The structural properties of 5-methyl-2-phenyl-2H-1,2,3-triazole-4- carboxylic acid and chromogenic mechanism on its rhodamine B derivatives to Hg2+ ions.

5-Methyl-2-phenyl-2H-1,2,3-triazole-4-carboxylic acid (MPTC), a newly synthesized compound, was explored to study the structural properties and theoretical spectra by using GaussView5.0 program package and the time dependent density functional theory (TD DFT). The calculated quantum chemical values suggested that it is easy for MPTC to lose electron with weak electron accepting ability. And the results of experimental measurements on fluorescence and absorption spectra were consistent with that of the calculated spectra in great degree. In addition, MPTC was successfully used and synthesized a novel rhodamine B derivative RMPTC containing 1,2,3-triazole unit. It is found that there is special chromogenic response of RMPTC to Hg2+ ions in N, N-dimethylformamide (DMF)-H2O (v/v=1/1, Tris-HCl, pH7.4) with the triazole appended colorless chemosensor turned to pink and enabled naked-eye detection. The fluorescence signal for RMPTC-Hg2+ system was not affected by other coexisting metal ions. The 1:2 stoichiometric structure of RMPTC and Hg2+ is confirmed using a Job's plot estimation and TD DFT calculations. The corresponding "off-on" fluorescence mechanism of RMPTC binding to Hg2+ which were ascribed to Hg2+ inducing the ring-opened rhodamine B moiety were proposed. This study was an advancement for the application of 1,2,3-triazole compound in photophysical chemistry field and provides guidance for exploring simple and high-selectivity Hg2+ probes in aqueous solutions under physiological conditions.