Sequential Fluorescence Recognition of Molybdenum(VI), Arsenite, and Phosphate Ions in a Ratiometric Manner: A Facile Approach for Discrimination of AsO(2)(–) and H(2)PO(4)(–)

[Image: see text] 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 (C1) with an 81-fold fluorescence enhancement. Interestingly, dihydrogen phosphate causes dissociation of C1 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 × 10(–8) M for Mo(VI), 1.2 × 10(–10) M for AsO(2)(–), and 3.2 × 10(–6) M for H(2)PO(4)(–), whereas the respective association constants are 4.21 × 10(5) M(–1) for Mo(VI), 6.49 × 10(4) M(–1) for AsO(2)(–), and 2.11 × 10(5) M(–1) for H(2)PO(4)(–). 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.