Dual Spectroscopic Responses of Pyridinium Hemicyanine Dyes to Anions

The absorption and fluorescence spectroscopic responses of three pyridinium hemicyanine dyes to anions F − , Cl − , Br − , I − , H 2 PO 4 − , HSO 4 − and OAc − were investigated. At lower concentrations of OAc − (less than 1 equiv.), both the absorption and the fluorescence intensities of 1 – 3 were more effectively changed than F − at identical concentrations. At higher concentrations of OAc − (more than 1 equiv.), the interaction was opposite for each compound. 1 H NMR results indicated the interaction between 1 , 2 or 3 and F − proceeded through hydrogen bonding. The results showed that these dyes are promising to develop dual fluorescence and chromogenic chemosensors toward F − and OAc − according to the subtle difference in the affinity of F − and OAc − .