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Surface plasmons drive single-bond chemistry

Method can be used to pinpoint reactions to a designated region within a single molecule

by Mitch Jacoby
January 23, 2022 | A version of this story appeared in Volume 100, Issue 3


A pair of micrographs and a model of a porphyrin.
Credit: J. Am. Chem. Soc.
These scanning tunneling microscope images show that one of the molecule’s four trimethylsilyl groups (bright spots) has been dislodged.

The energy of electron vibrations can be focused on a single bond in a complex molecule, selectively driving chemical reactions just at that spot, according to a study detailing the process (J. Am. Chem. Soc. 2022, DOI: 10.1021/jacs.1c11547). The method can be used to tailor-make nanoscale devices and to mediate chemical reactions that are inaccessible via standard thermal means. Surface plasmons, or collective electron vibrations, can be triggered by light interacting with nanosized structures on metal surfaces. Researchers have previously tapped this effect to drive chemical reactions. Some scientists have used scanning tunneling microscopes (STMs) to confine the plasmon to the region near the instrument tip, limiting the number of molecules energized by the plasmonic field. Linfei Li, Nan Jiang, and coworkers at the University of Illinois Chicago wondered whether plasmons could be confined to a much finer scale—to just one bond in a single molecule that has several bonds of that type. The team experimented with a copper-bound porphyrin molecule that has four equivalent trimethylsilyl (TMS) groups. They brought the STM’s silver tip extremely close (about 1.5 Å) to one of the TMS lobes, confining the plasmon until it broke the C–Si bond tethering that lobe to the molecule. Before-and-after images confirm the method’s exquisite dexterity.


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