The molecule pentacene morphs as it gains electrons IBM Research

Some of the innermost workings of molecules are being revealed for the first time. When molecules gain an electric charge, their structure can change, and now we have watched it happen.

Shadi Fatayer and Leo Gross at IBM in Zurich and their colleagues examined four types of molecule using an atomic force microscope, which runs a tiny probe across the molecule to build an extraordinarily detailed picture of its constituent atoms and bonds.

To charge each molecule, they ran a small voltage across the probe and the surface the molecule sat on, allowing the probe to transfer electrons to the molecule one at a time. The entire experiment took place in an extremely cold vacuum chamber to make sure the molecule wasn’t moving or being disturbed by any outside forces.


“When we add or remove single electrons, we see how that changes the structure of the molecule,” says Gross. “We already knew that it happened, but we didn’t know how the structure changes exactly and that was really hard to access.”

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The four different molecules exhibited different behaviours when charged. In one compound, azobenzene, which is often used in molecular machines, the whole molecule twisted. In another, pentacene (pictured above with false colours), some areas of the molecule became more reactive because of the extra electrons.

The lengths of the bonds change in porphine

Tetracyanoquinodimethane changed the types of bonds holding its atoms together and moved on the surface it was placed on. In porphine, the lengths of the bonds changed, as did the types of bonds.

“Porphine is related to chlorophyll and haemoglobin so it’s very important in biology,” says Gross. “These molecules charging is what happens when haemoglobin transports oxygen in your body or when chlorophyll converts light into energy.”

Understanding these molecular effects better will help us use the molecules more effectively, the researchers say. “This will help us to improve our materials, to improve our devices and to improve our understanding of nature,” says Fatayer.

Journal reference: Science, DOI: 10.1126/science.aax5895