Exploration of fluorescence behavior of an imidazolium-based chemosensor in solution and in the solid state and its turn-on response to Al3+ in pure aqueous medium

Abstract

An imidazolium-based quinoline Schiff base ImSB was developed and fully characterized by FT-IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry, and X-ray crystallography. The fluorescence behaviour of ImSB in solution and in the solid state, keto–enol stability at different concentrations and pH in aqueous medium were investigated. The UV-visible and fluorescence studies were performed to determine the response of ImSB towards different ions in aqueous medium. ImSB showed a turn-on fluorescence behaviour with high selectivity towards Al³⁺ over various cations and anions due to chelation-enhanced fluorescence (CHEF), inhibition of photoinduced electron transfer (PET) and restriction of CN isomerization. The low detection limit for Al³⁺ was 54 nM and Job's plot confirmed 1 : 1 stoichiometry between ImSB and Al³⁺ with a high binding constant value of 4.16 × 10⁶ M⁻¹. Monitoring of Al³⁺ was also demonstrated in real water samples (mineral, river and tap water). The structural and electronic parameters of ImSB and ImSB-Al³⁺ were also studied theoretically.