Tuning the Luminescence of Metal–Organic Frameworks for Detection of Energetic Heterocyclic Compounds

Herein
we report three metal–organic frameworks (MOFs),
TABD-MOF-1, -2, and -3, constructed from Mg2+, Ni2+, and Co2+, respectively, and deprotonated 4,4′-((Z,Z)-1,4-diphenylbuta-1,3-diene-1,4-diyl)­dibenzoic
acid (TABD-COOH). The fluorescence of these three MOFs is tuned from
highly emissive to completely nonemissive via ligand-to-metal charge
transfer by rational alteration of the metal ion. Through competitive
coordination substitution, the organic linkers in the TABD-MOFs are
released and subsequently reassemble to form emissive aggregates due
to aggregation-induced emission. This enables highly sensitive and
selective detection of explosives such as five-membered-ring energetic
heterocyclic compounds in a few seconds with low detection limits
through emission shift and/or turn-on. Remarkably, the cobalt-based
MOF can selectively sense the powerful explosive 5-nitro-2,4-dihydro-3H-1,2,4-triazole-3-one with high sensitivity discernible
by the naked eye (detection limit = 6.5 ng on a 1 cm2 testing
strip) and parts per billion-scale sensitivity by spectroscopy via
pronounced fluorescence emission.