Highly selective CHEF-type chemosensor for lutetium (III) recognition in semi-aqueous media

A simple phosphoryl quinolone (L) based sensor has been synthesized for the selective recognition of Lu³⁺ by spectrofluorimetric method. In methanol-water (1:1, v/v), the ligand L exhibits a weak emission peak at 400 nm upon excitation at 280 nm. Upon interaction with various f-metal and other selected metals from s, p, and d-block elements, the fluorescence of L is selectively enhanced in the presence of Lu³⁺ due to the chelation enhanced fluorescence (CHEF) effects. The quantum yield (φ) of L (φ = 0.063) is enhanced to φ = 0.118 upon chelation with Lu³⁺ ion. From the titration experiment, the limit of detection (LOD) of sensor L to recognize Lu³⁺ is estimated down to 24.2 nM, which is much lower than the WHO guidelines (76 μM) in drinking water. The formation of host-guest complexation between L and Lu³⁺ in 2:1 binding stoichiometry is studied by Job's method and the binding constant is estimated by band fit analysis (logK_f = 5.1). Further, the coordination behaviour between L and Lu³⁺ is well supported by FT-IR, ¹H NMR, ¹³C NMR, ³¹P NMR, ESI mass spectral data and the theoretical results.