Effects of Extending the π-Electron System of Pillaring Linkers on Fluorescence Sensing of Aromatic Compounds in Two Isoreticular Metal–Organic Frameworks

Abstract

A new porous metal–organic framework (TMU-21) that is isostructural to our recently reported TMU-6 is introduced. The structure of this framework has been determined by X-ray crystallography and further characterized by Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. Its structural features as well as its stability and porosity were studied. These two metal–organic frameworks are interesting candidates for a comparative fluorescence study. Thus, their potential abilities to sense nitrobenzene, benzene, and polycyclic aromatic hydrocarbons, namely, naphthalene, anthracene, and pyrene, were investigated. This study clearly shows an important contribution of extending the π-electron systems of pillaring linkers in the ability of metal–organic frameworks to sense aromatic compounds.

Urea Metal–Organic Frameworks for Nitro-Substituted Compounds Sensing

“…Nitroaromatics are oxidizers due to a low-lying unoccupied π* orbital, which can accept an electron from the excited state fluorophore, thus efficiently quenching the fluorescence emission of this compound . Fluorescence quenching of nitroaromatics based on π-interactions, namely, π···π stacking and C–H···π interactions, has been the subject of numerous investigations. − Accordingly, chemists have designed a variety of molecular receptors based on aromatic groups, which favor π–π stacking interactions between MOF and nitro-analytes. ,,− In this regard, we have been interested in evaluating the potential of urea-functionalized MOFs as hydrogen-bond-donating receptors for nitroaromatics recognition. The fluorescence properties of both compounds were first investigated by immersing activated TMU-31 and TMU-32 in six different solvents, namely, toluene, benzene, dimethylformamide, hexane, acetone, and nitrobenzene (Figures S11–S14).…”

Metal(II) Coordination Polymers Derived from Mixed 4-Imidazole Ligands and Carboxylates: Syntheses, Topological Structures, and Properties

“…The N-donor ligands as well as the polycarboxylates, as two most commonly used organic linkers in the assembly of MOFs, have been widely designed and selected for their various coordination modes, and modifiable backbones. The N-donor ligands with rod-type two-connector between the two terminal coordination groups, for example, 4,4′-bipyridine(bpy), 1,2-bis(4-pyridyl)ethane(bpe), or their analogues, can be employed as ‘pillars’ together with the carboxylate ligand to meet the requirement of coordination geometries of metal ions in the assembly process [18,19,20,21]. More recently, we have designed a novel type of 4-imidazol-containing ligands with versatile coordination modes such as 1,4-di(1 H -imidazol-4-yl)benzene and 1,3,5-tri(1 H -imidazol-4-yl)benzene, and successfully constructed a series of porous metal-imidazolate complexes, which exhibit exceptional gas adsorption properties [22,23].…”

Function–Topology Relationship in the Catalytic Hydrolysis of a Chemical Warfare Simulant in Two Zr‐MOFs

“…These results clearly indicate that the fluorescence response of Zr‐bcu‐tmuc toward DMNP is more effective and faster than that of Zr‐fcu‐tmuc. The photoinduced electron transfer (PET) mechanism has been widely invoked in the fluorescence detection of analytes, and is confirmed by 1) linear SV behavior and 2) the absence of overlap of the UV/Vis absorption band of the analyte and the PL emission band of the sensor [43, 44] . Because no significant overlap of the UV/Vis absorption region of DMNP and the emission bands of the Zr‐MOFs was observed (see Figure S23), PET is probably the main quenching mechanism in this system.…”

“…mechanism has been widely invoked in the fluorescence detection of analytes,a nd is confirmed by 1) linear SV behavior and 2) the absence of overlap of the UV/Vis absorption band of the analyte and the PL emission band of the sensor. [43,44] Because no significant overlap of the UV/Vis absorption region of DMNP and the emission bands of the Zr-MOFs was observed (see Figure S23), PET is probably the main quenching mechanism in this system.W eh ave previously reportedt he florescence sensing ability of MOFs with extended aromatic systems towardsn itro aromaticss uch as nitrobenzene [45] and trinitrophenol [46] based on the PET mechanism. Similarly to these reported results, here, the electron-withdrawing nitrophenoxy substituent of the DMNP molecule makes it ah ighly suitable fluorescenceq uenching agent due to electron transfer from the electron-richZ r-MOF backbonet ot he electron-deficient DMNP.…”