Colorimetric and fluorescence "turn-on" recognition of fluoride by a maleonitrile-based uranyl salen-complex

The synthesis and characterization of two new uranyl-salen complexes, 1e2, based on a 1,2-diaminomaleonitrile unit, is described. Spectroscopic studies to evaluate their potential as colorimetric probes for fluoride detection in chloroform and dichloromethane were undertaken. Compound 2 exhibits a 'turn-on' response characterized by a naked-eye colorimetric change for the selective recognition of fluoride in both solvents. DFT calculations show that the stabilization energy for the formation of the host:guest complex follows the trend F > Cl > Br hence supporting the experimental data.