The ins and outs of diradical nanographene
Clar’s goblet is a polycyclic aromatic hydrocarbon with an unconventional source of magnetism. This bow tie shaped nanographene, which was predicted by Erich Clar in the 1970s, possesses an even number of carbon atoms and π-electrons, but the connectivity of the carbon atoms prohibits pairing of all electrons into π-bonds. The resulting diradical character makes the molecule very reactive and, thus, unstable under standard conditions. Mishra, Beyer and colleagues have now synthesized Clar’s goblet on a gold surface under ultra-high vacuum conditions. By means of low-temperature scanning tunnelling microscopy and spectroscopy, they have unveiled the structure of the molecule and its antiferromagnetic ground state, and controllably manipulated the radical character. The cover art is based on a scanning probe image revealing the carbon–carbon bond structure of Clar’s goblet and shows an artificial ensemble of nine molecules.
Letter by Fasel et al.; N&Vs by Melle-Franco