Schiff base derived Fe3+-selective fluorescence turn-off chemsensors based on triphenylamine and indole: synthesis, properties and application in living cells

Two Schiff base derivatives (S1 and S2) containing triphenylamine and indole fluorophores groups have been synthesized via a one-pot reaction and utilized as fluorescence turn-off sensors towards Fe3+ ions in THF. S1 and S2 demonstrated fluorescence turn-off sensing towards Fe3+ ions, via photoinduced electron transfer (PET). The 2 : 1 stoichiometries of the sensor complexes ([S1, S2] + Fe3+) were calculated from Job plots based on UV-vis absorption titrations. The detection limits (LODs) of [S1, S2] + Fe3+ sensor responses were calculated by their standard deviation, linear fitting and from their fluorescence binding isotherms. More importantly, [S1, S2] + Fe3+ sensors were found to be active in aqueous media within a wide range of pH values. In addition, biological imaging and membrane permeability demonstrated that S1 could act as a turn-off fluorescence chemosensor for Fe3+ in living cells.