Synthesis, characterization, and electrochemical properties of phenyl-coupled diimidazolium hexafluorophosphate ionic liquids

In recent years, functionalized ionic liquids (ILs) have attracted widespread interest due to their unique physicochemical properties. Accordingly, in this work, a series of phenyl-coupled diimidazolium hexafluorophosphate ionic liquids (P-DRIMF) with different R-groups in the sidechain of the imidazolium ring were synthesized and characterized. Moreover, their electrochemical properties, e.g., electrochemical window, impedance, and stability, were further investigated via electrochemical analysis. Results showed that the IR, 1 H NMR, and X-ray diffraction of P-DRIMF match well with the expected structures, as well as they were crystallized and belong to monoclinic or triclinic systems. On the other hand, the electrochemical window could increase from 2.73 V to 3.28 V with the extended alkyl sidechain R-group of the imidazolium ring, and the unsaturated vinyl group would result in a worse electrochemical window. Notably, modified glassy carbon electrodes (ILs/GCE) could perform low impedance, high stability, and improve the electrochemical response. In this case, there was a 2- to 4-fold improvement in response to phenolic compounds, while the response to other compounds still needs further improvement. Overall, this work may shed light on the design of ILs and their applications in electrochemistry.