Highly Fluorescent Imidazole Probes for the Pico Molar Detection of CN(-) ion and Application in Living Cells.

A series of four imidazole based fluorescent receptors (R1-R4) containing two different signaling units were synthesized for the sensing of specific anions. R1 and R2 act as excellent colorimetric sensors via color change from yellow to orange and pink in presence of F (-) , AcO (-) and CN (-) ions. R1 and R2 show intramolecular charge transfer (ICT) band at 414 nm and 434 nm and were red shifted into 500 nm and 510 nm respectively, with the addition of above anions. Anion complexes of R1 and R2 were found to exhibit remarkable orange and red fluorescence under UV light which is consistent with an emission observed at 594 nm and 618 nm respectively. Likewise, quenching in the green fluorescence of R3 and R4 was found under UV light accompanied with quenching of emission at 530 nm and 541 nm. Selective colorimetric sensing of CN (-) ion is also achieved in 3 % aq. DMF medium. Intracellular uptake of CN (-) ion by R1 was achieved in living RAW 264.7 cells. Finally, practical application of R2 to detect CN (-) and F (-) ions present in aqueous solution of cassava flour and toothpaste also performed.