Ionic Liquids As a Medium for STM-Based Single Molecule Conductance Determination: An Exploration Employing Alkanedithiols

A scanning tunnelling microscope (STM) has been used to measure the single-molecule conductance of a homologous series of α,ω-alkanedithiols in the room-temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIOTf). The alkanedithiol system is chosen because it is a well-known model system for single-molecule conductance evaluation, hence allowing us to evaluate ionic liquids as a medium for such determinations. The STM-based measurements have been made in the RTIL under environmentally controlled conditions with the exclusion of water and oxygen. Conductance values measured in the RTIL for the low ( A ) and medium ( B ) conductance groups compare very well with those previously made in different environments including air and organic solvents. Anomalous length dependence of the conductance has been observed for the shorter alkanedithiols in RTILs, and this is compared with similar previous observations for measurements in air. These measurements made on the model alkanedithiol system show that single molecule conductance can be reliably determined in ionic liquids. Indeed, given the physical attributes of ionic liquids, they are an attractive medium for such measurements.