Electrochemistry as an Attractive and Effective Tool for the Synthesis and Immobilization of Porphyrins on an Electrode Surface

Abstract

Magnesium(II) 10-phenyl-5,15-p-ditolylporphyrin is easily and cleanly transformed by electrolysis. A nitro group is first introduced at the free meso position by anodic substitution. Hydrogenation into the amine is then carried out electrocatalytically under ambient conditions with water as a hydrogen supplier. The synthesized porphyrin under the nickel(II) form can be covalently grafted onto a platinum electrode by electrochemical reduction of the diazonium cation, generated in situ by a reaction of the nickel(II) aminoporphyrin with sodium nitrite and trifluoroacetic acid. The electrosynthesized thin film gives an electrochemical response typical of a porphyrin material. Films grown under our conditions have a maximum surface coverage of approximately 5×10(-10) mol cm(-2). The modified electrode exhibits a reproducible electrochemical behavior and a good level of stability over potential cycling and exposition to air.

Direct Grafting of Free‐Base meso‐Triarylporphyrins on Electrode Materials through Diazonium Reduction: Reversible Zinc(II) Metallation of the Resulting Materials

“…This CV evolution is rather typical of the electrochemical reduction of aryl diazonium salts for which the formation and growth of the grafted organic layer progressively limits and finally extinguish further reduction of the diazonium cations . This process was similar in the previous studies on the reduction in acetonitrile of porphyrin diazonium salts . Noteworthy, scanning through the 0.4 V peak (from 0.5 to 0.35 V vs. SCE, 30 scans) also leads to the modification of the electrode, but with much lower efficiency.…”

“…The mechanism involves secondary additions of the aryl radical or the diazonium cation onto the aryl backbone of the grafted molecules . It must be underlined that, for the Ni(PDTP) film, although electrodeposited in identical conditions, Γ max is much lower (on GC, reduction by a factor of 10; see Table ) and corresponds to the monolayer state . We have no detailed explanation for this difference yet.…”

“…This reaction has been investigated in organic and aqueous media and in ionic liquids using various materials and several aryl derivatives. Only three manuscripts have dealt with the electrografting of porphyrins from diazonium precursors so far . Firstly Gross et al .…”

“…have reported on the electrografting of tetraphenylporphyrin to electrode surfaces through a para ‐phenylene spacer (see Scheme ). More recently, we performed the direct covalent grafting onto a platinum electrode of the nickel(II) 15‐phenyl‐10,20‐ditolylporphyrin complex [ Ni(PDTP) , Scheme ] via the electroreduction of the corresponding meso ‐diazonium salt, generated in situ from its meso ‐aminoporphyrin precursor . Although the direct connection of the porphyrin core to the electrode surface is a novel feature which could offer new opportunities, this modified electrode might suffer from the difficulty to remove the Ni(II) center and/or to change it with another metal.…”

Introducing Molecular Functionalities within High Surface Area Nanostructured ITO Electrodes through Diazonium Electrografting

“…HCl (VWR Prolabo, 37 %) and NaOH (VWR Prolabo) were used as received. H 2 (PDTP)‐NH 2 was synthetized according to the literature …”