Ion Transfer Voltammetry in Polyurethane Thin Films Based on Functionalised Cationic [6]Helicenes for Carbonate Detection

We explore here molecular ion-to-electron redox probes based on cationic diaza, azaoxa, and dioxa [6]helicenes and their derivatives as ion-to-electron transducers for the electrochemical detection of anions. These cationic [6]helicenes exhibit reversible and reproducible oxidation/reduction behavior and facilitate the anion transfer of Gaussian shape into polymeric thin layer sensing films. Films composed of bis(2-ethylhexyl) sebacate (DOS), polyurethane (PU), tetrakis(4-chlorophenyl)borate tetradodecylammonium salt (ETH 500) and [6]helicenes were interrogated by cyclic voltammetry. Even though the peak separation of 90 mV is larger than ideal, the observed peak width at half maximum of 130 mV and the linear relationship between current and scan rate are near theoretical values, confirming a surface confined process. A Nernstian shift of the peaks with increasing carbonate concentration is obtained in the presence of carbonate ionophore VII incorporated into the thin sensing film. The concentration of carbonate was determined in an unfiltered sample of the Arve river (flowing from Chamonix to Geneva) and compared to a reference method (automatic titrator with potentiometric detection). The results suggested that cationic diaza [6]helicene functionalized with two bromine atoms is an attractive molecular ion-to-electron transducer for anion-selective electrodes.