Highly selective Cu detection with a naphthalimide-functionalised pillar[5]arene fluorescent chemosensor.

Ligand 1, a rim-differentiated pillar[5]arene macrocycle modified with five naphthalimide groups through click chemistry, serves as an effective ratiometric fluorescent chemosensor for Cu. In contrast to the monomeric naphthalimide control compound 2, which shows only monomer emission, ligand 1 demonstrates dual emission characteristics encompassing both the monomer and excimer of the naphthalimide moieties. The binding properties of ligand 1 toward 15 different metal ions were systematically investigated in CHCl/CHCN (v/v, 1 : 1) by UV-vis and fluorescence spectroscopy. Remarkably, ligand 1 exhibits exceptional selectivity for Cu ions. Upon complexation with Cu, the excimer emission of ligand 1 diminishes, concomitant with an enhancement of its monomer emission. The binding ratio for 1·Cu was determined to be 1 : 1, with an association constant of (3.39 ± 0.40) × 10 M calculated using a nonlinear least-squares curve-fitting method. Furthermore, the limit of detection (LOD) was found to be 185 ± 7 nM. Our results from H NMR titration, high-resolution mass spectrometry analysis and density functional theory calculations of 1·Cu suggest synergistic coordination between Cu and the triazole groups on ligand 1.