Theoretical investigation of the electronic coupling element in bis-ruthenium porphyrin dimers

Abstract

The electronic coupling element for electron transfer is studied in three ruthenium-porphyrin dimers. The dimers are models for compounds that have been previously studied experimentally and allow investigation of orientation effects and linkage effects and comparison of axial ligand effects on the electronic coupling. The geometries used in this study were obtained from B3LYP geometry optimizations in a DZ basis, and the coupling element was calculated as half the energy splitting between pairs of symmetry-related orbitals using Hartree–Fock, B3LYP Kohn–Sham, or INDO orbitals. The results suggest that all three methods give qualitatively similar values of the coupling at a given geometry and that the coupling involving the highest occupied molecular orbital can be changed markedly by changes in orientation or by changes in ligation external to the main pathways for coupling. Following discussion of the results we suggest directions in which future methodological developments will be critical in furthering our ability to understand and predict electron transport.