Electron Tunneling in Quasi-One-Dimensional Resonant Molecular Systems. Ab Initio Study

Abstract

The method of tunneling currents is applied for study of electron-tunneling dynamics in quasi-one-dimensional donor−bridge−acceptor systems in which the bridge is composed of a sequence of atoms located on a straight line connecting donor and acceptor complexes. Such a system provides a simple model for the description of electronic processes in molecular wires. Of our particular interest are the following questions: how exactly does an electron tunnel through an atom or a molecule, and what is the precise meaning of “through-bond” and “through-space” tunneling, the concepts frequently used in the description of electron tunneling in proteins. Our method consists of an ab initio electronic structure calculation of the spatial distribution of tunneling currents occurring during the tunneling transition in the system, when an electron tunnels from the one end of molecular wire to the other. The analysis is based on calculation of two diabatic electronic states corresponding to localization of a tunneling electron on donor and acceptor sites, respectively. All electrons in the system are taken into account at the Hartree−Fock level, and as such the method allows us to examine the reaction of the valence electrons on the bridge to the tunneling charge. The symmetry of the chosen system allows a relatively simple way for a complete and detailed analysis of the spatial distribution of the currents in the system. These results provide new insights into the nature of long-distance electron tunneling in organic media.