The Luminescence Origin Study Of Metal-Organic Framework Detecting Guest Molecules

Metal-Organic Frameworks (MOFs), a new fascinating class of porous materials, have been received widespread attention in recent years. They have been extensively studied for their rich structural chemistry and diverse functionalities. Especially luminescence MOFs, they have a good application prospect in numerous areas, which are based on their ultrahigh porosity, enormous internal surface areas and a lot of possible luminescence properties. By using of their excellent luminescent properties, a variety of chemical sensors have been developed to detect small molecule, ions, volatile organic compounds and so on. So luminescence MOFs have a great potential to detect indoor formaldehyde and explosives molecule.Hydrogen bond is the most widespread kind of weak interactions in supramolecular. It not only dominates the nature of the ground state, but also plays an important role in many photophysical processes and photochemical reactions in the electronic excited state. Many proton donor and proton acceptor (such as-OH and-NH2) exist in MOFs, they form a large number of hydrogen bonds with guest molecules or themselves. These hydrogen bonds not merely make an important contribution to MOFs’ self-assembly process, they also play a crucial role in MOFs’ luminescence, absorption and molecular recognition.Density Functional Theory (DFT) and relativistic Time-Dependent Density Functional Theory (TDDFT) have been carried out to investigate luminescence property and adsorption behaviors of the MOFs, Zn3(BTC)2(DMF)3(H2O)·(DMF)(H2O). We proved that the MOFs can absorb formaldehyde and other small molecules through the analysis of the binding energy. We pointed out that the luminescence mechanism of the MOFs is ligand-based luminescence by the analysis of frontier molecular orbitals (FMOs) and the corresponding electronic configurations of the MOFs and its hydrogen bond complexes. But when the CH2O hydrogen bond complexes are forming, the luminescence mechanism will change into dominating by the guest-induced luminescence. Accordingly, the Zn3(BTC)2(DMF)3(H2O)·(DMF)(H2O) has the potential for formaldehyde detection in environment.DFT and TDDFT also have been carried out to investigate luminescence property of [Zn(NH2bdc)(bix)·(DMF)2]n and its hydrogen bond complexes. Through the analysis of FMO and the corresponding electronic configurations of the MOFs and its hydrogen bond complexes, we proved that the luminescence mechanism of the MOFs is ligand-based luminescence instead of Ligand-to-metal charge transfer luminescence. We explained why the fluorescence of [Zn(NH2bdc)(bix)·(DMF)2]n is enhancement by the effect of hydrogen bond change under the excited states. Similar to the previous system, when the nitrobenzene hydrogen bond complexes are forming, the luminescence mechanism will change into dominating by the guest-induced luminescence. Accordingly, the MOFs has the potential for nitrobenzene explosives detection.