| Detection of metal ions is important due to their huge impact in biological systems and the environment. Among the various detection methods, fluorescent chemosensors are attractive for the detection of toxic and biologically important analytes due to their high selectivity and sensitivity as well as ease of use in solution. However, many sensors suffer from disadvantages such as a tedious synthetic protocol, instability in solution, and non-selectivity. Thus, the design of simple, stable and selective fluorescent chemosensors is highly desirable. We have employed a practical method for the construction of imine-based fluorescent chemosensors via the condensation of anthraquinone crown ether with aromatic amines in the presence of titanium tetrachloride and DABCO. Both mono- and di-substituted imines have been synthesized in addition to reduced analogues. Most importantly, CE-1,2-benzo diimine, among others, showed high binding affinity towards Ba(II) ions compared to sixteen other metal ions and fluoresces from the OFF to the ON state. After reduction of the internal carbonyl in CE-benzo-15-crown-5 imine with sodium borohydride, this macrocycle showed remarkable fluorescence selectivity for Mn(II) and Zn(II) ions in a proposed tautomerization reaction that produces the corresponding anthracene derivative. |
