Influence of Electronic Configurations on the Modulation of Fermi/Orbital Junction Energies for Directional Electron Transport through 3d1, 3d3, and 3d5 Metallosurfactants

Abstract

Two new metallosurfactants containing the 3d1 vanadyl(IV) and 3d3 chromium(III) ions bound to the phenylenediamine-bridged phenolate-rich ligand LN2O2 were designed, deposited as monolayer films on gold electrodes, and probed for directional electron transfer in Au|LB|Au junctions. Both [V═OIVLN2O2] (1) and [CrIII(LN2O2)(MeOH)(H2O)]Cl (2) promote current rectification. Through a concerted experimental and computational effort, we compare the behavior of 1 and 2 with that of our previously studied 3d5 [FeIII(LN2O2)Cl] (3). Based on the analysis of comprehensive electrochemical, spectroscopic, and microscopy results allied to DFT calculations, we propose distinct mechanisms by which electronic configurations influence the energy gap between the electrode Fermi levels and the different molecular orbitals responsible for electron transport. While the 3d5 species 3 shows electron transport through the metal-based SOMO located above the Fermi levels of the electrode, the 3d1 species 1 uses a metal-based SOMO below Fermi, and the 3d3 species 2 takes advantage of a ligand-based HOMO, which becomes available when a bias is applied.