A multifunctional fluorescent and colorimetric receptor 1 ((E)-N'-((8-hydroxy-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)methylene)benzohydrazide) for the detection of both Al(3+) and CN(-) in aqueous solution has been developed. Receptor 1 exhibited an excellent selective fluorescence response toward Al(3+). The sensitivity of the fluorescent based assay (0.193 μM) for Al(3+) is far below the limit in the World Health Organization (WHO) guidelines for drinking water (7.41 μM). In addition, receptor 1 showed an excellent detection ability in a wide pH range of 4-10 and also in living cells. Moreover, receptor 1 showed a highly selective colorimetric response to CN(-) by changing its color from colorless to yellow immediately without any interference from other anions.

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A new highly selective colorimetric chemosensor 1 (E)-9-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol was designed and synthesized for the sequential detection of Cu(2+) and CN(-). This sensor 1 exhibited an obvious color change from yellow to orange in the presence of Cu(2+) in a fully aqueous solution. The detection limit (0.9 μM) of 1 for Cu(2+) is far lower than the WHO limit (31.5 μM) for drinking water. In addition, the resulting Cu(2+)-2· 1 complex can be further used to detect toxic cyanide through a color change from orange to yellow, indicating the recovery of 1 from Cu(2+)-2·1. Importantly, chemosensor 1 could be used to detect and quantify Cu(2+) in water samples, and a colorimetric test strip of 1 for the detection of Cu(2+) could be useful for all practical purposes.

A new metal ion sensor that contains quinoline and pyridylaminophenol has been synthesized. In acetonitrile and in the presence of Zn(2+), the sensor fluoresces. In contrast, in aqueous solutions the sensor fluoresces in the presence of Cd(2+). The fluorescence of the molecule is selective for Zn(2+) or Cd(2+) and shows no fluorescence with other metal ions. The crystal structure of the Cd(2+) complex shows coordination through the amide and phenol oxygens, as well as the amine nitrogen of the sensor. The sensor also acts as a colorimetric sensor for Co(2+) by changing color from colorless to yellow. The color change is selective for Co(2+) and is not observed with other metal ions. The unique combination of pyridine and phenol groups with quinoline results in the properties of this sensor.

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A new multifunctional and highly selective chemosensor for Co(2+) and Cu(2+) was designed and synthesized. could simultaneously detect both Co(2+) and Cu(2+) by changing its color from pale yellow to pink and to orange in a near-perfect aqueous solution. The binding modes of to Co(2+) and Cu(2+) were determined to be a 2 : 1 complexation stoichiometry through Job's plot, ESI-mass spectrometry analysis and (1)H NMR titration. The detection limits (1.5 and 2.1 μM) of for Co(2+) and Cu(2+) were lower than the DEP guidelines (1.7 μM for Co(2+)) and the WHO guidelines (31.5 μM for Cu(2+)) for drinking water. The chemosensor could be used to quantify Co(2+) and Cu(2+) in water samples. Moreover, could be used as a practical, visible colorimetric test kit for both Co(2+) and Cu(2+). The sensing mechanisms of Co(2+) and Cu(2+) by were supported by theoretical calculations.