Integrated pyrazolo[1,5-a]pyrimidine-hemicyanine system as a colorimetric and fluorometric chemosensor for cyanide recognition in water.

A new probe for cyanide detection based on the integrated pyrazolo[1,5-a]pyrimidine-hemicyanine (PpHe) system was synthesized in an efficient and straightforward manner using microwave-assisted heating. Photophysical studies in a 100% aqueous solution demonstrated high cyanide selectivity and detection limits as low as 600 and 86 nmol L for UV-vis absorption and fluorescence emission, respectively. Both values are well below 1900 nmol L, which is the maximum concentration permitted for drinking water by the World Health Organization (WHO). HRMS analysis and NMR experiments were performed to confirm the mechanism of detection based on blocking the ICT phenomenon via nucleophilic addition of CN on the C˭N bond (iminium salt moiety) of the probe.