Strategy to Design a Flexible and Macromolecular Sensor to Bind Cd²⁺ Ions: A Complete Photophysical Analysis and...

A novel triazole-bridged coumarin-benzimidazole-conjugated fluorescence sensor (4) has been developed for selective detection of Cd²⁺ over other competitive metal ions. The sensor exhibited quick "turn-on" responses upon interaction with a very low level of Cd²⁺ (14 nM). The photophysical changes in the complexation of Cd²⁺ with sensor 4 have been explained through the excited-state intramolecular proton transfer mechanism. The involvement of benzimidazole and triazole moieties in Cd²⁺ binding was confirmed by different spectroscopic techniques such as UV-vis, Fourier transform infrared, nuclear magnetic resonance, and ESI mass. The diameter of the circular shape of the sensor decreased upon complexation with Cd²⁺, which was confirmed by field-emission scanning electron microscopy. Furthermore, the quantum chemical (density functional theory) calculation supported the mechanism of interactions and the mode of binding of 4 toward Cd²⁺. The sensor was more effective for finding Cd²⁺ in two living cells, C6 (rat glial cell) and Hep G2 (human liver cell).