Electron transfer behavior at polyoxometalate-adsorbed alkanethiol self-assembled monolayers

The interaction between polyoxometalate (POM) anions, SiMo12O404−, and a self-assembled monolayer (SAM) of dodecanethiol (DT) on Au surfaces was investigated using electrochemical methods, X-ray photoelectron spectroscopy, and scanning probe microscopy. The SiMo12O404− ions adsorb on the SAM of DT on Au to form a composite organic–inorganic hybrid layer. The adsorbed SiMo12O404− ion on the SAM layer shows its characteristic redox waves with an electron transfer rate slower than that on a bare Au electrode. The electron transfer behavior at DT−SAM could be regulated by the adsorption of SiMo12O404− depending on the charge of the investigated electroactive species: a significant increase toward a positively charged Ru(NH3)63+ ion, a moderate increase toward a neutral 1,1′-ferrocenedimethanol molecule and a slight decrease toward a negatively charged Fe(CN)63− ion. The effect of the chain length of alkanethiols on the adsorption of SiMo12O404− ion was also investigated: as the chain length decreases, the amount of the adsorbed POM increases and the electron transfer rate through the composite layers increases. The nature of SiMo12O404− ions adsorbed on the SAMs of alkanethiols on Au is discussed in detail.