A tricorn-rhodamine fluorescent chemosensor for detection of Co²⁺ ions

A novel chemosensor TrisRh based on tris(2-aminoethyl)amine and rhodamine 6G is designed and synthesized as a fluorescence turn-on probe for Co²⁺ ions that is paramagnetic with a property of quenching fluorescence. Rhodamine spirolactam forms are nonfluorescent, whereas, ring-opening of corresponding spirocyclic induced by Co²⁺ results in strong fluorescence emission. Upon the addition of Co²⁺ ions, TrisRh can display significant enhancements in absorbance and fluorescence intensity as well as evident colorific transformation, which can be perceived by the naked eye. The association stoichiometry of TrisRh to Co²⁺ ions was inferred to be 1:1 through Job's plot and electrospray ionization mass spectrometry analysis. The binding model was speculated from Fourier transform infrared spectra and ¹ H-nuclear magnetic resonance technologies. Significantly, the limit of detection was determined to be as low as 1.22 nmol. Furthermore, TrisRh can exhibit robust anti-jamming ability against other interference metal ions.