Selectivity in single-molecule reactions by tip-induced redox chemistry

• Published in: Science (American Association for the Advancement of Science) 2022-07, Vol.377 (6603), p.298-301
• Main Authors: Albrecht, Florian, Fatayer, Shadi, Pozo, Iago, Tavernelli, Ivano, Repp, Jascha, Peña, Diego, Gross, Leo
• Format: Article
• Language: English
• Subjects: Chemical reactions; Chemical synthesis; Chlorine; Chrysene; Intermediates; Isomers; Reaction products; Scanning tunneling microscopy; Selectivity; Voltage; Voltage pulses
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.abo6471

Controlling selectivity of reactions is an ongoing quest in chemistry. In this work, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from the tip of a combined scanning tunneling and atomic force microscope. Characterization of voltage dependence of the reactions and determination of reaction rates demonstrate selectivity in constitutional isomerization reactions and provide insight into the underlying mechanisms. With support of density functional theory calculations, we find that the energy landscape of the isomers in different charge states is important to rationalize the selectivity. Tip-induced selective single-molecule reactions increase our understanding of redox chemistry and could lead to novel molecular machines. Control over the reaction products of a unimolecular transformation on a surface have been induced and visualized with a scanning tunneling microscope (STM) tip. Albrecht et al . synthesized a tetrachlorotetracene molecule and absorbed it on a thin salt layer grown on copper (see the Perspective by Alabugin and Hu). Under cryogenic conditions, voltage pulses from the STM tip led to the elimination of the chlorine atoms and produced intermediates with a large central ring. Subsequent voltage pulses created other isomers of this molecule, a diyne and a chrysene-based bisaryne, in reactions that could be reversed with opposite polarity pulses. —PDS Different bonds are formed selectively in a molecule by atom manipulation with the voltages applied using a scanning probe tip.