Synthesis of 9-ethyl-3-isothiacyanato carbazole for turn on fluorescence for rapid and selective detection of Cd2+ in aqueous system

Abstract

A remarkable instantaneous visual change from colorless to faint blue coloration is observed selectively for cadmium cation (Cd2+) using a simple carbazole derivative 9-ethyl-3-isothiocyanatocarbazole (CIT) in aqueous medium in presence of other heavy transition metal ions. Chemical characterization of synthesized 9-ethyl-3-isothiocyanatocarbazole is fully performed by FT-IR, 1H NMR, 13C NMR and single crystal XRD. The theoretical result and experimental values were found to be satisfactorily support each other. From the HOMO-LUMO energy calculation and different thermodynamic parameter, chemical activity and kinetic stability of the molecule has been established by studying density functional theory (DFT). No significant changes found in fluorescence intensity for CIT with varying temperature and pH in medium. The addition of Cd2+ ion in CIT solution exhibits a significant enhancement in fluorescence intensity at 482 nm (ФF = 0.16) and the colour changes instantaneously within a few second. The stoichiometric ratio of the sensing moiety formed in situ was found to be 2:1 from Job's plot and shows the presence of stable Chelation Enhanced Fluorescence (CHEF) mechanism. The average life time of the stable combined CIT with Cd2+ moiety is remarkably higher by 3.29 ns than the native ligand and with other metals. The detection limit is 0.95 μM (S/N = 2). Thus, reported carbazole derivative has excellent promptness, sensitivity and selectivity for the detection of Cd2+ ion in water medium.