11 Aug 2022

Triangulene synthesised after 70 years, carbon magnets on horizon

A crystalline nanographene with magnetic properties has been predicted theoretically since the 1950s, but until now has been unconfirmed experimentally except at extremely low temperatures.

Researchers from Osaka University and Osaka City University have synthesised and crystallised a molecule that is otherwise too unstable to fully study in the laboratory, and is a model of a revolutionary class of magnets.

Since the first reported production in 2004, researchers have been hard at work using graphene and similar carbon-based materials to revolutionise electronics, sports, and many other disciplines. Now, researchers from Japan have made a discovery that will advance the long-elusive field of nanographene magnets.

A crystalline nanographene with magnetic properties has been predicted theoretically since the 1950s, but until now has been unconfirmed experimentally except at extremely low temperatures.

Graphene is a single layer, two-dimensional sheet of carbon rings arranged in a honeycomb lattice. It exhibits efficient, long-distance charge transport and has a much higher strength than similarly thick steel.

Nanostructures of graphene have edges that exhibit magnetic and electronic properties that researchers would like to exploit. However, graphene nanosheets are difficult to prepare and it is difficult to study their zigzag edge properties. Overcoming these challenges by using a simpler, yet advanced, model system known as triangulene is something the researchers at Osaka University have aimed to address.

“Triangulene has long eluded synthesis in a crystalline form because of its uncontrolled polymerisation,” say researchers Shinobu Arikawa and Akihiro Shimizu. “We prevented this polymerization by steric protection—bulking up the molecule — and did so in a way that didn’t affect its underlying properties.”

The researchers’ triangulene derivative is stable at room temperature but must be kept in an inert atmosphere because it slowly degrades when exposed to oxygen. Nevertheless, crystallisation was possible — which has enabled confirmation of its theoretically predicted properties.

These results have important applications. Researchers can extend the long-sought synthetic procedure reported here to increase the number of carbon rings in the molecule and perform chemical syntheses of advanced forms of nanographene.

In so doing, Osaka University and Osaka City University researchers may be able to synthesise materials that are fundamental to future advanced electronics and magnets and can supplement the ubiquitous silicon.

Reference: “Synthesis and isolation of a kinetically stabilized crystalline triangulene,” Journal of the American Chemical Society.