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Electronic transport between Au surface and scanning tunnelling microscope tip via a multipodal cyclodextrin host–metallo-guest supramolecular system



An elementary supramolecular conducting system was constructed using a novel (±)-thioctic acid-functionalized β-cyclodextrin host deposited on a gold (Au) surface and an iridium-bearing guest molecule with biphenyl tails to insert specifically into the cyclodextrin cavity. The resulting supramolecular system was used to investigate remote electron communication between the flat Au surface and the platinum (Pt)/iridium (Ir) tip of a scanning tunnelling microscope. The morphology of the surfaces after successive deposition of host molecules followed by guest molecules was investigated. Formation of features of 2 nm size was shown on the Au surface functionalised with the supramolecular system. I–V spectroscopic analysis of the tunnelling current through this supramolecular layer revealed the relation between the effective barrier height and tunnelling distance. Thus, in the supramolecular host–metallo-guest system, a small increase of conductance is observed, compared to the layer without the guest. This can be attributed to the presence of the Ir-guest, which eventually creates intermediate energy states between the Au substrate and the Pt/Ir tip. Copyright © 2011 John Wiley & Sons, Ltd.