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Rhodamine B 8-hydroxy-2-quinolinecarboxaldehyde Schiff base (1) has been investigated as a colorimetric and fluorescent "off-on" probe for the recognition of Cu(2+) in aqueous solution. Probe 1 was synthesized by condensation of rhodamine B hydrazide and 8-hydroxy-2-quinolinecarboxaldehyde, which exhibited good selectivity for Cu(2+) among a range of biologically and environmentally important metal ions. The Cu(2+) recognition event undergoes a Cu(2+) promoted hydrolysis of probe 1 to release rhodamine B and the recognition process is barely interfered by other coexisting metal ions.

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A new thiourea based receptor (1) was synthesized and applied to fluoride ion recognition in acetonitrile solution. Receptor 1 displayed dual changes in absorption and fluorescence emission intensities selectively for fluoride ions. The interaction of 1 with fluoride undergoes a deprotonation process that is confirmed by 1 H NMR titration.

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