A series of highly sensitive and selective fluorescent and colorimetric “off-on” chemosensors for Cu (II) based on rhodamine derivatives

Several rhodamine-B (C.I. Basic Violet 10) hydrazide derivatives were employed as specific fluorescent and colorimetric chemosensors for Cu2+ in neutral buffered media. The probes exhibited selective “off-on” type changes in both absorption and emission spectra toward Cu2+ ions compared to other metal cations, which was attributed to transformation of the non-fluorescent and colorless spirolactam derivative to the ring-opened, fluorescent, pink coloured amide. Further studies of structure-activity relationship revealed that the designated acyl hydrazone skeleton moiety shared by these chemosensors, derived from the dye hydrazide and salicylaldehyde analogues, determines the selectivity for Cu2+ over other cations.