Durable organic radicals

Highly reactive organic radicals, which are compounds with unpaired electrons, usually have short lifespans. Before long they are either oxidized or undergo intermolecular dimerization and lose what defined them in the first place — electrical charge.

To create a more stable organic radical and one easier to handle in the lab, graduate student Jonathan Barnes and colleagues at Northwestern University in Evanston, Illinois, and Youssry Botros, a chemist with Intel Corportation and King Andulaziz City for Sicence and Technology (KACST), Riyadh, used unpaired electrons to temporarily reduce the repulsion charge between a pair of identical tetracationic rings, each carrying four positive charges, and bring them together. They published their findings in Science.

The attractive forces of the unpaired electrons were stronger than the repelling positive forces of the molecules, locking the two molecules in a mechanical bond that lasted weeks, even in air or water. The molecule guards its unpaired electrons at the centre of the two rings. And when the compound is oxidized and the unpaired electrons lost, the mechanical bond holds its grip —preventing the positive forces from breaking the two rings apart.

"We made these rings communicate and love each other under certain conditions, and once they were mechanically interlocked, the bond could not be broken," says Barnes.

The mechanical bond stacks the two rings together, with the electrons facing inwards so they do not react with the environment. It can accept up to 8 electrons in total. It could be useful in batteries, semiconductors and electronic memory devices.

"A big goal in the field of portable electronic devices is to one day produce flexible displays that can be rolled up like a newspaper. We hope our compound can contribute to this emerging field of organic-based energy storage devices since it is such a good acceptor of electrons," says Sir Fraser Stoddart, the principal investigator of the study.

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