New coumarin-urea based receptor for anions: a selective off-on fluorescence response to fluoride

A novel fluorosensor for anions, 1,11-bis(4-methylcoumarin-7-yl)-6-methyl-1,3,6,9,11-pentaazaundeca- 2,10-dione (L), which contains two coumarineurea units spaced by a flexible diethylenetriamine fragment, was easily prepared in 65% yield by a one-pot two-step procedure. The binding ability of L toward several anions (G) was evaluated by 1H NMR, UVevis, and fluorescence titration. It was found that L forms stable [LG] and [LG2] species in both DMSO and CH3CN solvents. Furthermore, the fluorescenceemission of L in the visible range (400 nm) is affected by the presence of anions; it is quenched by acetate, chloride, and pyrophosphate while it is enhanced by fluoride. Thus, this novel fluorosensor provides a selective offeon response to the presence of fluoride in solutio