Rhodamine based “turn–on” molecular switch FRET–sensor for cadmium and sulfide ions and live cell imaging study

[Display omitted] •A rhodamine-based turn-on fluorescence probe (RBD4) was synthesized and characterized by 1H NMR, 13C NMR and ESI–MS.•The X-ray crystal structure analyses exhibit the spirolactone of fluorescent sensor RBD4.•Highly selective towards Cd2+ ion over other metal ions conformed by XRD, SEM, EDAX and FT–IR studies.•The 1:1 stoichiometric structure between RBD4 and Cd2+ were supported by Job's plot, Benesi-Hildebrand plot and DFT theoretical calculations.•RBD4 fluorescent sensor was used in imaging Cd2+ in cultured HeLa cells. A novel fluorescent chemosensor based on a rhodamine derivative (RBD4) was designed, synthesized, and used as a selective Cd2+ ion sensor. The structure of the fluorescence sensor (RBD4) is confirmed through single crystal X-ray study. On the basis of the Förster resonance energy transfer mechanism between rhodamine and pyridine conjugated dyad, a new colorimetric as well as fluorescence probe was synthesized for the selective detection of Cd2+. This sensor shows high selectivity towards Cd2+ ions in the presence of other competing metal ions. On the basis of thorough experimental and theoretical findings, the additions of Cd2+ ions to the solution of RBD4 helps to generate a new fluorescence peak at 590nm due to the selective binding of Cd2+ ions with RBD4 in a 1: 1 ratio with a binding constant (K) of 4.2524×104M−1. The detection limit of RBD4 for Cd2+ was 1.025×10−8M, which presented a pronounced sensitivity towards Cd2+. The in situ generated RBD4–Cd2+ complex is able to selectively sense S2− over other anions based on the displacement approach, given a remarkable recovery of fluorescence and UV–vis absorption spectra. The fluorescence sensor has also exhibited very good results in HeLa Cells imaging under physiological pH.