An imidazole based luminescent Zn (II) metal–organic framework for sensing of nitroaromatic explosives

Abstract

The Zn(II)-based IFP-1 (IFP = imidazolate framework Potsdam) was successfully synthesized by solvothermal process to detect the nitroaromatic compounds (NACs) including nitrobenzene (NB), 1,3‑dinitrobenzene (1,3-DNB), 1,2‑dinitrobenzene (1,2-DNB), 1,4‑dinitrobenzene (1,4-DNB), 4‑nitrotoluene (4-NT) and 2,4,6-trinitrophenol (TNP). It was found that IFP-1 gives the maximum emission intensity at 338 nm upon excitation at 288 nm. The quenching constant (KSV) for all the analytes was found in the order as follows: TNP > DNP > NB > NT > 1,2-DNB > 1,4-DNB > 1,3-DNB. The localization of the amide group of 2-methylimidazolate-4-amide-5-imidate ligand in the walls of the channels provides feasible interacting sites for incoming analytes. These suitable geometrical characteristics of IFP-1 provide close proximity to NACs leading to their prompt sensing ability. The fluorescence intensity was reduced by 71 % in the presence of TNP. IFP-1 shows high selective detection of TNP even in presence of other nitroaromatic compounds. However, the sensing ability of IFP-1 towards TNP is highest over other NACs with high quenching constant (Ksv) of 1.12 × 105 M−1 and a low detection limit of 0.23 µM, indicating a good detection limit. A detailed investigation has been carried out on the fluorescence quenching mechanism by DFT calculation. This study showed that the high sensitivity of the compound towards TNP is possible because of the formation of non-fluorescent ground state complex formation driven by strong pi-pi stacking interaction and electrostatic hydrogen bond interactions.