Coumarin-hemicyanine-based ratiometric fluorescent probes for detection of strong acidity.

Fluorescent probes for determination of strongly acidic pH values are urgently needed, especially the ones with ratiometric signal changes. Here, two fluorescent probes (CP and CyC) based on coumarin-hemicyanine were synthesized. Both probes emitted red fluorescence under weakly acidic to weakly alkaline conditions, whereas blue fluorescence under strongly acidic conditions. Notably, probe CP displayed good stability, water solubility, anti-interference ability, repeated utilization and instant response. Encouraged by the good performance, probe CP based test strips were used to indicate the pH of aqueous solutions, and to detect HCl or NH 3 vapor in air reversibly. [Display omitted] • Two ratiometric fluorescent probes to detect extreme acidity are synthesized. • The probe CP shows desired properties and good performance in detecting pH. • The probe CP can be conveniently used on paper strips and in real water samples. [ABSTRACT FROM AUTHOR]