A hydroxyl-functionalized ligand was designed for the construction of metal-organic framework (MOF) materials with the aggregation-induced emission (AIE) feature, in which the fluorescence can be deliberately tailored: quenching the fluorescence to an "off" state by the decoration with heterocyclic auxiliary ligand 4,4'-bypyridine (Bpy) in the framework as a quenching agent and triggering the enhanced fluorescence to an "on" state by removal of Bpy through the metal competitive coordination substitution strategy. Our study shows that the occurrence of exciton migration between the AIE linker and conjugated auxiliary ligand Bpy causes fluorescence quenching. Time-dependent density functional theory was employed to understand the photoinduced electron transfer process and explain the origins of fluorescence quenching. Using this strategy, the prepared MOF material can perform as a fluorescence "off-on" probe for highly sensitive detection of Al in aqueous media. The hydroxyl group plays a crucial role in sensing as it can selectively chelate Al, which is directly related to the dissociation of nonfluorescent MOF and consequent activation of the AIE process.

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One tetracarboxylate functionalized benzene-cored tetraphenylethene derivative was designed as a linker for construction of aggregation-induced emission (AIE) active metal−organic frameworks (MOFs), which exhibit the distinct AIE behavior. Two two-dimensional MOFs materials, MOF-1 and MOF-2, have been successfully synthesized by using the organic linker precursor. Photophysical studies reveal that both MOFs exhibit remarkable fluorescent properties with the absolute quantum yield as high as 43%. The high PL efficiency, good water stability, as well as the electron-donating nature of prepared MOF materials, allow us to explore their potentials in sensing applications for electron-deficient nitro explosives in aqueous media. Especially, water-stable MOF-2 exhibits superior sensitivity and selectivity toward 2,4,6-trinitrophenol (TNP) over other selected nitro analytes, including nitromethane, 2,3-dimethyl-dinitrobutane, nitrobenzene, 2,4,6-trinitrotoluene, 2,6dinitrotoluene, 2,4-dinitrotoluene, 1,3-dinitrobenzene, with the detection limit for TNP as low as 0.49 μM (∼110 ppb). In virtue of its excellent detection efficiency, applicability in water and reusability, MOF-2 can be a promising fluorescent sensor material for the practical TNP sensing.