Cyanide chemosensors based on 3-dicyanovinylpyrazolo[1,5-a]pyrimidines: Effects of peripheral 4-anisyl group substitution on the photophysical properties.

Novel dual-mode colorimetric/fluorometric probes based on 3-dicyanovinylpyrazolo[1,5-a]pyrimidines for cyanide (CN-) sensing have been developed (DPPa-c). These probes displayed high selectivity and sensitivity toward CN- over other interfering anions, with a detection limit (LOD) as low as 610/170 nmol L-1 (absorption/emission) for some of the prepared probes. After a reaction with CN-, low-fluorescent DPPa-c showed a significant decrease of the intramolecular charge transfer (ICT) bands at approximately 390 nm (color changes from yellow to colorless) and exhibited up to an 82-fold fluorescence enhancement at approximately 465 nm (strong blue-light emission). The successive introduction of 4-anisyl (4-MeOPh) groups on periphery of the heterocyclic core had a dramatic influence on both the photophysical properties and CN- detection capability. The number of channels for CN- quantification in the absorption spectra increased from 1 in DPPa to 3 in DPPc. Moreover, the fluorescence emission LOD decreased from 300 nmol L-1 in DPPa to 170 nmol L-1 in DPPc. Finally, the selectivity toward CN- demonstrated a notable improvement when the probe had three 4-anisyl groups in its periphery (i.e., DPPc).