Colorimetric detection and differentiation of fluoride and dihydrogenphosphate anions

Benzylidene malononitrile derivatives 2-4 with H-bonding donors were synthesized and studied to colorimetrically detect anions. Compound 3 allows selective colorimetric detection of F− and H2PO4− in organic solvents via intermolecular hydrogen binding, and can distinguish H2PO4− from F− by adding a protic polar solvent such as water. In contrast to compound 3, compound 4 exhibits its selectivity to AcO− superior to H2PO4−. This disparity is likely to be related to the different number and position of OH groups in a benzene ring, which lead to different electronic and steric effects.