Tokyo researchers synthesize long light-emitting molecular spirals with controlled handedness

New synthesis strategy controls structure

Researchers led by Professor Ken Tanaka developed a stepwise assembly framework to overcome synthetic challenges. The team synthesized a pi-extended carbo[17]helicene featuring seventeen consecutive benzene rings in its backbone. Assistant Professor Juntaro Nogami explained that their precursor contained four triyne units connected through a central triphenylene framework. This design differentiated inner and outer units to control cyclization order and reduce steric interference.

Catalyst reactions build helical framework

The group utilized an asymmetric nickel catalyst to perform four successive [2+2+2] cycloaddition reactions. These reactions constructed the initial helical framework while maintaining precise control over molecular handedness. The Scholl reactions, which are subsequent oxidative cyclization processes, created extra carbon-carbon bonds to finish the backbone. Graduate student Takeshi Ichimura and Dr Futo Morita contributed to this collaborative effort between the two institutions.

High purity confirms success

The resulting molecule achieved an enantiomeric ratio of 98 to 2, demonstrating effective control over its handedness. Analysis using single-crystal X-ray structure verified that one of the world's longest helical backbones exists. The study was published in the journal Nature Synthesis on October 14, 2026. This development addresses the difficulty of extending helical backbones while maintaining precise control over chirality.