A new cell permeable quinazoline based receptor (1) selectively senses HSO4 ions of nanomolar region in 0.1 M HEPES buffer (ethanol–water: 1/5, v/v) at biological pH over other competitive ions through the proton transfer followed by hydrogen bond formation and subsequent anion coordination to yield the [LHSO4]LH+$3H2O (2) ensemble, which has been crystallographically characterised to ensure the structure property relationship. This non-cytotoxic HSO4 ion selective biomarker has great potential to recognize the intercellular distribution of HSO4 ions in HeLa cells under fluorescence microscope.
