[60]Fullerene–porphyrin–ferrocene triad self-assembled monolayers (SAMs) for photovoltaic applications

A new triad array, C60–triosmium cluster-zinc porphyrin–ferrocene complex 1, Os3C60ZnPFc, was prepared by the decarbonylation of Os3(CO)9(μ3-η2:η2:η2-C60) (9) and subsequent reaction with an isocyanide ligand containing porphyrin and ferrocene. This novel triad array exhibits well-defined and stable electrochemical properties in solution due to a robust bonding mode between the C60 and the triosmium cluster. Compound 2, Os3C60SiZnPFc was prepared in a manner similar to that of compound 1 from Os3(CO)8(CN(CH2)3Si(OEt)3)(μ3-η2:η2:η2-C60) (10) and an isocyanide ligand containing porphyrin and ferrocene. The SAM of triad 2 (2/ITO) was fabricated by immersion of an ITO electrode into a chlorobenzene solution of 2 and diazabicyclooctane (2:1 equiv.), and characterized by UV–Vis absorption spectroscopy and cyclic voltammetry. The triad SAM exhibited ideal, well-defined electrochemical responses and high stability due to the stable C60 π-delocalized system via a linkage with the metal cluster center as well as a robust bonding mode. The photoelectrochemical properties of the 2/ITO triad were investigated by a standard three-electrode system in the presence of an ascorbic acid sacrificial electron donor. Reproducible photocurrent was generated by excitation of the porphyrin moiety in the triad SAM with visible light.