Organic photoelectrochemical cell mimicking photoinduced multistep electron transfer in photosynthesis: Interfacial structure and photoelectrochemical properties of self-assembled monolayers of porphyrin- linked fullerenes on gold electrodes

Article abstract of DOI:10.1246/bcsj.72.485

Self-assembled monolayers (SAMs) technique has been applied to porphyrin-linked fullerene systems to mimic supramolecular photoinduced charge-separation (CS) events in photosynthesis. Porphyrin-linked C₆₀ molecules with a sulfide group were designed to self-assemble on a gold surface using S-Au interaction. The structure of the SAMs formed on gold electrodes was investigated by spectroscopic methods including X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)-visible spectroscopic ellipsometry, UV-visible absorption spectroscopy, and Fourier transform infrared (FTIR) spectroscopy as well as electrochemical studies. These results indicate that the SAMs have loosely packed structure; the porphyrin- C₆₀ molecules are tilted and nearly parallel onto the gold surface. Short- circuit photocurrent with a level of sub-μA cm^-2 was observed for the photoelectrochemical cell in the presence of methylviologen (MV) under illumination with ca. 4 mW cm^-2. The maximum intensity of the photocurrent in free-base porphyrin-C₆₀ system is five times larger than that in the corresponding free-base porphyrin system, indicating that C₆₀ is an effective mediator in multistep electron transfer (ET) processes. A possible mechanism for the photocurrent generation is discussed in terms of the photodynamics of porphyrin-linked fullerenes in solution.