Mechanically-Tunable Quantum Interference in Ferrocene-Based Single-Molecule Junctions

Abstract

Ferrocenes are ubiquitous organometallic building blocks that comprise a Fe atom sandwiched between two cyclopentadienyl (Cp) rings that rotate freely at room temperature. Of widespread interest in fundamental studies and real-world applications, they have also attracted<br>some interest as functional elements of molecular-scale devices. Here we investigate the impact of<br>the configurational degrees of freedom of a ferrocene derivative on its single-molecule junction<br>conductance. Measurements indicate that the conductance of the ferrocene derivative, which is<br>suppressed by two orders of magnitude as compared to a fully conjugated analog, can be modulated<br>by altering the junction configuration. Ab initio transport calculations show that the low conductance is a consequence of destructive quantum interference effects that arise from the hybridization of metal-based d-orbitals and the ligand-based π-system. By rotating the Cp rings, the hybridization, and thus the quantum interference, can be mechanically controlled, resulting in a conductance modulation that is seen experimentally.<br>

Mechanical single-molecule potentiometers with large switching factors from ortho-pentaphenylene foldamers

“…1-25) (Fig. 5c) [4][5][6][7][8][9][10]46,47,[51][52][53] . It is reported that the para-polyphenylenes can have a conductance enhancement of one order of magnitude by changing the tilted angles attaching the gold electrode 8,9 .…”

“…The alkanes 5 , silanes 6 , and other linear systems with cis-trans isomers are common structures used as mechanical triggered switches because their conductance can be modulated by mechanical force via the deformation of the flexible alkane chains or cis-trans isomerization. The switching factor, defined as the ratio of the conductance of the highest conductance state to that of the lowest conductance state, is an important parameter to quantify modulation ratio 5,7 . The most-reported molecules usually have low mechanical switching factors~10 [4][5][6][7] .…”

“…The switching factor, defined as the ratio of the conductance of the highest conductance state to that of the lowest conductance state, is an important parameter to quantify modulation ratio 5,7 . The most-reported molecules usually have low mechanical switching factors~10 [4][5][6][7] . Although it is reported that precise control of tilted angles of molecular wires can lead to a conductance increase of an order of magnitude up to 25-folds [8][9][10] , these switching factors are still far from satisfactory.…”

Advances and challenges in single-molecule electron transport

“…Mechanical control of destructive QI is also thought to be responsible for the large conductance fluctuations seen in experiments on ferrocene-based molecular wires (Camarasa-Gómez et al, 2019). In this case, the proposed effect derives from a rotational degree of freedom that can switch the junction's QI from destructive to constructive and back.…”

“…This behavior has been taken as a hallmark in the experimental discovery of the FCB. In the context of nanoscale devices, the FCB was first observed in carbon nanotubes (Leturcq et al, 2009), where the blockade survives over several charge states N. A molecular FCB was first observed by Burzurí et al (2014) in an Fe 4 complex. The FCB has some remarkable consequences for the charge-carrier dynamics (Koch, von Oppen, and Andreev, 2006).…”