Aminophenyl and aminomethylphenyl monolayers have been electrografted to glassy carbon and pyrolyzed photoresist film from the corresponding diazonium ions using a protection-deprotection strategy based on Boc (tert-butyloxycarbonyl) and Fmoc (fluorenylmethyloxycarbonyl) groups. After grafting and then deprotecting films of Boc-NH-Ar, Fmoc-NH-Ar, and Fmoc-NH-CH2-Ar, depth profiling by atomic force microscopy confirmed that the resulting amine-terminated films were monolayers. In contrast, after deprotection, Boc-NH-CH2-Ar gave a multilayer film. Electroactive carboxylic acid derivatives were coupled to the monolayers through amide linkages. Electrochemical measurements revealed that the deprotected Fmoc-NH-CH2-Ar monolayer gave the highest surface concentration of coupled nitrophenyl and ferrocenyl groups and DFT calculations established that this monolayer has the highest theoretical surface concentration of those examined.

Electrografting of aryl films to electrode surfaces from diazonium ion solutions is a widely used method for preparation of modified electrodes. In the absence of deliberate measures to limit film growth, the usual film structure is a loosely packed multilayer. For some applications, monolayer films are advantageous; our interest is in preparing well-defined monolayers of reactive tethers for further on-surface chemistry. Here, we describe the synthesis of an aryl diazonium salt with a protected carboxylic acid substituent. After electrografting to glassy carbon electrodes and subsequent deprotection, the layer is reacted with amine derivatives. Electrochemistry and atomic force microscopy are used to monitor the grafting, deprotection, and subsequent coupling steps. Attempts to follow the same procedures on gold surfaces suggest that the grafted layer is not stable in these reaction conditions.

International audienceElectroreduction of 4-nitrobenzenediazonium ions at highly ordered pyrolytic graphite (HOPG) gives a nitrophenyl film that is shown by noncontact atomic force microscopy (AFM) to be continuous and of multilayer thickness. Investigation of the same surface by ultrahigh vacuum scanning tunneling microscopy (UHV-STM) reveals molecular species immobilized on the step edges, but only mobile species on the basal planes. After several scans across an area of basal plane, atomic-level resolution images of clean, defect-free graphite surfaces are obtained. The same behavior is observed with a film deposited by reduction of 4-((triisopropylsilyl)ethynyl)benzenediazonium ion. Throughout extensive STM measurements we find no evidence for covalent attachment of aryl groups to the basal plane and conclude that our results can be best explained by the formation of films of physisorbed oligomeric species. After heating above 300 °C, nitrophenyl films are more stable to STM imaging but no longer contain nitro groups. Increased cross-linking within the film from coupling of radicals formed by thermal decomposition of nitrophenyl groups may be responsible for the more robust film structure