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

Abstract

There are several binding groups used within molecular electronics for anchoring molecules to metal electrodes (e.g., R–SMe, R–NH2, R–CS2−, R–S−). However, some anchoring groups that bind strongly to electrodes have poor/unknown stability, some have weak electrode coupling, while for some their binding motifs are not well defined. Further binding groups are required to aid molecular design and to achieve a suitable balance in performance across a range of properties. 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) and detailed surface spectroscopic analysis. We demonstrate that the methyl carbodithioate ester acts as an effective contact for gold electrodes in STM‐BJ measurements. Surface enhanced Raman measurements demonstrate that the C=S functionality remains intact when adsorbed on to gold nanoparticles. A gold(I) complex was also synthesised showing a stable C=Sׄ→AuI interaction from the ester. Comparison with a benzyl thiomethyl ether demonstrates that the C=S moiety significantly contributes to charge transport in single‐molecule junctions. The overall performance of the CS2Me group demonstrates it should be used more extensively and has strong potential for the fabrication of larger area devices with long‐term stability.