A guest-responsive fluorescent 3D microporous metal−organic framework derived from a long-lifetime pyrene core

The carboxylate ligand 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy)—based on the strongly fluorescent long-lifetime pyrene core—affords a permanently microporous fluorescent metal-organic framework, [In2(OH)2(TBAPy)]·(guests) (1), displaying 54% total accessible volume and excellent thermal stability. Fluorescence studies reveal that both 1 and TBAPy display strong emission bands at 471 and 529 nm, respectively, upon excitation at 390 nm, with framework coordination of the TBAPy ligands significantly increasing the emission lifetime from 0.089 to 0.110 ms. Upon desolvation, the emission band for the framework is shifted to lower energy: however, upon re-exposure to DMF the as-made material is regenerated with reversible fluorescence behavior. Together with the lifetime, the emission intensity is strongly enhanced by spatial separation of the optically active ligand molecules within the MOF structure and is found to be dependent on the amount and chemical nature of the guest species in the pores. The quantum yield of the material is found to be 6.7% and, coupled with the fluorescence lifetime on the millisecond time scale, begins to approach the values observed for Eu(III)-cryptate-derived commercial sensors.