Nitrophenyl groups in diazonium-generated multilayered films: which are electrochemically responsive?

Area of Science:

• Electrochemistry
• Surface Chemistry
• Materials Science

Background:

• Electrografting enables the creation of functional organic layers on electrode surfaces.
• Nitrophenyl groups are redox-active and can be utilized in electrochemical applications.
• Understanding film structure's influence on electrochemical properties is crucial for device design.

Purpose of the Study:

• To investigate how the structure of electrografted nitrophenyl layers affects solvent accessibility, electroactivity, and chemical reactivity.
• To elucidate the role of nitrophenyl groups as redox mediators within the film.
• To determine the impact of initial electrochemical treatment on film properties.

Main Methods:

• Electrografting of nitrophenyl-containing organic layers onto glassy carbon electrodes.
• Cyclic voltammetry and electrochemical impedance spectroscopy to study electron transfer.
• Kinetic measurements to assess reactivity towards residual water.
• Analysis of film reorganization and porosity changes after potential sweeps.

Main Results:

• Electron transfer is facile and largely independent of film thickness and structure, attributed to self-mediated electron transfer.
• An initial potential sweep increases film porosity by desorbing non-adsorbed material and reorganizing the structure.
• Surface-attached nitrophenyl radical anions react with residual water, with reaction rates varying based on group location within the layer.
• Kinetic measurements can distinguish subtle differences in the layer's microenvironment.
• A portion of the electrochemical signal originates from 4-azonitrophenyl moieties formed during electrografting.

Conclusions:

• Electrografted nitrophenyl layers facilitate efficient electron transfer through redox mediation.
• Electrochemical activation enhances layer porosity and influences reactivity.
• Kinetic analysis of surface-confined redox species provides insights into film structure and environment.
• The electrografting process can introduce unintended moieties that contribute to the overall electrochemical response.