Atomic manipulation has been used to create the most complex molecule ever assembled using this technique. The structure is a molecular wire with a carbon backbone that was manipulated to have as many as eight triple bonds. This new approach to making molecular wires could aid the fabrication of carbon nanoribbons and molecular electronics.
Atomic force microscopy (AFM) allows researchers to mechanically ‘feel’ the contours of single molecules on surfaces and thereby record images of their shapes. Scanning tunnelling microscopy (STM) enables similar imaging feats using the tunnel effect which depends on the variations in very small distances between probe and surface. As the STM requires application of a voltage, it can also serve to add or remove electrons from the molecule being studied, and thereby trigger a reaction. The progress of the reaction can then be monitored in structural terms by AFM which can make use of the same setup.
This new approach of triggering reactions by applying voltages to specific atoms was pioneered synthetically in 2016 by Leo Gross at IBM Zurich, where both STM and AFM were invented a generation earlier. Together with Diego Peña and colleagues from the University of Santiago de Compostela in Spain, the IBM group focused on Bergmann cyclisation, a reversible interconversion between an anthracene-like triple ring diradical and a version where two of the rings are merged into one that includes two carbon–carbon triple bonds and thus represents a cyclic diyne. The diyne is a promising prodrug that can potentially be used to form the highly potent and reactive diradical in the body.
Using targeted voltage pulses administered through an STM tip, the Zurich researchers could convert a dibromo derivative of the triple ring molecule into the diradical, then into the cyclic diyne, and back to the diradical, each time monitoring the structural changes by AFM.1
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