Chemists Synthesize 1,878-Carbon Hexagon | Chemical & Engineering News
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Web Date: December 1, 2014

Chemists Synthesize 1,878-Carbon Hexagon

Organic Chemistry: The 12-nm-wide hydrocarbon wheel lies flat and doesn’t collapse thanks to six supporting spokes
Department: Science & Technology
News Channels: Nano SCENE, Organic SCENE, JACS In C&EN
Keywords: macromolecules, organic solar cells, synthesis
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ORGANIC FEAT
A scanning tunneling micrograph reveals an array of 12-nm-wide hexagonal wheels. The gray overlay shows the structure of the 1,878-carbon hexagon.
Credit: J. Am. Chem. Soc.
A micrograph of large organic hexagons.
 
ORGANIC FEAT
A scanning tunneling micrograph reveals an array of 12-nm-wide hexagonal wheels. The gray overlay shows the structure of the 1,878-carbon hexagon.
Credit: J. Am. Chem. Soc.

German chemists have reinvented the wheel. They report the synthesis of a 12-nm-wide organic hexagonal wheel that has the chemical formula C1878H2682 (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja5096705).

Assembling large, flat molecular discs is tricky, says Sigurd Höger of the University of Bonn, in Germany. Molecules with hollow middles start to collapse when they reach about 5 nm wide. Höger’s group came up with a way to support larger rings by giving them spokes.

In the new 1,878-carbon molecule, the spokes radiate from a central hub like a bicycle wheel. The hub consists of a benzene ring sporting six phenyl rings. To each phenyl ring, the chemists attached an arrow-shaped piece containing a spoke and two rim segments. Both the spokes and the rims are made from linear oligo(phenylene-ethynylene-butadiynylene). The ring forms when the rim segments covalently link up. The rims and spokes are decorated with 12-carbon alkyl side chains to increase the wheel’s solubility in organic solvents.

The chemists, with the help of Bonn colleague Stefan-Sven Jester, elucidated the molecule’s overall structure and shape using scanning tunneling microscopy.

The high cost of creating C1878H2682 makes it an unlikely candidate for commercial applications, Höger says. However, he sees it as a model compound for studying light-harvesting electronics. In particular, Höger plans to use the molecular behemoth as a scaffold in organic solar cells to test fullerenes as electron acceptors in such devices. They could stack the discs into tubes and insert fullerenes into the triangular pores, allowing the fullerenes to line up so that electrons generated by other materials in the cell could easily hop from one fullerene to another and on to an electrode.

Theoretically, the scientists could lengthen the building blocks even further to make a goliath, 20-nm-wide wheel. “I would love to see it,” Höger says, but attempting it requires funding and a willing graduate student.

 
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