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Molecular structure elucidation with charge-state control

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Science  12 Jul 2019:
Vol. 365, Issue 6449, pp. 142-145
DOI: 10.1126/science.aax5895

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Visualizing molecular charging

High-resolution atomic force microscopy (AFM) has been used to control and image the charge state of organic molecules adsorbed on multilayer sodium chloride films. Fatayer et al. biased an AFM probe tip with a voltage to charge and discharge molecules such as azobenzene and porphine from cations to anions. Subsequent imaging with carbon monoxide–functionalized tips revealed changes in the conformation, bond order, and aromaticity of the organic molecules resulting from charge-state changes.

Science, this issue p. 142

Abstract

The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity, and aromaticity, with implications for on-surface synthesis, catalysis, photoconversion, and applications in molecular electronics. On insulating, multilayer sodium chloride (NaCl) films, we controlled the charge state of organic molecules and resolved their structures in neutral, cationic, anionic, and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using carbon monoxide (CO)–functionalized tips. We detected changes in conformation, adsorption geometry, and bond-order relations for azobenzene, tetracyanoquinodimethane, and pentacene in multiple charge states. Moreover, for porphine, we investigate the charge state–dependent change of aromaticity and conjugation pathway in the macrocycle. This work opens the way to studying chemical-structural changes of individual molecules for a wide range of charge states.

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