Discriminative detection of nitro aromatic explosives by a luminescent metal–organic framework

Nitro aromatics are the principal components of explosives used in acts of terrorism and within improvised explosive devices, among others. Although high sensitivity towards nitro aromatic explosives has been demonstrated, selective detection and discrimination are critical for practical applications. Fluorescence quenching of metal–organic frameworks (MOFs) is sufficiently sensitive to detect any nitro explosives, but discriminative detection with different numbers of –NO2 groups is rare. Here we report a stable fluorescent MOF, [Zn2(NDC)2(bpy)]·Gx, 1 (where NDC = 2,6-naphthalenedicarboxylic acid, bpy = 4,4′-bipyridine, and G = guest solvent molecules), whose fluorescence is quenched by trace amounts of nitro aromatics introduced from solution or in vapor phase. The steady-state and time-resolved experiments show that the quenching process is dynamic in nature and the interactions (dipole–dipole, π-stacking) between the MOF and nitro explosives play a crucial role in the discriminative detection of nitro aromatics with different numbers of –NO2 groups.