Novel fluorescent sensors based on coumarin-hydrazide-hydrazone hybrid for the detection of CN−, Co2+ and Ni2+ ions: DFT and bioimaging in living cells

Abstract

Novel coumarin-hydrazide-hydrazone hybrids, (E)-7-(diethylamino)-N′-(2-hydroxy-3-methoxybenzylidene)-2-oxo-2H-chromene-3-carbohydrazide (1) and (E)-7-(diethylamino)-N′-(4-(diethylamino)-2-hydroxybenzylidene)-2-oxo-2H-chromene-3-carbohydrazide (2), were synthesized and investigated their chemosensor properties. The sensors showed recognition properties of CN−, Co2+, and Ni2+ ions. After interaction with the cyanide anion, the coumarin-hydrazide-hydrazone sensors exhibited a color change visible to the naked eye, from yellow to colorless under daylight and from blue to green under UV light. The sensors exhibited a significant fluorescent enhancement response to the cyanide anion by the intramolecular charge transfer (ICT) mechanism. Furthermore, the recognition of cations was observed by the redshift of the emission band based on the complexation mechanism of Co2+ and Ni2+ ions with the sensors. Sensor 1 showed that CN− and Ni2+ ions could be detected at a limit of detection (LOD) of 0.187 μM and 0.169 μM, respectively, while sensor 2 showed that Co2+ anion could be detected at a LOD of 0.177 μM. Anion and cation recognition mechanisms were also investigated by Density Functional Theory (DFT) analysis for the sensors. Cell viability and proliferation-based cytotoxicity (MTT) and live cell imaging assays of sensor 2 were performed to elucidate whether it could be used as cell bioimaging. It was determined that sensor 2 was not cytotoxic against the A549 cell line at the concentrations where it could act as a chemosensor for the detection of CN−, Co2+, and Ni2+ ions, and it penetrated into the cell and accumulated around the nucleus. These properties of sensor 2 indicate that it can be used as a potential sensor in cell imaging systems. In addition, the photophysical properties of the sensors in various solvents with different polarities were investigated using spectroscopic techniques for absorption and emission maximum wavelengths. The thermal stability of the sensors was determined by Thermal Gravimetric Analysis (TGA), and it can be said that the theoretical and experimental studies are in perfect harmony.