Concentration effects of porphyrin monolayers on the structure and photoelectrochemical properties of mixed self-assembled monolayers of porphyrin and alkanethiol on gold electrodes

A systematic series of mixed self-assembled monolayers (SAMs) of porphyrin and alkanethiol have been prepared to examine the concentration effects of porphyrin monolayers on the structure and photoelectrochemical properties o f the mixed SAMs on a gold electrode. The measurements of ultraviolet-visib le absorption spectroscopy in transmission mode and cyclic voltammetry of m ixed SAMs of porphyrin and alkanethiol have revealed that the porphyrin int eraction in the mixed SAMs decreases with increasing the relative ratio of the alkanethiol to the porphyrin. Photoelectrochemical measurements were pe rformed in an argon-saturated Na2SO4 aqueous solution containing methyl vio logen as an electron carrier using the modified gold working electrode, a p latinum wire counter electrode, and an Ag/AgCl reference electrode. The qua ntum yields of the photocurrent generation remain constant (0.26 +/- 0.04%) with an increase in the relative ratio of the alkanethiol to the porphyrin in the mixed SAMs, which is consistent with the constant porphyrin fluores cence lifetime (similar to 40 ps), irrespective of the porphyrin ratio in t he mixed SAMs on the gold electrode.