Isolated π-Interaction Sites in Mesoporous MOF Backbone for Repetitive and Reversible Dynamics in Water.

We reported the introduction of π-interaction sites into a series of chemically robust metal-organic frameworks (MOFs), MOF-526, -527 and -528 with progressively increased pore size, 1.9 nm to 3.7 nm, and the inclusion and release of large organic molecules in water. The mesopores in these MOFs leads to fast adsorption kinetics, while the π-interaction between isolated porphyrin units in MOF backbone and polycyclic structure of the organic guests provides excellent reversibility. Specifically, seven large organic dyes are quantitatively captured by the porphyrin units of these MOFs in a 2:1 molar ratio, and exhibiting unprecedented kinetics for MOFs [e.g. 4.54×10^5 L/mol for rhodamine B (RhB)] at extremely low concentration (10 ppm) in water. Rotational-echo double-resonance (REDOR) NMR experiments revealed the distance between the guest molecules and porphyrin units in MOFs was in the range from 3.24 to 3.37 Å, confirming the specific π-interaction. Repetitive and reversible dynamic was achieved in these MOF for 10 complete inclusion-release cycles without any decay in performance, which are ideally suited for the removal and recycle of large polycyclic organic molecules from water. The performance of MOF-526 rivals the state-of-the-art carbon and polymers.