Influence of Peripheral and Ancillary Changes on the Electron Transport of HS3d⁵ FeIII Metallosurfactants – Substituents, Chain Length, Subphase Polarity, and Junction Electrodes

Our ongoing efforts to design metallosurfactants capable of directional electron transport led to pondering on the effects of peripheral changes, and the development of 3d5 FeIII systems where iodo groups replace the usual tert-butyl groups attached to phenylenediamine-bridged phenolate donors. We present the results for two newly designed metallosurfactants, namely, [FeIII(L1)Cl] (1) and [FeIII(L2)Cl] (2), where 1 incorporates shorter hydrophilic alkoxy chains than 2. These species had their electronic and electrochemical properties evaluated by experimental and computational methods. We also considered ancillary changes, such as subphase polarity effects on their interfacial properties of Pockels-Langmuir monolayer films on water and Langmuir–Blodgett monolayer films on gold electrodes, evaluated by multiple surface-dedicated methods and probed for directional electron transfer in Au|LB|Au and Au|LB|EGaIn junctions, prior to comparison to the previously published t-Bu-substituted standard [FeIII(LtBu)Cl] (3). These modifications led to significant modulation of metal-based SOMO energy levels toward the Fermi energy levels of the electrode from 1.0 eV in 3 to ca. 0.5 eV in 1 and 2, which result in better rectification ratios (RR = [I at – V/I at + V]) than those for 3.