Cd-Based Metal–Organic Framework Containing Uncoordinated Carbonyl Groups as Lanthanide Postsynthetic Modification Sites and Chemical Sensing of Diphenyl Phosphate as a Flame-Retardant Biomarker

With the judicious selection of an appropriate semirigid polycarboxylate, 2,5-bis(3',5'-dicarboxylphenyl)benzoic acid (H5bdba), and an inorganic metal ion, a novel anionic framework, {[NH2(CH3)2]2·[Cd3.5(bdba)(Hbdba)(H2O)1.5]}n (Cd-MOF), has been synthesized solvothermally. Single-crystal measurement results show that the prepared Cd-MOF features a three-dimensional structure containing two types of one-dimensional channels, and as we expected, there exist accessible uncoordinated -COOH groups on Hbdba pointing toward the rhombus channels. Powder X-ray diffraction and thermogravimetric analysis measurements were performed for the thermal and chemical stability analysis of Cd-MOF. In addition, the lanthanide(III)-functionalized hybrids, Ln(III)@Cd-MOF, were initially prepared by coordinated postsynthetic modification to incorporate luminescent Ln(III) ions into the structure. The luminescence properties of the hybrids are studied, and the results show notable and specialized fluorescent sensitization of Cd-MOF to Tb(III) ions. Moreover, the Tb(III)@Cd-MOF hybrid with outstanding fluorescence properties was developed as a highly sensitive and selective luminescent probe for the biomarker diphenyl phosphate (DPP) based on multiquenching effects. Tb(III)@Cd-MOF is the first case to realize the detection of urinary DPP through lanthanide metal-organic framework fluorescence spectrometry and shows practical detection potential.