Towards molecular electronic devices based on ‘all-carbon' wires

Nascent molecular electronic devices based on linear ‘all-carbon' wires attached to gold electrodes through robust and reliable C-Au contacts are prepared via efficient in situ sequential cleavage of trimethylsilyl end groups from an oligoyne, Me₃Si-(CC)₄-SiMe₃ (1). In the first stage of the fabrication process, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate, which ultimately serves as the bottom electrode, using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, AuCCCCCCCCSiMe₃ (AuC₈SiMe₃). In the second stage, treatment of AuC₈SiMe₃ with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer AuCCCCCCCCH (AuC₈H). The reactive terminal CC-H moiety in AuC₈H can be modified by ‘click' reactions with (azidomethyl)ferrocene (N₃CH₂Fc) to introduce a redox probe, to give AuC₆C₂N₃HCH₂Fc. Alternatively, incubation of the modified gold substrate supported monolayer AuC₈H in a solution of gold nanoparticles (GNPs), results in covalent attachment of GNPs on top of the film via a second alkynyl carbon-Au σ-bond, to give structures AuC₈GNP in which the monolayer of linear, ‘all-carbon' C₈ chains is sandwiched between two macroscopic gold contacts. The covalent carbon-surface bond as well as the covalent attachment of the metal particles to the monolayer by cleavage of the alkyne C-H bond is confirmed by surface- enhanced Raman scattering (SERS). The integrity of the carbon chain in both AuC₆C₂N₃HCH₂Fc systems and after formation of the gold top-contact electrode in AuC₈GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal-monolayer-metal devices AuC₈GNP featuring ‘all-carbon' molecular wires were characterised by sigmoidal I-V curves, indicative of well-behaved junctions free of short circuits.