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

A novel gas sensing mechanism exploiting the luminescence modulation upon NO2 adsorption is here demonstrated. Two isostructural lanthanide based-metal-organic frameworks are used including a recognition center (aminogroup) 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 photoluminescent 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.