An amino acid-functionalized coordination polymer of Cd(II) as a fluorescent probe detecting Cu(II) ion

Cd(II) complex 1, namely {[Cd(HL)]·CH3OH}n was design as a new fluorescence probe for measuring concentration of Cu2+ ion in aqueous solution. Complex 1 is a 3,6-connected double-layered porous metal–organic framework, which was synthesized by optimizing the ratio of Cd(OH)2 and a new ligand 4'-(((1-carboxyethyl)amino)methyl)-[1,1′-biphenyl]-3,5-dicarboxylic acid (H3L) under solvothermal conditions. It not only had good thermal and solvent stabilities, but also displayed a strong solid-state fluorescence centered at 375 nm with a moderate quantum yield of 37.12% under excitation at 275 nm. More importantly, its fluorescence could be obviously quenched by the addition of Cu2+ ion. The fluorescence quenching may be caused by the weak coordination interaction between Cu2+ and the uncoordinated imino N in ligand (HL)2–, as well as the slightly competitive absorption of excitation light by Cu2+. In the low concentration range of Cu2+ ion, the fluorescence quenching efficiency of complex 1 is closely related to the concentration of Cu2+ ion, and the relationship between fluorescence quenching efficiency and the concentration of added Cu2+ ion could be well fitted by Stern-Volmer equation with KSV being 1.589 × 104 M−1 and the detection limit for Cu2+ ion being 5.7 μM. Our case may provide potential applications for the detection of Cu2+ ion in daily domestic water.