Electron Transport through a Coordination Junction Formed by Carboxy Thiophenols and Bivalent Metal Ions

Electron transport through a series of molecular junctions (CTP-M) composed of two carboxyl thiophenols (CTPs) on each gold electrode coordinating with a divalent metallic ion (M) in the center has been investigated using the density functional theory combined with nonequilibrium Green's function (DFT-NEGF) approach. The electronic structure, I–V characteristics, density of states (DOS), and transmission spectra of all CTP-M models have been calculated and compared to the junction without the metallic ion (CTP-H). While strong electronic coupling is established in the coordination structure, the transportation is efficient, showing higher junction conductance as compared to CTP-H. On the contrary, weak electronic coupling is formed between the carboxyl groups and the alkali metal ions (CTP-Mg and CTP-Ca) due to a twisted configuration, exhibiting smaller junction conductance. The strong dependence of the current on the coordination complex has been interpreted with the fine structure of the tunneling barrier. H-bonds result in a bump in the tunneling barrier profile, impeding the electron transfer. When the transition metal ions were incorporated into the molecular junction, the central part of the tunneling barrier turns into an energy well, facilitating the electron transfer. This study provides an effective method to control the interface electron transport required in the construction of flexible wearable electronic devices and functional electronic molecular devices.