First rhodamine-based “off–on” chemosensor with high selectivity and sensitivity for Zr4+ and its imaging in living cell

A new pyridine–thiophene appended rhodamine-based probe RhPT was synthesized as “off–on” chemosensor for Zr4+. Rhodamine spirolactam or spirolactone derivatives are nonfluorescent and colorless, whereas ring-opening of the corresponding spirolactam/lactone gives rise to strong fluorescence emission and a pink color. However, in the present case, chemosensor RhPT shows high sensitivity and selectivity toward Zr4+ ions by exhibiting both colorimetric and fluorescence responses in CH3OH–water (4:1, v/v, 10 μM HEPES buffer, pH 7.4). The selectivity of RhPT to the various metal ions was investigated. A color change and marked enhancement of fluorescence was found in the presence of Zr4+ due to the ring open reaction of rhodamine. The sensor shows extremely high fluorescence enhancement upon complexation with Zr4+ and it can be used as a “naked eye” sensor. The visual detection is possible by a sharp change in color. In addition, the turn-on fluorescent probe upon the addition of Zr4+ was applied in live cell imaging.