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Rearrangements that change the connectivity of a carbon skeleton are often useful in synthesis, but it can be difficult to follow their mechanisms. Scanning probe microscopy can be used to manipulate a skeletal rearrangement at the single-molecule level, while monitoring the geometry of reactants, intermediates and final products with atomic resolution. We studied the reductive rearrangement of 1,1-dibromo alkenes to polyynes on a NaCl surface at 5 K, a reaction that resembles the Fritsch–Buttenberg–Wiechell rearrangement. Voltage pulses were used to cleave one C–Br bond, forming a radical, then to cleave the remaining C•–Br bond, triggering the rearrangement. These experiments provide structural insight into the bromo-vinyl radical intermediates, showing that the C=C•–Br unit is nonlinear. Long polyynes, up to the octayne Ph–(C≡C)8–Ph, have been prepared in this way. The control of skeletal rearrangements opens a new window on carbon-rich materials and extends the toolbox for molecular synthesis by atom manipulation. Atomic manipulation was used to control the reductive rearrangement of 1,1-dibromo alkenes to acetylenes on a NaCl surface at 5 K, and the stages of the reaction were visualized with atomic resolution using AFM. Polyynes ranging from triyne to octayne were prepared in this way, and STM was used to map their frontier orbitals and determine their transport gaps.

Dissolved organic carbon (DOC) is the largest pool of exchangeable organic carbon in the ocean. However, less than 10% of DOC has been molecularly characterized in the deep ocean to understand DOC's recalcitrance. Here we analyze the radiocarbon (14C) depleted, and presumably refractory, low molecular weight (LMW) DOC from the North Central Pacific using atomic force microscopy to produce the first atomic‐resolution images of individual LMW DOC molecules. We evaluate surface and deep LMW DOC chemical structures in the context of their relative persistence and recalcitrance. Atomic force microscopy resolved planar structures with features similar to polycyclic aromatic compounds and carboxylic‐rich alicyclic structures with less than five aromatic carbon rings. These compounds comprise 8% and 20% of the measurable molecules investigated in the surface and deep, respectively. Resolving the structures of individual DOC molecules represents a step forward in molecular characterization of DOC and in understanding its long‐term stability. The marine dissolved organic carbon (DOC) reservoir is similar in size to that of atmospheric carbon dioxide and plays an important role in the ocean carbon cycle. DOC comprises a vast mixture of diverse molecules, the majority of which remain structurally uncharacterized. Identification of DOC molecular structures will aid our understanding of DOC cycling. Here, we present the first images of individual DOC molecules using atomic force microscopy. We compare images of low molecular weight DOC molecules extracted from samples collected at different depths in the North Central Pacific. Our results help unravel the molecular architecture, formation processes, and cycling of marine DOC in the ocean. This work demonstrates that atomic force microscopy can facilitate structure determination in oceanic mixtures and provide an additional complimentary toolbox for analytical techniques in geophysical relevant environments. Real‐space visualization of single molecules in low molecular weight marine dissolved organic carbon (LMW DOC) is demonstrated using atomic force microscopyComparison between surface and deep LMW DOC reveals a greater fraction of aromatic structures in the deep oceanIdentified compounds are generally similar to black carbon, polycyclic aromatic compounds, and carboxylic‐rich alicyclic molecules (CRAM)

Intermolecular single-electron transfer on electrically insulating films is a key process in molecular electronics1–4and an important example of a redox reaction5,6. Electron-transfer rates in molecular systems depend on a few fundamental parameters, such as interadsorbate distance, temperature and, in particular, the Marcus reorganization energy7 . This crucial parameter is the energy gain that results from the distortion of the equilibrium nuclear geometry in the molecule and its environment on charging8,9. The substrate, especially ionic films10 , can have an important influence on the reorganization energy11,12. Reorganization energies are measured in electrochemistry13 as well as with optical14,15and photoemission spectroscopies16,17, but not at the single-molecule limit and nor on insulating surfaces. Atomic force microscopy (AFM), with single-charge sensitivity18–22, atomic-scale spatial resolution20 and operable on insulating films, overcomes these challenges. Here, we investigate redox reactions of single naphthalocyanine (NPc) molecules on multilayered NaCl films. Employing the atomic force microscope as an ultralow current meter allows us to measure the differential conductance related to transitions between two charge states in both directions. Thereby, the reorganization energy of NPc on NaCl is determined as (0.8 ± 0.2) eV, and density functional theory (DFT) calculations provide the atomistic picture of the nuclear relaxations on charging. Our approach presents a route to perform tunnelling spectroscopy of single adsorbates on insulating substrates and provides insight into single-electron intermolecular transport. An atomic force microscope is used as an ultralow current sensor to measure the reorganization energy of a single naphthalocyanine molecule during a redox reaction on a NaCl film.