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 inorg. anions. 1H NMR studies and mol. modeling 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->NO3->HSO4-. The fluorometric response of 2 to anions is orders of magnitude more sensitive than that of just 6-methoxy-1-methylquinolinium, ligand 1.