Electrochemistry and photoelectrochemistry of transition metal complexes in well-ordered surface layers

Two methods for preparing organized, multicomponent assemblies of electroactive complexes are described. Using a cationic silane reagent, a thin layer of zeolite or pillared clay particles can be tethered to an electrode surface. The silane provides a binding site for anionic complexes such as Fe(CN)₆^4- and Mo(CN)₈^4-, while the zeolite or clay component binds electroactive cations such as Os(bpy)₃²⁺, Ru(bpy)₃²⁺, and metallocenes. These assemblies act as rectifiers electrochemically because of spatial ordering of their electroactive anionic and cationic components. Clay-modified electrodes containing Ru(bpy)₃²⁺ and Mo(CN)₈^4- or Fe(CN)₆^4- can also act as photodiodes, because of efficient electron transfer quenching of photoexcited Ru(bpy)₃²⁺ by the film-bound anions. Another strategy for preparing organized electroactive films on surfaces involves the sequential adsorption of the components of the zirconium phosphonate structure from aqueous solution. Films produced in this way are morphologically similar to Langmiur-Blodgett multilayers. By incorporating both organic phosphonate and inorganic phosphate groups into the film, pillared materials with molecular sieving properties can be synthesized. These films bind electroactive cations smaller than the pillar height (ca 10 Å) and exclude larger cations. Spatially organized cation/anion electrode assemblies can thus be prepared which also act as current rectifiers.