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

Abstract

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 AsO2–, and 3.2 × 10–6 M for H2PO4–, whereas the respective association constants are 4.21 × 105 M–1 for Mo(VI), 6.49 × 104 M–1 for AsO2–, and 2.11 × 105 M–1 for H2PO4–. The L is useful for efficient enrichment of Mo(VI) from aqueous solution, while M1 efficiently removes AsO2– from environmental samples by solid-phase extraction.