Rhodamine Based Turn-On Sensors for Ni(2+) and Cr(3+) 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+).