A highly selective fluorescent chemosensor for fluoride based on an anthracene diamine derivative incorporating indole

A new fluorescent sensor 1 for F− was designed and synthesized through the condensation of 1,8-anthracene diamine and indole-2-carboxylic acid via DCC. Upon mixing with F− in DMSO:CH2Cl2 (1:9, v/v), the increases in fluorescence could be observed. No obvious changes could be found upon the addition of other anions such as Cl−, Br−, I−, NO3−, HSO4−, H2PO4−, AcO−. Job plots indicated the formation of 1:1 complex of 1 and F− with association constant K = 7.3 × 104 M−1. 1H NMR titration experiments indicated that fluoride anion had strong hydrogen bonding interactions not only with the N–H of the amide but also with the indole N–H and the 9-H of anthracene. This rigidified the structure and led to the reduction of the efficiency of the PET process and the enhancement of fluorescence intensity.