direction using a chiral solvent

Helical GNRs have drawn interest as a route to chiral carbon materials for optical and electronic devices, but achieving a controllable, switchable twist has been an unsolved problem. [4]Helicene, a four-ring helicene unit, was considered too configurationally unstable for this purpose, since it flips its own handedness too quickly to hold a fixed twist on its own. The team took the opposite approach: rather than avoiding this instability, they built a long ladder-polymer chain entirely out of [4]helicene units, fusing them together through quantitative intramolecular multifold cyclization of a nonhelical precursor polymer. Because each subunit is mechanically coupled to its neighbors along the rigid, constrained framework, the helicity inversions of adjacent units became correlated, producing long, interconverting sequences of right- (P) and left- (M) handed [4]helicene subunits rather than random, uncorrelated flipping.

Researchers at Nagoya University have synthesized a helical graphene nanoribbon (GNR) whose handedness can be switched on demand. The team built what they call a poly[4]helicene nanoribbon, a ladder-type polymer made entirely of [4]helicene subunits, and showed that dissolving it in a chiral solvent locks the ribbon into a single, uniform spiral direction, right- or left-handed depending on which mirror-image form of the solvent is used.Helical GNRs have drawn interest as a route to chiral carbon materials for optical and electronic devices, but achieving a controllable, switchable twist has been an unsolved problem. [4]Helicene, a four-ring helicene unit, was considered too configurationally unstable for this purpose, since it flips its own handedness too quickly to hold a fixed twist on its own. The team took the opposite approach: rather than avoiding this instability, they built a long ladder-polymer chain entirely out of [4]helicene units, fusing them together through quantitative intramolecular multifold cyclization of a nonhelical precursor polymer. Because each subunit is mechanically coupled to its neighbors along the rigid, constrained framework, the helicity inversions of adjacent units became correlated, producing long, interconverting sequences of right- (P) and left- (M) handed [4]helicene subunits rather than random, uncorrelated flipping.

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