Semipermeable, Chemisorbed Adlayers of Focally-Substituted Organothiol Dendrons on Gold

A series of focally substituted organothiol dendrons of the first through third generation were used to construct adlayers on a gold surface. The presence and structural features of these adlayers were confirmed by X-ray photoelectron spectroscopy, infrared spectroscopy, and ellipsometry. The relative coverage and/or permeability of these adlayers was studied using capacitance and electrochemical blocking experiments. It was found that as the number of hyperbranches in the dendron increased from one to three, the dendron adlayers became initially less and then more permeable. This result indicated a tradeoff between size and packing efficiency when using these molecules to cover a surface. These data also suggest that the dendrons have formed homogeneous but permeable adlayers on the gold surface rather than adlayers consisting of islands of material. These adlayers showed large differences in their ability to trap and hold a small molecule, trans- cyclohexanediol, within them.