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Physical Chemistry

Triangulene trapped

Elusive and reactive polybenzenoid molecule is made for the first time

by Bethany Halford
February 20, 2017 | A version of this story appeared in Volume 95, Issue 8

An atomic force microscope image of triangulene.
Credit: Nat. Nanotechnol.
This atomic force microscope image reveals triangulene on a copper surface.

Chemists have been dreaming of triangulene since the 1950s. That’s when Erich Clar, the University of Glasgow chemist considered the father of modern polycyclic aromatic chemistry, first proposed the structure for the C22H12 molecule, also known as Clar’s hydrocarbon. Despite triangulene’s even numbers of carbons and electrons, it is connected in such a manner that all of its electrons are impossible to pair up. Consequently, two electrons sit unpaired, making the molecule an extremely reactive biradical, as Clar discovered when he tried to synthesize it. Scientists at IBM Research, Zurich, and the University of Warwick now report the first synthesis and characterization of triangulene (Nat. Nanotechnol. 2017, DOI: 10.1038/nnano.2016.305). The researchers, led by IBM’s Niko Pavliček, made triangulene one molecule at a time by placing a dihydrotriangulene precursor on a copper, xenon, or NaCl surface and then using the probe tip of a combined scanning tunneling and atomic force microscope to shoot electrons at it until they knocked off two hydrogens, thereby generating triangulene. Pavliček and coworkers were surprised to discover that triangulene did not bond to the copper surface, possibly because its unpaired electrons are in π orbitals and are perpendicular to the metal surface.


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