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Divergent Adsorption-Dependent Luminescence of Amino-Functionalized Lanthanide Metal-Organic Frameworks for Highly Sensitive NO2 Sensors.

A novel gas sensing mechanism exploiting lanthanide luminescence modulation upon NO2 adsorption is here demonstrated. Two isostructural lanthanide-based metal-organic frameworks are used including a recognition center (amino-group) that provides high selectivity for NO2 molecules. Energy transfer from the organic ligands to Ln is strongly dependent on the presence of NO2, resulting in an unprecedented photo-luminescent sensing scheme. Thereby, NO2 exposition triggers either a reversible enhancement or a decrease of the luminescence intensity, depending on the lanthanide ion (Eu or Tb). Our experimental studies combined with DFT and complete active space self-consistent field calculations, provide understanding of the nature and effects of NO2 interactions within the MOFs and the signal transduction mechanism.