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Direct Imaging of Covalent Bond Structure in Single-Molecule Chemical Reactions

Science  21 Jun 2013:
Vol. 340, Issue 6139, pp. 1434-1437
DOI: 10.1126/science.1238187

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Watching Organic Reactions

Single-molecule studies can overcome the difficulty of inferring the various outcomes of reactions in ensemble measurements. De Oteyza et al. (p. 1434, published online 30 May; see the Perspective by Giessibl) used a variation of noncontact atomic force microscopy in which the imaging tip was derivatized with a single CO molecule to obtain subnanometer-resolution images of conjugated organic molecules undergoing reaction on a silver surface. Different thermally induced cyclization reactions of oligo- (phenylene-1,2-ethynylenes) were observed.

Abstract

Observing the intricate chemical transformation of an individual molecule as it undergoes a complex reaction is a long-standing challenge in molecular imaging. Advances in scanning probe microscopy now provide the tools to visualize not only the frontier orbitals of chemical reaction partners and products, but their internal covalent bond configurations as well. We used noncontact atomic force microscopy to investigate reaction-induced changes in the detailed internal bond structure of individual oligo-(phenylene-1,2-ethynylenes) on a (100) oriented silver surface as they underwent a series of cyclization processes. Our images reveal the complex surface reaction mechanisms underlying thermally induced cyclization cascades of enediynes. Calculations using ab initio density functional theory provide additional support for the proposed reaction pathways.

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