An ESIPT characteristic “turn-on” fluorescence sensor for Hg2+ with large Stokes shift and sequential “turn-off” detection of S2– as well as the application in living cells

[Display omitted] •A “turn-on” fluorescent probe ol-PIP selectively responded to Hg2+ with large Stokes shift of 180 nm.•Subsequently, strong emission of ol-PIP–Hg2+ was quenched followed by S2–.•The process of the sequential sensing was realized in cells imaging. An excited state intramolecular proton transfer (ESIPT) characteristic “turn-on” fluorescence sensor for Hg2+ with large Stokes shift was fabricated and then it had ability to sequentially detect S2– by the “turn-off” fluorescent signal in aqueous media. On account of it, a simple fluorescence probe ol-PIP based on the phenanthro[9,10-d]imidazole moiety bearing two phenol fragments was synthesized. Probe ol-PIP showed gradually the fluorescence enhancement with the increasing of water fraction due to the aggregation affect. Sequentially, the moderate fluorescence emission of ol-PIP in aqueous media was continuously and selectively illumined by the successive addition of Hg2+ with about 180 nm Stokes shift. Furthermore, the persistent “turn-on” fluorescence intensity could be quenched to the original state of ol-PIP in presence of S2–. This on–off sensing process was sustained for five times with the alternative addition of Hg2+ and S2–. The limits of detection for Hg2+ and S2– were 6.45 × 10–7 and 3.46 × 10–7 M, respectively. In addition, ol-PIP was successfully applied in Hg2+ detection in real water samples; simultaneously, ol-PIP with low cytotoxicity was also successfully used as a bioimaging reagent to detect Hg2+ and S2– in living cells.