A novel "turn-on" fluorescent probe based on triphenylimidazole-hemicyanine dyad for colorimetric detection of CN- in 100% aqueous solution.

A new colorimetric fluorescent probe (MCy) for CN- is designed and synthesized based on triphenylimidazole-hemicyanine dyad. The probe shows high selectivity towards CN- in 100% aqueous solution even in the presence of other competitive anions such as F-, Cl-, AcO-, NO2-, H2PO4-, I-, SCN-, SO42-, NO3-, HCO3-, Br- and S2-. Upon nucleophilic addition of CN- to the indolium group, the probe displays large blue-shift in UV-vis spectrum and remarkable "turn-on" fluorescence owing to the disruption of intramolecular charge transfer. Meanwhile, the probe also undergoes a naked-eye discernible color change from orange to light pink in the sunlight as well as an obvious fluorescence color change from non-emissive to bright blue under a UV lamp. The detection limit of CN- in aqueous solution can be as low as 20.6nM, which is much lower than the permissible level of CN- in drinking water according to the WHO. In addition, the probe has been successfully used to determine CN- in real water samples as well as to fabricate test paper kit for CN- detection.