A triple action chemosensor for Cu²⁺ by chromogenic, Cr³⁺ by fluorogenic and CN^- by relay recognition methods with bio-imaging of HeLa cells

A triple action chemosensor (R1) bearing a rhodamine and thiophene moiety was synthesized by a simple condensation reaction. The sensing behaviour and selectivity of the synthesized chemosensor toward metal ions were studied by UV-Vis and fluorescence spectroscopy. The chemosensor recognized Cu²⁺ and Cr³⁺ ions with significant changes in UV-Vis absorbance and fluorescence intensity. The results showed that Cr³⁺ induced greater fluorescence enhancement whereas Cu²⁺ ions bound strongly with the receptor by showing a strong absorption band at 554 nm but with weak fluorescence. A visible colour change was observed by the addition of Cu²⁺ and that colour change is due to the opening of the spirolactam ring triggered by the addition of Cu²⁺ ions. Job's plot analysis indicated a 1:2 and 1:1 binding stoichiometry between the chemosensor and Cr³⁺/Cu²⁺. Subsequently, the R1 - Cu²⁺ complex chemosensor was employed to detect CN^- in the presence of different anions, such as F^-, Cl^-, Br^-, I^-, AcO^-, H₂PO₄ ^-, HSO₄ ^-, NO₃ ^- and ^-OH. In addition, the live cell imaging of HeLa cells using R1 and Cr³⁺ was demonstrated successfully.