CHAIN-LENGTH EFFECT ON PHOTOCURRENT FROM POLYMETHYLENE-LINKED PORPHYRINS IN SELF-ASSEMBLED MONOLAYERS

Disulfides, with a series of alkyl spacers containing porphyrins at bo th 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 sho wed that as the length of the spacers increases, the SAMs tend to form a highly ordered structure on the gold electrode. Photoelectrochemica l studies, using modified Au and Pt electrodes, were carried out in th e presence of methyl viologen as an electron carrier. The photocurrent s decrease dramatically with a decrease in the spacer length, indicati ng that there are two competitive deactivation pathways for the excite d porphyrin, i.e., the quenching by the electrode and electron carrier .