An acridone-based receptor, Acridox-R offers sensitive and selective detection of F- by means of color change from yellow to orange and emission switch-on response. Other anions, AcO-, Cl-, Br-, I-, NO3-, SCN-, and HSO4- revealed none or at best weak optical perturbation even at 10-fold higher concentration. The N-H deprotonation is supported by H-1 NMR and the detection limit is 1.93 x 10(-7) mol L-1.