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

Rationally designed multiple hydroxyl-group-based chemosensors L1-L4 containing arene-based fluorophores are presented for the selective detection of Al3+ and Ga3+ ions. Changes in the absorption and emission spectra of L1-L4 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 L4, showing the best results. The interaction of Al3+/Ga3+ ions with chemosensor L4 was investigated by fluorescence lifetime measurements, whereas Job's plot, high-resolution mass spectrometry, and 1H NMR spectral titrations substantiated the stoichiometry between L4 and Al3+/Ga3+ ions. The solution-generated [L-M3+] species further detected pyrophosphate ion (PPi) by exhibiting emission enhancement and a visible color change. The binding of Al3+/Ga3+ ions with chemosensor L4 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.