Engineered Bifunctional Luminescent Pillared-Layer Frameworks for Adsorption of CO2 and Sensitive Detection of Nitrobenzene in Aqueous Media.

Through a dual-ligand synthetic approach, five isoreticular primitive cubic (pcu)-type pillared-layer metal-organic frameworks (MOFs), [Zn2 (dicarboxylate)2 (NI-bpy-44)]⋅x DMF⋅y H2 O, in which dicarboxylate=1,4-bdc (1), Br-1,4-bdc (2), NH2 -1,4-bdc (3), 2,6-ndc (4), and bpdc (5), have been engineered. MOFs 1-5 feature twofold degrees of interpenetration and have open pores of 27.0, 33.6, 36.8, 52.5, and 62.1 %, respectively. Nitrogen adsorption isotherms of activated MOFs 1'-5' at 77 K all displayed type I adsorption behavior, suggesting their microporous nature. Although 1' and 3'-5' exhibited type I adsorption isotherms of CO2 at 195 K, MOF 2' showed a two-step gate-opening sorption isotherm of CO2 . Furthermore, MOF 3' also had a significant influence of amine functions on CO2 uptake at high temperature due to the CO2 -framework interactions. MOFs 1-5 revealed solvent-dependent fluorescence properties; their strong blue-light emissions in aqueous suspensions were efficiently quenched by trace amounts of nitrobenzene (NB), with limits of detection of 4.54, 5.73, 1.88, 2.30, and 2.26 μm, respectively, and Stern-Volmer quenching constants (Ksv ) of 2.93×103 , 1.79×103 , 3.78×103 , 4.04×103 , and 3.21×103  m-1 , respectively. Of particular note, the NB-included framework, NB@3, provided direct evidence of the binding sites, which showed strong host-guest π-π and hydrogen-bonding interactions beneficial for donor-acceptor electron transfer and resulting in fluorescence quenching.