Perylene diimide appended with 8-hydroxyquinoline for ratiometric detection of Cu²⁺ ions and metal displacement driven "turn on" cyanide sensing

Perylene diimide (PDI) 3 and 4 appended with 8-hydroxyquinoline derivatives have been synthesized and their photophysical and spectroscopic properties have been experimentally determined. Moreover, PDIs 3 and 4 show ratiometric behavior to detect Cu²⁺ colorimetrically with visible color change from coral red to light pink, whereas 3 and 4 show "turn-off" behavior in fluorescence with lowest limit of detection 5×10^-7 M. The PDI 3 could be further utilized for ratiometric CN^- detection colorimetrically and as "turn-on" sensor for CN^- detection fluorometrically with lowest limit of detection 8×10^-6 M. The comparison of spectroscopic properties of PDI 1-4 highlights the importance of linking 8-hydroxyquinoline units on the PDI core at bay position for achieving Cu²⁺ recognition event into ratiometric signal.