A Systematic Study of Methyl Carbodithioate Esters as Effective Gold Contact Groups for Single-Molecule Electronics

Currently, there is an array of binding groups for use within molecular electronics for anchoring molecules to metal electrodes (e.g., R–SMe, R–NH2, R–CS2−, R–S−). The problem is that some anchoring groups that bind strongly to electrodes have poor/unknown stability, or they have weak electrode coupling. More binding groups are required for molecular design with good stability and strong binding to the electrodes. Here, we present an in-depth investigation into the use of carbodithioate esters as contact groups for single-molecule conductance measurements, using scanning tunnelling microscopy break junction measurements (STM-BJ). We demonstrate using a series of novel molecular wires that the methyl carbodithioate ester acts as an effective contact for gold electrodes in STM-BJ measurements without deprotection. Surface enhanced Raman measurements demonstrate that the C=S functionality remains intact when adsorbed on to gold nanoparticle surfaces. A gold(I) complex was also synthesised showing a C=Sׄ→Au(I) interaction highlighting that the ester remains intact while binding to a gold centre. Comparison with a benzyl thiomethyl ether demonstrates that the C=S significantly contributes to charge transport in single-molecule junctions. The synthetic accessibility and performance of the functional group reported here demonstrates that it should be used more extensively and has strong potential for the fabrication of larger area devices with long-term stability.