Electrochemical polymerisation of newly synthesised 3,4-ethylene dioxythiophene-N-heterocyclic carbene iron complexes and application as redox mediators

Immobilization of redox active complexes as electrodes modifier is appealing for a large set of applications such as sensing, electrolysers or fuel cell. In this work iron based N-heterocyclic carbene complexes bearing an 3,4‑Ethylene dioxythiophene (EDOT) moiety in the side chain have been prepared following two different synthetic approaches determined by the length of the lateral chain. The approaches exploit carbonyldiimidazole (CDI) as the coupling agent between the –CH2OH moiety of the hydroxymethyl-EDOT and the –OH functionalized N-heterocyclic carbene iron complex or the imidazolium salt precursor. In both cases, the syntheses allow to obtain functional monomers suitable for electrochemical polymerization in the form of thin films on conducting substrates. The modified electrodes have been characterized by ATR-IR, showing successful copolymerisation to functionalized poly(3,4‑ethylene dioxythiophene) (PEDOT), by cyclic voltammetry (CV), demonstrating the dominant and reversible redox response of NHC-iron complexes, and by SEM-EDS, which provides the average copolymerisation ratio. The capability of the NHC-iron complex to act as a redox mediator has been assessed by using the functionalized device for glucose detection.