Carbazole-based Schiff base: A sensitive fluorescent ‘turn-on’ chemosensor for recognition of Al(III) ions in aqueous-alcohol media

Abstract

Carbazole-based Schiff base chemosensor was synthesized in one-pot synthesis using 2-hydroxy-1-naphtaldehyde for fluorescent sensing of Al3+ ions. Characterization of the ligand (L) was revealed through spectroscopic and physicochemical techniques. The fluorescence emission responses of L to various metal ions and anions were investigated. The chelation was studied by UV–vis, 1H NMR, LC-MS/MS, fluorescence titration and Job’s plot analysis. Bathochromic shift resulted from charge transfer from L to electrophilic Al3+ ion was observed in the chelation of L with Al3+. The potentiality of L to be a distinguished probe to detect Al3+ ions was due to a chelation enhanced fluorescence (CHEF) effect, concomitant with noticeable fluorescent enhancement. A significant fluorescence enhancement at 533 nm was observed in ethanol–water (1:1, v/v) solution upon addition of Al3+ along with a distinct color change from yellow to white. Non-fluorescent ligand exposed highly sensitive turn-on fluorescent sensor behavior for selectively sensing Al3+ ions via 1:1 (ligand:metal) stoichiometry. The ligand’s specificity in the existence of other tested metal ions and anions indicated no observation in color change. The ligand-Al3+ complex formation was reversible upon addition of chelating agent EDTA. The ligand interacted with Al3+ ions with an association constant of Ka = 5 × 104 M−1. The limit of detection (LOD) was found to be 2.59 × 10-7 M. The synthesized Schiff base could efficiently detect Al3+ ions as a fluorescent sensor.

Keywords

• Schiff base
• Fluorescent chemosensor
• ESIPT
• Al3+
• Job’s plot
• CHEF effect