Structure and photoelectrochemical properties of porphyrin-linked fullerenes on a gold surface using a self-assembled monolayer technique

Abstract

Self-assembled monolayers (SAMs) have recently attracted much attention as a new methodology among a variety of thin film preparation. There have been several reports of fullerene SAM. These fullerene thin films seem to be the most promising candidates for realizing photovoltaic and optoelectronic devices at the nano-scale level. We have applied this technique to donor-linked fullerene systems and have developed supramolecular porphyrin-C<SUB>60</SUB> molecules that are designed to be self-assembled on gold surface. Such systems are expected to mimic supramolecular photoinduced charge-separation events in photosynthesis. Porphyrin-linked C<SUB>60</SUB> bearing a methylthio group was prepared by 1,3- dipolar cycloaddition of the azomethine ylide porphyrin with C<SUB>60</SUB>. SAM was formed by soaking Au electrode into a CH<SUB>2</SUB>Cl<SUB>2</SUB> solution of the porphyrin-C<SUB>60</SUB> dyad. Structure of the SAM was investigated by spectroscopic methods including X-ray photoelectron spectroscopy and ellipsometry and electrochemical studies. The large photocurrent with a level of sub-(mu) A/cm<SUP>2</SUP> was observed for the photochemical cell in the presence of methyl viologen under illumination with approximately 10 mW/cm<SUP>2</SUP>. Possible mechanism for the photocurrent generation is discussed in terms of the photodynamics of porphyrin-linked fullerenes.