Multifunctional Carbazole-Based Ionic Liquids

In this study, a new class of polymerizable ionic liquids were synthesized and modified upon conductive surfaces to enhance the sensitivity and/or selectivity of the electrodes, or to be electrochromic films. At suitable conditions, the poly-ionic liquids were soluble in some organic solvents. Ionic liquids (ILs) have shown the advantages on electroanalysis when they were modified on electrode surface. Electropolymerization might be a good approach for the modification of ILs on conductive surface. Various carbazole-based ILs (Figure 1) were synthesized in this study and they were electropolymerized on indium tin oxide (ITO) electrodes by cyclic voltammetry in ILs BMP-TFSI, BMIm-PF6 and etc., as well as in conventional solvents (i.e. acetonitrile, methanol and DMSO)[1]. Electrochemical oxidation of the carbazole pendant units affords a conjugated polymer network (CPN) film of polycarbazole and the polymer is expected to have good conductivity on the conducting surface[2]. The electrode with electropolymerized ILs shows improved activity towards the oxidation of uric acid (UA), compared with that of unmodified electrodes. The polymerized ILs also exhibit electrochromic properties. The ITO electrodes modified with polycarbazole ILs show color change from deep green to pale yellow while the applied potential was scanned from +1.2 V to -0.2 V and vice versa. On the other hand, bipyridinium (viologen) ionic liquids modified with carbazole via an alkyl spacer were synthesized and their electrochromic behavior in liquid state was studied in various ILs or conventional volatile organic solvents. Viologen is a well-known electroactive material with three different redox states: the dication, the radical cation and the neutral compound. The colors of radical cations depend on the groups substituted on the nitrogen atoms of the viologen moiety[3]. By introducing the carbazole groups, colors different from those observed for the traditional viologen compounds were recorded. This behavior is currently studied.   [1] D.-X. Zhuang, P.-Y. Chen, Journal of Electroanalytical Chemistry, 2009, 626: 197–200. [2] Antonio F. Frau, Nicel C. Estillore and Rigoberto C. Advincula,ACS Appl. Mater. Interfaces, 2010, 2: 3726–3737. [3] N. Jordao, L. Cabrita, F. Pina and L.C. Branco, Chem.-Eur.J., 2014, 20: 3982–3988.   Figure 1