Phenothiazine–aminothiourea–Hg(II) ensemble-based fluorescence turn-on toward iodide in aqueous media and imaging application in live cells

•One dual-functional fluorescence probe based on phenothiazine was designed.•P1 shows a highly selective fluorescent response to trace amounts of Hg2+.•[P1+Hg2+] ensemble is also further successfully utilized for detection of the I−.•This system can also be applied in Human Umbilical Vein Endothelial Cells. A phenothiazine–aminothiourea-based open chemosensor (P1) has been designed and synthesized, which exhibits high selectivity toward Hg2+ by forming a 1:1 complex. In its Hg2+ ensemble, it is reported as a highly sensitive and selective probe for the detection of iodide based on the displacement approach in aqueous solution. The addition of iodide to a solution of phenothiazine–aminothiourea–Hg2+ ensemble resulted in a rapid and remarkable fluorescence off–on (emission at 565nm). The practical use of an ‘ensemble’ was demonstrated by its application to the detection of iodide in the living cells.