Multifunctional lanthanide MOF luminescent sensor built by structural designing and energy level regulation of a ligand

Abstract

In order to reduce usage cost and simplify the detection process, it is necessary to develop multifunctional and multi-emitter Ln-MOF luminescent sensors. The structure and property of Ln-MOFs are mainly controlled by ligands. As a typical aromatic nucleus, naphthalene groups not only can emit fluorescence and regulate the energy levels of a ligand but also can participate in π–π stacking. As a type of directional weak interaction, hydrogen bonding interactions have caught wide attention in catalysis, molecular recognition, self-assembly, etc. So we designed a “V” shaped ligand containing naphthalene groups and “OC–NH” groups as guided by DFT calculations. The obtained Eu-MOF can achieve simultaneous luminescence of the ligand and Eu³⁺. Single crystal X-ray diffraction revealed that π–π stacking interactions and hydrogen bonding interactions played an important role in the crystallization process. The luminescence spectra showed that the Eu-MOF has two luminescent centers and can be developed as a ratiometric luminescent sensor. The luminescence of the Eu-MOF can undergo an obvious color change from red to white as the temperature rises from 120 to 400 K and the Eu-MOF has a satisfactory relative sensitivity and a small temperature uncertainty. Moreover, the Eu-MOF can detect picric acid selectively and the K_SV can reach 53 339 M⁻¹. Thus, the Eu-MOF can be used as a multifunctional and multi-emitter luminescent sensor and the designed strategy also can provide inspiration for further research on Eu-MOFs.