A polynuclear hetero atom containing molecular organic scaffold to detect Al3+ ion through a fluorescence turn-on response

Abstract

A simple polynuclear hetero atom (N and O) containing molecular organic scaffold/probe, 3 has been designed and synthesized and explored as a potential chemosensor to detect Al³⁺ (22 nM; ∼0.6 ppb) ion in a HEPES buffer. Upon interaction with different metal ions and anions the weak emission intensity (switched Off) of 3 (at 528 nm; λ_ex = 376 nm) was enhanced significantly (switched On; ∼6.0 fold; Φ_3+Al³⁺ = 0.07) only in the presence of Al³⁺ wherein, the color of the solution changed from a naked-eye sensitive fluorescent dark green to bright yellow-green. The observed chelation enhanced fluorescence (CHEF) is attributable to restricted ESIPT and CN isomerization processes due to complexation between the potential coordination sites (N and O atoms; hard base) of 3 and Al³⁺ (hard acid) in a 1 : 1 stoichiometry, consequently. The mechanism of the interaction has been confirmed by the change in optical behaviors, ¹H/¹³C NMR, FTIR, and ESI-MS spectroscopy data analysis. Moreover, chemosensor 3 has also been utilized to detect Al³⁺ in real water samples and on test paper strips.