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

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.

Giant Conductance Enhancement of Intramolecular Circuits through Interchannel Gating

“…Usually, QI in singlemolecule junctions describes [12][13][14][15] the interference between the different molecular orbitals in the molecule. In addition, topology-broadly achieved by building parallel molecular channels into a single-molecule structure connected by covalent bonds-can also affect 5,[16][17][18][19][20][21] (Figure 1A) the conductance of the molecular junctions. In the latter case, the superposition law provides 3 a total conductance (G tot ) expressed as…”

Nonadditive Transport in Multi‐Channel Single‐Molecule Circuits

“…The latest studies have been carried out on a few two-terminal circuits consisting of separated molecular fragments as transport pathways, as well as a few multi-terminal circuits with the equivalent substituent positions. [27,34,35,38,40] It is reasonable to expect that more complicated QI effects could take place in multi-terminal molecular circuits. When there are multiple terminal anchors involved in a molecular circuit, a large part of the molecular fragment is shared by different transport channels, hence, strong interference interactions and other novel interesting phenomena may take place.…”

Density functional theory based electron transport study of coherent tunneling through cyclic molecules containing Ru and Os as redox active centers

“…For the molecules in Ref. 22 we found that the throughspace coupling between the two anchor groups is the decisive parameter causing DQI effects in the interesting energy region, i.e. in the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and close to the Fermi level E F .…”

“…Experimentally, the design and synthesis of branched compounds containing ferrocene moieties in each branch has been proposed 19 for the purpose of creating single molecule junctions, where the combination of quantum interference effects with redox gating for coherent electron tunneling as well as the electrostatic correlation between spatially distinct redox centers for electron hopping 20 can be explored. A detailed theoretical analysis of branched compounds containing ferrocene centers has been published in our previous work 22 . In order to assess the generality of this analysis we apply the same models and methods to cyclic Me 2 (P(CH 3 ) 2 ) 8 (C 2 H 4 ) 4 (C 6 H 4 ) 4 bis(pyridyl-diacetylide) molecules (Fig.…”