Effect of immobilized electron relay on the interfacial photoinduced electron transfer at a layered inorganic-organic composite film on gold

A layered composite film of CdS nanoparticles and a 1,6-hexanedithiol self-assembled monolayer (SAM) fabricated on a gold substrate was modified with 11-ferrocenylundecanethiol (FcC₁₁SH), which is expected to act as an electron relay, by immersion into its hexane solution. X-ray photoelectron spectroscopy and electrochemical measurements revealed that FcC₁₁S(H) is mainly located on the gold surface, and partly on the CdS nanoparticle layer. The FcC₁₁SH modification induced a significant difference in the photoelectrochemical characteristics of the composite film. The photocurrent increased and decreased at potentials more positive and negative than the redox potential of the ferrocene moiety, respectively, leading to a positive shift in the onset potential for the photoinduced anodic current. A change in the transient photoresponse was also observed. Efficient electron transfer by the ferrocene moiety immobilized between the gold substrate and the CdS nanoparticle layer accounts reasonably for the behavior mentioned above.