A Novel Cr(3+) Fluorescence Turn-On Probe Based on Rhodamine and Isatin Framework

A novel turn-on fluorescent dye (E)-3',6'-bis(diethylamino)-2-((1-(naphthalen-2-ylmethyl)-2-oxoindolin-3-ylidene)amino)spiro[isoindoline-1,9'-xanthen]-3-one (RBNI) based on a rhodamine-isatin hybrid molecular architecture was synthesized by condensation of isatin derivative with rhodamine hydrazide. The dye RBNI is selective and sensitive for recognition of Cr(3+) ion in aqueous CH3CN media over other tested metal ions. The sensor shows large fluorescence enhancement upon complexation with Cr(3+) and simultaneous color change occurs from colorless to pink-red. Spectroscopic study predicted 1:1 binding stoichiometry between RBNI and Cr(3+) ion and this was again verified through ESI-MS (Electrospray Ionisation Mass Spectrometry). Detection limit of Cr(3+) ion by this dye was calculated to be 2.4 μM. Furthermore, the potential application of this dye for the monitoring of Cr(3+) ions in pond water and tap water samples was demonstrated.