Hydrothermal Preparation of Five Rare-Earth (Re = Dy, Gd, Ho, Pr, and Sm) Luminescent Cluster-Based Coordination Materials: The First MOFs-based Ratiometric Fluorescent Sensor for Lysine and Bifunctional Sensing Platform for Insulin and Al.

Through the powerful hydrothermal method, five rare-earth (Re = Dy, Gd, Ho, Pr, and Sm) three-dimensional (3D) cluster-based metal-organic frameworks (MOFs) have been synthesized, namely, [Dy(L)(HO)(DMF)] (1), {[Gd(L)(HO)(DMF)]·DMF} (2), {[Ho(L)(HO)(DMF)]·0.5DMF} (3), {[Pr(L)(HO)(DMF)]·0.5DMF} (4), and {[Sm(L)(HO)(DMF)]·DMF} (5; HL = terphenyl-3,4″,5-tricarboxylic acid), which have been determined by single crystal X-ray analyses and PXRD characterization. Structural analyses reveal that, in 1-5, these L ligands are linked by five different rare-earth centers, forming the iso-structural nanoporous frameworks. PXRD patterns of bulky samples 1-5 also are consistent with theoretical PXRD patterns confirming their purity. Solid state photoluminesce of free HL and 1-5 at room temperature also has been investigated indicating strong ligand-based emissions. Besides these, fluorescent dye Rhodamine B (RhB) can be introduced into MOF1 forming the composite material RhB@MOF1 with a high quantum yield of 35%. It is noted that, through deliberately tuning the morphologies of nanoparticle MOF1 under different ultrasonic conditions, RhB@MOF1 can be utilized as the first ratiometric fluorescent sensor to effectively discriminate l- and d-lysine from other amino acid molecules with high K values and low LOD values. On the other hand, 2 was for the first time to be utilized as an excellent bifunctional MOFs-based sensing platform to detect insulin and Al with a low detection limit in the human serum solution.