PARTIAL ELECTRON-TRANSFER IN OCTADECANETHIOL BINDING TO GOLD

Langmuir-Blodgett transfer of octanedecanethiol (C18SH) containing mon olayers onto gold-coated glass slides under potentiostatic conditions leads to a quantitative characterization of C18SH chemisorption on gol d. The thiol-gold bond involves a partial electron transfer from sulfu r to the gold substrate. The C18SH partial charge number was determine d to vary linearly with the potential of gold substrates from 0.30 at -0.30 V to 0.45 at 0.70 V vs SCE. Only ca. 81% of C18SH molecules appe ar to chemisorb upon LB transfer at 20 mN/m. This is likely a result o f some orientational restrictions (e.g. tilt and registry with the gol d surface lattice) imposed on the system by the lateral pressure durin g LB transfer. The requirement of monolayer charge neutrality, stemmin g from a negligible capacitance of the Au/LB monolayer interface, resu lts in a dissociation of thiol's proton to an extent equal to the char ge transferred due to C18SH chemisorption.