The thiol (-SH) moiety has long been utilized across multiple disciplines for anchoring individual molecules to metal substrates or in preparing robust self-assembled monolayers (SAMs). As the prototypical linker group for gold, the single-molecule conductance characteristics of various components functionalized with thiols – typically comprising phenyl (e.g. the Tour wires) or α,ω-alkane backbones – have been intensively studied by numerous groups. Such investigations have frequently yielded conflicting results, however, with studies often citing complicating factors such as the connectivity of the sulphur (binding at atop, hollow sites, etc), or the measurement of more than one molecule in each junction. Though a consensus has recently been reached for the conductance of 1,8-octanedithiol, several questions regarding the wide variety of results remain unanswered. We apply the scanning tunnelling microscope-based break junction technique to study the conductance of different components comprising thiol, thioether and thiolate linker groups, also characterizing SAMs using surface voltammetry and x-ray photoemission spectroscopy. We find significant differences between the single-molecule conductance of thiol-terminated molecules in solution and in SAMs, and propose a new model to explain our observations. This work helps to rationalize the inconsistent body of literature and offers new perspectives on the nature of the sulphur-gold bond in a SAM.

Single-molecule conductance measurements in solutions and self-assembled monolayers

255th National Meeting (2018)

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