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

Abstract

The thermodynamics and kinetics of adsorption of the redox-active dendrimers diaminobutane-dend-(NHCOFc)8, (dendrimer-Fc8), diaminobutane-dend-(NHCOFc)16, (dendrimer-Fc16), diaminobutane-dend-(NHCOFc)32, (dendrimer-Fc32), and diaminobutane-dend-(NHCOFc)64, (dendrimer-Fc64) containing 8, 16, 32, and 64 ferrocenyl moieties on the periphery, respectively, have been studied using electrochemical and electrochemical 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 well-characterized by the Langmuir adsorption isotherm. The kinetics of adsorption were activation-controlled and the rate constant decreased with decreasing size of the dendrimer. Potential scanning past +0.60 V, where the ferrocenyl sites are oxidized, gave rise to the electrodeposition of multilayer equivalents of the dendrimers. The additional material gradually desorbed upon rereduction, so only a monolayer equivalent remained on the electrode surface. Impedance analysis of the resonator response suggests that at multilayer equivalent coverages, the adsorbed 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 monolayer coverages, the adsorbed films appear to exhibit rigid film behavior. Using tapping mode atomic force microscopy we have been able to image dendrimer-Fc64 adsorbed onto a Pt(111) surface. The images reveal that the apparent size of the dendrimer adsorbed on the surface is significantly larger than estimated values based on calculations, which is ascribed to a flattening of the dendrimer upon adsorption.

Modeling Nanosized Single Molecule Objects: Dendronized Polymers Adsorbed onto Mica

“…Indeed, computer simulations of DPs with a relatively low number of repeat units (i.e. [25][26][27][28][29][30] show end cap effects (results not shown) that resemble the deformability of dendrimers adsorbed on surfaces. In these DPs dendrons located at the two ends tend to use the available space and the hemispherical end caps to align in the direction of the macromolecular backbone, whereas in adsorbed dendrimers at low g dendrons tend to occupy the spherical free volume around the core 17 to form very flat structures.…”

Electrochemical study of β-Cyclodextrin binding with ferrocene tethered onto a gold surface via PAMAM dendrimers

“…18,26 Due to the combination of its simplicity and the relevant thermodynamic information that it provides, this model is by far the most popular isotherm which, also, has been successfully used for dendrimer modified electrode studies: 27,28 (9) where C is the molar concentration of CD in solution, and K stands for the apparent association constant related to the formation of the Fc CD complexes (equal to the reciprocal of the equilibrium constant for equation 6), which may be related to the free energy of the CD adsorption in the limit of very low surface coverage by CD, G is derived taking into account lateral interactions between the adsorbed molecules. Thus, the parameter a reflects the strength of the intermolecular interactions between CD adsorbates, which may be considered dependant on the dendritic size, because of the changing surface geometry.…”

Synthesis of a Novel Ferrocene-Based Epoxy Compound and Its Electrochemical Behavior

“…The initial oxidated active sites may affect the subsequent oxidation of the remaining iron (II) and result in a higher oxidation peak leading to the emergence of double peaks [26]. As in CH 2 Cl 2 , the solubility of the oxidated active sites was less than the other three and some oxidized active sites deposited on the electrode surface [8,27]. Charge transfer in deposited solid films was more difficult than in the solution and the redox peaks appeared at a higher potential; furthermore, there were fewer oxidized active sites in the solution to interact with the rest iron (II) which results in the decay of the other peak.…”