A multidentate ligand chromophore with rhodamine-triazole-pyridine units and its acting mechanism for dual-mode visual sensing trace Sn2+

A multidentate ligand chromophore, combining rhodamine, triazole, and pyridine units, was identified and developed for the first time. Using triazole and pyridine rings as coordinating functional recognition groups, it was expected to selectively recognize Sn2+ to form some stable 5-member or 6-member rings with nitrogen and oxygen atoms. Under the optimized conditions, the ligand chromophore could selectively react with trace Sn2+ in CH3CN/H2O (99/1, v/v), accompanying with obvious changes in fluorescent spectrum, ultraviolet-visible spectrum and visual color. For fluorescent analysis, a turn-on fluorescence at 587 nm was found and increased linearly in the range of 1.2–6.2 × 10−7 mol L−1 Sn2+ from colorless to orange. For ultraviolet-visible one, a new absorption peak at 560 nm emerged with a linear range of 2.0–11.0 × 10−7 mol L−1 Sn2+ from colorless to pink. The action mechanism between the ligand chromophore and Sn2+ was confirmed basing on ultraviolet-visible titration, 1H NMR titration, Job's plot, binding constants and theoretical calculation in detail.