A naphthalene-based azo armed molecular framework for selective sensing of Al3+

Abstract

An azo armed Schiff base chemosensor was synthesized based on a naphthalene fluorophore, which transduces greenish-yellow emission by complexing with Al³⁺. It emits greenish-yellow fluorescence through restricted CN isomerization, chelation-enhanced fluorescence, and the photo-induced electron transfer mechanism. The clear visible transformation of the achromatic ligand to a chromatic ligand by the 1 : 1 complexation with Al³⁺ is substantiated by ESI-MS spectra. ¹H NMR, ¹³C NMR, and FTIR spectroscopies are used to characterize the HL. The selectivity of the HL for Al³⁺ in the presence of other metal ions was investigated through absorbance and fluorescence spectroscopies. The average lifetimes of HL and L–Al³⁺ have been evaluated using a time-resolved photoluminescence experiment to explore the sensing mechanism. The Al³⁺ sensing mechanism was also established by density functional theory calculations. A reversibility experiment was performed, demonstrating that Al³⁺ binding to HL is reversible. The pH variation on luminescence affirms that the HL can survive in physiological pH. Finally, the lower limit of detection of 5.4 × 10⁻⁷ and a good response in a cytotoxicity and cell imaging study confirm the usability of the ligand as an indelible signature of an effective biosensor for target Al³⁺.