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

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
some interest as functional elements of molecular-scale devices. Here we investigate the impact of
the configurational degrees of freedom of a ferrocene derivative on its single-molecule junction
conductance. Measurements indicate that the conductance of the ferrocene derivative, which is
suppressed by two orders of magnitude as compared to a fully conjugated analog, can be modulated
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.