Amine-terminated monolayers on carbon: preparation, characterization, and coupling reactions

Area of Science:

• Surface chemistry
• Electrochemical methods
• Materials science

Background:

• Amine-terminated monolayers are crucial for surface functionalization.
• Electrografting offers a versatile method for creating such surfaces.
• Protection-deprotection strategies are essential for controlled monolayer formation.

Purpose of the Study:

• To electrograft aminophenyl and aminomethylphenyl monolayers using Boc and Fmoc protecting groups.
• To investigate the monolayer formation and surface characteristics after deprotection.
• To couple electroactive derivatives and evaluate surface concentrations.

Main Methods:

• Electrografting of diazonium ions onto glassy carbon and pyrolyzed photoresist films.
• Utilizing tert-butyloxycarbonyl (Boc) and fluorenylmethyloxycarbonyl (Fmoc) protection-deprotection strategies.
• Atomic force microscopy (AFM) for depth profiling and characterization.
• Coupling of electroactive carboxylic acid derivatives via amide linkages.
• Electrochemical measurements and Density Functional Theory (DFT) calculations.

Main Results:

• Successful formation of amine-terminated monolayers (Boc-NH-Ar, Fmoc-NH-Ar, Fmoc-NH-CH2-Ar) confirmed by AFM.
• Boc-NH-CH2-Ar resulted in a multilayer film after deprotection, unlike the other tested compounds.
• The deprotected Fmoc-NH-CH2-Ar monolayer exhibited the highest surface concentration of coupled nitrophenyl and ferrocenyl groups.
• DFT calculations supported the experimental findings, indicating the highest theoretical surface concentration for Fmoc-NH-CH2-Ar.

Conclusions:

• The Fmoc-NH-CH2-Ar monolayer provides an effective platform for high-density surface functionalization.
• Electrografting combined with Fmoc protection/deprotection is a robust strategy for creating well-defined amine-terminated surfaces.
• This approach enables the immobilization of electroactive molecules for potential applications in sensors and electrocatalysis.