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 of the mixed SAMs on a gold electrode. The measurements of ultraviolet-visible absorption spectroscopy in transmission mode and cyclic voltammetry of mixed SAMs of porphyrin and alkanethiol have revealed that the porphyrin interaction in the mixed SAMs decreases with increasing the relative ratio of the alkanethiol to the porphyrin. Photoelectrochemical measurements were performed in an argon-saturated Na₂SO₄ aqueous solution containing methyl viologen as an electron carrier using the modified gold working electrode, a platinum wire counter electrode, and an Ag/AgCl reference electrode. The quantum 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 fluorescence lifetime (∼40 ps), irrespective of the porphyrin ratio in the mixed SAMs on the gold electrode.