Ratiometric Luminescent Sensor of Picric Acid based on the Dual-Emission Mixed-Lanthanide Coordination Polymer.

Powerful explosive sensor plays a key role in public security and environmental protection. Herein we report a series of isostructural lanthanide metal-organic frameworks [LnL(NMP)] (LnL, Ln = Eu , Gd, Tb, Dy, Ho and Er, NMP = N-methyl-2-pyrrolidone) and mixed-Ln LnL (EuTbL, EuGdL, TbGdL and EuTbGdL), which were synthesized by using [1,1':4',1″-terphenyl]-2',4,4″,5'-tetracarboxylic acid (HL). Luminescence studies show that both HL and GdL emit strong fluorescence and phosphorescence at 77 K while only fluorescence at room temperature, and TbL exhibits strong Tb characteristic emission though the energy difference between the triplet excited state of HL (20661 cm) and the D energy level of Tb (20500 cm) is very small. By doping Eu and Tb into GdL, we obtained EuTbGdL emitting warm white light. For TbGdL showing the dual-emission, the Tb emission decreases slowly, however, the ligand emission is sharply quenched upon increasing the concentration of PA from 0 to 60 μM, rendering TbGdL an excellent mixed-lanthanide MOF ratiometric luminescent PA sensor.