Flexible Strategy for Immobilizing Redox-Active Compounds Using in Situ Generation of Diazonium Salts. Investigations of the Blocking and Catalytic Properties of the Layers

Abstract

A versatile two-step method is developed to covalently immobilize redox-active molecules onto carbon surfaces. First, a robust anchoring platform is grafted onto surfaces by electrochemical reduction of aryl diazonium salts in situ generated. Depending on the nature of the layer termini, -COOH or -NH(2), a further chemical coupling involving ferrocenemethylamine or ferrocene carboxylic acid derivatives leads to the covalent binding of ferrocene centers. The chemical strategy using acyl chloride activation is efficient and flexible, since it can be applied either to surface-reactive end groups or to reactive species in solution. Cyclic voltammetry analyses point to the covalent binding of ferrocene units restricted to the upper layers of the underlying aryl films, while AFM measurements show a lost of compactness of the layers after the chemical attachment of ferrocene centers. The preparation conditions of the anchoring layers were found to determine the interfacial properties of the resulted ferrocenyl-modified electrodes. The ferrocene units promoted effective redox mediation providing that the free redox probes are adequately chosen (i.e., vs size/formal potential) and the underlying layers exhibit strong blocking properties. For anchoring films with weaker blocking effect, the coexistence of two distinct phenomena, redox mediation and ET at pinholes could be evidenced.

Electrografting of calix[4]arenediazonium salts to form versatile robust platforms for spatially controlled surface functionalization

“…Accordingly, ferrocene moieties were covalently introduced through an amide bond formation with ferrocenemethylamine (FcCH 2 NH 2 ) following a procedure previously described (Fig. 7) 51 .…”

The reduction of 4-nitrobenzene diazonium electrografted layer: An electrochemical study coupled to in situ sum-frequency generation spectroscopy

“…Depending on the group borne by the aromatic moiety, diazonium compounds have been exploited in many research fields such as energy conversion and storage [11,12], molecular electronics [13,14], and chemical [15e17] and biochemical [18,19] sensing. They may also be used for further functionalization by means of chemical reactions such as amine/carboxyl condensation [20,21] or the trendy click chemistry [22e24], or by electropolymerization in the case of conjugated monomer-functionalized diazonium [8,17,25,26].…”

New insight into 4-nitrobenzene diazonium reduction process: Evidence for a grafting step distinct from NO2 electrochemical reactivity

“…The immobilized group affords specific chemical and physicochemical properties to the surface which are exploited in many application fields such as molecular electronics [5,6], energy conversion [7][8][9] and chemical [10][11][12] or biological [13,14] sensing. Depending on the aim of the work, it can also be used for further modification using chemical reaction such as click chemistry [15][16][17] and amine/carboxyl condensation [18,19] or to directly interrogate the functionalized surface.…”