Anion-induced fluorescence quenching and excimer formation of anthracene-imidazolium receptor

New anthracene based fluorescent anion receptor bearing two imidazolium units linked by methylene spacers at 9,10-positions has been synthesized. Complexation behavior and fluorescent properties of the receptor with inorganic anions (Cl-, Br-, I-, NO3-, HSO4-, and H2PO4-) in acetonitrile were investigated by H-1 NMR spectrometric and fluorimetric titrations, and fluorescence lifetime measurement. At low receptor concentration level (0.1 mu M), fluorescence of the receptor was quenched by formation of 1:1 host-guest complex with the anions. At relatively higher receptor concentrations (above 1.0 mu M), H2PO4- anion quenched the monomer emission mainly by the excimer formation due to anion-induced ground state aggregation. Fluorescence lifetime measurements revealed that quenching mechanisms are different between halide ions and oxoanions.