Strategy to Design a Flexible and Macromolecular Sensor to Bind Cd(2+) Ions: A Complete Photophysical Analysis and Bio-Imaging Study

[Image: see text] A novel triazole-bridged coumarin–benzimidazole-conjugated fluorescence sensor (4) has been developed for selective detection of Cd(2+) over other competitive metal ions. The sensor exhibited quick “turn-on” responses upon interaction with a very low level of Cd(2+) (14 nM). The photophysical changes in the complexation of Cd(2+) with sensor 4 have been explained through the excited-state intramolecular proton transfer mechanism. The involvement of benzimidazole and triazole moieties in Cd(2+) 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 Cd(2+), 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 Cd(2+). The sensor was more effective for finding Cd(2+) in two living cells, C6 (rat glial cell) and Hep G2 (human liver cell).