REDOX-ACTIVE FERROCENYL DENDRIMERS - THERMODYNAMICS AND KINETICS OF ADSORPTION, IN-SITU ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE STUDY OF THE REDOX PROCESS AND TAPPING MODE AFM IMAGING

The thermodynamics and kinetics' of adsorption of the redox-active den drimers diaminobutane-dend-(NHCOFc)(8), (dendrimer-Fc(8)), diaminobuta ne-dend-(NHCOFc)(64), (dendrimer-Fc(64)), diaminobutane-dend-(NHCOFc)( 32), (dendrimer-Fc(32)), and diaminobutane-dend-(NHCOFc)64, (dendrimer -Fc(64)) containing 8, 16, 32, and 64 ferrocenyl moieties on the perip hery, respectively, have been studied using electrochemical and electr ochemical quartz crystal microbalance (EQCM) techniques. All of these materials adsorb onto a Pt electrode surface. At an applied potential of 0.0 V (vs SSCE), where the ferrocenyl sites are in the reduced form and the dendrimers are neutral, the adsorption thermodynamics are wel l-characterized by the Langmuir adsorption isotherm. The kinetics of a dsorption were activation-controlled and the rate constant decreased w ith decreasing size of the dendrimer. Potential scanning past +0.60 V, where the ferrocenyl sites are oxidized, gave rise to the electrodepo sition of multilayer equivalents of the dendrimers. The additional mat erial gradually desorbed upon rereduction, so only a monolayer equival ent remained on the electrode surface. Impedance analysis of the reson ator response suggests that at multilayer equivalent coverages, the ad sorbed dendrimers do not behave as rigid films and that incorporation of significant amounts of solvent and/or salt accompany the adsorption of these materials at such high coverages. On the other hand, at mono layer coverages, the adsorbed films appear to exhibit rigid film behav ior. Using tapping mode atomic force microscopy we have been able to i mage dendrimer-Fc(64) adsorbed onto a Pt(111) surface. The images reve al that the apparent size of the dendrimer adsorbed on the surface is significantly larger than estimated values based on calculations, whic h is ascribed to a flattening of the dendrimer upon adsorption.