Anomalous length dependence of conductance of aromatic nanoribbons with amine anchoring groups

Two sets of aromatic nanoribbons, based around a common hexagonal scaffolding, with single and dual terminal amine groups have been considered as potential molecular wires in a junction formed by gold leads. Charge transport through the two-terminal device has been modeled using density functional theory (with and without self-interaction correction) and the nonequilibrium Green's function method. The effects of wire length, multiple terminal contacts, and pathways across the junction have been investigated. For nanoribbons with the oligopyrene motif and conventional single amine terminal groups, an increase in the wire length causes an exponential drop in the conductance. In contrast, for the nanoribbons with the oligoperylene motif and dual amine anchoring groups the predicted conductance rises with the wire length over the whole range of investigated lengths. Only when the effects of self-interaction correction are taken into account, the conductance of the oligoperylene ribbons exhibits saturation for longer members of the series. The oligoperylene nanoribbons, with dual amine groups at both terminals, show the potential to fully harness the highly conjugated system of $\pi$ molecular orbitals across the junction.

Figure 1

The 4R (pyrene diamine), 5R (perylene tetraamine), coordinated by single and dual Au adatoms, respectively, and 2R (napthalene tetraamine), coordinated by dual adjacent Au adatoms, in the two-terminal device.

Figure 2

Upper panel: Current vs bias voltage for the 1-4-7-10R series of wires between the Au(001) terminals. Lower panels, from top to bottom: The zero-voltage transmission probability for the 1R, 4R, 7R, and 10R nanoribbons, respectively. The energy is given relative to the Fermi level. Details of the transmission probability around the Fermi level for 1R wire are shown in the inset.

Figure 3

Upper panel: Current vs bias voltage for the 2-5-8-11R series of wires, coordinated via single Au adatoms by the terminals. Middle panel: Current vs bias voltage for the 2-5-8-11-14-17-20R series of wires, coordinated via dual Au adatoms by the terminals. Lower panel: The same as in the middle panel, after application of the ASIC.

Figure 4

Panels show, from top to bottom, the zero-voltage transmission probability for the 2R, 5R, 8R, 11R, 14R, 17R, and 20R nanoribbons, respectively. The energy is given relative to the Fermi level.

Figure 5

Energy bands of the electronic states of the wire whose unit cell is shown in the inset. Only the states in the vicinity of the Fermi level are shown. The states corresponding to the frontier MOs are highlighted around the zone center. The orbital shapes of these states at the zone center are also shown.

Figure 6

Upper panel: The zero-voltage transmission probability $T\left(E\right)$ for the 1R junction. The out-of-plane $p$ orbital contribution to the partial density of states (PDOS) from an edge C atom, a central C atom, and N atom are also shown. Lower panel: Similar as in the upper panel for the 2R junction. Only the ASIC-uncorrected results are shown for both 1R and 2R.