Ferrocene (Fc) is a widely used building block of molecular rectifiers in the context of molecular electronics. Here, we studied the molecular organization and charge transport properties of the Fc-substituted, triptycene-based tripodes (Fc-Trip), assembled on Au(111) in the self-assembled monolayer-like fashion. The most intriguing property of this system is the occurrence of two distinctly different conductance states, high and low (HCS and LCS, respectively), which can be accessed dynamically by either asymmetric or symmetric bias sweeping in molecular junctions featuring bottom Au (substrate) and top EGaIn electrodes. For the asymmetric sweeping mode, the difference between these states results in an effective rectification ratio (RR) of ∼400–600 at such a small bias as 0.1–0.2 V, which is in contrast to other Fc-based molecular rectifiers showing high RR at a bias of 1.0 V and higher. Following a literature model, the observed behavior was explained by bias-induced, nonreversible oxidation of the Fc groups in combination with conformational changes in the molecular film. The above results show that redox groups in ME systems, including metallocenes in particular, can exhibit a complex behavior that can only be observed by the variation of the sweeping mode and monitoring of individual sweeps.
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