Abstract: Luminescent metal-organic frameworks (MOFs) are of interest primarily in connection with the possibility of their use as sensors, since when different analytes (gases, metal cations, small organic molecules) interact with the surface of the frameworks, its photophysical properties – wavelength and emission intensity may vary significantly. The mechanisms of interactions between the analyte and MOF, leading to the luminescent sensing response, in most cases are very complex and practically unexplored. Two selected cases are discussed in the presentation. One of them is related to luminescent zirconium-organic framework assembled from [Zr6O4(OH)4]12- oxo-clusters and 4,4'-(2,1,3-benzooxadiazole-4,7-diyl)dibenzoate anions, which demonstrates a highly sensitive emission enhancement response to ammonia and amines in water with part-per-billion limits of detection (LOD).1 The luminescence enhancement mechanism was rationalized on the basis of DFT analysis of the interaction between ammonia molecule and 2,1,3-benzooxadiazole fragment which revealed a non-covalent N-H···N interaction leading to strong symmetry disruption of the electronic density distribution in the excited state, resulting in emission enhancement. The second case describes the luminescence quenching response of terbium(III)-based MOF with a flexible tetracarboxylate ligand towards sulfadiazine (SDI) antibiotic with extremely high sensitivity (LOD 0.48 nM) and high selectivity (antibiotics of three other groups demonstrated no strong quenching). In our previous works the luminescence quenching was in good correlation with relative HOMO/LUMO orbital energies of MOF models and analytes – if the photoinduced electron transfer (PET) process was possible, strong quenching was observed.2 However, in the discussed case, we have found that two different antibiotics, ciprofloxacin (CIP) and SDI, which have similar HOMO/LUMO levels and for both of which the PET process is possible, demonstrate quite different luminescence behavior. To the best of our knowledge, for the first time we propose a new approach to analyze the PET in MOF-analyte supramolecular complexes based on the extended analysis of electron density distribution in the excited state by TD-DFT calculations. As a result, peculiarities of non-covalent interactions between the analytes (CIP and SDI) and MOF model were revealed; the calculations of analyte-MOF supramolecular complexes allowed to highlight the difference in charge transfer between the analyte (CIP and SDI) and MOF in the excited state.

Cite: Potapov A. , Pavlov D. , Yu X. , Benassi E. , Fedin V.
Unraveling the luminescent sensing mechanisms of metal-organic frameworks through MOF-analyte interaction analysis
3rd International Symposium “Noncovalent Interactions in Synthesis, Catalysis, and Crystal Engineering” 19-25 Aug 2024