PREPARATION AND CHARACTERIZATION OF DENDRIMER MONOLAYERS AND DENDRIMER-ALKANETHIOL MIXED MONOLAYERS ADSORBED TO GOLD

Single-component monolayers of dendrimers and two-component monolayers consisting of dendrimers and n-alkanethiols immobilized on Au substra tes are described. Single-component monolayers are prepared by exposin g an Au substrate to ethanolic solutions of amine-or hydroxy-terminate d polyamidoamine (PAMAM) dendrimers. The resulting monolayers are high ly stable and nearly close-packed for dendrimer generations ranging fr om 4 to 8 (G4-G8). Electrochemical ac-impedance measurements indicate that the dendrimer surface is very porous toward the electroactive red ox couple Fe(CN)(6)(3-/4-). Ferrocene-terminated dendrimer monolayers have also been investigated. Exposure of higher-generation dendrimer m onolayers to ethanolic solutions of hexadecanethiol (C16SH) results in a dramatic compression of the dendrimers, and causes them to reorient on the surface from an oblate to prolate configuration. The dendrimer s originally present on the surface do not desorb as a consequence of this configurational change. Comparison of the extent of adsorption of C16SH in different media (vapor-phase N-2, hexane, and ethanol) shows that solvation of the dendrimers is the primary driving force for the structural change. Finally, the reactivity and stability of the dendr imer monolayers is investigated by on-surface functionalization of the dendrimer monolayer with 4-(trifluoromethyl)benzoyl chloride. The phy sical and chemical properties of the single- and two-component monolay ers are evaluated by using reflection infrared spectroscopy, ellipsome try, contact-angle measurements, ac-impedance spectroscopy, cyclic vol tammetry, and surface acoustic wave (SAW)-based analyte-dosing experim ents.