Selective Detection of Fe(III) and Al(III) Using an Azo-Functionalized Rhodamine B Chemosensor: Expansion to F- Ion Detection by Al(III)-Probe Complex.

An azo-functionalized Rhodamine-B based chemosensor, HL [4-((E)-(3-((Z)-((3',6'-bis(diethylamino)-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)imino)methyl)-5-ethoxy-4-hydroxyphenyl)diazenyl)benzoic acid], has been developed and spectroscopically characterized. Impressively, among competitive cations, the sensor can detect Al(III) and Fe(III) in a methanol-water (9:1, v/v) medium by changing its optical color and turning on fluorescence response. The low limit of detection (LOD) value (72 µM) and the sensor's reproducibility assure us about its practical applicability. The spirolactam ring opening in the presence of two target cations induces the luminescence character to the chemosensor, and the NMR spectrum validates this fact. The HL-Al(III) complex can selectively detect F- ion among several competing anions via turn-off fluorescence in a methanol-water medium. Coordination of F- to the metal ion frees the bare probe with its ring-closing form, leading to fluorescence quenching. Mass spectral data and Job's plot confirm the 1:1 probe-analyte stoichiometry. As a practical application, the sensor can quantify Al(III) in commercially available pharmaceutical samples, and the Sensor-Al(III) complex can detect F- in locally available water samples.