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 indude direct covalent attachment and physisorption of pyrene-appended molecular compounds to electrodes with aromatic character through pi-pi 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 Xray photoelectron spectroscopy, fluorescence spectroscopy, and electrochemical techniques. An electron -transfer rate constant (kappa(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 kappa(app) was measured to be 9 +/- 2 s(-1).