A new fluorescent chemosensor for fluoride anion based on a pyrrole–isoxazole derivative

Molecules containing polarized NH fragments that behave as anion-binding motifs are widely used as receptors for recognition and sensing purposes in aprotic solvents. We present here a new example of a receptor, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (receptor 1), which contains pyrrole, amide and amino subunits. This receptor shows both changes in its UV–vis absorption and fluorescence emission spectra upon the addition of F(−), resulting in highly selectivity for fluoride detection over other anions, such as Cl(−), Br(−), I(−), HSO(4)(−), H(2)PO(4)(−) and AcO(−) in CH(3)CN. (1)H NMR titration, time-dependent density functional theory (TDDFT) calculations and other experiments confirm that the sensing process is brought about by deprotonation of the pyrrole-NH in receptor 1.