Sequential Fluorescence Recognition of Molybdenum(VI), Arsenite, and Phosphate Ions in a Ratiometric Manner: A Facile Approach for Discrimination of AsO2- and H2PO4-

An amide-based smart probe (L) is explored for nanomolar detection of Mo(VI) ion in a ratiometric manner, involving hydrogen-bond-assisted chelation-enhanced fluorescence process through inhibition of photoinduced electron transfer process. The recognition of Mo(VI) is associated with a 17-fold fluorescence enhancement and confirmed by single-crystal X-ray diffraction of the resulting Mo(VI) complex (M1). Further, M1 selectively recognizes arsenite through green emission of their adduct (CI) with an 81-fold fluorescence enhancement. Interestingly, dihydrogen phosphate causes dissociation of Cl back to free L having weak fluorescence. The methods are fast, highly selective, and allow their bare eye visualization at physiological pH. All of the interactions have been substantiated by time-dependent density functional theory calculations to rationalize their spectroscopic properties. The corresponding lowest detection limits are 1.5 X 10(-8) M for Mo(VI), 1.2 x 10(-10) M for AsO2-, and 3.2 X 10(-6) M for H2PO4-, whereas the respective association constants are 4.21 X 10(5) M-1 for Mo(VI), 6.49 X 10(4) M-1 for AsO2-, and 2.11 X 10(5) M-1 for H2PO4-. The L is useful for efficient enrichment of Mo(VI) from aqueous solution, while M1 efficiently removes AsO(2)(- )from environmental samples by solid-phase extraction.