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Issue 61, 2016, Issue in Progress
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Scanning tunnelling microscopy analysis of octameric o-phenylenes on Au(111)

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Oligomeric o-phenylenes are an emerging class of helical molecules that exhibit complex conformational behaviour, which is determined by their terminal groups and the solvent environment. Using scanning tunnelling microscopy (STM), we investigated the conformational behaviour of octameric o-phenylenes (OP8s) featuring Br or NO2 terminal groups (OP8Br and OP8NO2). These o-phenylene oligomers are known to adopt a well-defined helical conformation in the solid state, but undergo a rapid helical inversion in solution at ambient temperature. We show that STM microscopy allows the direct observation of perfectly and partially folded helical conformers of OP8Br and OP8NO2, both of which are simultaneously present in their respective molecular films on Au(111). Possible electronic interactions between the Au(111) surface and the exposed π-system of the OP8 derivatives might result in a thermodynamic bias able to stabilize the metastable, partially folded conformation. Recent studies have revealed that the helical inversion rate of OP8NO2 in solution decreases substantially upon oxidation to the corresponding radical cation (OP8NO2˙+). The OP8NO2 and OP8NO2˙+ film morphologies on Au(111) observed by STM differed substantially with respect to each other, most likely reflecting differences arising from the conformational states of OP8NO2 and OP8NO2˙+ at the molecular level, as well as improved charge-transport properties of the oxidized state.

Graphical abstract: Scanning tunnelling microscopy analysis of octameric o-phenylenes on Au(111)

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The article was received on 18 Mar 2016, accepted on 06 Jun 2016 and first published on 06 Jun 2016

Article type: Paper
DOI: 10.1039/C6RA07173B
Citation: RSC Adv., 2016,6, 55970-55975
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    Scanning tunnelling microscopy analysis of octameric o-phenylenes on Au(111)

    S. Marqués-González, S. Fujii, T. Nishino, Y. Shoji, F. Ishiwari, T. Fukushima and M. Kiguchi, RSC Adv., 2016, 6, 55970
    DOI: 10.1039/C6RA07173B

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