Electron transport across π-stacked oligophenyls system: A density functional theory approach

To understand the π–π stacking interaction between layers of graphenes or polymers, parallel oligophenyls with π-stacked units have been studied with non-equilibrium Green’s function formalism and first-principle density functional theory from two aspects. With the increasing number of π-stacked units, the π–π stacking interaction between parallel oligophenyl chains is enhanced whereas the coupling between the central molecules and the electrodes is weakened. The two effects reach a balance in the parallel oligophenyls with 5 π-stacked units. The π–π stacking interaction is weakened exponentially with the separating distance. Large separating distance impedes electrons to pass through parallel molecules. These results provide a fundamental discussion on issues related to conjugated polymers and, in particular, organic semiconductor thin film devices.