A novel phosphate chemosensor utilizing anion-induced fluorescence change

The neutral receptor NN'-bis{3,5-di[(1-pyrenylmethyl)carbamoyl]benzyl} pyridine-2,6-dicarbamide (2) provides a pseudo-tetrahedron cleft and multiple hydrogen bondings to form a 1:1 complex with phosphate ion in a highly selective manner, by comparison with other anions (F-, CI-, Br-, SCN-, AcQ(-), NO3-, ClO4-, and HSO4-). The binding strength can be inferred from the emission intensity ratio of the pyrene monomer (lambda(max) 377 nm) to the excimer (lambda(max) 477 nm). Fluorescence titration, X-ray analysis, and NMR studies support a proposed complexation model.