Electron transport processes in on/off states of a single alkyl-tailed metal complex molecular switch

Abstract

Voltammograms and current–voltage (I–V) characteristics are measured to elucidate electron transport processes in the bistable conducting states of single molecular junctions of a molecular switch, alkyl-tailed Ru^II terpyridine complexes. (1) On the basis of the Ru-centered electrochemical reaction data, the electron transport rate increases in the mixed self-assembled monolayer (SAM) of Ru^II terpyridine complexes, indicating strong electronic coupling between the redox center and the substrate, along the molecules. (2) In a low-conducting state before switch-on, I–V characteristics are fitted to a direct tunneling model, and the estimated tunneling decay constant across the Ru^II terpyridine complex is found to be smaller than that of alkanethiol. (3) The threshold voltages for the switch-on from low- to high-conducting states are identical, corresponding to the electron affinity of the molecules. (4) A high-conducting state after switch-on remains in the reverse voltage sweep, and a linear relationship of the current to the voltage is obtained. These results reveal electron transport paths via the redox centers of the alkyl-tailed Ru^II terpyridine complexes, a molecular switch.