CHEMICAL GATING OF A MOLECULAR BILAYER RECTIFIER AT CLAY-MODIFIED ELECTRODES

Conductive SnO2 electrodes modified with a 1-2 monolayer thick coating of a cationic silane bind Al13O4(OH)283+-pillared montmorillonite. Th e cationic polymer provides binding sites, which are electrochemically accessible to the SnO2 electrode, for iron(III) tetrakis(4-sulfonatop henyl)porphyrin (FeTPPS3-) anions. Electroactive cations such as Ru(NH 3)63+ and Os(bpy)2pyCl+ adhere to the clay surface, at sites too remot e for direct electron transfer with the electrode, and oxidation/reduc tion of these ions is mediated by FeTPPS3-. The axial ligation of the metalloporphyrin anions changes reversibly with solution pH, and in we akly basic solutions electron transfer between these anions and the el ectrode is very slow. Cyclic voltammetry and UV-visible spectroscopy s how that the FeTPPS3-contained within the silane film behaves as a pH- sensitive gate for electron transfer to and from the cations bound to the clay surface. When the formal potential of the clay-bound cation i s sufficiently different from that of FeTPPS3-, proton-gated current r ectification can be observed electrochemically.