Optical sensing of hydrogen sulphate using rhodamine 6G hydrazide from aqueous medium

This communication reports the application of rhodamine 6G hydrazide (L) for the selective colorimetric and turn-on fluorescent sensing of hydrogen sulphate ions from aqueous medium. The ring opening of the colourless spirocyclic form of L was selectively triggered in the presence of HSO₄^- among the other tested anions (F^-, Cl^-, Br^-, I^-, AcO^-, H₂PO₄^-, NO₃^-, ClO₄^-, CN^-, HO^-, AsO₃^3- and SO₄^2-), which gives rise to a pink colour and strong fluorescence in the visible region. Sensor L showed a detection limit down to micromolar range without any interference from the other tested competitive anions. Sensor L was applied for the construction of two inputs (HO^- and HSO₄^-) INHIBIT type molecular logic gate and naked-eye detection of HSO₄^- using test paper strips.