Electron transport behavior of quinoidal heteroacene-based junctions: effective electron-transport pathways and quantum interference.

Abstract

The electron transport behaviors through a series of molecular junctions composed of tetracene (TC) and S/O substituted-TC (S/O-TC) have been studied by using density functional theory (DFT) combined with non-equilibrium Green’s function (NEGF) method. The unique transport behaviors have been interpreted with correlated quantum interference and electron transport pathway models. In the TC system, two dominating electron transfer channels exist as demonstrated by the detailed pathway analysis of the transmission. In the substituted S/O-TC systems, the electron transport behavior is regulated through either constructive or destructive quantum interference due to the existence of the additional p-electrons, showing the significant diversity of the current-voltage curves. Compared to the TC molecule in the bias region from 0 to 1.0 V, the α-connected molecular junction exhibits greater current, while β-connected molecular junction shows smaller current. The substitution with O and S atoms shows minor effect on the conductance of the molecular junctions. In order to clarify the role of heteroatoms, a series of artificial models designed by removing certain sulfur and carbon atoms in -S-TC have been investigated in detail. The results have demonstrated that only the left S heteroatom contributes to the junction conductivity through the constructive quantum interference. It has been also observed that current exchange occurs between the two electron transfer channels.