Multidentate thiolate films were prepared by solution phase deposition of dendritic oligothiols on gold surfaces. The dendritic molecules contain three (G0) and nine (G1) thiol groups at the periphery and a functional group (bromophenyl) at the corn. The films were characterized by contact-angle goniometry, ellipsometry, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). Results of the XPS measurement indicate the presence of ∼20% of unbound S in the G0 films while ∼28% in the G1 films. Some of the unreacted thiol groups may be located at the upper part of the films and some of the bromophenyl groups at the lower part of the films. Three G0 molecules (containing three SH groups) cover about the same area on the substrate as one G1 molecule (containing nine SH groups), and both of the films exhibit similar thicknesses, indicating the flattening of the dendrons to maximize the bonding of SH groups to the gold surface. The G1 films exhibit higher stability than the G0 films, and both of them are much more stable than octadecanethiolate monolayers on gold in hot solvents, attributed to the formation of multiple S-Au bonds per dendron unit. The high stability of the films allows for the palladium-catalyzed Heck reaction on thiolate films. Treatment of both the G0 and G1 films with 4-fluorostyrene under Heck reaction conditions led to the disappearance of about 76 and 68% of the Br atoms among which about 60-70% were replaced by the 4-fluorostyryl groups, as shown by XPS. Prolonging the reaction time did not consume the remaining Br atoms, probably due to unfavorable orientation of the bromophenyl groups and/or the presence of adjacent thiol groups that may deactivate the catalyst in the film assembly.

Multidentate carbosilane films were prepared by thermally induced hydrosilylation of allyl-terminated carbosilane dendrons of generations 0, 1, and 2 (G0-G2) on hydrogen-terminated silicon(111) surfaces. The dendron molecules contain three (G0), nine (G1), and twenty-seven (G2) allyl groups at the periphery, and a bromophenyl functional group at the focal point. The dendron films were characterized by contact-angle goniometry, ellipsometry, Fourier transform infrared spectroscopy in the attenuated total reflection mode, and X-ray photoelectron spectroscopy (XPS). Upon hydroboration of the remaining allyl groups in the films, the percentage of the introduced boron atoms in the films were measured by XPS. The results indicate the presence of roughly 20%, 27%, and 46% of unreacted allyl groups in the G0, G1, and G2 films, respectively. The mechanistic aspects of the chemisorption of these dendron molecules on H-Si(111) surfaces are discussed. XPS studies indicate that seven G0 molecules cover approximately the same area on the substrate as three G1 molecules and one G2 molecule. After treatment of the G0, G1, and G2 films with 4-fluorostyrene under the Heck reaction conditions, the XPS studies indicate that about 84%, 71%, and 55% of the Br atoms were consumed, yielding the replacement of ca. 58-70% of the reacted Br atoms by the fluorostyryl groups. The remaining bromophenyl groups were inactive toward the Heck reaction, probably due to their disfavorable position/orientation in the films.