New carbazolo[1,2-a]carbazole derivative as ionophore for anion-selective electrodes: remarkable recognition towards dicarboxylate anions.

A new carbazolo[1,2-a]carbazole derivative was synthesized by expanding the binding cavity to explore the possibility of hosting larger anions such as dicarboxylate anions. The compound was incorporated as an ionophore into a membrane for an anion-selective electrode. The response of the electrode was evaluated for oxalate, malonate, succinate, glutarate and adipate in terms of calibration characteristics (slope, limit of detection and linear range of the response), response time, repeatability, reproducibility and selectivity. Nernstian reproducible responses, with very good detection limits, fast responses and selectivity not previously observed, were found for all the dicarboxylates anions, and the results were especially good in the case of glutarate. In order to obtain additional structural information about the complex formed between the ionophore and the dicarboxylate anions, (1)H NMR and fluorescence studies were carried out. The observed potentiometric selectivity depends on the good correspondence between the size of the carbazolocarbazole cavity and the length of the dicarboxylate anion, as supported by the NMR and fluorescence studies.