Coumarin-Based Dual Chemosensor for Colorimetric and Fluorescent Detection of Cu in Water Media.

A novel coumarin derivative () was synthesized and used as a colorimetric and fluorescent probe for selective detection of Cu ions in the presence of other metal ions, with the detection limits of 5.7 and 4.0 ppb, respectively. Cu ion reacts with probe to form a 1:1 stoichiometry complex, resulting in a remarkable redshift of absorption maximum from 460 to 510 nm, as well as almost completely quenching fluorescence intensity of probe at the wavelength of 536 nm. These changes can be distinctly observed by naked eyes. In addition, the working pH range of probe is wide and suitable for physiological conditions, thus probe may be used for detection of Cu ions in living cells. The stable structures of probe and its 1:1 complex with Cu ion were optimized at the PBE0/6-31+G(d) level of theory. The presence and characteristics of bonds in compounds were studied through atoms in a molecule and natural bond orbital analysis. The formation of the complex led to a strong transfer of electron density from probe as a ligand to Cu ion, resulting in breaking the π-electron conjugated system, which is the cause of fluorescence quenching and color change of Cu complex.