Preparation of 4,4'-bis-(carboxyl phenylazo)-dibenzo-18-crown-6 dye and its application on ratiometric colorimetric recognition to Hg2+.

A multifunctional dye, 4,4'-bis-(carboxyl phenylazo)-dibenzo-18-crown-6 dye (BCADC) was designed and prepared via diazotization and coupling reaction of dibenzo-18-crown-6 with p-amino benzoic acid. The dye, combining crown ether ring, azo and carboxyl group, exhibits well-defined Hg(2+)-selective ratiometric colorimetric behavior, with the maximum absorbance peak changing from 354 nm to 408 nm exclusively. Under the optimum conditions, the recognition to Hg(2+) has a linear range of 2.5-58×10(-7) mol L(-1) with a 0.9978 correlation coefficient. The method was applied to analyse 3 environmental water samples with a detection limit of 2.9×10(-8) mol L(-1) and a relative standard deviation (R.S.D.) lower than 3.7% (n=5). The action mechanism between BCADC and metal ions was discussed by means of Job's plots and theoretical calculations.