Function-Oriented: The Construction of Lanthanide MOF Luminescent Sensors Containing Dual-Function Urea Hydrogen-Bond Sites for Efficient Detection of Picric Acid

Two novel lanthanide metal-organic framework (Ln-MOF) luminescent sensors for the detection of picric acid have been successfully assembled. Following a function-oriented strategy, urea hydrogen-bonding functional sites were introduced into two MOF frameworks. A structural analysis indicated that the two MOFs have the exact same structure, namely 2D layers with diamond-shaped holes that are accumulated into a 3D framework through the hydrogen-bonding interactions between urea and carboxylate groups. Interestingly, only half of the urea units are involved in supporting the MOF framework through N-H...O hydrogen-bonding interactions, whereas the other half are located in the pore channel and act as empty recognition sites. Abundant N-H urea bonds are present in the inner walls of three types of interpenetrating 1D channels. Luminescence studies revealed that the two Ln-MOFs exhibit high sensitivity, good selectivity, and a fast luminescence quenching response towards picric acid. In particular, the two Ln-MOFs can be simply and quickly regenerated, and exhibit excellent recyclability. In summary, we have successfully used a function-oriented strategy to achieve multiple functions in a ligand to construct lanthanide MOF luminescent sensors for the detection of picric acid, thereby providing a potential strategy for the future development of MOF luminescent sensors with a specific target.