Luminescence-Color-Changing Sensing toward Melamine Based on a White-Light-Emitting Film

Isostructural lanthanide coordination polymers, [Ln­(d-DBTA)­(d-HDBTA)­(H₂O)₅]_n (Ln-d-DBTA; d-H₂DBTA = d-O,O′-dibenzoyl tartaric acid; Ln = La, Ce, Nd, Eu, Gd, and Tb), are synthesized and characterized. By uniformly doping this amphophilic Ln-d-DBTA into a poly­(methyl methacrylate) (PMMA) matrix, we prepare stable films with tunable luminescence color, even white-light emission. Except for providing the blue-light component, the PMMA matrix plays indispensable roles in dispersing the 1D LnCPs via hydrogen bonds, transferring electrons to organic ligands by means of photoinduced electron transfer, and further sensitizing the luminescence of lanthanide ions. Then, a bifunctional sensing process toward melamine in various dairy products is conducted in terms of luminescent intensity and color. Consequently, the as-prepared white-light-emitting film exhibits 0.012 mg/kg limit of detection and obvious luminescence-color changes from white to blue. The excellent sensitivity, reliability, selectivity, stability, competitiveness, and recyclability state the promising practicality in monitoring quality of dairy products. In this work, using a battery of experimental techniques and theoretical calculation, we show how the PMMA matrix connects the LnCPs and promotes their photophysical properties, what changes have taken place for the energy- and electron-transfer pathways of the as-prepared chemosensor after adsorbing melamine, and why this convenient testing material is applicable.