Interfacial Electron Transfer of Ferrocene Immobilized onto Indium Tin Oxide through Covalent and Noncovalent Interactions

The immobilization of molecular species onto electrodes presents a direct route to modifying surface properties with molecular fidelity. Conventional methods include direct covalent attachment and physisorption of pyrene-appended molecular compounds to electrodes with aromatic character through π-π interactions. A recently reported hybrid approach extends the synthetic flexibility of the latter to a broader range of electrode materials. We report an application of this approach to immobilization of pyrene-appended ferrocene onto pyrene-functionalized indium tin oxide (ITO). The modified ITO surfaces were characterized using X-ray photoelectron spectroscopy, fluorescence spectroscopy, and electrochemical techniques. An electron-transfer rate constant ( k_app) of 100 ± 8 s^-1 was measured between the electrode and immobilized ferrocene using electrochemical methods. For comparison, a ferrocene-modified electrode using conventional covalent attachment of vinylferrocene was also prepared, and k_app was measured to be 9 ± 2 s^-1.