Microscopes can detect the structural change in a molecule when it ‘relaxes’ after gaining an electron.

Researchers have used powerful microscopes to learn how additions and subtractions of charge, or ‘redox reactions’, affect electrons that are orbiting molecules. But researchers know less about how such reactions alter molecules’ geometric structure.

To investigate, Philipp Scheuerer at the University of Regensburg in Germany, Nikolaj Moll at IBM Research-Zurich in Rüschlikon, Switzerland, and their colleagues used an atomic-force microscope. This instrument has a probe whose tip consists of a single molecule that senses tiny atomic-scale forces. When scanned over molecules of interest, the probe evaluates their topography by measuring the attractive and repulsive forces felt by the probe’s tip.

The team first analysed the structure of a neutral molecule that consists of a copper atom at the centre of a shallow dome of nitrogen, carbon and hydrogen atoms. The researchers then injected an electron into the molecule.

Observations and computer simulations showed that, when charged, the molecular structure ‘relaxes’ and sinks toward the surface on which it sits, while the central copper atom is pushed upwards by 5 trillionths of a metre.