A concave fluorescent sensor for anions based on 6-methoxy-1-methylquinolinium.

The ligand 2, in which three fluorogenic 6-methoxy-1-methylquinolinium fragments are appended to a mesityl platform, in MeCN forms 1:1 adducts with halides and other inorganic anions. (1)H NMR studies and molecular modelling indicate that 2 provides a cavity for anion inclusion and establishes electrostatic interactions with the guest. Anion inclusion induces quenching of the fluorogenic fragments with an efficiency decreasing along the series Br(-)>>I(-)>NCS(-)>>Cl(-)>NO(3) (-)>HSO(4) (-). The fluorimetric response of 2 to anions is orders of magnitude more sensitive than that of just 6-methoxy-1-methylquinolinium, ligand 1.