Synthesis and Characterization of a Visualization and Water-Soluble Fluorescent Probe for Al3+

In order to improve the water-solubility of 4-(2'-hydroxypheny1)-pyrimido[1,6-a]benzimidazole and 4-(2'-hythxyphenyl-4'-isopropoxy)-pyrimido[1,6-a]benzimidazoles, they were sulfonated in 98% H2SO4. Sodium 4-(2'-hydroxypheny1)pyrimido[1,6-a]benzimidazole-5-sulfonate (L1), sodium 4-(2'-hydroxyphenyl)-pyrimido[1,6-cdbenzimidazole-3',5',10'-three-sulfonate (L2), sodium 4-(2',4'-dihydroxyphenyl)pyrimido[1,6-a]benzimidazol-5-sulfonate (L3) were obtained and indentified by the method of NMR, IR and MS. Fluorescence spectra of L1, L2 and L3 were detected, and they have the ESIPT effect with a large Stokes shift (175 similar to 225 nm). The structures of these compounds could be complex with Al3+, and the fluorescence spectra of Al3+ in Li, L2 and L3 were analyzed. The results showed that L2 exhibited good sensitivity selectivity to Al3+. The fluorescence of L2 was strengthened dramatically in the presence of Al3+. Other metal ions, such as Cu2+, Hg2+, K+, Mg2+, Na+, Ni2+, Pb2+, Zn2+, Cr3+, Fe3+ induced negligible fluorescence strengthening for L2 under the same conditions. When the concentration (0 similar to 20 pmol/L) of Al3+ was increased, the fluorescence intensity of L2 (10 mu mol/L) was also increased. The Job's plot and fluorescence titration indicated that the stoichiometry of L2-Al3+ was 1: 2 and the detection limit of Al3+ was 0.073 mu mol/L. Moreover, L2 was used for the visual detection of Al3+.