New synthesis controls handedness in 17-ring molecular spiral

A Japanese team built a carbon-based molecular spiral with 17 consecutive benzene rings and controlled its handedness at an 98:2 enantiomeric ratio, meaning one mirror-image twist accounted for 98 parts out of 100. Nature Synthesis published the study on Oct. 14, 2026. The ratio describes stereochemical makeup, not overall yield, which the study does not provide.

What is a helicene, and why does handedness matter?

Helicenes are organic molecules made from benzene rings arranged in a spiral. Their rigid, stable helices are chiral, meaning they can exist as non-superimposable mirror images, often called left- and right-handed forms. Carbohelicenes, including the new compound, contain only carbon and hydrogen.

These molecules can emit circularly polarized luminescence, or light whose electric field rotates left or right as it travels. Because helicenes generate and manipulate that light, researchers see them as candidates for chiral optoelectronic materials. The study points to 3D displays and anti-counterfeiting inks as possible uses, though it describes neither an operating device nor a commercial ink.

Making these materials harder requires more than adding rings. Fused rings increase atomic crowding, called steric congestion, and molecular strain; extending the carbon framework sideways adds structural complexity. The central synthetic challenge is to lengthen the helix while keeping one twist strongly favored. The new work attacks both problems by controlling the order of ring closures.

How did four reactions build the 17-ring spiral?

“The two inner triyne units were configured to form less sterically crowded helicene structures, whereas the two outer units generated more sterically demanding helicene structures,” assistant professor Juntaro Nogami said. The key was sequencing.

• Build the precursor. Four triyne units—sections containing carbon-carbon triple bonds—connect through a central triphenylene carbon framework. The inner units occupy positions that permit less crowded ring formation, while the outer units create the more demanding structures. This arrangement aimed to control the reaction order and reduce interference between the growing helices.
• Close four rings. An asymmetric nickel catalyst drove four successive [2+2+2] cycloaddition reactions. In plain terms, these ring-forming reactions joined reacting sections while the catalyst helped control the molecule’s handedness.
• Lock and extend the framework. Subsequent oxidative cyclization reactions, called Scholl reactions, formed extra carbon-carbon bonds, completed the [17]helicene backbone and extended its π-conjugated system sideways. π-conjugation means that overlapping electron paths run across connected parts of the carbon structure.

The final product had an enantiomeric ratio of 98:2. Single-crystal X-ray structural analysis confirmed a helical backbone of 17 consecutive benzene rings, plus the lateral π-extension, placing it among the world’s longest helical backbones. The X-ray result establishes the molecule’s shape; it does not establish performance in a display or ink.