Turn-On Fluorescent Sensors for the Selective Detection of Al³⁺ (and Ga³⁺) and PPi Ions

Abstract

Rationally designed multiple hydroxyl-group-based chemosensors <b>L1</b>-<b>L4</b> containing arene-based fluorophores are presented for the selective detection of Al³⁺ and Ga³⁺ ions. Changes in the absorption and emission spectra of <b>L1</b>-<b>L4</b> in ethanol were easily observable upon the addition of Al³⁺ and Ga³⁺ ions. Competitive binding studies, detection limits, and binding constants illustrate significant sensing abilities of these chemosensors with <b>L4</b>, showing the best results. The interaction of Al³⁺/Ga³⁺ ions with chemosensor <b>L4</b> was investigated by fluorescence lifetime measurements, whereas Job's plot, high-resolution mass spectrometry, and ¹H NMR spectral titrations substantiated the stoichiometry between <b>L4</b> and Al³⁺/Ga³⁺ ions. The solution-generated [<b>L</b>-M³⁺] species further detected pyrophosphate ion (PPi) by exhibiting emission enhancement and a visible color change. The binding of Al³⁺/Ga³⁺ ions with chemosensor <b>L4</b> was further supported by density functional theory studies. Reversibility for the detection of Al³⁺/Ga³⁺ ions was achieved by utilizing a suitable proton source. The multiionic response, reversibility, and optical visualization of the present chemosensors make them ideal for practical applications for real samples, which have been illustrated by paper-strip as well as polystyrene film-based detection.