Salicylidene derivatives have been developed as a new set of highly sensitive chromogenic and fluorogenic sensors for anions. A systematic synthesis and investigation of salicylidene derivatives reveals their complementarity with fluoride, acetate and phosphate ions, which can be utilized in anion-sensor binding. Synthesis of receptors proceeded at room temperature or by microwave irradiation, both achieving yields of 80-95 percent with a short reaction time. A substantially red-shifted fluorescence and absorption of receptors in acetonitrile was enhanced upon addition of fluoride, acetate and dihydrogen phosphate depending on the extent of conjugation, nature and the site of substituents in the system. Intense color change and high binding constants demonstrates high sensitivity for fluoride ions as compared to other anions that could allow detection under both visual and fluorescence emission conditions. Investigation of behavior of receptors with anions in different solvents reveals the interaction to be hydrogen bonding in nature.
Due to the importance of fluoride in clinical treatment of osteoporosis and its toxicity from over accumulation in bones there is an increased interest in developing selective optical methods for the detection of fluoride anion. Anion recognition and sensing are of interest because of their importance in biological environmental assays and efforts are paid for developing sensitive methods. We synthesized salicylidene furfurylamine 1 and studied spectral properties. Compound 1 fluoresced strongly and the fluorescence was strongly enhanced in the presence of anions as fluoride at low concentrations. A substantially red-shifted emission in acetonitrile was observed. The excitation at 390 nm and the emission was observed at 469nm. Fluoride showed strong absorption and fluorescence enhancement with a significant Stokes shift. Acetate, dihydrogen phosphate, showed small effect, while chloride, bromide had no significant effect.