Electrochemical Properties of a Verdazyl Radical in Room Temperature Ionic Liquids

Junqiao Lee,Rebecca O Fuller,Debbie S Silvester,Allan J Mckinley,Chiara Caporale

doi:10.1071/ch19575

Abstract

Room temperature ionic liquids (RTILs) have been widely investigated as alternative electrochemical solvents for a range of dissolved species over the past two decades. However, the behaviour of neutral radicals dissolved in RTILs is relatively unexplored. In this work, the electrochemistry of a stable verdazyl radical – 1,5-dimethyl-3-phenyl-6-oxoverdazyl (MPV) – has been studied on a platinum thin-film electrode using cyclic voltammetry and chronoamperometry in 10 different RTILs. The organic solvent propylene carbonate is also employed as a comparison. The nature of the solvent system was found to have a large effect on the electrochemical behaviour, particularly on the reduction reaction of the verdazyl radical. Chronoamperometry on a microdisk electrode was used to calculate diffusion coefficients (D), and plots of D versus the inverse of viscosity were linear, suggesting typical hydrodynamic diffusional characteristics of the radical, in line with the behaviour of dissolved neutral and charged compounds (e.g. ferrocene and cobaltocenium) in RTILs. Overall, this study demonstrates that different RTILs have a significant influence on the electrochemistry of MPV, and therefore careful selection of the solvent system for electrochemical applications is advised.

Highlights

Room-temperature ionic liquids (RTILs) are a unique class of solvents that are made up entirely of cations and anions
Given the obvious advantages of Room temperature ionic liquids (RTILs) as solvent systems, and the potential applications of the family of verdazyl radicals, we present a first look into the electrochemical mechanism of MPV (Fig. 3) in RTILs
Due to the use of a quasi-reference electrode, the potentials of all cyclic voltammetry (CV) were corrected with respect to an internal reference – the ferrocene/ferrocenium (Fc/Fc+) redox couple – to allow comparison of the redox potentials in the different solvents

Summary

Introduction

Room-temperature ionic liquids (RTILs) are a unique class of solvents that are made up entirely of cations and anions. Given the obvious advantages of RTILs as solvent systems, and the potential applications of the family of verdazyl radicals, we present a first look into the electrochemical mechanism of MPV (Fig. 3) in RTILs. We discuss the relationship between diffusion coefficient and solvent viscosity in terms of hydrodynamic theory and Stokes-Einstein behaviour.

Results

Conclusion