Phenolic nitroaromatics detection by fluorinated metal-organic frameworks: Barrier elimination for selective sensing...

Many piesce of research have been performed to detect nitroaromatic-compounds (NACs) by metal-organic frameworks (MOFs). Despite extensive studies, there are still significant challenges like selective detection of specific NAC group in presence of other NACs. Here, we have integrated two functionalization strategies through decoration of pore-walls of the MOFs with trifluoromethyl groups and extension in π-conjugated system. Based on this idea, trifluoromethyl TMU-44 (with the formula [Zn₂(hfipbb)₂(L1)]_n.DMF, H₂hfipbb = 4,4'-(hexafluoroisopropylidene) bis(benzoic acid), L1 = N,N'-bis-pyridin-4-ylmethylene-benzene-1,4-diamine) and TMU-45 (with formula [Zn₂(hfipbb)₂(L2)]_n.DMF, L2 = N,N'-bis-pyridin-4-ylmethylene-naphthalene-1,5-diamine) frameworks have been synthesized. The aromatic skeleton of TMU-44 is based on phenyl rings while TMU-45 aromatic skeleton is extended by replacement of phenyl with naphthyl core. Measurements reveal that these MOFs are highly sensitive to phenolic NACs especially 2,4,6-trinitrophenol (TNP) with high quenching efficiency of 90% for TMU-44 (K_SV = 10,652 M^-1, LOD = 6.9 ppm) and 99% for TMU-45 (K_SV = 34,741 M^-1, LOD = 2.07 ppm). The proposed detection mechanism can be associated with hydrogen bonding between OH group of phenolic NACs and trifluoromethyl groups of TMU-MOFs as well as π(rich)∙∙∙π(deficient) interaction between π-conjugated backbone of TMU-frameworks and π-deficient ring of NACs.