Rhodamine Based Turn-On Sensors for Ni2+ and Cr3+ in Organic Media: Detecting CN− via the Metal Displacement Approach

Two novel sensors bearing rhodamine B and quinoline units have been synthesized. One of these, 1 , allows sensitive and selective detection of Ni 2+ and Cr 3+ by forming non-fluorescent ( 1 -Ni 2+ ) and fluorescent ( 1 -Cr 3+ ) complexes respectively. Both metals trigger the formation of highly colored ring-open spirolactam. These form excellent probes for CN − which quenches the fluorescence of the 1 -Cr 3+ complex by extracting the Cr 3+ . Both Cr 3+ and Cu 2+ gave color changes with 2 , but they are easily identified separately via the large fluorescence enhancement that occurs only with Cr 3+ .