Quantum interference in coherent tunnelling through branched molecular junctions containing ferrocene centers

TL;DR

This theoretical study explores quantum interference effects in branched ferrocene-containing molecular junctions, revealing how structural features and local charging influence conductance through destructive quantum interference.

Contribution

It combines NEGF and DFT methods to analyze quantum interference in ferrocene-based molecular junctions, identifying structural causes of DQI and effects of local charging.

Findings

Destructive quantum interference occurs near the LUMO in these molecules.

Structural through-space coupling causes the DQI minimum.

Local charging alters conductance by about one order of magnitude.

Abstract

In our theoretical study where we combine a nonequilibrium Green's function (NEGF) approach with density functional theory (DFT) we investigate branched compounds containing ferrocene moieties in both branches which due to their metal centers are designed to allow for asymmetry induced by local charging. In these compounds the ferrocene moieties are connected to pyridyl anchor groups either directly or via acetylenic spacers in a meta-connection where we also compare our results with those obtained for the respective single-branched molecules with both meta- and para-connections between the metal center and the anchors. We find a destructive quantum interference (DQI) feature in the transmission function slightly below the lowest unoccupied molecular orbital (LUMO) which dominates the conductance even for the uncharged branched compound with spacer groups inserted. In an analysis based on mapping the structural characteristics of the range of molecules in our article onto tight-binding models, we identify the structural source of the DQI minimum as the through-space coupling between the pyridyl anchor groups. We also find that local charging on one of the branches only changes the conductance by about one order of magnitude which we explain in terms of the spatial distributions of the relevant molecular orbitals for the branched compounds.