Fluorescence anion sensors based on combination of conformational restriction and photo-induced electron transfer

Six fluorescence and colorimetric sensors (1–6) were designed and synthesized through a facile method. These compounds, whose structures were characterized by 1H NMR, elemental analyses and MS, could be easily prepared by simple synthesis method. In these sensor molecules, azo group and conjugated di-benzene unit acted as a chromophore and a fluorophore; respectively, and phenol moieties are anion binding sites. In dry DMSO solution, significant red shifts in UV–vis spectra with visible color changes were observed when the sensors were exposed to anions with strong base. Particularly, the simple compounds gave interesting fluorescence changes upon presence of anions, which probably resulted from electronic effects of the substituent. The sensors (1–3) with the nitro group exhibited ‘turn-on’ fluorescence responses to anions due to conformational restriction and 4–6 with absence of –NO2 group showed ‘turn-off’ fluorescence responses to anion owing to photo-induced electron transfer.