Electron transfer properties of mono- and diferrocenyl based Cu complexes attached as self-assembled monolayers on gold electrodes by “self-induced” electroclick

Abstract

Two new Cu complexes bearing a 6-ethynyl bis-(methyl-pyridyl)amine (6eBMPA) moiety, as an electroclickable function linked to a ferrocenylbased triazolyl arm (ligands 3 and 4) have been synthetized and characterized by UV-Visible, EPR spectroscopies and cyclic voltammetry in acetonitrile. Two different spacer groups between the terminal ferrocene and the triazolyl group were inserted: an hexyl chain in the case of the complex Cu-3, an ethenyl-bridged diferrocenyl system for the complex Cu-4. The monoelectronic oxidation of the diferrocenyl species yields a stable mixed-valence complex. NIR-Visible spectroscopic studies show a moderate interaction between ferrocenyl units (class II according to the Robin-Day classification). The immobilization of these systems as SAMs on an azidoundecanethiol modified gold electrode has been successfully operated by using the "self-induced electroclick" procedure. The voltammetric characterization of the surface-tagged Cu complexes indicates that good surface coverage was achieved, with moderately fast electron-transfer reaction between the electrode and the redox active immobilized systems (k 0 (Cu) = 2-4 s −1 , k 0 (Fc) = 20-90 s −1). Remarkably, the rate of charge transport is significantly controlled by the nature of the spacer on the ferrocenyl triazole arm.

Immobilization of Monolayers Incorporating Cu Funnel Complexes onto Gold Electrodes. Application to the Selective Electrochemical Recognition of Primary Alkylamines in Water

“…Additionally, the anchoring of calixarene complexes on the modified surface is assisted by supramolecular interactions (hydrophobic effect) due to first grafted calix[6]­tren copper complexes. Notably, the value of k (1.35 × 10 –4 s –1 ) is significantly lower by 1 order of magnitude than those obtained for grafted ferrocene or small Cu complexes (typically between 2 × 10 –3 and 3 × 10 –3 s –1 ) . Such a result can be ascribed to steric effects of the calixarene ligand, which slow down the rate of the click reaction on the gold surface.…”

“…As a first step, the gold electrode was soaked in an ethanolic solution of undec-10-yne-1-thiol for 24 h (Scheme ). After thorough washing with absolute ethanol and purified water, the modified electrode was introduced into an aqueous HEPES buffer solution (pH = 9.4) containing 20 μM [ 3 ·Cu­(H 2 O)] 2+ as well as 20 μM Cu catalyst [Cu­(6-BrTMPA)­(H 2 O)] 2+ (TMPA = tris­(2-pyridylmethyl)­amine) . The grafting of the Cu-calix[6]­tren complex was achieved by cycling 30 times the potential between 0.70 and −0.30 V vs saturated calomel electrode (SCE) with a 3 min hold at −0.30 V between each cycle.…”

“…Surface coverage ratio θ (i.e., ratio of time-dependent surface concentration vs maximum surface concentration) was evaluated by peak integration and plotted against time (Figure B, red curve). As a first approach, the kinetics were assumed to follow a Langmuir isotherm model (black curve, n = 1 see below) based on a pseudo-first-order reaction, as previously done with analogous complexes or ferrocene grafted by electroclick. ,, As shown in Figure B ( n = 1), the simulated curve does not match with the experimental plots ( k = 1.35 × 10 –4 s –1 ). No better fit could be obtained by variation of the k value, which indicates that the grafting process does not follow a classical Langmuir isotherm model.…”

Electronic Properties of Mono‐Substituted Tetraferrocenyl Porphyrins in Solution and on a Gold Surface: Assessment of the Influencing Factors for Photoelectrochemical Applications

“…Therefore, k ET was estimated assuming the ideal situation in which a = 0.5, that is, symmetric energy barriers for the redox reactions were considered. [25] Under these simplifications, the electron transfer rate constant was determined as the intercept of the straight line obtained by the plot of DE p vs log(u s ) according to the equation: [37] …”

Electrochemical nanoarchitectonics and layer-by-layer assembly: From basics to future

“…14) [346,347]. This surface immobilization of copper complexes lead to tunable electron transfer and electrocatalytic activity [348,349]. The main advantage of this technique is due to the absence of copper salt in solution, which would cause interference with biological materials.…”