Chain Length Effect on Photocurrent from Polymethylene-Linked Porphyrins in Self-Assembled Monolayers

Disulfides, with a series of alkyl spacers containing porphyrins at both ends, were prepared to evaluate the effect of the spacer length on the interfacial structure and photoelectrochemical properties of self-assembled monolayers (SAMs) on a gold electrode. The structure of the SAMs was investigated using UV−visible absorption spectroscopy, cyclic voltammetry, and photoelectrochemical studies. These measurements showed that as the length of the spacers increases, the SAMs tend to form a highly ordered structure on the gold electrode. Photoelectrochemical studies, using modified Au and Pt electrodes, were carried out in the presence of methyl viologen as an electron carrier. The photocurrents decrease dramatically with a decrease in the spacer length, indicating that there are two competitive deactivation pathways for the excited porphyrin, i.e., the quenching by the electrode and electron carrier.